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Old 05-04-2013, 09:14 PM
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coldlegs (Stephen)
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Adding a barlow to an ONAG with an MPCC on a newt question

Yep. I've got an ONAG with a baader MPCC coma corrector attached to a QHY10C sitting on a 10" F5 DIY serrurier truss (R.F Royce primary) with about 25mm backspace left. My question is is it possible to keep that lot and put a 2X power mate on the front and not have the MPCC over correct the image? Are there any ONAG users here who have tried please let me know? I would have a wild shot at it myself but the damn clouds are back!

Cheers
Stephen
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Old 06-04-2013, 12:14 PM
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LightningNZ (Cam)
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Would you even need the MPCC after doubling your focal ratio? There must be someone in your local area with a 2" barlow you could try for a night?
-Cam
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Old 06-04-2013, 02:11 PM
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PRejto (Peter)
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I just brought back an ONAG + Astrophysics 2" Barlow after visiting the USA. The AP barlow screws directly onto the scope port of the ONAG so it goes right into the focuser. My camera - using a T-thread adapter - screws directly onto the imaging port of the ONAG.....the distance seems just about correct to give me f15 from my TEC140.

Unfortunately I was misled by a statement on the spec page of my ST-i guiding camera. The page indicates c mount, when in fact the threads are actually M28.5 female (1.25" filter threads). I bought a c mount adapter to fit the guider to the ONAG and of course it doesn't work. Blue Fireball (in California) makes an adapter (T-03) that will go from 28.5 to T-thread female.

I also found that I can mount my Moravian G2-8300 camera such that it does not impede the guide camera stage at all. To keep the camera from touching the TEC140 nosepiece clamp I am using a Baader click lock extension tube.

Have I tried it yet? No....clouds, rain and more rain, but I will test this ASAP, without the guide camera if necessary just to find focus.

Peter
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Old 06-04-2013, 07:31 PM
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coldlegs (Stephen)
Chopped its rear end off!

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"Would you even need the MPCC after doubling your focal ratio?"

Doubling doesn't quite get rid of the coma. It's close but no cigar. If I use the Televue "big barlow" which I've also got and ditch the Baader corrector I'll have an extra distance of about 86mm to the ccd which according to the Televue graphs will give me a focal ratio of about F15. That will probably do for some DSOs like M104 etc. It still won't get me F10 but I may have to live with that.
Cheers
Stephen
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