RC6... Collimation, here I come!

[Ags]

I have been thinking about a scope acquisition for my HEM15 mount, as a replacement for my C6. I thought about a planetary specialist  scope like a Classical Cassegrain 8", or a small photo newt at the other end of the scale, but in the end I went for a Ritchey Chretien 6"... It seems like the ideal scope to go after galaxies and planetary nebulae. I only have moderately small chip (ASI485) so I haven't purchased a tilt adjuster for the focuser - I will probably add that later. I know RC collimation is a famously fiddly thing. I hope to get close enough with a cheshire and finish the process with star testing. I may end up buying more collimation mcguffins before I'm through!

I thought I would pick up the RC6 for galaxy season. I'm curious to see if the scope produces better stars than the C6 did, and if the scope is less vulnerable to wind than the C6 and it's obligatory dew shield.

Interestingly, the scope gives one degree FOV with my ES60 20 mm eyepiece, so I hope it will also work a DSO scope. Not too sure it will work on planets, but I hear RCs perform OK on the Moon at least.

Edited April 1 by Ags

[Adreneline]

13 hours ago, Ags said:

I know RC collimation is a famously fiddly thing. I hope to get close enough with a cheshire and finish the process with star testing. I may end up buying more collimation mcguffins before I'm through!

You probably don't want to hear this but I found I couldn't get a satisfactory collimation with the stock focuser unit - too much droop from the draw tube. I upgraded to a Baader DST and found collimation to be much easier and all done with a Baader laser collimator and a star test. I sold my RC purely cos' it was getting too much of a lift for my ageing hands - I was frightened to death I'd drop it one cold night. Like so many astro things I now regret selling as the images it produced when used with an ASI294MC (also sold  ) were very good indeed.

[dweller25]

16 minutes ago, Adreneline said:

You probably don't want to hear this but I found I couldn't get a satisfactory collimation with the stock focuser unit - too much droop from the draw tube.

I also had this issue !

So you may need the tilt plate.

Edited April 2 by dweller25

[Ags]

Just now, Adreneline said:

You probably don't want to hear this but I found I couldn't get a satisfactory collimation with the stock focuser unit

No I don't want to hear that! But I can get the GSO tilt adjuster which should resolve the issue. Also I am not hanging anything heavy off the focuser - just an uncooled camera, a reducer and no filter wheel etc.

13 minutes ago, Adreneline said:

I now regret selling as the images it produced when used with an ASI294MC (also sold  ) were very good indeed.

Say more things like this

[Ags]

It should arrive on Monday! I hope this scope will also work well for spectroscopy - I have a grating flying over with a relative later in the spring.

[Clarkey]

I have an RC8 which I am a fan of. Collimation is a bit tricky, but once set it hardly moves. I probably only collimate once a year, even when it was regularly moved. With a small chip and the RC6 I think collimation will be fine.

FWIW, I did change the focuser on mine, but I was using a cooled mono camera with filter wheel. Getting the primary mirror and focuser aligned on the same axis is fairly critical for good collimation. Fortunately mine was very nearly spot on. (I purchased the tilt plate but never needed it). If I get the secondary perfectly aligned with the centre of the focuser, I just need to tweak the primary with a star test.

I have a recent M101 in the deep sky imaging section which will give you an idea of what the scope will do.

[Ags]

I have some trepidations about the collimation - I got it at a nice discount as a customer return from FLO so perhaps the previous owner hit a collimation wall?

[Clarkey]

Hopefully not. Although a little tricky, I think the fear of RCs is worse than reality - unless you get a really bad one. My collimation is based on the DSI guide. I also got some good information from @fwm891, which I may need when I clean the mirrors in the summer.

[Ags]

The first rule of cleaning mirrors is Don't Clean the Mirror  

[Clarkey]

On 03/04/2024 at 23:28, Ags said:

The first rule of cleaning mirrors is Don't Clean the Mirror

Second rule: if you can't see a reflection you are either a vampire or you need to clean the mirror😁

[Ags]

My pet RC "Archie" arrived today. First impressions are favorable, it seems solidly and simply made. The focusser looks quite reasonable, although I know it may be one of the most replaced focussers in the hobby... The dust cap is a bit flimsy, it looks more at home on top of a yoghurt pot! Being such a back-heavy scope, they could have ran the dovetail all the way to the back of the tube. It looks like I can put a dovetail on the other side, which would be a useful carry handle.

Not a fan of collimating the secondary with an allen key over an exposed primary mirror!

From the fractured polystyrene, it seems it had a few bumps on the way to me. Hopefully I can check the collimation properly over the weekend, but a rough "hall of mirrors" check looking down the tube suggests there's nothing extremely wrong with the alignment.

[Ags]

Had some patchy clear skies after midnight, enough for a star test. I'll need to work on the collimation clearly. 

[Ags]

Tried out my FLO Premium Cheshire Collimator.

Before:

After:

 

Aligning the primary has pushed the secondary out a bit again, I'll do another iteration tonight. So far it looks like the focusser is reasonably aligned...

[Ags]

Not sure I can get closer with a Cheshire. Tonight the stars!

[dweller25]

Looking good 👍

[Ags]

Tested on a neighboring tree, view looks sharp at 150x, less so at 225x, but it’s hard to judge by day with the razor-thin depth of focus. If the weather stays like this, I should be able to do another star test tonight.

[Ags]

Tonight the stars were just about visible through several layers of cloud, so I could do a star test. A defocused star looked almost symmetrical, but the became triangular closer to focus. This means, i think, that I was too enthusiastic in tightening the screws on the primary mirror. I I'll back these off tomorrow and try again.

[Ags]

Regretting I wasn't braver last night. I should have had a go at those collimation screws last night!

[Ags]

I have given up on the Cheshire as a collimation aid. It requires common sense and judgement, which isn’t something I’m noted for! I have switched to using my camera, and made good progress tonight. Collimation is not perfect yet but it is a lot closer than ever.

[Ags]

I think I have it close enough for a first photo. Stars are round and pointy on axis, I may need to do a few iterations to clean up the corners but I draw the line at collimating in a fine drizzle!  The clouds got too thick to check the corners  after tightening the locking nuts on the primary, but it was looking ok at last check.

[Ags]

After last night's photographic collimation, I stuck in the Cheshire again at lunch time to see if it agreed with the camera. The Cheshire is saying the scope is way out of collimation... I think the issue is the focusser is not square and it is joined to the primary mirror, so the Cheshire will always give a wrong answer. However, I think the Cheshire is useful for collimating the secondary at least.

[Clarkey]

Mine is the same. I use a Reego for the secondary and star test for the primary. Cheshire or Laser is well off.

In theory once you have the collimation spot on you could add a tilt corrector to get the secondary on the same axis as the primary. You could then use a Cheshire. However, I only collimate about once per year so it is not that critical.

[Ags]

I took the scope out to align the finder today, and gave it a bit of a bump… I hope the collimation is still ok 😐

On 18/04/2024 at 20:51, Clarkey said:

Mine is the same. I use a Reego for the secondary

TS sell the same thing, never seen it called a Reego before. It looks however that I can collimate both mirrors with my camera, and I strongly prefer collimating directly with the intended imaging device. The end result is the end result, if you see what I mean?

[david_taurus83]

Are these the same as an SCT where you only adjust the secondary? 

Edited April 20 by david_taurus83

[Ags]

No, you ideally adjust the primary, secondary and the focuser! But with a smaller chip like mine you can get away with mostly adjusting the primary.