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Problems with image.

Acquisition Deep Sky Troubleshooting Artifacts
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Jerry Gerber avatar
Jerry Gerber avatar
Here's a integrated image, after calibration, cosmetic correction, debayering and registration.   There's much wrong with this image.  The stars are not round and sharp.  I am also wondering what's causing the diagonal color shifts on all 4 corners of the image.   No processing has been done, other than BG neutralization, dynamic BG extraction and stretching.  I know there will be some vignetting with the .7 reducer and the camera I used, but this doesn't look like vignetting.  Are the four corners a result of the meridian flip?

Camera:  ASI2600MC
Telescope:  Edge HD 8" with .7 reducer

I also included two 240" subs directly from the camera.  In the first sub, the stars look OK.  But in the 2nd sub, taken consecutively after the 1st sub, the stars look elongated. 

Anyone know what's causing these numerous problems?  ASIAIR reported my polar alignment to be less than 1' from ideal..

Best,
Jerry

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Nick Grundy avatar
Nick Grundy avatar
Hi Jerry, I see this level of stacking issues when I combine different optics/cameras and dont set multi-band-blending in AstroPixel. On the sub difference, were you getting clouds? possible on your guide star? I was imagine last night out here and we had clouds roll in sporadically from 3am-5am that messed with some of my subs
Jerry Gerber avatar
Jerry Gerber avatar
Nick Grundy:
Hi Jerry, I see this level of stacking issues when I combine different optics/cameras and dont set multi-band-blending in AstroPixel. On the sub difference, were you getting clouds? possible on your guide star? I was imagine last night out here and we had clouds roll in sporadically from 3am-5am that messed with some of my subs

Hi Nick,

I don't know what would be the equivalent of multi-band blending in PixInsight.  I'll have to see if I can find out.  I don't think clouds came in at all that night.  Would clouds cause stars to elongate, or would the clouds mess up the guiding, which could cause the elongation?
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andrea tasselli avatar
andrea tasselli avatar
In short:

1. Poor focus
2. Poor flat
3. (Possibly) poor collimation

As for the issue with tracking that's the mount + OAG (if you have one).
Lynn K avatar
Lynn K avatar
" I am also wondering what's causing the diagonal color shifts on all 4 corners of the image."

During meridian flip, Camera came loose and rotated. Consequently two groups of images stacked with two different  compositions.

I agree with Andrea's conclusions. 

Lynn K
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Jerry Gerber avatar
Jerry Gerber avatar
Lynn K:
" I am also wondering what's causing the diagonal color shifts on all 4 corners of the image."

During meridian flip, Camera came loose and rotated. Consequently two groups of images stacked with two different  compositions.

I agree with Andrea's conclusions. 

Lynn K

imaging camera definitely did not come loose, but I did rotate the guide camera with the OAG.
Arun H avatar
Arun H avatar
It is very obvious that you have one set of images rotated with respect to the other. 

Blinking through the raw images in PixInsight should tell you when this occurred.

Other than that, I agree with what others have said. Systematically removing flex (loose connections, play, loose wires that can drag) in your system, getting your guiding to be good, good flats and calibration, collimation, etc. should result in improvements.
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Jerry Gerber avatar
Jerry Gerber avatar
Thanks all for your comments.   I am seriously thinking of selling the Edge and getting a 130-152mm refractor.  When I bought the Esprit 100 last fall, I immediately started getting high quality images.  The whole process from setup to post processing is very enjoyable for me.  

The Edge is a different story.  I honestly don't want to collimate or dealing with mirror shift– I want to spend my time imaging when I am outside, not tinkering with the optics.  I am like a guy who loves to drive a nice car but has no interest in getting under the hood and messing with stuff.   Computer processing is a totally different story–I find it very enjoyable and challenging and always eager to learn more.

The thing about refractors that I love is that the stars are sharp and pinpoint–assuming the optical quality and mechanical quality are up to par.  I can spend up to $5000 or $6000 for a refractor and am thinking of the Askar 130 PHQ or the Explore Scientific 127.  My AM5 mount can handle the Askar with a 11 lb counterweight but no more than that. 

Sorry for changing the subject but if anyone wants to suggest a refractor around 1000mm FL I am all ears!
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Brian Puhl avatar
Brian Puhl avatar
Jerry Gerber:
Thanks all for your comments.   I am seriously thinking of selling the Edge and getting a 130-152mm refractor.  When I bought the Esprit 100 last fall, I immediately started getting high quality images.  The whole process from setup to post processing is very enjoyable for me.  

The Edge is a different story.  I honestly don't want to collimate or dealing with mirror shift-- I want to spend my time imaging when I am outside, not tinkering with the optics.  I am like a guy who loves to drive a nice car but has no interest in getting under the hood and messing with stuff.   Computer processing is a totally different story--I find it very enjoyable and challenging and always eager to learn more.

The thing about refractors that I love is that the stars are sharp and pinpoint--assuming the optical quality and mechanical quality are up to par.  I can spend up to $5000 or $6000 for a refractor and am thinking of the Askar 130 PHQ or the Explore Scientific 127.  My AM5 mount can handle the Askar with a 11 lb counterweight but no more than that. 

Sorry for changing the subject but if anyone wants to suggest a refractor around 1000mm FL I am all ears!



Fracs are the way to go.   Theres so many people in this hobby that love their Celestron gear, but I'll never touch it....      I started out with a Newt, and now I have a 70mm widefield frac as well.   Right off the bat the frac was competing with my newt in terms of image quality (after drizzle).    I'm right there with you, a 120-130mm frac is in my future.     SVX, Espirit, and TS Photoline are the ones I've been eyeballing.
andrea tasselli avatar
andrea tasselli avatar
Refractors are pretty good as guidescope, nearly indispensable in fact. And that is about it.
Jerry Gerber avatar
Jerry Gerber avatar
andrea tasselli:
Refractors are pretty good as guidescope, nearly indispensable in fact. And that is about it.

Well, we each have our subjective opinions.  I've compared hundreds of images taken with SCTs  with images taken with refractors.  The refractor images nearly 100% of the time look better to my eye.  The stars are smaller, sharper and rounder.   The contrast is better.  And for me, I don't want to spend time collimating.

Unless you're getting into 16" planewave or larger scopes that require a permanent observatory, I'll go with the refractor!

So, to each his own.
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Arun H avatar
Arun H avatar
If you are just starting out, a refractor is a good way to go. They hold collimation very well, and are generally considered to be bullet proof. For the most part, you can use them in your backyard or put them on the back seat of your car and drive them to some dark sky site and they'll hold up very well. My personal experience has been with Stellarvue and Astro-Physics. You can forget about buying a new AP refractor, but a Stellarvue 130 mm refractor with field flattener will give you 910mm of focal length. There are other choices, but I'm not that familiar with quality and consistency. If you do go the Stellarvue  route, I'd recommend paying extra for the Feathertouch focuser. Having used these focusers on two of my scopes and comparing them to the Stellarvue focuser on my 80mm - the Feathertouch is super smooth and holds and moves loads without complaint. It will hold vertical weight for weeks or more without changing focus. Worth the premium over the Stellarvue focuser.

Andrea's complaint against a refractor probably comes down to not being value for money for aperture - I think it is hard to find a worse value for money per inch of aperture than a refractor, but that's made up for in other ways, simplicity of use being one of the most important.
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andrea tasselli avatar
andrea tasselli avatar
Arun H:
If you are just starting out, a refractor is a good way to go. They hold collimation very well, and are generally considered to be bullet proof. For the most part, you can use them in your backyard or put them on the back seat of your car and drive them to some dark sky site and they'll hold up very well. My personal experience has been with Stellarvue and Astro-Physics. You can forget about buying a new AP refractor, but a Stellarvue 130 mm refractor with field flattener will give you 910mm of focal length. There are other choices, but I'm not that familiar with quality and consistency. If you do go the Stellarvue  route, I'd recommend paying extra for the Feathertouch focuser. Having used these focusers on two of my scopes and comparing them to the Stellarvue focuser on my 80mm - the Feathertouch is super smooth and holds and moves loads without complaint. It will hold vertical weight for weeks or more without changing focus. Worth the premium over the Stellarvue focuser.

Andrea's complaint against a refractor probably comes down to not being value for money for aperture - I think it is hard to find a worse value for money per inch of aperture than a refractor, but that's made up for in other ways, simplicity of use being one of the most important.

While I agree in the main to the sentiments expressed above I'd warn that as the saying goes: "there are exceptions to the rules and rules to the exceptions". I had witnessed premium refractors out of collimation and no way to collimate them back other the returning them to the manufacturer.

And curiously enough my first serious imaging platform (other than photo lenses) was a long focus cassegrain,  a 6" mak at f/12 and 1.8m of FL. Unguided. I never felt the urge to get me a refractor as a main imager. And as for disparaging SCTs, well, I know better.

If ain't difficult ain't worth it
Jerry Gerber avatar
Jerry Gerber avatar
andrea tasselli:
Arun H:
If you are just starting out, a refractor is a good way to go. They hold collimation very well, and are generally considered to be bullet proof. For the most part, you can use them in your backyard or put them on the back seat of your car and drive them to some dark sky site and they'll hold up very well. My personal experience has been with Stellarvue and Astro-Physics. You can forget about buying a new AP refractor, but a Stellarvue 130 mm refractor with field flattener will give you 910mm of focal length. There are other choices, but I'm not that familiar with quality and consistency. If you do go the Stellarvue  route, I'd recommend paying extra for the Feathertouch focuser. Having used these focusers on two of my scopes and comparing them to the Stellarvue focuser on my 80mm - the Feathertouch is super smooth and holds and moves loads without complaint. It will hold vertical weight for weeks or more without changing focus. Worth the premium over the Stellarvue focuser.

Andrea's complaint against a refractor probably comes down to not being value for money for aperture - I think it is hard to find a worse value for money per inch of aperture than a refractor, but that's made up for in other ways, simplicity of use being one of the most important.

While I agree in the main to the sentiments expressed above I'd warn that as the saying goes: "there are exceptions to the rules and rules to the exceptions". I had witnessed premium refractors out of collimation and no way to collimate them back other the returning them to the manufacturer.

And curiously enough my first serious imaging platform (other than photo lenses) was a long focus cassegrain,  a 6" mak at f/12 and 1.8m of FL. Unguided. I never felt the urge to get me a refractor as a main imager. And as for disparaging SCTs, well, I know better.

If ain't difficult ain't worth it

Andrea, I really didn't disparage the SCT.  Just because it may not be right for my purposes and interests says nothing about whether it's best for someone else.  We all have different preferences and different amounts of time and energy to devote to this pursuit.
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