You might find that exposure from a sufficiently distant, possibly diffuse light source will give a more even exposure on the original neg.
Also contact print the neg under even light on grade 5 paper or with grade 5-6 VC filter to make uneven development more apparent.
Yes, I'd expose and print like Lee suggests. To quantify evenness you can check the center and 4 corners with your densitometer (or send it to one of us).
Originally Posted by Lee L
Thanks guys. Any suggestions on a light source?
And I assume I set my light meter to f1?
I'd expose the film in a film holder with a light from across the room.
Haaa, Let's see... I just went through this...
TMY-2, set enlarger so incident meter reads EV0 with the "flat" dome (at ISO 100)
Expose for 5 seconds...
That gives me the same amount of "light" as my sensitometer.
Now you want something middle gray I suppose, a density around say 0.60 sound good?
That graphs under Stouffer scale step 14 which is 1.98 density.
So if you expose film that much less than the full 5 seconds at EV0, you will possibly get 0.60 density when developed.
1.98 divided by 0.3 is 6.6 stops...
So somewhere about an 1/8 or 1/15 second should do the trick...
Is there any light fall off in your enlarger....I'd check that with a light meter before using that method. I know that I get a little fall off with my D2 in 4x5. If you do it in-camera, I'd still check the corners just to see how much light variation there might be.......also, you might defocus heavily just to remove any texture
You can test for enlarger light evenness with a spot meter, aiming it at the center, corners etc from the lens axis. Don't overcomplicate this.
Regarding the Mod54, I'm testing this product now as it happens. One thing I don't like already, the tabs that hold the film extend too far out into the image area, causing tiny scratches on the base side of the film as the film slides up and down in the holder during inversion. I'm also finding I need significantly more than 1L of developer for it to work properly (not a problem, but worth noting). Lastly, I would suggest doing only two sheets at a time in this thing rather than 6. Testing is preliminary so far, but I still find tray development in a thin wire slosher to be the easiest way to get uniform development, including Pyro. The only thing better than the slosher is doing a single sheet in a tray. Of course the Jobo is reputed to be excellent, but I've never used one.
I would suggest using a zone 7 density rather than zone 5 because in my experience uneveness problems will show up more.
Back in my days of shooting products on a blank light grey it was a real headache getting it even.
Also because it is useful to have your zone 7 processing time down.
If using your enlarger make sure it is way out of focus from the light source.
Jeff we would do a basic copy shot of a large greycard.. make sure that the original is evenly lit.
process as normal and read the film on a densitometer.
If all is well each film that is in different positions of the rack , or each film within the run if Jobo should read identical.
If not your process is off.. I suspect this has to do with the nitrogen burst thread and it is a really good idea to do this, test to check for even development
If you do not have a densitometer on hand someone in your area could read the film and sharpie the numbers.
We measured 9 spots on each film to see how even the run is.
Originally Posted by Jeff Bannow
All enlargers with lenses have light falloff, unless you have a density filter/diffuser made especially for a particular magnification ratio and lens and aperture.
Exposing a film under the enlarger is a different test. That is a test of enlarger light evenness.
Graph shows composite results from 135 and 150mm Schneider Componon-S. The picture is a piece of film exposed under an enlarger and processed to a high gamma to accentuate unevenness.