Looking for advice/ideas on testing evenness of development

[villagephotog]

I've started to dig a little deeper into testing how even my (B&W) development is on both 120 and 4x5 and could use some input.

I don't have an enlarger (more below). So, as a first go, I've been photographing a large piece of dull-white drawing paper in indirect, very even daylight (open shade), using 4x5 sheet film (a couple of different films and developers). Before shooting, I check the target's reflectance with the spotmeter on my Minolta Flashmeter VI, and the target surface has always measured within 1/10 f-stop across the image area. I use my 210mm lens at f/22, 2-3 ft. away from the paper but focused at infinity, to try to minimize optical vignetting and blur any details on the paper surface. So far, I've developed the negatives in a Jobo tank/reel rotated on a Beseler motor base, using appropriate times/temps for different developer/film combos. I examine the negatives on a light table by eye; some look perfect but with others, I've seen faint uneven developing. Then I scan them and push the contrast fairly dramatically; this reveals much more apparent unevenness, even in the negs that look good on the light table to my eye. (Fairly certain my scanner is not a factor in these results and 100% sure my display is not.)

To make a long story short, I'm doubting my test method -- shooting the same setup with my digital camera and pushing the contrast also produces what looks like odd development artifacts, even though I am smart enough to not run my raw digital files through a tank of chemistry . I'm now pretty certain that the texture of the paper is showing up as mottling, and maybe also some very subtle reflectance differences that I failed to measure with my spot meter. Some optical vignetting is also apparent, but I can identify and discount that.

So I think I'd like to take the target paper and the lens out of the equation. An enlarger seems like the obvious solution -- i.e. expose a sheet of film with one -- but, as I said, I don't have one. I could look for a smoother paper target, but I'm dubious that will make a big difference (could be wrong). Any suggestions or clever ideas for how to expose a sheet of film (or frames on a roll) to really even light that I don't have to second-guess? Also, any other input on this question is welcome.

 

[Kino]

Throw the image grossly out of focus when shooting.

 

[ic-racer]

Expose the sheet film to a light bulb across the room for a brief time to get an even density over the film plane.

Even development is often overlooked. Good job to tackle this issue.

 

[Alan9940]

Ideally, as you've already surmised you really want just the film exposed to absolutely even light. This is harder than it sounds and I think @ic-racer has a good idea; basically, toss a huge soft-box of light at the film. A mid- to light-gray density on the film will easily reveal any uneven development issues. But, as you go down this rabbit hole keep in mind that minor density variations will only be visible in subject areas such as clear blue sky. IOW, I wouldn't get too paranoid about it.

 

[gorbas]

Nothing helps evenness of artificial light source as distance from it. Further is better.

 

[MattKing]

Don't forget that some lenses don't give results that are even across the frame, for all magnifications.
For example, you don't want to spend hours and $ trying to even out the exposure from a really wide angle lens.
The advice up thread to throw the image out of focus is probably helpful.
In addition, if you have a really sensitive incident meter well set up for copy work, or even a good enlarging meter, you can test the evenness of the light incident on the subject before tripping a shutter.

 

[Kino]

With the bare bulb method mentioned above, wouldn't you need an estimated minimum/maxium exposure to avoid just hyper sensitizing the emulsion or totally fogging the film?

 

[Milpool]

With the bare bulb method mentioned above, wouldn't you need an estimated minimum/maxium exposure to avoid just hyper sensitizing the emulsion or totally fogging the film?

You want to evenly fog the film enough so that when it’s developed it has roughly a midtone density. With a bulb reasonably far away you can estimate the illuminance. Then you adjust everything so you end up with an exposure time you can control approximately enough by hand (say 1s).

It’s easier to do in-camera. Stick with a longer focal length lens stopped down a few stops. It isn’t very difficult to cobble together an evenly illuminated target in a number of ways. Keep the camera close to the target, focus at infinity. For LF make a cardboard mask for the lens to avoid bellows flare.

It is usually easy to discern uneven development, mottling etc from exposure unevenness.