#1  
Old 31-03-2010, 01:03 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
x0.63 Reducer on C11

Hi guys, I got a 0.63 Hirsch Reducer/Corrector that I want to try on my C11. Just checking if anyone had tried these for imaging on a C11 SCT and what the recommended spacing should be to the CCD. Also trying to use it with an OAG (meade) so I hope there's enough space to fit it in between the reducer and the camera. Thanks for any tips.
Reply With Quote
  #2  
Old 31-03-2010, 01:21 PM
Barrykgerdes
Registered User

Barrykgerdes is offline
 
Join Date: Feb 2007
Location: Beaumont Hills NSW
Posts: 2,900
Hi Marc
I think the're meant to go between the telescope back plate and the OAG. If you have a crayford type focuser it will go between the telescope back and the focuser.

There is a basic design for these reducer, correctors that assumes they are a certain distance from the focal point to get the best correction. A few years ago when CCD chips were quite small it probably did not matter but with the large chips we have now position may be a lot more critical for flattening and comma correction.

Barry
Reply With Quote
  #3  
Old 31-03-2010, 01:25 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by Barrykgerdes View Post
Hi Marc
I think the're meant to go between the telescope back plate and the OAG. If you have a crayford type focuser it will go between the telescope back and the focuser.

There is a basic design for these reducer, correctors that assumes they are a certain distance from the focal point to get the best correction.

Barry
Yeah I removed the focuser so the Corrector screws directly into the mirror cell. Then I have spacers and/or the OAG, then the camera. Just trying to figure out the distance to see if I can fit the OAG within the imaging train. Otherwise I'll have to guide somewhere else.
Reply With Quote
  #4  
Old 01-04-2010, 02:48 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
*bump*

anyone?
Reply With Quote
  #5  
Old 02-04-2010, 01:05 AM
AlexN's Avatar
AlexN
Tunnel Vision

AlexN is offline
 
Join Date: Mar 2008
Location: Caboolture, Australia
Posts: 6,796
Marc, I went for 115mm as thats the word I got from CN...

It seemed to give a fairly good FOV across the QHY8...
Reply With Quote
  #6  
Old 02-04-2010, 08:22 AM
peeb61's Avatar
peeb61 (Paul)
Always looking up

peeb61 is offline
 
Join Date: Jan 2007
Location: Wollongong
Posts: 716
Hi Marc,
I have been having issues with my f/10 LX200 and the Meade f/6.3 focal reducer using my Canon 350D, given yours would be a different set up slightly re: equipment, I too was told 115mm for my set up, yes I could focus in the center of the field but around the outside I had "Pac-Man type stars, I later email Bintel with one of my 2 min exposures showing the errors and Don emailed me with this reply:

"Is the scope a SCT or ACF.

If the later the f/6.3 will not work properly and spacing will be of the utmost critic.
As the ACF scopes are already produced a flat field image and the problem is that a reducer / corrector can further flatten the field so that curvature may be reversed.

If it is an SCT see the below details from S&T Review about correct spacings.

Popular f/6.3 reducers sold by Celestron and Meade for their f/10 Schmidt-Cassegrains are designed to be used with a 105-mm separation between the back surface of the reducer and the detector (be it film, CCD, or whatever) altering this spacing changes the compression factor — great for fine-tuning a CCD system. Increasing the separation increases the amount of compression and thus reduces the effective focal length. Ideally we could increase the separation enough to accommodate small pixels. In practice, however, either image quality or, more likely, mechanical restrictions imposed by the telescope’s focusing system will limit the amount of compression that can be obtained.

If you are using a microfocuser it should be placed after the microfocuser and before T- Adapter and T-Ring.

Hope this is helpful"


As you can see I need the 105mm separation to which I've tried and did another 2 min exposure on the same object.


The results were clearly better, the stars around the outside had lost this "Pac-Man type feature" but was faced with another problem, zooming in on these stars around the outside showed rotational/un-polar aligned characteristics... in the centre of the image the stars are elongated NE to SW, at the bottom right corner the stars are elongated NW to SE and then halfway in between they're bl#$%y round!


I have later found the O-Ring holding the lens's in place on the focal reducer was somewhat loose, only slightly, so after a tightening up I am now on the testing once again to try this out, as my problem may be the focal reducer it's self, one of the dud ones that was marketed.


A mate also has the same focal reducer to which we will try if mine fails then we will know for sure.


Sorry if I went on a bit but the spacing for my set up is definitely 105mm.


Paul




Reply With Quote
  #7  
Old 02-04-2010, 10:34 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by AlexN View Post
Marc, I went for 115mm as thats the word I got from CN...

It seemed to give a fairly good FOV across the QHY8...
Thanks Alex. I'll have to try that too.

Quote:
Originally Posted by peeb61 View Post
Hi Marc,
I have been having issues with my f/10 LX200 and the Meade f/6.3 focal reducer using my Canon 350D, given yours would be a different set up slightly re: equipment, I too was told 115mm for my set up, yes I could focus in the center of the field but around the outside I had "Pac-Man type stars, I later email Bintel with one of my 2 min exposures showing the errors and Don emailed me with this reply:

"Is the scope a SCT or ACF.

If the later the f/6.3 will not work properly and spacing will be of the utmost critic.
As the ACF scopes are already produced a flat field image and the problem is that a reducer / corrector can further flatten the field so that curvature may be reversed.

If it is an SCT see the below details from S&T Review about correct spacings.

Popular f/6.3 reducers sold by Celestron and Meade for their f/10 Schmidt-Cassegrains are designed to be used with a 105-mm separation between the back surface of the reducer and the detector (be it film, CCD, or whatever) altering this spacing changes the compression factor — great for fine-tuning a CCD system. Increasing the separation increases the amount of compression and thus reduces the effective focal length. Ideally we could increase the separation enough to accommodate small pixels. In practice, however, either image quality or, more likely, mechanical restrictions imposed by the telescope’s focusing system will limit the amount of compression that can be obtained.

If you are using a microfocuser it should be placed after the microfocuser and before T- Adapter and T-Ring.

Hope this is helpful"


As you can see I need the 105mm separation to which I've tried and did another 2 min exposure on the same object.


The results were clearly better, the stars around the outside had lost this "Pac-Man type feature" but was faced with another problem, zooming in on these stars around the outside showed rotational/un-polar aligned characteristics... in the centre of the image the stars are elongated NE to SW, at the bottom right corner the stars are elongated NW to SE and then halfway in between they're bl#$%y round!


I have later found the O-Ring holding the lens's in place on the focal reducer was somewhat loose, only slightly, so after a tightening up I am now on the testing once again to try this out, as my problem may be the focal reducer it's self, one of the dud ones that was marketed.


A mate also has the same focal reducer to which we will try if mine fails then we will know for sure.


Sorry if I went on a bit but the spacing for my set up is definitely 105mm.


Paul



Thanks for all the info Paul. My SCT is the old type. I have tried last night different spacing. The closer I was to the corrector the worse the field curvature but the rounder the stars (down to 30mm spacing). The further I was the flatter the field (to some extent) but the edge stars were absolutetly shocking (went up to 80mm. I stopped as the stars were getting worse). Star shapes went from 0 to > as you've described so I though I was way to far. Will have to look more into this. My collimation in CCD Inspector was under 3" and I know the optics are aligned as the hyperstar flat on the corrector with no tilt delivers a perfect field. Each test was done on 60s guided exposures and carefully focused with a bathinov mask. I shot around Alpha Crux. Will post some of the shots to illustrate. Have you got any link to yours so I could have a peek? Thanks mate.
Reply With Quote
  #8  
Old 02-04-2010, 11:12 AM
peeb61's Avatar
peeb61 (Paul)
Always looking up

peeb61 is offline
 
Join Date: Jan 2007
Location: Wollongong
Posts: 716
Marc,
Here are the images from 115mm and 105mm.
Both images exposed for 2 min at 800iso uncropped just reduced for this site.

The first image is the distance set at 115mm and the second at 105mm.

As soon as I test the set up after the focal reducer ring was tightened I will post again.

Hope this helps

Paul
Attached Thumbnails
Click for full-size image (Eta at 115mm.JPG)
130.9 KB259 views
Click for full-size image (Eta at 105mm.jpg)
182.1 KB249 views
Reply With Quote
  #9  
Old 03-04-2010, 09:33 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Thanks again Paul - keep me posted. It does look very similar to what I've been getting. I will try the optimal spacing you're recommend. I did a bit of research since on CN and joined two SCT yahoo groups so I'll report back when I have more info.
Reply With Quote
  #10  
Old 03-04-2010, 12:52 PM
peeb61's Avatar
peeb61 (Paul)
Always looking up

peeb61 is offline
 
Join Date: Jan 2007
Location: Wollongong
Posts: 716
No problems Marc,
Between the two of us hopefully we can work this out.

Paul
Reply With Quote
  #11  
Old 04-04-2010, 09:42 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Hi Paul, I had a chat with Scott Tucker from Starizona. From what I've gathered so far the old Celestron & Meade SCT range have both spherical primaries and secondaries. The corrector plate takes care of coma and spherical abberations. Theorically the further the corrector plate is from the primary the more correction to the coma (without moving the secondary).

So it's fair to assume that if you focus by moving the primary the further away from the corrector plate and add tubes to the back focus you'll correct coma better than having the primary up the baffle tube closer to the corrector. Will try that.

The Meade ACF range introduced a hyperbolic secondary to deal with Coma. Celestron HD range on the other hand have the same optics but deal with coma by adding a doublet inside the baffle tube in the same plane as the primary to correct the field. Other than than the optics are the same. I asked if Celestron would provide the doublet as a retrofit but I hear it is very unlikely.

Having said that I'm looking into this which is made in Germany by Philip Keller. I believe he makes the Keller correctors in the ASA range and this mob has an SCT corrector (x0.8) wight a pretty good looking spot diagram. So I'm going to try this next and get one shipped.
Reply With Quote
  #12  
Old 04-04-2010, 09:50 AM
gbeal
Registered User

gbeal is offline
 
Join Date: Oct 2004
Location: New Zealand
Posts: 4,345
Marc,
good to see some light at the end of this tunnel. When I saw the Keller name I though ohmygawd it will cost more than the C11, but then I saw Teleskope Service. They are a good crowd to deal with.
Keep the masses informed please.
Gary
Reply With Quote
  #13  
Old 05-04-2010, 03:19 PM
peeb61's Avatar
peeb61 (Paul)
Always looking up

peeb61 is offline
 
Join Date: Jan 2007
Location: Wollongong
Posts: 716
Great work marc,
I still haven't has a night to test this focal reducer, too many things have cropped up and the weather here in Wollongong have been terrible...cool nights but cloudy, overcast and rain.

This corrector from Phillip Keller looks promising.

Paul
Reply With Quote
  #14  
Old 06-04-2010, 04:57 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Ordering it now. Just working out the spacers and compression rings as it has to go from M48 to M42 for the QHY8. I reckon it's gonna rain for another 2 extra weeks now... Spacing is 97.5mm from the base of the M48 male thread. So counting the back adaptor ring on the C11 cell that puts the camera in the vicinity of 110mm which is the "ideal" back focus. Although this ideal back focus has been argued not to make any difference in image quality within a range from 96mm up to even 157mm. Can't wait to see the results now. The edge stars will still be chonky of course to some extent but much smaller chonky size so easier to "hide" or round at processing time
Reply With Quote
  #15  
Old 08-04-2010, 07:04 AM
peeb61's Avatar
peeb61 (Paul)
Always looking up

peeb61 is offline
 
Join Date: Jan 2007
Location: Wollongong
Posts: 716
Great news Marc,
Keep us all informed...weather here still crap but I have to admit today the clouds are moving with the high winds coming through...rid of one problem and another pops it's head.

Still early in the day, things could change.

Paul
Reply With Quote
  #16  
Old 31-08-2011, 03:02 PM
Poita (Peter)
Registered User

Poita is offline
 
Join Date: Jun 2011
Location: NSW Country
Posts: 3,586
Wasn't there an Astrophysics corrector that was recommended for the C11?
Reply With Quote
  #17  
Old 31-08-2011, 03:05 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by Poita View Post
Wasn't there an Astrophysics corrector that was recommended for the C11?
I ended up getting the TSSCKorr2 . Worked quite well.
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 12:00 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement