Focusing a SCT

[oldturk]

Greetings and apologies if this subject has been aired in the past. The SCT has a very wide focusing range and old gits like me become easily confused when changing from visual to camera, or using the focal reducer. Each of these changes requires several rotations of the focus knob. When changing back, I have no idea where I am. Are there any solutions other than a brain transplant for me?

Brian.

[brantuk]

I've not seen a solution to this Brian. Some Sct's have a dual speed focuser attached with a graduated scale like refractors and drawtube so you can note the focus positions. But Sct's normally just have the focus knob. I guess you can set a reference position and count turns from there.

For the cameras it's best to focus using a bahtinov mask. You can also get software controlled motor focusers that may (or not) have set points in the software - but failing that I think we are stuck with the usual focusing knob

[Psychobilly]

I added a graduated "knob" to the focuser and kept a note on the number of revs needed to make the large focus changes when changing setups..

A larger diameter focus knob also makes fine focusing a lot easier... or for a quick fix.. use a peg...

Peter...

[Merlin66]

A vegemite lid (drilled with a 1.25" hole for the rubberised Celestron knobs) can be "graduated" along the rim and used to find and repeat focus.

Cheaper than the ScopeStuff version from the US.

*EDIT* Image attached

[Space Bat]

This is a problem - wish there was a better way....I tend to fudge my way into focus rather than any technique

I am usually ok with switching between reducer and the DSLR and normal....but using the DFK is a real pain as FOV is so small...and much swearing can be heard when trying to use this...

[oldturk]

Thank y'all for the help and advice. A combo of graduated rim and counting rotations seems to be the answer - now was that three or four turns...

[valleyman]

Once focused with a large EP say 30mm then as you put smaller EP's in turn focuser clockwise. mmmmmmmmmmmmmm or was it anti cloakwise.

[Merlin66]

I've just added (like many before me...) the S/W electronic focuser motor to the C11.

An aluminium bracket from the "spare" finder screws on the OTA holds the motor. I just used the knurled knob that comes with it for the ED80 as a pinion....a small length of felted draught excluder superglued as the drive belt onto the existing rubber focuser knob....majic!

Now I can control the focus from the desk using the Shoestring adaptor FCUSB

The Shoestring Astronomy Store - Focus Motor Control Products

[oldturk]

Thanks Merlin66 - a neat option. B

[BlueAstra]

Here's another motor focus option if you fit the feather touch micro focusser. I use a bahtinov mask to focus. What I then did was note the number of full turns of the corse focusser from my camera setup to various visual setups (eg with/without barlows) and keep a record in my notes. That way I can easily get into rough focus prior to a fine focus with the mask.

[Woody]

Love the Vegemite lid Mod.

I would do the same on my Mak bit I don't like Vegemite;)

[Psychobilly]

Other potted spreads or beverages are available

[Merlin66]

I can ship "Vegemite Focus Adjusters" (Patent pending) worldwide...I just have to increase my consumption to meet demand!

(Wot - an Aussie who doesn't like Vegemite - C'mon mate! ;-) )

[Woody]

Yeah, I am letting the team down.

Ah well you know what they say, you either love it or hate it:)