Testing for film speed "focus at infinity"

[OMU]

This question may be asked before, but can't find the answer.

I'm trying to find my personal film speed E.I. for fomapan 200.
I have an Gandolfi 8x10 and an Nikkor-T ED 600 mm.

If I should focus at infinity, (as Ansel Adam writes) I'll have to place my grey card "in the neighbor's garden" and it will appears as a stamp on the film.

If I focus at infinity an fill the film whit the gray card, it's impossible to measure any different with the density meter.

Any suggestion?

[Goldman]

I shoot 4x5, but to find my film speed I put my grey card closer and focus. The gray card should fill up the screen. Than mesure and shoot. I am doing this for 30 years and I am happy with the result. (Even Ansel Adams can be wrong, Nobody is perfect!)

Bill

[Jim Noel]

This question may be asked before, but can't find the answer.

I'm trying to find my personal film speed E.I. for fomapan 200.
I have an Gandolfi 8x10 and an Nikkor-T ED 600 mm.

If I should focus at infinity, (as Ansel Adam writes) I'll have to place my grey card "in the neighbor's garden" and it will appears as a stamp on the film.

If I focus at infinity an fill the film whit the gray card, it's impossible to measure any different with the density meter.

Any suggestion?

The objective is to have the gray card out of focus so that texture does not enter the equation. Focus at infinity and then place the gray card in position to fill the frame.

[jp]

Focusing at infinity also removes the variable of compensation for bellows draw.

[OMU]

The objective is to have the gray card out of focus so that texture does not enter the equation. Focus at infinity and then place the gray card in position to fill the frame.

Have tried that, but the film get so even exposed that it's difficult to measure the different in densities in the different exposures.

[neil poulsen]

I focus right on my target, but make sure that it's evenly lit. Knowing the focal length of the lens and the distance to the target, I can calculate the bellows correction. I reverse correct the evaluated speed with this bellows correction.

[OMU]

I have done some test according to the advisees above, got my IE to 100 ASA. In Xtol 1:1 . Normal development time in a tray, it seems as 7:45 is about right time. 20 degrees C.

Neil, I would like to get your mathematic formula to calculate the bellow correction.

[ic-racer]

If you need to have the target in focus you could add this bellows factor calculator to the target and read the factor off your ground glass as you work.
http://www.southbristolviews.com/pics/Graphic/SBVCALC.pdf

[Jim Noel]

Have tried that, but the film get so even exposed that it's difficult to measure the different in densities in the different exposures.

Your exposures should be a third of a stop apart and easily distinguishable.

[Kevin Crisp]

I agree completely with Jim. Focus at infinity. Have the evenly colored/shaded card closer to fill the frame. It MUST be evenly illuminated. Check corners and sides with a spot meter to make sure they are the same.

If the exposures are 1/3d stop different, the density change should be obvious, particularly if you put the negative on a white sheet of paper, unless your development time is so far off you aren't getting any real density. The difference should really jump out at you if you put the negatives on a white sheet of paper.

If you are measuring with a densitometer and there is not a significant, orderly increase in density, something is wrong. You aren't exposing enough and/or developing enough. The shutter speed must be a known good one, and it is far better to change exposure by using the aperture than changing shutter speeds.

[Ken Lee]

A common misunderstanding is that 18% represents middle gray. This may not always be so: it depends on lighting conditions. The official instructions which accompany the Kodak gray card advise us to expose an additional one-half f/stop after measuring the light with a gray card when shooting outdoors... or is that 1 full f/stop ? There is some controversy about this subject and about those instructions.

You might find this interesting: The Myth of the 18% Gray Gard. (http://www.kenleegallery.com/html/tech/index.php#myth)

If you want to test with a spot meter, I recommend you meter a variety of objects in your scene. That may be a safer approach than basing everything on the measurement of a single target of questionable utility.

[ic-racer]

At least in terms of the usual exposure index testing, the target can be any shade of gray or white. The target's zone is assigned by the tester. It is not a property of the target.

[patatperigord]

Other folks have implied and/or hinted at what I am going to say, but perhaps differently.

Ansel was probably thinking of his view camera when he said/wrote this. Focusing at infinity is the one spot where you are absolutely certain that there is no bellows factor at all. And thus you also have consistent repeatability across your entire set of lenses. As someone has already said, place your card(s) to fill the frame (or as I sometimes do is put a grey card, a white card, and some black velvet at once allowing me to check 3 different tones on a single sheet of film). I don't want the object to be in focus because I want to "smooth out" the texture for consistent tonality when measuring the film density with a densitometer.

[Peter De Smidt]

Focus at infinity. Photography an evenly lit black card (or similar) in shade. It doesn't have to be in focus, and it doesn't have to fill the frame. It just has to big enough to read the density on the negative. This is for Zone I testing. For zone VIII (i.e. development), do the same thing with a white card in sun. Check out the Zone VI Manual by Fred Picker.

[Kirk Gittings]

The objective is to have the gray card out of focus so that texture does not enter the equation. Focus at infinity and then place the gray card in position to fill the frame.

exactamundo.

[OMU]

Focus at infinity. Photography an evenly lit black card (or similar) in shade. It doesn't have to be in focus, and it doesn't have to fill the frame. It just has to big enough to read the density on the negative. This is for Zone I testing. For zone VIII (i.e. development), do the same thing with a white card in sun. Check out the Zone VI Manual by Fred Picker.

Tanks a lot to all of you. It was what Peter wrote that I couldn't figure out. I thought my gray card had ti fill the frame :-)

[Jim Noel]

This question may be asked before, but can't find the answer.

I'm trying to find my personal film speed E.I. for fomapan 200.
I have an Gandolfi 8x10 and an Nikkor-T ED 600 mm.

If I should focus at infinity, (as Ansel Adam writes) I'll have to place my grey card "in the neighbor's garden" and it will appears as a stamp on the film.

If I focus at infinity an fill the film whit the gray card, it's impossible to measure any different with the density meter.

Any suggestion?

Focus at infinity, then swing the camera around so the gray card fills the image area.

[OMU]

Tanks Jim :-)

[Drew Wiley]

Gray cards are all over the place in terms of quality control. Even those from the same mfg can vary 10% or more. And even the best ones which are close to spec new can fade or discolor. For fussy work like testing or calibration I keep on hand a carefully stored MacBeth Color Checker chart, which includes a full gray scale, and a neutral hue version of it, unlike most. Then you need to distinguish between shooting them in shade or in direct sun. The former is likely to be more accurate with black and white film. Testing color films is a bit more involved. But in the field there is simply no substitute for experience and being comfortable with your chosen meter. But until one starts actually printing their negs and becomes somewhat proficient at that, it's hard to peg down a personal standard for a particular film/developer regimen. Right foot forward, left foot forward, right foot, left food, shoot, print, shoot, print....

[Bruce Barlow]

These days, as someone who used to sell a film speed test kit including a .1 ND filter (which was accurate, Drew), I find myself skipping a film speed test, rating the film at half the box speed, and doing a decent development time test.

Close enough for photography. The negs are beautiful, with wonderful densities in the shadows.

Since I have an evil sense of humor, sometimes I'll run a film speed test just for fun. It almost always indicates the ISO I'm using.

Life's to short to spend it testing.

[Drew Wiley]

That's kinda what I do with certain brands. Box speed divided by the standard 50% Marketing BS Coefficient. It has proven a good starting point for testing, and
sometimes even for the final result. But film curve shapes differ, so just one shoe size never fits every foot.

[patatperigord]

Gray cards are all over the place in terms of quality control. Even those from the same mfg can vary 10% or more. And even the best ones which are close to spec new can fade or discolor. For fussy work like testing or calibration I keep on hand a carefully stored MacBeth Color Checker chart, which includes a full gray scale, and a neutral hue version of it, unlike most. Then you need to distinguish between shooting them in shade or in direct sun. The former is likely to be more accurate with black and white film. Testing color films is a bit more involved. But in the field there is simply no substitute for experience and being comfortable with your chosen meter. But until one starts actually printing their negs and becomes somewhat proficient at that, it's hard to peg down a personal standard for a particular film/developer regimen. Right foot forward, left foot forward, right foot, left food, shoot, print, shoot, print....

What Drew reminds me that I am really testing for just two things. One, am I getting a Zone II that is reasonably reliable -- that's what my meter needs. Two, I am developing this film long enough that I'm not getting highlights that are so think that I am unable to burn large areas within about 30% of the base exposure time making a print (in my case, on Grade 3) on my favorite paper with a common general purpose developer.

Since I shoot exposure zones 1, 2, 3, 7 and 8 if the grey card that I stick in for "grins" is off a bit, it doesn't mean much.

[Drew Wiley]

I'm trying to remember the brand of a gadget I recently bought. It's made of fabric around a hoop just like a portable bounce reflector, and folds and twists into a very small lightwt portable pack. It's gray on one side - and pretty damn close to 18% (better than most gray cards), and white on the other side. Got it from
B&H. It's marketed for setting gray balance in DLSR's, but is a very practical film metering device too. It's hard to carry around a big gray card. Yet I needed something large to facilitate neutral Zone III pre-flashing of Ektar color neg film on location to remove excess blue from shadows under open skies in mixed light
scenes (with a flashing attachment over the lens which includes a diffuser and warming filter, of course). I was really surprised how practical this folding gray
disc is. They come in various diameters.

[Bob Salomon]

These are extremely accurate for grey as instead of using inks use specially formulated paints that have exactly equal parts of the primary cools. And they are washable since they are a plastic rather then paper or cardboard.

http://www.novoflex.com/en/products/useful-accessories/grey-cards/