SCT baffle tube

[Joshua Bunn]

Hi everyone,

Recently i read something on the net about looking down the baffle tube of a SCT, from the imaging end, and seeing all of the secondary mirror, and this is where im unsure, maybe all of the primary reflection or something - I know, pretty vague, but Its a little vague in my memory. :shrug: It definetly said something about seing something in the secondary or around it :question:
I think the issue was in relation to whether the secondary mirror and baffle tube sizes were right for each other such that all the light gathered by the secondary mirror is delivered to the focal plane.
Has any one seen such an article talking about this?
Im aware there are articles about the baffle tube being the correct design so it eliminates stray light - this isnt what am after, I found some of them while doing some searches for the above information, so if anyone would like to see these, i can provide a link.

Thanks

[Poita]

It's all a bit vague :) My first question would be what are you trying to achieve/worried about.
Is it something re your particular scope, or just out of general interest?

[Joshua Bunn]

Yes, you got that right, :lol:,
It was something i read and, in the past i had been looking down the baffle tub of my scope so i wanted to compare - to see how my scope compared to how they are suppose to be designed. Optics are rather interesting IMO. Also out of interest re SCT design. BTW, the scope is a LX200 12" ACF.

thanks

[issdaol]

Hi Joshua,

Sounds strangely like checking Secondary Mirror On Axis alignment for a Classical Cassegrain.

A Cassegrain has a long baffle tube protruding from the Centre of the Primary Mirror. You should be able to see the whole of the Secondary Mirror with equidistant spacing around the entire circumference.

Cheers

[Joshua Bunn]

Thanks Issdaol,
Yes this is the case, and i gues i should have my eye at the focal point?
BTW, can someone inform me as to how to reply to multiple messages with quotes in the same reply message?:shrug:

[mill]

Just click the plus sign next to the quote sign and then at last one you want to quote press the quote button.

[Joshua Bunn]

Thanks Mill.:thumbsup:

[multiweb]

I drew a template on flute panel (image #1) a while ago to help me eyeball those reflections on my C11. The issue is to keep your eye inline with the primary axis so having this board with a peep hole helps. All you have to do is match the larger of the two circles within 10mm of the edges of your primary. Move back and forth until you match it to the edge of your mirror. When you move side ways you'll see something like image #2. Next step is to move so you match the horizontal/vertical lines both in the primary reflection and in the secondary reflection in the primary. From there if you're off (picture #3) or in the ball park (picture #4) is pretty easy to visualise. What's good about this system is that it is repeatable and you can place your eyeball pretty much in the same spot every time. HTH.

[Joshua Bunn]

thanks Marc for your description.

Josh