240 f-9 G claron aperature scale question

[mark]

I got my G/claron in the mail and the aperature scale is a piece of clear plastic with F stops going from 9-90 over the previous aperature scale. This is usable but I want to know how to test whether this home made scale is correct.

Has anyone had SKgrimes do an aperature scale and how much was it?

[lee]

I have had 2 shutters engraved by SKGrimes in the past. They did a great job on each. The website talks about how much it is. I opted to have the engraving done on the shutter and not on plates. Seems it was about $45.

lee\c

[Jim Jones]

I would check the accuracy of any scale by measuring the apparent diameter of the diaphram opening from the front of the lens. Divide this figure into the focal length to get the f/number. To avoid parallax, your eye should be some distance from the lens, or should be moved by about the diameter of the aperture so you are looking directly into the lens, not at a slight angle. There are other ways which are unnecessarily precise.

[mark]

how do you measure the diameter

[Capocheny]

Mark,

I've also had S.K. Grimes set up an aperture scale on one of my lenses... they did a great job and the end result was beautiful.

I couldn't recommend them highly enough for this kind of work.

Sorry, I can't recall what they charged me for the job.

Cheers

[MichaelBriggs]

how do you measure the diameter

As Jim says, you sight from a distance at the front aperture, through the front lens cell. Lay a mm rules across the front cell. Set the aperture control against the f-stop mark that you want to check. You want to sight from a distance large compared to the distance from the aperture to the ruler. Then just to read the two mm values at the edges of the aperture and take the difference to get the diameter.

For f9, the aperture blades should have just cut into the circular opening -- at least that's how my 270 mm G-Claron works. As Jim said, the diameter should be focal length divided by f-number. So 240 mm / f9 gives 27 mm, 240 mm / f16 gives 15 mm, etc. When I just tried measuring my 270 mm G-Claron (factory shutter), the diameter values that I obtained by sighting a ruler agreed to within one mm of the expected values from the aperture setting.

[Jim Jones]

how do you measure the diameter

A transparent plastic ruler works well. Rulers with graduations printed on flat plastic work better than the ones with the graduations molded in.