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Steve Goldstein
14-Oct-2012, 17:29
I picked up a pretty nice 19" Red Dot Artar in barrel (from a press camera) for cheap. I have access to a full machine shop and a machinist for the cost of a case of root beer, so that part of the equation is covered. Once I get my hands on an appropriate shutter, how do I figure out the correct spacing of each cell from the iris? I can use the spacings of the barrel mount, but I suspect this optimizes for close up rather than something more useful like 1:10 or infinity.

Do factory-shutter-mounted RDAs use the same cells as the barrel mounts? If so, can someone with a factory job measure the overall length? That would also be useful - I can compare it with my barrel-mounted lens. I realize that wouldn't tell me anything about the distance of each cell to the iris, but it's better than nothing.

Is there anyone in the Boston, MA area with a factory-shutter-mounted 19" I could measure?

None of the threads I found, including this one http://www.largeformatphotography.info/forum/showthread.php?82259-Mount-a-Goerz-Apochromat-Red-Dot-Artar-19-quot-in-shutter answer my question.

Dan Fromm
14-Oct-2012, 18:39
Steve, measure the barrel. Cell seating surface-to-cell seating surface is the cell spacing.

Why do things the hard way?

Leigh
14-Oct-2012, 19:14
The cell spacing is the cell spacing. Duplicate the current value.

Any attempt at further optimization would require a full optical bench and a LOT of experience doing that type of work.

- Leigh

ic-racer
14-Oct-2012, 20:54
You should be able to easily detect changes in field flatness at infinity. You can screw the lens elements in and out and see how it changes the sharpness of the far edges as long as you have a view camera big enough to capture the whole image circle on the ground glass or film. If you are mounting it on a camera that only uses the center of the image circle, it won't matter much how you space it.

Amedeus
15-Oct-2012, 00:09
I'm with Leigh on this one. If you change the cell spacing of what the manufacturer considers "optimal", you will change spherical aberration, coma, field flatness etc. The focal distance will also change slightly but the latter is easily corrected for.

As Dan and others have said, measure the barrel and ensure the same distance exists in the shutter mount solution.

ic-racer
15-Oct-2012, 05:21
what the manufacturer considers "optimal"

I don't think the OP has that information, unless you want to offer it, thus the need for an empiric solution.

Dan Fromm
15-Oct-2012, 05:55
I don't think the OP has that information, unless you want to offer it, thus the need for an empiric solution.

Ic, the lens is in barrel, it isn't pair of loose cells. As I pointed out in post #2, he has the information in hand.

Emmanuel BIGLER
15-Oct-2012, 06:12
ensure the same distance exists

We could even add that there is a kind of a technical miracle in 4/4 symmetric dialytes : although they were designed for copy work at short distances, they work so well at large distance without changing anything that the best is to do as if you had in mind to use them at short distances. You should actually use them at large distances (eventually, do not disclose this to the forum ;) )

And yes, we all have read that Fuji-C lenses are optimized for infinity, and we are certainly convinced that the recent Apo-Tele Compact 350 mm from Schneider-Kreuznach (which is actually apo and compact, but not at all telephoto, strictly speaking) is not at all intended for copy work at short distances ...

I have in mind a 750mm Apo Germinar lens (a 4:4 symmetrical dialyte, aus Jena-Saalfeld a design similar to the apo-ronar or apo-artar) used by Jörg Krusche from Germany ; at one of our friendly LF meetings in France he showed us test shots made at large distances with this lens ... since then, I no longer care for the distances where I use my apo ronars ..

Steve Goldstein
15-Oct-2012, 06:48
Thanks everyone. As Dan reminded, the lens is presently in its barrel so I can measure the distances from the seating surfaces to the iris, as well as the thread dimensions. Now to find an Ilex #4, or a Copal 3...

Emmanuel BIGLER
15-Oct-2012, 07:01
You can also mount a dialyte in front of a shutter, this is what Jörg Krusche did for his 750 mm Apo Germinar. Of course, the bigger the lens, the bigger the shutter, and a front-mounted lens will always require a bigger behind-the-lens shutter than a shutter mounted between cells. (http://www.flickr.com/photos/43175600%40N00/358087941)

Leigh
15-Oct-2012, 07:17
I don't think the OP has that information, unless you want to offer it, thus the need for an empiric solution.
It's the length of the barrel as shipped from the factory. Doh...

- Leigh

c.d.ewen
15-Oct-2012, 08:48
You should be able to easily detect changes in field flatness at infinity. You can screw the lens elements in and out and see how it changes the sharpness of the far edges as long as you have a view camera big enough to capture the whole image circle on the ground glass or film. If you are mounting it on a camera that only uses the center of the image circle, it won't matter much how you space it.

AIR, I've used a barrel-mounted 19" RD Artar on a 12x20 with no noticeable aberrations.

Having your machinist measure the barrel is the only way to insure accuracy.

As an amateur machinist, I've mounted lenses into Copal 3 shutters. My notes show that for a 19" RD Artar with S/N 801xxx, the barrel length was 1.865" and the front to iris measurement was 1.133". The front cell thread was 2.310"-2.339" 36 TPI, and the rear cell was 2.322"-2.351" 36 TPI.

Here's why you can't just use someone else's measurements to make an adapter: I recently came across a loose adapter I had made some time ago. It's clearly marked as an adapter to mount the rear cell of a 19" RD Artar into a Copal 3. Measuring it, I see that it's more than twice as large as an adapter would be using the above measurements. Since I've sold any and all 19" RD Artars I might have once owned, I can't reconcile the discrepancy. YMMV.

Print out the table on this page (http://www.skgrimes.com/products/new-copal-shutters/standardcopals) from the SK Grimes website for your machinist. It has the Copal 3 specifications he'll need.

Charley

Leigh
15-Oct-2012, 09:03
The front cell thread was 2.310"-2.339" 36 TPI, and the rear cell was 2.322"-2.351" 36 TPI.
Interesting specs, given that the Copal shutters are metric.

The correct dimensions are 58x0.75. That's a thread of 33.87 TPI, not 36, and major diameter of 2.2835".

- Leigh

E. von Hoegh
15-Oct-2012, 09:08
Interesting specs, given that the Copal shutters are metric.


- Leigh

But 19" Red Dot Artar barrels are inch standard. That's what the specs are for.

c.d.ewen
15-Oct-2012, 13:52
But 19" Red Dot Artar barrels are inch standard. That's what the specs are for.

Tee-hee-hee. Leigh's undies are showing! :D :D :D

Charley