large format lens testing (method confirmation question)

[pellicle]

Hi

I dunno.

When I don't like a lens I find myself not using it, and it is a candidate for disposal. There is no need to test it.

certainly if I was "well heeled" I'd just grab the better lens (in my case I've been eying off the Nikkor 90mm f8) but not having access to a ready supply of funds I'm trying to see if

1. my expectations are too high
2. if I can get any quantative measure to compare the lens I have with the tests of the lens I'm interested in
3. by evaluating my technique seeing if the improvement can come from my technique (meaning I don't need to spend $700 on a lens)

however ... all donations are accepted :-)

[df cardwell]

Scattered observations

Diffraction limit: f/22. ALL good lenses perform the same at f/22 (as soon as you image on film).

From a practical point of view, a PERFECT lens will image no finer detail than .0125 mm at f/22.... 80 lp/mm
(f/32 = 55 ------ f/16 = 110)

.............

You are testing a camera system (meaning the flaws introduced by ground glass placement,
focus error, and film flatness, film performance, etc.). Your RESULT does NOT isolate the Fuji lens,
it integrates the lens into the rest of the stew.

Have you confirmed the ground glass is in the exact place ?

WHAT KIND OF FILM ARE YOU USING !!!!!!????????? DEVELOPER ???

........

Koren's test measures the point where the SUM of the lens contrast and the film contrast becomes noise.
If you are using a normal film at a normal development, you can't get better than 100 lp/mm from it.

IF a perfect lens at its perfect aperture can image 100, and the film can image 100, this is your formula:

1/R = 1/Rfilm + 1/Rlens 1/R = 1/100+1/100 R=50

Increase the contrast of the film, you can image a higher result:

1/R = 1/200 + R/100 R=67

Factor in diffraction, your results are really pretty awesome.

..........

There is really NO difference in the performance of a Fuji / Nikon / Schneider / XYZ design. The only difference will be from sample to sample. The best way to see where you might be losing performance in your camera system to to check the ground glass placement.

Then, the best way to improve your 'acutance' is to use a film like TMY or TMX.

..........

All 'sharpness' issues have to consider the contrast of the scene. A nice winter landscape will lack the contrast of summer sun. This means that you can't get some theoretically perfect contrast from a low contrast scene using a film and developer intend for making pictures. This is why Sharpness of Seeing is more important than the Sharpness of your Lens. If you compose an image using adjacent tones (middle gray next to dark gray) your image will look soft, regardless of your equipment. If you compose black against middle gray, it will have more snap.

[keithwms]

Whoa wait a sec df, who shoots everything at f/22? Not I for one. Isn't the whole point of using an LF camera to be able to manipulate the plane of focus so that you don't have to stop down excessively to compensate for the much larger circle of confusion? And conversely, to be able manipulate OOF transitions so that the tightest focus is placed where you want it? My, I guess I have been doing it all wrong Then again, nobody invited me into the f/64 (or should I say f/22?) club so I am still a free spirit.

Seriously, I just don't think anybody should assail someone who wants to learn how to test lens resolution. C'mon now, if it's not for you then don't do it. But at some point people should learn about the difference between high and low frequency information and how colour rendition affects focus and so forth. These are really basic issues that the O.P. apparently wants to learn about.

*Of course* the image is the most important thing. So...? We should shut off our brains and just make spectacular images? Great, let's do that....

(no offense intended, I am sarcastic after 2 cups of strong coffee...)

[df cardwell]

Keith

OP tested his lens at f/22 because he thought that it would not be affected by diffraction.
Since Diffraction IS in fact determining the outcome of his test, I brought it up.

Testing is kinda fun. But our run-of-the-mill photo gear is so good,
we have to be very rigorous WITH our tests to get answers that are helpful.

d

[keithwms]

Agreed

[pellicle]

Hi

df

Scattered observations

lots of good ones too ... I'll chew on this and reply to some of them later (should you be so kind as to be following up on this)

Keith

I didn't feel assailed ... I'm sorta used to terse and my thesis examiners were about the same (only that counted more for me ;-)

[Ralph Javins]

Good morning, Pellicle;

Nice to see that someone else has discovered that there is more to lens testing than just the lens resolution numbers you get from a test target. And, of course, which target? Your observation on the limiting factor of the sensor in a digital camera is one that is overlooked fairly often.

Nice thread. Thank you for bring it up. An enjoyable read, including your detailed comments on your own site.

[pellicle]

Hi

Scattered observations
Diffraction limit: f/22. ALL good lenses perform the same at f/22 (as soon as you image on film).

ok ... I will try with f8 and f16 to see if there is noticable advantage.

You are testing a camera system (meaning the flaws introduced by ground glass placement,
focus error, and film flatness, film performance, etc.). Your RESULT does NOT isolate the Fuji lens,
it integrates the lens into the rest of the stew.

that is true, but then all testers must use something to hold the lens and something to read the information, so like any testing procedure I have my system and they have theirs ... now your next question is a step towards confirming how well I've performed this analysis on my testing equipment.

Have you confirmed the ground glass is in the exact place ?

yes, although I have not measured it with a probe but only by exposing film.
My procedure was to:

1. place a ruler on the desktop
2. with the camera looking down at the desktop at about 30deg inclination I focused on the 15cm point of the ruler (about mid way) using my Fujinon 180mm lens @ f5.6 and at a magnification of about 1:2
3. I confirm focus with a x10 loupe and take a sheet for examination

This rough test indicates the the center of focus is pretty darn close to where I think it is and the movement of film plane by as much as a 0.1 mm in this case will show up

Also, my sheets are awfully flat (its surprising) which I attirbute to the humidity here in houses in Finland. (I almost never have 120 film curl for instance)

WHAT KIND OF FILM ARE YOU USING !!!!!!????????? DEVELOPER ???

well, there is no need to yell ... and besides there are bold and underline provided here for emphasis ...

In this instance I was using ADOX CHS film processed in a BTZS tube using D-76 neat and rolled gently during the entire 6 minutes at 22deg C

If you are using a normal film at a normal development, you can't get better than 100 lp/mm from it.

I've heard something like that before. I'm willing to accept that, but no matter I don't think I'm likely to get that value :-)

IF a perfect lens at its perfect aperture can image 100, and the film can image 100, this is your formula:

1/R = 1/Rfilm + 1/Rlens 1/R = 1/100+1/100 R=50

well I'm not familiar with that way of dealing with accumulation of error in the system ... but I'm not sure how to apply (my chemistry background) knowledge to this system.

I'm more aquainted with how to include errors as %age or as plus minus values.

however it seems rather a conservative calculation (which is good) and so should result in a worst case estimate. I'm ok with that.

Increase the contrast of the film, you can image a higher result:

1/R = 1/200 + R/100 R=67

Factor in diffraction, your results are really pretty awesome.

ok ... well ... that's good to know :-)

..........

There is really NO difference in the performance of a Fuji / Nikon / Schneider / XYZ design. The only difference will be from sample to sample. The best way to see where you might be losing performance in your camera system to to check the ground glass placement.

ok ... well, you see ... not having had one I have no basis for comparison. Which is the goal of this exersize .. a basis of comparison.

The tests by Perez and Thalmann

seem to show that there is a substantial difference between the Nikkor 90f8 and (for example) the Schneider SA

f/16 67 67 60
f/16 60 54 21

its the edges which really make me interested in this lens as I like to do work with either a 6x12 roll back or a "split sheet" method like this

All 'sharpness' issues have to consider the contrast of the scene. A nice winter landscape will lack the contrast of summer sun.

it depends, for example here



I think that the black on white edge shaprness of the willow on the snow was as important as anything for making the image.

Strangely I was unsatisfied with the sharpness from this situation, but in a MUCH lower contrast was very happy with this lenses production



which was my 180 (mate, that lens is great!) Looking at this, and thinking about what you say below, perhaps its the black on grey again ... as the shadow details of twigs in the murky light at the bottom are where its "gosh" for me.

This means that you can't get some theoretically perfect contrast from a low contrast scene using a film and developer intend for making pictures. ... If you compose black against middle gray, it will have more snap.

I gess that's why this image worked out so well ... black on grey



down on the corner here ...



anyway, thankyou for all your information and suggestions. I'll try the f8 and f16 and post results

:-)

[pellicle]

Keith

Whoa wait a sec df, who shoots everything at f/22?

well ... me sometimes. I prefer not to go bigger than f11 and so I'm usually somewhere around that or f16 on either of my lenses.

[pellicle]

I said above that I would compare the lens at f8 and f16, so here is that comparison. I processed the f8 / f16 image on a single sheet (using a half dark) and shifted the lens to keep the test target in the center of the image circle



please click on thumbnail for larger view (as I didn't wanna waste anyone's screen size)

I can see a little bit in it ... perhaps with better gear it might be clearer. Personally I'm comfortable with them being quite similar (meaning that diffraction is less of an effect than I'd have thought)

NOTE: the lens is wide open at f8 and f64 is the smallest aperture.