#1  
Old 16-07-2018, 08:54 AM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
FS60CB flattener - eggy stars

Referring to the FS60CB system chart and use of the flattener.

Having followed the diagram and all combinations of adapters / elements shown, stars in all corners are eggy. More like long grain rice?

Thinking this through. Given that there is no way of attaching the flattener backwards, it seems that the distance between the flattener and camera rotator / focus tube and / or flattener and camera is important - though, the SD ring is optional, which leaves distance to the camera.

Worse, could the flattener elements have moved? Is that likely? I do not recall dropping the flattener and there are no rattles.
Attached Thumbnails
Click for full-size image (Screenshot_20180716-093142.jpg)
174.0 KB28 views
Reply With Quote
  #2  
Old 16-07-2018, 09:06 AM
Lognic04's Avatar
Lognic04 (Logan)
Registered User

Lognic04 is offline
 
Join Date: Mar 2016
Location: Melbourne, VIC
Posts: 889
I have the same issue with my MT - no matter the spacing there are always edge problems
Reply With Quote
  #3  
Old 16-07-2018, 01:44 PM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
Looking around, this question has been asked before, one way or another. And, I'm not sure why the documented setup doesn't work for me. Takahashi specs cite 56mm back focus. Now back focus appears to be as indicated in the diagram. However, another source suggests BF is measured from the back of the flattener. I'll measure it all up and see what gives.

Edit: 'Metal back focus' is the distance from the union of the flattener and camera adapter to the photographic plane.
Attached Thumbnails
Click for full-size image (FS-60CB_cotes_700.png)
13.7 KB20 views
Click for full-size image (takbackfocus.jpg)
200.3 KB19 views

Last edited by rcheshire; 16-07-2018 at 02:12 PM.
Reply With Quote
  #4  
Old 16-07-2018, 02:04 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 7,033
Where are all the TAK experts on this? Certainly sounds like spacing, at least on any other scope it might be. You could try increasing the spacing a bit at a time. Most reducer correctors seem to have a tolerance range of at least +-2mm. A variable spacing ring is a nice tool for this sort of fiddling.
Reply With Quote
  #5  
Old 16-07-2018, 02:17 PM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
I may have asked too soon. Added metal back focus table which includes a definition. It's just the way the information is presented. It doesn't matter whether a spacer is used ahead of the flattener. Providing there is sufficient focus travel, which gives me an idea to minimize camera tilt.
Reply With Quote
  #6  
Old 16-07-2018, 05:13 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Metal back is ALWAYS from the very rear of the flattener (or reducer) - NOT accounting the threads - to the sensor plane.

Last edited by LewisM; 16-07-2018 at 07:18 PM.
Reply With Quote
  #7  
Old 16-07-2018, 06:22 PM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
Thanks for the absolutes... Logan, if I find a way to tweak this, I'll report back.
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 10:25 PM.

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