Motofocus or Crayford?

[Daz1969]

Hi there, Iam going to be doing some deep space pics shortly but need to upgrade my sct standard focuser.

Question is what do i get ? Iam very keen on the look of the JMI motorfocus but price is about £150 and puts me off a tad. I have now found a 2 speed Crayford type for sct's on Ebay for £70 (nicer sounding number!)

Can any one tell me the pros and cons for either focuser ?

I cant afford to make the wrong decision so if it means saving up for the more expensive option then so be it.

Many thanks

Daz:icon_salut:

[Daz1969]

Thinking about it,if i did get a crayford do i need to de activate the sct focus knob in some way. What happens to it after the crayford is fitted?

So many questions:)

Daz

[philsail1]

Hello Daz.

Well, I'm in the same position as you - in thinking of buying a "Crayford" focuser for my Celestron C8 SCT. (Seems like you've spotted a bargain on e-bay! Just ensure that the one you are looking at can be rotated 360 degrees once fitted to your scope, otherwise it could foul the existing focuser).

Once fitted, the existing focuser doesn't necessarily become redundant (and you don't need to de-activate it). From what I've read, you may still find that you have to use it occasionally, to achieve focus when attaching something to the end of the Crayford. (Crayfords on SCT's may not have enough "travel" to achieve focus on their own - this isn't a drawback, it's just one of those things with Crayfords and SCT's).

Regarding electric focusers. I bought one for my Skywatcher 200mm Newt, but didn't like it. It worked fine, giving a very precise focus at all times. I just found that it was slow to change focus - say when I want to add my binoviewers (which need a lot of adjustment on the focus range), even on the course focus movement. I would say that if you can get an electric focuser with some sort of "clutch" where you can disenguage the mechanism whenever you might need to adjust the range of focus quickly, then that would be ideal.

That's about all I know on the subject! I'm sure other will soon give further (and perhaps more knowledgeable advice soon).

Best wishes,

philsail1

[Daz1969]

Thanks for that Phil, Am totally in two minds as to what to do. As usual the price is a big factor for me, Mmmm , Idealy i would like to find a 2nd hand jmi motofocus for around £80 but i think i may be waiting a while as i have never seen many come up for sale.

Good luck with yours!

Daz

[philsail1]

Thanks Daz - I'm leaning towards the "Scopes n' Skies" Crayford at £116.00.

Regards,

philsail1

[Daz1969]

Anyone else have any thoughts ?

Daz

[m.tweedy]

I currently own a C8 SCT and have a WO crayford focusser attached. I tend to achieve rough focus with sct focusser and have the crayford set at mid point then achieve fine focus with the crayford. works well for me. If necessary you can achieve very fine focus with one of the focus masks available online.I have never had a motor focusser as I feel I can achieve better focus on the current set up and there are enough wires hanging around in the dark drawing power and waiting to be snagged.

[Daz1969]

Sounds like folk like the crayford. I still cant help thinking that an electric one would eliminate the shakes when focusing.

Yet crayford a fair bit cheaper.

Oh what to do ?

[philsail1]

Daz,

A further thought on electric focusers.

Yes, an electric focuser would totally eliminate the "shakes" when focusing, but you are still left with the fact that hitting that "sweet spot" with any focuser is, at the end of the day, entirely dependant on the MK1 eyeball. Even with the "fine" foacuser on my SCT, I'm still playing about for several seconds trying to decide the exact point of perfect focus. I find my eyes watering sometimes! I have heard (can't remeber where) that with any focuser, it is best to reach focus whilst racking the focus one way (can't remember whether it's when focusing "in" or "out." Your eye is supposed to recognise the best focus only in one direction. They say the military teach this type of focusing. (You might try "googling" "How to reach perfect focus").

As I said in my previous post - I personally found an electric focuser a bit fiddly to use, for the simple fact that I could not disengage it to alter focus rapidly when needed. (and even with the electric focuser, I found myself still playing it backwards and forwards to get that "perfect" spot!).

I think a "Crayford" would work well with an SCT - because of the fact that it would eliminate mirror shift (thus reducing much of the shakiness in focusing using the standard SCT focuser) and because a "Crayford's" focusing movement is "in" and "out" I think this would make focusing that much easier and steadier on an SCT.

Regards,

Philsail1

[Daz1969]

Yeah Phil, i think you may be right about the crayford eliminating mirror shift ! Iam so confused now.

I plan to do a lot of imaging so the speed of focusing is not realy an issue for me.

Mmmmm. Dont know what to do.

Cheers

Daz

[GazOC]

I use both "systems", IMHO motor focus is better for imaging but I prefer the simplicity of the Crayford for visual, I also prefer also the tactile feedback of moving the focuser myself (I don't know why??!?!) when I'm observing.

[Daz1969]

Cheers Gaz,

I think in reality iam try to justify the electric one. I realy do like the idea of not touching the scope at all during focusing,so maybe leaning toward the elec one.Mmmmmmmmmm i think:icon_scratch:

Daz

[GazOC]

I think its easier to justify an electric focuser if you are intending to do a lot of imaging. For visual a dual speed Crayford is more than good enough (you could even make a case that the dual speed is overkill!!).

Just my 2p. YMMV.

[Daz1969]

Thanks for your advise chaps i have made up my mind !

ELECTRIC IT IS !

Just got to find one for the right money now.

Thanks again

Daz