Does all refractors need baffles?

[jorn]

I am building a very short focal langth telescope at f 3. Does it need baffles?

[Whippy]

From what little I know about optical design, putting baffles in a refractor running at f3 are the least of your worries...

Tony..

[Milamber]

All optical systems can benefit from baffles - the more chance there is of stray internal light reflections the more they are needed. Ergo, a shorter fl scope would maybe have less need of them than a longer fl scope but I think Tony has it right, you've got more important issues ahead of you (like flat fields and tiny depth of field) to worry about first.

Arthur

[Doc]

F3 will be very hard to achieve.

Wish you luck.

[Capricorn]

A baffle or two will do no harm. A couple of low ones will simply intercept any light reflecting along the tube body. It is light coming in from the side that you will be trying to block.

I assume that this is for a finder scope?

Presume you have the lens?

If not have a look at surplusshed they sell optics and have a few at f/3 also f/2 and f/2.5. Nice looking 60mm dia 150mm fl.

[jorn]

The lens look like this :

Its made for projecting large images on a screen.

It uses 4 lenses in 3 groups and it's on 300mm and dia 100mm (f3) The image circle on infinity is around 350 mm ! So i guess the lens could be used for large format photography. What i was hoping for was a small compact refractor with let's say 20x enlargement. If anyone has another idea, please let me know.

[DeanWatson]

Mmm- it'll give hideous image quality, especially at the edge of the field of view. You'd be better off with an F5 4 inch refractor methinks. Also, sounds alot of optical elements. The more you have, the more light loss you'll experience, negating the aperture advantage.

Might be an interesting experiment mind you, but not a useful instrument.