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Anyone doign DSO AP with their SCT?

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#1 shiner

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Posted 26 December 2012 - 12:19 PM

I use my CPC 1100 for observing and my ED80 refractor for imaging.
I am looking for a more "powerful" imaging scope to complement the ED80 so I can get better image scale on stuff liek individual galaxies, globulars etc.

I hear some say the F10 ratio of the SCT is a no-go for AP. Anyone here think otherwise?

How do you guide etc?

I am very tempted to get a C9.25 OTA.....

Thanks for your thoughts and ideas.

#2 David Pavlich

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Posted 26 December 2012 - 01:32 PM

Take a look in the DSLR and CCD imaging section. There's a few that venture into the f10 vicinity. It's a bit challenging, but it can be challenging and is done successfully.

David

#3 Kevdog

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Posted 26 December 2012 - 01:45 PM

Throw the focal reducer on there and it's f6.3 at about 2300mm IIRC. You don't say if you have a wedge or not, but you'd need the wedge too.

#4 shiner

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Posted 26 December 2012 - 03:55 PM

Thanks for the thoughts. I would not be using my CPC, I'd be buying another C9.25 OTA to go onto my NEQ6 mount.

My CPC1100 is for keeps as my visual rig.

#5 Footbag

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Posted 26 December 2012 - 04:58 PM

I currently image with my Edge HD 800 but started imaging with a CPC-800 wedge mounted. All of the images in my signature were taken with these two setups in addition to my WO66 refactor.

I don't think it is bad advice to suggest a small refractor and a good quality GEM for anyone approaching AP as a hobby. The lighter, smaller and faster scope will provide very good images to a beginner within a few outings. Finding a mount that can carry an SCT for imaging requires some "reading into" of manufacturers weight ratings. Many newcomers don't understand that and that is why the importance of a quality mount cannot be understated.

As well, imaging at f10 will require longer exposures than many newcomers can adequately achieve. Before I got a guiding setup, I maxed out at 30-45s exposures. At the time I was happy with my images, but looking back they were terrible. It took me 2 years before I fully understood drift alignment and got what I'd call respectable images. But looking back, some of my beginning images taken with the WO66 and guiding through the SCT were also respectable.

It is for that reason, I always suggest a small refractor and discourage SCTs for beginning imaging. Now, all of that said, I believe SCT's are excellent imaging scopes. If you understand all of the variables, they have a strong place in a imagers lineup.

So.. if you are decided on an SCT, I'd consider the Edge series. You will have perfect stars to the edge, unlike the C9.25. They also have mirror locks which overcomes one of the SCT biggest problems, mirror flop. If you can't spend the money, go with the 8" Edge. From a practical standpoint, the slight difference in resolution would be negligible and most often beyond seeing. As well, according to rumor the 8" Edge focal reducer is coming out in January and the 9.25 is some time off. I struggled between the 8, 9.25 and 11 but am happy with my choice.

#6 rmollise

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Posted 26 December 2012 - 06:29 PM

F/10 = punishingly long exposures and guiding is very critical. Very few objects outside small planetary nebulae really need f/10.

#7 wolfman_4_ever

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Posted 26 December 2012 - 06:32 PM

As Rod said, longer exposures and guiding is very critical.. I push my SCT to even higher f ratios when imaging globulars in Andromeda..

#8 jaddbd

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Posted 26 December 2012 - 06:55 PM

+1 on everything said so far...

It is all about the mount (the mount, the mount) and the seeing at 2800mm. On my rig that gets me 0.51 arcsec/pix. Its more managable with a reducer, but not still no cakewalk. Rod just made the point I was going to make - For planetary's it is a weapon of choice when the conditions dictate. I've spent enough hair pulling sessions to know not go there unless the seeing is exceptional, and then only with a self-guiding camera (and then you need luck getting a guide star at F10). The other downside that I have with a C11 (metal tube) is it's ability (or lack there of) to hold focus when the the ambient temp is droping at any kind of rate (refocus needed every 2F-3F degrees of change).

John D

#9 John Miele

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Posted 26 December 2012 - 07:04 PM

Hi,

f/10 is not where you want to start with imaging but if you are like me, after a while, f/10 and longer focal lengths are where you will want to end up. The widefield stuff is fun at first and then it becomes...well...boring :tonofbricks:. How many widefield M42s can one stand! It's the closeups of galaxies, planetaries, and globs that are seldom seen that are most fun (to me). Of course, YMMV!...John

#10 David Pavlich

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Posted 26 December 2012 - 10:17 PM

Keep in mind that Meade is going to be shipping their f8 version of their ACFs soon. And they have a purpose built f5 reducer for it.

David

#11 Patrick

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Posted 27 December 2012 - 12:51 AM

Thanks for the thoughts. I would not be using my CPC, I'd be buying another C9.25 OTA to go onto my NEQ6 mount.

My CPC1100 is for keeps as my visual rig.




We have very similar thoughts here. My CPC1100 is my 'grab and go' visual scope for star parties and outreach. It's a scope I plan to keep for a while, too.

I'm currently piecing together an imaging setup using an 8" EdgeHD as my primary scope with an AT66ED refractor as the guide scope/wide field imaging scope. I choose 8" because it will ride a little better on the CGEM mount and because the focal length will not be so difficult to guide. An 8" with an Optec f/6.2 focal reducer will have a focal length of about 1240mm. That's a fairly nice place to be.

With a focal length less than 1500mm, guiding with a guide scope is more practical. At very long focal lengths, guiding with an off-axis guider becomes more important. I have not been successful in using an OAG, so I'm staying away from focal lengths greater than 1500mm.

Patrick

#12 freestar8n

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Posted 27 December 2012 - 06:31 AM

The widefield stuff is fun at first and then it becomes...well...boring . How many widefield M42s can one stand! It's the closeups of galaxies, planetaries, and globs that are seldom seen that are most fun (to me). Of course, YMMV!...John



That is more my feeling also. With shorter focal length you can "take a picture" of something, but with longer focal length you can "reveal detail within" something. I would recommend a small refractor and guidescope for someone getting started, but for people who want to take it further, high res. work has its own rewards. I don't think it requires a high end mount, and instead results tend to be limited by technique, software, and low expectations. Results with my relatively humble setup (c11 on cge or cge-pro) are on the metaguide site. I do recommend OAG at long focal length, but the recent FlexRX result may change that.

There is also a downside to wide field work, which is that gradients can be a nuisance, which puts processing demands on a new imager. It's less of an issue with a narrow field.

I think f/10 and long focal length are less of a win for faint objects that don't have much detail - such as the cocoon nebula. But for objects with detail such as galaxies and complex Ha regions, high res has benefit. Instead of wide field images of nebulosity in our own galaxy, you can aim for detail in the Ha regions of other galaxies.

Just measure your fwhm's in arc-seconds, and methodically work on your setup and technique to determine what is limiting it and how it can be reduced. Experiment, and don't just follow anecdotal advice.

Frank

#13 jaddbd

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Posted 27 December 2012 - 11:45 AM

I am with you guys on preferring a longish focal length. I spend most of my time at f8 2000mm. With better skies I would go bigger and longer.

JD

#14 akulapanam

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Posted 27 December 2012 - 12:19 PM

The F.63 Celestron focal reducer will put you under 1500mm for any scope except for the C11. This will also put you at almost the same speed as a ED80 F7.5 with a .8 reducer.

As mentioned above there are some targets like planetary nebula that really do need F10 or C11 like field length to pull details out of.

Personally I think you need both a short focal length refractor for the wide field shots and a long focal length scope so you can get the details. That's why I'm going to mount a AT72 or 65 on top of my CPC.

One other thing you might consider is getting either a Orion or Astro-Tech imagine Newtonian or a Astro-Tech Ritchey Chretien on a CGEM. These are the other scopes I considered before buying the CPC and wedge. I did consider the Edge but the lack of a focal reducer option kept me a way. Depending on your budget and timeline you might also want to consider a Meade once we get some more clarity on their financial situation, although in general I think you overpay for the same scope with them.

Besides looking at others photos I think Carte De Ciel is great for seeing what you can image and at what resolution with a given setup.

http://www.astronomy...-your-dslr-c...

#15 astrovienna

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Posted 27 December 2012 - 02:43 PM

Okay, I'll be the contrarian. ;) I'm not sure you need to buy a new scope to hit the small FOV targets you're looking at. A good wedge for your CPC1100 is a lot cheaper.

I image with a CPC1100 on a Milburn wedge at f6, using an SXVR-H694. I guide with a Flea3 on an OAG (Taurus Tracker III). Take a look at the galaxies and planetary nebulae on my website (linked below), and you'll get an idea what you can achieve with this setup. And my recent images (which I'll post as soon as I can dig out from under a mountain of Jupiter data) are better than those. I finally got an absolute focuser in early summer, and I'm now much more aware of precise focus. In good seeing, I now routinely get stars with an HFR of 1.5 arcsecs in 5-10 minute exposures. (And Frank may scold me for being satisfied with only that! :) )

If you've already learned the ropes with your ED80, I think you can make the leap to long FL imaging without too much trouble.

Kevin

#16 jgraham

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Posted 27 December 2012 - 05:48 PM

I primarily use two Cats for imaging... a 6" f/5 SN for wide field and an 8" f/10 SCT for narrow field. Actually, with the APS-C size chip in my DSLR the field of view of the SCT is very nice. Autoguiding is a must for long exposures and my SCT is fitted with an off-axis guider. I really like the nice contrasty images of the SCT at f/10.

#17 Cepheus Elf

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Posted 27 December 2012 - 06:46 PM

I have used a c9.25 on an eq6 mount for imaging planetaries and double stars. I kept getting slightly elongated star images - even with very short exposures which puzzled me for some time. I finally pinned the problem down to vibration from the eq6 motors - Not a problem with my short focal length scopes, but very apparent at image scale of the C9.25. It may be just my mount, but it's just something to be aware of...!

All the best,
Mick

#18 rflinn68

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Posted 28 December 2012 - 09:33 AM

Just now getting into it with my cats. I bought the Celestron f/6.3 reducer/corrector and have done some testing with my C8 with good results. I now have imaging scopes with focal lengths of 420mm (AT65EDQ), 800mm (AT8IN), 1260mm (C8 @ f/6.3), and 1575mm (M10 @ f/6.3). I'm not near good enough yet to try the cats at f/10

#19 RogerRZ

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Posted 30 December 2012 - 07:50 PM

I shot this last week with a C8 reduced to f/6.3. 20X5 minute subs, shot through an Ha filter. I don't think we ever get the seeing here to shoot at 2000mm focal length...

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#20 Ron7915

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Posted 17 October 2013 - 03:04 PM

I image with f10 Here are a couple of my images. These were binned 1x1
http://www.flickr.co...08/10213703383/
http://www.flickr.co...08/10074729456/

#21 PGW Steve

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Posted 17 October 2013 - 03:25 PM

14" LX200R with STT8300M, three 30 minute exposures through a 3nm Ha filter.

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#22 Bruce FitzGerald

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Posted 17 October 2013 - 09:08 PM

AP at F11 just isn't that hard if you are methodical, keep a log and know your equipment.

M42 at F6.3 October 16,2013. C-14 CGE Pro, SBIG ST4200XCM color camera. 30 2 minute exposures stacked and corrected with one flat frame and 30 dark frames.

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#23 rigel123

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Posted 18 October 2013 - 11:59 AM

I picked up a gently used C9.25 to use for planet imaging and had no plans to try it on DSO's. Then one night I tried it for fun on some very small but bright planetaries and was pleasantly surprised. Not sure I'll ever try it for really long exposures with it with my setup but you never know.

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