Results 1 to 5 of 5
  1. #1
    Kel123's Avatar
    Kel123 is offline Main Sequence
    Points: 2,735, Level: 33
    Level completed: 90%, Points required for next Level: 15
    Overall activity: 4.0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!5 Threads Achievement!50 Posts Achievement!365 Days+ Registered Achievement!
    Join Date
    Mar 2017
    Location
    Lagos, Nigeria
    Posts
    109
    Points
    2,735
    Level
    33
    Thanks
    44
    Thanked 4x 4 Posts

    Default 2" Filter and Back Focus on Skywatcher 80ED with FF/FR



    I am contemplating getting a 2" STC Duo Narrowband filter for my modified Canon T3i , which will be used on an Skywatcher Evostar 80ED scope alongside the dedicated focal reducer/ff.
    The problem I see is that since the fr/ff requires 55 mm back-focus and the current setup is spot-on with the canon adapter, adding a filter to the train will increase the distance between the sensor and the ff/fr, thereby going out of focus. For example, the filter thickness is specified as "1mm Glass, 3.5mm Rim" .
    Another option I have is to go for the clip-in filter but that will deny me the opportunity of using it on an OSC if I so choose later. I also want the freedom of adapting the 2" filter to my EF-S lenses with a step down adapter later for wild-field milkyway imaging as all my prime lenses are for EF-S mount. Apparently I cannot use these lenses with the clip-in filter. The 2" will also remain useful if I go for a full frame camera tomorrow.

    Please I will appreciate your input on the way forward on this issue.

    Thanks
    Last edited by Kel123; 05-11-2019 at 06:26 PM.

  2. #2
    Kel123's Avatar
    Kel123 is offline Main Sequence
    Points: 2,735, Level: 33
    Level completed: 90%, Points required for next Level: 15
    Overall activity: 4.0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!5 Threads Achievement!50 Posts Achievement!365 Days+ Registered Achievement!
    Join Date
    Mar 2017
    Location
    Lagos, Nigeria
    Posts
    109
    Points
    2,735
    Level
    33
    Thanks
    44
    Thanked 4x 4 Posts

    Default Re: 2" Filter and Back Focus on Skywatcher 80ED with FF/FR

    Still hoping for a reply from someone with an experience or an idea of this situation

  3. #3
    KathyNS's Avatar
    KathyNS is offline Super Moderator
    Points: 173,440, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 62.0%
    Achievements:
    200+ Posts Achievement!Ghost Achievement! Averaging 5+ posts a day!First 1000 Experience Points400+ Posts AchievementGot three Friends
    Awards:
    Reply Award
    Join Date
    Nov 2010
    Location
    Nova Scotia
    Posts
    25,192
    Points
    173,440
    Level
    100
    Thanks
    6,660
    Thanked 14,988x 9,544 Posts
    Blog Entries
    3

    Default Re: 2" Filter and Back Focus on Skywatcher 80ED with FF/FR

    The filter should go ahead of the FR/FF. Is that possible in your configuration?

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.


    DSO AP:
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,LRGB filters; KWIQ/QHY5 guide
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    ; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome;
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    (pier);
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    .

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.

  4. The Following User Says Thank You to KathyNS For This Useful Post:

    Kel123 (05-12-2019)

  5. #4
    Kel123's Avatar
    Kel123 is offline Main Sequence
    Points: 2,735, Level: 33
    Level completed: 90%, Points required for next Level: 15
    Overall activity: 4.0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!5 Threads Achievement!50 Posts Achievement!365 Days+ Registered Achievement!
    Join Date
    Mar 2017
    Location
    Lagos, Nigeria
    Posts
    109
    Points
    2,735
    Level
    33
    Thanks
    44
    Thanked 4x 4 Posts

    Default Re: 2" Filter and Back Focus on Skywatcher 80ED with FF/FR

    Wow! That is quite an idea. I never thought about that because I have never imagined any optic can go before a FR/FF. I am not sure that the filter will have the right threading both sides. I will sure find out. So glad I am getting somewhere
    Thank you so much.

  6. #5
    Kel123's Avatar
    Kel123 is offline Main Sequence
    Points: 2,735, Level: 33
    Level completed: 90%, Points required for next Level: 15
    Overall activity: 4.0%
    Achievements:
    2 Posts Achievement20 Posts Achievement!5 Threads Achievement!50 Posts Achievement!365 Days+ Registered Achievement!
    Join Date
    Mar 2017
    Location
    Lagos, Nigeria
    Posts
    109
    Points
    2,735
    Level
    33
    Thanks
    44
    Thanked 4x 4 Posts

    Default Re: 2" Filter and Back Focus on Skywatcher 80ED with FF/FR

    Following your suggestion, I did a little research and arrived at a workable solution with this adapter https://www.firstlightoptics.com/ada...-reducers.html

    It lets you thread in a 2" filter at one end and the Skywatcher FF/RF at the other end. It is then pushed into the focuser draw tube and held in place by two screws . The only downside is that it is a push-fit from where every other part of the train will be hanging. I presume it will be sturdy enough. It also adds a few millimeters to the effective focal length of the telescope since you will need the original diagonal adapter to hold it in place. That adapter is usually unthreaded and replaced with ff/fr. I wonder if that affects the job of the focal reducing aspect.

    Thanks

 

 

Similar Threads

  1. Skywatcher Evostar 80ED DS-PRO vs old Skywatcher 80ED
    By svetimas in forum Refractor Telescopes Forum
    Replies: 2
    Last Post: 01-17-2019, 07:20 PM
  2. HD 11" and Nightscape CCD Back focus
    By jimdrever in forum CCD Imaging Forum
    Replies: 4
    Last Post: 08-20-2014, 06:01 PM
  3. 2" EP back focus question
    By Gregg1956 in forum Telescope Eyepieces Forum
    Replies: 2
    Last Post: 06-28-2014, 03:43 AM
  4. Jumping in with both feet, a couple questions about "back-focus"...
    By blkbagger in forum Astronomy Beginners Forum
    Replies: 7
    Last Post: 05-01-2013, 08:52 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBulletin® Version 4.2.0
Powered by vBulletin®
All times are GMT. The time now is 01:45 AM.