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spotlight cone stars?

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#1 Mark Bailey

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Posted 14 June 2021 - 10:59 PM

I mounted a fully modified Canon Rebel on a Losmandy G-11 on a cement pier with a Canon 24-105 L lens at 105mm. I used PHD2 to guide.

 

I forgot to add the clip-in infrared filter.

 

Attached is one of the uncalibrated subs, 300s at 800 ISO. I am wondering about the spotlight, cone shaped stars in the corners.

 

In spite of my efforts, is the mount out of polar alignment? Is it the nature of the lens? Operator up in the night?

 

Mark

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#2 galacticinsomnia

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Posted 14 June 2021 - 11:22 PM

I mounted a fully modified Canon Rebel on a Losmandy G-11 on a cement pier with a Canon 24-105 L lens at 105mm. I used PHD2 to guide.

 

I forgot to add the clip-in infrared filter.

 

Attached is one of the uncalibrated subs, 300s at 800 ISO. I am wondering about the spotlight, cone shaped stars in the corners.

 

In spite of my efforts, is the mount out of polar alignment? Is it the nature of the lens? Operator up in the night?

 

Mark

Looks good to me, may want to adjust your exposure a bit, but looks  good from here, but I don't have the source...of course...

 

Keep shooting and rockin.  Ran it through Astrometry.net and can see you are right in there with some glowing multicolored nebulosity.
Enjoy !

Clear Skies !!


 


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#3 galacticinsomnia

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Posted 14 June 2021 - 11:29 PM

I mounted a fully modified Canon Rebel on a Losmandy G-11 on a cement pier with a Canon 24-105 L lens at 105mm. I used PHD2 to guide.

 

I forgot to add the clip-in infrared filter.

 

Attached is one of the uncalibrated subs, 300s at 800 ISO. I am wondering about the spotlight, cone shaped stars in the corners.

 

In spite of my efforts, is the mount out of polar alignment? Is it the nature of the lens? Operator up in the night?

 

Mark

 
Seems the glowing is appropriate for the target..
2021-06-14_212525.jpg


Clear Skies..


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#4 Mark Bailey

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Posted 15 June 2021 - 12:41 AM

Thanks for the help. Yes, I was hoping to capture the glows of the region. My concern is the weird shape of stars in the corners. It is hard to see in this low res image perhaps . . .



#5 DubbelDerp

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Posted 15 June 2021 - 07:58 AM

It looks to me like a lens aberration, especially since it's a zoom lens. The added IR I'm sure didn't help, but I wouldn't think it would account for all of the corner deformations. Did you stop down the aperture at all? If not, that might help a bit.



#6 michael8554

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Posted 15 June 2021 - 08:05 AM

The elongated stars in the corners are due to Coma.

 

Not something you would notice on daytime snaps with that lens, so the makers don't much bother with correcting it.

 

"fully modified Canon Rebel" - what does that mean ?

 

Has it had both filters removed - a Full Spectrum mod ? Then a separate IR filter is required.

 

Or just one filter removed to enhance Ha ? That means the IR filter hasn't been removed, so you don't need a separate IR filter.



#7 Mark Bailey

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Posted 15 June 2021 - 08:16 AM

Thanks guys.

 

I am surprised and disappointed to get that much aberration/coma in an L lens. But that certainly explains it.

 

I did shoot with the aperture wide open.

 

Yes, I should have said my Rebel has a full spectrum modification. I am getting rusty. And yes, I needed to put in the UV/IR filter. Rusty, like I said.

 

Next time I'll stop down a bit, use the filter, and crop.

 

Thanks again.

 

Onward.


Edited by Mark Bailey, 15 June 2021 - 08:31 AM.



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