Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_solar_25.thumb.jpg.f1d5d01d306644f613efd90ef96b314c.jpg

elrico

F6.3 FR

Recommended Posts

Does anyone know the correct spacing to get 6.3 using the Celestron 6.3 FR , 9.25 Celestron evo and the Atik Infinity Colour

thanks 

Share this post


Link to post
Share on other sites

a good start would be to position the CCD chip 110mm behind the reducer.

  • Like 1

Share this post


Link to post
Share on other sites

Elrico,

Here's a handy calculator that will give you a starting point for focal reducer spacing.  For the 9.25 SCT use the moving mirror equation.

http://www.wilmslowastro.com/software/formulae.htm#FR

I get 105mm for no spacing between the FR and scope.  If the FR is spaced out from the scope, the effective focal length changes because the mirror moves for focusing.  You can also try different spacings to get different focal reductions.  The 105mm should give you f6.3.

Don

  • Like 1

Share this post


Link to post
Share on other sites

Don,

I've raised the issue before with WilmslowAstro...their calculator doesn't effectively take into account the changing focal length/ focal ratio when the reducer is "moved".

I have a spreadsheet which does include this factor.

 

reducers_V2b.zip

  • Like 2

Share this post


Link to post
Share on other sites
52 minutes ago, Merlin66 said:

Don,

I've raised the issue before with WilmslowAstro...their calculator doesn't effectively take into account the changing focal length/ focal ratio when the reducer is "moved".

I have a spreadsheet which does include this factor.

 

reducers_V2b.zip

The calculator has an input for scope to FR spacing.  Are you saying it's not accurate or has the calculator been updated?

Don

  • Like 1

Share this post


Link to post
Share on other sites

Don,

As the back focus distance changes so does the focal length of a SCT. This means that the final focal ratio will change.

The Wimslow formula did not accurately take this into account.

  • Like 1

Share this post


Link to post
Share on other sites

Is the back focus of the infinity 13mm deducted from the  suggested spacing, ie: remove Visual back, screw on 6.3 FR, T adaptor spacer, infinity.

eg 105mm from FR to infinity Chip or deduct 13mm from the 105mm ??

Just asking haha

Many thanks

Edited by elrico

Share this post


Link to post
Share on other sites

Elrico,

I think what's important is that you get the FOV and image scale that you want.  That will be a function of your sensor size (11mm diagonal for the Infinity) and effective focal length.  Try to get 105mm from the back of the focal reducer to the sensor.  With an SCT, you can screw the FR directly to the rear threads of the scope.  Test it out and put the image in astrometry.net and get the FOV.  Once you get that, there are programs that will give you the focal length you have based on the sensor size.  In any case, if it gives you the image scale you want then you have a winning setup.  If you want something wider (shorter FL), you need more spacing, and if narrower (longer FL), less spacing.  The wider you go, the more likely you will run into aberrations and vignetting.

Hope this helps.

Don

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.