I see some units come with different size correctors; Williams Optics has a 1.6X Siebert has the 1.8X TV 2x ..is this for fast and slow scopes? what would I need for my f/5 Genesis? and a different one for my MN66?? thank you for your help.. JM
question on correctors
Started by Midnight Sun, 08/21/2006 02:41PM
Posted 08/21/2006 02:41PM
Opening Post
Posted 08/22/2006 02:15AM
#1
I see some units come with different size correctors; Williams Optics has a 1.6X Siebert has the 1.8X TV 2x ..is this for fast and slow scopes?
John, the quick answer is no. How much magnification you will have to accept to make the binoviewer focus is a function of how much in-focus your scope has in reserve. The optical path length through a binoviewer is on the order of 110mm. Assuming that you use the same diagonal as you use for mono, the scope's focuser would need to be racked in over 4" on your TV to come to focus without any corrector!
The less in-focus you have in reserve, the more you have to move the focal plane back, which means more magnification. Often Cassegrains like your MN66 don't need any correction at all because the motion of the primary when focusing is magnified by the secondary. Also, there are other ways to skin the cat. Denkmeier and Siebert both offer a clever dual lens system that effectively reaches out and grabs the light cone forward of the focuser and brings it back to the binoviewer. The very expensive A-P Baader binoviewer uses a very compact prism diagonal to reduce path length compared to a mirror diagonal.
On your TV you can measure the in-focus available, but the actual calculation for what rated magnification corrector you would need is complicated (for me, anyway). To give you an idea of the relationship between corrector mag and in-focus required, go to the A-P website at
http://www.astro-physics.com/index.htm
select 'accessories' then 'visual accessories' and finally 'Mark V Binocular Viewer.' Scroll down to the bottom of that page and it gives the required in-focus for several configurations.
Good luck,
Milt
John, the quick answer is no. How much magnification you will have to accept to make the binoviewer focus is a function of how much in-focus your scope has in reserve. The optical path length through a binoviewer is on the order of 110mm. Assuming that you use the same diagonal as you use for mono, the scope's focuser would need to be racked in over 4" on your TV to come to focus without any corrector!
The less in-focus you have in reserve, the more you have to move the focal plane back, which means more magnification. Often Cassegrains like your MN66 don't need any correction at all because the motion of the primary when focusing is magnified by the secondary. Also, there are other ways to skin the cat. Denkmeier and Siebert both offer a clever dual lens system that effectively reaches out and grabs the light cone forward of the focuser and brings it back to the binoviewer. The very expensive A-P Baader binoviewer uses a very compact prism diagonal to reduce path length compared to a mirror diagonal.
On your TV you can measure the in-focus available, but the actual calculation for what rated magnification corrector you would need is complicated (for me, anyway). To give you an idea of the relationship between corrector mag and in-focus required, go to the A-P website at
http://www.astro-physics.com/index.htm
select 'accessories' then 'visual accessories' and finally 'Mark V Binocular Viewer.' Scroll down to the bottom of that page and it gives the required in-focus for several configurations.
Good luck,
Milt
Funding Member
