Metering with Bulb mode.


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Jul 21, 2005
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#1
Hello all,

I'm kinda confused with the metering when I use bulb mode on my camera. I'm using an FM2n, and as you know it's a all-manual camera, and the metering will go off whenever I switch to the bulb mode. For starters, how do I know whether I've gotten the right exposure? And for a 'correct exposure' (in this case, I mean it's not under or over exposed), how do I know how long I can leave the shutter open? Does it mean that the longer I leave my shutter open, the more exposed the film will get? Thanks.

Tim.
 

Jul 21, 2005
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#3
So you have to depend on your luck and experience to get that exposure you want? Wow, that sounds tough.
 

foxtwo

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#4
There is one trick I use with my FM2n & FE2.

For example, say you are using 100ISO film. And TTL metering tells you that at maximum aperture, and at 1sec, it is still underexposed. What you do is that you turn the ISO knob to 800 and check the metering. If it's still under, turn it to 1600, check. Still under? Repeat. What this is is that it gives a rough guide on how many stops are you under, so you can inturn calculate how much time you need to expose for.

Now let's say you get a correct metering at 3200. 100ISO -> 3200ISO is 5 stops (of light) difference. Hence meaning, time for exposure, calculating from 1sec, is 30secs.
1sec -> 2sec -> 4sec -> 8sec -> 15sec -> 30sec
(1stop) (2stop) (3stop) (4stop) (5stop)​

This gives a rough estimate of the correct exposure. But actually if you are shooting at very long exposures, you don't really need to time down to the last second. Make sure you bracketing too, although you should already be bracketing most of what you shoot.
 

foxtwo

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#5
I forgot to add. When you are ready to take the shot, reset ISO to the original, and take with the new shutter speed.
 

Jul 21, 2005
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#6
Oh, haha, thanks fox, now I know. :)

So for bracketing, let's say exposure time is 30sec, I shoot another frame at 15 sec and another at 60 sec?
 

foxtwo

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#7
Yeah that's fine. If you're able, experiment. -1, -1/2, 0, +1/2, +1 for both negatives & slides. Negatives will mark difference at around -1 to +1 stop, slides as little as -1/2 to +1/2 stop.
 

catchlights

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#9
When shooting long exposure with film, you need to factor Reciprocity Failure for the film.

Read the recommendation compensation for exposure from the data sheet of the film you use.[SIZE=-1][/SIZE]
 

student

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Jul 26, 2004
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#10
foxtwo said:
There is one trick I use with my FM2n & FE2.

For example, say you are using 100ISO film. And TTL metering tells you that at maximum aperture, and at 1sec, it is still underexposed. What you do is that you turn the ISO knob to 800 and check the metering. If it's still under, turn it to 1600, check. Still under? Repeat. What this is is that it gives a rough guide on how many stops are you under, so you can inturn calculate how much time you need to expose for.

Now let's say you get a correct metering at 3200. 100ISO -> 3200ISO is 5 stops (of light) difference. Hence meaning, time for exposure, calculating from 1sec, is 30secs.
1sec -> 2sec -> 4sec -> 8sec -> 15sec -> 30sec
(1stop) (2stop) (3stop) (4stop) (5stop)​

This gives a rough estimate of the correct exposure. But actually if you are shooting at very long exposures, you don't really need to time down to the last second. Make sure you bracketing too, although you should already be bracketing most of what you shoot.
You forgot to take into account reciprocity failure.
 

student

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Jul 26, 2004
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#11
And you probably have to reduce development time.
 

foxtwo

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#12
student said:
You forgot to take into account reciprocity failure.
That's not something a normal user would encounter, is it? At what times would reciprocity failure occur for a given film?
 

catchlights

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#13
foxtwo said:
That's not something a normal user would encounter, is it? At what times would reciprocity failure occur for a given film?
catchlights said:
When shooting long exposure with film, you need to factor Reciprocity Failure for the film.

Read the recommendation compensation for exposure from the data sheet of the film you use.
Is in the data sheet.
 

student

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#14
foxtwo said:
That's not something a normal user would encounter, is it? At what times would reciprocity failure occur for a given film?
More than 1 second.
 

student

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#15
foxtwo said:
That's not something a normal user would encounter, is it? At what times would reciprocity failure occur for a given film?
The newer T-grain films may be better. But still would have reciprocity failure at say >10 seconds (recalling from memory, I always carry a reciprocity card for the film I am using)

All the older films will have a problem when exposure is more than 1 second.
 

litefoot

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Jan 27, 2005
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#16
foxtwo said:
That's not something a normal user would encounter, is it? At what times would reciprocity failure occur for a given film?
Varies with film. Reciprocity implies the relationship between f/stop and shutter speed. It fails when the film breaches its specified limits. You will not only get inaccuracies in exposures, sometimes there will be shifts in colour balance.
 

litefoot

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#17
catchlights said:
When shooting long exposure with film, you need to factor Reciprocity Failure for the film.

Read the recommendation compensation for exposure from the data sheet of the film you use.[SIZE=-1][/SIZE]
Although it is rare but it could possibily happen on the upper end too which is the higher shutter speed end.
 

catchlights

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#18
litefoot said:
Although it is rare but it could possibily happen on the upper end too which is the higher shutter speed end.
Yes, 1/10,000 or higher something like that.

We hardly do high-speed photography and also special equipment needed for this kind of photography, so most of the time we mention reciprocity failure is refer to long exposure.


Hi LordAeRo & foxtwo,

The longer the exposure time, you need to compensate for more, each type of film are different, so can’t tell you how much to compensate, if you shooting color, prolong exposure time will result in color shift also.

Not to worry too much, just study the data sheet for the film you use, they do indicate how much compensation needed.

Hope this help.
 

ricohflex

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Feb 24, 2005
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#19
LordAeRo said:
Hello all,

I'm kinda confused with the metering when I use bulb mode on my camera.
Tim.
I think this is a feature of the FM2 camera design to save battery
Buy a hand held meter if you take lots of "bulb" shots
Some measure up to many hours of exposure

Kodak exposure guide is useful. Read it and match time to situation.

Some cameras have "time" mode
You click the shutter release and shutter opens and does not close
Click the shutter again and it closes.

If you want a camera that can handle "bulb" shots with style, buy the OLYMPUS OM4Ti on sale now by Zuiko. It has Off The Film metering even in bulb mode.
That means if the light suddenly shifts after you clicked the shutter, you will still get a perfectly exposed shot.
I think it can expose to many hours in bulb mode.
With this camera, no need to have separate hand held meter.
 

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