Secondary Size question

[toryglen-boy (Duncan)]

Howdy!

i want to get close to the same flat field that an RC would give me, but it appears i have champagne tastes, on a beer budget.

So, here is my plan...

the secondary on my 200mm F5 scope, is a little too small, i can really see it with severe vignetting on my images, although there is no surprise in that, i already have an MPCC, that i cant use with the QHY8 at present, as i need to get around to ordering an adaptor from Peter Lee in HK, but at any rate, would a larger secondary, and an MPCC give me much of the same effect as a 200mm RC?


my thinking is, the larger secondary would help with vignetting, and the MPCC would give a flat field, buy what do i know, thats why i am asking on here!

anyone care to postulate what size secondary i would need?

[bojan]

Have a look here:
http://www.dalekeller.net/ATM/newton...t/newtsoft.htm
This free software will answer all your questions :-)

This one is a bit more involved, however much better in terms of optical ray0tracing/design.. also free.
http://bhs.broo.k12.wv.us/homepage/a...ot/winspot.htm

[toryglen-boy (Duncan)]

Originally Posted by bojan

Have a look here:
http://www.dalekeller.net/ATM/newton...t/newtsoft.htm
This free software will answer all your questions :-)

This one is a bit more involved, however much better in terms of optical ray0tracing/design.. also free.
http://bhs.broo.k12.wv.us/homepage/a...ot/winspot.htm

Thanks for that Bojan, it gives those that know what they are doing the power to get the answers, as my knowledge of optics is fairly limited, i was hopeing someone could just answer in simple terms.

Not that i am not grateful !!

[bojan]

sorry.. I was too hasty :-) Can you give us some numbers and measures, like diameters of the mirrors, focal lengths, tube diameter, length of focuser etc.. I will enter this into newtwin and calculate the best secondary diameter for you

[bmitchell82 (Brendan)]

the answer is yes it will decrease your vignetting... the answer is No it will not make your scope like a RC...

[toryglen-boy (Duncan)]

Originally Posted by bojan

sorry.. I was too hasty :-) Can you give us some numbers and measures, like diameters of the mirrors, focal lengths, tube diameter, length of focuser etc.. I will enter this into newtwin and calculate the best secondary diameter for you

Hi fella, its 200mm F5, and at this point thats all i know, will post some number tonight