14 replies to this topic

[maxsid]

Hello,

As some of you know, I recently took my RC6 apart and cleaned the primary mirror.

Since then things went from bad to better and then to good and than to bad again.

 

Trying to use cheap tools.

 

-- I bought a new laser collimator. It's cheap but much better than the one I had before.

-- Found some old instructions recommending to "reset" the primary.

   - loosen the small set-screws on the primary and screw the larger screws all the way in.

   - this helped a lot. adjusted the secondary with the laser collimator and everything was in a "close to good" state.

-- Found some instructions on using Bahtinov to fine-tune the primary

   - move a bright star with Bahtinov to every corner

   - adjust the primary for the worst corner until Bahtinov looks better.

   - this seems to be working. I only adjusted one corner so far . My worst corners are on the top.

 

Currently, ASTAP reports 20% tilt.

 

May 23, 2024. Bortle 8.

NGC5466.

 

RC6 at native 1380mm. F9.

RST-135 mount. Guided.

7x120s. 14 minutes (clouds came).

 

Stacked in APP.

Processed in PI.

 

Edited by maxsid, 24 May 2024 - 04:30 AM.

[F.Meiresonne]

Does this really work with a Bahtinov mask..i did not find any interney sources about that.

 

I wonder also, why you have lost the 'good', maybe the screws were not tighted enough. Then again, as i experienced, you might not overdo it, cause one gets easily pinched optics...

 

Still waiting to test mine under the stars, but the weather has been so bad and still is. Some regions in Belgium got flooded by rain...Flanders region, where i live, got spared, more or less.

Edited by F.Meiresonne, 24 May 2024 - 01:24 PM.

[unimatrix0]

 

 

-- Found some instructions on using Bahtinov to fine-tune the primary

   - move a bright star with Bahtinov to every corner

This may not work with an RC scope. 

 

I follow the Deep Sky Instruments instructions.   

 

You got 2 things to collimate under the stars.  On Axis = Primary adjustments   Off Axis= Secondary adjustments

 

The basic TLDR run down is you center a star, not a very bright one-  defocus to small donut- take a 5-10 second exposure and look at the shape the shape of that single star will tell you how to adjust your primary only

Keep doing the adjustments until you got a round shaped star with no distortion. 

 

Off Axis adjustments involve stars that are around - not centered.  For the shape of those, the secondary mirror  needs to be adjustments and not to touch the primary again.  This isn't about their shape individually but whether or not they are showing a symmetry in all corners. Example: all of them elongated the same symmetric way or all of them are round indicates good secondary mirror collimation.   See the document below that I linked in.  

 

I made this simpler for myself, knowing that I can get the secondary dead on much easier than the primary, without any stars. That's just using a simple Cheshire eyepiece and centering the dot, like  on a Newtonian. 

 

The only thing I had to tune was the primary mirror, using the method I just described above. 
Right here: 

https://www.deepskyi...ure_Ver_1.0.pdf

Edited by unimatrix0, 24 May 2024 - 01:33 PM.

[maxsid]

Frank,

I was going to try DSI method next.

Need Milky Way reasonably high for that.

And good weather too.

Thanks!

 

This may not work with an RC scope. 

 

I follow the Deep Sky Instruments instructions.   

 

You got 2 things to collimate under the stars.  On Axis = Primary adjustments   Off Axis= Secondary adjustments

<..>

The only thing I had to tune was the primary mirror, using the method I just described above. 
Right here: 

https://www.deepskyi...ure_Ver_1.0.pdf

[maxsid]

Freddy,

It went bad again because I played with collimation too much...

Here's where I found the Bahtinov info - https://deepspacepla...rccollimate.php

 

Does this really work with a Bahtinov mask..i did not find any interney sources about that.

 

I wonder also, why you have lost the 'good', maybe the screws were not tighted enough. Then again, as i experienced, you might not overdo it, cause one gets easily pinched optics...

 

Still waiting to test mine under the stars, but the weather has been so bad and still is. Some regions in Belgium got flooded by rain...Flanders region, where i live, got spared, more or less.

[maxsid]

OK...

Tried DSI method.

On-axis only.

Worked great. Now ASTAP reports only 4% tilt for a single 10s exposure.

 

What was strange about DSI instructions - when they say Tighten I had to actually Loosen.

Mirrored.

Not sure why.

 

Edited by maxsid, 29 May 2024 - 03:41 AM.

[maxsid]

Same NGC5466. Same Bortle 8. 1.7 hours.

After proper collimation.

 

I am actually happy with the outcome.

Will not touch the collimation again (for a while).

Will see if it holds when I travel.

 

Edited by maxsid, 29 May 2024 - 04:44 AM.

[F.Meiresonne]

There is a little distortion in the stars pointing to up right in 3 corners.  Only the stars up left seem not to have it.

 

But it is minor, very minor. I would not ttweak he collimation further. You have to pixelpeep to see it.

[maxsid]

Yes, I think I am done for now with collimation.

Good enough for me.

Thanks!

 

There is a little distortion in the stars pointing to up right in 3 corners.  Only the stars up left seem not to have it.

 

But it is minor, very minor. I would not ttweak he collimation further. You have to pixelpeep to see it.

[Mert]

Well done, that looks very good!

[pfile]

 

The basic TLDR run down is you center a star, not a very bright one-  defocus to small donut- take a 5-10 second exposure and look at the shape the shape of that single star will tell you how to adjust your primary only

Keep doing the adjustments until you got a round shaped star with no distortion. 

what i do instead is take the defocused bright star and move it around by slewing the mount until it looks pretty concentric, no matter where that is on the sensor. then i move the primary mirror to re-center the star. that's a lot easier than trying to adjust the star until it looks better. you can iterate on this to improve the on-axis star.

 

rob

[pfile]

OK...

Tried DSI method.

On-axis only.

Worked great. Now ASTAP reports only 4% tilt for a single 10s exposure.

 

What was strange about DSI instructions - when they say Tighten I had to actually Loosen.

Mirrored.

Not sure why.

 

xherc-5-flattener-sm.jpg

 

were you outside of focus or inside of focus? that can reverse the directions.

[maxsid]

Interesting idea!

Will try this some day - thanks!

 

what i do instead is take the defocused bright star and move it around by slewing the mount until it looks pretty concentric, no matter where that is on the sensor. then i move the primary mirror to re-center the star. that's a lot easier than trying to adjust the star until it looks better. you can iterate on this to improve the on-axis star.

 

rob

[maxsid]

As instructed (if I understood correctly), I moved the camera/sensor away from the scope.

 

were you outside of focus or inside of focus? that can reverse the directions.

[maxsid]

Thanks, Mert!

 

Well done, that looks very good!