Celestron 14" EdgeHD on Skywatcher EQ6 Pro Mount

[MichaelBruno]

OK, and once again thanks for all the feedback on this thread.

As per my last reply, I had pretty much resigned myself to getting a 150+mm APO refractor for that EQ6, so I set about trying to find the best bang for buck in terms of lightweight large aperture refractors.

Predictably I ended up in the SCT domain instead and started looking hard at the EdgeHD's from Celestron.

They start at 8" and go all the way up to the 14".

The OTA's alone are reported as weighing in as follows:

EdgeHD 9.25" 9.5kg

EdgeHD 11" 12.7kg

EdgeHD 14" 20.9kg

The attractive thing about the EdgeHD is that the Focal Length issue, which everyone in the know here has been cautioning me about, is elegantly addressed with these EdgeHD scopes.

For example, you can use the 14" EdgeHD at a focal length of F11 for visual and astrophotography at the rear of the OTA. F11 means that the 2800mm focal length gives excellent magnification on a 35mm format DSLR, but of course at a very narrow field of view - requiring very accurate and stable mount performance.

If you want to go wide field, you can mount your imager (CCD or DSLR) at the prime focus location on the front of the OTA. This is called Faststar or HyperStar configuration, on account of the faster equivalent photon capture times when compared to longer focal length work.

This allows you to use the scope at F2, or as I understand it, approximately 500mm Focal Length.

Now we're in that "happy place" when it comes to astrophotography and focal length.

My understanding is that with a small focal length, tracking accuracy and mount stability are less critical due to the large field of view - I get this loud and clear now!

Since I plan to use a DSLR Canon EOS550D (Rebel in the US) I need to use either the 11" or the 14", since the physical size of the DSLR at prime focus would obstruct too much of the primary on the 9.25" or smaller.

The Celestron guys on-line go "on and on" about the 3x image flatness of these EdgeHD's and fancy coated optics for pin point stars etc. It looks like these OTAs were designed especially for DSLR and the more expensive larger format CCD imagers.

I am looking to take advantage of the superb 18Mpixel CMOS sensor in the Canon 550D. It's probably worth mentioning that the camera body weight is les that 0.6kg. A lightweight 18Mpixel camera on a large aperture F2 OTA sure sounds like a perfect state of the amateur art imaging system to me.

So, sold on the F11/F2 versatility & FLAT performance of the EdgeHD, I am back where I started in selecting the best aperture option for my already purchased EQ6 Pro...

The 11" OTA is precisely half the weight of the EQ6 25kg payload rating. Many astrophotographers suggest that you should never load your mount at more than half the max payload rating for serious astrophotography. I can't help but ask myself whether these words of wisdom are relevant to F2 OTA setups. Surely a widefield F2 high pixel count (high resolution DSLR) system could

tolerate a little more jitter or tracking error?

So my greedy thoughts turn back to that oh so desirable 14" aperture EdgeHD, which still weights in at 4kg less that the EQ6 mount published max capacity...

(OK, OK, I realize that published capacity means "It won't break capacity", and not "It will work well capacity", but not breaking or stripping gears is OK for me at this point)

Many would caution me about the additional weight of the guide scope, eye pieces & imager. I plan to add only the 0.6kg of the Canon DSLR, and possibly an LVI autoguider camera with a light weight refractor to plug into the EQ6 ST4 port.

I'll probably end up at the 25kg full mount capacity, due to the weight of the autoguider optics (3kg) and 0.15kg LVI Smartguider camera.

Surely I'm not the first person to try and mount an EdgeHD 14" on an EQ6 Pro mount. Has anyone out there tried this already?

All said and nothing done, that's where my thoughts as regards the best possible OTA for an EQ6 Pro mount are at, at least at this moment. I'll keep updating this thread until I have images to demonstrate the capability of my ultimate decision on what to do with an EQ6 Pro mount....

[Astro_Baby]

I'm not an imager but I'd suggest if the scope is only 4kg shy of the mounts max weight capacity then your in trouble, by the time you add a guidescope, guide camera, main camera, dew shield, filter wheel, heater band etc the scope will easily be over the max capacity of the mount.

I'd suggest even for visual it may be painful. Its not execatly the same but I have a very overweight 8" scope on an HEQ5 and while I am within the mounts limits even visual with the scope is hard work. When I put a lighter tube on it its worth an extra inch of apertrure to have such a stable mount.

I dont image but I can imnagine if a mount is only beraley stable enough for visual then it wont be easy getting pictures where steady is going to be essential.

[MichaelBruno]

Thank Astro-Baby for your thoughts.

Please consider that the 14" OTA is only 787mm long, physically.

The shorter scope should help with stability and ease of balance.

Also note that I plan to use the DSLR Canon 550D, and would not need a filter attachment.

As for dew shields : I have fortunately not needed one yet.

Thats at least 1 nice thing aboutthe highlands of sunny South Africa.

[adamsp123]

Hi Michael,

I have read your other thread and now this one and what I see is a case of aperture fever . As some have said on your other thread a big scope on an EQ6, especially one with a high F ratio will IMO be a complete nightmare.

Have a look at what the good imagers are doing and see the scope sizes used, most come nowhere near what you are contemplating and for good reason.

Aperture is not, repeat not, that important for imaging, it is all about image scale and F ratio and a system that will work.

Why not get a smaller scope for imaging and get a large Dob for visual?

I am using a 190MN on a Vixen Atlux and I wouldn't want to go any heavier for imaging, the 190MN IMO is an excellent imaging scope but even a small aperture Refractor on an EQ6 would be an excellent choice.