I mounted my first lens into a shutter!!

[Ash]

So far I've:
-modified a monorail camera to accept a packard shutter and barrel lenses;
-stripped a field camera and sanded it down, refinished it, DIY'd a 4x5 reducing back for it;
-modified an obselete packard-like shutter to work on a spring tension and cable release behind a barrel lens;
-turned a solid wooden surveyors tripod into a camera tripod;
-successfully removed and traded the Kalart rangefinder from a Speed Graphic
-some other stuff I can't really remember

Next job: mount a lens in a shutter!!!



Thanks to Don for trading the Kalart, I had a (Polaroid) Prontor Press shutter.

I had tried to mount the Dagor 180mm elements using tape. This worked but it was far from ideal (see here: http://www.largeformatphotography.in...ad.php?t=26358) and I managed to get a nice shot from it (see here: http://i2.photobucket.com/albums/y43...lydiard1sm.jpg )



So long story short, Don also included the pieces that originally held the Ysaron lens from the shutter. I took a drill bit to both pieces, and cleaned them out until they were just the ring with the flange/thread.

The front needed some loctite putty to hold in place.

The rear pressure-fitted tight, which is good, but the size of the rear element means it has to be screwed in after the mounting ring is on and tightened.

Both front and back rested happily on the flat side of the rings, so I need not worry about whether the pieces are parallel. I've not checked to see if the front and back are close enough, but in fairness for a first attempt I'm pretty pleased I got this far!!






Free lens (gift from grandfather)
Free shutter (well... traded for a piece of a camera)
Free mounting

That just saved me a few hundred on SK or LensN2

You can see the putty from through the rear. To avoid any issues that will be painted matt black in the coming days.

[Nick_3536]

Did you measure to make sure the spacing didn't change?

[Ash]

No not really. I made a mental note of the rough distance by eye between the elements and the aperture iris, and compared that to the lens elements before attaching to the new mounts. It was close to the original, which is good enough for me.

[Dave_B]

Ash:
It may be good enough for you but may not be good enough for the lens physics to work properly. Modern lenses can use shims that are a few to a few tens of thousanths of an inch thick to get the spacing correct in a shutter. Typical tolerances for machined mechanical parts are +/- 0.001 inches for optical systems and shims are often used to get to get things aligned to these kinds of distances. You may want to borrow a caliper and check that you have the distances the same as you found them. That care in getting the distances correct is part of what an SK Grimes does for you when they charge you what they do to mount a lens in a shutter. It often requires a spacer to be machined. They do it because it is important for the lens to work properly.
Good luck,
Dave B.

[Ash]

Hi Dave,

Your points are relevant, but maybe my youth gets the better of me.

I fully understand that when you pay a qualified and experienced machinist a lot of money, they will get the perfect result for you. I don't have the money to do that. This is also a recreational activity for me.

I would gladly sacrifice some coverage, sharpness (edge-to-edge or OOF/DOF area), etc, to simply USE the lens. It sat without use for months due to lack of a shutter. I now have a usable lens, even if it isn't perfect.

[Ash]

In fact, since the lens spacing seems to be such a big issue... WHY is it such a big issue?

Does anybody have a detailed explanation of the effects, with visual proof??

[Nick_3536]

It's an issue because it changes things -) Some lens designs I think are more critical then others. I don't remember how the dagor fits in there.

[Ash]

This is an early Serie III/2 Goerz Dagor = Double Anastigmat. It's the same pattern on either side, mirrored (i think?). If it is mirrored I can only see the effect being a change in FOV and fall-off on the corners where the inner elements don't match up the light-waves completely???

[Dave_B]

Ash:
I don't know how much physics you know but a simple way to begin to understand the optics and the sensitivity to alignments is to think of focussing an image on the ground glass in your camera. Typically movements of the lens of a fraction of a mm matter to the sharpness of the image one sees on the ground glass. The more wide open the lens, the more critical the focus is in terms of getting a sharp image. Smaller apertures give you more room for error. That same fraction of a mm, roughly, also matters to the internal spacing of the lens elements in terms of getting a sharp image.
There is a middle ground between not caring and getting SK Grimes to do it. Find a machine shop, borrow a micrometer and measure before and after you mount the lens. Brass or aluminum sheet can be cut with a shear or scissor and used to shim the spacing to the correct thickness. Even plastic sheet can be used to shim things pretty well. Without much effort or any fancy equipment other than a micrometer you should be able to get things to within a few thousanths of an inch. If you wanted to learn something about your lens, you could even add and substract spacers and watch what happens to the sharpness of the image on your ground glass as you adjusted the spacing through the optimal setting. That's probably how the old time lens makers adjusted things without a micrometer. They tweaked and adjusted until they got a good result. A lot of trial and error but it works.
Good luck,
Dave B.

[Donald Qualls]

Ash, in designing a lens, you can think of the air spaces between the glass elements as elements in their own right, "negative" in the sense that, with an optical index near 1 (a vacuum is a perfect 1.00000, air is around 1.001, give or take) an airspace between two glasses has the opposite effect a glass element the same shape would have with air on both sides.

However, if you change the *thickness* of a lens element (even the air element in the middle that houses the shutter and aperture), you change some of the optical characteristics. Push the front and rear groups apart, and you allow the converging or diverging light, the dispersing or anti-dispersing colors, more space in which to do whatever they're doing before they hit the next piece of glass, which is *supposed* to work perfectly with the other glass and air elements in the lens to produce a final image that, within limits of focal magnification and off-axis angle, is of sufficient quality for photographic (or telescopic, as the case may be) purposes.

Generally, changing the spacing from what the original manufacturer specified will degrade the image; lens designs (even those decades too old to have been subjected to extensive numeric optimization) are pretty carefully optimized. That said, different designs will show more or less degradation when you change spacings; a Tessar, for instance, is tolerant enough of front-to-second element spacing to use front element movement as the focusing movement instead of unit focusing with only a very small compromise in terms of spheric aberration: unit focused Tessars are generally accepted to be "better" than front-focusing versions, but the difference is small enough that stopping down to f/8 pretty much erases it. By contrast, if you change the spacing between front and rear groups of a Plasmat type (like most modern LF lenses with "normal" coverage, as opposed to "wide angle"), you very quickly degrade the image from very good to so-so to "better off with a pinhole".

I don't know the optical layout of a Dagor, and I'm not an optician in any case, but as you'd described the setup you used, you're only a little work from recreating the original Dagor's barrel spacing: you need to measure, as accurately as possible, the spacing you had when the Dagor was tape-mounted (since it was obviously performing pretty well at that point), and then adjust the spacing of your new setup to match that; I expect that will require removing some material from the exposed edges of the old Ysaron cells so they seat flush with the ends of the existing shutter's mount, but can't swear to it.

The simplest *accurate* way to do that is to take the Ysaron cells to a competent machinist and have the ends machined, effectively turning those cell rings into the sort of adapters you'd pay through the nose for S.K. Grimes to make for you, but doing it in a way any machinist can understand and manage -- no cutting of very odd bastard threads, no trying to *measure* odd bastard threads to match them, etc, just a simple cut-to-size operation without damaging the threads already on the original cell rings.