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Author Topic: f stop/sensor size realtionship  (Read 16215 times)

BJL

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f stop/sensor size realtionship
« Reply #40 on: May 09, 2005, 11:37:03 am »

Ray,
    the frequent checking of photosites for fullness is a "parallel process", done independently and simulteanously at each photosite, and at a rate of maybe 10,000 times per second or less. In the modern jargon of computing speed, about 0.000001GHz: an absolute snail's pace, and not requiring any processing power beyond that in the sensor itself.

About progress in different sizes, I am mainly interested in the range of DSLR's from mainstream makers, not tiny digicams or the small and shrinking market for format larger than 35mm. This partly because I suspect that DSLR makers are likely now locked into formats by the current array of lens formats from 35mm down to 4/3.

Comparison to performance weaknesses of far less expensive compact digicams aimed at quite different customers is fairly irrelevant to bottom line questions like "which choice will give me the best performance for a given price?"

In almost three years since Canon and Kodak first anounced their 35mm format DSLRs, we have seen just one substantially new 35mm format sensor, one sensor revision, and one sensor and product line abandoned (the Contax DSLR). to ne sensors if you count Canon's 1.3x for the 1DMkI. This has moved the maximum pixel count from 13.5MP to 16.5MP, with little change in prices, and with just two camera makers participating.

In the same period, seven DSLR makers and six sensor makers have offered at least half a dozen new sensors, several updates of existing sensors, considerably more new models, rapidly dropping prices, pixel counts increases from 6MP to 8MP and then 12.4MP. (By the way, they have also repeatedly confounded the pessimists and cynics by reducing noise levels along with those increases in resolution and reductions in pixel size.) The tempo seems far faster at the smaller end of the DSLR world.

By the way, at the next size level down, the 2/3" digicam sensor format and "prosumer digicams" seem to be in retreat or at least stagnation, as if the entry level DSLRs are taking away market share. So in that battle, the larger format seems to be winning; it is not all one way or the other. Unless 2/3" is just losing out to 1/1.8".

P. S. Perhaps I should qualify my speculation about 35mm format digital possibly falling off the R&D pace. 35mm digital is in a better situation than MF film for sharing of technology with smaller formats, through being backed by one major mainstream camera maker, and a fair degree of overlap in lenses. Better than than situation at Hasselblad, Rollei, Bronica, and Mamiya, and even Pentax with its mostly separate lens systems.
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Bobtrips

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« Reply #41 on: May 12, 2005, 10:25:23 am »

OK, let's turn up the heat under the 'big boy' cameras a bit more.

Fuji just released a compact digital with 'usable' ISO 1600.  

F10Zoom Review

Looks like rapid sensor sweeping won't be necessary to solve the small camera - high ISO problem.  

(And it might explain why we haven't seen a Fuji monster zoom with IS.)
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BJL

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« Reply #42 on: May 13, 2005, 02:36:35 pm »

Bob,

   that is a reasonable "optimization" approach, to which I will just add one thing: the inability to have the gear with you at the right place and time prevents some photos from being taken. So even your "special built MF jobbie"  will not in practice do it all.

The gear that allows me to get the greatest number of good results is not the same as the gear that would give slightly better image quality except that it is sitting back at home or in the car because I do not have a pack mule. Another reason for having cameras in several formats: even Ansel Adams used a miniature format camera (Contax 35mm) at times.
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Ray

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« Reply #43 on: May 16, 2005, 11:57:53 pm »

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I believe that you are one of many serious photographers who did this with film: a 6x7cm format camera as well as a 35mm, right? And this somewhat common approach of using both 35mm and medium format usually has the pattern I have suggested:
- the smaller format is better for "limited light" situations where the larger format would need to be used at uncomfortably high ISO speed, with long telephoto being a common case
- the larger format is better in situations where you can get all the light you need to work at low ISO: tripods and stationary subjects, flash or studio lighting usable, and so on.

BJL,
You're right, I did pick up a couple of used MF film cameras and a number of lenses before getting my first digital camera, the D60. The previous owners were no doubt professionals who were dumping the gear because of a move to digital. I thought the price at the time was really good. Couldn't resist  :D .

However, having previously switched from Minolta to Canon a short time earlier, there was no significant advantage to either format regarding focal length for me at the time. My MF lenses range from 50mm to 300mm in primes; my Canon EOS lenses from 28-135 (zoom), 90mm TS-E and later a Sigma 20mm.

The choice of MF gear in any situation was really a trade-off between convenience factors and absolute image quality. The RB67 (nicknamed 'the tank') was versatile in its range of lenses (4 primes from 50mm to 300mm), but weighed a tonne. The Fuji GSW690 lll (6x9cm) has a fixed 65mm lens; the body's made of carbon fibre so it's very light and is very backpackable but not at all versatile in its range of lenses.

I keep telling myself I must use this MF gear more often, but I've been spoiled by the huge convenience of the DSLR. There are no pixel-peeping issues here. The greater efficiency (convenience) factor of the digital camera is so great, it dwarfs all other considerations. I have dozens of packets of film still in the fridge but well past their use-by date, both MF and 35mm.

Having bought additional lenses in the meantime for the D60 and 20D, I now have a focal length range, in 35mm terms, of 16mm to 900mm (using a 1.4x converter) with just 3 lenses.

All that remains is for Canon to produce an upgrade to the 20D which matches or exceeds the performance of the D2X, has autofocus capability at f8 and costs significantly less than the D2X.

I'm with you Canon! You can do it  ! The money's in the bank waiting  :D .
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BJL

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« Reply #44 on: May 17, 2005, 02:59:53 pm »

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So, three levels of 'bodies'.  

...

And the lenses largely interchangeable across the three bodies.
There is where it falls down a bit; in practice the lens interchangeability is not so good, in large part due to the dominance of zoom lenses, whose preferred focal length ranges tend to be rather format specific.

The great majority of lenses being bought and used with DSLRs now are either unusable with 35mm format (Nikon DX, Canon EF-S, Olympus 4/3, Pentax DA, Minolta DT, Sigma DC, etc.), or are zoom lenses of focal length ranges that are inconvenient and unpopular with 35mm format (like 50-200 f/4-5.6: not many people use cheap, slow, 200mm zooms with 35mm format DSLRs do they?)

It works a bit better for the small elite who go the other way: those who primarily use high end 35mm format DSLR bodies and lenses can use all those lenses when occasionally slumming it with a smaller format, augmented by a few "D" lenses. Even then, lenses like 24-70 or 28-70 give a somewhat unpopular FOV range when cropped (would you buy a 40-110 lens for 35mm format?)

The makers of several different SLR formats (like Pentax, Mamiya, Fuji and Bronica) never did a lot in the way of cross-format lens compatability. This is probably a sign that there are performance virtues to using a lens designed for the format in use, rather than one for a format more than twice as large.
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Ray

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« Reply #45 on: May 18, 2005, 06:23:55 am »

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I am amazed to see both of you interested in an idea I have had for a while: a fully professional level Canon DSLR in EF-S format, for situations where "agility" and the longer telephoto reach of any given lens through using smaller pixels is an advantage. The long awaited EOS-3D?
BJL,
I was always interested in that idea. It's just that I've been unduly influenced by knowledgeable people telling me that the 1Ds had already reached the resolution limits of 35mm format lenses. When the 1Ds Mkll came out, there was great skepticism that those smaller pixels would serve much purpose.

We now find that a smaller format camera with a 1.5 crop factor and a pixel density equivalent to 27mp on a 35mm format sensor (the D2X) delivers better image quality than the 1Ds and almost matches the resolution of the much more expensive 1Ds Mkll.

Which is more likely; that Canon will eventually produce an upgrade to the 20D that matches the performance of the D2X but at a lower price, or that Canon will eventually produce a much cheaper version the the 1Ds Mkll?
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BJL

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« Reply #46 on: April 29, 2005, 12:17:40 pm »

As Ray said, the comparison seems fair, in the sense that those "equivalent apertures" gather light from the subject at the same total rate, and so can deliver the same amount of light to each pixel (if pixel counts are equal), and so potentially the same "signal" at each pixel. (Eqivalent DOF and diffraction effects too, but I should pass on that one!)

The mathematics: Intensity of illumination per unit area is measured by aperture ratio, so total rate of illumination of the whole sensor is measured by sensor area divided by the square of the aperture ratio.


If noise levels per pixel were similar, you might be fairly close to image quality parity in many respects (though probably not dynamic range).

In practice a few things are likely to complicate the comparison. For examples of one going in each direction,
1) far larger sensors with larger pixels are likely to have an advantage in light detection efficiency, due to more precise operation of the larger microlenses
2) smaller pixels will produce less dark current noise, some sources of which follow a "per unit area" empirical pattern.
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BJL

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« Reply #47 on: April 30, 2005, 11:43:55 am »

Ray, I will not repeat my calculations unless there is demand, but I am fairly sure of the following [and optimistic but less sure of the guesses in brackets.]

a) once controllable noise sources ("total dark noise") are reduced enough and photon shot noise is the limit, there is no advantage to image merging; the S/N ratio at any given pixel is determined simply by the number of photons used to make that pixel, due to that square root law.
[Dark noise levels seem to be approaching this point, for photographic purposes; maybe within one stop or so?]

 dynamic range is indeed a clear current advantage to larger photosites and sensors; DR expansion strategies like frame blending will potentially neutralize that advantage, but no more.
[My guess is that in-camera and even in-sensor methods will eventually take care of DR limits, without need for multiple exposures and stationary subjects.]

c) since DOF and diffraction limitation for the same FOV are equal for the same aperture diameter (f-stop proportional to focal length), the two likely limits to small formats and photosites are that (1) photosites have to be bigger than the wavelength of light, and (2) lens abberations probably set a lower limit on aperture ratio, more or less independent of format, if one seeks images that are "sharp and contrasty from corner to corner". With current DSLR formats, limit (1) only comes in at extremely high pixel counts, and at extremely larger apertures due to diffraction limitation, so lens abberations seem likely to be the main practical limit in the long run.

[My current guess is that about f/2 might be the limit, and maybe not even that low; if so formats much smaller than the current smallest DSLR formats will always be distinctly hampered. Lower f-stops work with some 35mm lenses, but with extremely shallow DOF that probably hides sharpness limitations towards the edges of the frame. My optimism about f/2 in a small enough format comes from the apparently good corner to corner, wide open performance of the Olympus 4/3 format 50/2 and 150/2 lenses, including MTF 50% and better at 60lp/mm. But these are both "narrow FOV lenses", 24º and 8º respectively; edge and corner performance on normal to wide lenses is a tougher design challenge.]


Good hints as to the lens design limits of smaller formats might keep coming from Olympus in particular, as they are working wth the smallest SLR format, and are the only company designing new lenses reaching f/2 for any of the new DSLR formats, and the main one designing new primes for these formats. (To be fair, the new Nikon 200/2 might count as a digital, DX format oriented design, despite also working with 35mm format.) Another coming indication of the current state of the art for low f-stops in smaller formats might be the wide open performance of the forthcoming Olympus constant f/2 zooms.
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Ray

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« Reply #48 on: May 03, 2005, 12:43:31 am »

My fault. Rereading your earlier post I see you've got it all pretty much covered.

What's not clear is just what range of charges could such a small photosite, not much bigger than the wavelength of red light, hold?

Could in-camera blending of multiple exposures really neutralise the DR advantage of the larger format, ie., the signal-to-noise advantage of the larger pixel?

Currently, small format digicams have an obvious advantage of allowing the use of  faster shutter speeds for same FOV and same DoF shots. If I try to use the same f stop (say f2) with a larger format camera, I get extremely shallow DoF, which may be the opposite of what's required.

But isn't this advantage of the smaller format really illusory? I can trade off the superior S/N of those larger pixels by bumping up the ISO till I get the same shutter speed.

Example: Comparing a camera the size of the FZ20 with the 350D that Bobtrips referred to earlier; if we have a situation where the FZ20 will use 1/30th at f2.8 at ISO 100, then for the same FoV and equivalent DoF at the same ISO setting, we'd be using about 1/2 sec exposure at f10.36. But we've got the option of using ISO 1600 with the 350D which would bring us a back to a shutter speed of 1/30th.

Now, without getting into arguments about which image would be superior (which will depend on a range of other noise reduction technologies that may have or may not have  been implemented in a particular camera), I think it would be fair to say in principle that the speed advantage of the smaller format has already been neutralised and is therefore an illusion.

If we take these trade-offs to the nth degree and begin implementing in-camera blending of multiple frames, we arrive at a point where the speed advantage of the smaller format is no longer illusory. It becomes a real disadvantage[/i].

For example: Starting with an exposure in accordance with the sunny 16 rule, a contrasty outdoor scene will require 1/100th sec at ISO 100 and f16, or 1/400th at f8 (I've found this to be an excellent approximation).

If we consider the imaginary camera I've designed with a diffraction limited F1/5.4mm lens with equiv DoF to a 35mm FF 43mm lens at f8, the exposure required at F1 for that same contrasty scene would be 1/25,600 of a sec. And that just gets us the highlights.

If we take a series of shots, say 8 separated by 1 stop intervals (not by any means an excessive quantity considering what people are already doing in PS CS2's HDR), we arrive at a total exposure time of 1/100th sec. And that's not counting any delay between one shot and the next.

At the end of the day, the photon shot noise seems to be the insurmountable barrier as well as diffraction.
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Ray

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« Reply #49 on: May 03, 2005, 09:34:25 pm »

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Ray, now I am confused.

I find that difficult to believe BJL. You seem have every angle of this comparison between small and large format covered in terms of mathematical relationships and trade-offs almost  :) .

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I thought that we were agreed that the lower total dark noise levels (in electrons) is, for the time being, a potential S/N advantage to a smaller sensor.

Not quite. As I've understood it, this advantage is completely offset by the increasingly larger role of photonic shot noise as the sensor gets smaller.

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You realy are passionate about denying any possible advantage to smaller formats, aren't you? One seriously wonders why medium format lost so much ground amongst professionals to the smaller 35mm format if the latter had so little in its favor!

Now I know that you know there are huge economic factors which have had a major influence on this downward shift in format size in the digital era. The general public doesn't need or want digital backs that cost as much as a luxury car in order to produce 30x40" prints as sharp as drum-scanned 4x5 film. Even when it was quite clear that 35mm film could never compete quality-wise with MF film, the action still remained around the development of ever more sophisticated 35mm cameras.

I'm simply trying to find a real advantage to the smaller format other than weight and price. Perhaps this is because I don't use my Sony DCS T1 much.

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On the second point, I thought it was decided in a previous discussion that at a given angular FOV, pixel count, and camera weight, the same shutter speed is needed to freeze camera motion adequately. Since FOV counts, not focal length itself, it should be not 1/f, but 1/(35mm equivalent f).

I might have missed that particular thread, but thanks for mentioning it again. It makes perfect sense the way you've phrased it but leaves one wondering about the happy coincidence that such a simple rule should apply specifically to the 35mm format.

In any case, that's another possible advantage of the smaller format that lingered in my mind and has now been dashed  :) .
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BJL

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« Reply #50 on: May 05, 2005, 11:40:08 am »

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a) My role in this current debate about large sensors versus small is more of a 'devil's advocate' role against the ultimate triumph of the small sensor.

 Can photonic shot noise, the major noise component in small sensors and perhaps the ultimate barrier to further improvement of image quality, be tackled.

c) Can technology get around this DR limitation of the small photosite by constructing really deep wells and/or merging several shots in-camera? Maybe.

d) If the larger format sensors employ similar technology to produce extra deep wells and automatic merging of different exposures in-camera, could the smaller format ever compete, eh!?
OK that is more reasonable! I must have imagined you speculating about a future low cost 6MP 35mm format sensor option.

a) I have not noticed anyone in this forum arguing that smaller formats wil completely displace 35mm foramt and larger, but I suppose some such hard core "little-endians" do exist. I am personally willing to concede a continued 5% or so of DSLR sale volume to formats bigger than 1.5x!

I suggest that the two best argument for lower size limits are
1) downsizing lenses for smaller formats will naturally be limited to improving resolution (lp/mm) not quite as fast as image size reduces, so a smaller format is inherently limited to somewhat lower ability to record detail, in the sense of "line pairs per picture height".
2) optical design limits on aperture ratios lading to permanent speed disadvantages for too small formats. Maybe there will never be excellent optical performance below about f/2 or even higher.

 almost certainly not. Shot noise is an observed feature of the light arriving at the lens; we are stuck with it.

c) almost certainly yes. Yet another possibility with CMOS is sensors with an extremely high frame rate, so that they can be read numerous times during a single exposure, completely eliminating highlight headroom limits. One way or another, I am very confident that highlight headroom can be eliminated as a limitation on dynamic range.

d) absolutely yes! Once highlight headroom is essentially eliminated as a constraint, there is absolutely no DR advantage to a larger format, as the DR is unlimited in either case. That leaves only shadow noise/speed trade-offs, which naturally tend to either a tie or a win for smaller photosites so long as fast enug lenses canb be used.

The question on this point is whether larger sensors with their inherently larger dark noise electron counts can compete, in particular given their naturally higher cost. The lens limitations (speed and resolution) menioned above are the big-endian's best chance, with compact digicam formats already permanently boxed out of the high end I would say.
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Bobtrips

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« Reply #51 on: May 06, 2005, 12:57:19 am »

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Big sensor retaliates, "So what! We've already done that. We're into the billions of photons old chap. We use huge lenses diffraction limited at f2, schleimflug tilt effects and DoF bracketing. Who kidded you that you could ever compete?
The joker in the deck is the market.

At this point in time more people seem to want little things than want big things.  If the goal is to produce a camera capable of making a 12" x 18" print with great resolution and great DR and great everything else and you've got two cameras - one big and one little ....

I don't know anyone who would ever argue that little cameras will somehow be more 'capable' than large cameras.  MF film cameras were more capable than 35 mm film cameras. The market went with smaller.

Thing is, small cameras are likely to keep on getting better over time.  Half-frames are replacing 35 mm film, full-frames are replacing MF film.  In a generation or few we may see quarter-frames doing the work that 35 mm film once did and full-fames moving into the LF film world.
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BJL

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« Reply #52 on: May 06, 2005, 11:15:11 am »

Ray, you seem to be severely misunderstsanding what I am saying about eliminating dynamic range limitations. It is NOTHING to do with increasing sensitivity, or the maximum usable ISO; quite the contrary in fact.

Both blending and the other methods already being tried out work by using long enough exposures to handle shadows well, while avoiding blown-out highlights. The plausable goal is totally eliminating the UPPER limit on the amount of light that a highlight photosite can receive during an exposure without problems, not lowering the minimum amount of light needed, which I think we agree is ultimately limited by photon noise. It is about allowing long exposures and very low effective ISO speeds.

The elimination of highlight headroom limits is very far from Star Trekky wishful thinking; let me say something yet again: methods for doing this are already in use, in video surveillance cameras! (And blending is another less convenient such method.)

At heart, all that is required is to check the photosites periodically during an exposure, and read out the ones that are close to full. By noting the different read-out times at different photosites, the correct relative illumination levels can be computed. Thus every photosite can potentially be read out when it has received enough light to have a healthy S/N ratio, if you can wait long enough on the shadow pixels. And motion blur will be minimized in well lit regions, since they are effectively exposed at the highest ISO appropriate to thier light levels!


P. S. you might be more enthusiastic about my argument that there will never be a good quality, general purpose, interchangable lens camera system in a format smaller than the current smallest DSLR format, 4/3. (Ignoring the debate about whether there is or will ever be such as system in 4/3 format!) The lower size limit set by the "law of diminishing returns" has been reached if not exceeded by current DSLR formats: camera and lens costs and sizes can not be reduced much further, and so on.
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Bobtrips

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« Reply #53 on: May 06, 2005, 12:51:06 pm »

I suspect we will be able to  divorce shallow DOF and aperture before long.  

So if we are limited to f2.0 or even f2.8 (as opposed to f1.4 for larger formats) do you think people will buy a larger (and very likely more expensive) system for that additional bit of performance?

(As an aside, I'm assuming that 1/50, f2.8, ISO 100 is approximanetly the same exposure value across formats.)
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Ray

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« Reply #54 on: May 06, 2005, 10:48:52 pm »

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As I have said before, methods already exist to essentially eliminate the effects of well capacity limits; for example, reading out each well as it approaches being full. Most of your arguments crumble once that is achieved, because it is not possible for a larger format to offer better than the UNLIMITED highlight headroom and dynamic range of a smaller one.
BJL,
Are you absolutely certain about this   ?

The central part of my argument got lost somewhere. It's this. I agree that the application of much technological wizadry could eventually create a small camera capable of outstanding performance on a par with what we currently get from bigger DSLRs and even what we hope to get in the future from DSLRs, but only if the research dollars go in that direction and cease to flow to further development of the larger format cameras.

The argument that this appears to be what is happening and that large format digital cameras will eventually cease to be economically viable and become dinosaurs, is another issue.

I am merely concentrating on the inherent potential of two hypothetical formats that differ greatly in size. In relation to that argument you are making some controversial statements, the logic of which I find difficult to follow.

Let's get down to some more examples using simple maths. Compare two sensors of equal pixel density but the smaller sensor has 1 micron photosites and the larger sensor has 10 micron photosites. The smaller camera has an f1 to f4 lens. The bigger camera has an f4 to f32 lens. DoF at f1 on the smaller camera is equal to DoF at f10 on the bigger camera. Both sensors have eliminated all dark noise. Photon noise is the only noise.

What you are proposing, if I've understood you, is that we could completely sacrifice the speed advantage of an f1 lens by using the same exposure duration that the larger camera would use at f10. As soon as a photosite is full, the charge is read, transferred, dumped (whatever) but essentially noted. The fact that pixel #1124 was filled 200 times during a 1/100th sec exposure and pixel #13 only once, is recorded and used to construct an image with full dynamic range.

This is a great idea, but suppose the larger camera adopts the same technique?

Here are what I think the issues are.

(1) Nothing happens instaneously (except perhaps in fictitious quantum computers using qantum entanglement). In practice, if we want to get that photosite #13 to fill just once (representing the darkest part of the image) it is going to take a somewhat longer exposure than the larger camera would use at f10. This effectively means the smaller camera would have optimal performance at say ISO 64 as opposed to ISO 100 for the larger camera. So already the larger camera has a speed advantage at equivalent DoF before we've even applied this amazing technology; the opposite of what we're used to.

(2) But the big issue is the significance of the far lower S/N of the bigger sensor. To refresh, 1000 electrons at full well have 33 electrons of photonic noise. 100,000 electrons have only 317 electrons of photonic noise.

If we employ this same technique with the larger camera, we don't need to wait until the well is full. For the same Signal-to-Noise, we can set the camera to transfer the charge (or note the charge) when the well reaches 10,000 electrons (1/10th full well). This effectively means we get the same DR performance of the smaller camera, but at a yet higher ISO setting.

And we haven't even begun to consider the benefits of those diffraction limited F4 lenses on the bigger camera, which I surmise would be ideal for noise-free hand-held shots at ISO 128,000 (or even higher) in the Vatican Museum   .

Let's face it, BJL, these tiny digicams, however sophisticated, are just toys for the consumer mass market   .

Note, I'm jumping in here a second time to correct my maths. Such gross errors are intolerable (no calculator at hand). I figure 33:1000 is equivalent to 317:10,000. The bigger well, 100x the area, needs to be only 1/10th full to match the S/N of the smaller well; ie. we can get the same results at f10 using less than 1/10th the exposure, combining points (1) and (2).

It can be seen if we start using F4 on the larger camera, the ISO benefits (shutter speed) are enormous.
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BJL

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« Reply #55 on: May 07, 2005, 06:32:49 pm »

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but only if the research dollars go in that direction and cease to flow to further development of the larger format cameras.
Ray,

   we seem to be close enough to agreement, but this comment is very telling. How do you think the allocation of research efforts is going between formats, maybe grouped as digicam (2/3" and below), the mainstream digital SLR formats (4/3 to 1.5x), 35mm format (including 1.3x?), and bigger than 35mm format. One dominant trend I see is that sensor and camera makers want to reduc costs by getting the best performance possible out of the smallest sensor possible, but with significant inertia in DSLR sensor sizes once a DSLR format has been chosen and lenses made for it.

The indications from the rate of introduction of new sensors and new camera models are of a bottom heavy pattern, with every step up that size ladder having a lower level of activity. This is almost inevitable given the very bottom heavy distribution of sales and revenues. As far as I can tell, Digital Rebel (or D70) revenues alone greatly exceed those of all 35mm format DSLRs combined.  In fact, as far as I can tell, even the Four Thirds format probably now outgrosses all of 35mm in the digital world. And 1/1.8" probably trounces 35mm.

So my guess is that amongst interchangable lens camera systems, the current mainstream DSLR formats will have the fastest technological development. Just as MF fell of the R&D pace decades ago, maybe 35mm format is next.
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Ray

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« Reply #56 on: May 09, 2005, 11:43:06 pm »

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   the frequent checking of photosites for fullness is a "parallel process", done independently and simulteanously at each photosite, and at a rate of maybe 10,000 times per second or less. In the modern jargon of computing speed, about 0.000001GHz: an absolute snail's pace, and not requiring any processing power beyond that in the sensor itself.

Are you sure that's fast enough, BJL? I'm no mathematician or electronics expert, but as I understand a GHz is a thousand, million Hertz.  0.000001 is a millionth. A millionth of a GHz is a mere 1,000 Hertz. Okay, what's the occasional zero between friends  .

For sampling to be accurate, it needs to be a 'bare-bones' twice as fast as the activity that's being sampled but preferrably at least 4x as fast or even greater. If we try to mimic with a small photosite the performance of a larger photosite with a full-well capacity of say 100,000 electrons that might fill in 1/100th of a second exposure say, then we'd be looking at a 4x sampling rate of around 40 million Hertz. No problem I guess, but what about the time it takes to discharge and reset a particular photosite and the time it takes to process that data in 16 bit mode (and possibly much higher with this technology) for a good quality RAW image, plus all the other noise reduction techniques that take up real time?

If you shift ground and exclude all the P&S cameras, which there's good reason for doing because there seems to be a big size gap between the 2/3rds format (6.6mmx8.8mm) and the Oly E-1 (13.5x18mm), then all the arguments become more nebulous. Absolute pixel size (or more accurately pixel pitch because manufacturers don't seem to publish the actual pixel size) seems to have less effect than design, noise reduction techniques and such factors as 16 bit processing (or greater) as opposed to 10, 12, or 14 bit processing.

I just did a quick check of the format sizes ranging from the Oly E-1 to the P25. The size differences are fairly evenly spaced with the biggest gap occurring between FF 35mm and the P25 which has about double the area.

It's to be expected that there's going to be a bit of temporary overtaking between one format and the next one up in size.

You must be a bit disappointed that the small brother of the DSLR brigade (the Oly E-1) has not yet overtaken anyone  :(  .
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BJL

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« Reply #57 on: May 12, 2005, 03:43:00 pm »

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I meant that you must be disappointed the Olympus 4/3rds system has not yet overtaken in performance and image quality the next format up in size, the Canon 20D.
Ray,

   do you really think that I believe that smaller formats are overall superior to larger ones? If so, I need to clarify my mostly centrist position.

a) many claims for natural advantages of one format size over another are greatly exagerated or completely untrue, being based on overlooking some relevant factors (e.g. ISO vs f-stop.)

 larger formats tend to have some advantages, at least with current technology:
i) Bigger maximum aperture diameters are possible, allowing greater extremes of high shutter speed and low DOF.
ii) Greater dynamic range when it is possible to get "full exposure" (exposing to the right at minimum ISO, and so almost filling the electron wells at highlights).

c) Smaller formats also have some natural advantages:
i) Less dark current noise (electrons per pixel), potentially improving S/N ratio when a need for both adequate shutter speed and adequate DOF resticts one to less than full exposure (i.e. all electrons wells significantly less than full, even at the brightest highlights).
ii) Size, weight and cost, which can indirectly lead to higher image quality by allowing you to own or carry more or better equipment.

d) With advantages in both directions, it is not the case that either a bigger or a smaller format has an automatic image quality advantage; such simplistic dogma is for partisans of the "digital format size cold war". Only when the specific photographic goals and the specific formats being compared are specified can a useful image quality comparison be made. E.g. is 16x24mm (Nikon) or 645 medium format better for action photography?


If I seem to favor smaller formats, it is mostly because I am so often responding to exagerated or untrue claims in favor of larger ones: partisans of "bigger is better" are far more common in discussion forums than partisans of "small is beautiful".
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Bobtrips

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« Reply #58 on: May 13, 2005, 12:56:28 pm »

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Ray,

    here is my overall perception. The best format for one's purposes is one that is just big enough to offer
I tend to look at camera selection in terms of the percentage of possible shots that one will not be able to take with a given camera.

There's possibly a camera out there which will 'do it all'.  Maybe a special built MF jobbie with incredibly fast burst rates and capable of using very long lenses.  Something in the, say, $75k+ range that weighs in a 25+ pounds.

OK, none of us (except Michael ;o) is likely to go that route.  So whatever we choose means that we write off a certain percentage of possible shots from the entire picture universe.

As soon as you decide that full-frame 35 mm digital is the answer you've limited your shooting portion of the universe.  But due to cost and weight decisions you may choose to pass on the non-achievable shots.  

The same holds with other camera choices.  I find it uncomfortable to walk for 8-12 hours a day, day after day, carrying even a dSLR and a couple of lenses.  

I'm interested in seeing small sensor lens cameras improve in ability so that I can reduce the (even now currently small) number of shots that I can't get with current monster zoom cameras.  

I pass on the low ambient motion shots, I have to struggle to get some indoor shots without flash, and I have to use PS to create shallow DOF.  But I get the 95%+ shots that I want with a one pound camera.

Get me an 8 meg 12x camera with Fuji's high ISO ability and some software that does a better job of shallow DOF and there's little that I won't be able to do with a tiny monster.
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BJL

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« Reply #59 on: May 16, 2005, 04:24:32 pm »

Ray,

   I believe that you are one of many serious photographers who did this with film: a 6x7cm format camera as well as a 35mm, right? And this somewhat common approach of using both 35mm and medium format usually has the pattern I have suggested:
- the smaller format is better for "limited light" situations where the larger format would need to be used at uncomfortably high ISO speed, with long telephoto being a common case
- the larger format is better in situations where you can get all the light you need to work at low ISO: tripods and stationary subjects, flash or studio lighting usable, and so on.

What I envision is that for a sufficiently serious photographer it could similarly make sense to use several digital cameras in formats at similarly large jumps in size, about a factor of two to four in sensor area, or "one to two stops". Smaller image format changes than that can probably be handled adequately by cropping down to the desired size, so using the next available format up from what is "ideal" for the situation.

Of course our host Michael does this at about four levels! Mainly 36x48mm ("near 645") and 24x36mm ("35mm"), but also with 15x22.5mm ("1.6x"), and one or two digicams at 6.6x8.8mm (2/3") and smaller.


P. S. If and when you add a 24x36mm format DSLR to your kit, I think it will be more likely that you prefer the 15x22.5mm format 20D to it on some of those long walks!

P. P. S. I like your idea of redefining "digital medium format": the most common DSLR formats from 13.5x18mm (4/3") to 16x24mm (DX) do seem to sit in the middle: about three time bigger than the dominant "digital miniature formats" like the 4.3x5.8mm of 1/2.5", with the "digital large formats" of about 36x48mm being about three times bigger again.
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