How to Optimize an Apo Ronar for Infinity

[Daniel Unkefer]

From a thread over on phototrio.com

"Procedure was described in "Internationale Phototechnik" issue 8/1993..."

"Focus the center of your ground-glass on fine structures in the distance like leafless trees or high grasses with a strong loupe at wide open aperture. Shift the rear frame of your camera to the left and the front frame to the right up to the point you can see the structures get blurry. Unscrew the front group of the lens circa 2 mm (1 line or 0.08 inch) from the shutter or barrel and look for the fine structures, twigs or leafs. Adjust the distance between the front group and the shutter up to the point the structures are as sharp as possible without any coma and blur. Refocus if necessary during the adjustment. Place a steel or brass shim of the determined thickness between shutter and front group. If the thickness of the shim is the correct one there is no difference in image quality between the center and the edge of distant subjects. For close-up work remove the shim or place a much thinner one." Additionally when you unscrewed the from cell to its optimal place then you may count the tours (and fraction of a tour) you need to screew again the front cell. If we multiply the number of tours by the thread pitch then we have the thread thickness we need."

"That operation mostly optimizes image quality off center, in the corners and mid. Probably many (or most) long Ronars around have the optimal inter-cell distance for close work, this can be known by checking if the corners in the image improves when the front cell is unscrewed a bit. For very long focal Ronars that effect should be noticed less as we take more the center of the image circle, still it would be well noticed when shift/rise performed. "

I'm interested to know if anybody here has shimmed their Apo Ronars? Doesn't sound too hard to do....

[Tin Can]

The hard part is making the shim

I used to shim big Diesel engines with 0.001" or 2 to change the head to cylinder distance to test head gasket

We had a big hand made dept to make the shims and any other odd thing

I still have a set of Rule Die punches but not every size, my biggest is 3"

We can buy round Rule Dies, but 2 must be set in very good plywood, with rubber push outs, then use a press

The Rule Die dept could make any shape or size, they welded/ground them to size. 10 people did that on 3 shifts

Creating a Two Piece Steel Rule Cutting Die Board Using a Gerber Precision Router.

[Tin Can]

Now we use water jet and laser

[PRJ]

Thanks for posting that Daniel. I've wondered about that over the years. My 300 APO Ronar doesn't have any shims, but it was made for a shutter so I've always assumed it was also shimmed for it. Just a guess, but makes sense. I've never noticed any lack of sharpness that is for sure.