Ground glass for 6x9 !

[pb908]

My mess ikonta with novar NEVER give me good result. My Bessa II with C-Skopar ALWAYS give me good result, but a can see a small amount of back focus wide open. I was about to get rid of the ikonta until last night when I saw one (and only) sharp picture which come from few rolls of Ikonta's result.
I was wondering why,for a reason I never get good result, but one shows me amazing sharpness which I remember it was taken at wide open (f4.5) and 1/10s+timer.

did my hand shake badly for the whole rolls and ruin the result? I believe not, as with bessa I can take 1/10 and get nice result.

is there any focus issue? How do I check it?
Collimation with dslr and long tele lens (istD+F*300f4.5) show me that infinity focus is perfect (or maybe I was doing wrong?). Then I google around to find more clue, and found that a better acuracy of collimation can be done with ground glass. how do I get one? I know that focusing screen of old slr can be use as well, but I need bigger area for 6x6/9. It's imposible!

but I was wrong. When I tried to measure the film area with ruller (i was about to make 645 mask for my bessa), I suddenly got a great idea, a cheap nice ground glass replacement, from a plastik ruller !!

what I do, I cut the plastic ruller to have 9cm length, and with a very fine grit sand paper (1200-1500), I make one side of the ruller to become dull/doff, just a few swipe here and there and it is done. My new 6x9 ground glass.

I tape it down on the film area, rest nicely on the two roller bar with the doff surface facing the lens.
And with a release cable at bulb, a 10x magnifier, and a roll of measuring tape, I check focus accuracy for all of my MF folder.
My bessa, yes, back focus a little bit, one piece of paper shim fix the problem. Checked at close distance (1m) and infinity, wide open, it's as accurate as I want it to be.
My mess ikonta, when I set the lens at 5m, the ground glass shows me that it focus at infinity. When I set focus at 2.5m, it actually focus for 5m. What the heck, now I know why it NEVER give me good result !
I need to play around with the front element ring alignment or make a thick shim to fix it, still on going task, but you get the idea.

a cheap plastic ruller do the job ! Hopefully this helps other

 

[graywolf]

The rollers are not where you want to index the ground glass. The film rail above and below the film gate are the proper place. The ground side goes against them. That is the film plane that the pressure plate pushes the film against.

 

[pb908]

Thanks tom, for pointing me the right position.
In my bessa II, the height of film rail above and below the exposure area are the same as the roller. But not the same in my Ikonta.
it's mean than I need to make different "ground glass " for different camera.

 

[kuzano]

Tupperware or plastic food container....

Tupperware or plastic food container....

I've done the same thing with a piece cut from a semi-clear tupperware or cheap food container. Put the frosted surface of the plastic cut out against the film plane. Check for focus at various settings.

 

[Roberto V.]

Thanks tom, for pointing me the right position.
In my bessa II, the height of film rail above and below the exposure area are the same as the roller. But not the same in my Ikonta.
it's mean than I need to make different "ground glass " for different camera.

If the distance between the rails is different, you'll have to make a new one.