Quote:
|
Originally Posted by BC
If a scope was 1250mm focal length and half the diameter it would be f/10, and suddenly really good for planets. So how come letting in a quarter of the light transforms this into a good planet viewer?
|
There is nothing to say that a well made f5 is any less capable of good planetary performance than a scope at f10.
There are two factors at play here.
1: It is much easier to manufacture quality optics at f10 than at f5.
2: The f10 will have a much larger "diffraction limited" field of view. If the subject is kept in the centre of the FOV this isnt an issue.
You wont gain anything by masking the scope down. You arent improving the figure of the optics and are throwing away resolving power. To mask down a 10 inch GS scope enough to remove the spider and secondary holder from the light path, you are down to about 90mm aperture .