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Old May 24th, 2008, 06:15 PM   #1
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Join Date: Jun 2003
Location: Miller Place, NY
Posts: 820
1-1/4" close nipple as distance holder

I've just finished a small modification of my static depth of field adapter, built following Daniel Schweinert's design, and thought I'd pass along a tip.

A few weeks ago, I noticed my adapter had problems with infinity focus. Since I haven't had the chance to shoot any far away subjects, I'd never noticed before, but things were indeed very slightly soft at that focus setting. It occurred to me that my initial positioning of Daniel's SH-57ND ground glass holder could have been off.

Using a pair of Vernier calipers with a depth bar, I checked all of my distances, and lo and behold, the screen was just a fraction of a millimeter too far back. I'm using a set of M42 lenses (my grandfather owned them, and it'd be a shame to let them go to waste), and I need an adapter to use them on the EOS mount. Well, it so happens that the M42 to EOS adapter I've got sets the lens forward about 1.5 millimeters. On top of that, the Nikon D focusing screen is recessed about 0.4 millimeters from the face of the SH-57ND. I had originally set the holder at a distance of 44mm. Do the math, and just my luck, the screen is almost 46 millimeters from the flange. The proper distance for M42 is 45.46 millimeters. Isn't that always the way?

In addition to all of that, the PVC pipe I'd originally used to position the holder was difficult to cut with any precision, giving the screen a slight tilt in one direction. Not noticeable, but something I wanted to fix while also adjusting the FFD. How to accomplish this? All sorts of ideas raced through my head, but being in the plumbing industry (use the materials you're comfortable with, you know?), I eventually settled on attempting to use a steel nipple screwed into the back of a floor flange. The back is the flat side, and would give me a nice surface on which to set the EOS tubes. I used inch and a quarter (inside diameter, since it's plumbing material; all of our stuff is measured ID) since the diameter allowed the nipple to support the ground glass holder without obstructing the two screws. This wasn't strictly necessary, however, and you could probably use any size that fits in the extension tubes.

Anyway, it turns out that when threaded into the flange, a close nipple is too short, while a shoulder nipple is too long. This drove me crazy for a couple of days, until it struck me to measure the close nipple by itself, ignoring the flange altogether. 43.5 millimeters. Absolutely perfect. For everything to work correctly, the distance from the face of the EOS bayonet mount to the face of the screen holder could be a maximum 43.56mm (45.46 - 1.5 - 0.4 = 43.56), so this was ideal. And straight out of the factory, the measurement was incredibly consistent around the entire circumference. Set all of my pieces on a nice flat surface, dropped in the holder, hot glued it in place, and voila! Infinity focus.

Since we bought two of each item to be on the safe side, I measured the other close nipple as well, and it was also 43.5mm long, consistent all the way around, so with any luck others will find a similar, if not identical measurement. Knowing that many of us are fans of Daniel's design, and knowing what a pain it is to position something like these holders properly, I figured I should post a quick note for anyone struggling with this. There aren't many of you using M42 lenses, I imagine, but you never know. The screw mount 50mm 1.4 Takumars are plentiful and affordable on eBay, after all.

If anyone's interested in doing what I did, Home Depot, Lowes, their international equivalents, or any local plumbing supply should have these things. You can do a Google image search for any of this stuff to see what it looks like (just make sure SafeSearch is on when searching with the word nipple, or you'll get what I'll simply call 'unrelated' results), but the employees should know what they are. Close nipples are all thread, shoulder nipples have a tiny sliver of pipe remaining.
Robert Martens is offline   Reply With Quote
Old May 24th, 2008, 10:00 PM   #2
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Join Date: Dec 2003
Posts: 4,364
Plumbers rule or at least their supplies do.

I am not one of them but my home made adaptor which I have titled AGUS35 APVE is made from swere pipes and caps. - "AGUS35" after the original alternative adaptor maker and APVE for "Australian Plumbers Version Erecting" (flip).

I also made a PD150 lends hood bayonet to 52mm 0.7mm thread adaptor using two pieces from a sink drain fitting.
Bob Hart is offline   Reply With Quote
Old May 24th, 2008, 10:27 PM   #3
Major Player
Join Date: Jun 2003
Location: Miller Place, NY
Posts: 820
We do indeed, Bob, we do indeed. Glad to hear our industry has helped you, if only in some small way.

By the way, my first post counts as a service call; you all owe me two hundred bucks.
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