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PostPosted: Sun Dec 10, 2017 4:25 pm 
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Joined: Tue Dec 05, 2017 11:53 am
Posts: 501
But just how good are Acromat scopes

I don't want an APO

thanks

http://www.opticstar.com/Run/Astronomy/ ... 10_1_1_245

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Celestron 8" Edge HD Evolution, Esprit 120mm triplet, 72mm APO, Sky Tee 2, 6" reflecting scope, William Optics Binoviewer, Quark Daystar Ha Chromosphere on 72mm ED, LVW8mm eyepiece and Celestron 19mm Axiom, matched W.O 10 and 20mm, and a few others, D4s, D810,

For info, I am Autistic, Aspergers, ADHD, therefore if I come over as a little "short" on occasions it is not intended, thank you


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PostPosted: Sun Dec 10, 2017 4:29 pm 
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Joined: Mon Jan 18, 2010 9:25 am
Posts: 5298
They are excellent if long focal ratio.
Preferably f/15 but f/10 also.
But they must be good quality.

I have excellent 120mm f/8.3 and smaller f/14 or f/15.

Skywatcher may be O.K.

The Russian Tal 100mm f/10 is supposedly good.

The Pentax 100mm f/12 is unbelievably good.
135mm f/16 Merz excellent.
Cooke 150mm f/15 excellent.
Harvard 9.5 inches f/12 also good.
Northumberland 12 inches f/18? also excellent. But the new objective probably special glass.

Horace Dall ~108mm f/30 camera obscura objective maybe the world's best.

What size do you want?

Regards,
David


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PostPosted: Sun Dec 10, 2017 5:11 pm 
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Joined: Fri Dec 03, 2004 9:58 pm
Posts: 3547
Location: Wellingborough
Hi Skyhawk. There seems to be a problem with the link you gave. Did you mean this one:

http://www.opticstar.com/Run/Astronomy/ ... 10_1_1_245

regards,

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Brian
52.3N 0.6W
Wellingborough UK.

254mm LX90 on Superwedge, WO ZS66SD, Helios 102mm f5 on EQ1, Hunter 11x80, Pentax 10x50
ASI120MC Toucam Pros 740k/840k/900nc mono, Pentax K110D
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PostPosted: Sun Dec 10, 2017 10:11 pm 
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Joined: Mon Jan 18, 2010 9:25 am
Posts: 5298
Thanks Brian,
I couldn't get it to work.

Regarding chromatic aberration.
A 3 inch f/9 doublet refractor.
4 inch f/12
and 5 inch f/15
are reckoned to be CA free.

However, using the stricter Conrady limits it would be.
3 inch f/15
4 inch f/20
and 5 inch f/25.

However, in the real world a Tal 1000mm f/10 is reckoned to be very good.

I have no idea what size is intended.

Weight, portability, fixed mount or not are all important especially as we get older.

Regards,
David


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PostPosted: Mon Dec 11, 2017 10:48 am 
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Joined: Mon Jan 09, 2006 11:05 am
Posts: 5275
Location: Lancashire
APO refractors are expensive, but no mention has been made of the cheaper semi-apos.
I have a semi-apo CELESTRON 80mm/f.7.3 refractor and it gives superbly sharp results. This particular model isn't produced now, but there are equivalents out there.

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PostPosted: Tue Dec 12, 2017 10:08 am 
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Joined: Tue Dec 05, 2017 11:53 am
Posts: 501
Thanks all

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Celestron 8" Edge HD Evolution, Esprit 120mm triplet, 72mm APO, Sky Tee 2, 6" reflecting scope, William Optics Binoviewer, Quark Daystar Ha Chromosphere on 72mm ED, LVW8mm eyepiece and Celestron 19mm Axiom, matched W.O 10 and 20mm, and a few others, D4s, D810,

For info, I am Autistic, Aspergers, ADHD, therefore if I come over as a little "short" on occasions it is not intended, thank you


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