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102mm F7 Kunming refractor comparisons

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#1 GOLGO13

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Posted 15 August 2012 - 10:59 AM

I recently picked up one of these for pretty cheap on Astromart. My scope has a William optics focuser vice what these originally came with (understand the original focusers were pretty bad).

Last night was my first good night (seeing and transparency). I find the images are quite good. In my limited comparisons between my 80mm and the 102, I can tell the 80mm uses better glass/coatings (FPL 53), but the 102 is way better than the 102mm F10 achro I used to have. I only see tiny color on really bring objects.

I was wondering if anyone has compared these scopes to high quality scopes like Televue and such.

Below is a link to the Orion one. These are no longer made, but seem like a nice option given the F7 focal ratio. I mount it on my Vixen Porta mount and it's pretty grab and go. I'll post a pic later.

http://www.telescope.../346/p/9012.uts

#2 Jon Isaacs

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Posted 15 August 2012 - 11:25 AM

Hi:

I had the Astro-Tech version, the AT-102ED. I owned it for about 2 years, I loved that scope, used it a lot and had a great time with it from both my backyard and dark sites. My experiences were probably about like yours, my 80mm FPL-53 is a better scope but the added aperture more than made up for it.

It was good enough, I used it enough that I decided to treat myself to a top quality 4 inch apo and bought a used NP-101 fitted the Feathertouch microfocuser. There is a noticeable difference. For the things I do, the NP-101 is flawless, the focuser is smooth and powerful, the micro-focuser never acts up. Optically there is no chromatic aberration, even on Venus, even out of focus even at the highest powers. The field is wide and flat, the 31mm Nagler + NP-101 is about as perfect as it gets. At high powers, on the planets or double stars, it is limited only by it's aperture.

The AT-102ED is a good scope and a great value. It does everything competently, no serious flaws. The difference is that the NP-101 does everything about as well as it can be done, the difference in any one aspect is most often small but it's the sum of those small differences that makes the NP-101 such a nice scope.

Still, if I had to sell the NP-101, I would be very happy with the AT-102ED, it's a good 'un.

Jon

#3 GOLGO13

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Posted 15 August 2012 - 11:45 AM

My biggest issue is choosing my next quality scope...which could be many years away so probably not a big deal. I think the 4 inch size is nice. Still pretty portable, a little more aperture than my 80mm. But for my next big purchase, I'm debating between a 12-15 inch premium dob or a 5-6 inch apo (pretty different scopes I know). I'd need a new mount with the apo most likely. My Sky view pro is pretty good...and I have a better tripod than what it normally comes with. But 20+ pounds is probably not a good idea.

As of right now I'm pretty happy with my scopes. I think right now I'm going to focus on getting some better eyepieces. Sold all my naglers for funding something I can't remember. So I'll probably go Ethos or Delos, and build that up a little.

If I go to a Star Party, usually other folks have nicer scopes...so I can mooch off them ;)

#4 Binojunky

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Posted 15 August 2012 - 01:00 PM

One thing about the lower cost scopes is that if like me you attend several star parties a year you find it can be rough on equipment, thats why I leave my premium stuff at home and take the less costly stuff, if damage or loss happens then its not the end of the world, my favourite star party scope is a simple achromat in the 4 to 5" range on a Versago mount,DA.

#5 GOLGO13

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Posted 15 August 2012 - 02:42 PM

Very good point Binojunky. You can still get some good views, and not worry as much about issues at the party.

Good reason to keep a few lower cost items. I've got lower cost covered top to bottom right now ;)

#6 GOLGO13

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Posted 15 August 2012 - 07:22 PM

Below is a picture of the scope.

Posted Image

#7 Markus Tang

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Posted 15 August 2012 - 09:37 PM

I once read a review about it compared with SW100ED.
This is one I want to buy in the future.

#8 Jon Isaacs

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Posted 15 August 2012 - 09:40 PM

I once read a review about it compared with SW100ED.
This is one I want to buy in the future.


The main thing is this scope is about 26 inches long, the ED-100s are about 36 inches long. Optically one has to say that the 100mm F/9 FPL-53 Objective of the ED-100s is better than the 102mm F/7 HK-61 objective...

For the things I do with a 4 inch scope, 36 inches @F/9 is too long.

Jon

#9 GOLGO13

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Posted 15 August 2012 - 09:58 PM

Yeah...weight and portability was my main reason for buying the scope. It's hard to find that in the 100mm range at a low cost. I was surprised this scope got discontinued. Maybe it wasn't selling too well. There were 3 or so companies selling it.

#10 Scott Beith

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Posted 16 August 2012 - 06:48 AM

Below is a picture of the scope.

Posted Image


Yep - the WO 102SV. Very nice!

#11 Markus Tang

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Posted 16 August 2012 - 08:43 AM

Yeah...weight and portability was my main reason for buying the scope. It's hard to find that in the 100mm range at a low cost. I was surprised this scope got discontinued. Maybe it wasn't selling too well. There were 3 or so companies selling it.

Perhaps there is also another reason--the rings.KUO's rings are more stable than SW'S and can install more accessoreis. ;)

#12 GOLGO13

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Posted 10 September 2012 - 09:03 AM

Update on this scope.

Had perfect conditions this morning, so I thought I would wake up early and test the scope out on Jupiter, Venus and the moon.

Venus had fairly strong Chromatic Abboration. I was not really surprised given a F7 doublet with cheaper glass; it was there no doubt.

Jupiter had a little CA, but not nearly as bad as Venus. Probably was affecting the view a little.

The moon had no CA, and actually looked very good. I was actually able to push the moon to 285X and it was still very sharp. I was impressed by that.

So still a pretty good scope, but yes it does have some CA on the brightest objects. I don't know if I would be that happy with it if I had paid 900 or more on it. But at 350 I'm quite OK with it.

#13 Binojunky

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Posted 10 September 2012 - 10:28 AM

I bought one of these a couple of years back on clearance, it was a dog, wouldn,t even come to focus(not enough infocus)I did eventualy get it to work with a 1.25 diagonal however its in the store room collecting dust, my Explore Scientific AR102 is another story though, a terrific achromat,DA.

#14 jrbarnett

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Posted 10 September 2012 - 03:01 PM

Incidentally the long f/9 100EDs are not heavy. Because they use thin walled tubes, simple focusers and fixed dew shades, thin tube rings, etc., they are often lighter than many compact, retractable dew shade 3" scopes much less 4" scopes. A long tube can create a significant moment arm if the tube is also reasonably heavy. In the case of the Synta 100EDs though, the tubes are so light pretty much any mount can handle them.

The meter-long tube is not the most convenient for automobile transportation or storage though.

Does your focuser have the WO swan logo on the fine focus knob?

Regards,

Jim

#15 GOLGO13

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Posted 10 September 2012 - 04:32 PM

Yes...the stock focuser was replaced by a WO focuser.

I understand the stock focusers with these scopes were problematic. So I believe most vendors or owners replaced theirs.

The focuser on it works good.

#16 Jon Isaacs

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Posted 10 September 2012 - 09:34 PM

Yes...the stock focuser was replaced by a WO focuser.

I understand the stock focusers with these scopes were problematic. So I believe most vendors or owners replaced theirs.

The focuser on it works good.


I believe I have the original focuser for your scope. If I am not mistaken, you purchased this scope from Keith Kinneson?

Jon

#17 GOLGO13

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Posted 10 September 2012 - 10:44 PM

yep...did you ever get it working? Is it just a bad design?

#18 Jon Isaacs

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Posted 11 September 2012 - 06:08 AM

yep...did you ever get it working? Is it just a bad design?


I never was able to get it working properly. Generally the trouble with the Asian Crayfords are the two speed units are rough and/or slip. Keith's focuser had a different problem, I could set it up as a single speed and adjust it so it was smooth and could lift a reasonable amount of weight and then it would just loosen up and start slipping. I checked the bearings, everything I could, I never figured it out.

It was very similar to my Astro-Tech focuser but not as heavily built, the drawtube and the body are thinner. I do not believe this scope was an Astro-Tech, rather it was sold by someone out of California but I can't remember the exact name.

Jon

#19 CollinofAlabama

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Posted 17 June 2013 - 05:40 PM

I've got one of these, and purchased a used Orion 80mm ED single speed Crayford from a guy in Brooklyn -- thanks Andy -- on a recent visit to New Jersey. Used to own the 100mm F/9 ED, btw. Although I agree with Jon, that F/9 scope is just too long (needs a mount too high up, that would need to be too heavy, and in West Texas, is too much of a wind sail), I still liked the simple but effective single speed Crayford focuser of the F/9 and ED80 scopes. Appreciate the light weight, too. The 102mm F/7 is perfect to me as for tube length and size on my existing mounts (PortaMount and EQ-3). Still, the stock dual speed focuser on the Orion F/7 is, well, not so hot.

How does one get it off? I see the small black metal screws down the indention at 120* angles. Do I unscrew them? I don't see anything to attach the single speed Crawford on the tube, proper. Will I need some kind of adapter? Who might sell one? Any information is appreciated.

The color correction may be less than my most excellent AT80ED, but it's still miles ahead of any achro I've ever looked through. I'm not bothered by its lack of color perfection. I can ignore this amount of CA, and find it kind of quant, like using UO orthos in a newtonian. My ability to purchase a "premium" refractor is gonna have to wait a while. I enjoy being married. Spending $50 on a used focuser -- no problem. Spending $5k on a telescope? Muchos problemas con la esposa. No, gracias.

#20 dennilfloss

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Posted 17 June 2013 - 06:20 PM

Would a filter like a Baader Fringe Killer still help in dealing with the little CA shown by those ED doublets?

#21 Jon Isaacs

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Posted 17 June 2013 - 06:24 PM

How does one get it off? I see the small black metal screws down the indention at 120* angles. Do I unscrew them? I don't see anything to attach the single speed Crawford on the tube, proper. Will I need some kind of adapter? Who might sell one? Any information is appreciated.



Collin:

I wouldn't bother with trying to replace the current two speed focuser with another single speed, it's much easier just to disable the two speed micro-focuser and use the current focuser as a single speed.

The roughness is caused by the micro-focuser so if it disabled, you are home free. Assuming the Orion is like the AT-102ED, the easiest way to disable to the two speed is this:

Underneath the focuser knobs, these is a stainless steel bushing/collar with three small set screws at 120 degrees apart. If you loosen these so the collar is free to move, the two speed is disabled and the focuser work smoothly as a single speed. If you want a photo, I can take one.

Jon

#22 CollinofAlabama

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Posted 18 June 2013 - 12:02 AM

Gosh, Jon, I'd appreciate it. No big rush, but if you get a chance to snap off a shot, that'd be great. Still like the idea of the lightweight ED80 single speed Crayford on it. Honestly, at F/7, a single speed's all I need for fine focus, provided its good, and the Orion old school 80 and 100ED focusers were (and in my case, are). But any advice offered that covers either course, provided I get smooth focusing, is the right path for me. Again, no rush but if you can snap off a shot, can't hurt.

#23 beanerds

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Posted 18 June 2013 - 07:12 AM

Jon , I did exactly the same thing , works a treat .
Then I dissasembled the whole thing , and found the 3 balls that drive the 10-1 reduction were made out of this kind of black rock material ?? , not round , or uniform in size , also the 3.2mm stainless steel shaft that drives the lot was only 3mm in diameter ,, damn .
After a bit of a dig around , I found that "NTN" bearings made a ball race # 6304LLU/2AS have real hardened and spherical balls that fitted my focuser's brass race ,.
I hand made a piece of 3.2mm , 316 S/S TIG wire to use as a shaft and its still working today , nice , not FT quality but a lot better than what left the factory and ended up on my ED80 ...
Brian.

#24 Jon Isaacs

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Posted 18 June 2013 - 07:38 AM

Jon , I did exactly the same thing , works a treat .
Then I dissasembled the whole thing , and found the 3 balls that drive the 10-1 reduction were made out of this kind of black rock material ?? , not round , or uniform in size , also the 3.2mm stainless steel shaft that drives the lot was only 3mm in diameter ,, damn .
After a bit of a dig around , I found that "NTN" bearings made a ball race # 6304LLU/2AS have real hardened and spherical balls that fitted my focuser's brass race ,.
I hand made a piece of 3.2mm , 316 S/S TIG wire to use as a shaft and its still working today , nice , not FT quality but a lot better than what left the factory and ended up on my ED80 ...
Brian.


Brian:

I have messed around with the darn things, replaced the balls, the shafts, polished the races... I had some luck improving them but they were never smooth enough for me.

As far as the black balls... I have a focuser that came off a Astronomy Technologies 102mm F/7, not an Astro-Tech, it's the small company that according to Jim Barnett is in the same strip mall as StellarVue.

It's very similar to the Astro-Tech Focuser but lighter duty. The 4 upper bearings that the drawtube rides in had a 0.5mm thick plastic layer. It was probably an experiment to see if it would prevent marking the anodizing.

Whatever, it developed flats in the plastic. I was very confusing.. I would disassemble the focuser, put it back together and it would work for a short while. But then it would quit, the focuser just spun. I finally noticed the flats... I worked at first because they were not aligned, but they would soon be aligned and the darn thing would just spin..

jon

#25 Jon Isaacs

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Posted 18 June 2013 - 07:45 AM

Gosh, Jon, I'd appreciate it. No big rush, but if you get a chance to snap off a shot, that'd be great. Still like the idea of the lightweight ED80 single speed Crayford on it. Honestly, at F/7, a single speed's all I need for fine focus, provided its good, and the Orion old school 80 and 100ED focusers were (and in my case, are). But any advice offered that covers either course, provided I get smooth focusing, is the right path for me. Again, no rush but if you can snap off a shot, can't hurt.


Collin:

I think if you disable the 2 speed you will probably like the focuser as a single speed, it's more robust than the ED-80 focuser... And it's a whole lot easier to make happen.

I recently purchased a Skywatcher Pro focuser on Astromart for $65, it's the same thing as the ED-80 with different paint and a two speed. It's on my Orion SkyView 100mm F/6 achromat, it's surprisingly good, I had to shorten the drawtube and it needed some adjustment but it'll handle a 20mm type 2 Nagler without a problem.

Also, if you post of photo of the underside of your focuser, I can edit it and show you where the set screws are.

Jon






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