Modern Photography: How to Test Your Lenses

Andreas Thaler · Nov 25, 2024

(PDF, 28 pages)

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Chan Tran · Nov 25, 2024

So if we get the target then shoot it with a high resolution digital camera we can just pixel peep the file and we don't need 20x to 30x magnifier right?

BrianShaw · Nov 25, 2024

I summarize this to 1 sentence quoted from the article, "In order to test a camera lens, pictures should be taken with it." I need no further details.

Andreas Thaler · Nov 25, 2024

BrianShaw said:
I summarize this to 1 sentence quoted from the article, "In order to test a camera lens, pictures should be taken with it." I need no further details.

What is probably meant is that you should take test shots with the lens whose performance you want to know about.

There are differences between lenses of the same model due to manufacturing tolerances.

Mr Bill · Nov 25, 2024

Chan Tran said:
So if we get the target then shoot it with a high resolution digital camera we can just pixel peep the file and we don't need 20x to 30x magnifier right?

Hi, I'm not sure if you're being serious, but on the surface this would seem to be correct. The reality, however, is that a digital camera, being a so-called sampled device, will almost certainly introduce what they call "spurious resolution." So something like a 3-bar target might turn into 2 bars or 4 bars, etc., etc.

The standard way to prevent this in a digital camera is, or at least used to be, to put what I still call a "blur filter" (aka anti-alias filter) over the sensor. The idea is to "fuzz up" the image detail enough that it can't produce "aliasing" at the sensor. And obviously, an intentionally blurred image can no longer show the true capability of the lens.

FWIW blur filters on digital cameras are/were generally not strong enough to completely prevent aliasing. (Image detail would suffer too much.) The frequencies of detail vary by angle and, in a Bayer type filtered sensor, by color. So you may also get color aliasing, etc.

In short, a conventional type of digital camera is not a good match with something like a 3-bar resolution target. (I didn't read the article... I'm just making a presumption this is the sort of thing they're doing. )

Chan Tran · Nov 25, 2024

Mr Bill said:
Hi, I'm not sure if you're being serious, but on the surface this would seem to be correct. The reality, however, is that a digital camera, being a so-called sampled device, will almost certainly introduce what they call "spurious resolution." So something like a 3-bar target might turn into 2 bars or 4 bars, etc., etc.

The standard way to prevent this in a digital camera is, or at least used to be, to put what I still call a "blur filter" (aka anti-alias filter) over the sensor. The idea is to "fuzz up" the image detail enough that it can't produce "aliasing" at the sensor. And obviously, an intentionally blurred image can no longer show the true capability of the lens.

FWIW blur filters on digital cameras are/were generally not strong enough to completely prevent aliasing. (Image detail would suffer too much.) The frequencies of detail vary by angle and, in a Bayer type filtered sensor, by color. So you may also get color aliasing, etc.

In short, a conventional type of digital camera is not a good match with something like a 3-bar resolution target. (I didn't read the article... I'm just making a presumption this is the sort of thing they're doing. )

But a digital camera can resolve a lot more details than the film can so if anything the film can reveal you should be able to do that with a digital camera.

Paul Howell · Nov 25, 2024

Although not quite the same procedure I tested all of my 50mm lens I had at the time, Konica, Miranda, Minolta, Pentax (K, M42) Peteri, Mamiya, Yashica and a few others. I used an old AF lens testing cart, my sons high school microscope, and microfiche film. Like the modern testing method there is a chart for the distance from the lens to the target. I set up camera on my Husky tripod on my patio in open shade. What I found was all of the lens I had could resolve Tmax 100 at 200LIPM. As microfiche can resolve 800LMP I found that the Konica 50 1.7 and Miranda 50 1.9 did the best, out performing Pentax. I did not have a Leica, and although I did have a Nikon lens no body, and no Canon lens. My guess is a modern lens will out resolve Tmax 200, so unless you are shooting and printing high resolution digtial, microfich or otho not sure what the point would be. On the other hand if you shoot older lens, say from the 50s to 70s then you might find a surprise.

Next time I am at my storage unit I will see if I can dig out the test chart so I can scan it.

Mr Bill · Nov 25, 2024

Chan Tran said:
But a digital camera can resolve a lot more details than the film can so if anything the film can reveal you should be able to do that with a digital camera.

Umm... maybe, maybe not, depending. If you actually tried to measure "resolving power" of a "system" via a typical digital camera (and assuming a typical 3-bar res target), I think you'll find that you cannot actually come up with a firm number. There will be a range where the spurious resolution confuses the issue.

FWIW there are, or at least used to be, special films that could outresolve any digital sensor that I knew of. But this sorta misses the point of someone testing their own camera/lenses. They typically wanna know what they can potentially get onto a pictorial film that they might actually use.

Taylor Nankervis · Nov 25, 2024

Sounds very techie...
I test my lenses in the real world by shooting subjects where the performance of lens (and photographer! ) is clearly on display for judgement.

Snap.

Sirius Glass · Nov 26, 2024

While one could purchase a chart such as the Air Force on mentioned in the article, one would need a enlarger to have a large enough image of various places in the chart to evaluate the lens. Which also includes some assumptions about the enlarger and its lens.

Modern Photography: How to Test Your Lenses

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