Top Hat for Kodak Master View

[lenser]

Okay. The time has come to adapt my Turner-Reich 15/24/36 to my 8x10 Kodak Master View so I can take advantage of the longest focal length.

The bellows draw is 28 inches at full extension which works fine with the 15 and 24 inch ranges just the way they are, but is well under what is needed for even infinity focus with the 36 inch orientation. Taking off the ground glass back and moving it back until the I could see sharp focus at about 25 feet gave me the need for an extension of around 13 inches which I could do by having my machinist buddy make a huge shim for the back which might be impossible to properly anchor, or by having him make a top hat style lens board of that length.

The lens board front standard opening is 4 5/8 "so I'll likely have 4 1/2" or less with the needed wall thickness.

I have a concern that I might experience vignetting with what amounts to a 13 inch tube, most of which will be jutting out behind the rear mounted element in this longest configuration.

Could any of you optical geniuses out there share your thoughts before I invest lots of time and money on this creation?

Thanks.

Tim

[N Dhananjay]

Wouldn't advise it - you would certainly experience vignetting and it make the use of any front movements impossible, even assuming you had really long arms to reach the front standard.

Try the following. I am assuming you are mounting the 36" element behind the shutter. Try mounting it in front. With most convertibles, when using one element, the nodal point shifts to outside the lens. This is why your bellows draw is about 41" for a 36" lens - the nodal point is about 5" behind the end of the element, inside the bellows. If you mounted the element to the front of the shutter, the nodal point is now about 5" in front (in other words, its a bit of a tele). So, you should require around 30" extension, give or take. The Kodak Master can actually give you quite a bit more by using front tilt and rise, but that would involve new bellows with more extension. But I would try this configuration first. I find that I can use a 30" Artar with the 28" bellows unless I'm focussing close.

I should also add this caveat. Having the converted element behind the shutter is the preferred pace usually since th sposition of the stop helps with control of aberrations. But, given the tradeoffs involved and given that it is a convertible we are talking about, stopping down and a strong monochromatic filter should help. At any rate, it might be weel worth trying this before heading down other sopes.

Cheers, DJ

[Lynn Jones]

Hi Tim,

The darned things are heavy as lead, have strange lens boards and short bellow draw. Your best 8x10 buy with excellent features would be the Calumet C1, preferably the earlier turquoise colored model, wt 13 lbs. The later models in black were of aluminum and weighed 19 lobs, but still excellent models. They were 35" (89cm) could deal with very short lenses, had recessed boards, 5x7 and 4x5 reducing backs, and used Deardorff lens boards. The focus is very smooth using V drive rather than rack and pinion.

Lynn

[Mark Sawyer]

With a 13" tube weighted at the front, it will torque on the KMV front standard enough to drag it into an unwanted tilt, unless you rig up some propping system.

A square extension rather than a tubular "top hat" would help with vignetting at the corners.

You might also consider a shorter extension up front, and a second extension at the rear, between the rear standard and the back, or putting all the extension at the back, which would eliminate vignetting concerns.

Any of these will severely limit how much you can use movements.

Just thoughts...

[lenser]

Thanks to everyone who has answered with their good ideas.

I've tried looking at the lens with the 36" element in back and in front of the shutter and I don't see an appreciable difference in magnification or sharpness. This brings up the question of why is there a difference and what is that difference in performance between having the lens behind as is recommended and having it in front which does allow for a much shorter top hat board?

Again, thanks to edveryone for helping on these questions.

Tim