Half Aplanat in Copal 3

[jb7]

One of my pet hates is people posting crappy iPhone pictures to photography sites. In a classic example of, ‘Do as I say and not as I do’ what follows is a series of crappy iPhone pictures.

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I need a longer lens, and I have a Suter Aplanat B, it’s around 18”fl. A single group is around 800-900mm fl, a bit longer than I’d like, but still usable. According to the numbers, this should be around f/16.

I also have a Copal 3 shutter, so here’s an inexpensive way to marry the two.

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You’ll need some components, from wherever you can get them. Mine cost around $6 including postage. First, you’ll need to replace the standard retaining ring on the shutter with a filter step down ring- in my case a 77mm- 62mm. This might also be useful if you have a Copal 3 shutter without a retaining ring, they’re very inexpensive.

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Next, you’ll need a metal lens hood, the ones with threads on the front as well as on the filter end. The first one I bought turned out to be too long, designed for a telephoto. I got another, for a standard lens, which was shorter. This size hood places the lens at the correct distance from the diaphragm, well, at the same spacing as the complete Suter Aplanat.

The filter thread on this hood is 72mm, the opening is around 70mm, One half of the aplanat fits in with 2mm to spare. In order to centre the lens, I cut out three small pieces of 1mm thick material, and inserted them into the gaps at 120º intervals.

Next came the messy part. I didn’t want this to be a permanent conversion, I wanted to be able to re-use the Aplanat, if I needed to. So I chose to use a hot glue gun. It looks awful, but it produces a strong bond, and will be completely reversible. Squirt the glue into the gap, and wait for it to cool.

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[jb7]

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The front end of the hood screws onto the outer threads of your new retaining ring, at 77mm this is the maximum size that can be accommodated comfortably on the back of a Linhof board.

So now you have a mountable achromat. For those rare occasions when you really want to use a long lens, or any lens really, you’ll need to carefully remove and store the original cells from the Copal 3, and screw this assembly onto your new retaining ring.

Since the maximum diameter of the opening for the lens is somewhere around 70mm, further step-downs can be used to mount smaller objectives in additional hoods. I use the Linhof boards on larger adapter boards; I’d have a problem fitting this particular lens through the standard opening. Just something to be taken into consideration…

I’ve only just put it together, so I don’t have any results from it yet, but I’ll get onto it as soon as it stops raining, probably sometime around April…

[Ramiro Elena]

I can't fully understand each step but it looks good and smart. I like to use cemented fronts from Petzvals in a Compound 3 shutter I have laying around. I've even started a spread sheet with measurements to have a better idea of what combinations I can make with the stuff I have.
I've also tried to use step up rings but never got anything successful. The main problem I see with theses lenses is the spherical aberration which tends to be too much towards the edges.

[Will Frostmill]

thank you for posting this, I was just thinking about doing this today!
I was planning on using a simple meniscus lens stuck on the back of a suitable shutter, something in the 300-600mm range for 8x10. My only quibble is I'm going to have to look up what the best distance from the aperture is for meniscus lenses.

Will

[Ramiro Elena]

What is the difference between placing it in front or behind the shutter? How do you calculate the distance and what does it affect?

[jb7]

What is the difference between placing it in front or behind the shutter? How do you calculate the distance and what does it affect?

The difference, I think, is that placing the element behind the shutter will produce barrel distortion, in front of the shutter will produce pincushion distortion. At least this is the case in my experience, with planoconvex and biconvex lenses. I haven't tried this one yet, it's been the worst January since records began... Really like your half lens pictures Ramiro-



thank you for posting this, I was just thinking about doing this today!
I was planning on using a simple meniscus lens stuck on the back of a suitable shutter, something in the 300-600mm range for 8x10. My only quibble is I'm going to have to look up what the best distance from the aperture is for meniscus lenses.

Will

I tried looking it up, even asked a question here - http://www.largeformatphotography.info/forum/showthread.php?53706-Meniscus-Lenses-Another-question-for-Mr-Galli-and-others but I didn't get an answer. In my case, I spaced it the same distance from the iris as on the full Aplanat, but I seem to remember reading that the spacing is determined by the curvature of the concave surface facing the iris, though this may only be correct for a fixed aperture. Trial and error might be the solution, but I doubt it's going to be that far off, in my case...

[Andrew Plume]

yes, entirely agree

the shutter should be mounted in front of the lens and not behind, the opposite than for a Packard

plenty of European manufacturers, such as Luc manufactured front mounting shutters for using barrel lenses

.......and yes, Joseph, if and when it stops raining, something that those in California are more in need of

regards

andrew

[jb7]

Thanks Andrew-

Of course, in the first reply above, I should have been more specific, and said 'Iris' instead of shutter...

[mdarnton]

I don't fully understand the whole thing either, but I wonder if there would have been a possibility of substituting an o-ring for the hot glue. I've been thinking of trying to use o-rings as temporary mounting rings for lenses I want to move around, by assigning the screw-mounted flange to the primary board and using o-rings as mounting nuts for other boards.

[jb7]

I used the hot glue because it's completely removable, if necessary, and the brass flange is quite heavy.

Those metal lens hoods are really cheap; to dedicate one to a specific shutter mounted on a board using the step down ring instead of a retaining ring would give you the possibility of an interchangeable set, using lenses glued to dedicated step rings to screw into the hood.

I have used an o ring to retain a lens in a shutter before, but only a small one in a Compur 00, diameter around 19mm. I'm not sure if I'd trust an o ring with anything much larger-

[Ramiro Elena]

Wouldn't it be the same if one were to flip the lens instead of placing it behind or in front of the shutter in order to control aberration?
I've been doing:
Camera->lensboard->Compound3 shutter->front of a Petzval (hood included)
I've found that flipping the lens inside the mount got rid of a little aberration. Closing the iris to a smaller aperture helps too but makes the image sharper.

[jb7]

Wouldn't it be the same if one were to flip the lens instead of placing it behind or in front of the shutter in order to control aberration?
I've been doing:
Camera->lensboard->Compound3 shutter->front of a Petzval (hood included)
I've found that flipping the lens inside the mount got rid of a little aberration. Closing the iris to a smaller aperture helps too but makes the image sharper.


As far as I can remember, distortion is not considered to be an aberration. The type of distortion, however, pincushion or barrel, can be influenced by the position of the iris. Perhaps applying the iris directly to the lens would minimize the effect, I don't know. I haven't any experience putting the front group of a Petzval in front of an aperture, either way around, but my guess would be that there would be little difference...