Achieving film-like resolution, lens requirements?

Question

I am considering moving up to a full frame camera and want to know how my image results will compare to film.

According to Kodak, a 35mm film cell has 6000 lines of resolution. Olin Lathrop gave a great answer, basically saying that even though film theoretically has about a 19 Mpix resolution, due to grain noise and the improved dynamic range of a sensor, his 12.1 Mpix camera gave better results than film.

According to the answers in a different question, high-quality slide film, handled carefully at a slow speed can get over 20 Mpix, but since full frame DSLR is around 24 Mpix, and is fast with good response, we might expect full frame to dominate 35mm film in quality, even if it is slide film. However...

My question is how the lens fits into all this. I thought that resolution is limited by the airy disk of the lens. Are the typical lens used with DLSRs of sufficient resolving power at F2 that they exploit the full sensitivity of a full-frame sensor?

Answer 1

I am considering moving up to a full frame camera and want to know how my image results will compare to film.

My standard cautionary remark is that moving to full frame is not necessarily moving "up".

Your photos will not become better by buying more expensive equipment. I've seen a lot of disappointed and frustrated people who try that.

"up"

Define "up". What do you expect to achieve from your camera and lens that's you want to be better than what you have now ?

Unless you've a clear idea of this and it's tangible, then you're possibly wasting your time and money.

My question is how the lens fits into all this. I thought that resolution is limited by the airy disk of the lens.

Are the typical lens used with DLSRs of sufficient resolving power at F2 that they exploit the full sensitivity of a full-frame sensor ?

Typical mainstream modern lenses (including kit lenses) have very good to excellent resolution characteristics in my experience. I've been of the opinion that (in real world shooting) the combination of a modern crop or full frame DSLR with a modern lens can wipe the floor with film. Some people really object to that idea, but that's my view. It's not just the lens, it's the combination of capabilities.

"Sensitivity" is how well a sensor captures light. It's got nothing to do with the lens.

Resolving power is a combination of factors and aperture and depth of field play a huge part here.

So while a lens may have, on paper, outstanding optical performance, the reality is that you won't be shooting paper targets all the time (hopefully).

A typical F2 lens used on full frame will probably have from poor to very good resolution figures that vary across the frame of the image (and that's assuming you're shooting a flat target). It is very typical of all wide aperture lenses that they are relatively weak wide open.

It is typical of all lenses that they have peak resolution across the frame at a mid-range aperture, like f8. After f8 things drop off due to diffraction and that's unavoidable.

But if you shoot normally at f2 with a lens on full frame (or crop frame), then the vast majority of your field of view is probably out of focus (due to narrow depth of field). Depth of field is a much more significant factor than anything else in resolution.

So obsessing about the resolving power of the lens is just chasing dragons.

Worry more about contrast and bokeh (that's the quality of the blur, not the amount ). Lenses with good resolution do not always have good contrast characteristics, and wide aperture lenses need a good bokeh (if possible) to gave a smooth and non-distracting out of focus blur.

For my style of shoot contra-light is important, and knowing this is important in choosing a lens. A lens with good resolution characteristics would not be a choice for me if another lens had better contra-light performance.

There's more to picking a lens than raw resolution tests.

Answer 2

DxOMark is probably the best source for this, they test camera/lens combinations. They have a sharpness score measured in "perceptual megapixels", i.e. how many megapixels would you need to reproduce all the detail the lens/sensor combination can capture.

Take the Nikon D750, a 24 Mpx full frame like your suggested standard. There are several lenses (sort by 'sharpness') that give the full 24 Mpx, while the low end lenses come is at around 10 Mpx. The sharpest lenses tend to be on the pricey end, but there are sharp sub-$1000 alternatives as well.

The diffraction limit is only one constraint out of many, other lens aberrations reduce the effective resolution as well. What you get in practice depends on both the sensor and the lens, as well as camera settings and your technique. (Which may include sticking to a narrow range of f-stops, and using a tripod, mirror lock-up and a remote release if you are aiming for maximum resolution at slower shutter speeds. You also need a way to present the photo that can show all those megapixels - monitors, 4k TVs and small prints can't. But all of this is the same for film.)

That said, resolution isn't everything, and in most cases you won't really notice if you end up with say 18 Mpx instead of 24. In many common scenarios you don't care much about sharpness towards the edges either, because the subject tends to be in the center (e.g birds), and the lens that's sharpest in the center may have less total resolution than another that's medium sharp everywhere.

TLDR: Yes, there are lenses that can give full resolution for a 24 Mpx full frame sensor. And no, they are not necessarily 'typical', especially not if you consider kit lenses and superzooms typical. And at typical settings in typical use cases, even less so - it takes dedicated effort to squeeze the maximum achievable resolution out of your equipment, whether it's film or digital.

But for most photographers and most photos, 'good enough' resolution is indeed good enough, and other aspects of the lens - say weight, weather sealing, autofocus - become more important.

Answer 3

I am considering moving up to a full frame camera and want to know how my image results will compare to film.

If you print at sizes small enough to keep resolution over 240 ppi, the digital will look most likely better. So if you plan on purchasing 24+MP camera and print no larger than 13x19", you don't have to worry. If you print very large, like over 20x magnification and don't use any special techniques, the film may look better when compared to digital (you won't have better actual resolution, but magnified grain is still sharp).

My question is how the lens fits into all this. I thought that resolution is limited by the airy disk of the lens.

The better the lens, the better the resolution.

Are the typical lens used with DLSRs of sufficient resolving power at F2 that they exploit the full sensitivity of a full-frame sensor?

It depends what you consider a typical lens (that can be shot at f/2). Most will deteriorate the image quality at f/2 to some extent (corners, overall contrast, even overall resolution). If you need flawless performance at f/2 and 24+MP, you need to look at lenses like Zeiss Otus, modern Leica M lenses or similar.

It is important that once you start to pixel peep, you'll start realizing that camera resolution and lens quality is not enough to keep the overall image quality at 100%. If you do not pay attention to exposure time, do not use quality tripod, quality tripod head etc., your image quality won't be perfect. The other thing is if you need perfect.

Answer 4

There are a lot of differences between film and digital that are more noticeable than maximum resolution: Color space/gamut, highlight rolloff, dynamic range, etc.

There can be a lot more differences between two different types of film that are more noticeable than maximum resolution. Not to mention that maximum resolution will vary greatly from slower films to higher speed films. All digital sensors, even of the same size and resolution, are not equal either. Even the same sensor is not able to record as much detail at higher ISO settings that normally result in a lower signal-to-noise ratio than at lower ISO settings.

So there's no real way to conclusively answer if a certain lens has the resolution needed at f/2 to "...exploit the full sensitivity of a full-frame sensor?"

Which FF sensor in particular? In what kind of light? Compared to which film? Using what post-processing or development/printing methods? Displayed in what type of medium at what display size? Color or B&W?

With either recording medium in real world usage, as opposed to shooting test charts in a lab, the lens is rarely the limiting factor. Camera/subject motion are probably most often the limiting factors. Insufficient illumination is probably high on the list as well.

When considering whether or not to move to a full frame camera, the maximum lens resolution at f/2 of a particular lens is probably well down the list of most important things to consider.

Answer 5

OK, will post as an answer, thanks.

6000 lines horizontal (3000 line pairs) would be 4255 dpi and 24 megapixels (assuming 35mm film). That would be an optimum maximum case for scanning high quality slide film. However, f/2 is not an optimum maximum case.

Good lenses might reach 100 lp/mm, which is 2540 lp/inch which is 5080 lines per inch. Not at f/2 however.

Answer 6

You can read semi-commercial explanations at places like digitaltrends . They point out the difference in the image aspect ratio available, for example.
After having spent [lots] of years designing and analyzing adaptive optic systems and sensor SNR requirements, I'm a bit biased, so take this next advice with that in mind: The larger the individual pixels are, the greater the signal dynamic range possible. Yes, it's great to have a gazillion pixels, but if they're so small that the actual "well" is limited in size, then you will lose contrast in some scenes. In addition, the larger the pixel wells, the more light collected and thus the less effect both photon shot noise and analog electrical noise have on image quality.
Obviously I'm ignoring the potential cost&weight difference in getting lenses to match large-area sensors, so keep that in mind as well.

Answer 7

Comparing a full frame digital camera to a 35mm film camera is one thing. Comparing it to film is another. No 35mm camera will compare favorably (in terms of resolving power) with a large format film camera. 4 x 5 sheet film has 163mm diagonal and 15 times the area of a 35mm sensor.

Sure a large format camera comes with tradeoffs. Everything in photography comes with tradeoffs.