Return to the Cloudy Nights Telescope Reviews home page
   · Get a Cloudy Nights T-Shirt · Submit a Review / Article   

Click here if you are having trouble logging into the forums

Cloudy Nights - Official Forums of the 2009 International Year of Astronomy
Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
  You are not logged in. [Login] Forum Archives · Entrance · Main Index · Search · New user · Who's Online
FAQ · Calendar

Equipment Discussions >> ATM, Optics and DIY Forum
Previous thread Previous   Index   Next thread Next   Threaded Mode Threaded  

Pages: 1
backwoody
Pooh-Bah


Reged: 01/08/07
Posts: 1114
Loc: Idaho USA
Calculating exit pupil new
      #3371689 - 10/04/09 10:44 PM
Edit post Edit   Reply to this post Reply   Reply to this post Quote Quick Reply: Quick Reply  

I've drawn a mental blank on a question asked me by another amateur astronomer about exit pupil calculations for a given telescope and eyepiece.

How is exit pupil calculated? As I recall, it depends on focal length, aperture, f/ratio, and the field stop of the EP in use.

Thanks in advance for refreshing my poor memory.

--------------------
woody

a parsec farther out...


12.5" f/4.8 custom truss dob, EQ platform

Post Extras: Print Post   Remind Me!   Notify Moderator  
Gene Baraff
sage


Reged: 03/22/09
Posts: 246
Loc: Berkeley Heights, N.J.
Re: Calculating exit pupil new [Re: backwoody]
      #3371703 - 10/04/09 10:49 PM
Edit post Edit   Reply to this post Reply   Reply to this post Quote Quick Reply: Quick Reply  

Exit pupil equals the diameter of the objective divided by the magnification of the scope

or what is exactly the same thing,

equals the focal length of the eyepiece divided by the f/number of the objective.

Gene Baraff

Post Extras: Print Post   Remind Me!   Notify Moderator  
backwoody
Pooh-Bah


Reged: 01/08/07
Posts: 1114
Loc: Idaho USA
Re: Calculating exit pupil new [Re: Gene Baraff]
      #3371727 - 10/04/09 11:00 PM
Edit post Edit   Reply to this post Reply   Reply to this post Quote Quick Reply: Quick Reply  

Thanks Gene. So, confirming with an example, a 24mm eyepiece used in my f/4.8 newtonian would yield an exit pupil of 7.29mm. Correct?

Of course, a 7.28mm exit pupil is only usable for someone with youthful eyes...

thanks again.

--------------------
woody

a parsec farther out...


12.5" f/4.8 custom truss dob, EQ platform

Post Extras: Print Post   Remind Me!   Notify Moderator  
Gene Baraff
sage


Reged: 03/22/09
Posts: 246
Loc: Berkeley Heights, N.J.
Re: Calculating exit pupil new [Re: backwoody]
      #3371770 - 10/04/09 11:31 PM
Edit post Edit   Reply to this post Reply   Reply to this post Quote Quick Reply: Quick Reply  

Quote:

Thanks Gene. So, confirming with an example, a 24mm eyepiece used in my f/4.8 newtonian would yield an exit pupil of 7.29mm. Correct?





No. I get 24mm divided by 4.8 = 5mm

Gene

Post Extras: Print Post   Remind Me!   Notify Moderator  
backwoody
Pooh-Bah


Reged: 01/08/07
Posts: 1114
Loc: Idaho USA
Re: Calculating exit pupil [Re: Gene Baraff]
      #3371799 - 10/04/09 11:53 PM
Edit post Edit   Reply to this post Reply   Reply to this post Quote Quick Reply: Quick Reply  

Of course, Gene. I inadvertently made the calculation for a 35mm ep - which would yield an exit pupil of 7.29.

For the 24mm, it's 5mm indeed.

thanks again for the help.

--------------------
woody

a parsec farther out...


12.5" f/4.8 custom truss dob, EQ platform

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1

Previous thread Previous   Index   Next thread Next   Threaded Mode Threaded  

Extra information
7 registered and 6 anonymous users are browsing this forum.

Moderator:  Don W, Mike I. Jones 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 86

Jump to

CN Forums Home



Cloudy Nights Sponsor: Astronomics