sharpness, megapixels, sensor sizes

[joofa]

With your permission,

I thought there was that hypothetical MF back that is supposedly faster than speed of tablets!
However, just like many aspects of modern MF today that seems more DIY than industrial, a proper LCD is not yet discovered !

Trust me FredJeang, you ain't seen modern Physics yet. I will put my faith in the proper LCD being discovered than Tachyons. If the following seem too illogical and magical to you then know that it is real academic physics and not some vodoo science:

Zombie cats that are simultaneously alive and dead, infinite parallel universes, going back in time, an accursed single particle that can pass through two physically separate slits at the same time, universe being filled with some "dark matter" that perhaps can't be seen, strange dimensions that never rolled out properly, negative probabilities, negative mass, zero-point energies, particles that can fly faster than speed of light but can't slow down to a lesser speed, strange strings that are the core of the universe, jinxed objects influencing each other's state when they are not even near together, creating matter out of void, and a slew of other illogical, magical, unseen, unobserved, unfathomable entities that shall make your head spin so fast that even electrons will be envious of !!!!!!!!!!!


Joofa (spinning and shaking in my boots as I write this).

[ErikKaffehr]

Hi,

You probably stop down to achieve larger depth of field (DOF). Using a larger sensor would require stopping down even more to achieve the same DOF, so it may not be the ultimate solution. Also, costs for sensors increase stiffly with size, and once you reach P65+ you don't really have anywhere to go.

There are three ways to increase DOF:

1) Stopping down
2) Scheimpflug (tilting lens)
3) Merging images with different focus, using programs like Helicon Focus. This obviously need static subjects.

A discussion of these techniques is given here: http://echophoto.dnsalias.net/ekr/index.ph...ng-the-dof-trap

The discussion is based on full frame DSLR but should be as valid for MFDBs or even film.

Best regards
Erik

Steve, exactly. So, what to do if the situation demands f22? Well - as Doug said, and as I teach - you can't beat physics. So if you must shoot at f22, the only way to achieve higher net image quality is ... to stop worrying about pixel sizes (anything from 12 microns down is fine), and just use a larger area sensor. More mm^2. Something that the large format film guys have known for decades.

[ondebanks]

Trust me FredJeang, you ain't seen modern Physics yet. I will put my faith in the proper LCD being discovered than Tachyons. If the following seem too illogical and magical to you then know that it is real academic physics and not some vodoo science:

Zombie cats that are simultaneously alive and dead, infinite parallel universes, going back in time, an accursed single particle that can pass through two physically separate slits at the same time, universe being filled with some "dark matter" that perhaps can't be seen, strange dimensions that never rolled out properly, negative probabilities, negative mass, zero-point energies, particles that can fly faster than speed of light but can't slow down to a lesser speed, strange strings that are the core of the universe, jinxed objects influencing each other's state when they are not even near together, creating matter out of void, and a slew of other illogical, magical, unseen, unobserved, unfathomable entities that shall make your head spin so fast that even electrons will be envious of !!!!!!!!!!!


Joofa (spinning and shaking in my boots as I write this).

Don't forget negative refraction, too! This may have a radical future impact on photography - using negative index metamaterials to achieve resolution beyond the conventional diffraction limit.  

[BJL]

Steve, exactly. So, what to do if the situation demands f22? Well - as Doug said, and as I teach - you can't beat physics. So if you must shoot at f22, the only way to achieve higher net image quality is ... to stop worrying about pixel sizes (anything from 12 microns down is fine), and just use a larger area sensor. More mm^2. Something that the large format film guys have known for decades.

To ondebanks and Doug Peterson: if you need to use a high f-stop like f/22, it is almost certainly in order to get adequate DOF, and in that case, a larger format will not help one iota, due to the higher f-stop needed with a larger format to get that same DOF. The scaling rules have been discussed many times in these forums, and it goes like this:

- to make any use of the larger format, you need to produce a larger image on the larger sensor, by increasing focal length

- to get equal DOF and equal OOF effects when images are displayed at equal size, the f-stop must be increased in proportion to focal length (so each circle of confusion on the image at the focal plane is enlarged by the same factor as the image itself)

- this increases diffraction spot size by the same factor as the image size, and thus

- when images are displayed at equal size, diffraction and OOF effects are equal.

For equal subject distance, the effective aperture diameter (a.k.a. entrance pupil size) determines the degree of both diffraction and OOF/DOF effects relative to the size of the image of the subject itself. That is, effective aperture diameter determines the angular extent of diffraction and OOF blurring.

[Rob C]

Trust me FredJeang, you ain't seen modern Physics yet. I will put my faith in the proper LCD being discovered than Tachyons. If the following seem too illogical and magical to you then know that it is real academic physics and not some vodoo science:

Zombie cats that are simultaneously alive and dead, infinite parallel universes, going back in time, an accursed single particle that can pass through two physically separate slits at the same time, universe being filled with some "dark matter" that perhaps can't be seen, strange dimensions that never rolled out properly, negative probabilities, negative mass, zero-point energies, particles that can fly faster than speed of light but can't slow down to a lesser speed, strange strings that are the core of the universe, jinxed objects influencing each other's state when they are not even near together, creating matter out of void, and a slew of other illogical, magical, unseen, unobserved, unfathomable entities that shall make your head spin so fast that even electrons will be envious of !!!!!!!!!!!


Joofa (spinning and shaking in my boots as I write this).

All of which tends to comply with my belief in a non-religious, non-denominational God. Why should a next-life be considered a silly idea? Just because we can't explain it today? In my own lifetime I have seen, and also experienced first-hand, things for which I find no rational explanation. No, I will not amplify, and if anyone elects to doubt me, that's just fine by me.

Rob C

[fredjeang]

All of which tends to comply with my belief in a non-religious, non-denominational God. Why should a next-life be considered a silly idea? Just because we can't explain it today? In my own lifetime I have seen, and also experienced first-hand, things for which I find no rational explanation. No, I will not amplify, and if anyone elects to doubt me, that's just fine by me.

Rob C

Rob, I certainly think that we are far from understanding the Universe. I have also seen strange things with no rational explainations.
I can beleive in paranormal phenomenons, although I've been trying to manifest through some strange physic laws a Leica M9 with no success so far.
There must be a way to make this Leica travel from the factory to my office, faster than the speed of light with instant teleportation and without paying one euro...mmm...
Any idea?

[BJL]

Rob, I certainly think that we are far from understanding the Universe.

For sure, since as far as I can tell from reading these forums, we are far from even understanding Depth Of Field!

[Rob C]

For sure, since as far as I can tell from reading these forums, we are far from even understanding Depth Of Field!

And certainly not Depth of Focus, nor the difference between them!

But seriously, the cynical view of the meaning, value or rationale of life is the product of a little knowledge being a dangerous thing. I don't think we will ever reach a state of understanding whilst we are alive; as a tribe, we seem to self-destruct ever time we appear to be a little closer to that understanding. It could be that we were never meant to reach a position of understanding, that it (such understanding) would take away all the incentives, all the drive and all the spirit that has made the world what it is, for better or even for worse, and end in the dying of the breed through hubris or, alternatively, despair.

Rob C

[ondebanks]

To ondebanks and Doug Peterson: if you need to use a high f-stop like f/22, it is almost certainly in order to get adequate DOF, and in that case, a larger format will not help one iota, due to the higher f-stop needed with a larger format to get that same DOF. ...

BJL, you're right of course. But I should have been clearer what I mean by "higher net image quality".

For what I shoot, that often means "keep the same lens f.l. & f-stop, and get a more expansive FOV" on a larger format. [Of course that won't suit many other people's composition scenarios]

But for all cases, even when you follow all the scaling rules, don't forget that while your image DOF and angular COC have not improved, you have magnified the image and spread it over more pixels (of the same size), so the net signal to noise has improved. Tonal transitions etc. will be smoother.

You are also now oversampling the PSF compared to the case with the smaller sensor, so you have more scope for PSF-based techniques like deconvolution, which can restore the resolution lost to the larger COC - giving you another net gain in the plane of focus.

[BJL]

BJL, you're right of course. But I should have been clearer what I mean by "higher net image quality".

For what I shoot, that often means "keep the same lens f.l. & f-stop, and get a more expansive FOV" on a larger format. [Of course that won't suit many other people's composition scenarios]

That sort of comparison makes no sense to me. When you want that wider FOV, you can get it in the smaller format by using a suitably shorter focal length, and the image quality achieved with that same preferred FOV is what should be compared. And if you have DOF needs this require higher f-stop, not equal f-stop in the larger format.

More generally, if certain features are desired in a composition, such as a certain FOV, a certain DOF, a certain aspect ratio, or a certain degree of subject motion blurring/freezing and thus a certain shutter speed, then image quality comparisons should be based on how the alternatives (like different formats) handle that desired composition, or if they can handle it at all. This means that typically, optimal choices of focal length, f-stop and shutter speed and/or ISO speed will be different for different formats. Imposing choices that are optimal for one format on another format where they are not optimal gives a biased comparison.

But for all cases, even when you follow all the scaling rules, don't forget that while your image DOF and angular COC have not improved, you have magnified the image and spread it over more pixels (of the same size), so the net signal to noise has improved. Tonal transitions etc. will be smoother.

I agree that when the larger format puts more pixels on the subject, there is potential for image quality improvements, particularly when a longer shutter speed is possible (as needed if one wants equal DOF, FOV, and ISO speed), so that each of the more numerous pixels can gather about the same amount of light. That is the scenario in which larger formats have particularly been preferred.

[ErikKaffehr]

Hi,

One issue with "20+" MP back is that they are physically smaller than the high resolution backs. So you essentially have a crop factor, as with APS-C vs. full frame. Now, with APS-C this problem was somewhat mitigated by camera vendors designing lenses for APS-C.

Problem with MFDBs is that there are a lot of sensor sizes so I guess no one will build lenses specially for reduced frame sensors. If you don't need wide angles it's a non issue.

Best regards
Erik

I think that it is indeed important.

In the testings I've been able to acheive to know what I really need (with C1 but it has little to do with the software itself IMO), the greater are the resolution and pixel-pitch are indeed more demanding and all the chain involved has to be on par.

I found (today) that the balanced between PP workflow-price and IQ is "desequilibrate" with the biggest backs because one little "mistake" on the chain like lens quality means that you do not reach the expected results.
In that sense, I do agree 100% with Michael Reichmann, who has reiterate this fact over and over again here.

I can not buy an high-end back, but in the personal testings have been doing with rented or files nicely provided by friends etc...that even if I had the money now to invest in such backs, I would not go further than 40MP. In fact, 20-30 is the ideal compromise IMO. (I'm not saying here that the high-end backs are not superiors)

Keep in mind that the printings, when made by real gurus (and in that sense I doubt that the photographer can be both the artist and the printer to the same level, but that is another debate), can do miracles with 22MP files. I am talking about really big prints. Not a long time ago, when 60MP backs did not exist yet, some artists where doing big enlargment with the availble resolutions and it was great, and they were sharp.

[BJL]

One issue with "20+" MP back is that they are physically smaller than the high resolution back ... Problem with MFDBs is that there are a lot of sensor sizes so I guess no one will build lenses specially for reduced frame sensors.

I mostly agree, since the main target of the DMF systems seems to be the highest priced, largest sensor options, but there are a few exceptions:
- Pentax seems committed to 44x33mm format for its so-called 645D system, and has already introduced a new 55mm normal lens targeted at that format, so might well follow up with wide angle lenses for that format.
- Hasselblad has one wide angle lens specifically for 48x36mm format, its 28mm.

But even so, no DMF system has anything nearly as wide as 35mm format has long offered, or even as wide as the "less professional" (code for "smaller format") systems like EF-S, DX, 4/3 and Micro 4/3 systems offer.

[mikesnorth]

A colleague and I did a bit more testing, etc and found some cool results, together with help from some great online info sites.

Posted the results in our blog here:
http://www.sunshinecompany.co.za/index.php/blog

[ondebanks]

When you started this thread, you said: "The P25 produces sharper images at anything greater than f/16." [compared to the H4D-50]

So if I read your blog correctly, you are now saying the opposite?