#1  
Old 28-08-2014, 09:05 AM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,372
TS Optical TSRCflat3 flattener

I bought a TSRCflat3 flattener for my RC12. I have bought adapters etc and collimated the telescope to a high degree. The flattener gives a pretty reasonable adjustment to flattening the field (probably half of the field curvature) but it is not what I was hoping for at all.

The image is focused (see center image)

I think there is an element of tilt and I can shim for that. What I would like to know is how do I get this field flat? Is anyone getting good results with this flattener? Any optical experts have any ideas on how to combat this problem?

Rotating the imaging train does not change the results either. The bottom left looks like it is approaching being flat but still a little way off. I have also included an out of focus star shots from the centre of the field. I look forward to any help available.
Attached Thumbnails
Click for full-size image (bottom left corner.jpg)
133.5 KB91 views
Click for full-size image (bottom right corner.jpg)
143.5 KB75 views
Click for full-size image (Left corner.jpg)
154.9 KB70 views
Click for full-size image (top right corner.jpg)
125.8 KB71 views
Click for full-size image (center.jpg)
41.8 KB86 views
Click for full-size image (collimation.jpg)
89.6 KB85 views
Reply With Quote
  #2  
Old 28-08-2014, 09:13 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,125
Do you have the corrector's distance spot on? Have you tried moving it in or out. Center field out of focus looks a tiny bit out but not much. The edges might be related to some residual field curvature. Tweaking spacing might fix that.
Reply With Quote
  #3  
Old 28-08-2014, 10:21 AM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,372
Quote:
Originally Posted by multiweb View Post
Do you have the corrector's distance spot on? Have you tried moving it in or out. Center field out of focus looks a tiny bit out but not much. The edges might be related to some residual field curvature. Tweaking spacing might fix that.

Yes the corrector is spot on according to what I have been told. The back focus is 106mm and I am told that is from the rear of the thread. The STXL with filter wheel back focus is 61.84mm. That leaves 44.16mm for adapter. My adapter is 44.2mm. I measured it recent just to make sure.

Collimation could do with a tiny tweak, though I doubt it would have much effect. Perhaps remove the slight elongation to the right side.

I did move the flattener out by 3mm as suggested by TS Optical but it seemed to make the problem worse. I don't have the ability to move it in unfortunately. I don't have a smaller adapter to make that work.

I wonder if the problem is related to the optimum distance of the mirrors. I am within a millimetre or two of that from what I understand, so maybe this is where the problem really lies?
Reply With Quote
  #4  
Old 28-08-2014, 03:02 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,090
I would suggest focusing on the centre of the frame, then checking the corners - see what they look like. Then, move your focuser in (or out, depending on the curvature) so the corners are in focus and the centre out of focus. This will at least tell you if the collimation is good and if its really field curvature. what do you think?

Josh
Reply With Quote
  #5  
Old 28-08-2014, 11:23 PM
ericwbenson (Eric)
Registered User

ericwbenson is offline
 
Join Date: Sep 2009
Location: Adelaide, Australia
Posts: 198
Hi Paul,
It's been a while...
+1 to what Joshua said. The stars in the corners when focused (so that the center is out) will show you the best that the flattener could hope to do. In order to fix anything else (mostly off-axis astig and coma from what I can see), the system needs a corrector. Remember an RC is not entirely coma free, it has a coma free zone, and only if the hyperboloids hit the prescription, and it is definitively prone to off-axis astigmatism, this may be the wall you are hitting. (Doug G. once mentioned to me that he could start to see the off-axis astig on his uncorrected 12.5 RCOS with his KAF6303, so the KAI11000 would definitively show it).

I believe changing the mirror spacing primarily affects the amount of spherical aberration in the system (SC's are like that, as are CDKs). There is a point where it is minimized. On my system it has to be better than +/-1 mm (so says PWI). PWI supplies a Ronchi eyepiece and spacer tube to adjust the mirror spacing until the Ronchi shows a null. I gather GSO doesn't supply this? If they can tell you the correct distance the Ronchi should be from the back plate, you could then borrow my Ronchi and cut a 1.25" ID tube to the right length.

The flattener can add it's own aberrations too unfortunately, to observe those rotate the flattener wrt the OTA and the camera (you sorta did that already), but keeping the camera fixed wrt the OTA might help in the diagnosis.

Best,
EB

p.s. Congrats on the Malin!

Last edited by ericwbenson; 28-08-2014 at 11:37 PM.
Reply With Quote
  #6  
Old 28-08-2014, 11:37 PM
ericwbenson (Eric)
Registered User

ericwbenson is offline
 
Join Date: Sep 2009
Location: Adelaide, Australia
Posts: 198
Hey Paul,
Check out this comparison of an RCOS with and without corrector using a KAI-11000.

http://www.rcopticalsystems.com/acce...rrector_RC.pdf

Remember the above isn't only a flattener, and hence cost somewhere in the 2K (70mm) to 4K (100mm) $ range.

EB
Reply With Quote
  #7  
Old 29-08-2014, 07:07 AM
Logieberra's Avatar
Logieberra (Logan)
Registered User

Logieberra is offline
 
Join Date: Mar 2010
Location: Canberra
Posts: 1,543
Paul

Did you consider this one as well?

http://www.teleskop-express.de/shop/...rkuerzung.html

2" corrector for f/8 RC telescopes - without altering the focal length
Suitable for all GSO RC telescopes from 6" to 16" and for all RC telescopes with F8

I was considering it...

Will you return yours, if it's not working?
Reply With Quote
  #8  
Old 29-08-2014, 08:34 AM
Logieberra's Avatar
Logieberra (Logan)
Registered User

Logieberra is offline
 
Join Date: Mar 2010
Location: Canberra
Posts: 1,543
Quote:
Originally Posted by ericwbenson View Post
Hey Paul,
Check out this comparison of an RCOS with and without corrector using a KAI-11000.

http://www.rcopticalsystems.com/acce...rrector_RC.pdf

Remember the above isn't only a flattener, and hence cost somewhere in the 2K (70mm) to 4K (100mm) $ range.

EB
Here's some more on the RCOS FF. They are a match made in heaven.

http://www.astrosurf.com/antilhue/rcosff.htm

I wonder if GSO is planning on releasing something special for their big RCs. Surely?
Reply With Quote
  #9  
Old 29-08-2014, 01:29 PM
Peter.M's Avatar
Peter.M
Registered User

Peter.M is offline
 
Join Date: Sep 2011
Location: Adelaide
Posts: 914
Quote:
Originally Posted by Logieberra View Post
Paul

Did you consider this one as well?

http://www.teleskop-express.de/shop/...rkuerzung.html

2" corrector for f/8 RC telescopes - without altering the focal length
Suitable for all GSO RC telescopes from 6" to 16" and for all RC telescopes with F8

I was considering it...

Will you return yours, if it's not working?

I would hate to see the vignetting with a 2 inch corrector and the stl
Reply With Quote
  #10  
Old 29-08-2014, 02:25 PM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,372
Quote:
Originally Posted by Joshua Bunn View Post
I would suggest focusing on the centre of the frame, then checking the corners - see what they look like. Then, move your focuser in (or out, depending on the curvature) so the corners are in focus and the centre out of focus. This will at least tell you if the collimation is good and if its really field curvature. what do you think?

Josh

Yes good idea Josh. I will undertake this for further determination of what is going on.

Quote:
Originally Posted by ericwbenson View Post
Hi Paul,
It's been a while...
+1 to what Joshua said. The stars in the corners when focused (so that the center is out) will show you the best that the flattener could hope to do. In order to fix anything else (mostly off-axis astig and coma from what I can see), the system needs a corrector. Remember an RC is not entirely coma free, it has a coma free zone, and only if the hyperboloids hit the prescription, and it is definitively prone to off-axis astigmatism, this may be the wall you are hitting. (Doug G. once mentioned to me that he could start to see the off-axis astig on his uncorrected 12.5 RCOS with his KAF6303, so the KAI11000 would definitively show it).

I believe changing the mirror spacing primarily affects the amount of spherical aberration in the system (SC's are like that, as are CDKs). There is a point where it is minimized. On my system it has to be better than +/-1 mm (so says PWI). PWI supplies a Ronchi eyepiece and spacer tube to adjust the mirror spacing until the Ronchi shows a null. I gather GSO doesn't supply this? If they can tell you the correct distance the Ronchi should be from the back plate, you could then borrow my Ronchi and cut a 1.25" ID tube to the right length.

The flattener can add it's own aberrations too unfortunately, to observe those rotate the flattener wrt the OTA and the camera (you sorta did that already), but keeping the camera fixed wrt the OTA might help in the diagnosis.

Best,
EB

p.s. Congrats on the Malin!

Thanks Eric.

I now have the optimum spacing distance. I am told it is 687.89mm from centre of both mirrors. Not sure how I go about measuring that.

Good idea about the Ronchi eyepiece. I will let you know when I will need it.

Yes I was thinking the flattener would introduce aberrations if the mirrors were not at optimal. Ted and I were discussing this fact the other night.

LOL GSO does not provide such things. Remember cheap comes with its own issues, and this is one of them.

Quote:
Originally Posted by Logieberra View Post
Paul

Did you consider this one as well?

http://www.teleskop-express.de/shop/...rkuerzung.html

2" corrector for f/8 RC telescopes - without altering the focal length
Suitable for all GSO RC telescopes from 6" to 16" and for all RC telescopes with F8

I was considering it...

Will you return yours, if it's not working?
This is actually not the recommended one. It says it will work but limits the size of the sensor you can use. My Flattener is the 3" version which is supposed to work with larger sensors. Not planning on sending mine back. I am sure it works but need to sort distances etc. I am now told by TS that a figure between 106 and 109mm will work. I am there so now it must be either/or both distances of mirrors and degree of tilt.

Quote:
Originally Posted by Logieberra View Post
Here's some more on the RCOS FF. They are a match made in heaven.

http://www.astrosurf.com/antilhue/rcosff.htm

I wonder if GSO is planning on releasing something special for their big RCs. Surely?
Short answer is no. Jim is great with reflecting surfaces. He admits that he is not a refracting expert. So GSO has no plans at all to manufacture correctors at all. It will need to be handled by other parties. Hence why we have seen all manner of correctors being used without any announcements by GSO to make one for their RC range. The one they provide for their other gear is to the best of my knowledge made from an outside source.
Reply With Quote
  #11  
Old 23-07-2019, 12:48 AM
nickbtx (Nick)
Registered User

nickbtx is offline
 
Join Date: Sep 2011
Location: USA
Posts: 7
Quote:
Originally Posted by Paul Haese View Post
My Flattener is the 3" version which is supposed to work with larger sensors. Not planning on sending mine back. I am sure it works but need to sort distances etc. I am now told by TS that a figure between 106 and 109mm will work.

I realize this is an old thread, but in event someone is searching on the subject and comes across this topic, like I did, I thought I'd provide a little additional information.


I recently added a TSRCFlat3 to my 12"RC (Orion Telescope - US) to hopefully correct the astigmatism I was seeing on my KAI-11002 sensor. According to manufacturer, Telekop Service, the recommended working distance from the female thread is 89.5mm +/-2mm so I had an adapter made that put it at exactly 89.5mm. I still have a little tweaking to do, but so far I'm quite pleased with the results.


I'm not sure if TS redesigned the flattener at some point in the last few years or if they reevaluated the optics and changed the recommended distance. Regardless, if you try one of the current run of TSRCFlat3 flatteners, I would highly recommend you shoot for the 89.5mm.


Clear skies,
Nick
Reply With Quote
  #12  
Old 23-07-2019, 10:10 AM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,372
Nick,

the flattener I bought was another one (probably for a refractor by the looks of it) and I am glad to hear the new flattener actually works. I never got the one described here to work; it was close but not spot on. I have been looking at the new one for sometime and wondered if it would actually work. Good to hear that it does work. I might actually buy that one now, though I am concerned about back focus because I am using an AOX as well as an STXL with integrated guiding filter wheel and Astrodon filters. That might be a problem.
Reply With Quote
  #13  
Old 24-07-2019, 12:26 PM
nickbtx (Nick)
Registered User

nickbtx is offline
 
Join Date: Sep 2011
Location: USA
Posts: 7
Hi Paul,
I forgot to mention in my post, the TSRCFlat3 shortened my FL by about 6mm. In other words, after inserting the flattener, I had to move my camera in 6mm to reach focus. All said and done, it required removing 3" of spacer rings in front of the focuser to accommodate the 42mm flattener and adapters. Before you commit, let me get some good data and I'll post a pic or two to show the results. I've got my grandson for a couple of weeks so it may be a bit. ;-)

Nick
Reply With Quote
  #14  
Old 24-07-2019, 08:54 PM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,372
Thanks Nick for the information. When you get a few images up, feel free to post them in this thread. It will be helpful in making a decision if I buy the flattener you have bought. I note that with my back focus from the AOX to the sensor on the STXL with integrated guiding filter wheel I have only about 3mm to make an adapter, which is not much. This could be a bit tricky as I want the AOX in the train.
Reply With Quote
  #15  
Old 26-07-2019, 05:13 PM
benklerk
Registered User

benklerk is offline
 
Join Date: May 2008
Location: Katoomba
Posts: 218
I also bought the TSRCFlat3 about a month ago for my GSO RC 14". It's still sitting in the box as I'm still building my obs and haven't tried it out. I bought all the adapter so it should be easy to install everything. Should be in about a month before I'm all setup. The camera I have is the Moravian G4-16000.

This is how I worked out the adapters I need.
The camera distance to OAG is 61.5mm
2x 10mm extenders
M68 to M69 Adapter 5.3mm
Baader filters are 3mm
Comes to 89.8mm
Reply With Quote
  #16  
Old 26-07-2019, 05:18 PM
Atmos's Avatar
Atmos (Colin)
Ultimate Noob

Atmos is offline
 
Join Date: Aug 2011
Location: Melbourne
Posts: 6,231
Quote:
Originally Posted by benklerk View Post
I also bought the TSRCFlat3 about a month ago for my GSO RC 14". It's still sitting in the box as I'm still building my obs and haven't tried it out. I bought all the adapter so it should be easy to install everything. Should be in about a month before I'm all setup. The camera I have is the Moravian G4-16000.

This is how I worked out the adapters I need.
The camera distance to OAG is 61.5mm
2x 10mm extenders
M68 to M69 Adapter 5.3mm
Baader filters are 3mm
Comes to 89.8mm
You're actually at 85.8mm I'm afraid.
A 3mm filter adds 1/3rd to the optical back focus (subtracts from the mechanical).
61.5+20+5.3-1=85.8mm
Reply With Quote
  #17  
Old 26-07-2019, 05:50 PM
benklerk
Registered User

benklerk is offline
 
Join Date: May 2008
Location: Katoomba
Posts: 218
Quote:
Originally Posted by Atmos View Post
You're actually at 85.8mm I'm afraid.
A 3mm filter adds 1/3rd to the optical back focus (subtracts from the mechanical).
61.5+20+5.3-1=85.8mm
You sure? I was told you add the filter thickness into the total backfocus.

If that is true do you know where I can pickup 3 m68 or m69 1mm extenders. It would save the hassle importing them.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 12:14 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
SkyWatcher Australia
Advertisement
Bintel
Advertisement
Lunatico Astronomical
Advertisement
Celestron Australia
Advertisement
Meade Australia
Advertisement
NexDome Observatories
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement