Microscope headpiece dovetail dimensions

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jin
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Post by jin »

Hi Rylee Isitt,

Thanks for your drawing, my adapter finally arrived this afternoon and I have a question with regards to how critical is the alignment of the center to the objective in real life shooting.

This is when I compare the locking screw's position using this adapter and the 'original' - the one used for directing the light to the objective, it seems to be about 1~1.5 turns different.

Pls. advice.
jin

Rylee Isitt
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Post by Rylee Isitt »

You had one fabricated? To what tolerances, and what microscope are you using it with? I'm sorry that I wasn't as clear when I replied, but this design is not 100% done. We're still working on some of the more critical dimensions. We're definitely very close, but not necessarily 100% confident of them. But I was on a smartphone with a bad connection at a time, so I didn't take as much time to reply as I could have.

I'd love to see photos of the adapter!

We're still a bit unsure if we got the dimensions correct, to be honest... and since I went away over the holidays, I didn't have a chance to work on this until now. I took an measurement over pins the other day, and measured the minimum diameter with a ad-hoc blade micrometer. These measurements indicated to me that the drawing as-is is *slightly* off. But Charles and I are still doing measurements...

But a typical tolerance of 0.005" translates to 0.127mm - that alone will lead to small centering issues and may entirely explain your observations.

Slight off-center alignment is not an issue at all, so long as the fit is light-tight. The only issue I can think of this causing is possible asymmetrical vignetting. If you don't see vignetting, then there's no issue. But try to judge centering some other way, if you can, I'm not sure using turns on the locking screw is the best way.

Rylee Isitt
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Post by Rylee Isitt »

I have spent most of the day doing measurements, and believe I can confidently confirm that the dovetail angle is 60 degrees!

I took two sets of over-pin measurements using different pin diameters (2.75mm and 4.28mm) and got an angle of 59.92 degrees from my Olympus BH2 dovetail.

I also recently measured the minimum diameter of the dovetail using calipers and razor blades (a bit awkward, so I repeated the measurement more times than usual to be sure it was repeatable). This value is 36.06 mm from my dovetail, and since I'm not sure to what tolerance it was manufactured, that may or may not represent a difference from what is currently in our design...

The math was based on http://www.neme-s.org/Model_Engineer_Fi ... Slides.pdf (thanks to Charles Krebs for sending that link to me).

If you wish to see the measurements and math, the excel sheet is here: http://www.ryleeisitt.ca/BH2-dovetail-measurements.xlsx

Rylee Isitt
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Post by Rylee Isitt »

New designs and over-pin measurements:

Image
Image

jin
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Post by jin »

No worry and I'm not blaming anybody here as I took my own risk and went ahead to get the adapter fabricated. Basically I'm just reporting my observation (my visual check, so may not be accurate or scientific) seen on my two Olympus BMH microscopes but I'm happy that i can finally mount the camera on the scope and soon be able to start taking photo.

The critical dimension seen to be the 60 deg and it looks close enough when I putting the original dovetail ring side-by-side in reverse orientation.

Anyway, I will try to take pic of the adapter later, with and without mounted on the scope for your comment.

See link http://s483.beta.photobucket.com/user/BJTan/library/ for some quick shots.

Rylee Isitt
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Post by Rylee Isitt »

Hi Jin,

The changes I recently made to the design were very minor, and I suspect that in practice (due to machining tolerances), they wouldn't have made much of a difference, since they are just beyond typical (0.005 inch) machining tolerances. Charles and I also have different dovetails - both are Olympus, and designed to work with the same scopes, but since they are not identical copies we`re likely to come up with different numbers no matter what.

The difference in locking screw position you're seeing could be due to tolerances alone - both the Olympus part and the part you had fabricated will almost certainly be different, no matter how closely we nail down the ideal measurements.

A full turn on my locking screw represents a fairly small offset. I haven`t measured the locking screw pitch, but it looks to me to be about 0.75 mm. That kind of shift is not going to impact the image.

One thing you can do to try to measure this is to close down the iris of your microscope as much as you can and adjust the condenser to render the smallest point of light on the slide that you can. Using a low magnification lens and the official Olympus parts, make sure the iris is centered. Then, photograph something with the same closed-down iris using your new adapter and see whether or not the spot of light is still in the center of the frame. You can also try using a very bad NON-plan lens, and see if the central area of focus is nicely centered.

In any case, As long as the adapter is nice and flat, and light-tight, I don`t think you`ll be disappointed. You will want to line the inside of your adapter with flocking or matte black paint, to prevent internal reflections. Such reflections can ruin an image...

yanyading
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Post by yanyading »

Very great information...
--
UV is the Key to High Resolution Microscopy

Rylee Isitt
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Post by Rylee Isitt »

The final drawings prior to machining:

Image
Image

I am accepting requests for orders of this part in the equipment exchange forum: http://www.photomacrography.net/forum/v ... hp?t=19298

jin
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Post by jin »

Rylee,

Just my user experience and you may want to have some kind of 'anti slip' treatment made on the 5mm outer ring and/or if possible to also increase the 5mm thickness to say, 8mm for more grip when tightening to other adapter, just for your info.

cheers!

Rylee Isitt
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Post by Rylee Isitt »

Hi Jin,

M42 lenses have about the same amount of thread (4.75mm), so many M42-based extension tubes and adapters out there expect no more than about 4-5mm of thread. Whatever other adapters you use with this part, they need to make contact with the flat, upper seating surface. Using more turns of thread there would interfere with that goal.

I am wondering if the threads on your unit were made somewhat loose-fitting. Can you describe exactly what is going on? Is it that your adapter is still loose, even when screwed down to the surface?

I am going to measure a few more M42-based things, and see if it's safe to increase the thread depth to 4.75mm. Any more than that, though, is probably risky.

jin
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Post by jin »

Hi Rylee,

I was actually referring to the outer ring - the 5mm, +/-0.125mm portion but not the no. of thread :-)

So far the adapter works fine in term of form/fit and function and currently i'm just spending time on the lighting and learning to take photomicrography as this is totally new to me.

Rylee Isitt
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Post by Rylee Isitt »

Ah, I see what you mean!

Yes, I can certainly increase the depth of that part, to 10mm. I'll run that past any interested folks to be sure that won't cause problems. Thanks for bringing that issue to light!

For your part, which is already made, you can wrap a rubber band around it. Get the right sized rubber band, and you should be able to solve your problem.

Did you make your part out of aluminum? If so, you might run into a problem where the aluminum "galls" and actually begins to stick to the other part. If that happens, it could be extremely difficult to unscrew the part afterwards - I've had that happen with camera filters and been quite dismayed. The anodized finish on the threads wears off eventually, and then the aluminum galls. If you used aluminum, you might want to use some thread lubricant to prevent that problem. But you have to be careful - some lubricants will evaporate and risk depositing films on your optics! To be honest I'm not sure what type of lubricant to recommend there.

I'm having these machined with steel, to help avoid galling issues.

Charles Krebs
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Post by Charles Krebs »

I would not increase the 5mm thickness. There are times when even a mm or two "closer" to the objective may be necessary. If the adapter is too thick you may be out of luck, especially if you want to use this on an infinity BX trinoc head and want to make a custom adapter that is parfocal with the eyepieces. . It is easy to add distance if needed. If you add in the dovetail depth of 6mm you have 11mm of metal to grab. I can't see this as an "issue".

Rylee Isitt
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Post by Rylee Isitt »

Good point, Charles. I do have a lot of very skinny adapters and haven't had issues with grip... even the ones that are just smooth, polished metal.

Perhaps it's not worth fiddling with the design at this point. Those who wish to machine this themselves can easily change dimensions a bit, specify T2 thread instead of M42, etc.

grgh
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post subject

Post by grgh »

amended as i had not noticed date of first post.

my advice would have been to purchase a 5in, 125mm.

contour shape profile gauge, the all metal pins and holder ones are best,
around 7-8$ at last purchase.

always work for myself when angles diameter and depth are needed.

hope you got sorted anyhow.

grgh
used to do astronomy.
and photography.
Zeiss Universal Phase contrast.
Zeiss PMII
B&L stereo zoom.

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