# Thread: "Half Stops" and the aperature dial

1. ## "Half Stops" and the aperature dial

This may be a silly question, but I am not sure. I am doing some film speed tests, and I will be testing in half stop increments via aperature.

It just occured to me that a half a stop between, say F16 and F11 may not be midway between the two numerals on the shutter dial.

Is this true, or, is half the distance on the dial, between to F stop numerals actually an increment of half a stop?

Thanks!!

2. ## "Half Stops" and the aperature dial

Its close enough.

Cheers,

Dan

3. ## "Half Stops" and the aperature dial

the numbers would not be right if you took the average mathmatically, but if the center space betwween is half as much open , that is what you want.. dave.

4. ## "Half Stops" and the aperature dial

This was the subject of a long discussion here or maybe in the rec.photo large format group a while back. You're correct that midway between the two isn't exactly half a stop. However, in order to get to the exact half stop point I think you'd need an instrument more precise than the aperture lever on most lenses and eyes better than most of us have. As someone else noted, the difference between the actual half stop point and the halfway point marked on the aperture dial isn't enough to have any practical effect.

5. ## "Half Stops" and the aperature dial

It's kind of funny seeing people say "close enough" when photographers (for the most part) tend to bitch about shutters that are a half stop off! :-)

hehehe

6. ## "Half Stops" and the aperature dial

Bob, many people are too <obscenity deleted> compulsive about precision in a process that is inherently full of approximations.

Cheers,

Dan

7. ## "Half Stops" and the aperature dial

Thanks for the replies. I didn't think the difference would matter a huge amount, but, thought I would ask. Don't some photographers seem to decrement their film speed by a 1/3 stop? I got to wonering how they are measuring that- by aperature? If so, then finding the location of 1/3 stops on most aperature dials seems problematic, if it is possible at all. They couldn't really be testing 1/3 stops via exposure time, unless they are dealing with really long exposures, and, even then, reciprocity would seem to cause all sorts of imprecision. Anyway, I went ahead and "eyed it" and set my aperature knob at what appears to be halfway between stops. My film test seemed to go well- tonight I will check out the densities, and see what I can learn.

Thanks! James

8. ## "Half Stops" and the aperature dial

Don't some photographers seem to decrement their film speed by a 1/3 stop? I got to wonering how they are measuring that- by aperature? If so, then finding the location of 1/3 stops on most aperature dials seems problematic, if it is possible at all.

I have a couple of newer shutters that are marked in 1/3 of a stops and it makes it pretty easy to find the position. That said some of my shutters aren't consistant enough for that.

leec

9. ## "Half Stops" and the aperature dial

"Don't some photographers seem to decrement their film speed by a 1/3 stop? I got to wonering how they are measuring that- by aperature? If so, then finding the location of 1/3 stops on most aperature dials seems problematic, if it is possible at all. "

you just eyeball it...

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