OAG & Orion ED80T CF

[DonB]

I have an Orion ED80T CF and am getting a Sony A6000 mirrorless camera and want to get an OAG for autoguiding.

The max backfocus on the scope is 127mm, the flange focal distance on the camera is 18mm. Unfortunately those are all the dimensions I've been able to find.

I've found 9mm thin OAGs, 27mm OAGs but have no idea what would be the best fit. Manuals for OAGs with dimensions seem scarce.

I understand that the imaging and guide camera must be at the same light path length, but without the specifications on the OAG can't see how to determine what that length should be.

How does one work this out to determine which OAG would be the best fit for this scope & camera and what spacers are needed? Any other considerations?

The Lumicon Easy-Guider (http://www.lumicon.com/store/p/170-Newtonian-Refractor-Easy-Guider-2.aspx) looks like a substantial unit which gets some positive comments, as do several others like the TS OAG9 (http://www.teleskop-express.de/shop/product_info.php/info/p641_Off-Axis-Guider---only-9mm-length---with-T2-adaptation---Special-Offer.html). What appears to be a larger prism size on the Lumicon is attractive.

Any suggestions or comments?

:thanx:

db

[traveller]

Hi Don,
IMHO, OAG for an ED80 is a bit of overkill. I have (and recommend) a simple 50mm finder guider. I basically set up the scope, polar align. Then use the 50mm finder guider and PHD to guide.
I am currently experimenting with an OAG set up with my C8 and f6.3 reducer, has been frustrated by weather in Melbourne, so cannot comment on the OAG path. But for a short FL of an ED80, a simple finder guider would be sufficient.

Bo

[DonB]

Hi Bo,

Thanks for the helpful reply. My concern with the guidescope is alignment. It seems I would have to check it each time I set up, and getting the alignment spot-on could be a bit of a hassle. (Mind you, I haven't done it but looking at the brackets it seems that way)

The OAG seems simpler do deal with although finding a guide star may be harder.

I'm not in a rush so will continue to gather info for a while.

Cheers,

db

[Amaranthus]

Don, I use an Orion TOAG with a 0.8 FR on my ED80T CF, and it works brilliantly, with no problem in bringing it to focus. If you have a sensitive guide camera (I use an ASI120MM) then finding stars is no problem at all.

[DonB]

Hi Barry,

Thanks for the reply, that's good news! I was wondering about the pixel size on that camera.

When you use the NEX-3 with the TOAG on the ED80T what adapters & spacers do you use?

[Amaranthus]

I use the Vello T-mount adapter: http://www.bhphotovideo.com/c/product/839140-REG/vello_la_nex_t_lens_mount_adapter.h tml

Gives me a perfect 55mm spacing from the Sony NEX-3 sensor to the TV 0.8 FR once the TOAG width is accounted for. I also use my CCD with it, and with the filter wheel and OAG I require no additional spacers. At the OAG end, I use a 5mm spacer for this setup.

[DonB]

Thanks Barry, useful info.

[traveller]

I haven't found alignment to be an issue, esp with the relative wide field of ED80. I use a 8x50 Finder scope and once the polar alignment is set, I switch over to the 50mm finder guider and guide with phd. I had some success with this approach for 5 mins of guided exposure. http://www.iceinspace.com.au/forum/showthread.php?t=126010
Bo

[Slawomir]

Hi Don,

I wholeheartedly recommend you to use an OAG with this scope; I had very good results using OAG with this scope and imaging with a 0.8 reducer.

At first I tried guiding with a 50mm guide scope, but had problems with flex. IMHO focuser and carbon fibre tube in ED80T CF are not that great and there is even a bit of movement between focuser and the tube. I noticed this issue with movement in two ED80T's. Optics are great though. I used epoxy cement to secure carbon tube in the focuser, and I am also using additional ring to hold the carbon tube firmly in place.

So, from my experience with this scope, OAG all they way :-)

[DonB]

Thanks Bo, I'd say more than 'some success' with that image. Very nice.

And thanks for sharing your experience Slawomir, very useful info.