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Barney

Barney

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Wayne
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What do you do with your bits when calculating exposure?

If I shoot under box and the meter says, for instance, f 8.6 , do you go f8 or f11, If I am shooting 200 at 160 the half stop brings it back to a full stop over or correct. Which is best and why?

I hope that makes so kind of sense.
 
To put this in perspective:

If you use a leaf shuttered camera, the actual exposure depends on the aperture. By which I mean that the actual amount of light hitting the film doesn't follow the reciprocity law. Look up shutter efficiency. You may find that there's a 33% discrepancy in the actual exposure at small stops - erring towards overexposure. Would you allow for this? I thought not.

The difference in percentage exposure between f/8 and f/11 if the correct aperture should be f/8.6 is

f/8 86.5% error
f/11 61.12 error

Shutter problem is about the same as the largest one.

So much for theory. I'd go with the larger aperture if negative film, and if I ever used slide film, the smaller of the two. Or set a half stop. Some lens let you do that, or even 1/3 stops on LF lenses.
 
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In practice, if you want absolute accuracy, allow for

incorrect lens aperture markings
shutter speeds that are not absolutely accurate
lens light transmission - use T stops not f stops.

And, if using a spot meter, allow for flare in the optical system. It can amount to up to 2 stops in my experience - and that depends on what's just outside the metered area, so it can't be allowed for as always being the same.

I've probably missed a few as well...
 
StephenM said:
So much for theory. I'd go with the larger aperture if negative film, and if I ever used slide film, the smaller of the two. Or set a half stop. Some lens let you do that, or even 1/3 stops on LF lenses.
Click to expand...
As far as I can remember, ALL of the lenses I have ever used allow at least half stops, if not third stops, to be selected. But not all have the divisions marked or have click stops, so there may be some guesswork required.
 
StephenM said:
To put this in perspective:

If you use a leaf shuttered camera, the actual exposure depends on the aperture. By which I mean that the actual amount of light hitting the film doesn't follow the reciprocity law. Look up shutter efficiency. You may find that there's a 33% discrepancy in the actual exposure at small stops - erring towards overexposure. Would you allow for this? I thought not.

The difference in percentage exposure between f/8 and f/11 if the correct aperture should be f/8.6 is

f/8 86.5% error
f/11 61.12 error

Shutter problem is about the same as the largest one.

So much for theory. I'd go with the larger aperture if negative film, and if I ever used slide film, the smaller of the two. Or set a half stop. Some lens let you do that, or even 1/3 stops on LF lenses.
Click to expand...

I have never heard of it never mind allow for it.
 
StephenM said:
In practice, if you want absolute accuracy, allow for

incorrect lens aperture markings
shutter speeds that are not absolutely accurate
lens light transmission - use T stops not f stops.

And, if using a spot meter, allow for flare in the optical system. It can amount to up to 2 stops in my experience - and that depends on what's just outside the metered area, so it can't be allowed for as always being the same.

I've probably missed a few as well...
Click to expand...

I have no chance
 
Barney said:
What do you do with your bits when calculating exposure?

If I shoot under box and the meter says, for instance, f 8.6 , do you go f8 or f11, If I am shooting 200 at 160 the half stop brings it back to a full stop over or correct. Which is best and why?

I hope that makes so kind of sense.
Click to expand...
My method is to just relax about it. Half a stop here or there with neg film isn't going to do much. And you haven't said how you're metering! Hand-held or through the lens; reflective, spot or incident?

With neg film I tend to rate at box but reflective-meter off the shadows. There are other permutations!

With slide film it gets more tricky & as Stephen said above, err on the downside - but if the reflectivity in the scene is unusual, as with snowy landscapes, you have a choice of metering locally off something that you feel is in the mid-range, or taking a general reading and opening up a stop & a half at least.

You have every chance! Keep having fun! Results will feed back to you.
 
Kevin Allan said:
As far as I can remember, ALL of the lenses I have ever used allow at least half stops, if not third stops, to be selected. But not all have the divisions marked or have click stops, so there may be some guesswork required.
Click to expand...
RB lenses have detents for have stop, Bronica Seiko have no detents, can they still be set in between the whole numbers?
 
droj said:
My method is to just relax about it. Half a stop here or there with neg film isn't going to do much. And you haven't said how you're metering! Hand-held or through the lens; reflective, spot or incident?

With neg film I tend to rate at box but reflective-meter off the shadows. There are other permutations!

With slide film it gets more tricky & as Stephen said above, err on the downside - but if the reflectivity in the scene is unusual, as with snowy landscapes, you have a choice of metering locally off something that you feel is in the mid-range, or taking a general reading and opening up a stop & a half at least.

You have every chance! Keep having fun!
Click to expand...

Incident meter Droj
 
Up for neg, down for slide. But do you want to be Ansel Adams or Edward Weston? By all accounts Ansel was tight, whilst Edward was loose, exposure-wise!
 
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Barney said:
I have never heard of it never mind allow for it.
Click to expand...
It's in my book. Both leaf and focal plane shutters have efficiency limitations, but different. If anyone wants it explained, I can do it. But I suspect Wiki will do the job with diagrams. I can't put diagrams in text.
 
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