what Size secondary for a 16"

[Daniel-K]

Im in the process of upgrading to a 16" scope but what size secondary mirror is best for visual?

Dan

[Moonshane]

What is the focal ratio Daniel ?

[estwing]

you on a build Danny-boy?

[crashtestdummy]

Have a look on the Oldham optical site at mirror sets and they usually list the secondary sizes for each size/focal ratio

[Daniel-K]

Sorry it's 1800 F4.5

No cal but im close to getting a sumrian. Had a good offer on a mirror just need to figure out a way to collect it

[Mike73]

I have a 75mm in mine Dan, same primary.

I think the standard GSO secondary for this mirror is 82mm so the 75mm just covers it but only just! It was what Michael recommended at the time anyway.

[Daniel-K]

thanks mike I think I'll go for the 82mm then.ive got to send it to Michael so he can put a heater on

[faulksy]

if you go down the 00 route with the secondary they fit heaters

[Mike73]

thanks mike I think I'll go for the 82mm then.ive got to send it to Michael so he can put a heater on

Dan if you are getting Michael to make one just tell him exactly what equipment you use and let him work out which mirrors will be best. He's the one thats built hundreds of scopes and has the experience.

Also make sure you tell him if you are using Paracorr 2, SIPS, what focuser you have or want and what EP's you have? Its a custom scope Dan, give him the correct details and he'll build the scope around that.

[swamp thing]

Dan

Is that as big as you're ever going to go......?

If not I'd pass on a 16" after a 14" it's not a big upgrade. I'd hang on for a bigger upgrade myself.

Just my 2p's worth.

[estwing]

Yep I'd skip to at least 18" I went from 12.5" to 18" people say 4" min but 14" is a great platform to observe with....er I'm not helping here!?!? Sorry!

[Moonshane]

this is more of a complex issue than it seems at first - you need to consider focal ratio, primary size , the types of eyepieces you use and the types of observing you prefer.

my 16" f4 is 82mm I think and anywhere between that and 75mm should service most generalist purposes I would think.

there's a good section on this in the Kriege and Berry book which I will try and sort out later.

[kev]

In particular how far the focal plane is from the secondary

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