C11 Edge HD and CGEM DX mount

[scotty87]

hi guys, how well does the cgem dx cope with a C11 HD and all the equipment for astro photography ?

I've also read that the scope will be a good choice for planetary imaging but not for DSO's because of the focal length ?

how well do the focal reducers work in the real world ? I've read that they don't seem to work well with the edge. celestron are making one for it tho, will that be any different ?

do you loose magnification with a focal reducer ? i.e: is using a 15mm eyepiece with a 0.5 focal reducer the same as using a 30mm eyepiece ? with that assumption do the longer eyepieces reduce the focal length of the scope ?

i apologise for the 3 million questions but i just cant seem to get my head around them lol.

i suppose the bottom line is i really want a c11 HD but i also want to do AP on DSO's. does the focal length really give you that hard a time ? is there any equipment out there which will allow me to add onto the scope to make it any easier ?

thanks,

scott.

[ollypenrice]

Personally I would only try to do DS imaging at C11 focal length on a premium mount and wouldn't go below a Losmandy G11. It isn't weight, it's tracking accuracy. This has to be excellent at long FL.

The pre Edge C11 gives a reasonable field in terms of curvature and illumination with an F6.3 flattener but it is not going to give a perfect result right across a DSLR chip. The Edge will do so but the Edge doesn't have a reducer and F10 is hopeless for DS imaging, so who knows what Celestron are playing at there.

If you have a 2 inch back and widefield EP there is no point at all in using a reducer visually. The baffle tube is the limiting factor. If you only have a 1.25 back end then the reducer will reduce mag and increase field in your 1.25 EP.

The term magnification is not used in imaging but there we talk about image or plate scale. Even with reducer the C11 is going to be great for small galaxies and planetaries but is too 'zoomed in' for many nebulae to fit on your chip.

Olly

[Beyond_Vision]

I agree with Olly it's not an ideal instrument to start on for DSO work. It will however make a good planetary scope. There really isn't any one scope that covers all bases. This is why people will often end up with several scopes to cover a range of focal lengths. I would suggest concentrating on getting a good solid Equatorial mount as is possible. This will stand you in good stead for upgrading scopes as and when. Something like the CGEM or EQ6Pro upwards.

Regards

Kevin

[E621Keith]

I think Optec makes a reducer for EdgeHD and Meade ACF

Optec :: NextGEN Ultra WideField 0.7XL

[michael.h.f.wilkinson]

I think Optec makes a reducer for EdgeHD and Meade ACF

Optec :: NextGEN Ultra WideField 0.7XL

Now that sounds like a very interesting development. Suddenly the C11 Edge HD makes more sense.

[scotty87]

i thought i was making headway but ive gone all confused again now lol.

this focal reducer thing is baffling me too much, i understand what your saying olly... i think lol. a standard focal reducer will "work" on a standard SCT but not the edge ? i have read this so its nice to get a confirmation, it seems there are some people who can get a focal reducer to "work" and some cant.

i have taken this snippet off another site i dont understand it, but maybe you guys could explain it better for me :

I think eventually when this reducer is produced by Celestron, it will be a reducer/flattener lens. It seems by reducing the already-flattened image, you get some curvature introduced. Or, I can see that the stock flattening lens could somehow be replaced as a way to get reduction/flattening. We'll see.

@beyondvision, the cgem dx is stated to hold 50lbs, 10lbs more than the regular cgem. i know olly recommended the g11 but by the time you put the equivalent goodies on it the mount is £3300 + .

does anybody else think the mount will/will not be up to the task ?

@E621Keith, can you confirm that the FL you linked to actually works differently to the rest on the market ? i cant seem to find anything on it sorry. it would be funny though if optec beat celestron to it in making a FL which worked properly with the edge HD

i always wondered why most of you guys had a vast array of scopes.... now i know why lol

thanks for the replies, keep 'em coming

[x6gas]

I have an Edge HD 11" on a CGEM DX, although I have had it outside only a few times due to the clouds and work commitments.

Here are my thoughts. The CGEM DX is an excellent and capable mount (though I don't have experience of anything other than this and my CG5-GT). It easily handles the payload of the scope and my Atik OAG/EFW2/383L+. is rock steady, GoTo is spot on and it tracks very well. That said, I've done no imaging with it thus far aside from webcaming Jupiter - but it will hold that on the centre of the SPC880 sensor for a good 5 minutes at f20. The mount looks gorgeous and is internally wired so is nice and neat. I have no experience of the NEQ6 Pro so can't compare...

Now to the scope...

I've been pretty impressed with the views in the 11HD but there is a caveat: I do wonder whether it is that much better than the standard C11 for the following reasons:

If you plan on using it for DSO, you will probably want a reducer and for 'well corrected SCTs' like the Edge HD you do need a custom reducer which is made for that particular aperture scope - standard SCT correctors WILL NOT WORK. Celestron themselves have promised one, but it has been much delayed. The 11" version is supposed to be in production, but I don't know of anyone who has actually seen one. It needs to sit up close to the corrector lens in the scope which is causing difficulties, I understand. As you say Optec have already produced one and FLO will be stocking it, but are still talking to Optec about details as I understand it...

So here's my point: If you are using the scope for planetary, then you'll have the planet in the centre of the field of view so you don't really need a well corrected scope; if you are doing DSO stuff, you are probably going to use a reducer anyway. The Optec reducers for the Edge scopes are expensive, I doubt the Celestron units are going to be any cheaper, if they ever arrive... so I do wonder if I wouldn't have been better off with a standard C11 and using whatever corrector is needed (indeed if needed) as I think that's actually more flexible than having the corrector mounted inside the scope... The C11 is less expensive, and the correctors also less expensive so overall, much less expensive... So while I am very happy with the Edge I do think I may have been as happy with the standard C11.

Now I do plan to use the 11HD for small DSOs at f10 - I know that this will be challenging and no idea how successful I'll be, and I will use my Newts for larger DSOs - so hopefully the EdgeHD will outperform an uncorrected C11 there - but again, could get a corrector for less than the difference in price between the C11 and 11HD...

The other "pro's" of the Edge scopes are mirror locks (very useful) and cooling vents (no idea how much this reduces cool-down time).

HTH. If you have any questions then I'll be very happy to try to answer them.

Cheers, Ian

[E621Keith]

Sorry wrong link

Optec :: Lepus Telecompressors

The reducer appears to be model specific.

OPT listed the C11 HD version for $275 USD and as in stock

Optec Lepus HD Telecompressor ? Celestron C11 EdgeHD Edition - OPT Telescopes

[scotty87]

Ian, you have just explained everything i was trying to ask. thank you i appreciate it .

by the time i get myself sorted out (moving out just after Christmas) its going to be march/may until i can get myself one of these, so hopefully people will start to use these new focal reducers and we can see if they are any good. im hoping to see your attempts of DSO's now at f10 aswell in the near future.

i do think it will be better now though if i keep to the planets starting out and maybe get a "fast" newt for DSO's. where does it end ?

one thing is bugging me, the focal length is f10 on a C11, that focal reducer is 0.62x

will the focal reducer bring the focal length down to f9.38 or f3.80 or f6.20 ?

thanks keith for the link

[michael.h.f.wilkinson]

Ian, you have just explained everything i was trying to ask. thank you i appreciate it .

by the time i get myself sorted out (moving out just after Christmas) its going to be march/may until i can get myself one of these, so hopefully people will start to use these new focal reducers and we can see if they are any good. im hoping to see your attempts of DSO's now at f10 aswell in the near future.

i do think it will be better now though if i keep to the planets starting out and maybe get a "fast" newt for DSO's. where does it end ?

one thing is bugging me, the focal length is f10 on a C11, that focal reducer is 0.62x

will the focal reducer bring the focal length down to f9.38 or f3.80 or f6.20 ?

thanks keith for the link

The latter : 0.62 x 10 = 6.2.

[scotty87]

ok so f6.2 isnt too bad for DSO's is it ?

I know there will be some nebula's e.t.c i wont be able to get the full view of, but shouldn't be too bad ?

back to square one... lol

[Dunkster]

So what's all this "Fastar" capability... I thought this was supposed to reduce FL down to like f 2.something for AP? Wouldn't this eliminate the need for a reducer?

[E621Keith]

So what's all this "Fastar" capability... I thought this was supposed to reduce FL down to like f 2.something for AP? Wouldn't this eliminate the need for a reducer?

The Fastar system replaces the secondary with a camera. I don't think Celestron make Fastar optics anymore, instead the scopes use Starizona's Hyperstar.

Fastar/ hyperstar turned the SCT into what is essentially a Schmidt camera. The scope cannot be use for visual in this mode, and the camera must have a narrow cross section so it doesn't obstruct the light path.

you can find more information here

HyperStar

Since the EdgeHD corrector lens is located inside the baffle, it will not interact with the hyperstar's light path, so there are no benefit using a EdgeHD C11 instead of a regular SCT C11.

People say the critical focus zone on a Hyperstar SCT is extremely narrow and the scope can only be focus by moving the primary mirror, as such, a hyperstar SCT will need a high precision electric focuser to focus.

[RobH]

I spoke to Celestron US's technical department a couple of weeks back, and the reducers for the 11 and 14 inch are due out either this month or next (can't remember exactly), and the 8 and 9.25 later in the year.

Thay are designed, like the optec, to sit as close to the flattening element as possible.

Rob

[x6gas]

People say the critical focus zone on a Hyperstar SCT is extremely narrow and the scope can only be focus by moving the primary mirror, as such, a hyperstar SCT will need a high precision electric focuser to focus.

Collimation is also critical and, I hear, very tricky.

My 383L+ is not the ideal cross section for Hyperstar and also I wonder if the cabling to the camera would produce diffraction spike(s) - and not four symetrical 'pretty' ones you get from spider vanes on a newt... The hyperstar is also mega money... I think I'll stick to my f/4.5 10" newt for faster DSO imaging.

[x6gas]

im hoping to see your attempts of DSO's now at f10 aswell in the near future.

Yes, and I'm hoping to produce some at some stage! To be honest, I've not had much time with the scope as of yet. I'm using the current moon and reasonably clear skies to try to get the set-up shaken down (for once the moon light helps!) - there is lots of new territory for me, including moving to off-axis guiding instead of a seperate guidescope. I'm not expecting much from this season other than climbing a steep learning curve...

I did have a peek at M42 visually yesterday using a cheap (and quite poor) 32mm plossl and i was amazed at the quality of view. The scope is much more forgiving than my newts. The supplied 2" 23mm Axiom EP is just amazing...

[Dunkster]

Since the EdgeHD corrector lens is located inside the baffle, it will not interact with the hyperstar's light path, so there are no benefit using a EdgeHD C11 instead of a regular SCT C11

Thanks Keith! Very interesting reading.

@OP sorry for the diversion

[scotty87]

Dunkster no worries the fastar thing was totally overlooked by me, thanks for bringing it up. but it seems it isnt what id want unfortunately.

cant wait now, over half way there in the piggy bank