Focuser types

[Marcelo F.]

Are there advantages and disadvantages between different types of focusers?
Or is a Crayford type focuser superior to a Hexafoc (helical rack) type focuser in all respects?

[PeterD]

Hexafoc is Bresser's name for their version of a rack and pinion focuser with a hexagonal draw tube. IMHO there is nothing helical about it. I have got it on one of my refractor and I must say it is a pleasant focuser to use. Rock solid, smooth and nice looking. Can be fitted with 1:10 reducer.
I have no personal experience with Crayford but I understand it uses friction between a roller and a draw tube instead of rack/pinion action. Supposed to be smoother.

[Lady Fraktor]

Both styles of focuser work well.
Like everything in this hobby there is low and high quality.
I would not say a crayford is superior to a R&P though I have yet to find anything to beat a Feathertouch crayford.
Depending on what your plans are, either may work well for you.

[Gordon]

Most of my scopes came with 2-inch crayford focusers. These worked well until I started to do astrophotography, and began using an electronic focus motor, then they started to slip because of the weight of the cameras. I attempted to adjust them and could never find the right "spot" to make them work properly. So I switched over to rack and pinion focusers and I've been very happy with them.

[Bigzmey]

While I don't do AP my experience with visual observing mirrors Gordon's. I prefer rack and pinion over Crayford focusers, because crayfords tend to slip under load. It does not take that much: 2" diagonal + glass grenade or filter wheel and wide field EP.

Linear Bearing Crayford Focusers handles load a bit better, but I have to keep playing with tension all the time: too little and draw tube slips under the weight and too much focuser wheel slips and you can't focus.

Rack and pinion - you set the tension once and forget.

[OzEclipse]

I agree with the opinions already stated but I would express it a little differently.....

Neither cheap poorly made "Rack and Pinion Focusers" nor cheap "Crayford Focusers" work very well for astrophotography.
They can also be very frustrating and less than ideal for visual observing.

I have a low profile Feathertouch Crayford on my 18 inch dob and it works beautifully at both low and high magnifications.

My Vixen VC200L has an excellent quality rack and pinion focuser. The last prime focus image I took had maintained the camera focus from the previous image some weeks earlier even though I had removed and reattached the camera. I didn't need to refocus.

My ED80 refractor came with a cheap and nasty Skywatcher single speed Crayford. It really limited the telescopes visual and photographic performance. The ED80 only cost me about USD300 in 2004. Eventually I relented and purchased a middle of the road GSO crayford 2 speed focuser. It is nowhere near as good as the two high end focusers described above but it does the job.

A good focuser is a worthwhile investment but if you have a cheap scope, you can easily spend much more on a good focuser than the scope. Some premium focusers can be adapted to all types of scope simply by buying a different focuser base. So you should keep the original focuser from your scope, if you decide to sell the scope, refit the original focuser before selling and fit the good focuser to your next scope. You won't recoup the cost of a good focuser fitted to a cheaper scope.

Joe

[Richard]

As mentioned it all comes down to money , but as I am not a big fan of the 'toothless wonder , crayford ' only had one good one a WO on my ex WO ED 80 , but here one can get a good rack and pinion for the price of a low quality Crayford
As Joe mentioned any substantial improvements , like finder, focuser and of course eyepieces , always keep the original when one sells the scope and if you are leaving the hobby then sell them separately

[Marcelo F.]

Thank you all for your opinion and description of your personal experiences with each one.
I just now noticed that the images are not showing up.
Here they are:



The second image explains what they mean by "helical rack" , for anyone who is used to working with motion transmissions knows that the inclination of the teeth decreases the contact area and in turn makes the movement smoother.

[Bigzmey]

Thank you all for your opinion and description of your personal experiences with each one.
I just now noticed that the images are not showing up.
Here they are:



The second image explains what they mean by "helical rack" , for anyone who is used to working with motion transmissions knows that the inclination of the teeth decreases the contact area and in turn makes the movement smoother.

This is my favorite type. As smooth as crayford but without slippage.

[Lady Fraktor]

Yes the hexfocuser does do a fine job, I have one on my Bresser 102mm f/13 and after some initial tweaking it works very well.

[PeterD]

The second image explains what they mean by "helical rack" , for anyone who is used to working with motion transmissions knows that the inclination of the teeth decreases the contact area and in turn makes the movement smoother.

Marcelo, my bad. I have never noticed the teeth are angled. I checked my refractor this morning and they are angled indeed.

One drawback with hexafoc: The drawtube extends by 45mm only. If one needs more a spacer ring has to be fitted.