Decisions on a Prism?!

[Rob]

All,

So I'm trying to decide on if to grab a Prism for my New (old) Revelation 80ED F6.8 scope. I know its kinda on the cusp of a good/not so good idea due to its F Ratio. I just can't decide.... Any thoughts?.

Cheers Rob

[jetstream]

👎

my vote

[Rob]

Needless to say I've always been a Dielectric Mirror Guy!.. Just been reading a lot about Prisms and planet performance. Having said that I'm sure one would perform very well in the 127L at F9.5!

 

[John]

I'd tend to go for a mirror at F/6.8. Thats what I use with my Vixen ED102SS F/6.5, Skywatcher ED120 F/7.5 and TV Ranger F/6.8. The Tak FC-100DL F/9 gets the Baader T2 Zeiss prism.

[Scott42]

are we talking 1.25" diagonal or 2"?   If you're trying to keep it small & light the Takahashi 1.25" prism would be nice, it has a very short light path, it worked fine on my f/7.5 refractor.  Probably better to stick with a mirror diagonal in the 2" size IMO.

[Stu]

I've used prisms quick successfully in my Tak which is f7.4. F6.8 is probably on the cusp of being better using a mirror. I was impressed by the performance at f7.4 though.

[Paz]

I'd vote for a mirror diagonal unless you are struggling to get enough in focus in which case a prism diagonal might make the difference.

[Rob]

Thanks all for the replies. Yes it would be a 1.25" for weight & travel reasons, and yes I agree on the cusp thus causing the dilemma.

Well I have a 2" Dielectric diagonal, and I also have an old 1.25" TAL diagonal. To be far the old TAL is quite impressive on contrast. Its from a TAL 200K -  and machined from a single block of aluminum, however what I don't like is that there's no compression ring to clamp the EP in, but I have replaced the steel screw with an Ali one.

Rob

Edited September 26, 2019 by Rob