SG Adams, I've been testing

This is to follow up on an old discussion. I told you I was going to do formal

tests of a couple of normal lenses for 2x3 Graphics.

 

Well, I've got a couple of Edmunds 83,001 test charts and have tried them out.

The results are interesting, preliminary, far from conclusive. I can't for the

life of me come close to Chris Perez' resolution on film and I think we're using

the same emulsion. Acros, ISO 100. This is very disturbing.

 

Subject to the very real possibility that I blew it badly -- some of the lenses

I tried were on improvised boards, their axes probably weren't perpendicular to

the film plane -- my results with respect to normal lenses for 2x3 Graphics are

broadly consistent with his.

 

But nowhere as good, so I'll have to try again, and harder. Check focus between

shots. Bracket focus. It isn't clear that vibration is a problem, even with my

Speed's focal plane shutter. But film flatness or really strange field

curvature IS a problem, will try again with a different roll holder.

 

Item: at f/16 and f/22, my 103/4.5 Graftar is sharper centrally than the two

Ektars I tested. Less sharp in the corners. There were alignment issues, so I

can't be sure about it, but I got nearly as good results with a (probably) late

'20s 4"/4.5 Aldis Uno that is actually a triplet too.

 

Item: my uncoated 101/4.5 Ektar is sharper centrally at f/5.6, f/11, f/16, f/22

than my 105/3.7 Ektar. But the 105 is as sharp in the corners. This last is

not consistent with Chris' results. The 101's resolution in the corners is

limited by astigmatism; I scored a group/element as resolved only if both of its

set of bars had a clear area (at 40x) between the central and outer bars. In

the corners the 101 lost one set long before it lost the other. Classic

astigmatism.

 

Item: I botched most of the shots with my beloved 4"/2.0 TTH but it is clearly

sharper centrally, possibly not in the corners, than the 101 Ektar. This really

casts doubt on my old informal lens test protocol; it doesn't seem to give good

answers about corner sharpness.

I would think that sheet film would be much more flat than roll film for tests like this.

Also check very carefully to make sure that your ground glass panel holds the glass at the right offset distance. Just a little error there and it could throw everything off.

 

You also mention the focal plane shutter's vibration: That's an interesting question! Any possibility of testing with and without that shutter, say maybe by making a shot with the lens's shutter, and another with the FP? It would be interesting to see the results from that.

 

I've got a couple of old Speeds that howl so loud -- and I can feel the camera vibrate! -- that I'm afraid to even try using barrel lenses on them.

Wouldn't vibration in a FP shutter cause jagged lines (in the direction of travel)? And what plane the vibration was strongest in would have some influence too, I think.

Patrick, Michael, Charles, thanks very much for the helpful suggestions.

 

The problems are so inconsistent that I suspect operator (that's me) error most of the time. For example, some lenses were sharp at one edge of the frame and nowhere else. Others were reasonably ok everywhere, just not as sharp as hoped/expected.

 

MIchael, that I got good and bad with the same focusing panel points to me. I've occasionally thought I'd got good focus when out shooting and missed horribly. After one of these episodes I did some very controlled testing (copy stand, flash illumination, ... ) and was able to verify that focusing panel and film plane were in register. I found that problem, and it was me.

 

Michael, Charles I see no signs of motion blur. Remember that the FPS makes its bang at the end of its travel. I used it only with lenses in barrel.

 

Procedure was:

 

Focus lens wide open. Focus on center target, check focus on corner target, if need be rotate camera on tripod head to bring both points into good focus.

 

Remove focusing panel.

 

Attach roll holder. Transitional Graflex 8 shot; knob wind but with pin rollers at the ends of the gate.

 

Close front shutter.

 

Cock front shutter, set aperture.

 

Fire it with dark slide in. I used a long cable release.

 

Cock again, remove dark slide, fire again.

 

Insert dark slide, advance film.

 

Set aperture (I shot at f/5.6 or so, f/11, f/16, f/22) and repeat until done with lens.

 

I looked at the negatives at 40x with my stereo microscope. I scored a group/element as resolved if there were clear (ok, very very dim) spaces between the center and two outer bars, horizontal and vertical. I could have logged radial and tangential resolution separately, decided to be very conservative. I could go to 60x, don't think that will change anything.

 

Cheers,

 

Dan

Pick a lens, put all the other stuff and the testing crap away, and go take some photographs.

Bill, thanks for the advice. Of course that's what I should do. Except that every once in a while nothing works as intended and then it helps to diagnose the problem.

I believe Chris Perez uses Tmax 100 for his tests. Like Patrick said, you should really try out some sheet film for the tests. The roll holders, especially the old knob wind ones, are known to have issues with film flatness, even with the rollers. I don't think for this type of test you will ever get consistent results with ANY roll holder unless you could get hold of one of the vacuum types. Good luck with your tests, it sounds interesting.

Interesting early results, Dan. Does your RFH have an insert with a flat pressure plate, or a curved one? I've been arguing for some time that it's the pressure plate, not the pin-rollers, that matter where film flatness is concerned in the old Graphic rollholders. Also, if you suspect a film-flatness issue, check (and double-check) that the spring on the shell is providing adequate pressure to keep the insert where it's supposed to be.

 

The Graftar results are pretty surprising, IMO.

Michael G., I always take my own results with a grain or several of salt because of the risk of operator (that's me, and I make mistakes) error, am similarly skeptical of others' results for the same reason. Anyway, the RFH has a flat pressure plate. Thanks for the suggestion to check the shell's spring. I will, and I have a much newer shell to compare with, possibly use. I didn't use the newer one because its a Graflex/Subsea and its carrier's film advance, even after overhaul, is really stiff. I could also try again with one of my Adapt-A-Roll 620s.

 

About the Graftar. I've been seeing comments for a while that the Century Graphic economy lenses (Graftar, Graflar, who knows what else?) aren't as bad as rumored. So the result isn't a complete shock but since its mine I don't have a lot of faith in it.

 

Cliff, I moved to roll film years ago to have a better choice of emulsions, perhaps I should reconsider.

 

I got the oddest results with lenses on improvised boards. I think I'd better revisit my basic temporary board -- foamcore cut to fit inside the front standard's light trap -- design. Foam core taped to the front standard might give better parallelism.

Surprisingly, the images you'll get with roll film are somewhat larger than those on sheet film.