How Big Is Too Big?

[Gary Ferguson]

As a darkroom printer I arrived at certain guidelines for enlargements. They weren't rules as such, but observations that tended to fit with my own experiences.

4x or 5x enlargement was not difficult, undemanding of equipment and technique. This degree of enlargement served up both the 6"x4" holiday snaps from 35mm, or delivered a magnificent 16"x20" print from a more carefully executed 4"x5" negative.

7x or 8x enlargement was entirely possible, and reliably so under both good conditions and bad. But it did require that some attention be paid to technique, and it did start to show the differences between good and average equipment. This was the normal "enthusiast's enlargement", yielding the de facto 35mm standard 8"x10" print, or a 16"x20" from a medium format negative.

10x enlargement was ambitious. This was time to take a deep breath and concentrate because most prints at this level of enlargement would compare unfavourably with ones from the next larger negative size. 10x was printing on 11"x14" paper from a 35mm negative, and you'd usually see straight away that it wasn't medium format. It could still be a convincing print that withstood close inspection, but only if every single link in the photographic chain was meticulously handled.

12x to 15x enlargement represented the absolute limit. Not only was equipment and technique stretched to breaking point, but you really needed the photographic gods to be smiling on you. The truth was that the great majority of negatives could not sustain this degree of enlargement without their technical shortcomings becoming manifest, and if you were successful at this scale it was likely to be serendipitous and unrepeatable. In other words, I may have made a print that was a 12x enlargement or even greater, but I didn't have that intention when I took the shot.

So what were the standards that drove these guidelines? Well, I never bought into the theory that viewing distances increase in proportion to print size. Apart from artificial restrictions like a poster innaccessibly displayed on the side of a building, it seemed to me that there's something in the very nature of a photograph that invites leisured, intimate scrutiny. And for many subjects, often found in landscape or architectural photography, abundant detail is necessary for the success of the image.

Now here's the thing. Personally I don't find much in digital photography that might change the enlargement guidelines of silver photography. Grain may be solved and film curl replaced by sensor alignement; but from diffraction to camera shake, depth of field to mirror slap, we're still dealing with the same practical restrictions on fidelity. Yet somehow in the digital world huge enlargements seem to be regarded as a pixel given birth right, so an A2 print from an APS sized sensor doesn't even raise an eyebrow.

I'm looking at the 11x prints I'm making from a Canon 1Ds Mk II and concluding that I'm already pushing my luck. I'm not sure what would be the practical benefits from a new 22MP Canon uber kamera that could be realised in a print.

So my question is this, what is the realistic relationship between sensor size (not pixel count) and print size?

How big is too big?

[Ray]

So my question is this, what is the realistic relationship between sensor size (not pixel count) and print size?
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As I understand, Gary, there's no direct relationship between sensor size and print size. It's the pixel count and lens quality that determines how big a print you can make, that will withstand close scrutiny. The 16 megapixels of the 1Ds2 are good for a 14"x21" print at 240ppi. You could also make a print of around 18"x28" using 180ppi and no interpolation, but there would be a risk that some folks with really keen eyesight might see a hint of jaggies, so it would probably be advisable to interpolate the image (add more pixels) so it becomes 240ppi at that size.

Film really is in a different ball park. You have grains and clumps of grains that unavoidably get enlarged in proportion to the print size. Pixels also get enlarged but you can create more of them through the process of interpolation.

[Hank]

It depends a lot also on how the photo will be used, how it was processed, and how far away viewers will stand.  

To my certain knowledge billboard photos aren't restricted to shots from 11x14 negatives, to cite an almost-frivilous example of the extremes, yet image quality is sufficient to support a major ad industry.

[ijrwest]

Digital enlargement is a bit different to traditional film enlargement, because we can interpolate and sharpen digital images, and digital printers don't lose contrast on bigger prints. The best measure for digital print quality from a well-sharpened image seems to be the print dpi. An 11x enlargement from a 1Ds2 is equivalent to 320dpi. For top quality prints that may be about right, although I have always been happy with 280-300dpi.

Iain West

[BJL]

As I understand, Gary, there's no direct relationship between sensor size and print size. It's the pixel count and lens quality that determines how big a print you can make, that will withstand close scrutiny.
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Agreed: from everything I have seen and read, the ultimate enlargement limit of images from the Canon 1DsMkII is still sensor resolution, at least when one uses the best available lenses. And why not use the best lenses once you have payed almost $8,000 for the body?!

For example, the Canon 24-70 f/2.8 is said by Norm Koren to resolve about 61lp/mm at 50% MTF, and it takes about three Bayer pattern pixels to resolve one line pair, so that corresponds to about 180 pixels per mm, or 5.5 micron pixel spacing (as in the Nikon D2X). So sensor resolution will only match that lens' resolution at about 28MP in the 24x36mm format of the 1Ds family. And I would guess that a number of good primes resolve better than that zoom.

[Gary Ferguson]

"For example, the Canon 24-70 f/2.8 is said by Norm Koren to resolve about 61lp/mm"


I'm not so sure. Staying with your argument, how many lp/pm would you want in the final print? For quality work there seems to be a consensus that about six lp/pm would be a reasonable number, personally I'd argue for more but I'll live with six. In which case the x10 enlargement limit I spoke about earlier would still apply. In other words the A3/A3+ paper size is about the most you could reasonably expect to reach from a 35mm sized sensor with careful technique.

However, the quality test that I'd advocate is sterner; I'd ask at what point does an enlargement start to look significantly inferior to one made from a larger negative? In the days of film IMO a 35mm could generally hold its own up to a 10"x8" print, for a really good negative you could push that up to an 11"x14". After which the challenge becomes almost impossible as you pushed further into medium format territory.

What I see in my prints (using a 5D, 1Ds Mk II, P25 with a Hasselblad, and a P25 on a Linhof movement camera stitched to a sensor equivilant size of 49mmx71mm) is that even though digital gives a little more enlargement capability than film, especially with longer prime lenses, it's not that much more. And why should it be?

To go back to the 28MP Canon you mentioned (and I agree that something like it is sure to arrive before too long), some will look at that pixel spec and conclude that 240 dpi will get them pretty close to a 20" x 30" print. From 35mm? Surely it's time for a sanity check. What would the practical depth of field constraints be for an 18x or 20x enlargement? What back-breakingly heavy tripod would be required to still every last micron of vibration? And if there's a growing sense of dissatisfaction now with Canon's wide angles, what would the feeling be when those same optics are scrutinised at massive enlargement scales?

[michael]

I also disagree with my friend Norm's calculations. Not with the fact that the math may be right, but that in the real world the numbers don't correlate with experience, mine or that of other photographers whose judgement I respect. I'm talking about on prints.

Right now we are lens constrained in most cases, not sensor constrained.

Michael

[BJL]

Right now we are lens constrained in most cases, not sensor constrained.

Michael
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Michael, does that also apply to Canon's best primes? The comments of yours I can recall are about Canon's zooms, and maybe some if its wide angle primes, which apparently fall a bit short of the state of the art for 35mm format wides.

Not that this effects the big picture, which is that for a Canon SLR to give significantly more resolution that what is possible with the 1Ds is likely to restrict one to a small elite selection of their current lenses, and likely put pressure on Canon to add some new high end lenses.

[BJL]

To go back to the 28MP Canon you mentioned ... What would the practical depth of field constraints be for an 18x or 20x enlargement? What back-breakingly heavy tripod would be required to still every last micron of vibration? And if there's a growing sense of dissatisfaction now with Canon's wide angles, what would the feeling be when those same optics are scrutinised at massive enlargement scales?
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All good points! In particular, the greater magnification of Out Of Focus effects ("DOF") with greater enlargements progressively pushes one to higher f-stops, while the need to control diffraction pushes one to smaller f-stops, and at 28MP, these jaws might close in many situations, offering no aperture size that adequately balances the OOF diffraction effects on the sharpness/detail/resolution that 28MP is capable of.

By the way, this effects even larger formats like MF backs equally, just shifting the relevant aperture ratio about one stop higher. I am still waiting to see how those OOF/diffraction trade-offs play out with the new digital backs at 30MP and up.

[Gary Ferguson]

"I am still waiting to see how those OOF/diffraction trade-offs play out with the new digital backs at 30MP and up"

I take your point. The 30MP+ backs are a little rich for my blood, but I'm using a 22MP back and I've concluded that the phrase, "there's no such thing as a free lunch" could have been coined for photography!

I'm increasingly using the digital back mounted on a large format/movement camera in order to try and control depth of field with camera movements rather than stopping down. However, even when the shot allows this strategy there's still the problem of aligning the back with sufficient precision, just a speck of lint or dust in the mounting can be enough to throw the results out.

Still, if it was easy I guess we'd all be doing something else!

[Ray]

Surely it's time for a sanity check. What would the practical depth of field constraints be for an 18x or 20x enlargement?

There are two aspects to DoF. A scientific one based upon absolute resolution (ie. lp/mm of different parts of the scene) and a subjective one based upon an 'impression' from an appropriate viewing distance.

A consequence of lens improvement is that the parts of the image that are in focus will be sharper, but the parts of the scene 'not in focus' will not be sharper. There is consequently a greater disparity between what's in focus and what's not in focus, and therefore an 'actual', lp/mm, scientific, shallower DoF.

This seems unavoidable. But I would question the sanity of anyone who expects out-of-focus parts of any image to be as sharp as in-focus parts. We all know there is only one plane of focus.

There are always technological means being developed to overcome such problems. If your pixels are too small to generate sufficient dynamic range, try filling and emptying them several times during one long exposure. If the scene itself is just too contrasty for even relatively large pixels, then employ AEB and blend the images in PS. If you have a conflict between DoF requirements and absolute resolution, ie. if you insist that 30x40" prints should have the same DoF close up as they do from a 'normal' viewing distance, then you will have to employ ADOFB (auto depth of field bracketing which hasn't been developed yet but no doubt will by the time we get 28MP 35mm sensors). There are already available programs that blend differently focussed images to create enormous DoF from the scientific lp/mm perspective. All that's required now is an automation of that process.

What back-breakingly heavy tripod would be required to still every last micron of vibration?

As BJL has implied, it's all to do with pixel count and FoV. As regards holding the camera steady, it makes little difference if we have 28mp on a 35mm sensors, a 2/3rds sensor 1/16th the area, or an MF sensor 4x the area. The camera has to be held equally steady for all formats, for the same FoV and pixel count. The sorts of things that will change the outcome, however, are vibrations from mirror slap and mechanical shutters. The EVF cameras with electronic shutters will have the advantage with extremely high pixel count sensors.

And if there's a growing sense of dissatisfaction now with Canon's wide angles, what would the feeling be when those same optics are scrutinised at massive enlargement scales?

It's always unfortunate when one aspect of technological development streaks ahead of another essential component in the system. One would hope that Canon's new lenses would be up to the task when they introduce their ultra-high pixel density FF 35mm cameras. Perhaps we might even be able to trust them not to release a 28mp body until they've designed an appropriate lens. Who knows! Perhaps it depends on how savvy they think the camera buying public is.

There's an interesting analogy with Hi Fi audio here. For a long time now, amplifiers have exceeded the specifications of loudspeakers. Your sound quality is basically limited by the quality of your loudspeakers and your living room acoustics. You can spend as much on a state-of-the-art amplifier as on a Canon 1Ds2 body (and more). But any improvement with your existing loudspeakers in the same living room would be less noticeably than the resolution improvement of a 20D over a D60.

It's the perrenial problem again. Things that have to interface with 'reality' (ie. outside controlled laboratory conditions) are really difficult to improve. There are too many variables.

I'm editing this post in order to have a liitle rant which I think is relevant. My latest computer was built about 6 months ago. A Pentium dual core 64 bit processor, 3 GB of RAM and 400GB of Hard Drive. It was supposed to be my main computer for editing and storing photos. It's a white elephant. My Xrite-DTP94 colormeter does not yet have a 64 bit driver. I cannot calibrate my Sony CRT monitor with my fastest and best computer because production of a 64 bit driver is too difficult for X-rite or ColorEyes. And this is essentially a laboratory situation; just the monitor, the video card and the software. Very disturbing!

[Lin Evans]

Another thing which thus far has not been discussed is frame content and how that relates to enlargeability.

I'm fond of saying that for enlargement purposes film is grain limited while digital is resolution limited. So with film, no matter what the subject matter grain becomes the limiting factor usually long before resolution exhaustion. Because of the very clean nature of digital, it's quite possible at some point in the enlargement process to actually see the effects of resolution exhaustion.

This brings up the issue of frame content. Both frame content and subject impact enlargeability. In general, the more real world geography which is captured in a frame the more stringent the resolution requirements for a given print size. The amount of fine detail which presents itself to be defined in a hyperfocal, wide angle landscape verusus that in something like a head and shoulder portrait with an OOF background is markedly different. So the resolution requirements for a worst case scenario (finely detailed, hyperfocal, wide angle langscape) and a much better case scenario (head and shoulder portrait with OOF and virtually featureless background) differ accordingly.

I've seen excellent 50 inch prints of head and shoulders portraits made from a D30 (3 megapixel) capture and very marginal 16x24" prints of hyperfocal, wide ange, finely detailed landscaes made with my 1DS (11 megapixels).

To be overly simplistic - there is a finite amount of fine detail of any serious importance in a normal head and shoulders portrait. Eyes, lips, a small amount of visible hair, skin pores (not that we really want to even detail this). In a wide angle, hyperfocal landscape filled with vegetation, rocks, etc., there is by comparison nearly an infinite amount of detail to deal with.

Bottom line is that when using today's fine digital equipment we must be sensitive to not only the amount of magnification in the enlargement but also to the subject and the angle of view encompassed in the capture.

Best regards,

Lin

[Gary Ferguson]

Lin, you make some valuable points, and I'd like to take them further.

You argue that some subjects have inherently more detail or information than others, and therefore require different levels of resolution to be successfully photographed.

I agree, but I believe that as well as the inherent detail within a scene, we also have an inherent set of expectations regarding the amount of detail or information we expect to see in a photograph. These expectations are based on our basic experiences of seeing the world around us.

For example, a macro photograph of a fly that shows the structure of the fly's eye is so astonishing that we'll forgive many technical shortcomings and still regard it as "sharp". Conversely, with many of the cityscapes/architectural shots that I take, the viewer has a clear shopping list of expectations. So, if there's wording on a distant street poster, even if rendered very small, they expect to be able to read it.

[dmerger]

Do some relatively large, sharp photos reveal more detail than a person would discern when looking at the actual scene?  For example, could a distant poster be legible in a photo, but not when viewed with an unaided eye from the same position where the photo was taken?  If so, is this extra detail produced even with lenses wider than a "normal" lens?

I've not done any tests, but it seems to me that I often see details in some of my photos that I could not see when I took the photos.  Maybe my memory is faulty or I just didn't notice such details when I took the photos, but I seem to see more detail in some photos even when shot with a fairly wide lens.

[Gary Ferguson]

"Do some relatively large, sharp photos reveal more detail than a person would discern when looking at the actual scene?"

Great question! As you pointed out it depends on the focal length of the lens, but that's certainly what I'd aim to deliver to the viewer, it's what I'd call the "binocular effect". Have you ever noticed that if someone picks up a pair of binoculars they stare fascinated at objects that normally wouldn't entertain their attention?

I've noticed that when confronted with a scene in real life the brain fills in many of the details, but when confronted with the same scene in a photograph the viewer interogates it much more objectively and literally.

For example, I once did a series of rooftop views. While taking the shots I'd try and find the distance when I could no longer distinguish between concrete, brick, and rendered brick. The problem is that in real life you're influenced by other clues, does the building have a slate roof, or chimneys, is it located in a predominantly Victorian section of town? I'd factor these clues into the decision, so it wasn't purely a visual question of how well could the texture of a wall be discerned. But in the final print it was a purely objective, is that brick or just an orangey brown splodge? Yes or no.

[benInMA]

I think the brain instantly filters out much of what you see so you can make very fast decisions in terms of motor skills, responding to the important things in your environment, etc..

When you look at a photo much of that is flipped off since it's a 2-D representation, that's when you notice all the little details, and that's where a sharp photo comes into it's own.

Lately I've been shooting with a tripod and stopping down more then usual.  One thing I am definitely noticing is the more depth of field you have and the sharper the image, the more critical it is to notice all those details in the shot.  Because you are going to notice them when you look at the print even though your brain filtered them out when you visualized the shot.

Relevant to the Essay about lifting the shroud I guess.

[dwdallam]

One thing that is in the future too is not better interpolation software, which is formidable and will get better, but something that will definitely be better.

I don't know how long it will take, but I do know that a bit map type image, like RAW files, converted will be HUMONGOUS, like maybe 100GB or more--someone else will need to do that math.

I'm talking about bmp to vector conversion. Once that happens, you can use any MPs necessary to get the detail you want, and you will lose nothing to infinity when enlarging. I remember when early versions of Flash came out it had a bmp to vector conversion option. It was buggy and would crash your computer half the time, or take 2 days to convert a 600 x 600 BMP to a vector. But it did work kinda. However, a 100K file turned into a 10 MB file--when it worked.
 
When we do get to true vector images, or true vector conversion, our enlargement troubles will be over forever. They are enlargeable to infinity with no loss of detail etc. It just takes a huge amount of stored calculations to reproduce bmp images, and that is why the file containing those mathematical calculations is so huge. At least that is how I understand it generally.

BTW--Just how good is the best enlargement software nowadays?

[BJL]

An afterthought on my previous comments: I expect that we will move to sensors having noticeably higher resolution than lenses, so that resolution will be noticeably lens limited, but with sensors still holding resolution a bit below the ultimate potential of the lenses. (Apparently this has been so with larger format for some time.)

I expect this because
- When a lens and sensor have roughly equal resolution, the combined resolution is noticeably less that that of either component, so simultaneously the lens holds back the resolution potential of the sensor and vice versa.
- Thus, increasing sensor resolution somewhat beyond that of the lens can still improve overall resolution, getting closer to squeezing the most out of the lens. (The reverse is true too: increasing lens resolution beyond that of the sensor will also improve overall resolution.)
- There is now far more potential for increasing sensor resolution than lens resolution, and the cost of increasing sensor resolution is far lower, so I expect sensors to move ahead of lenses rather than the other way around.

In other words, the component of a system that is the most difficult and expensive to improve tends to end up being the weak link in performance, and I suspect that a collection of high end lenses is now that "most expensive and most difficult to improve" part of  a high end DSLR system.

[Ray]

In other words, the component of a system that is the most difficult and expensive to improve tends to end up being the weak link in performance, and I suspect that a collection of high end lenses is now that "most expensive and most difficult to improve" part of  a high end DSLR system.
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Do I get a sense here that you are coming around to my point of view on this issue, BJL   . Ie., it might be easier to build an MF lens that's fully diffraction limited at f16 than it is to build a 35mm lens that's fully diffraction limited at f8. Or to put it another way, an MF lens that can deliver 50 lp/mm at 50% MTF at f16 is a more realistic proposition than a 35mm lens that can deliver 100 lp/mm at 50% MTF at f8. (For all I know, there might already exist such MF lenses capable of good contrast at 50 lp/mm and f16.)

[dwdallam]

I agree wiht this line of thought. There are limitations to anything, analog ( physical) being a point in case. Digital, however, can get better in spite of physical limitations, as long as mathmatical limitations are not met. As I stated above, we can at this time convert a digital image, or a film image to digital, and then convert that to a vector graphic, which is a mathmatical computation of tonality. Now we can rezise it to infinity without degradation. The technology, however, is not nearly ready for the consumer. How far off is that? I don;t know becsaue I haven't kept up with it, but barring any huge leaps in storage, storage speeds, and processing power in teh next 5 years, I'd say it's decades off. That's why Flash limits itself to flat colors, and recently some "fake" shadowing, which is really several layers of flat colors that are made to look like a featherd shadow. Note I didn't say "feathered edge" because true vector graphics do not suffer from artifacting nor jaggies.

Do I get a sense here that you are coming around to my point of view on this issue, BJL   . Ie., it might be easier to build an MF lens that's fully diffraction limited at f16 than it is to build a 35mm lens that's fully diffraction limited at f8. Or to put it another way, an MF lens that can deliver 50 lp/mm at 50% MTF at f16 is a more realistic proposition than a 35mm lens that can deliver 100 lp/mm at 50% MTF at f8. (For all I know, there might already exist such MF lenses capable of good contrast at 50 lp/mm and f16.)
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