Which OAG?

[pmrid]

I'm setting up a 10"imaging newtonian. And I'd like to guide via an OAG. So the imaging train would be:
MMPC; then
OAG;then
CCD.

Trouble is, the spacings - getting the guide camera and imaging camera parafocal while at the same time keeping the required 55 mm backfocus for the MMPC.

I have an Orion OAG and another one from that crowd in Germany (name presently escapes me - Teleskop somethig I think) and neither works with the cameras I have.

I am using a QHY5 as a guide cam. The sensor sits about 13mm below the black metal lip. And I'm using a QHY10 CCD in which the snsor sits 20 mm behind the beveled front lip.

There's no problem getting the QHY10 properly spaced 55 mm behind the MMPC. But the minimum position in which I can put the OAGs still is about 10 mm to far out for the QHY5.

SO my quest now is to find an OAG that gives me the flexibility I need. I suppose one of those super-narrow-bodied ones will be the best choice. I think they come in at about 9 mm - but after you add any adapters required for connecting cameras, that probably will blow out.

Any ideas/suggestions would be welcome.

Peter

[rustigsmed]

Hi Peter,

you should be able to easily find space with thin OAG's such as http://www.teleskop-express.de/shop/product_info.php/info/p641_Off-Axis-Guider---only-9mm-length---with-T2-adaptation---Special-Offer.html I would have thought? I was turning my mind to this today as to whether I should use my MPCC or RCCI for my new CCD. You could add a 10mm spacer then perhaps a 17-23 variable spacer on the MPCC side of the OAG eg http://www.teleskop-express.de/shop/product_info.php/info/p4512_TS-variable-M48--2--filter-thread--extension---17-23-mm.html

Camera 13mm - t2 adaptor 2mm - tsoag9 9mm - m48 10mm spacer - 17-23mm spacer @21mm - MPCC = ~55mm

Russ

edit: I always get confused trying to calculate these things, email TS they are helpful finding solutions.

[glend]

Peter if you'd like to sell your OAGs that you have and can't use, just PM me their details, if they can fit my DSLR I might be interested.

[RobC]

Peter,

Have a look at he Celestron OAG. It is designed for the parfocal back focus you require for the QHY5 And MMPC.

http://www.celestron.com/browse-shop/astronomy/astroimaging-accessories/guiders/off-axis-guider

Cheers

Rob

[codemonkey]

I can't vouch the spacing etc as I only use a frac, but I can vouch for the Celestron: very nice piece of kit, only which I'd bought one earlier.

[pmrid]

Thanks guys. I have bought a slimline (10.5 mm) Orion. But I can see what you mean about the Celestron. Funny though, I see that the Celestron has a female thread on the CCD side. Pretty well every camera I know has a female thread on the front.
Peter

[Slawomir]

Hi Peter,

I had slimline OAG from Orion and it is a fine OAG but IMO one drawback with this particular design is that too many parts in it are held by setscrews (possible flex). A wiser than me friend of mine improved rigidity of the OAG very simply by replacing some of the tiny setscrews with solid screws.

Just my two cents.

[Eden]

I second Slawomir's comments above. The unit can become fiddly and unstable after being adjusted several times; in particular the guide camera attachment, which needs to be moved up or down in order to achieve guide camera focus. Replacing the setscrews with something better is a wise move, for sure.

[pmrid]

Thanks for the heads-up Brett and Slawomir. I'll take that advice as soon as the device arrives.
Peter