Feathertouch vs Crayford for SCT

[hunterknox]

Hi all,

I'd like to upgrade the focuser on my C8. Can anyone talk me through the pluses and minuses of the feathertouch microfocuser (which still moves the primary mirror) vs. a decent Crayford?

[ollypenrice]

I have a Crayford on a Meade, though only a Revelation version. I'm not a Crayford fan, preferring an R and P any day, but I see the issue as being the moving of the mirror. If Feathertouch don't do a rear mounted R and P I'd go for a Moonlite Crayford myself. These hold the flattener in the drawtube to preserve chip distance, which is nice. I see one a couple opf times a year when a guest brings one down. http://www.franskroon.nl/equipment.htm

Olly

[Merlin66]

I find the feathertouch ideal on the C9.25 - very little (if any) mirror flop - that's to focus and hold a star on a 20 micron slit.

The Crayford adds to the rear weight and distance and impacts on the positioning of focal reducers etc.

I'd go for the feathertouch first - try it and if it works also for you then issue solved.

[m.tweedy]

Hi all,

I'd like to upgrade the focuser on my C8. Can anyone talk me through the pluses and minuses of the feathertouch microfocuser (which still moves the primary mirror) vs. a decent Crayford?

I had a WO Crayford on my C8 which worked very well so much so that when I got the C11 that had a feathertouch microfocusser on it I still went and got a moonlite crayford as it eliminates mirror flop. I get rough focus on the normal focusser and fine tune it with the crayford.

[johninderby]

The Microfocuser works very well on the 8". The focuser shaft that moves the mirror only has one bearing and the focuser shaft can twist from side to side a bit as it's only held in position by the one bearing. The microfocuser has two bearings, one each at the top and bottom of the microfocuser housing. The focuser shaft is therefore held in position more securely which greatly reduces the twisting or side to side movement of the focuser shaft and therefore helps stabilise the mirror itself. It doesn't completely eliminate the mirror shift but greatly reduces it.

The regular 2" FeatherTouch crayford is quite compact and a lot lighter than a MoonLite, but more expensive.

So on the C8 the Microfocuser will work just fine but when you get to the C11 it isn't as good at reducing mirror shift simply due to the heavier mirror.

John