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kevin M13
member
Reged: 03/07/09
Posts: 93
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Need help understanding some details in planetary imaging. I believe I am seeing limited in my neck of the woods at 43 deg N. I am currently using a 140mm refractor and Phillips 900. Folks have already suggested going up in aperture and continuing on with the phillips.
I just had a not so good experience with a 9.25 that had pretty severe focus shift maybe some mirror slop and soft visual images. So I returned it primarily due to the 3 jupiter focus shift with a double bounce on both sides of focus as I didn't buget for an add-on focuser.
I can try again with another 9.25 or perhaps 10' f6 newt or I can get a c8 AND a IS camera. Would the 8" actually outperform the 140mm refractor in the imaging area? It certainly doesn't in the visual arena. The 140 blows away any scope I've ever had for planetary obeservation, but I do understand that imaging is different.
So, 9.25 with my existing web cam or C8+new IS cam. My budget is about 800-900. The trouble with the 10' f6, is that I can't seem to find any. I have plenty of mount for a 10" although EP height would be high with my 50" pier.
Kevin
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Mike Phillips
Pooh-Bah
Reged: 02/21/06
Posts: 1461
Loc: Swift Creek, NC - 35.682 N, 78...
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Yikes. I can't really offer any solid advise with experience. More aperture is better... dunno...
I had to prime the responses up a bit too!
Mike
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Gallery/Blog/RSS/Tutorials
Mike's Lesson on Seeing, Collimation and Focusing
**NEW** VIDEO HowTo: Planetary Processing Routine v8 **NEW**
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KyleEdwards
member
Reged: 09/04/07
Posts: 61
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Quote:
Would the 8" actually outperform the 140mm refractor in the imaging area? It certainly doesn't in the visual arena. The 140 blows away any scope I've ever had for planetary obeservation, but I do understand that imaging is different.
An apeture of 140mm gives a resolving limit of around 0.83 arcseconds, an apeture of 8 inches gives a resolving limit of 0.57 arcseconds. That makes a difference in planetary imaging, especially with small targets like Mars or Uranus.
Also the higher apeture will give you more light gathering power, resulting in faster exposures. In planetary imaging, faster exposures can help you catch the fleeting moments when the atmosphere is most stable.
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Kyle Edwards
Solar System Imaging Simulator
My Astrophotography Gallery
Edited by KyleEdwards (10/24/09 11:29 PM)
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whduke
professor emeritus
Reged: 04/22/08
Posts: 645
Loc: Clayton NC
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If you have a 9.25 Celestron stick with that, its a really good scope. Only once you figure out the details of how it operates. Trust me I know!! I have owned refractors, and MAKs, but the Celestron 9.25 is a harder scope to operate. If you want great images you must learn how to collimate, cool the scope, and learn about seeing. The mirror shift problem, I dont know, and I have never had that problem with my scope. I would make another post on mirror shift, so that everyone can help you. Their is a reason why most people use a SCT, and newtonians for planetary, so I would suggest sticking with it. If you are into planetary imaging it is not easy, and takes time to learn how to get great images. In the past year you can see how mine have improved every step of the way. If I were you I would get a DMK 21 cam, filter wheel, and filters (ask before you buy), and I would get another focuser to fix the mirror shift. Just be patient, learn the scope, and watch your images improve overtime!! Hope this helps
PS
With the soft images that probably would be collimation. If you are new to it I would be glad to help.
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CELESTRON 9.25
Mount EQ-CG5
DMK21AU04
Astronomik LRGB
Orion Filter Wheel
Neximage Camera
Powermate 2.5x
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whduke
professor emeritus
Reged: 04/22/08
Posts: 645
Loc: Clayton NC
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This is a very expensive hobby, you also need a good quality barlow. let us know if you have collimated on the airy disk of a star, what cooling method you use, and how you judge seeing. That would be a big help! 
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CELESTRON 9.25
Mount EQ-CG5
DMK21AU04
Astronomik LRGB
Orion Filter Wheel
Neximage Camera
Powermate 2.5x
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kevin M13
member
Reged: 03/07/09
Posts: 93
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Thanks all, and thanks Mitchell. Let me clarify a couple things. I no longer have the 9.25. I sent it back as it had issues in my opinion. I have owned several c11s, and a couple c8's. One of the C8's was by far the best sct I've ever owned or used. I wish I still had it. It was an orange c8 that was at least 1/5th PTV at the ep with buttery smooth focus, and minor image shift. I am very familiar with very high mag airy disc/first diffraction ring collimation. It was more the focus shift that bugged me about that particular 9.25. It also appeared to have some zones.
It have the web cam now. I can buy an 8+DMK or a 9.25 alone. Or if I am going to need a crayford, than I might be able to squeeze that in the budget as well with the C8. I may sell my refractor some day and get a nice Mewlon or MAK, but like to do a variety of things. As mentioned, the refractor is hands down near the best visual scope I've owned and kills on doubles and deep sky imaging. I'm expanding my interests into better planetary images, and some photometry so I want to pick another SCT up.
Kevin
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Frostpaw
member
Reged: 05/17/07
Posts: 39
Loc: Seattle, Washington, USA
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I currently have a C9.25. I'm pretty certain I'm seeing mirror shift in my Jupiter images. If I collimate on a star at 90 degrees altitude and then slew to Jupiter, I'm not only out of focus I am out of collimation as well.
I'm planning on getting a crayford focuser sometime soon to help address the mirror shift issue.
I dunno about getting a 10" newtonian as an alternative. That is a bulky scope compared to an SCT.
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kevin M13
member
Reged: 03/07/09
Posts: 93
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Thanks for the info. I had ruled out the newt. Just trying to choose between the c8/DMK combo, or getting a 9.25 and sticking with my Phillips.
I'm closing in on a couple options. I sure wish I had the old c8 I had with super smooth better than average optics with very small shift.
Oh well.
Kevin
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WayneJ
super member
Reged: 08/20/09
Posts: 107
Loc: West Chester, PA
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I don't have an opinion on which SCT to use, but do think that SCT's are the best overall solution for planetary imagers (unless you have the space and funds to build a large newt with premium optics)... but along with any SCT will be image shift due to mirror flop, hence the need for mirror locks. You can also use a rear-mount focuser... and that's highly recommended since the mirror-moving focusers of all SCT's are inadequate for planetary imaging.
Another thing is that most SCT's leave the factory with the right parts, but should be completely disassembled and properly reassembled with correct lubrication, screw torques, etc. I recently took a friend's C9.25 that he was about to send back for being "defective", removed the corrector and mirror cell, re-mounted the secondary, greased the baffle tube, and reassembled it. He thought it was a new scope. Also, once he learned to "set" the mirror by using the focus to push the mirror "up" and then use a rear-mount focuser for fine-focus, he was able to take full advantage of his gear.
Then of course, the weather in our area went to hell and he hasn't had a clear night in 2 weeks 
WJ
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<========>
Imaging Gear:
Meade 10" LX50 EMC
Celestron Neximage
Starlight Instruments Feathertouch Focuser
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kevin M13
member
Reged: 03/07/09
Posts: 93
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An update. Appreciate everyones help.
I have a C11 on the way! The seller whom i talked to on the phone, said it's the best SCT he's ever seen and his favorite scope among many premium scopes. If it's half the scope he claims, I should be a happy camper. I've owned a couple C11s in the past but one had some severe mirror flop issue, and the other was a bit soft.
The 9.25 I had recently for short period of time had some SEVERE focus shift.
Anyway, now I need to get a new powermate as the 4x I used with my refractor is a bit much.
Would you folks recommend a 3x or 2.5x with a C11 and SPC900?
I look forward to understanding how much my 5.5" aperture was limiting my images. I have been pretty impressed with what folks are doing in here with 9.25s and C11s.
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