Exposing for lights or shadows with negative film?

Started 3 months ago | Questions thread
Horiz Opposed
Horiz Opposed Contributing Member • Posts: 601
Re: Exposing for lights or shadows with negative film?

Phil A Martin wrote:

Horiz Opposed wrote:

Bags27 wrote:

Easiest way to protect shadows is for normal photos just rate the film around 1/3 of an f-stop slower. A lot of folks, for example, shoot Tri-X at around 320. Develop normally, though, again, some folks will take maybe 30 seconds off the development time. YMMV.

1/3 stop, I have to disagree. My comments refer only to shooting black and white negative film.

Having done tons of exposure and development tests over the years, including reading and charting the difference in the various densities of developed film with a densitometer, 1/3 of an f-stop is not going to do it.

In fact, if you take 3 forty year old film cameras of the same model, and time the shutters, I’ll give you $50 if two of them are within 1/3 of a stop of the shutter speed they are supposed to have. Brand new they could be 1/3 stop different.

Practically speaking, unless you are adjusting the aperture on a view camera lens, or using a fully automatic camera with stepless electronic shutter, you cannot even adjust by 1/3 stops.

But many film cameras allow you to adjust ASA/ISO or exposure compensation dial by 1/3 stop and that's the way to do it.

If you need more detail in the shadow areas, anything less than doubling your exposure is just not going to make that much of a difference.

It doesn’t matter where you adjust unless the camera can steplessly be set, which is what I said in my post. Yes, if a camera can be steplessly set, your method works, but my comments cover all of the thousands that cannot.

Starting with a ss of 1/125 for example, 1/60 is 2x the light, so maybe 1/90 is 1.5x. This is rough, but lets say 1/100 is about 1/3 more light than 1/125.

Most shutters do not have a setting for 1/100, nor can the aperture be set 1/3 more. They usually go in half stops at best. Shutter many times in full only.

The choice here is a full stop for shutter speed, 1/2 or 1 full stop for aperture. Explain how to make a 1/3 stop adjustment.

So my point to Bags27 was that giving that advice to people who are seeking input about how to expose their b/w negative film was:

1-not going to solve the detail problem (1/3 more not enough)

2-not always mechanically possible

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