Lens diaphragm setting

[Conrad_S]

Hi,
I have Schneider Kreuznach Symmar 1:5,6/150 with Copal pres no 1. shutter and there is no scale for the diaphragm setting. What is the best Idea to put the stops? Is the scale linear?

[johnielvis]

not linear----you'll have to measure---full open is 5.6...f8 is closed down to a diameter equal to sqr root of 2 of full opening.....f11 is equal to half the diameter of full open...like that in steps of square root of 2....

[John Koehrer]

Doesn't SK Grimes sell scales?

[Conrad_S]

Doesn't SK Grimes sell scales?
I will ask.
I believe in math, but the way with measuring amount of light through the lens may be more adequate?

[Jim Jones]

The f/number is the diameter of the aperture (as seen through the front elements of the lens) divided into the focal length. When measuring this diameter, keep your eye a good distance from the lens. For temporary use I write the f/number on white tape.

[rdenney]

I will ask.
I believe in math, but the way with measuring amount of light through the lens may be more adequate?

I've tried it and I think the way focus screens gather and integrate light makes it too unpredictable. I took a spot meter and carefully measured the center spot on my focus screen, adjusting the aperture in marked stops on a known-good lens and shutter. I did not get one-stop differences in readings on the screen. I'm back to making careful measurements with calipers. Often, one can go in two-stop intervals, where the diameter decreases by half (and is thus easy to measure), and then guesstimate the intervening stops nearly enough.

Some apertures are designed to provide even stop spacings on the control lever, and some are not. If they are, that interpolation because easy. But even without it, I can usually get within a half a stop or better. Then, test with film if the application (e.g. Velvia) is demanding.

Grimes will do this, and will engrave the lens barrel with the markings (which is, I think, the costly part of what they do). Personally, I'm happy with fine-point Sharpie markings on a piece of tape.

Rick "whose first attempt at this was good enough even for Velvia" Denney

[domaz]

Get a digital caliper (Harbor Freight has a popular one that is cheap) and just start measuring, and as Rick says a piece of tape or a cut piece of white label paper works great for affixing to the shutter and writing the resulting f numbers.

[Conrad_S]

Well, I have found a repair guy, who is a making shutters repair. I will try to get help from him. Measuring the diameter of aperture hole is challenging. How to measure? With what? If I make it not correctly (i.e. not precisely) I will get wrong results.
The next small thing is that I'm in central Europe. It's quite far from Boston :-)

[Sirius Glass]

SKGrimes will make a scale for you. He did for me.

Steve

[ic-racer]

I will ask.
I believe in math, but the way with measuring amount of light through the lens may be more adequate?

As you stop down the intensity changes more in the center than the edges. This is of course very pronounced with wide field large format lenses. So, where are you going to measure to calibrate your T-stop scale? The "F-stop" calculation avoids those issues, that is why it is so popular with the LF lens makers.
Having said that, when I do use a TTL measurement, I use the Horseman meter that averages the whole negative area.

[BradS]

The f/number is the diameter of the aperture (as seen through the front elements of the lens) divided into the focal length. When measuring this diameter, keep your eye a good distance from the lens. For temporary use I write the f/number on white tape.

This is the method I have used in the past and it works very well. There is really no need to do anything more complicated.