... Roman, Short focal lengths are nice because they allow wide fields. Another big advantage, to me, is the shorter tube length. If a 6 f/4 is as long as aMessage 1 of 45 , Mar 19, 2006View Source
> It was not my post but I will answer anyway...
> What is wrong with short EFL? Why 6" f/4 apo telescope is worse than
> 6" f/8 one if OTA lengthes are equal? High relative aperture is
> definitely good for CCD imaging. You are always can use cheap
> 2x barlow lens for 6" f/4 apo but you will have problems with 2X focal
> reducer with 6" f/8 telescope.
Short focal lengths are nice because they allow wide fields. Another big
advantage, to me, is the shorter tube length. If a 6" f/4 is as long as a
6" f/8, then it is not as portable and not as easy to mount as a 6" f/4 that
is 24 inches long. The big advantage of a short tube is gone.
Clear skies, Alan
... Another possibility I ve recently encountered is a variation of the Schupmann. While the lens tilts probably won t let it be pushed for speed, it can beMessage 45 of 45 , Jul 20, 2007View Source--- In ATM_Optics_Software@yahoogroups.com, chris1011@... wrote:
>Another possibility I've recently encountered is a variation
> In a message dated 3/17/2006 5:31:03 PM Central Standard Time,
> dschaack@... writes:
> > Many years ago I asked a question in this newsgroup about possibility
> > of the correction of secondary spectrum with standard glasses,
> I think you can, but the designs always seem to come out with very long
> distances for short EFLs.
of the Schupmann. While the lens tilts probably won't let it
be pushed for speed, it can be compact relative to the focal
length, e.g.(145 mm f/10):
http://users.rcn.com/rflrs/Schupmann01-50x.len OSLO input file
http://users.rcn.com/rflrs/Schupmann01-50x.prg KDP input file
http://users.rcn.com/rflrs/Schupmann01-50x.txt TEXT prescription
http://users.rcn.com/rflrs/Schupmann01-50x.zmx ZEMAX input file