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Time for a bigger optical tube? Need suggestions

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#1 Ron (Lubbock)

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Posted 15 May 2013 - 06:06 PM

Lately, I have been wanting to get a larger aperture scope for imaging in order to get better resolution and shorten the amount of exposure time needed to finish a photo project.

I predominantly do imaging at a dark sky site that requires some travel. Rapid set-up and alignment are vital, obviously. All imaging is presently done with my C8 optical tube (1996 vintage, with Starbright coatings) and f/6.3 focal reducer on a CGEM mount. My favorite targets are galaxies and planetary nebulae, so I am usually imaging at long focal length (1280 mm or sometimes 2032 mm). However, I would not want to go any longer than 2032 mm if possible. I'm already binning 2x2 at 1280 mm and want to keep the same camera.

There are two competing scenarios for upgrading the equipment, and I'm hoping to get some suggestions and insights here.

The first option is to get a 10" or 11" optical tube and put it on my CGEM. I like the CGEM mount; it is very portable, and the firmware allows me to set up and polar align rapidly. With this scenario, I am limited to optical tubes that can keep me under the recommended 45 lb. equipment limit of the CGEM. That means I can only go to a 10" or 11" scope, unless someone here knows of a mythical featherweight 12" OTA. LOL.

There are a few scopes that fit Option 1: the Meade 10" LX200 f/8 ACF, a C11, or a 10" f/8 Ritchey-Chretien. While a lot of people like the RC design for AP, it may not be a good choice for me. We have a lot of airborne dust here, and I have to clean my corrector plate on the C8 after every 2nd or 3rd imaging session. I think an open-tube RC would fill with dirt so fast that I'd be able to grow tomatoes in it after a month. You're welcome to try to convince me otherwise on the RCs, though. The C11 is not optimal due to its focal length (~2800 mm).

Thus, I think the Meade f/8 10" ACF is the winner for Option 1. The lingering concerns are 1) the 10" scope may not be enough of an upgrade to warrant mounting a 33 lb. OTA vs. the 13 lb. OTA I currently use, and 2) mirror flop, which may not be a serious issue because I guide on-axis at full focal length. Does anyone here image with the 10" ACF, and if so, can you tell me how much of an upgrade it is over a C8? Worth the extra weight and expense?

Option two is to spend a whole lot more money for a much sturdier mount and a significantly larger OTA (12-14"). The problem here is that a lot of my sessions are one-man setups. However, I will entertain any ideas out there for a semi-portable setup that gets me up to 12" or 14" aperture. I'm willing to push the limits a bit.

Please leave any suggestions, or comments on my thought process here. Appreciate it!

#2 timps

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Posted 15 May 2013 - 11:22 PM

Have you thought of a fast refractor? I am not an AP expert but was under the impression that for photography the speed of the scope was more important than the aperture.

#3 Ron (Lubbock)

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Posted 15 May 2013 - 11:56 PM

Fast refractors are out. Though they can provide nice wide-field views, they don't do much for the small objects I like to photograph. I'm looking for more aperture. ;)



#4 timps

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Posted 16 May 2013 - 04:40 AM

I wouldn't think going from 8" to 10" is much of an upgrade, especially for AP. What about a C14 edge HD on a CGEM-DX mount? Or you could go the Meade 12" ACF with their EQ mount.
Both would be great for visual too.

#5 orlyandico

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Posted 16 May 2013 - 09:18 AM

wouldn't even an 8" EDGE give enough focal length? (un-reduced)? or the AT8RC? or a C9.25 + the Starizona reducer?

What's your keeper rate with the CGEM? I have a CGEM and I wouldn't wish to image with it at 2000+ mm at all. A guy on the CelestronCGEM mailing list does so successfully but he has an AO unit.

#6 Ron (Lubbock)

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Posted 16 May 2013 - 09:59 AM

I mostly use the f/6.3 focal reducer @ 1280 mm. The keeper rate is pretty high-above 90%. Last time I was out, I kept 21 consecutive 5 min. subs before dew ruined my session. I don't do enough at 2000 mm focal length to give a good estimate of the keeper rate there, but it is possible with the CGEM. Here's a recent pic of a small planetary, NGC 4361, taken at 1280 mm with the CGEM. This target is only 80 arcseconds wide, so the mount is performing at a pretty high level. I doubt that I could get sharper stars with the optics I have, as the FWHM of stars in the 5 min. subs is about the same as in 10 second subs.

Posted Image


The Edge HD scopes have a focal length issue for me. They're f/10 or f/11 and have focal lengths well in excess of 2000 mm. The C14 HD is at f/11 and 3910 mm. I cannot imagine a portable setup that would allow autoguiding at that focal length. I don't see any way to get it down to 2000 mm or lower other than Hyperstar, which is too low.

#7 EFT

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Posted 16 May 2013 - 10:25 AM

A 10" or 11" is really going to be pushing it on the CGEM, but if that was the choice that you were making I would have to go with the large aperture and the proven performance of a C11HD. Add the focal reducer if necessary. Your mount will need to be working very well and your technique will need to be very good to achieve good results with this combination. If you are not up to a challenge, then I would not go large than the C9.25HD.

#8 Ron (Lubbock)

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Posted 16 May 2013 - 10:46 AM

Thanks, Ed. I was worried that even a 10" might be too much for the CGEM, but hearing it from someone who makes a business out of hypertuning mounts really makes me think twice.

Some of the comments in this thread have me thinking that Option 2 is the better one.

#9 EFT

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Posted 16 May 2013 - 11:23 AM

The CGEM DX presumably holds the C14, but I would consider that visual only. It's good for the C11. The C14 is difficult to go portable with. Most of the mounts that really handle it well are both expensive and very difficult to travel with, especially alone. I guess that my ultimate advise for a portable setup would be the C11 and CGEM DX for an "inexpensive" mount or one of the higher end mounts with the C11. I'm not sure if you have ever put a C14 up on a mount before, but it is not a chore that I enjoy at all.

#10 Ron (Lubbock)

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Posted 16 May 2013 - 01:51 PM

I agree that the C14 exceeds most peoples' definition of portable. I guess the next question would be whether a Meade 12" ACF, a regular C11 or a C11 Edge HD would be the better choice. I'm not thrilled with the need to buy a huge focal reducer for the C11 HD, so part of me would want to go with the regular C11 at a much lower price point and a weight of only 27.5 pounds. I do have to wonder why I see so many used C11s for sale in classifieds, though. Mirror flop? Field curvature?

The Meade ACF 12" is really tempting due to its f/8 focal ratio and extra inch of aperture. However, at 56 lbs., it will be a bear to load up, weighing even more than a C14.

If I end up getting a much bigger scope, I would probably opt for a Paramount MX. I do not want to mess around with the mount if I'm going to make a major financial project out of this. Any thoughts on this mount?

#11 woodworkt

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Posted 16 May 2013 - 02:08 PM

A heftier mount will definitely run the cost up, but it needn't mean less portability or a more difficult one-man setup. An AP900 mount head, for example, breaks down into two parts, one about 18 lb, and one about 24 lb... neither of which weighs as much as, say, a Losmandy G11. If you look around, you may be able to put together a configuration where your least portable items are your batteries and maybe your OTA.

All that said, unless you're really looking to move to an ultimate imaging setup, like a 12" Officina Stellare or Planewave CDK mounted on an AP900 or Paramount MX, you might try kind of an incremental approach.

You could start by finding a mid-weight OTA you'd be willing to lift onto a mount each time you go out to image, maybe a C11 Edge with the matched 0.7x focal reducer (which should end up around 1950mm fl?) and see how it does with your mount. You could look at some more exotic options, like a 10" ASA or 10" Tak astrograph, but I can't comment on their performance or weight, I just know they exist.

Then, if you find you're not happy with the combination's tracking performance, upgrade the mount at that point, knowing that there are some portable options out there that you could move to if needed.

Good luck, whatever you decide.
--Ken T.

#12 Ron (Lubbock)

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Posted 16 May 2013 - 03:01 PM

Interesting suggestions. Seems like quite a few nominations of the C11 Edge HD in this thread, so perhaps I should look more closely into it. I guess I have to decide if I want to explore the incremental route, possibly being left with used equipment I have to sell later, or just bite the bullet and "go big" the first time.

#13 EFT

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Posted 16 May 2013 - 03:12 PM

Interesting suggestions. Seems like quite a few nominations of the C11 Edge HD in this thread, so perhaps I should look more closely into it. I guess I have to decide if I want to explore the incremental route, possibly being left with used equipment I have to sell later, or just bite the bullet and "go big" the first time.


It is almost always my suggestion that, if you can afford it and your goals are in line with it, go with the higher end gear to start with. It can save a lot of frustration and even money down the line compared to stepping up by buy, selling, buying . . . Nothing "wrong" with the mid-level gear, it just may not match your goals very well.

#14 kfiscus

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Posted 16 May 2013 - 04:36 PM

PM sent.

#15 fmhill

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Posted 16 May 2013 - 08:43 PM

Here is another vote for a EdgeHD 11"... I was a bit afraid of the size however a friend has one and convinced me the size of the 11" is not a problem and now that I have it, I'm glad I went with the 11"...

#16 Ron (Lubbock)

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Posted 16 May 2013 - 10:39 PM

What mount did you put your Edge HD onto?

#17 Ron (Lubbock)

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Posted 02 July 2013 - 03:50 PM

Well, I finished my upgrade project, so I thought I'd update this thread. Paramount MX and C11 Edge HD are officially on their way! :refractor:

I probably would not have picked the Edge HD had it not been for the repeated recommendations here and elsewhere. I just don't see a lot of people imaging with them, probably due to the fear of long focal lengths, which is justified. However, I want the increased aperture for the smaller targets I like to do, and the Edge is going to give me a lot of aperture, a flat field, and a closed tube that won't fill up with dust during my imaging session.

Since I decided to forgo the Celestron focal reducer for the time being, which is arguably crazy, there was no option other than obtaining the best of the rock solid mounts. Software Bisque will have new MX mounts available in 3 to 4 weeks, I love all the features they have, and my order is placed. I managed to find a simple solution to the portable power supply, so I should be in business by the end of the summer. I am admittedly still concerned that I live in a normally windy location and will be attempting to image at 2800 mm. However, I will keep the C8 with focal reducer for those less than ideal nights.

Thanks for all the suggestions, and wish me luck!

#18 korborh

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Posted 02 July 2013 - 08:05 PM

Good luck with the C11 Edge Ron.
No you are not crazy to forgo the FR......I am forgoing the FR for the C14 Edge! Long FL imaging can be quite rewarding with targets and details that are not achievable otherwise.

You have nothing to worry with the PMX. Just don't waste time and get into the trap of trying un-guided on that scope unless you are willing to sacrifice image quality. No guide scope either. You will have to guide - OAG or ONAG.

#19 Ron (Lubbock)

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Posted 03 July 2013 - 02:41 AM

Thanks for the advice. When I see people say they get 20 minute unguided subs with their high-end mounts, I figure it is someone with a lot of experience with their equipment who probably has a permanent setup. I already have an ONAG and love it, so rest assured it will be put to work on the new scope!

#20 bilgebay

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Posted 03 July 2013 - 02:54 AM

Congratulations Ron. Both are very good investments!






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