ETX90 for CaK Work

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marktownley
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ETX90 for CaK Work

Post by marktownley » Mon Apr 04, 2016 1:33 pm

I was having a clear out this morning and selling some bits and pieces second hand and was going to sell my ETX90 but couldn't bring myself to do it.

Have I read somewhere that a reflector like this has no spherical aberration or I am just hoping?

I tried my 85mm Beloptik tri-band ERF and it fits really nice in the ETX90 screw on dew shield, might give it a try when the sun is out.

Anybody any thoughts? Valery?

Thanks

Mark
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Valery
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Re: ETX90 for CaK Work

Post by Valery » Mon Apr 04, 2016 5:56 pm

Sell it and use your TAL100 !


Valery
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Re: ETX90 for CaK Work

Post by marktownley » Mon Apr 04, 2016 6:07 pm

Ha ha ha! Fair enough! :D
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Re: ETX90 for CaK Work

Post by marktownley » Tue Apr 05, 2016 6:03 am

Hopefully should be a bit of sunshine today, I have it all set up ready so will give it a quick blast...
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Derek Klepp
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Re: ETX90 for CaK Work

Post by Derek Klepp » Tue Apr 05, 2016 11:32 am

One things for sure Mark you,ve got to appreciate Valery,s honest replies.

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Re: ETX90 for CaK Work

Post by marktownley » Wed Apr 06, 2016 3:55 pm

Derek Klepp wrote:One things for sure Mark you,ve got to appreciate Valery,s honest replies.
Lol, I know, I like them :D

I did try earlier today and the results were dog awful! Won't be using this. At least i'll be a few quid up selling it ;)
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Re: ETX90 for CaK Work

Post by mdwmark » Thu Apr 07, 2016 6:10 am

Hi Mark,
I don't think that scope is corrected that far down in the blue. If the AR is a standard TIO2,SIO2 4 layer then it will be absorbing a lot below 400nm.
I have seen them used at Ha but not at K-line. That my be why it didn't look good when you tested it.
Mark W.

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Re: ETX90 for CaK Work

Post by marktownley » Fri Apr 08, 2016 8:01 am

Thanks Mark! Definitely not well corrected as the following image testifies. Very interesting about the coatings too, makes perfect sense as I had to rack the exposure right up, and also fits in with similar findings which i've had with my Meade AR5 refractor at 393nm in terms of having to get the exposure time right up. Also backed up with my observations visually with my Meade series 4000 plossls giving dimmer views with a Daystar CaH I have been testing compared to brighter views with Tele Vue plossls of same focal length. I wonder if the TV are using MGFl2 coatings compared to the TiO2 of the Meade?

Anyway, a view through the ETX90... (80mm aperture) pretty yuck I think!
etx90 cak.png
Compare this to the same area with the ED80 stopped down to 60mm
ar12528-cak-bw-60mm.jpg
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