Collimating a GSO RC6 - Issues!

[jjosefsen]

I wanted to come back here and let you know how I am getting on with the RC now that I finally had a clear night to test, albeit under a 100% illuminated moon.

This is a quick 2 panel Ha image of NGC 7822 aka Sharpless 2-171, with almost 2 hours on each panel, and as mentioned under a full moon.

Quick and dirty process with a bit of Deconvolution, Noise reduction and a stretch.

 

In the end I didn't  quite go all the way as @davies07 suggested, and remove the secondary mirror and use the disc method.

I collimated using the REEGO Pro and MoR module, but the information you provided gave me the understanding of what was going on, and what I needed to fix.

This was particularly helpful as TS Italia has still not released a manual of how to use the MoR, but basically the same principles as your fine documentation.

I didn't even fine tune on a star for this image, so there is maybe still a little room for improvement, but I was desperate for some data after months of clouds.

 

Again thank you for the assistance, it was/is much appreciated!

 

//Clear skies, Johannes

Edited December 21, 2021 by jjosefsen
missing words

[Adreneline]

15 minutes ago, jjosefsen said:

This is a quick 2 panel Ha image of NGC 7822 aka Sharpless 2-171, with almost 2 hours on each panel, and as mentioned under a full moon.

Glad to see you finally got the chance to try out the RC. I would be well pleased if that was my image .

Adrian. 

[Mike_]

Hi,

     Having spent many hours trying to collimate my RC6 I found the 2" focus aperture (draw tube?) had issues. If I place an autocollimator in it, the secondary mark is off centre. Using a Cheshire with 2" to 1.25" adapter its in the centre, a laser would return down the centre also. (both of these failed the star test) Placing the camera assembly in it, using the collimation where the mark is off centre was actually the correct one. If I collimated so everything was in the centre the star test would result in oblong out of focus stars. This has driven me nuts for a month, I emailed GSO and they said the primary to secondary mirror should be 286mm. Nice to know but impractical to measure even with a 3D lidar (tried that). - While using the autocollimator I noticed if it was inserted with slight slide pressure (same as camera weight?) everything would be spot on in the centre. It still isn't brilliant, the back focus maybe out since Im also using a 0.67x reducer which is more like 0.64x, or 883mm - No spacer rings are used between scope and focuser. A 5mm ring Ill test after the reducer. Image of M45 attached with the current collimation. Camera is the ASI178MC. It helps to print a set of concentric circles to act as a reference when bench collimating the RC. - After initial Cheshire secondary mark alignment, Laser primary, check with Cheshire and finally the autocollimator. The autocollimator will show the circle set reflecting back. Annotated images from the various tools attached. - Still work in progress...

Update: The ASI CCTV Lens in its holder inserted into the 2" focuser with ImageJ and the concentric circles plugin shows the alignment, shame this doesnt run on a realtime video feed. Ive asked the author of AstroDMX if the reticle position can be changed for this purpose. 

Edited January 17, 2022 by Mike_
Added concentric circles example.

[teoria_del_big_bang]

Having just acquired an IOptron RC6, through an impulse buy, I have spent most of today reading up on what I need to do to get this scope imaging.
And to be honest I am now a bit scared and thinking maybe this scope is beyond me.

So the scope is cheap fr what it is but what scares me is how much more cost and time I need to put into this to give me good images.

• Difficulties in collimating.
• Stock focusser weak and poor design with the  focuser tube is attached to the primary mirror cell.
• In the description for this scope it says the RC optical design delivers coma, spherical and chromatic aberration free results, perfect for color or monochrome imaging and as such did not expect to need to add a flattener or reducer to the optics but most of what I have read so far suggests you need to use one.

So my major worries are:

• I do not have lots of experience with collimation, I have collimated newts but I think these are in another league regarding difficulty in collimation.
• If the focusser is not up to job then that needs changing.
• Do I need a flattener or reducer, and if so which is best ?
• I also understand that a tilt adjuster for the focusser is a good idea so once the scope is collimated you can adjust  out any tilt.

So whilst a lot of this does not necessarily faze me I do worry that I am throwing far more money at it than the cost of a the scope  would cost new. Hence to add all the above refinements the £400 scope then becomes a £1000 scope.
 

Are my worries justified and would I need the upgraded focusser, tilt adjuster and flattener / reducer ?

Steve 

[vlaiv]

2 minutes ago, teoria_del_big_bang said:

I do not have lots of experience with collimation, I have collimated newts but I think these are in another league regarding difficulty in collimation.

I did not have heaps of experience with collimation when I gave it a go on my RC - and it was just usual stuff - find good tutorial and follow the steps.

Things behave the same - tighten / loose screws and observe what happens. Only difference was that I used camera instead of eyes to judge changes.

4 minutes ago, teoria_del_big_bang said:

If the focusser is not up to job then that needs changing.

I did change mine - but that is just because I really prefer threaded connection. At first - I used stock focuser and it was ok, but in the end decided to get an upgrade.

Try it first - it is not poor - maybe you'll find it to be sufficient for your needs.

5 minutes ago, teoria_del_big_bang said:

Do I need a flattener or reducer, and if so which is best ?

No you don't. I use my RC8 without flattener / reducer and it works fine up to 4/3 sensor. Maybe even APS-C would work, but I have suspicion that I would look into field flattening for such sensor size in 8" version.

With 6" version, since it is F/9 - maybe things are the same and maybe APS-C will make flattener more mandatory.

There are three options that people use:

1. Flattner without reduction

2. Reducer without flattening (or small amount of) - usually used is CCD47 / CCDT67 (first is Chinese knockoff and second is original - AP reducer for F/8 and slower systems with flat field).

3. Combination. Here I've heard that Riccardi x0.75 FF/FR works good and I think people tried other but I have no idea if there is preferred one. I will at some point try TSRED2 x0.79 to see how it works.

Just bare in mind that if you are using 2) - CCDT67 - although it works as x0.67 - depending on the sensor size - you won't be able to utilize full reduction. Field is corrected to about APS-C size so 28mm, maybe 30mm (this is 8" version - 6" maybe even less although given it is F/9 - it might be the same) - so if you reduce it - you might end up with corrected field smaller then sensor size.

4/3 sensor for example needs x0.72-0.75 reduction and more than that starts showing corner star aberrations.

In any case - nothing preventing you to just go without anything - I use mine like that most of the time.

12 minutes ago, teoria_del_big_bang said:

I also understand that a tilt adjuster for the focusser is a good idea so once the scope is collimated you can adjust  out any tilt.

I did not have issues with that, but yes - tilt adapter can be useful, much like with any imaging setup if you happen to have tilt. Here it's not guaranteed that you'll have it - so do collimation first if needed and only think about it if you end up seeing tilt in your images.

[Clarkey]

8 minutes ago, teoria_del_big_bang said:

And to be honest I am now a bit scared and thinking maybe this scope is beyond me

Don't be. I felt similar when I got my RC8. Collimation is tricky, but once sorted it is relatively simple. I now have my own method which works quite well. I collimate the secondary first (lining the centre spot reflection with the centre of the focused draw tube. I use a Reego, but you could probably do it with a Cheshire. I then align the focused directly with the centre of the secondary to get a near alignment. Once I have done this I use a star test (or lights on the M6 a few miles away also works) to get the primary collimated accurately.

WRT a reducer /flattened you will probably be ok without. I use my RC8 without a reducer or flattener and it is fine. I do have a CCD67 which is good, but not needed. As for the focuser, mine was iffy and I replaced it. However, it was better than many so you might be ok.

Work with it. I think they are great scopes.

[teoria_del_big_bang]

Thanks @vlaiv that gives me a lot more confidence and sounds a better idea to try what I have and then upgrade as I feel necessary.

Steve

[teoria_del_big_bang]

2 minutes ago, Clarkey said:

Don't be. I felt similar when I got my RC8. Collimation is tricky, but once sorted it is relatively simple. I now have my own method which works quite well. I collimate the secondary first (lining the centre spot reflection with the centre of the focused draw tube. I use a Reego, but you could probably do it with a Cheshire. I then align the focused directly with the centre of the secondary to get a near alignment. Once I have done this I use a star test (or lights on the M6 a few miles away also works) to get the primary collimated accurately.

WRT a reducer /flattened you will probably be ok without. I use my RC8 without a reducer or flattener and it is fine. I do have a CCD67 which is good, but not needed. As for the focuser, mine was iffy and I replaced it. However, it was better than many so you might be ok.

Work with it. I think they are great scopes.

Thanks 🙂
I will, I think I just saw so many negatives on other forums really not so much SGL that it worried me, now I feel much more confident. 🙂 

Steve

[teoria_del_big_bang]

I was hoping to use my ASI1600 with this rather than the QHY268 as I would leave that on the Esprit. 
I have seen others using this camera on tis scope so hopefully should be okay.

Steve

[fireballxl5]

I've been imaging with the StellaLyra f/9 RC6 this year and I do like it, mainly as it allows hi-res imaging in a easily transportable package.  Natively it does *not* cover an ASP-C sensor though.  I've recently got hold of the TS flattener but not had much opportunity to try it out properly,  however it does seem to work well.  In any case I've also got hold of a smaller sensor,  ASI533, that better matches my target imaging resolution and covers many of my preferred targets. I have the benefit of a fixed rig for wider fields. I'll likely be trying the 533 without the flattener as well.