Can anyone tell me where to find out the latitude for underexposure on various B/W films?

-- Sylvia Jones (sylvia_j@bellsouth.net), November 29, 2000

Answers

If you underexpose B/W film you'll have areas on the negative with nothing at all, which leads to featureless regions of black in the print, generally something to avoid. Much better to err on the side of overexposure when in doubt.

There're several ways to salvage an overexposed negative but there's not much to do when there's no info on the negative.

I derive much comfort from the use of a spot meter. That way, I know what's going where, exposure-wise.

-- Don Karon (kc6d@arrl.net), November 29, 2000.

When shadows contain no detail, I would say you are at or very near to underexposure. The "latitude" you experience with a film will depend somewhat on how you meter and process that film, i.e. where you place your densities on the curve. I tend to meter and process in a way that gives very little latitude. If I want to be extra safe, I overexpose by a stop, giving an exposure that might seem no more than normal to someone else. Maybe a more technically inclined correspondent can give a more scientific answer to your question.

-- Keith Nichols (knichols@iopener.net), November 30, 2000.

I'm not going to explain the zone system...But the answer depends on different on other factors as well, lets start with the scene contrast and the metering:

My Nikon F2 (or other cameras in matrix mode) will give an average value of required exposure, this is basicly fine as long as the contrast is 4 to 5 stops. Because everything will be recorded on film. If the contrast gets higher 6 or 7 stops, using the average metering your shadows will be thinner or not recorded on film. With a spot metering on the shadows, so that important shadows are 2 stops under the actual exposure you will perform this can be corrected.

So with an averaging metering low contrast scenes will be fine, but high contrast might require higher exposure, or latitude for underexposure is smaller with higher contrast.

So much about theory, shooting available light e.g. in theatres, I use Ilford HP5+ rated at 1600 to 3200, trying to meter for a medium gray with spot. So the maximum latitude for this film is 2 to 3 stops. Similar Tmax 400 can be used up to 1600, Tmax 3200 up to 12800. BUT you may not like the results and for most uses I would not recommend to underexpose a film.

Wolfram

-- Wolfram Kollig (kollig@ipfdd.de), December 01, 2000.

MY DEAR SYLVIA! YOU WILL FIND ANSWER NO WHERE. IF YOU USE 35mm JAPANESE CAMERA (CANON, NIKON,...) LEARN TO SPEND LIFE TOGETHER WITH THAT PROBLEM. 35mm REQUIRES EXTREMELY PRECISE WORK WITH EXPOSURE, BUT JAPANESE CAMERAS (EVEN THE BEST ONE) ARE NOT ABLE TO POP INTO THAT SYSTEM. IF YOU USE LEICA EQUIPMENT, OR SOMETHING AS THAT, THERE IS VERY PRECISE ANSWER ON YOUR QUESTION. UNFORTUNATELY ANSWER IS VERY LONG, EVEN FOR LEICA PHOTOGRAPHERS, BUT ONCE LEARNED IT WORKS. 25 YEARS I AM AFTER THAT ANSWER AND I GOT IT. IT WILL, FOR FIRST TIME COME OUT IN MY BOOK, I HOPE IN 2001. IF YOU NEED MORE INFORMATION JUST ASK, AND LET TALK ABOUT THAT. DOBRADOVIC@CPCPUMPS.COM

-- DANIEL OBRADOVIC (DOBRADOVIC@CPCPUMPS.COM), December 01, 2000.

Leica may well be the answer, but not to any intelligent question. Shadow detail depends on how much light is recorded on the film regardless of what camera & lens may be used. That is a function of exposure and lens light transmission, with lens quality a small part of the equation. Even a poor lens can give good shadows if you expose it properly.

-- Dan Smith (shooter@brigham.net), December 01, 2000.

If you use a conventional silver based film then under/over exposure are close i.e. correct exposure is critical.

However if you use a chromogenic film e.g. Ilford XP2 the lattitude is much larger. For example you can overexpose XP2 by say 3 stops and get excellent prints. If you set your ASA for XP2 at 400 you will get very good pictures but if you wish you can also expose at 50ASA - on the same film in the camera - in order to say get maximum depth of focus on particular shots.

That's why chromogenic films are sometimes called "idiot's film". It's almost impossible to over or under expose. Some very serious and famous photographers use XP2 so don't be put off by its flippant nomenclature.

-- Anthony Brookes (gdz00@lineone.net), December 03, 2000.

Bruce Barnbaum (I think) contends that any B&W film such as Tri-X can actually record up to an 18 EV range of film presumably with a lot of this range compressed into the toe and shoulder.

Presumably a master printer like Bruce can actually recover this information from toes & shoulders, but for rank tyros like me, chromogenic film and Tri-x do allow for some slop, up to about 7-8 stops, so I can be pretty casual about exposure for say low contrast street scenes on rainy days. Seems like XP2 super allows for more slop than Tri-x, but it ends up being harder to print.

-- Mani Sitaraman (bindumani@pacific.net.sg), December 04, 2000.

Please someone correct my explanation to Sylvia. Example: If you use a Kodak TMax 3200 ASA, you may choose to select your camera exposure index, as 800 ASA, and it will work fine. But it will accept if you select as if it has 1000 ASA, and the prints will be just fine too. And so on. But when you want to take pictures in very, very dark places you may select the stops (+ 1, +2 ), as if the film is much more sensitive to light (+1 means that you want that your 3200 ASA film act like a 6400 ASA; +2 like a 12800 ASA). In this case you must overdevelop the film, following Kodak's instruction tables.

I use the term latitude of a film as the capacity of a film for accept different light condictions, without loosing important information in dark or in bright areas of the picture. Of course that is not as simple as this, but I tryed. Does someone is interested in help me with this "amateur explanation for an amateur"?

-- Rui Edgar da Silva Guerreiro (redgar@navier.ist.utl.pt), December 14, 2000.