Does anyone get elongated stars with an OAG?

[RobH]

Hi all.

I just connected my SXH18/SX FW & SX OAG with a lodestar camera in it to my nice new TMB 80/480, and the stars in the OAG are streaks....not at all round.

I've also noticed this to some extent with different cameras in different OAG's on different scopes.

Does anyone have a solution?

Cheers

Rob

[SteveP]

Rob

I did have this problem when using an Astrodon MOAG with a FSQ 106ED. The elongated stars are caused by the prism not being fully parallel in the light cone and is most common with fast scopes, ie a steep light cone, and large chips. It didn't create a major problem with tracking but occasionally Maxim would get its knickers in a bit of a twist. Interestingly, the same MOAG had perfectly round stars on a slower (f7) scope

Don at Astrodon suggested that I slightly tilt the prism away from the direction of the light by adding slivers (about 8mm x 3mm) of sticky aluminium tape under the leading edge of the spacers which attaches the prism to the MOAG body. Trial and error showed that two pieces of tape were sufficient. Now I have round guide stars again

Why not also give Terry at SX a ring. He may have come across this problem already. I know he uses a fast scope (f5) himself

HTH

Steve

[Helen]

I have this problem with the SX OAG too Rob. It does seem to guide OK - although I have had problems with calibration. A solution would be good.

Helen

[RobH]

It makes sense that it is a tilt problem with the prism, as I mentioned, I've seen it before but not like this....these are definate long lines....no chance of a decent centroid.

Tonight was a complete change of rig combinations, so I expected to be messing around a bit.

I've actually ditched the OAG's for the night, and have the lodestar stuck into the 80mm scope and am using that as a guidescope with no problems.

Subs of NGC 2903 coming in very nicely.....still full of the lurgy, but feeling better being out imaging again

[Ibbo!]

I get the same thing with the brightstar OAG elongated stars

I've not had a problem until tonight

Just reset everything after SGL6 and Maxim had a major tantrum with the guidestar calibration as its taken over 1 1/2 hours for it to provide the red "L" shaped line

now doing subs of ngc3628 at f8 with the 102 Tak

if anybody does have a solution I would love to hear it

Steve

[RobH]

I've had this with the brightstar, Celestron radial, and SX OAG's.

It has been most noticeable at short FL's, and especially with my DSI.

[Ibbo!]

Mmmmm

Things were so bad I contemplated giving the laptop a damn good reprogramming with a large hammer (don't do axes)

The thing that helped tonight was doing a dark frame for the guider (MX716) which I've not had to do before

I'm doing 10 sec guide exposures and the "expletive" guidestar is now round and I'm getting errors of less than a pixel

The mount must have enjoyed its journey to Lucksall and back

Steve