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On a F/4 Astrograph.. a FOCAL REDUCER 0.80X after a COMA corrector on a F/4 Newtonian ?

XE1ZLG
16 Sep, 2019 20:42
I plan to do the Next experiment with my Orion 150mm F/4 newtonian..

Use the Skywatcher Quattro coma corrector on to 2" focuser hole after that thread the Orion 0.80X reducer on the M48 thread of the Coma corrector… to my Canon T6.

The plan is to get about F/3.2 on the Newtonian.

Yes .. I know I will have a lot of vignetting..
.but may be the subs will be very short as I am NOT USING any guide on the Eqm-35 PRO..

Any experience will be appreciated  !
Luis Gtz
Edited 17 Sep, 2019 00:08
2ghouls
17 Sep, 2019 18:48
If you already have all this gear, then feel free to experiment, but I don't think the Orion .8x reducer is designed to work that way so I'm not sure what to extpect.  The one I'm seeing specifically says "for refractor telescopes". The only reducer/corrector that comes to mind for Newtonians is the ASA 0.73x, but it's very expensive: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4685_ASA-2-inch-Newton-Coma-Corrector-and-0-73x-Reducer-for-Astrophotography.html
XE1ZLG
17 Sep, 2019 23:12
Yes I know that reducer that would do the job…. the problem is that it needs about 85mm of back focus and the 6 " Orion astrograph only has about 66mm .. that is the reason for try this setup.

I am waiting for both the coma corrector and the reducer.. I plan to test it next weekend if the sky clears…

clear skies … Luis
CrossoverManiac
20 Sep, 2019 02:24
I would suggest using a focal reducer specifically designed for a Newtonian and most focal reducers are not since they're designed for either a refractor or a Cassegraine with a much higher f-ratio than your typical Newtonian astrograph.  There is a combination coma corrector/focal reducer but it is rather pricey.

https://www.apm-telescopes.de/en/optical-accessories/flattener-reducer-correctors/ts-optics-2-newtonian-coma-corrector-0.73x-reducer-astrophotography

There will be some vignetting on the edges of your crop sensor because the fully-illuminated image circle is only 22mm (though it will correct for an image up to 30mm).

However, it is a 0.73x focal reducer so you'll get a bit more out of it than a 0.8x. Instead of an f/3.2, you'd get an f/2.92.  That would have your scope running a close second to a Celestron RASA or a Hyperstar-equiped SCT.

But if you want that 0.8x Orion focal reducer, I suggest getting through amazon.com.  They have a very generous return policy so if it doesn't work out for you, you can send it back and get a refund.
Edited 20 Sep, 2019 04:11
XE1ZLG
20 Sep, 2019 12:34
This is only a Experiment… lowering the focal ratio makes collimation more challenging…. I will try . If this do not get on focus I wll consider a dedicated focal reducer corrector !.

clear skies.
Edited 21 Sep, 2019 17:51
XE1ZLG
22 Sep, 2019 19:50
I tried the setup.. it can not achieve focus because the back focus of the newtonian is too short… I would need to change for a low profile focuser to achieve focus.
Clear skies..

Luis
John_Tucker
23 Sep, 2019 18:18
Luis Marco Gutierrez
Yes I know that reducer that would do the job…. the problem is that it needs about 85mm of back focus and the 6 " Orion astrograph only has about 66mm .. that is the reason for try this setup.I am waiting for both the coma corrector and the reducer.. I plan to test it next weekend if the sky clears…

clear skies … Luis

The link cited above says the backfocus on the ASA corrector/reducer is about 65mm.

I have the TS F2.8 "PowerNewt". Collimation is not that hard, but you have to get the spacing between the corrector and the sensor dead on.
XE1ZLG
25 Sep, 2019 14:17
Hi John ..  I have been looking this Ts 2.8 Hypergraph for a long time..

How fast it is compared to your others Telescopes ?  And how woks visually ?

Luis Clear skies.
CrossoverManiac
25 Sep, 2019 15:14
Luis Marco Gutierrez
Hi John ..  I have been looking this Ts 2.8 Hypergraph for a long time..How fast it is compared to your others Telescopes ?  And how woks visually ?

Luis Clear skies.

I looked into it too.  The f/2.8 hypergraph is just a f/4 astrograph Newtonian with the 0.73x focal reducer/coma corrector I mentioned earlier.  I don't live in Europe, so if I did go for the f/2.8 hyerpgraph, it would just be the focal reducer so I don't have to deal with the headaches of importing an entire telescope and the import taxes that come with it.  I don't know where you live but that might be an option for you unless the 0.73x only works that particular f/4 astrograph (though I doubt it's that picky).
 
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