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#1 Greg K.

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Posted 10 May 2013 - 06:40 PM

M13
From 2013/5/5
Canon T2i (550D) ISO 800
Celestron 11" SCT @ f6.3
QHY5L-II guided
15x120s light frames
BackyardEOS, PHD, DSS, Photoshop, etc.

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#2 zjc26138

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Posted 10 May 2013 - 07:12 PM

Excellent shot Greg!

#3 ewave

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Posted 10 May 2013 - 07:29 PM

Greg
Very nice photo! BTW, for the QHY5L-II, what software did you use to guide it with and which mount did you use?
Clear skies.

#4 Greg K.

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Posted 10 May 2013 - 07:47 PM

Greg
Very nice photo! BTW, for the QHY5L-II, what software did you use to guide it with and which mount did you use?
Clear skies.


PHD 1.14.2, (on the prerelease page) supports the QHY5L-II natively. Mount was a CGEM guided via the ST4 port.

#5 David Pavlich

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Posted 10 May 2013 - 09:20 PM

You've been busy, Greg. Nice work!!

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#6 Tom and Beth

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Posted 10 May 2013 - 09:36 PM

Nice shot.

#7 srosenfraz

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Posted 10 May 2013 - 10:26 PM

Very sharp, Greg - nice job!

#8 Greg K.

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Posted 10 May 2013 - 11:37 PM

Ok, I realized I had some data on this from about a year ago, same scope, camera, ISO and exposure so I decided to combine it all together. Here with 38x120s light frames.

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#9 srosenfraz

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Posted 11 May 2013 - 12:35 AM

All the better, Greg - really nice!

#10 Phil Hosey

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Posted 11 May 2013 - 11:56 AM

Hey Greg,
You've been putting up some nice images with the C11 and f/6.3 reducer lately! What are you using to connect your recucer to your camera? I have a similar setup to yours except that my reducer is the Celestron version. I'm also using the Celestron T-adapter that is supposed to put the reducer at the optimal spacing but it doesn't seem to work well at all. I get severe vignetting and the stars get distorted very quickly as you move from the center.
Keep up the good work!

#11 Greg K.

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Posted 11 May 2013 - 02:07 PM

I have an SCT T-adapter #93633-A that doesn't work so well with the reducer, like you said I get significant vignetting with that.

Instead I use an Orion 2" T-adapter, the threads on 2" barrel part just happen to match SCT threads.... So I just stick the reducer between them, as close to the camera as it can get.

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#12 Erk1024

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Posted 11 May 2013 - 02:12 PM

That's a beautiful shot Greg, nice work. Tight stars and good processing. That's a keeper. ;)

#13 Phil Hosey

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Posted 11 May 2013 - 03:39 PM

I have an SCT T-adapter #93633-A that doesn't work so well with the reducer, like you said I get significant vignetting with that. I don't think that's designed with DSLRs in mind, frankly - the chip sits too far back.

Instead I use an Orion 2" T-adapter, the threads on 2" barrel part just happen to match SCT threads.... So I just stick the reducer between them, as close to the camera as it can get.



Greg,
That's interesting, I happen to have one of those prime focus adapters as well (mine is Antares but looks identical to yours). By my calculations, the FR to sensor distance with the configuration you have is 64.5mm (9.5mm for the Orion camera adapter because the SCT threads eat up part of the distance putting the front of the FR inside it, 11mm for the T-ring and 44mm from the front of the camera to the sensor. That distance would effectively put you at f/7.7. Would be interesting if you could plate-solve a full frame of one of your images taken that way so that we can verify what your true f/ratio is.

#14 Greg K.

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Posted 11 May 2013 - 03:54 PM

I have an SCT T-adapter #93633-A that doesn't work so well with the reducer, like you said I get significant vignetting with that. I don't think that's designed with DSLRs in mind, frankly - the chip sits too far back.

Instead I use an Orion 2" T-adapter, the threads on 2" barrel part just happen to match SCT threads.... So I just stick the reducer between them, as close to the camera as it can get.



Greg,
That's interesting, I happen to have one of those prime focus adapters as well (mine is Antares but looks identical to yours). By my calculations, the FR to sensor distance with the configuration you have is 64.5mm (9.5mm for the Orion camera adapter because the SCT threads eat up part of the distance putting the front of the FR inside it, 11mm for the T-ring and 44mm from the front of the camera to the sensor. That distance would effectively put you at f/7.7. Would be interesting if you could plate-solve a full frame of one of your images taken that way so that we can verify what your true f/ratio is.


That's a good point - According to Astrobin/astrometry.net, I'm getting .42 arcseconds per pixel with this arrangement, that works out to a focal length of 2080mm, so it's about f/7.4 in actuality.

It would be shorter if I could ditch the 2" adapter and screw the FR directly to the rear cell, but orienting the camera would be difficult that way. :)

#15 Greg K.

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Posted 11 May 2013 - 04:14 PM

Here's a flat frame from this setup. Vignetting is pretty minimal and easily corrected.

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#16 Phil Hosey

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Posted 11 May 2013 - 04:39 PM

It would be shorter if I could ditch the 2" adapter and screw the FR directly to the rear cell, but orienting the camera would be difficult that way. :)


Actually that would make almost no difference in the effect f/ratio because it's the distance between the FR and the sensor that matters. Screwing the FR directly to the back of the scope would still give you the same distance between the FR and the camera's sensor. If you wanted to decrease the f/ratio, you would want to increase the distance betweent the FR and camera sensor. I'm planning to try this by adding a Baader Vari-lock T2 extension between the T-adapter and T-ring. It's about 20mm so I should be able to get it around f/7. I am going to have to get a 2" visual back though so I can rotation the camera to whatever position I want.

#17 Phil Hosey

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Posted 11 May 2013 - 04:40 PM

Here's a flat frame from this setup. Vignetting is pretty minimal and easily corrected.


Yea, that looks much better. I don't mind increasing the f/ratio if it means less vignetting and better looking stars.

#18 Greg K.

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Posted 13 May 2013 - 01:16 PM


It would be shorter if I could ditch the 2" adapter and screw the FR directly to the rear cell, but orienting the camera would be difficult that way. :)


Actually that would make almost no difference in the effect f/ratio because it's the distance between the FR and the sensor that matters. Screwing the FR directly to the back of the scope would still give you the same distance between the FR and the camera's sensor. If you wanted to decrease the f/ratio, you would want to increase the distance betweent the FR and camera sensor. I'm planning to try this by adding a Baader Vari-lock T2 extension between the T-adapter and T-ring. It's about 20mm so I should be able to get it around f/7. I am going to have to get a 2" visual back though so I can rotation the camera to whatever position I want.


The difference should be that with a shorter imaging train length, the scope's overall focal length is shortened to achieve focus, a quirk of moving mirror SCT design. The reducer would have the same reduction factor, but on a slightly shorter overall focal length. It would be interesting to play with anyway, maybe I need to spring for an AP 2" visual back. At least I could seat the 2" barrel shown above all the way in.

#19 Rutilus

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Posted 13 May 2013 - 01:49 PM

Superb shot of M13.

#20 Phil Hosey

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Posted 13 May 2013 - 07:27 PM


It would be shorter if I could ditch the 2" adapter and screw the FR directly to the rear cell, but orienting the camera would be difficult that way. :)


Actually that would make almost no difference in the effect f/ratio because it's the distance between the FR and the sensor that matters. Screwing the FR directly to the back of the scope would still give you the same distance between the FR and the camera's sensor. If you wanted to decrease the f/ratio, you would want to increase the distance betweent the FR and camera sensor. I'm planning to try this by adding a Baader Vari-lock T2 extension between the T-adapter and T-ring. It's about 20mm so I should be able to get it around f/7. I am going to have to get a 2" visual back though so I can rotation the camera to whatever position I want.


The difference should be that with a shorter imaging train length, the scope's overall focal length is shortened to achieve focus, a quirk of moving mirror SCT design. The reducer would have the same reduction factor, but on a slightly shorter overall focal length. It would be interesting to play with anyway, maybe I need to spring for an AP 2" visual back. At least I could seat the 2" barrel shown above all the way in.


Of course, you are correct, I forgot about the change in the overall focal length due to the moving mirror.

#21 nofxrx

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Posted 13 May 2013 - 07:35 PM

Excellent image, Greg!!
I am curious how much of this is cropped?
I am asking because the C11 is on my short list(that or the EDGE 925, but leaning towards the "good ol' C11"! :grin: ) and will be imaging with the same camera/sensor size..

Congrats on the image, this really is a beautiful M13!
Cheers!

#22 Greg K.

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Posted 13 May 2013 - 07:53 PM

Brent, full size is 4373px × 3209px so it's cropped to about 84% horizontally and 92% vertical of a T2i frame.

#23 JoeR

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Posted 14 May 2013 - 10:54 AM

Well done your globulars are looking nice. Good processing which is quite hard to do with these balls of stars.






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