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Hyperstar coma issues - please help me :)


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Hi, I've recently bought a second hand hyperstar V3 for my C8 edge hd. Unfortunately I still didn't manage to get a very flat image with it, at first I thought it's because lack of collimation and that I simply don't manage to do it correctly, but after a few more testing it seems like this is not the issue.

Currently I suspect that my issue is due to wrong backfocus, but I don't really have a way to test that because it could be a matter of millimeters and I don't have such small thread extensions.

The weird thing is that as far as I'm aware my backfocus should be spot on.
Here is the adapter I have to connect the camera to the hyperstar:

image.png.2b4a778989a72793183ab1add9580e11.png

Now according to the hyperstar C8 V3 specifications, the required backfocus is 39.8mm.

So with this adapter I have 22.3mm, I'm using the ASI071MC pro so the backfocus from the thread to the sensor here is 17.5mm, so in result, from the hyperstar to the camera sensor I have: 22.3 + 17.5 which is exactly 39.8mm, yet the coma is horrible...My pull/push screws are also on 0, so that should really be spot on...I tried adding a 4mm thread extension and that actually seems to help, not much but it did, still had a lot of coma though.

I'm not really sure what else I could try and would love to get some help, hope this is the correct forum to ask. Thanks!

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It's a bit difficult to see from that picture, but doesn't that threaded part of the adapter thread into the camera flange ?

Thus your distance would not be 22.3 mm + 17.5 mm, but it would be 22.3 mm - threaded part(looks to be ~4 - 5 mm) + 17.5 mm, leaving you short by the distance of the threaded part.

Adding 4 mm and getting a minor improvement would also explain this, you are moving in the right direction, but are not spot on yet.

The Hyperstar is extremely picky about backfocus distance, I found this piece of information on the Baader Planetarium site when I was putting together my own Hyperstar:

"The distances for adapting a camera to the Hyperstar system must be done with a precision of +/-0.3mm or better, otherwise the image quality will suffer."

 

Also remember that at F2 your critical focus zone is in the neighborhood of 10-15 microns (yes, that's 0.010-0.015 mm), which is going to make manual focusing challenging to say the least...

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  • 3 weeks later...
On 24/12/2019 at 10:49, MarcusH said:

It's a bit difficult to see from that picture, but doesn't that threaded part of the adapter thread into the camera flange ?

Thus your distance would not be 22.3 mm + 17.5 mm, but it would be 22.3 mm - threaded part(looks to be ~4 - 5 mm) + 17.5 mm, leaving you short by the distance of the threaded part.

Adding 4 mm and getting a minor improvement would also explain this, you are moving in the right direction, but are not spot on yet.

The Hyperstar is extremely picky about backfocus distance, I found this piece of information on the Baader Planetarium site when I was putting together my own Hyperstar:

"The distances for adapting a camera to the Hyperstar system must be done with a precision of +/-0.3mm or better, otherwise the image quality will suffer."

 

Also remember that at F2 your critical focus zone is in the neighborhood of 10-15 microns (yes, that's 0.010-0.015 mm), which is going to make manual focusing challenging to say the least...

It has been a while, but the issue was with the adapter I recieved, it wasn't the correct one for me.

I should be getting a new adapter soon, and hopefully that will work just fine with it.

Thanks :)

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  • 1 month later...

Hi! I am having the exact same problem, the only difference is my hyperstar is v4, but the camera (ZWO 071 MC Cooled) and it´s backfocus are the same (17.5 mm). I´ve wasted hours trying to fix coma problems with this setup, but it´s impossible.

I took some screenshots from my laptop last night to show how serious my problem is: https://wp.me/a6SKCz-1t8

As you may see, the star (sirius), is perfectly round in the middle, but distorts a lot on the edges. Coma points towards the center of the sensor, from any direction. This is why I´m assuming spacing is the problem.

What should I do? How can I make sure I buy the correct spacer?

Thanks a lot, glad you solved your problem! :D

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I bought my Hyperstar and Camera simultaneously and my (UK) retailer sensibly phoned Dean at Starizona to check if it needed a different adapter from tne Hyperstar in stock to achieve backfocus. It did. Four days later, I received the correct model shipped from the USA.

Pairing camera with the correct adapter appears crucial. A phone call to Starizina should assist you.

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On 05/03/2020 at 03:05, noah4x4 said:

I bought my Hyperstar and Camera simultaneously and my (UK) retailer sensibly phoned Dean at Starizona to check if it needed a different adapter from tne Hyperstar in stock to achieve backfocus. It did. Four days later, I received the correct model shipped from the USA.

Pairing camera with the correct adapter appears crucial. A phone call to Starizina should assist you.

Thanks a lot! I recently contacted Starizona and they´ve started trying some things before trying another adapter. I personally think this will a new adapter is the adecuate solution.

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  • 1 month later...
On 07/03/2020 at 17:25, guillespiers said:

Thanks a lot! I recently contacted Starizona and they´ve started trying some things before trying another adapter. I personally think this will a new adapter is the adecuate solution.

Kinda late to the party, hopefully you already managed to get it working.

I actually didn't had the chance to try that, but eventually opt(which I bought the hyperstar from) did send me the correct adapter.

That should be exactly the right backfocus now so I'm really hopeful.

Since it's f/2, incorrect backfocus really makes a difference here.

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