C5 V. C102: Any Advantage?
Posted 09 April 2014 - 02:09 PM
Am I missing something?
Posted 09 April 2014 - 04:12 PM
I have a 102mm f/7 ED refractor and a C5 and my impressions from a side by side comparison on Jupiter is that the refractor is a bit brighter and sharper than the C5. The 2" focuser on the C102 will allow a much wider TFOV as the C5 with it's 1.25" visual back is limited to ~1.3º. You can put a 2" SCT back on the C5 but it is debatable how much extra field you'll actually get due to the 27mm baffle diameter.
The C5 is much more compact. It does a nice job on the planets (significantly better than my 90mm mak) and is good on brighter DSOs at home. The size/weight is the reason I bought it. It packs some decent aperture into a small space and mounts on a photo tripod (I use a Bogen 3011 and UA DwarfStar combo that weighs 6lbs). I really like the scope.
Besides improving the CA, what are your goals in making the switch? It size important?
If you want something that can out perform the C102 you should look at the C6. It is larger than the C5 and would require a somewhat heftier mount, which for me puts it in another class in terms of portability. On the other hand it will probably work great on the mount you have for the C102.
Posted 09 April 2014 - 07:27 PM
Its an interesting comparison but if it were me - it'd be the C5 - so long as it was a good one . Slightly higher angular resolution, color free, great on doubles (I kno because my C6 is) and will split slightly tighter pairs. The compactness is a real point here too.
Either way your good but Id personally go with the sct. Strict collimation and it'll be a superb performer. And none of that blasted fringing.
Posted 09 April 2014 - 08:26 PM
Thanks for the link.
Buying a C5 is probably something that I will put on the backburner for now. I like the C102, but the CA is bothering me.
I continue to love my C90.
Posted 09 April 2014 - 08:40 PM
It's a great travel scope, and wonderful to use for a short session in the back yard.
Is there an advantage over a 102mm refractor? A lot depends on the refractor you have. The C5 is obviously easier to mount, and also has a greater range of back focus for photography. It also works well with inexpensive eyepieces, and due to the 1250mm focal length it does not require short focal length eyepieces to attain higher magnification.
My excellent example shows more details on Jupiter than a 4 inch F-6 achromat that I own, as the achromat has plenty of chromatic aberration.
It also came close in performance to a TV Genesis SDF I used to own, however the Televue did show better contrast.
Yes it has a large central obstruction, but the extra aperture does help make up for the contrast loss.
With that being said, if I didn't already own a C5, I'd probably purchase the C6.
Posted 10 April 2014 - 02:42 AM
Posted 10 April 2014 - 07:56 AM
I agree on the C6, they are much more compact than the C8 tube
as far as mount, My SLT Go-To mount holds my C6 just fine,
no trouble at all!
The C6 is one of the most influential scope tubes to come out in decades! I think the perfect starter scopes.
plus they are Pretty sitting in the corner..
Posted 10 April 2014 - 08:58 AM
C5 is smaller, easier to mount, perhaps more comfortable to use.
C5 has a narrower field, coma, field curvature, and less contrast than the C102.
Owned them both, own neither now.
SCTs advantage is packaging. It has always been packaging, and always will be packaging.
But the C5 falls a bit short in all performance criterion vs the f/10 acromat with maybe the exception of brightness, which can be important for planets (I like a bright image).
Get a C5 if you want one, and if your reason for wanting one is that they are compact, easy to mount, and comfortable to use, you will be happy.
But if you want it to give more enjoyable or more detailed views than a 100mm medium focal ratio acro, you might be disappointed.
C5 has its place and I found it much easier to deal with than the long acromat, but the views in the acro are better overall I would say.
Posted 10 April 2014 - 09:23 AM
Posted 10 April 2014 - 09:49 AM
(But dont listen to me I have two 5" scopes and a C102 and just enjoy different scope flavours for the heck of it )
Posted 10 April 2014 - 09:52 AM
As for achro filter info, you should find David Russell's comparo thread. He liked Baader 495 Longpass best, though for a faster scope than you have. I bought his Lumicon #8 for my C102 and am quite happy with it.
Posted 10 April 2014 - 09:50 PM
Posted 11 April 2014 - 12:36 PM
Posted 11 April 2014 - 05:56 PM
Posted 11 April 2014 - 06:23 PM
Posted 11 April 2014 - 07:23 PM
Posted 11 April 2014 - 08:53 PM
I completely agree. I owned 3 Celestron/Vixen 102s over the years and 2 were very good, and one was spectacular.
Slightly off topic but: It really ought to be mentioned that the early 1980's Japanese made C102 was often of a rather high optical quality. Some samples of those early Vixen 102's were of an especially high correction and smoothness of their figure and are around 1/8+ wave. The more recent Chinese sourced C102 and C102HD is simply not comparable to the old Vixen C102 and shouldn't be confused with it.
Posted 11 April 2014 - 11:16 PM
Would the Celestron version of this fluorite doublet be the same design as the Vixen? There is a Celestron 102 fluorite doublet for sale on the other site now.
The 102F was f/8.85 (902mm) and has a reputation for excellence. Here is a link to a brief bit of history and an overview by Roland Christen This was one of the first fluorites sold. I would definitely consider buying an 102F if you can find one...
Posted 12 April 2014 - 01:43 AM
The positives about the C6 are it's compact dimensions and relatively light weight. Weights at 9.5 lbs with 1.25 Inch di-electric diagonal and standard finder. Snaps to focus + knob is butter smooth and no image shift. Had mine an SLT mount no problem just a little focus wiggles fixed with anti vibe pads. You can have a C6 OTA for just over 400 dollars, the C5 spotter is more expensive I think.
Posted 12 April 2014 - 10:08 AM
I see mostly yellow fringing. Would the Baader Fringe Killer reduce that?
Posted 12 April 2014 - 12:25 PM
I own a Celestron Omni XLT 102mm f/10 achro refractor and I also have the Baader Fringe Killer. It does help with toning down CA but it gives a very slight yellow tint to objects.
Posted 12 April 2014 - 11:29 PM
Posted 13 April 2014 - 05:09 AM