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#951 Bomber Bob

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Posted 01 September 2020 - 10:52 AM

So for the cost of the 4" APO one can make a 8" Schupmann and have much better optical performance and more money left in your wallet.

 

Which begs the question:  Why aren't these being made / sold?  I got my AT102ED for $600.  If an 8" sold for close to that, I'd buy & try it.  I don't see anything in the schematics that look like they exceed Chinese fabrication abilities -- but maybe I missed something.



#952 Terra Nova

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Posted 01 September 2020 - 11:06 AM

So for the cost of the 4" APO one can make a 8" Schupmann and have much better optical performance and more money left in your wallet.

 

Which begs the question:  Why aren't these being made / sold?  I got my AT102ED for $600.  If an 8" sold for close to that, I'd buy & try it.  I don't see anything in the schematics that look like they exceed Chinese fabrication abilities -- but maybe I missed something.

Market inertia. The reluctance of people to buy a new design, especially a telescope that doesn’t look especially like a telescope. And the reluctance of a manufacturer invest in a project requiring a major re-tool to make said product. The only reason that GSO came out with their classical Cassegrains is that they were already making very good parabolic mirrors for their Newtonians, and they had been making R.C. Cassegrains for some time, so it wasn’t a big changeover to come out with their CC line. Basically, they were making most everything already, they just had to recombine some parts.


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#953 DAVIDG

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Posted 01 September 2020 - 11:32 AM

So for the cost of the 4" APO one can make a 8" Schupmann and have much better optical performance and more money left in your wallet.

 

Which begs the question:  Why aren't these being made / sold?  I got my AT102ED for $600.  If an 8" sold for close to that, I'd buy & try it.  I don't see anything in the schematics that look like they exceed Chinese fabrication abilities -- but maybe I missed something.

 As Terra points out it is  the same reason as why no one makes big long focus Newtonians on German Eq mounts, or slow F-ratio classic refractors any longer  What about Mak Newts  or  Schiefspeigler ,  folded refractors  or even off axis Newtonians.  They were once commercially  available but no longer.   It is all about making a profit and what the market wants. Right now it is fast F-ratio APO for astrohphotogrphy, or big   fast Dobs for deepsky hunting.  

 

                   - Dave 


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#954 Bomber Bob

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Posted 01 September 2020 - 12:12 PM

But... this design has been around for a long time...  Jump back 30 years:  I think there could've been a market for a 6" or 8" Schup -- especially if the retail price competed with the C8.  Lots of Refractor Fans back then...

 

Anywho, it's a neat design.  I wouldn't attempt it, though.  Much easier to buy a 6" achro lens, a couple of very good mirrors, and even I could make a folded frac.  But why?  APM (& now S-W) dangled those Big 6 EDs -- short, relatively lightweight, and near CA-free... works for me!



#955 Bomber Bob

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Posted 01 September 2020 - 05:36 PM

Here's a (saner) BB idea:  I kept the 4" F15 3B mirror set sold by Edmund.  IIRC, the Meade 107D has an optical window...  Seems that I could cannibalize the mirror cell & window cell from a 107D, add a longer aluminum tube, and voila -- a sealed small Cass with very good mirrors... 



#956 Terra Nova

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Posted 01 September 2020 - 06:04 PM

Here's a (saner) BB idea:  I kept the 4" F15 3B mirror set sold by Edmund.  IIRC, the Meade 107D has an optical window...  Seems that I could cannibalize the mirror cell & window cell from a 107D, add a longer aluminum tube, and voila -- a sealed small Cass with very good mirrors... 

It seems to me one of the biggest benefits of a true Cass over an SCT or a Mak is it’s open tube and resulting dew-resistance. 



#957 Bomber Bob

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Posted 01 September 2020 - 06:08 PM

True, but down here, the temperatures & changes are mild -- especially for smaller aperture CATs.  My Questar & C5 do fine.



#958 clamchip

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Posted 13 September 2020 - 12:06 PM

This is a fabulous site on "The Building of the 100 inch Telescope" I just finished a book

on the subject. The mirror was rejected and looking at the photo you can see the three layers

and all the bubbles described in the book.

A second mirror was poured in France but cracked so the decision was made to grind

and polish the rejected one, a process that took four years. 

https://www.mtwilson...inch-telescope/

 

Robert


Edited by clamchip, 13 September 2020 - 12:12 PM.

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#959 Terra Nova

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Posted 13 September 2020 - 12:36 PM

True, but down here, the temperatures & changes are mild -- especially for smaller aperture CATs.  My Questar & C5 do fine.

I think the Questar is small enough that most areas it’s in aren’t going to present any significant cool-down issues and the long dewshield forestalls dew formation. I never noticed a problem with either with my Questar. I never even had much of a cool-down problem with my old orange C-5 astro when I had it given it’s thin corrector plate, dew tho was a problem.  However both were more of a problem with the 5” Celestron Mak I had. It’s when you are getting in the realm of six inches or greater apertures, and especially so in the case of a Mak that cool-down becomes a more serious issue. Of course dew is another story. And that is where the open-tube CCs of 6” and larger begin to present a real advantage over Maks and SCTs. Of course the non-moving primary is another advantage.


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#960 clamchip

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Posted 14 September 2020 - 03:45 PM

Mt. Wilson and the fire:

https://mtwilson.z2s...i28b1Cv_jNV0W8o

 

Robert



#961 Terra Nova

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Posted 14 September 2020 - 09:41 PM

Update on Bobcat Fire (1.6 miles from Mt Wilson Observatory):

 

https://www.latimes....son-observatory



#962 Kasmos

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Posted 15 September 2020 - 03:07 AM

I sure hope the observatories survive.

 

I know it's been horrible for so many, but it's also sad to think how many animals have probably died and the accelerated loss of habitat. frown.gif


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#963 steve t

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Posted 15 September 2020 - 06:40 AM

Not to be a downer, but I will be so glad when 2020 is over.


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#964 Terra Nova

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Posted 15 September 2020 - 08:54 AM

Not to be a downer, but I will be so glad when 2020 is over.

Me too! And it had to be a leap year to add insult to injury so we get a whole extra day of the horribleness! tonofbricks.gif


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#965 sunnyday

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Posted 15 September 2020 - 08:56 AM

Not to be a downer, but I will be so glad when 2020 is over.

me too, there is a bug in it.


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#966 Kasmos

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Posted 15 September 2020 - 02:01 PM

Not to be a downer, but I will be so glad when 2020 is over

Sorry,

People were saying that 4 years ago.

I truely can't remember when a new year has been better than the last. 

Debbie-Downer.jpg

What makes anyone think 2021 will be better?


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#967 Terra Nova

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Posted 15 September 2020 - 02:06 PM

Sorry,

People were saying that 4 years ago.

I truely can't remember when a new year has been better than the last. 

attachicon.gifDebbie-Downer.jpg

What makes anyone think 2021 will be better?

All we can do is hope!

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#968 GreyDay

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Posted 15 September 2020 - 04:05 PM

Sorry,

People were saying that 4 years ago.

I truely can't remember when a new year has been better than the last. 

attachicon.gifDebbie-Downer.jpg

What makes anyone think 2021 will be better?

I once asked my Grandmother why old people were always so unhappy with the world? her reply was this, "imagine an hour glass labeled tolerance on the top half, and wisdom on the bottom. The wiser you get, the less tolerant you become"  another favorite was "in a world full of libraries the stupid have no excuse!" my gran was a real rough diamond :)


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#969 steve t

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Posted 15 September 2020 - 04:29 PM

Sorry,

People were saying that 4 years ago.

I truely can't remember when a new year has been better than the last. 

attachicon.gifDebbie-Downer.jpg

What makes anyone think 2021 will be better?

Wow, I didn't expect this to get into name calling



#970 Kasmos

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Posted 16 September 2020 - 12:50 AM

Wow, I didn't expect this to get into name calling

You misinterpreted my post.

The Debbie Downer image was directed at myself in a attempt to add a little levity to my pessimistic statements.


Edited by Kasmos, 16 September 2020 - 01:47 AM.

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#971 steve t

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Posted 16 September 2020 - 06:13 AM

Kasmos - No problem, I must be getting too sensitive in my old agesmile.gif

 

Regarding my post of being glad when 2020. is over. I was thinking of measurable issues that will hopefully be over/resolved by the end of the year  (CV-19, fires on the west coast, election..). 

 

You're correct, no one knows what 2021 will bring, but we can hope.


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#972 Scott99

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Posted 16 September 2020 - 11:40 AM

FWIW hoping the fires go away after 2020 is like hoping Venus cools down or Mars warms up after 2020


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#973 steve t

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Posted 16 September 2020 - 11:46 AM

I would have thought the winter weather would have helped extinguish the fires.

 

I'm tagging out on this topic. 


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#974 Scott99

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Posted 16 September 2020 - 02:46 PM

I hear you Steve, we'll all say a prayer for some early fall rains in CA, I think it's already happening this week in Oregon/Washington, just gotta hope it moves south.


Edited by Scott99, 16 September 2020 - 02:47 PM.

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#975 steve t

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Posted 16 September 2020 - 03:14 PM

Amen to that.




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