View Full Version : Aperture

John Kim
27-Nov-2008, 10:25

I don't know much about LF lenses.
Here is my lens which I am not familiar with.

The lens is labeled 165/6.3
My question is what is its true max aperture?
The fstop selector can go past 6.3 but 6.3 is the last labeled fstop on the lens.

I'm being vague but here are some animations to help you understand.

As you can see, the aperture blade closes in when at 6.3, but does not show when it is wide open past 6.3 (so I'm guessing 5.6?).

Why is it that only f/8 is the only fstop where the line beneath it is single whereas all the other fstops are underlined?

Correct me if I'm wrong but is my lens really a 165/5.6 rather than 165/6.3?

27-Nov-2008, 10:53
I believe uderline helps you to ifentify the F number for wich the point is. I believe they engraved f-stops for easy read but f-stop locations are so close the numbers would overlap.

The other issue, IMHO, is miss-alignment in your shutter. If lens says F6.3, it is 6.3. It should open all lamels at 6.3 shutter point, not beyond.

John Kim
27-Nov-2008, 10:59
But, it does the same on the opposite side for f/45 as well..

Vick Vickery
27-Nov-2008, 11:00
Many LF lenses will open their diaphrams slightly more than where the effective f-stop actually is. You can shoot wide open and gain a fraction of an f-stop at the cost of some sharpness, but the manufacturers don't recommend this. It can help a little at times when focusing.

John Kim
27-Nov-2008, 11:09
I just called up a friend of mine and he said the same thing you just said. As much as I did not want to interrupt his busy Thanksgiving Day, I wanted to be assured before I went to get my lens CLA'd. Thanks for your replies!

Walter Calahan
27-Nov-2008, 11:21
Very common.

Leonard Evens
27-Nov-2008, 16:04
I tried to measure the respective diameters and came up with 2,75 inches vs 3.25 inches. The ratio is about 0.846 and that times 6.3 is about 5.33, which is about 0.14 stops wider than 5.6. Also, because the larger aperture is close to circular, it could be as much as 1/3 stop wider than f/5.6. On the other hand, there may some other factor we are not taking into consideration.The only way to be sure would be to take two pictures under exactly the same lighting conditions and see if you can detect any change in density using a densitometer. But, a ratio of diameters of 0.846 is equivalent to less than 1/2 a stop, so it is not clear it would be easy to detect any difference.

John Kim
28-Nov-2008, 12:22
Thank you!

I'll be shooting C-41, and using its wide exposure latitude to my advantage.

I appreciate everyone's help!

28-Nov-2008, 17:34
My Schneider 120/5.6 opens up a wee bit past 5.6 too. Eyeballing the difference between 5.6 and 1/3 stop down vs. 5.6 and "full open," it looks to be about 1/6 of a stop more. Maybe makes focusing a teensy bit easier.


Dan Fromm
29-Nov-2008, 07:24
Folks, barrels and leaf shutters are pretty generic. Its common for the diaphragm in either to open wider than the lens mounted requires.

Before complaining about the waste, consider the cost of making lens-specific barrels and leaf shutters.

29-Nov-2008, 17:22
I have the same lens and like it. It's not perfect, but its a nice performer and folds up inside my Busch Pressman D. The aperture question was correctly answered above: when set to 6.3, that's what you get.