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How hard is it to make a reflector as good as mid-price ED or Apo refractor?

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#101 gnowellsct

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Posted 29 April 2018 - 03:46 PM

here

Attached Thumbnails

  • optical craftsmen OMI AP900QMD CN size.JPG

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#102 gnowellsct

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Posted 29 April 2018 - 03:46 PM

that was before moving it to the G11. I sold the pier.  GN



#103 CHASLX200

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Posted 29 April 2018 - 03:50 PM

I would die for that OTA if it was local. I loved my OMI mirrors.


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#104 Starman1

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Posted 29 April 2018 - 05:27 PM

You sold an AP mount to get a G11?


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#105 CHASLX200

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Posted 29 April 2018 - 06:23 PM

You sold an AP mount to get a G11?

You can buy 5 G11's for a AP mount.


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#106 SandyHouTex

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Posted 29 April 2018 - 06:55 PM

here

That’s a beautiful scope.


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#107 gnowellsct

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Posted 29 April 2018 - 09:42 PM

You sold an AP mount to get a G11?

Oh no Starman1!  This is a dual GEM household.  I just prefer to use this particular scope on the G11.  



#108 gnowellsct

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Posted 29 April 2018 - 09:44 PM

You can buy 5 G11's for a AP mount.

Not quite this is a 900 QMD.  I bought it some years ago for 3k and by the time I had all the upgrades it was 6.5k which is 2 G11 Gemini units or 3 G11 Stepper units.

 

I bought it because Argo Navis has mount modeling and AP has ducked that one for twenty years, never mind that Losmandy has it, never mind that Celestron has it, never mind that Meade has it, never mind that Vixen has it, etc.

 

Greg N



#109 azure1961p

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Posted 30 April 2018 - 11:55 AM

 

 

I learned rather rapidly that the 1965 mirror was total junk (had a fracture, there's a name for it that I'm forgetting) 

 

Greg N

 

 

Greg,

 

It's sh-t . We call it sh-t.

 

 

BTW, love the Kandinsky print!

 

Pete


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#110 Pinbout

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Posted 30 April 2018 - 02:31 PM

here

why not just make it a split truss... that way you can mount it on the gem or in a dob base.

 

med_gallery_106859_3508_39992.jpg


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#111 gnowellsct

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Posted 30 April 2018 - 09:48 PM

Yes that's an intriguing possibility, and I saw your other post, but my reward for using split truss on a GEM would be I would have a Newt on GEM and get to follow the eyepiece all over the sky and never sit down.  My SCTs and my refractors on GEMs allow me to sit.  I like that.  My dog likes that.

 

I might turn it into a dob.  There's a related thread in amateur telescope making.  It would really be more money down the rabbit hole.  I'm not sure I would reach for a ten inch dob in preference to my other rigs.  A 3 or 4 inch apo on an SCT provides capabilities that are not within the reach of any one class of scope by itself.  It is true that some people mount refractors on Newts but it is unusual, probably because of the weight issues.

 

Actually one of my original plans was to leave that rig you see in the picture in the garage.  My idea was that I could roll it out and use it as a home based scope.  In practice the idea turned into a disaster.  The wheels were too small, and small sticks would jam the pier.  The weight a GEM mounted OTA in motion produces random movements that seem to come out of nowhere and are utterly unpredictable.  We nearly lost the whole thing once.  In winter the snow and ice also prevented it from being a possibility.   Anyhow rolling that thing was a two man job and three would have been better still.    Roll out works well for people with smooth driveways in CA or AZ.  But due to trees I had to do much more.  I had to go all the way out in the street and then go another 200 yards to the end of the block where the sky was clear.  

 

So I had to abandon that idea and getting the thing to a remote site was NOT fun so it's got to go.  I could dob it but I suspect I'll end up selling it if I do.  But at least it would sell.  GN

 

Greg N

 

 

why not just make it a split truss... that way you can mount it on the gem or in a dob base.

 

med_gallery_106859_3508_39992.jpg



#112 gnowellsct

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Posted 30 April 2018 - 09:53 PM

here's a couple of pics.  I don't know if I have one of it on the G11 which is how I actually used it.  

 

Mirror specs:

 

OMI miror specs for replacment mirror.jpg

 

 

 

 

 

 



#113 gnowellsct

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Posted 30 April 2018 - 09:54 PM

protostar

 

 

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#114 gnowellsct

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Posted 30 April 2018 - 09:57 PM

The original Optical Kuhrapsman mirror had what's called an annealing fracture.  You hear about these but to find one is very rare.  I use the OC mirror as a doorstop now.  But I did well with the OMI.  The OMI is thinner too and the whole thing cools very quickly.  

 

Optical Craftsman 10in-05  CN Size.jpg


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#115 gnowellsct

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Posted 30 April 2018 - 10:04 PM

Greg and 1968 Optical Craftsmen - CN size.JPG



#116 gnowellsct

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Posted 30 April 2018 - 10:10 PM

Here I found one on the G11

 

geoffrey and Newtonian on G11 - CN.JPG



#117 gazerjim

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Posted 01 May 2018 - 12:05 AM

I have a home brew newtonian OTA with 8",  f/8 Royce mirror, minimum diameter secondary and simple cooling fan.

 

Have not used it in a long while and never compared it side by side with other types of optical systems.  But it was hands down a planet killer.  Can't prove it, but I seriously doubt an 8" refractor would show much more planetary detail.

 

Not that I wouldn't mind having a premium quality 8" APO !


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#118 Starman1

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Posted 01 May 2018 - 12:49 AM

here's a couple of pics.  I don't know if I have one of it on the G11 which is how I actually used it.  

 

Mirror specs:

 

attachicon.gif OMI miror specs for replacment mirror.jpg

Ooh.  Seriously turned edge.

Mask the outer 1/4", and the mirror would be significantly better.



#119 geyes30

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Posted 01 May 2018 - 02:43 AM

why not just make it a split truss... that way you can mount it on the gem or in a dob base.

 

med_gallery_106859_3508_39992.jpg

Danny,

 

I swear it's a coincidence, but the 8" F6 planetary scope I'm building looks very similar to this - 12 trusses, 3 sections, but I'll be using hexagons. I'm hoping it will outperform my C8 on planets!



#120 gnowellsct

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Posted 01 May 2018 - 04:40 AM

Greg,

It's sh-t . We call it sh-t.


BTW, love the Kandinsky print!

Pete


You are correct. It's also called an annealing fracture. Unfortunately bad manufacturing has an established history in the U.S. not just in China.

#121 gnowellsct

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Posted 01 May 2018 - 02:47 PM

Ooh.  Seriously turned edge.

Mask the outer 1/4", and the mirror would be significantly better.

Well I'm not one to dispute your choice of adjectives but I have had experience with a serious or severe TDE.  Imagine if you will the four diffraction spikes you get on a *bright* star.  Between those four spikes there is in the normal course of things some smaller fuzz due to the dancing seeing and ill defined edge of the star.  Now imagine (in focus)  long tendrils coming out from those in-between spaces, about 3x or 4x longer than the diffraction spikes, but thinner.  That is *serious* TDE.   None of that on this scope.

 

I'll stand by the views this scope offers, it's first rate.  But that said, it's hard to find a Newt mirror that might not be touched up with an outer mask.  If I convert it to a dob I'll experiment.  (Because I'll have easy access to the mirrror).

 

regards,

Greg N 


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#122 NHRob

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Posted 01 May 2018 - 05:32 PM

Barbie
Can u post pics of your dob? Would love to see it.

#123 Pinbout

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Posted 01 May 2018 - 06:01 PM

The original Optical Kuhrapsman mirror had what's called an annealing fracture.  You hear about these but to find one is very rare.  I use the OC mirror as a doorstop now.  But I did well with the OMI.  The OMI is thinner too and the whole thing cools very quickly.  

 

attachicon.gif Optical Craftsman 10in-05 CN Size.jpg

didn't you post this a couple of years ago?



#124 NHRob

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Posted 01 May 2018 - 06:03 PM

Who?

#125 Pinbout

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Posted 01 May 2018 - 06:03 PM

Barbie
Can u post pics of your dob? Would love to see it.

wish he'd post star test images... post them in the gallery as supreme examples of the excellence GSO can provide for everyone to see

 

https://www.cloudyni...355-reflectors/

 

and as you can see in the gallery the pics don't have to be perfect to actually see who good the mirror is. grin.gif


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