View Full Version : 90mm f/6.8 Caltar f-stops

26-Jan-2007, 14:36
Hi All,
So I bought a 90mm f/6.8 Calumet Caltar-II N MC lens - I believe it's a re-branded Rodenstock lens. There are a couple of things I have noticed about the f-stops. First, the f-stop ring goes beyond the scale at each end. Second, when I opened it up to mount in on the lens board, I noticed that when the f-stop rint is set right on 6.8, the iris is actually well outside the edge of the lens element. The iris doesn't reach the edge of the lens element until it is stopped down about 1/3 of a stop from 6.8. Given this I can't believe the markings are vary accurate. Is this common with these lenses? Should I send it out to S.K. Grimes to have new f-stops engraved on the lens?


Alan Davenport
26-Jan-2007, 15:34
You should probably shoot some test shots on transparencies.

Bob Salomon
26-Jan-2007, 16:46
Any camera repair shop can make scales. Blank scales are readily available from the Copal distributor, RTS. These can be ordered from any repair shop and most camera stores.

Frank Petronio
26-Jan-2007, 20:10
Tim at www.lensn2shutter.com does the scale calibrating too.

26-Jan-2007, 21:20
Hi all,
thanks for the replies. I'm not really sure what I'd do with a blank scale. If I do end up sending the lens out it will most likely be to SK Grimes simply because I have dealt with them before and they are relatively nearby - I live in NH and they're located in RI.
I find it a little strange that the scale on my lens is so far off - as far as I can tell it appears to be the original scale. Another reason for a new scale is this one is only marked in full stop increments - I prefer 1/3 stop increments.
So when an f-sopt scale is made, is it custom made for the lens, or are they just based on some standard?

Don Hutton
26-Jan-2007, 22:46
Any camera repair shop can make scales.
Wow - I'd love to know who else, apart from SK Grimes and Tim Sharkey constitute the "any camera repair shops" you mention....

26-Jan-2007, 23:29
If it's 1/3 stop off when you start seeing the aperture blades, it must be off by 1/3 stop. A good thing about Copal shutters is the aperture scale is linier. I'd do some testing by compensating the discrepancy (1/3 stop), and re-marking the scale with a Sharpie or sticking a note on the lens board should be easy...and then...considering the killer deal you made with the lens ($200, I presume? Caltar ROCKS if you are a buyer ;-), you'd still be ahead even after getting some professional assistance.

Jim Rice
27-Jan-2007, 08:08
As I recall (it's been a while), I think this is normal. How are your exposures?

27-Jan-2007, 11:16
I have the Rodenstock branded version of this lens. The aperature scale indicator for mine is aligned at 6.8 when you can just begin to see the iris by looking into the lens. No surprise here, that's the way it should work. How is your scale held on? If it is with small screws (mine is) you may be able to remove it, enlarge the holes with a small file, and re-attach at the correct place. From what I can tell the spacing between the f stops is fairly constant and so a simple shift should work, probably within 1/3 stop. If you do decide to have it done professionally, I can recommend S.K. Grimes. They have put an aperature scale on a lens for me and I was very pleased with the results. The third stop markings they add are a nice feature. If you want to check your scale, a dark room, a light box and an exposure meter (not a spot meter) should allow you to check the callibration reasonably well. A 35mm camera will also work as an exposure meter. You will want to play with the lens choice so that you do not get any stray light. You will want to use a light box or something else that is more spatially uniform than a light bulb as a light source.
Dave B.

Richard Kelham
27-Jan-2007, 16:07
Have you tried a test exposure? Have you tried measuring it, working on the basis that f number is focal length divided by apparent aperture diameter? Do you have lots of money burning a hole in your pocket?

If the answer is 'yes' to the last question, and by implication 'no' to the other two, then by all means send it to Grimes...


Jim Jones
27-Jan-2007, 21:58
It's not unusual for an iris to open and close beyond the indicated range of f/ stops. On my favorite 90mm WA, play in the aperture mechanism makes a difference whether I'm opening up or stopping down. It's easier to allow for this than tinker with the shutter and scale. Making a scale at home for some lenses isn't difficult, but requires awfully precise measurement on smaller WA lenses.