Celestron C11-S GT XLT GOTO questions

[Dunkster]

Indeed, and as SCTs are somewhat frowned upon in our damp(er) climate, I occasionally take a peek over the "other side", and they have some pretty fierce "discussions" even about this very thing. All I can really say is I'm glad I'm an SGL member

It would be a very interesting, albeit expensive, experiment to find out. I find the C11 rock solid on the NEQ6, but the NEQ6 is all the more beastly, at least by weight. If I knew the CG5/AVX would be "fine" for visual, the C11 would prolly get a lot more use Weather permitting of course

[Grotemobile]

This is what i have done to my C11.

New saddle & dovetail.I use it for

lunar & planetry Imaging.Works

very well .No good for DSOs.

Steve.

[xarcane]

Hi grotemobile

Is the C11 no good for DSO because of the f10? if this is the only issue then would the hyperstar solve this as I believe that it brings it down to f2.0?

If not then what other cons are there against this scope for DSO?

Sorry just one more question is it the case that most cassegrain's are not very good for DSO imaging?

thanks

[Dunkster]

Hyperstar would get you down to f/2.0, but that's still 560mm focal length and you have a big, heavy ota to guide. There lies the challenge With a small refractor, you have a lot less weight to move and guide.

However, for visual, I really like my quality time with my C11

[billhinge]

I aslo have the same C11 setup, I agree with customization it will work for lunar & planetary but until you try a smaller scope on the CG5 you don't appreciate life should be easier - it really depends on your stubbornness to get it working. A good 80mm on the CG5 is a more pleasurable experience

Best of both worlds would be C11 for planetary and smaller and faster scope for DSO (cheaper than hyper star without the weight issue)

[ollypenrice]

I'd suggest more homework on DS imaging.

F10 is very occasionally useful on a tiny number of small bright targets but in general is, honestly, useless. Unless using CCD rather than DSLR forget it straight away.

Focal lengths beyond a metre are not 'plug and play' on an NEQ6. It can be done but it needs experience and tuning. Weight is one small part of the mount problem. At long focal lengths accuracy is the big one. For a 2.5 metre focal length I wouldn't be interested in anything less than around £5K for the mount. People do manage it on cheaper mounts but they have been refining their act for years, not coming in as beginners. Bundling huge scopes on tottering little mounts is just cynical profiteering.

Hyperstar is fast but, again, works on the vendors' websites better than it does in the observatory. Very fast systems bring very big devils in the detail. Again, they can be solved but... how much solving do you want to do?

To get into DS imaging why use a whacking great telescope with long focal length and slow focal ratio requiring ultra-precise guiding? Why not tackle the considerable challenges of DS imaging with something a little easier? I use scopes from 85mm to 350mm and like the smallest one the best. It can't do everything but it can do this sort of stuff;

http://ollypenrice.s...E 2FLsV3-X3.jpg

http://ollypenrice.s...OSITE FL-X3.jpg

http://ollypenrice.s... IN sRGB-X3.jpg

http://ollypenrice.s...ODKHORSE-X3.jpg

You can put a scope like this on an HEQ5 and never lose a sub exposure. Bliss.

In imaging bigger isn't better.

Olly

http://ollypenrice.s...39556&k=FGgG233

[xarcane]

Thanks for all the advice so far. I thought it would be as simple as slapping on a hyperstar as some websites state it is so fast you dont need guidence and it's virtually snap and go!.

Though I do like your advice on getting another scope for DSO imagining.

I only have one question about the C11if it is not good for DSO imaging does that mean it's DSO capability for viewing isnt as great then? Or is it the case that imaging is a whole different ball game than viewing?

[ollypenrice]

Imaging is totally different. The only thing wrong with the C11 and other SCTs in visual use is that they have a limited field of view compared with, say, faster Newtonians. This does bother me but others don't mind. It depends on your observing preferences. The C11 has excellent optics. No doubt about that. But personally I like to have more field of view than I get from our 10 inch SCT. However, the SCT is a very convenient size to store and move around. No one scope does everything...

Olly

[xarcane]

Cheers Olly and great images btw

[Dunkster]

The C11 without a focal reducer can show a shade under 1 degree across, and with a focal reducer almost 1.5 degrees. There aren't many objects that are larger than this that aren't better viewed with a short focal length refractor, that you could also be using for DSO imaging. Best of both worlds

From a visual observer looking through the peep hole at imaging, imaging looks might complex to me

[vlebo]

Imaging is totally different. The only thing wrong with the C11 and other SCTs in visual use is that they have a limited field of view compared with, say, faster Newtonians. This does bother me but others don't mind. It depends on your observing preferences. The C11 has excellent optics. No doubt about that. But personally I like to have more field of view than I get from our 10 inch SCT. However, the SCT is a very convenient size to store and move around. No one scope does everything...

Olly

Can anyone put up a comparison diagram of the different field of view of a 11" SCT and a 10 or 12" newtonian. As the portability of the SCT appeals but I do like the wider field of view of a Newt.

Thanks

[billhinge]

It depends on the focal length of the newtonian and what eyepiece/camera you are using. I use Sky X as my planetarium software and you can set these types of view up quite easily, so can frame your dso on the computer as your camera would see it before hand

I'm guessing the free software can do the same thing and you can put your own numbers in for your own choice of equipment

[opticalpath]

The smaller FOV of the SCT referred to is due to its intrinsically longer optical focal length compared to a typical 'fast' newtonian of the same aperture. The C11 has a nominal focal length of 2800 mm; a 10" f/5 newtonian has a focal length of 1270mm. If you used the same eyepiece (or camera) in each scope, the C11 would give higher magnification and smaller FOV than the newtonian in the ratio 2800 / 1270 i.e about 2.2x. In practice, visually, the actual FOV achieved also depends on the type of eyepiece used, and on it's focal length.

For example, a plossl eyepiece with an 'apparent field' of 60 degrees and focal length of 26mm on the C11 would yield a magnification of about 108x (2800 / 26) and a FOV of 0.56 degrees (60 / 108). The same eyepiece on the f/5 newtonian would give about 49x magnification and 1.2 degree FOV.

Within limits, used visually, it's possible to achieve the same magnification and FOV in both scopes, by selecting different focal length eyepieces; it's just that one is somewhat more convenient for higher magnification, the other for wider field. In practice, the actual usable sharp FOV will be smaller in both scopes due to coma and other optical aberrations affecting outer regions of the field, unless correctors are used.

Adrian

[Zaphod360]

The C11 without a focal reducer can show a shade under 1 degree across, and with a focal reducer almost 1.5 degrees. There aren't many objects that are larger than this that aren't better viewed with a short focal length refractor, that you could also be using for DSO imaging. Best of both worlds

From a visual observer looking through the peep hole at imaging, imaging looks might complex to me

I'm a visual observer as well and in my CPC1100 I can get 1.05 degrees field of view, even with a reducer I can't get more than that without vignetting (I use an earthwin powerslide) is there a different reducer I could use to get 1.5 degrees? I use a 4" short tube refractor for the wide field objects but a little bit extra from my main OTA would be nice.

[Dunkster]

I'm a visual observer as well and in my CPC1100 I can get 1.05 degrees field of view, even with a reducer I can't get more than that without vignetting (I use an earthwin powerslide) is there a different reducer I could use to get 1.5 degrees? I use a 4" short tube refractor for the wide field objects but a little bit extra from my main OTA would be nice.

Sorry, human error in my calculations

C11 ~1 degree, C11 with 0.63x reducer/corrector ~1.33 degrees (reducer aperture is 41mm, but expect some vignetting with the steep light cone)

C11 Edge HD with 0.7x reducer ~1.36 degrees (reducer is full aperture, so using something like a Panoptic 41 or LVW 42mm will still vignette over ~1.36)

Zaphod360 - are you using the stock Celestron visual back or have you replaced it? The reason I ask is that the stock visual back that came with mine has an obstruction, restricting the diameter to 38mm. That may be causing a problem before the light even gets to the reducer. I'm sure someone will correct me shortly if I'm beating down the wrong path...

Anyhow, my dodgy maths doesn't detract from the fact that a 10" or 12" Dob with their shorter FL will give a substantially wider view.

[Zaphod360]

I've tried a couple of different visual backs but currently use a SCT threaded 2" diagonal. My own experience (only using the integrated reducer in my earthwin powerslide (which is an amazing piece of kit!)) was that I am still restricted to 1 degree. I say restricted but it was exactly what I was expecting when I bought the scope and am more than happy with it.

I'll have to do some research on this as I was under the impression that a C11 couldn't get more than 1 degree. Thanks for the info

[Dunkster]

That's an interesting piece of kit however, there's potentially multiple things at play here... introducing another device also runs the risk of increasing the backfocus and causing the FL to extend longer than specified. When the reducer is in play, it will also depend on the reducing factor, where that's 0.6x, 0.7x? Maybe I'm misreading the page on their site, but it says "40mm multi-coated optics" ... not sure exactly what this is referring to, but if it's the aperture then it's definitely restricting the aperture of your optical path compared with the widest 2" EPs available.