Help with crayford focuser info

[wizard007]

Hi guys,

I'm just looking for a little advise on the Crayford focuser.

I've got a 250PX Dob and when my wife and I observe together, having slightly different eyesight we're constantly twiddling the focuser and sometime nudging the object out of view!

Can someone explain to me the Crayfor focuser benefits?

As I understand it you have two speeds of focus allowing finer tuning. Is that all or are there any other benefits?

Are there different makes and if so which are the best for my scope?

[johninderby]

A dual speed crayford focuser to fit your scope would cost from £100.00 to £500.00. For about £129.00 you could get a SkyWatcher crayford that's a bolt on replacement (from FLO etc.). The focuser will be much smoother and more precise to use and the dual speed makes it easier to focus accurately. The fine focus knob only requires a finger touch to move and so it doesn't move the scope when focusing.

One important thing to watch out for is that the 250PX has a larger hole in the OTA for fitting the focuser than anyone else uses and the base plate that comes standard with most replacement crayfords won't quite cover the hole in the OTA and the bolt holes will be in the wrong place as well so you will need to get a new baseplate that matches the 250PX.

There are other choices such as MoonLite and Feather Touch but they're a lot more expensive. ££££

John

[Merlin66]

You should consider a Skywatcher electronic focuser motor; it will reduce the "shakes" to a minimum.

A change to the Crayford etc is usually driven by lack of back focus for imaging...

Ken

[wizard007]

One important thing to watch out for is that the 250PX has a larger hole in the OTA for fitting the focuser than anyone else uses and the base plate that comes with standard with most replacement crayfords won't quite cover the hole in the OTA and the bolt holes will be in the wrong place as well so you will need to get a new baseplate that matches the 250PX.

Thanks for the input guys.

The Skywatcher Crayford says it is an exact fit for 9" to 15" tubes.

Is that not the case with mine being a 10"

Skywatcher - Dual-Speed 2” Low Profile Crayford Focuser for Skywatcher & Celestron Newtonian Telescopes

[Chris H]

The Skywatcher dual speed is low profile and you need to check that it has enough out focus, if you have 2" ep's you may find that you need to add an extension tube to get them to come to focus.

[johninderby]

Thanks for the input guys.

The Skywatcher Crayford says it is an exact fit for 9" to 15" tubes.

Is that not the case with mine being a 10"

Skywatcher - Dual-Speed 2” Low Profile Crayford Focuser for Skywatcher & Celestron Newtonian Telescopes

The base fits from a 9" up to 15" tube, which covers every size in-between so it will fit yours just fine.

John