Flare is never a constant. It varies with the specific lens and bellows extension, type of bellows, orientation of the camera toward the angle of the sun, whether your camera is in the shade or sunlight when you are shooting, how effectively you have shaded the lens, etc. Trying to have a fixed factor for this is nonsense.
I should clarify that - film tests should always be done in a controlled manner, with minimal flare. Otherwise you have no base reference. Afterwards, in the field,
you can estimate its effect and compensate, just like a filter factor. Best just to avoid it by using a good compendium lens shade.
And to complicate it further, flare effect will also depend on the subject. Flare from a uniform, single-tone matt surface that fills the frame (and beyond) will be less noticeable than when photographing a glossy checkerboard of deep blacks and bright whites. Until I started reading Stephen's post, I was pretty much a flare-virgin, which had explained the issues I had with my early film tests, a few years ago.Originally Posted by Drew Wiley
As Drew says, and as I believe now, it is best to do film tests in a way that eliminates flare as much as possible. To do that, I expose test film sheets using an inexpensive Eseco sensitometer.
Mario, I wish I could make a good suggestion, but I cannot, since your testing procedure is different from mine. I start by establishing the development time, regardless of EI, then I proceed to establishing EI. This procedure is a simplified adaptation of BZTS test, and is similar to the procedure from Way Beyond Monochrome Ed 2 (WBM). You start by making a few, usually 5, identically exposed test sheets/strips which you develop for progressively longer periods of time, usually a sequence such as 4 min, 5.5 min, 8 min, 11 min, 16 min. Then you use your densitometer to read bars from each strip so that you can find out the curves (contrasts) of each dev time, which lets you decide which is the "normal" one for you. Only then you go ahead to measure the EI, using your newly found normal time.
Having said that, you need to have a ball-park estimate of EI so that you know how to expose the test strips! This should be the manufacturer-provided ISO or nearby. If you are wrong with that, you will end up either with strips that do not start at fb+fog (expose less) or which do not go to high enough densities (expose more).
If you are interested in this approach, you can use the Excel sheet provided by WBM, or my utility which will do the interpolation and find out the N-1, N, and so on times. Read about it here: http://www.apug.org/forums/forum37/1...-index.html#16 but make sure to use the newer code posted in post #32, which is here: http://www.apug.org/forums/forum37/1...-index.html#32
In general, some people test EI first, and some, like me, test dev times first, it seems to be a preference.
+100
It appears Drew and I agree 100% for once.
- Leigh
If you believe you can, or you believe you can't... you're right.
There are fifteen pages involved in this discussion. Personally, I think some of you guys are making this much more complicated than it needs to be. What you see with your eyeballs and how much it is what you wanted to do is what should be the result of all types of testing. If it looks good to you, a densitometer measurement won't change your mind. A benefit of sheet film is the ability to expose and develop exposures one by one. Find an evenly lit surface with texture. Meter it and find the exposure to give what you want to have as Zone V. Make one exposure at manufacturer's ISO and one at half that ISO. If you wish, make identical exposures one, two and three stops larger and smaller on the same sheet. Develop both with manufacturer's listed time for the developer of choice. Contact print both on the same sheet of paper for the MTMB amount of time and process for a standard time in a standard developer such as Dektol 1:1 or 1:2. Compare the prints to a standard like a zone scale printed in a book. The one that is closest to Zone V and the scale which looks closest to the printed scale in a book should give you an ISO to start with. Use this initial ISO to expose another series of exposures in the same manner as the ISO test and develop one with the developer and time you used to find the ISO. Develop another one 15% less, another one 20% less and another one 15% more. This should get you in the ballpark for N, N-1, N-2 and N+1. Make comparisons with your printed scale to see if you have done what it is you think you want to do. If it's not close enough for your tastes, try again with different times. Then go out and take pictures. If you want to try two exposure and development pairs, expose two the same and develop one with the time you envisioned when you made the exposure and proof it.(N, N-1, N-2, N+1) If isn't what you were looking for, make the time a little bit shorter or longer.
It is possible to make good photos by using this method to get yourself going. Experience out in the field will refine your techniques and results more than fiddling with measurements and formulas. Change one factor at a time when possible and remember the old maxim: "Expose for shadows, develop for highlights". Once you start getting the results you want using standard procedures then you can try something else to see if you can make pictures you like better. When you are reasonably happy with your method of making your negatives, then you can work on the sophistication of your printing methods. I'm anticipating many disagreeing with me but I'm OK with that. It works for me and works for the dude (who can find lots of buyers for his expensive B&W art photographs) that taught me to do it this way. Trust your eyeballs. If all the calculations make you feel better, go for it. That's my story and I'm sticking to it.
Factoring in average flare is just like normal processing is for the average Luminance range. It puts you into the ball park. Flare is next to impossible to calculate in the field, so you shoot for the middle to limit extremes in variance. Once again, average flare is beneficial to film speed making it about a stop faster than it would otherwise be. It's incorporated into the ISO test. As flare reduces the exposure range, it affects processing. The manufacturer's suggested normal process incorporates between 1 to 1 1/3 stops of flare.
80% of flare comes from the subject. A lens shade helps with the other 20%.
Have fun in the snow!
Clarification: I have done this on a single sheet of 8x10 film by pulling out the dark slide in six steps. This would be much easier with roll film. With 4x5, you might be able to put two or three exposures on one sheet or just use separate sheets if you don't want to fiddle too much. Film's getting expensive, though...
One thing to watch out for if doing full-sheet exposure tests is that the developer recommendations are based on uniform "average" density for the batch of film being developed. Doing a single sheet that's significantly over-exposed can result in developer exhaustion if the amount thereof is close to the minimum required for the film area.
If you develop multiple sheets with some over- and some under-exposed, the average density should avoid this problem.
- Leigh
If you believe you can, or you believe you can't... you're right.
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