Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Equipment

Pages: 1
mark379
sage
*****

Reged: 02/07/09

Loc: New Jersey
RACI FInders verses RA Reversed image : lim Mag
      #6046691 - 08/26/13 10:25 AM

Hello,
I'm just a bit curious on the limiting magnitude difference between the reversed image and correct image finders. Both are right angle, one is 8x50 reversed, the other 9x50 RACI
How much light does the prisim in the RACI "eat up" when it comes to faint stars?


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: RACI FInders verses RA Reversed image : lim Mag new [Re: mark379]
      #6046721 - 08/26/13 10:37 AM

I would expect you should see no difference, really. If the Amici prism is coated, and the other finder's prism is too, or if the other finder uses a standard aluminum coating (most likely) mirror, the transmission difference should be no greater than about 5%, which is about 0.05 magnitude. Even a 10% difference, which would apply if a mirror were dielectric, is still 0.1 magnitude.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: RACI FInders verses RA Reversed image : lim Mag new [Re: mark379]
      #6046722 - 08/26/13 10:38 AM

Quote:

Hello,
I'm just a bit curious on the limiting magnitude difference between the reversed image and correct image finders. Both are right angle, one is 8x50 reversed, the other 9x50 RACI
How much light does the prisim in the RACI "eat up" when it comes to faint stars?




My thinking:

Not enough to worry about and certainly not enough to make up for the advantage of the 12.5% greater magnification...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: RACI FInders verses RA Reversed image : lim Mag new [Re: Jon Isaacs]
      #6046747 - 08/26/13 10:52 AM

Indeed, the magnification difference will almost certainly be the dominant factor. A smaller exit pupil darkens the sky, thus allowing slightly fainter stars to shine through.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: RACI FInders verses RA Reversed image : lim Mag new [Re: GlennLeDrew]
      #6046765 - 08/26/13 11:01 AM

Quote:

Indeed, the magnification difference will almost certainly be the dominant factor. A smaller exit pupil darkens the sky, thus allowing slightly fainter stars to shine through.




Glenn:

The other night I was comparing two straight-through finders, both Synta, one was an 8x50, one was a 9x50. There was a clear difference in what was visible. The 9x50 also had a wider field of view so the 9x50 stayed on the scope.

Jon


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


Extra information
14 registered and 24 anonymous users are browsing this forum.

Moderator:  zjc26138, tecmage, rflinn68 

Print Thread

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


Thread views: 109

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics