Off Axis Guider questions

[daz]

Be gentle, I'm feeling a bit fick today!!!

OK, so, I am thinking of off axis guiding - reduce flexure, simplify rig, less weight, etc. etc....

I have two scopes - WO66 and ED80 and want to be able to use either scope. I am also in favour of screwing the train components together, instead of using thumscrews - things are centred, no chance of slipping out and hitting the floor, no flex (or [removed word] all flex) in the train.

That's where I'm aiming!!

Kit:

WO66 (SCT thread on drawtube)

ED80

SX Lodestar guide cam (C-mount thread)

SXVFH9 camera (T thread)

SX Filter wheel (T thread both sides)

WOFFII 0.8 reducer (SCT female thread telescope end, T thread camera end)

Hotech 2" SCA (male T thread on camera end)

Female SCT to Male T thread adapter

What I'm hoping for is to have the following combinations:

WO66 + FFII + OAG + FW + SXVF

WO66 + SCT-T + OAG + FW + SXVF

ED80 + SCA + OAG + FW + SXVF

ED80 + SCA + T-SCT + FFII + OAG + FW + SXVF

So, you can see that the common element is the OAG+FW+SXVF - and as far as I can see, I therefore need it be T-thread on both sides.

The FFII has a focal length of 56mm, the FW is 29mm deep and the chip on the SXV is 17.5mm back. So, the OAG only has 9.5mm to work with!!

The only thing I think is missing is Female T to Male SCT adapter for the last combination, although if push came to shove, I could use the 2" nosepiece on the FFII as normal....

So, my questions (yes, there is one coming )

1. Do my combinations make sense?

2. Is there an OAG t-threaded at both ends but only 9mm thick (the TS one is not T threaded!)

3. Should I use a different reducer with a longer focal point?

4. Am I going round the bend???

Any thoughts welcome

[Psychobilly]

TS one....

Can be adapted for T threads...

Off Axis Guider - only 9mm length - with T2 adaptation - Teleskop-Express: Astro-Shop + Fotografie + Naturbeobachtung

I am waiting for feedback on the EOS direct connect one...

[MartinB]

Ian King would be a good person to talk too Daz. He stocks the TS unit and adaptors and would be happy to have a natter. I think you should forget about the flattener with the H9, you just don't need it. If you want a reducer get the AstroPhysics CCDT67 reducer. This doesn't give any flattening and you can adjust the spacing to give the reduction you want. I used this with a zs66 and an H9 at one time, a great combination. I used mine with a tapered nosepiece but I'm sure there are other ways to go if you want to avoid push fit.

you might get distorted stars in the guider but that isn't a huge problem. When I was using my NS8 and off axis AO guider the guide stars looked dreadful but Maxim was still able to sort out an accurate centroid

[Merlin66]

What about putting the OAG before the FF??

The Lumicon OAG needs about 25mm and the Orion OAG about 35mm; the only narrow one is the Baader unit.

[daz]

Ken - I think the recommendation is not to, at least, what I've managed to read up on!

OK, so removing the FF from the train would solve the immediate problem, I think. It would just mean objects like M45/Rosette would have to be imaged in panes instead of one go...

More thinking

Will hopefully get to look at someone running an OAG at SGL5...

Martin - will do. Good idea

[Merlin66]

Daz,

Not sure where you got the recommendation, but Lumicon use exactly that solution in their Cassigrain OAG; the prism is mounted in front of the reducer lens.

[daz]

From TS actually Ken....

More digging

[MartinB]

What about the AP reducer I mentioned Daz. Wouldn't that fit the bill?

[daz]

Quite possibly Martin. Haven't spoken to Ian to discuss it all as yet.