Film resolving power and 4x5

[cirwin2010]

This may be a silly post, but this is for my own curiosity.

It is my understanding that photographic film can resolve between 100-200 lp/mm. For the sake of example let use Ilford HP5+ which, according to old internet sources, can resolve 100 lp/mm. Obviously this number can be much lower depending on developer, development technique, negative density, etc.

It is my understanding that the best large format lenses usually cannot resolve much more than 60 lp/mm, but lets say we have one of such lenses. If we ignore all other traits of a given film (speed, spectral sensitivity, contrast curve, etc.), is there any reason to use a higher resolving film (such as t-max) if we only care about detail retention? Assuming no loss through vibration or other external factors and perfect development of the film, would HP5+ record all 60 lp/mm that the lens is resolving? Is it a 1:1 relationship or does this not hold true?

[Drew Wiley]

Don't feel embarassed; there have been many similar queries. It depends on a number of factors, including how big an enlargement is in mind. HP5 is a lovely film, but I gave up using it except in 8X10 due to its rather mushy grain if enlarged more than 3X. And I develop it in PMK pyro, which actually optimizes its edge effect; therefore, within its "sweet spot" of magnification, from contact print size up to 3X, it can render an almost etched look when developed in PMK.

The other limitation I found with HP5 is that it doesn't handle high contrast scenes very well due to its long toe. But it can be wonderful in more moderate lighting conditions.

Forget about all that oversimplified lp/mm talk. There are plenty of very sharp large format lenses to choose from, if high resolution is your priority. So yes indeed, TMax 400 (TMY) will deliver a visibly more detailed, crisper image than HP5, and do so at higher magnifications; most other sheet films will too. But HP5 has its own special "look", which many photographers appreciate.

[Vaughan]

Depends on the lens. Process and enlarging lenses are extremely high resolution.

Remember that resolution is complex and depends on the interaction between the different parts of the system. Think Moir effects when image and sensor resolutions interfere. To get full resolution from the lens you want the film resolution to be higher, around double: Nyquist theorem.

Film is complex because it has depth, and it has grains which when developed form bundles of metallic silver. When you're looking at the image you're seeing the light that's passing between the bundles of metallic silver.

[Mark Sampson]

Most any LF lens made since WWII (and quite a few from before that) will provide all the resolution you could ever need, if used within their design limits. They were carefully designed and built to satisfy a demanding professional clientele. Even a fifty-year-old, single-coated Schneider Symmar-S can out-resolve any of the standard camera films of today. (I speak from personal experience here, from a past life in research.)
If you want the most resolution without extreme measures, use a modern lens and a medium-speed film like TMX-100. I prefer Ilford FP-4 these days, mostly because I'm used to it, and because I don't enlarge above 4x. Just do your exposure and development tests on with whatever film/developer combo you choose, and you'll find all the sharpness you require.

[esearing]

And do you need perfect resolution - most scenes we take with LF film look better when there is delineation in sharpness at different focal points. Digital photographs that stack photos with different focal points to have 100% of all areas in focus look unnatural to me.

[cirwin2010]

I think folks misunderstood my question. Simply put if I have a lens that can resolve 60 lp/mm and a film that can resolve 100 lp/mm, are all 60 lp/mm imprinted on the film? Or is the relationship not 1:1?

[Mark J]

It's more complex. The max resolved detail on the film is a combination of the MTF curves of the film and the lens.
As a simple answer to your question, if a lens can only just resolve 60cy/mm in the image in free-space, and the film can resolve a max of 100cy/mm for a high-contrast image/target, then you will get a image with less than either of those on the film - eg. 40cy/mm.

If you want to look into this more, have a look first on standard explanations of 'MTF' which is Modulation Transfer Function.

[Oren Grad]

It is my understanding that the best large format lenses usually cannot resolve much more than 60 lp/mm, but lets say we have one of such lenses. If we ignore all other traits of a given film (speed, spectral sensitivity, contrast curve, etc.), is there any reason to use a higher resolving film (such as t-max) if we only care about detail retention? Assuming no loss through vibration or other external factors and perfect development of the film, would HP5+ record all 60 lp/mm that the lens is resolving? Is it a 1:1 relationship or does this not hold true?

No, it does not hold true. Strictly speaking, the resolution of a composite optical system - for example, a lens plus developed film - can be calculated in mathematical terms as a convolution of the modulation transfer functions (MTFs) of the individual components of the system. If you're not very comfortable with calculus, there's no point even trying to understand the details of the calculation. There are crude rules of thumb - for example (1/Rs) = (1/R1 + 1/R2) - which provide an approximation through a simple algebraic manipulation of lpm numbers. But the key qualitative point is that the system resolution is affected by the resolution of all of the individual components of the system, so the resolving power of the film does affect the resolution of the final image even if it is greater than the resolving power of the lens.

EDIT: just saw Mark J's post. What I said above is just a more elaborate version of what Mark posted.

[cirwin2010]

No, it does not hold true. Strictly speaking, the resolution of a composite optical system - for example, a lens plus developed film - can be calculated in mathematical terms as a convolution of the modulation transfer functions (MTFs) of the individual components of the system. If you're not very comfortable with calculus, there's no point even trying to understand the details of the calculation. There are crude rules of thumb - for example (1/Rs) = (1/R1 + 1/R2) - which provide an approximation through a simple algebraic manipulation of lpm numbers. But the key qualitative point is that the system resolution is affected by the resolution of all of the individual components of the system, so the resolving power of the film does affect the resolution of the final image even if it is greater than the resolving power of the lens.

EDIT: just saw Mark J's post. What I said above is just a more elaborate version of what Mark posted.


It's more complex. The max resolved detail on the film is a combination of the MTF curves of the film and the lens.
As a simple answer to your question, if a lens can only just resolve 60cy/mm in the image in free-space, and the film can resolve a max of 100cy/mm for a high-contrast image/target, then you will get a image with less than either of those on the film - eg. 40cy/mm.

If you want to look into this more, have a look first on standard explanations of 'MTF' which is Modulation Transfer Function.

Thanks for the information! I just re-read the section on MTF in Image Clarity: High-Resolution Photography by John B. Williams. I still will have to read into this more to really grasp it, but I think I am starting to understand now. Also he had the same formula for calculating the resolution.

Going back to my above example and after playing around with some variables (and assuming I did my math right), there is a benefit to using a higher resolution film. Using a 60lp/mm lens and switching from a 100lp/mm film to a 200lp/mm film will show a net increase of about 8lp/mm. So the reality is it doesn't matter much.


This is still probably flawed as the MTF values for a given lens posted online are likely determined by looking at the results imprinted on a piece of film. So it is already being affected by the above mentioned formula. Probably makes this exercise moot in the end.

[Mark J]

Really what you need is the inverse MTF curve for the film - which is a graph showing what MTF is required to make a given spatial frequency visible. This starts low and goes higher, up to 1.0 MTF at the film's 1000:1 resolution limit. I have seen rare examples of this curve. Normally however you just get two points on the curve - namely the 1.6:1 and 1000:1 resolving power numbers. 1.6:1 is 23% MTF I belive.

If you have this ascending curve, plus the descending MTF curve for the lens, then it's just a matter of overlaying the two curves on the same scale and seeing where they cross.

[Drew Wiley]

Then you've got the variable of specific development, and not just the specific film. And with view camera lenses, tangential performance often comes into play due to movements. But I'm not going to deal with any calculus; I thought that was a job for dental assistants.

[jp]

It's not strictly applicable.. But in the realm of recording of analog signals to a digital medium, Nyquist Theorem promotes the idea that you need twice the sampling rate on the recording medium to not lose input information.
Analog to analog has many more variables than this, but I think the idea holds up well that the recording medium (film) should be twice the resolution if you don't want to notice lens resolution issues.

When it comes down to practice instead of theory, I contact print, and my paper has much less resolution than the film or lens.

[Drew Wiley]

And once you move beyond black and white film and into color film issues, it gets even more complicated.

[Joseph Kashi]

It's not strictly applicable.. But in the realm of recording of analog signals to a digital medium, Nyquist Theorem promotes the idea that you need twice the sampling rate on the recording medium to not lose input information.
Analog to analog has many more variables than this, but I think the idea holds up well that the recording medium (film) should be twice the resolution if you don't want to notice lens resolution issues.

When it comes down to practice instead of theory, I contact print, and my paper has much less resolution than the film or lens.

There is an additional limiting factor - no matter how high the resolution of the analog film medium, you will not get fine detail resolution greater than the resolution of the lowest-resolving input, which in this case is the stated lens resolution, which asymtotically approaches the measures 60 lpm film resolution. That's the ultimate limiting factor of the system's resolution.

However, as noted earlier, if that 60 lpm resolution was measured on film, then all of the other factors have already come into play and that would be the real resolution of the overall system using that lens and film and those taking, development, and measuring conditions. The aerial resolution of the lens in that instance would likely be somewhat higher.

It's always worth recalling though that the diffraction limits at normal large format apertures hover near 60 lpm ( IIRC), and lower at smaller apertures, another physical limiting factor not susceptible to tinkering or "improvement hacks".

Since we're discussing limiting factors, don't forget that the enlarging lens, enlarger negative table flatness and alignment, enlarging paper surface and capabilities, and condenser/cold enlarger head also inevitably negatively affect final print resolution.

At best, the normal human eye can perceive about 12 lpm in the final print, which is why early laser prints printed at 300 dpi. ( 25.4 mm per inch x 12 ). If you can actually resolve 60 lpm in the analog medium, then you are doing very well across a variety of complex system inputs that all conspire to reduce the effective overall resolution.

[Tin Can]

as my eyesight is not curable

I use ILFORD RC Pearl only

I worked with 2 one eye mechanics

different sides

they often banged heads

not funny