Designing a new affordable production-ready Autocollimator
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- Thread starter Reveni-matt
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Interesting.
I also feel the 10x eyepiece is too weak to judge correctly; the middle seems to be in focus beyond what my own eye can resolve.
Yes, and my star has no marks so I estimate, inner, middle and outer. It is actually pretty nice to instantly check a lens to see how much it deteriorates in the corners. . Most lenses I have tried allow viewing the far corners but wide open only. Though, the wide open performance in the corners is usually what is of interest (to me at least).
I had some bad lenses, finally got my hands on a good one direct from a manufacturer on Alibaba. I'll be able to source more when the time comes.
Siemens star off a mirror (I put some sharpie marks on it so I had a sense of how much of it was actually visible through the eyepiece)
Off film through a 50mm f2 lens on a K1000
The assembly so far. I made a melamine base, 1/2" thick with some more pieces screwed to the bottom. 25mm carbon fibre column, aluminum flange to join the two. 10mm carbon fibre rods to join the column clamp to the autocollimator itself. I'm very happy with this base build, it works really nicely. I think I'll be offering the AC with and without the base as a copy stand or even a tripod will work in it's place if you're more budget conscious or have something good already in your possession.
Aluminum body is working well, lens barrel seems to work well, but doesn't hold concentricity when being rotated. It returns to "zero" when rotated back into the same angle it was when you started. Working on a green LED lamp still, with and off the shelf USB powered constant current controller.
More soon. I've designed a jig to do wear testing on the lens barrel thread to see how the MJF printed threads hold up to tens of thousands of actuations. I have some new prints on the way with alterations I've made based on how things looked and felt with this first build.
Siemens star off a mirror (I put some sharpie marks on it so I had a sense of how much of it was actually visible through the eyepiece)
Off film through a 50mm f2 lens on a K1000
The assembly so far. I made a melamine base, 1/2" thick with some more pieces screwed to the bottom. 25mm carbon fibre column, aluminum flange to join the two. 10mm carbon fibre rods to join the column clamp to the autocollimator itself. I'm very happy with this base build, it works really nicely. I think I'll be offering the AC with and without the base as a copy stand or even a tripod will work in it's place if you're more budget conscious or have something good already in your possession.
Aluminum body is working well, lens barrel seems to work well, but doesn't hold concentricity when being rotated. It returns to "zero" when rotated back into the same angle it was when you started. Working on a green LED lamp still, with and off the shelf USB powered constant current controller.
More soon. I've designed a jig to do wear testing on the lens barrel thread to see how the MJF printed threads hold up to tens of thousands of actuations. I have some new prints on the way with alterations I've made based on how things looked and felt with this first build.
Latest prototype state. Working really well, just a few tweaks and improvements left.
Looks great, excellent news!
I don't know if you are going to incorporate it or not, but what I miss on my Pearl collimator (that the next model actually has) is the ability to read the focus scale in feet or meters right off the collimator barrel. I have to calculate the values with a table, but the other Pearl is engraved on the barrel.
This feature comes if very handy when making focus scales for home-made cameras.
This feature comes if very handy when making focus scales for home-made cameras.
Mine is a multi-turn barrel, I think it wouldn't be possible to do this way. Did the Pearl only turn one part of a revolution?
Looking good! What's the focal length @Reveni-matt ?
Honestly, the focus scale functionality is not that useful or accurate. With a collimating lens of 200mm, the lens would need to retract ~40mm to get a virtual target at 1m. And you then need to know with good accuracy the distance between the film plane of the camera and the principal plane of the collimating lens.
Honestly, the focus scale functionality is not that useful or accurate. With a collimating lens of 200mm, the lens would need to retract ~40mm to get a virtual target at 1m. And you then need to know with good accuracy the distance between the film plane of the camera and the principal plane of the collimating lens.
Actually, I think every suggestion I have has been with respect to features the Pearl 6800 has that my 6400 does NOT have.
I know you are pretty far along with your design, but have you seen the Camera Craftsman May-June 1978? They have a good technical article about the Pearl 6800 and its advanced features. With your muilti-turn barrel, I actually thought you were copying the Pearl C6800 already. I don't have a good picture but you can see here how they put the feet/meter numbers along side the millimeter scale vertically.
Depending on how you have done your millimeter scale, it is just a matter of doing the calculations and having the feet/meter numbers printed next to the millimeter scale.
BTW, the 6400 has a focus stage that is straight out of a microscope focus mechanism. The problem with that is that it has to be pretty stiff, otherwise it drops down with gravity. I think that is why the rotating barrel that you are doing is a better solution.
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243mm. Needing that much travel to reach 1m isn't great.
I wouldn't know how to find the principle plane of the lens I'm using. That's not great.
If I eliminated the objective focusing I could cut probably close to 20% off the price.
I did read this a while back. I was looking at Gokosha units mostly. Having the multi turn barrel gives a lot more control vs a rack and pinion microscope style (and easier to make) but it seems the required precision isn't very necessary. If the Pearl does it by rack and pinion, then it's suitably accurate.
Starting to consider removing the focus mount to lower costs and decrease complexity given it's not sounding super useful for most people.
On the other hand, a focusing lens is pretty useful for calibrating the collimator. And if you fall on a maladjusted (testing) lens that stops a bit before true infinity, you can easily confirm that by retracting the collimator lens a little. So maybe a short 10mm throw could be useful?
The target and eyepiece are threaded for calibration so it's not strictly required to have a movable objective as well.
Wouldn't you know it's maladjusted because you can't reach infinity? If it was going beyond infinity you'd see it pass through focus first.
I see your point about removing the ability to focus, otherwise your device may need to cost more than a used Gokosha or Pearl.
However, sometimes the autocollimator focus is needed. For example racking the test camera lens all the way back to infinity clears up the Siemens target, but is it as sharp as it will get? Will it get sharper if the focus of the test camera could be racked farther back?? Hard to know. At least with a focusing autocollimator you can zero in on the sharpest image of the target, then check to see if the autocollimator still reads zero.
However, sometimes the autocollimator focus is needed. For example racking the test camera lens all the way back to infinity clears up the Siemens target, but is it as sharp as it will get? Will it get sharper if the focus of the test camera could be racked farther back?? Hard to know. At least with a focusing autocollimator you can zero in on the sharpest image of the target, then check to see if the autocollimator still reads zero.
Well there you go, you guys sold me on keeping it.
It's going to be cheaper than the typical going rate for a unit online. Not to mention how scarce they are.
It's going to be cheaper than the typical going rate for a unit online. Not to mention how scarce they are.
It would be important to include detailed instructions for use with the collimator, because this device is not self-explanatory. Also information, what can be done with it.
This is beneficial for interested parties who have no experience with it and thus increases the potential customer base.
This is beneficial for interested parties who have no experience with it and thus increases the potential customer base.
Of course. I myself barely understand how to use it. Still exploring what it's capable of as well.
BTW @Reveni-matt how's the stiffness of the stand? At high magnifications, tiny vibrations will be apparent.
The magnification is not that high, the siemens star projection is around 3mm across on the film plane with a 50mm lens. There are vibrations if you touch it of course, it settles quickly and touching the base plate does not have much of an effect. I don't have any issues using it. The carbon fibre rods are very stiff and do a good job of damping as well.
@Reveni-matt you should try to test it with a slow & short lens. My DIY autocollimator (f=333mm) is super dim (on film) at ~45mm f/5.6. I adapted it to use a P67 200mm f/4 lens and it gets better.
Here's a 20mm f4 lens at f8, off a mirror:
Here's off film at f4:
The green LED is running at 500mA, probably putting out 1.5W.
Here's off film at f4:
The green LED is running at 500mA, probably putting out 1.5W.
Half silvered mirror, 1.1mm thick
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