SCT Collimation Failure: Can I call out the AA

[Tinker1947]

I use a UV/IR filter plus the 6.3f  Focal Reducer, you have either of these.......

I need to pick up on image processing , this was 6 X 300s @ 1600 iso, Guided, Canon 600D modded M101 ended up on the right side of the sensor....

[ChrisLX200]

Make sure you have not over-tightened the corrector plate clamp screws, my 10" LX200 arrived (new) with screws which pinched the plate and only by loosening them did I get round stars and good colimation results.

ChrisH

[Sp@ce_d]

I'm using one of my 314l+'s with a SX/OAG FW taken off the esprit80 which was working fine. There's a Hutech P2 in the nose and a 6.3 reducer inside the moonlite. I've only had this scope since start of March so I'm still getting it set up.

I'm pretty sure this is an optical issue & not guiding/PA but could be wrong. To me it looks like tilt as it runs corner to corner. Having been through the whole alignment with the laser inc. focuser I was a bit surprised this has come out so bad.

Here's a crop of a star from the 30s exposure. The ones in a 300s look the same. both guided.

[Sp@ce_d]

Make sure you have not over-tightened the corrector plate clamp screws, my 10" LX200 arrived (new) with screws which pinched the plate and only by loosening them did I get round stars and good colimation results.

ChrisH

Hmm so how do you tell whats tight enough? Finger tight or palm of hand.. They would keep going as they are. Also are you suposed to loosen the adjusters once the clamp screws are done. The Hutech Video seems to do this?

[ChrisLX200]

Hmm so how do you tell whats tight enough? Finger tight or palm of hand.. They would keep going as they are. Also are you suposed to loosen the adjusters once the clamp screws are done. The Hutech Video seems to do this?

 They only have to be tight enough to stop the plate falling out and prevent any overt movement, I can't descibe 'how tight' because it's done by feel - all I can say is just take up all slack. It's all plastic so there is no sudden 'stop' making it easy to overtighten.

The adjusters (colimating screws?) are a completely separate job.

ChrisH

[swag72]

Have you tried using it without the Moonlight on the back and just using the visual back and the stock focuser?

[Sp@ce_d]

 They only have to be tight enough to stop the plate falling out and prevent any overt movement, I can't descibe 'how tight' because it's done by feel - all I can say is just take up all slack. It's all plastic so there is no sudden 'stop' making it easy to overtighten.

The adjusters (colimating screws?) are a completely separate job.

ChrisH

Thanks Chris.. Yes.. I know what you mean, It hard to describe tightness. I'm pretty sure I haven't over done it but I'll re check. The adjusters I'm talking about are recessed allen screws in the edge of the tube. On Celestrons they seem to push the corrector plate about. There's 4 of them.

[Sp@ce_d]

Have you tried using it without the Moonlight on the back and just using the visual back and the stock focuser?

Not since collimating, as the whole routine is supposed to align the light path as one. However, I think I need to go right back to a minimal config and work forward to find this. Before I fitted the Moonlight I did some test shots with the photo back & reducer. They weren't perfect to my eye, seemed a bit "soft" to what I am used to compared to my fracs but quite reasonable I thought. I didn't mess about as the Moonlite was clearing customs & thought no point until the intended setup was on the scope. Maybe this is flex showing up after collimation & alignment. I'll dig out some subs without the Moonlite to compare again.

[ChrisLX200]

Thanks Chris.. Yes.. I know what you mean, It hard to describe tightness. I'm pretty sure I haven't over done it but I'll re check. The adjusters I'm talking about are recessed allen screws in the edge of the tube. On Celestrons they seem to push the corrector plate about. There's 4 of them.

Ah yes, these are for centralising the plate? Meades don't have these they just have little cork pads. Again, those just need to be barely touching the plate as any pressure at all is going to distort it - then you will have thermal shrinkage to consider which may add to it. Optics need a 'light hand'

ChrisH

[swag72]

Not since collimating, as the whole routine is supposed to align the light path as one. However, I think I need to go right back to a minimal config and work forward to find this. Before I fitted the Moonlight I did some test shots with the photo back & reducer. They weren't perfect to my eye, seemed a bit "soft" to what I am used to compared to my fracs but quite reasonable I thought.

The SCT will seem 'soft' when compared to a frac - I almost had kittens when I saw how large, soft and fluffy the Bahtinov mask spikes were!!! In fact everything will seem soft - That's part of the processing fun (!!)

[Sp@ce_d]

Right.. I forgot I shot this just before I fitted the Moonlite in March. M57 again ok it's a bit low down this time of year but compares with the one I did last night.

Stars are not perfect but it was a lot better!

Right. I think I'll take the Moonlite off and start again.

Phase 1

Collimate with the photo back making sure the corrector isn't pinched.

Star test

Imaging test - make sure it's right

Phase 2

Moonlite will go on

Align using the Advanced Laser technique.

Collimation doesn't get touched. The secondary is removed & only focuser adjustment is made to align

Star test

Imaging test

Anything I've missed or anyone see any flaws with this plan?