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Omni 150R or 102ED Apo?


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Hello everyone, I'm a semi-noobie to deep sky AP and am trying to pick a scope. I have a CG-5GT, Orion 80ST, Starshoot Autoguider, and a Canon 7D. I am using this set-up with a 400mm lens and have gotten some good shots of Andromeda, M33, M81, Antres, and such. I am now wanting to move up in Focal Length to image some DSOs and have decided I want to stick with refractors. I am looking for something with a 700-800mm FL and a FR of f/5-7. I am also looking at a budget of under $1,000.

I like the Celestron Omni XLT 150R because of the large apeture, 750mm FL, and fast FR of 5. I know the glass isn't top of the line but the other specs match my needs perfectly. I would purchase the OTA from a vendor who agreed to sell the OTA only for $699.

The Orion 102ED Apo has nicer quality glass but has a slower FR and is $100 more expensive. (I found it on handsonoptics.com for $799).

My concerns are:

How much color will show in the 150R images

Will a FR of f/7 be fast enough for a FL of 714mm on my unmodified CG-5 as a noobie?

Any thoughts will be helpful and greatly appreciated!

Edited by Timothyterpsalot
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I'm not an imager but I have a 6" F/8 refractor from the same stable as the Celestron 150R (ie: Synta) and that shows moderate false colour on brighter stars, the moon and planets. I use a corrector to reduce this greatly but I would have thought that an 150mm F/5 achromat is going to show loads of false colour which would surely impact it's imaging ability ?.

The 102ED (I have a Vixen ED102 F/6.5) on the other hand will show very little false colour on bright objects and virtually none on fainter ones.

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I am no expert on these things but I think for £1000 you could get a much better telescope.

Check telescope service,

ED & APO - Teleskop-Express: Astro-Shop + Fotografie + Naturbeobachtung

Some of their own brand scopes are supposed to be very good, a nice 90mm triplet APO or whatever but they have a good selection of scopes for your price range, Im sure somebody else would be able to tell you which are the best ones.

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The thing you need to be aware of here is colour correction and also with a camera like that, flat fields might be an issue too. Problem is with refractors is that the faster you go, the more likely you're going to get false colour especially with the budget end of the spectrum.

I wouldn't worry too much about speed here and go with an Orion ED 80 (80mm ED Apo Refractor Telescope Optical Tube | Orion Telescopes). You can also add the reducer/corrector in your budget too and I think that should keep you entertained for a while. Most people have used an ED80 (I have one) at some point for imaging and you'd have to spend a fair bit more money to get something better.

HTH

Tony..

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I am quite sure that the fast achromat would be utterly hopeless for imaging, I'm afraid. The camera is very sensitive and would reveal vast haloes round bright stars. I also doubt that the field would be anything like flat or the illumination even.

A refractor with a focal length of around 750mm is going to be quite big and if fast enough to use for imaging and apochromatic enough as well, it is going to exceed your budget. The various incarnations of the Skywatcher 120ED apo are excellent. So is the Mak Newt. (Not a refractor, I know, but as a refrctor fan I would still consider it.)

Your only hope is the used market or an increase in budget.

Remember that as focal length goes up so does the need for accurate guiding.

Olly

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The various incarnations of the Skywatcher 120ED apo are excellent.

They are indeed Olly, but as you rightly mention they are a little bit trickier to get right due to the focal length and size.

Just checking at Orion's website, the Eon 120 $1799 so it's way over budget. So unless you're prepared to scour the second-hand ads at places like astromart, your budget is a little limited for what you want. Another thing you might want to take into account is your CG5 mount isn't the greatest mount for DSO imaging, buying a scope with a longer focal length may well cause you a lot of problems. You might want to look into buying a better quality mount before spending money on a scope you might not be able to use.

Tony..

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Yes, Tony is right. The EQ5/6 level of accuracy is an absolute minimum for longer focal lengths and with a larger refractor it would really be the 6 for comfort.

I have two refractors, one offering 328 or 450mm focal length and the other 980mm. There are SO many targets for 450mm that you have no hope of living long enough to wear them out! here's what you get at 450 on a 15mm square chip;

640970712_Peb3M-S.jpg

737982273_yZHnW-S.jpg

Olly

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If you read the descriptions of the pictures many say they taken on the CG-5 and a Celestron C6. Many were with a focal reducer which would put them at around 800mm FL.

But the C6 is a folded design and the balance and weight are going to be significantly different from a similar FL refractor!

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It can. The problem is that a long instrument has more polar inertia than a short. It works the mount a lot harder. A big triplet lens given a shove by the wind a fair way from the fulcrum needs some stopping and some damping.

You will find, on occasion, wonderful images taken with kit that you may have found from experience to be less than wonderful. There are some clever people out there who make things work when they don't work for most people. In choosing your setup you might be better advised to ask, 'How many of you folks out there are imaging with a fairly large refractor on a CG5?' There will be quite a long silence, I honestly think.

I found an EQ6 okay but not lavishly okay for a Meade 127 triplet apo. I have upgraded that mount to a much more expensive Takahashi. Too much mount is wonderful, too little is an abject nightmare.

Ooh, by the way, the ED102 is about f10 if I remember? Have I got the right scope? That is too slow for deep sky imaging. You would need very long subs and very, very good guiding and polar alignment as a result.

Best wishes,

Olly

Edited by ollypenrice
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Ooh, by the way, the ED102 is about f10 if I remember? Have I got the right scope? That is too slow for deep sky imaging. You would need very long subs and very, very good guiding and polar alignment as a result.

Olly, I think the 102 that the OP refers to is what was (or similar) to the old bright yellow WO Megrez 102 that runs at f6. IIRC most people said it was alright for observing but the CA was too much for imaging.

Tony..

Edited by Whippy
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I am talkin about the Orion 102 Ed Apo which is f/7 and 714mm.

Thanks for the info, I have a lot to think about.

I don't know this one but f7 sounds credible for a semi apo doublet. Field flattener almost certainly essential hence respect for the chip distance.

Olly

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