For sale: machined Olympus BH dovetail to M42 adapters

Rylee Isitt · Post by **Rylee Isitt** » Sat Jan 19, 2013 2:40 pm

Hi everyone,

With much help from Rik and Charles and some beta-testing by Jin, I have designed a dovetail adapter meant to allow you to directly couple an SLR to an Olympus BH microscope or nosepiece having a major dovetail diameter of 42mm. The idea is that the adapter completely replaces the binocular or trinocular head, presenting an optics-free path to the camera sensor (you'd also need a M42->camera adapter, and M42 extension tubes or bellows to complete the task). There are more details and drawings below.

I am taking requests for this adapter until midnight (PST) on Tuesday (Jan 22, 2013). I'm not doing this for business or profit, so I am going to limit the order to about 10 in total. Likely, this will be the last such offer. However, you are free to machine this unit yourself, from the drawings provided below.

The price will probably be about $75 per part worst case scenario, plus whatever the shipping cost is to your area. Originally, the quote was around $50 or so per part, but I have decided to have the dovetail machined to a higher precision, which increased the cost. I will not expect/accept payment until I have the parts on hand, since I'll need to figure out the price per part based on the bill that I will get after the units are machined. I'll also quickly test out each unit to make sure the fit is acceptable before I hold you accountable for payment.

These will be made in unfinished steel. Each unit will come with a somewhat too-big piece of adhesive-backed ProtoStar flocking material, that you can cut to size and use to line the inside of the unit.

This project came about due to my desire to use an Olympus nosepiece/turret at the end of my bellows, allowing me to quickly cycle between lenses on my macro rig. I suppose it could also be used for microscopy, assuming that any objectives you use are fully corrected (eg, Nikon CF) or known to work nicely without corrective eyepieces.

Another forum member, Jin, was brave enough to machine one already, so we know it will fit and be reasonably well centered. I made a few small improvements since Jin's build, which are nearly within machining tolerances so probably won't have a noticeable effect.

Below is the drawing and an over-pin measurement.

If you are interested, please let me know how many units you want, and where I need to ship them to before midnight PST on Tuesday. I'll submit the order to my fabricator on Wednesday morning, and I'll likely have the parts in hand by the following Wednesday.

If you have any further questions, I'll be checking this forum several times a day.

Craig Gerard · Post by **Craig Gerard** » Sat Jan 19, 2013 2:59 pm

Rylee,

Sign me up for one

Thanks!

Craig

Rylee Isitt · Post by **Rylee Isitt** » Wed Jan 23, 2013 1:59 pm

Thanks to everyone who replied/PMed me with orders.

I've sent the order in, and am no longer accepting more.

I ordered a single spare - if someone is still interested, there's one left to be claimed!

Once I get the parts, I'll do some quick testing to make sure they fit, both with the Olympus nosepiece that I have, and with all (6 or 7) of my M42 adapters, bellows, etc.

Rylee Isitt · Post by **Rylee Isitt** » Tue Feb 05, 2013 2:13 pm

Just a heads-up, the last (spare) adapter is now claimed.

There has been a small delay, as my fabricator has had to order in some new steel for these parts. At last communication, the order was expected to arrive at the shop this week.

It normally takes 3 or so business days for parcels to get to me from other parts of the province, so I suspect I won't have the adapters on-hand until mid next week.

Rylee Isitt · Post by **Rylee Isitt** » Sat Feb 23, 2013 1:55 pm

So, there has been another delay.

First was that it took longer for the steel to arrive than I had hoped - it's there now. Second is that it sounds like my fabricator has been insanely busy, so I told him there wasn't a rush, and he's just getting around to my parts now.

The good news is that I will be receiving a part mid next week (It will be sent to me Monday, and takes 2-3 days to arrive by the postal system).

The bad news is that it's ONE part, not five.

The reason for this is that my fabricator has found that there are many M42x1.0 thread specifications, and they may not all be compatible. Inner/outer diameter and pitch is not always good enough with threads this fine. He wants me to test out the specification he's used to make sure it fits before he makes the other four parts. I have five or so M42 lens adapters, plus M42 extension tubes. I'll test the part on all of them to make sure it fits a wide variety of components.

In the meantime, if anyone can dig up more specific information on the M42 lens mount threads (more than just the inner diameter, outer diameter, and pitch), that could help. It would help to have a full profile, ie shape of the thread, angles of the sides, tolerances, etc.

Given these delays, and the fact that we're doing a prototype now, don't be itching to check your mailboxes just yet. This is going to take longer than I had suspected. Once I approve the prototype (or not), I'll get a new time estimate and/or revise the design if needed. My guess is, worst case, two weeks before I have all five in my hands.

Sorry about the delay, folks, but I suspect that it's better to have a part that fits, even if it takes a few more weeks.

rjlittlefield · Post by **rjlittlefield** » Sat Feb 23, 2013 2:18 pm

I had always assumed without checking that the thread form was ISO metric. Then I ignored the spec and cut my threads to fit using a sharp 60 degree chisel so the bottoms are sharp V's rather than rounded as the official form has them. I'm curious what other specifications your fabricator has found.

--Rik

Rylee Isitt · Post by **Rylee Isitt** » Sat Feb 23, 2013 2:39 pm

I've inspected my Pentax SMC M42 lens, and confirm that the thread's valley bottoms have sharp inside corners.

Thanks, Rik - I think that might help (and doing so would seem to maximize compatibility just in case the mating part has not rounded off the threads).

Rylee Isitt · Post by **Rylee Isitt** » Sat Feb 23, 2013 3:18 pm

Change of plans:

I'm sending my fabricator an assortment of 5 different M42x1.0 adapters to expedite the process.

Because of a delay in mail getting to me, but not one for outgoing mail (caused by a third party which takes mail from Canada Post and brings it to the university), this will be faster.

And he'll be able to quickly check if things fit right in the shop, eliminating the potential for back-and-forth through the postal system.

This means I won't be getting a part this coming week after all, but does mean that I'll get the whole order that much faster.

Also, yes, he's using ISO metric. I suspect the parts will fit without a problem, but he's just being careful

rjlittlefield · Post by **rjlittlefield** » Sat Feb 23, 2013 3:40 pm

Careful is good.

There's still a chance that the new parts might not fit some other part that itself is out of spec. I recently received 8 sets of M42 extension tubes from one of the low-priced Chinese suppliers. Of the total 24 tubes, two of them had female threads that were enough out of spec to matter. One tube was cut just a bit shallow. It would fit its own mates but not my M42 iris. Another tube was cut terribly shallow and wouldn't even fit its own mates.

--Rik

Rylee Isitt · Post by **Rylee Isitt** » Sat Feb 23, 2013 4:23 pm

Yeah, that's always been a concern for me when ordering the really cheap M42 stuff on eBay. But so for, it all seems to fit with everything else no problem.

I also have one of those M42 iris units - I bought it from jinfinance as some odd experiment I wanted to do with pinhole photography, but then I found out it didn't close down that far to make for a very good pinhole (but far enough to send me to the optometrist, as I could see better through it than through air, and yup - I ended up with glasses). I was thinking of buying a second and coupling them together to make a smaller effective pinhole.

Still, it's a nice unit - could it ever come in handy when coupled with objectives? The effective aperture is usually so high that I can't see the value in stopping down any further, but who knows. Maybe I'll find a use for it in a home-made abbe condenser or something?

rjlittlefield · Post by **rjlittlefield** » Sat Feb 23, 2013 4:47 pm

Rylee Isitt wrote: M42 iris...
Still, it's a nice unit - could it ever come in handy when coupled with objectives?

Sure. It's useful with deep subjects where you don't want to run the in-focus slab all the way back, but you do want to keep the remainder of the subject sort of recognizable and avoid the usual sudden transition from sharp to hopelessly blurred.

The logistics are that you install the iris but leave it wide open while shooting the in-focus slab, then at the back of the slab you shoot a few more frames with the iris stopped down to various sizes. Those may end up being effective f/200 or some such. In the plane of best focus the resulting image is horribly blurred from diffraction, but in the far background it's significantly sharper (OK, less blurred) than what the objective by itself will do. Stack that together with all the frames shot using the wide aperture, and you have the best of both worlds.

Depending on which objective you're using, you might need to stop down the aperture just a little bit for the in-focus slab also, just enough so the limiting aperture stays in the same place and you don't get perspective changes when you stop down.

--Rik

Rylee Isitt · Post by **Rylee Isitt** » Sat Feb 23, 2013 4:56 pm

Rik,

That never occurred to me. Great tip! I've always stacked the whole bloody thing, which has not always produced the best results.

Rylee Isitt · Post by **Rylee Isitt** » Wed Mar 06, 2013 10:02 pm

The parts arrived today! They fit well, although there is a problem with the inner (M30) threads - I'll explain below.

Centering is very good. Judging by eye alone, I can't see any offset from center on any of the parts. The dovetails are good.

The M42 threads are good and fit with every part I have, this includes four M42 to EOS adapters, some cheap M42 extension tubes, an M42 bellows, an M42 diaphragm unit, and a plastic M42 rear lens cap.

The units are nicely flat and make good contact with the seating surface of the BH nosepiece.

So, the little issue with the inner threads - I gather than when boring out the some of the threads from the dovetail side in order to remove sharp edges, he let the lathe go too far and took out too many threads. So, the threads do not run the entire length of the unit, and the amount of internal threads vary from unit to unit. One is almost complete. I don't think this should affect anyone, as the threads were really an afterthought and aren't necessary for the function of the adapter. If anyone really needs those inner M30 threads to run the entire length and come right to the surface, I'm afraid you're out of luck - however, the M42 threads are in good shape so you can always attach filters and such to those instead

The parts were cheap - $55 each - I suspect he gave me a break due to the inner thread issue.

Some photos are below.

Above is a photo of one of the adapters. This is representative of the other four.

In the image above you can see that the inner threads on four of the units only run for about 1/2 of the depth of the adapter. The fifth, in the lower right, has threads which run most of the length - but the beveled interior edges mean that you won't have much luck attaching anything to the M30 threads unless you can insert it fairly deeply into the adapter.

One of the five units is already flocked (the one I'm keeping in the upper left - it has the fewest inside threads, since I don't need them). The other four will be shipped with flocking if you want to use it - I strongly recommend it, or at least a blackening dip. The flocking will almost certainly be better than any dip or anodized finish you could get.