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Issues with my current setup?, C8HD @ ZWO ASI533

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#1 star_quake

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Posted 21 June 2021 - 01:27 PM

I'm looking for advice and comment on my current setup. 

This is my first season in this hobby.  I started out with a WO71 and was doing great and have progressed to the C8HD as galaxy season began.

 

I have a C8HD I'm running at F10 native with the Starizona backspace adapter and an ASI533 attached. 

I have had the guys at Starizona center the corrector plate and collimate with an eyepiece using their artificial star.

 

I use this for astrophotography pretty much exclusively, so I had to adjust the collimation because it was off when I attached my camara.

 

I'm concerned that I can't get a perfectly clean looking middle spike, they look tilted or something and I'm worried that no matter what I do the pictures will not be their best.

 

These are the bahtinov spikes I get when it looks to be perfectly focused, both manually and with the ZWO autofocuser. 

 

 

bahtinov_curves.jpg

 

 

This is the out of focus collimation rings, which is the best I could do.

 

after.png

 

 

Is this still out of collimation?  Is this normal for C8HD?  Am I being overly picky?

 

 

Here is an example of my best astrophoto so far...

 

M51_8x10_web.jpg

 

 

You can't really see it at this resolution, but the brighter stars have an odd shape to them due to them having what I would call a "pepsi" artifact?  Red on one side and blue on the other.  It varies in its degree of offensiveness based on the target.

 

I'm wondering if it is related to the collimation.  Or is this just inherent in the scope? 

 

As for the setup, its a SW 6r pro mount with the ADM deck plate and I'm using my WO71 with an ASI290 mini for the guiding.

The guide scope is piggy backed on top with a ADM mount connecting it to the C8HD. 

I'm using the PPEC on the mount.  I always run unfiltered as I am in a Bortle 4 zone. (West side of the Tucson mts)

 

I'm getting consistent guiding @ 0.4"-0.6", so I feel like that's as good as it gets for guiding even though I realize I am way oversampled at 0.38"/pix.

 

Maybe I'm asking more (or expecting more) from this setup than it's able to provide?  

 

 

 

Here is a zoomed in picture of the bright star to the right of M51

 

 

Star_crop.jpg

 

 

 

 

 


Edited by star_quake, 21 June 2021 - 02:11 PM.


#2 Tapio

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Posted 21 June 2021 - 02:03 PM

Could you provide us zoomed image of the star shapes you mentionen ?

How low/high was this when you imaged (targets lower could exhibit atmospheric aberrations).

 

Anyway that looks like an excellent M51 image.



#3 star_quake

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Posted 21 June 2021 - 02:12 PM

Could you provide us zoomed image of the star shapes you mentionen ?

How low/high was this when you imaged (targets lower could exhibit atmospheric aberrations).

 

Anyway that looks like an excellent M51 image.

 

All of my imaging is near zenith, within 30 degrees (2 hours of RA) on either side.

 

I've added a zoomed in picture of an example star in the original post.


Edited by star_quake, 21 June 2021 - 02:33 PM.


#4 alphatripleplus

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Posted 21 June 2021 - 02:55 PM

 

 

You can't really see it at this resolution, but the brighter stars have an odd shape to them due to them having what I would call a "pepsi" artifact?  Red on one side and blue on the other.  It varies in its degree of offensiveness based on the target.

 

I'm wondering if it is related to the collimation.  Or is this just inherent in the scope? 

 

 

Is the odd shape for the brighter stars consistent  across the FOV, or worse towards the edges, or one side?



#5 star_quake

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Posted 21 June 2021 - 03:48 PM

Is the odd shape for the brighter stars consistent  across the FOV, or worse towards the edges, or one side?

Good question.

 

The shapes look to be consistent from edge to edge.  

 

I assume you are asking with a question to the backspacing?

 

The sensor is so small relative to the image circle, I'm thinking it would be obvious if there was a backspacing problem?



#6 calypsob

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Posted 22 June 2021 - 10:20 AM

How oversampled are you? This may be atmospheric refraction

#7 unimatrix0

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Posted 22 June 2021 - 10:31 AM

 

I'm using the PPEC on the mount.  I always run unfiltered as I am in a Bortle 4 zone. (West side of the Tucson mts)

 

Absolutely no filter?  Have you tried UV IR cut filter? The 533 doesn't have a IR cut built in like some other cameras, I found it to be essential even broadband targets. Stars can look weird without one or with a very cheap one that did more harm than good. 


Edited by unimatrix0, 22 June 2021 - 10:33 AM.


#8 KTAZ

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Posted 22 June 2021 - 10:51 AM

I would definitely recommend a UV/IR cut. Baader makes a high quality one for a reasonable price. The shapes of your stars could be impacted by "bloom".

 

Collimation cannot be accurately judged with a donut of that size; it is too far from focus. The farther you defocus, the less sensitive that test becomes.

 

I am also currently walking down the EdgeHD path with a new 800. I am in the process of sending it back to Celestron because of difficulty in collimating it to retain a centered poisson spot. It is far too difficult for a scope fresh out of the box, and I am perfectly comfortable with the collimation process.

 

I have read several accounts pointing to difficulty in traditional collimation since the EdgeHD has additional lenses in the baffle that may be more sensitive to the positioning of the corrector/secondary. If I get Celestron to actually tell me anything about the positioning of my corrector/secondary (which was pretty far shifted from actual center) I will post it back to the community.



#9 star_quake

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Posted 22 June 2021 - 07:05 PM

Thanks for the ideas.

 

I've run the 533 on the WO71 for a couple of months with no filters and didn't have this issue, but I did buy an Astronomics UV/IR filter, so I'll give that a try next time.

 

As far as the collimation is concerned, it definitely wasn't a simple process for me.  My corrector and secondary was way off center from the factory and the guys at Starizona fixed it.  Like I said, it seemed perfect for visual at that point but since I use it for imaging I had to adjust it slightly.

 

It was difficult to see the diffraction rings as you get close to focus and there seemed to be no way for me to see a Poisson spot using a camara.  I used a very bright star and had it set on a 1 second loop to do the collimation.

 

All of the collimation instructions I have found do it with an eyepiece, but as soon as you attach a camara it's off.




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