Crayford Focuser Question

[Kerrp30]

When they state the size of a crayford Focuser such as 2" or 3" they are talking about the opening for the Eyepiece or other attachments, is that correct or is it the amount of travel the focuser has?

Reason I ask I noticed some scopes now have 3" why is that?

Thanks

Paul

[fredster]

Its the focuser draw tube diameter for accessories. Will also come with 3"-2" adapter and 2"-1.25" adapter.

[Bizibilder]

It is the size of the hole for the eyepiece etc. Normally 2" withan adapter for 1.25" is standard on any decent focusser.

Must.....type....quicker.......

[ollypenrice]

It is the size of the hole for the eyepiece etc. Normally 2" withan adapter for 1.25" is standard on any decent focusser.

Must.....type....quicker.......

I'm not sure this is right. EPs come in 1.25 or 2 inch but focusers come in three to four inch, and parhaps more. The issue is to do with imaging using large format sensors when you are using screw fit attachments. A 2 inch push fit would vignette a large sensor, as would a small diameter drawtube. Our TEC140 has a 3.5 inch drawtube which means that, with the dedicated flattener, it can cover a 60x70mm sensor (which I don't think exists in astro CCD yet but does in film). In a nutshell the 3.5 inch focuser (mercitully an R and P and not a Crayford) future proofs the instrument against the larger chips which will certainly come.

Olly

PS Forgive me but I'm a notorious hater of Crayfords, as is well known.

[Astro_Baby]

Indeed as will larger eyepieces. Explore Scientific already have a 3" eyepiece in development.