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Lens Testing without film

 
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woodplane



Joined: 20 Sep 2005
Posts: 33
Location: Chicago

PostPosted: Thu Oct 27, 2005 5:45 am    Post subject: Reply with quote

Hi all,
Taking blurry pictures while on vacation is an expensive way to find out which lenses are up to the task and which fall short. Unfortunately, this is what I did. My 135mm Optar at f 11 has blury corners. I would like to create a test target and see which of my lenses perform well. I think the test targets at http://www.normankoren.com/Tutorials/MTF5.html are good. I have read about some tests at http://www.hevanet.com/cperez/testing.html where, at the bottom, Linda A Whatley says she measured the resolution with an eyepiece at the film plane.

I like the idea of testing the lenses without wasting the time and the film required to take images at various f-stops for each lens. I have tried it, and find it difficult to view the test target through the lens with an eyepiece and try to read how many lines I can see. I think a negative on a light table would be better behaved in the sense that it just lays there.

Has anyone tried testing their lenses? Any advice on how to go about doing it?

Thanks,

Scott
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RichS



Joined: 18 Oct 2001
Posts: 1467
Location: South of Rochester, NY

PostPosted: Thu Oct 27, 2005 5:53 am    Post subject: Reply with quote

I do _rough_ testing by focusing on a wire fence in my backyard. I can tell the difference between say, my 12-19-25 T&R and my 12-21-28 Gunlach. But that's on the GG and fine resolution is difficult to see. It's more a judgment call...

I would suppose you could do better with a aerial image, but to do it right, you'd have to replace the GG with a clear glass and it would help if it had some kind of markings on it to aid your eye...

For me, I'll do the rough look-see on the GG and wire fence, then do the final judge on a negative. Polaroid Type 55 is great for this, but a little expensive...

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Dan Fromm



Joined: 14 May 2001
Posts: 1887
Location: New Jersey

PostPosted: Thu Oct 27, 2005 9:48 am    Post subject: Reply with quote

Quote:

On 2005-10-26 22:45, woodplane wrote:
Hi all,
Taking blurry pictures while on vacation is an expensive way to find out which lenses are up to the task and which fall short. Unfortunately, this is what I did. My 135mm Optar at f 11 has blury corners. I would like to create a test target and see which of my lenses perform well. I think the test targets at http://www.normankoren.com/Tutorials/MTF5.html are good. I have read about some tests at http://www.hevanet.com/cperez/testing.html where, at the bottom, Linda A Whatley says she measured the resolution with an eyepiece at the film plane.

I like the idea of testing the lenses without wasting the time and the film required to take images at various f-stops for each lens. I have tried it, and find it difficult to view the test target through the lens with an eyepiece and try to read how many lines I can see. I think a negative on a light table would be better behaved in the sense that it just lays there.

Has anyone tried testing their lenses? Any advice on how to go about doing it?

Thanks,

Scott

The ground glass is awfully hard to read, especially in the corners, when the lens is stopped down. And unless you shoot your lenses wide open, you should evaluate their performance at shooting apertures. So to know how a lens will perform, there's not much practical substitute for shooting some film.

Your blurry corners at f/11 are telling to shoot at a smaller aperture with your 135 Optar when you want better image quality in the corners. Try f/22.

I'm in a different situation than you, I shoot 2x3, not 4x5, and most of the lenses I've had to choose between have covered much larger formats than 2x3. You've learned that your Optar doesn't quite cover 4x5 at the apertures you want to use. In my case, hanging a lens in front of a Nikon has been a somewhat economical way of evaluating image quality at the center. And that, not image quality in the corners, has been good enough for me. But you don't have that luxury.

Cheers,

Dan
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Kin Lau



Joined: 14 Oct 2005
Posts: 1
Location: Toronto, Canada

PostPosted: Thu Oct 27, 2005 6:20 pm    Post subject: Reply with quote

Hi all,

I'm also new to 4x5's. I've shot some expired Polaroid and some paper blanks for testing so far, and it seems to work well as far as being cheap

Has anyone tried cutting up some 35mm bulk film and taping it to a film holder to do this kind of testing? It would be a lot cheaper than just about any cheap 4x5 film, and film speed is still a lot faster than paper speed.
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woodplane



Joined: 20 Sep 2005
Posts: 33
Location: Chicago

PostPosted: Thu Dec 08, 2005 5:57 am    Post subject: Reply with quote

I'd like to believe that I could use some of the old bulk 35mm film I have to test 4x5 lenses, but I don't think it can be held in place very well. The damned stuff wants to curl, both back into a roll, and in at the upper and lower edges. This is part of what I like about sheet film - the film stays in the plane of focus. The best I can think of is to cut 4" long strips and put the ends under the edge slots on a film holder, but I've tried this and it just doesn't work well.
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woodplane



Joined: 20 Sep 2005
Posts: 33
Location: Chicago

PostPosted: Thu Dec 08, 2005 6:06 am    Post subject: Reply with quote

I agree that film is the way to go. The idea is to measure image resolution on film, so use film.

I still want to cheap out on time, film, and money. I would like to try cutting a pair of dark slides such that 1/4 of the film is exposed at a time. This way I can make 4 exposures per sheet, and each exposure would get center to edge coverage.

Using the slide with the lower 1/4 cut out would be easy, but using the slide with the upper 1/4 cut out might be trickey. The spring-loaded felt at the top of the holder might object to having a dark slide edge attack it head-on. Has anyone tried this? What would be good for cutting dark slide material? Saw? Dremel abrasive wheel?
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Les



Joined: 09 May 2001
Posts: 2682
Location: Detroit, MI

PostPosted: Thu Dec 08, 2005 6:15 am    Post subject: Reply with quote

Yor are on the right track. I tried setting up half width darkslides so I could do panoramas and found you really do need to leave the far end open. As for cutting the darkslides, a plastic scribing tool for plastic works well. I always slip with a dremel, destroying the tool bit and gashing either the darkslide, my hand or both.
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t.r.sanford



Joined: 10 Nov 2003
Posts: 812
Location: East Coast (Long Island)

PostPosted: Thu Dec 08, 2005 3:19 pm    Post subject: Reply with quote

How about taping a piece of 35mm. film, cut to length, into a sheetfilm holder? The key would be to make the two pieces of tape the same length as the piece of film, and to apply them cautiously, using the sprocket-holes to position the inner edges.

It had not previously occurred to me, but if you took a bit of time to trim the film appropriately, you probably could orient a piece along the diagonal of the format, to test center and corners in one exposure.

You'd have to degunk the holder afterwards, but there are some tapes on the market that don't leave much residue. The transparent red tape that photolithographers use on litho film might be a good choice, if you can find it.
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woodplane



Joined: 20 Sep 2005
Posts: 33
Location: Chicago

PostPosted: Thu Dec 08, 2005 7:16 pm    Post subject: Reply with quote

If you need to leave the bottom open, then that means 2 exposures per sheet, each being 2x5. I still might try the 1/4 dark slide, using a junk holder, of which I have several, to see if I can do it w/o trashing the felt.

wrt taping 35mm bits to the holder - that just sounds like too much work. How would you then develop all those bits of film? I think it would be too hard to load a bunch of 5" strips in a reel for tank development.
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t.r.sanford



Joined: 10 Nov 2003
Posts: 812
Location: East Coast (Long Island)

PostPosted: Thu Dec 08, 2005 7:53 pm    Post subject: Reply with quote

Well, you could attach stainless-steel clips to both ends of every strip, thread the top clips onto a slender dowel or a piece of coat hanger wire, and dunk the ensemble in a deep tank.

That would presuppose your having a number of exposed strips for simultaneous processing; otherwise, it would be no great trick to get a single 5-in. length of film onto an edge-loading reel (or to develop it in a tray).

If one were prepared to make the rather extensive preparations needed for multiple exposures, those preparations should include devising a way to identify which strip was which -- perhaps by including large signs near the center of the target, marked with the aperture used for the exposure.
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woodplane



Joined: 20 Sep 2005
Posts: 33
Location: Chicago

PostPosted: Fri Dec 09, 2005 6:17 am    Post subject: Reply with quote

Yes, all lens tests should have the test target and sticky notes, one for the lens, the others for the f-stop and shutter speed. This works great unless the lens is so poor that you cannot read the sticky notes on the negative.
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45PSS



Joined: 28 Sep 2001
Posts: 3229
Location: Mid Peninsula, Ca.

PostPosted: Sat Dec 10, 2005 3:37 am    Post subject: Reply with quote



[ This Message was edited by: 45PSS on 2005-12-24 21:00 ]
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woodplane



Joined: 20 Sep 2005
Posts: 33
Location: Chicago

PostPosted: Sat Mar 01, 2008 1:22 am    Post subject: Lens Testing with Film (was Lens Testing without Film) Reply with quote

I am ressurecting an old post - seems unreal that was 2 years ago.

The goal is to shoot some resolution targets at various apertures using as little film as possible, both to be cheap and to save time. Four shots per sheet is the most one can do and still have center and edge in the frame. I had discussed cutting 1/4 of a light-stop, but that would require using 2 light stops, one with a lower corner removed, the other with the upper corner. A stop with the upper corener removed can't be pulled from a holder without tearing up the felt at the top.

The answer is to use the stop with the lower corner trimmed, shoot the 2 lower frames, then go to the darkroom and turn the film around so you can shoot the other 2 frames.
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Dan Fromm



Joined: 14 May 2001
Posts: 1887
Location: New Jersey

PostPosted: Sat Mar 01, 2008 3:14 pm    Post subject: Reply with quote

Using a couple of chopped dark slides to get multiple shots on a single sheet is an old idea. Your adaptation of it to lens testing is cute, if you have dark slides to sacrifice.

But b/w sheet film isn't that expensive, and all you need do to read it is develop it.

So y'r cute idea seems to me like too much effort for the amount of money it will save.

Good luck, have fun,

Dan
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troublemaker



Joined: 24 Nov 2003
Posts: 715
Location: So Cal

PostPosted: Sun Mar 02, 2008 2:07 am    Post subject: Reply with quote

I think cut dark slides aren't a great idea either. And since they are only designed to light seal when all the way in, and have a space between the slide and the film, would allow fogging. I don't like the tape idea either; too much fumbling around in the dark room, but not impossible, I surely do use tape and small pieces of paper to check local contrast and dodging and burning with curly FB paper.
Anyway, here's something you might try that will at least cut the cost for a sheet of film in half, litterally. If you have a 4x5 sheet you can cut in half, it should big enough to handle it into the film holder and should stay nice and flat. I was thinking to run it all the way to the far end close the dark slide, flip it over, and load the other half. There's test #1 and #2. I don't think the film will slide in the holder, but Iwould keep them flat and expose right away. If I were to try this Iwould not put the first piece I cut down and I would have the notch code on the other piece. How muchis Efke, about 0.75 for a sheet, so I have myself down to 0.38. The only other harbinger I can think of is I do not like tray developing and these strips would not then work in hangers.
To use roll film I might try putting thelensin question on myview camera and after locating center, use the movements to place the centered corner over the corner of the marks for the roll film back. Just a thought, but my 135's cover OK as mentioned above, stopped down. I think they are sharpest at f~16 to 22.
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