TTL metering and the FM3A

[jwcounts]

I've always wondered about this, and I've tried to test it but my

results seem conflicting. When I have it set on A (auto exposure),

the camera determines an exposure as I press the shutter based on

the amount of light coming through the lens. Is this a one-time-

only reading, or will the exposure change if lighting conditions

change? Lets say, for example, that I turn off all the lights in

room and fire the shutter. It doesn't detect a lot of light in the

room so it wants to do a really long exposure. But if I turn the

lights back on halfway through, will it continue to expose as though

the room were still dark (leading to overexposure), or will it

adjust the exposure to account for the brighter room?

 

Speaking of long exposures in the dark, I do this a lot, and I

usually stop down the lens to 8 or so and just use the auto function

(the first six or so photos in my portfolio were taken this way).

But, I've heard people say that this results in inaccurate

exposures. I've never had a problem with it, but my best results

come when I adjust it to +2. So sometimes the exposures last what

seems like several minutes, though I've never timed them with a

stopwatch. I guess my question is, is there an upper limit to how

long the shutter will stay open when used in this manner, and do

other people find this method to be inaccurate?

 

Another thing, in the camera manual it says that a small amount of

battery power is used even when the B setting is used. Why is

this? I thought it was completely mechanical at manual settings.

 

Thanks for any responses!

[alice_guy]

It will continue to expose for the shutter duration that it calculated when you pressed the shutter release, so yes, it will think that it's still dark.

 

As a note, your preference for ev comp of +2 for long exposures may be due to film reciprocity failure, which will vary depending on the film you're using. You can google for charts and recommendations for calculations on extra exposure needed for different lengths of long exposure and film combinations.

[mawz]

The only cameras capable of changing an ambient exposure during exposure are the

Pentax LX and a few Olympus OM's starting with (IIRC) the OM2n, all of which use TTL-OTF

metering for ambient exposure (As most Nikons do for TTL flash).

 

Metering, except Ambient TTL-OTF, gets less accurate the darker it gets, but likely your

exposure issues with long exposures are due to Film Reciprocity (As exposures get longer,

the film gets less sensitive, so it needs even longer exposures, which you need to

compensate for), I'd recommend using Fuji Neopan Acros 100 as it doesn't suffer from

Reciprocity until the exposure is longer than 120 seconds, where most films suffer

reciprocity as soon at 1-5 seconds.

[oceanphysics]

Films don't suffer from reciprocity. They suffer from reciprocity <i>failure</i>.

 

Reciprocity is the normal condition, where half as much light requires twice as much exposure. When light levels are low enough that this relationship no longer holds and you need more than twice as much lgiht, reciprocity has failed.

[bill a.]

I thought the F3 would do this as well (adjust exposure on the fly while the mirror was up)... no?

[mawz]

Bill,

 

The F3 does not do TTL-OTF anmbient metering, only TTL-OTF flash metering, it does vanilla TTL for ambient metering. The confusion comes from the fact that the metering cell in the F3 is multi-use, as it's used both for TTL ambient metering and TTL-OTF flash metering. Only cameras that do TTL-OTF ambient metering (Which comes down to the Pentax LX and a couple of Oly OM models) can change exposure length during exposure.