RC6 - Is this a Collimation or Tilt problem?

[dugnsuz (Doug)]

Hi all - RC Newbie here looking for some advice regarding what’s going on with my newly acquired RC6

Please have a look at the attached images - the centre star seems to have nice concentric circles around it (?collimation ok), but the edge stars are misshapen on left and right of image (?tilt)

? What problems am I looking at ?

Cheers
Doug

[Todo43 (Lachlan)]

Unfortunately I don't have an answer for you but I am very impressed by the size of your stars. I have just started using a 6RC and am struggling to get really small stars like you. Granted I am using a 533MC Pro so obviously the broadband will make them huge, and the suitability of the camera isn't perfect for the scope but it is an interesting observation. Well done!

[dugnsuz (Doug)]

Originally Posted by Todo43

Unfortunately I don't have an answer for you but I am very impressed by the size of your stars. I have just started using a 6RC and am struggling to get really small stars like you. Granted I am using a 533MC Pro so obviously the broadband will make them huge, and the suitability of the camera isn't perfect for the scope but it is an interesting observation. Well done!

Hi Lachlan - images are from my 3nm Ha filter, so that’s why they’re that small, the RGB stars bloat up real quick!
Doug

[atalas]

Hey Doug

What size chip you shooting with? looks like you need a corrector or If your using one spacing not right.....bit of tilt as well.

[Nikolas (Nik)]

Seems like a corrector issue and incorrect spacing rather than collimation. If there is tilt it would be only on one side of the image not all the corners

[atalas]

Originally Posted by Nikolas

Seems like a corrector issue and incorrect spacing rather than collimation. If there is tilt it would be only on one side of the image not all the corners

Yes true but I would add that If there was no tilt and just corrector issue I would expect all 4 corners to have identical distortion.

[dugnsuz (Doug)]

Originally Posted by atalas

Hey Doug

What size chip you shooting with? looks like you need a corrector or If your using one spacing not right.....bit of tilt as well.

2600MM APS-C sized sensor

Originally Posted by Nikolas

Seems like a corrector issue and incorrect spacing rather than collimation. If there is tilt it would be only on one side of the image not all the corners

Incorrect spacing? As in extension tubes?? (using 2 tubes - total of 75mm length) as per pic

Doug

[atalas]

Doug I take It your not using a field flattener? with the APS-C size chip you need one but with the APS and smaller sizes like the 8300 chip you would not....this is my experience with these GSO RC's.

So, If this is the case then you will need one to flatten the field more(the spacing for these is generally 55mm.....lots of info on this If you Google.

(On the tilt issue) These RC 6/8/10(non Truss) have the focuser mounted on the mirror cell and by looking at the photo of your rig I'm sure It's enough weight on the focuser to cause some tilt.....dumb design that GSO should of corrected by now like they did with the Truss models.

[atalas]

Also looking at your image again I think you might have some slight pinching of the main mirror....stars look slightly triangular another trait from the GSO factory! these scopes come well boxed and really don't need to have the to main mirror clamped down so tight for shipping.

[dugnsuz (Doug)]

Originally Posted by atalas

Also looking at your image again I think you might have some slight pinching of the main mirror....stars look slightly triangular another trait from the GSO factory! these scopes come well boxed and really don't need to have the to main mirror clamped down so tight for shipping.

Thanks Louie - so, you think those triangular stars are a symptom of mirror pinching rather than a collimation issue?

If so, do I have to take the scope apart to fix?

Cheers again
Doug

[atalas]

No your main problem is field flattening! sought this out first and then look at the other two issues mate.....one step at a time.

First tell us If your using a field flattener and then we can move on from there.

[dugnsuz (Doug)]

Originally Posted by atalas

No your main problem is field flattening! sought this out first and then look at the other two issues mate.....one step at a time.

First tell us If your using a field flattener and then we can move on from there.

I’ll put the hammer away for now then!

No flattener - was looking at the TS flattener before last night’s session got me worried te collimation
https://www.testar.com.au/collection...attener-for-rc

Doug

[atalas]

Man cost never stop..... should be good though and back focuser stated at 109mm....you'll be getting rid of any extension rings I'd say.

[dugnsuz (Doug)]

Originally Posted by atalas

Man cost never stop..... should be good though and back focuser stated at 109mm....you'll be getting rid of any extension rings I'd say.

The astro money pit continues to fill!


Few more pics - center of field, de-focused stars either side of focus (star close to Canopus hence big diff spike)


Any thoughts re collimation and star shape (pinch artefact)?

[atalas]

Collimation looks good with the second pic....first pic showing slightly off but that's probably due to focuser shift moving off centre where there's more field curvature.

NoteI'm not a optics expert) but don't open Fresnel rings so much because It's harder to see any defects in optics with the light spread out to far.

Having said that I don't see any issue in the mirror.....looks good.

What you can do while waiting for a flattener is pull the main mirror cell out from the back and take some pressure off the mirror clips and re collimate.

[dugnsuz (Doug)]

Originally Posted by atalas

Collimation looks good with the second pic....first pic showing slightly off but that's probably due to focuser shift moving off centre where there's more field curvature.

NoteI'm not a optics expert) but don't open Fresnel rings so much because It's harder to see any defects in optics with the light spread out to far.

Having said that I don't see any issue in the mirror.....looks good.

What you can do while waiting for a flattener is pull the main mirror cell out from the back and take some pressure off the mirror clips and re collimate.

Thanks for your advice Louie - much appreciated.
Doug