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Precision Back Focus and Tilt Adjuster from Octopi-Astro

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#1 bugbit

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Posted 30 September 2020 - 11:55 PM

Hello there. I thought this would be a good time to introduce myself and show you what I've been up to. My name is keith and octopi-astro is my new business that manufactures precision back focus and sensor tilt adjusters. This all started due to the frustration of trying to get the full size sensor of my QHY367c orthogonal on a 11" RASA. After dealing with this myself and reading the constant deluge of other CN readers posting regarding the same issues, I decided to go public with my solution.The 3 sets of push-pull screws of the prototypes work great, but a couple folks who's opinions I respect thought a unit with 4 sets of screws would be easier to fine tune, so that is what I will offer first. Originally, 100tpi screws (254um/revolution) were utilized but these new models will be provided with 80tpi screws (318um/rev) while they may be less accurate, they can be unscrewed and upgraded with differential adjusters that are rated at 25um/rev for folks with fast systems at a cost of roughly $200. The standard unit will be priced at $600 for now but may go up a bit in the future. Also, this unit is 5" in diameter so it is too large for the RASA 8 but there are plans to scale it down in the future. If you have any questions, remarks or other comments, feel free to pm me or on my website (under construction) at https://www.octopi-astro.com

 

 

4 tab tilt-backfocus adjuster.jpg

evolution of a adjuster.jpg


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#2 nPAE

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Posted 02 October 2020 - 10:12 AM

That looks a very nicely engineering and neat solution! Great laugh.gif


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#3 Lead_Weight

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Posted 02 October 2020 - 07:46 PM

Are these only for the RASA? Any chance you could create a design like this for image trains that doesn't take up a lot of back focus (maybe it's already like that)? I think there is one aftermarket unit now but it takes up 17mm. I think what's unique about your design is how the front plate is thin, and you just made the part you adjust face backwards around the outside of the camera. This is pretty clever, and makes the adjustments much more accessible.


Edited by Lead_Weight, 02 October 2020 - 07:59 PM.

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#4 bugbit

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Posted 02 October 2020 - 08:24 PM

Hello Andrew

Funny you ask as this model you are looking at was designed to go between a ASI filter wheel and a ASI6200 but the fellow that it was for sold his camera a few days back. These adjusters are semi generic as the inner clamp ring just has different size hole to fit various cameras. The back focus with it fully seated is about 5mm and can be adjusted out to roughly 11mm by using the 1/4-80 screws and if that is not fine enough adjustment you can screw out the push screws and screw in Differential Adjusters that have the same 1/4-80 outside thread but are extremely accurate at 25 um per revolution for a cost at $200 ($50 per) more per unit. The mounting is hard to see but it is a m68-1 thread and it also has #6-32 screw holes that are in the same pattern as a ZWO/ASI filter wheel at 40mm radius and 0-30 degrees to match.

I'm working on a single filter drawer that will use the same pattern for the RASA crowd and utilize baader filter holders so it will interchange between both types of users.

Thank you for your interest.



#5 Lead_Weight

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Posted 02 October 2020 - 08:32 PM

OK, so here's my setup with the ASI6200. Focuser, adapter to the flattener, flattener, 9mm M68 adapter, 5mm ZWO M68 Tilt adjuster, EFW, Camera.

 

So in practice, I would just remove the 5mm ZWO tilt adapter, and put your device around and in front of the camera, taking up 5mm. Everything else remains the same?

 

If that's the case, sign me up! 

 

IMG_2321.jpeg



#6 bugbit

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Posted 02 October 2020 - 08:41 PM

That's it pretty much. 1 problem though is it really should be centered at about 8mm. 5mm min - 11mm max so you have room to adjust your back focus in or out by about 3mm from the center. So, If it were me, I would lose the m68 x 9mm and use a 1 mm bushing or even jut as is with only 2mm of adjustment out and 4mm in. Remember there is about 6mm total to work with.

 

Just noticed the m68 x 9 adapter is a adapter and not just a spacer.


Edited by bugbit, 02 October 2020 - 08:43 PM.


#7 Lead_Weight

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Posted 02 October 2020 - 08:55 PM

That's it pretty much. 1 problem though is it really should be centered at about 8mm. 5mm min - 11mm max so you have room to adjust your back focus in or out by about 3mm from the center. So, If it were me, I would lose the m68 x 9mm and use a 1 mm bushing or even jut as is with only 2mm of adjustment out and 4mm in. Remember there is about 6mm total to work with.

 

Just noticed the m68 x 9 adapter is a adapter and not just a spacer.

Yeah, it is an adapter, it goes from the Sky-Watcher M66 flattener side to M68 OAG side. It's from Precise Parts, so I suppose I could order a smaller one, but I doubt I could get 2mm. According to Precise Parts the smallest they can machine is 7.7mm

 

If I move the camera setup to my Edge 11, the setup is a little different, as I have 2.5" Moonlite focuser, and it should be easier to connect and gain that space.



#8 bugbit

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Posted 02 October 2020 - 09:09 PM

I think we are on different pages here. Let me start over. This unit has a minimum bf of 5mm or a bit less and a max bf of 11mm or so. The idea was to market it in the middle at about 8mm so there is 3mm on either side to overcome whatever problem you were having getting back focus right and to be able to tweak out the tilt of the sensor. So mounting it at 5mm loses most of the adjustment room. The tilt adjuster on your camera is 5mm I believe so losing that would get you at the minimum bf which would work if you needed more but  it would be a paper weight if you needed less.  The m68 x 9mm adapter? What is the m66 thread? m68-1 or m68-0.75?


Edited by bugbit, 02 October 2020 - 09:11 PM.


#9 Lead_Weight

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Posted 02 October 2020 - 09:27 PM

I think we are on different pages here. Let me start over. This unit has a minimum bf of 5mm or a bit less and a max bf of 11mm or so. The idea was to market it in the middle at about 8mm so there is 3mm on either side to overcome whatever problem you were having getting back focus right and to be able to tweak out the tilt of the sensor. So mounting it at 5mm loses most of the adjustment room. The tilt adjuster on your camera is 5mm I believe so losing that would get you at the minimum bf which would work if you needed more but  it would be a paper weight if you needed less.  The m68 x 9mm adapter? What is the m66 thread? m68-1 or m68-0.75?

This is the Sky-watcher Esprit 100 flattener. So it's threads are M66x1. The back focus requirement is 63mm. The ZWO gear with 5mm tilt adapter is 55mm +1mm for filters. So I need 64mm total, and that's where the 9mm M66 to M68 adapter comes in.

 

I was thinking if I replace the ZWO tilt adapter for yours that's 5mm. But to get room to adjust it likely needs 8mm. The smallest I can get the adapter from Precise parts to replace the existing one is 7.7mm thick. That really only gives me 1.3mm of adjustment room.

 

These are the parts you're seeing in my photo, up to the 9mm adapter.

 

Screen Shot 2020-10-02 at 9.23.27 PM.png


Edited by Lead_Weight, 02 October 2020 - 09:28 PM.


#10 bugbit

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Posted 02 October 2020 - 09:47 PM

So you would need a m66-1 F to m68-1M adapter that is ideally 6mm long, That's tight.

At 7.7mm long that adapter would get you 1.3mm of inward adjustment and 4.7mm of out ward adjustment which isn't ideal but still works. Have you looked at my site in my sig yet?  If you look in the gallery, there are some pics of parts randomly strewn about that should give you a better idea of what you are looking at.  There is also a contact me at keith@octopi mail link that shoots to me here on my desk for private info transfer,shipping address,etc. Anyhow, take some time to think about it as I don't want to push anything on any one.


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#11 Lead_Weight

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Posted 02 October 2020 - 09:49 PM

I think the main thing was just clarification of how this works with non RASA systems, since that's what you mentioned in your original post. But looks like it will quite well. I'll be in touch. Thanks for the information.


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#12 alphatripleplus

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Posted 05 October 2020 - 07:22 AM

Is there a set of instructions you provide for the best technique for making adjustments with the tilt adjuster, or is pretty much trial and error?



#13 bugbit

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Posted 05 October 2020 - 09:02 PM

Hello Errol

I have some tips from my ups and downs experimenting with this. I'll need some time to put together a coherent essay on what I've found to ease the frustrations.


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#14 Benach

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Posted 17 October 2020 - 05:01 PM

bugbit: nice machining and design. But I wonder: what is the difference between this thingy and a normal orthogonal Kelvin clamp with matching interfaces and precision setscrews?



#15 bugbit

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Posted 19 October 2020 - 05:42 PM

bugbit: nice machining and design. But I wonder: what is the difference between this thingy and a normal orthogonal Kelvin clamp with matching interfaces and precision setscrews?

I had zero idea what a kelvin clamp is so ole google to the rescue and I got this:

 

 https://www.precisio...Trihedral.php  

 

and this: 

 

https://www.sonel.pl...lamp-1-kv-25-a/

 

so at this point I still have zero idea. Maybe I'm missing some thing in translation?



#16 Benach

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Posted 20 October 2020 - 09:44 AM

Hi Keith, thanks for the reply. No, nothing is wrong in translation. Below is a link. The cone-vee-flat arrangement is also known as a Kelvin Clamp:

https://wp.optics.ar...esTutorial1.pdf



#17 bugbit

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Posted 20 October 2020 - 02:21 PM

Hello Benach

 

Hi Keith, thanks for the reply. No, nothing is wrong in translation. Below is a link. The cone-vee-flat arrangement is also known as a Kelvin Clamp:

https://wp.optics.ar...esTutorial1.pdf

If you look at the photo's at the beginning of this thread you will see there is no cone-vee-flat arrangement involved so you would be a better judge of the difference between this thingy and a normal orthogonal Kelvin clamp with matching interfaces and precision setscrews.



#18 bugbit

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Posted 24 November 2020 - 10:00 PM

Here is a tilt and back focus adjuster with a ASI 6200 screwed to the top of a Baade UFC filter drawer for a 11" RASA. It could also be used on a 8" RASA with a camera that has 6.5mm of back focus.

 

IMG_7824r.jpg


Edited by bugbit, 24 November 2020 - 10:06 PM.

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