Methods and subtleties of clip testing
New to this forum, but quite a bit of experience in most areas of black and white, all formats, many processes.
And yet I have never in all my days done a clip test. What methods do people use for clip tests in 35mm? And for what reasons?
My most pressing concern is whether or not processing a small amount of 35mm film, in a reel (taped in or otherwise secured), will yield a result that is exactly the same as if a full roll were processed in the same chemistry at the same dilution for the same time. Do people do clip tests for precise tests like effective ISO, curves, etc?
Will the agitation currents might affect the film differently? Or will the developer oxidise/deplete faster or slower because of the smaller amount of film?
I can't say I've done a clip test either.
You would do a clip test (or snip test) if you have an important roll of film that you don't know how it was exposed. Like you inherit your grandfather's camera and find a roll of film in it. You might have pictures of your grandma as a young girl but don't want to take chances.
A more routine situation is doing a film sensitometry test. You want to develop short sections of film for different times. Each test is about six inches of film, and you want to develop it for different times like 4, 5, 8, 10, 12, 16 minutes.
In 35mm reels, development already varies between the outside, center, or in midsection of the roll of film.
True a test strip won't "use" the developer the same as a regularly exposed roll of film. The agitation will be different if you aren't using a whole roll of film too.
But I don't consider these variations critical, I mean I don't think they would cause a 5% change in results.
I personally just "expose" a sensitometry test at the end of a roll of film that I rewind early. I just run my tests in with my regular film runs, as a process control.
Thanks Bill, super helpful. I'm looking to dial in a few things, and it's just so much cheaper to expose a whole roll of a step wedge or something and just do clip after clip from that roll, instead of a whole canister, or sheet after sheet of 4x5.
I might want to sacrifice two rolls and see what how different the densities are between a whole roll and a clip of the same wedge or grey card.
If you are shooting gray card in camera to make test exposures, I recommend that you open the back of the camera in the darkroom and snip the sprockets to mark where the series end. Close camera and make another series etc. until the film is finished. Then when developing... Pull the reel, unwind and feel the first cut, and rip the strip off... continue developing a few minutes and pull the reel, feel for the next snip and rip. etc.
Not to discourage you from experimenting, but I don't think you need to "test" the effect of snip vs whole roll.
You are aware it's a variable that may exist - that's good enough to have awareness. Chances are you have many variables of the same magnitude - that are "out of control".
There IS a difference between tests and real runs. I deal with it, like I implied, by running tests at the tail end of regular developing runs. As statistics and process variability goes... none of my points are actually "on" the curve.
From my test "curve families" I draw a Time/Contrast Index chart. Each time I run a routine test, I'll add another point for the Time/Contrast Index chart. It's kind of like throwing darts. If it hits near where I aimed I'm happy. If it misses by a lot I start to look for mistakes.
My understanding of the value of a snip test is more to dial in a specific roll or sheet, than as a testing tool. For example with where there is some question about how to develop E6. I have not done snip tests from rolls because I have not had anything I was that worried about. (And typically if I make and exposure error it's normally a big one and adjusting development isn't going to fix it.)
For 4x5 I do shoot two sheets for important shots but that is more about dust or blinking subjects.
For testing 35mm film, since I hand load, I just roll a couple short rolls.
Mark Barendt, Ignacio, CO
"The mind that opens to a new idea never returns to its original size." Albert Einstein
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Just wild dreaming here but......
Most film is not sensitive to IR, but IR is blocked by silver - therefore it would be possible to build a B&W film processor which would continually scan the negatives as they developed, and develop until you reached a pre-set contrast ratio. Sort of the ultimate snip test.
Extending your idea some, you could wear IR goggles (for night-vision) and with an IR light-source in the darkroom, you could develop by inspection.
Originally Posted by Mark_S
Those must be pretty expensive...
Originally Posted by albada
They are not expensive anymore. The 1st generation device that I use (ATN Viper) can be had for $250-300. Others have talked about a toy called "Eyeclops" which may be serviceable (except much less convenient) for about $50.
But getting back to snip tests... Tkamiya has asked about how to get the worst possible grain from Tri-X...
This is a perfect example where snip tests will come in useful.
There are lots of ideas thrown out, develop in Dektol, overexpose, intensify, reduce. Four or five experiments could be done on one roll of film.
Clip tests in the traditional sense were for dialing in your E6 materials for color balance and speed.
My first mentor I assisted for would buy his E6 by the lot number and then test at the beginning and have the CC he needed for that entire batch.
It was helpful for film speed and if any pushing/pulling was needed.
This was for 120 and he did alot of magazine work that was offset printed and the printer wanted you to have your color right so it was easier for them.