Crayford focussers???

[trufflehunter]

Can someone please explain how a Crayford focusser differs from a regular rack and pinion? I've searched the web and can find plenty of references to them, ie "this telescope comes with a nice shiny Crayford focusser!", but nowhere can I find any mechanical details!

Just me being a sticky beak!

[atalas]

Good question Wayne !:confused:


Louie :confuse2:

[Howzat]

Found this on the astronomy.com forums

Although looking at my "crayford style" focuser it seems to still have a rack....
I might have to look into this further.... :confuse3:

[atalas]

I guess Phil that there are crayfords and then there are crayfords ! $$
Thanks for the info .

Louie:cheers:

[Starkler]

Typically the focuser tube runs between four small bearings on one side, and the round focuser knob shaft against a flat machined surface on the other.

The advantages are no slop or backlash in the movement.

[RAJAH235]

Have a look here. L.
http://www.bintel.com.au/JMI.html

[Starkler]

Found this picture of a home made crayford focuser.
Like they say a picture is as good as a thousand words.

http://users.pandora.be/Urania11/Temp/Focuser30.jpg

[Striker]

Gee you would think their would be some slippage with these focuser......whats stopping this from happening once she is loaded up.....intersting.

[mick pinner]

every good idea has it's drawbacks, unless you secure it with the locking screw it will move if knocked.

[Starkler]

I got that picture from cloudynight forum. Sorry I dont have a link to the thread, but having been asked the same question the OP showed a picture of the focuser supporting the weight of a full wine bottle.

[astro_south]

Guys

I have a DX2 crayford from JMI and it is great. If I extend the focuser out in the proper method and then try and push the drawtube back in it doesn't move unless I apply a reasonable amount of force. It will not move if you just bump it or touch it with your hand and it won't move in use if you bump your eye up against the eyepiece. I guess the friction force from the various rollers on the drawtube is enough to hold it in place.

I have found the focusing with this focuser much easier than with my other rack and pinion focusers.

If your focuser has gears (and I'm not an expert) then I would be questioning it being called a true crayford. If it is "crayford like" then it might use rollers at the top and still employ the r&p gears at the bottom. What do the focusers referred to as crayfords that come with the GS scope upgrades look like?

[slice of heaven]

What do the gs focusers look like?
Black

They are a true crayford style. As in starklers picture, but with dressing. Nice and smooth so far.
I think with rack and pinion you need a quality one.

Slice

[Howzat]

Here's a pic of mine

[videoguy]

Phil

Looks like a standard rack & pinion focuser typical of most synta manufactured newtonians. Generally ok for most low power observations but reveal a frustrating amount of shifting at real high powers even with the tension screw.

[slice of heaven]

Yours is not the crayford type Phil.
I think Froggy posted a pic of his scope with the crayford.

Slice

[Howzat]

That kind of sux seeing as I paid extra to get a crayford. . . .

[astro_south]

Phil

What was the exact wording of what you paid extra for and how much extra did you pay (if you don't mind me asking)?

[slice of heaven]

That does Suck.
Get on the blower asap and get it exchanged.
Who supplied yours?

[Starkler]

Phil it should look like this.
Heres my GSO crayford

http://gar.customer.netspace.net.au/scope2/crayf.JPG

[slice of heaven]

Same as mine.
But yours fits the 10" properly Starkler.
They've thrown the same model onto the 12s.

Slice

[Howzat]

I paid for a GSO Deluxe 12" dob, from Andrews Communications, which is supposed to have a crayford style focuser, BK7 mirror and cooling fan.
It has the fan but not the crayford. Is there any way to check if the mirror is BK7? Is it marked on the mirror any where?
I'll give Andrews a ring tomorrow anyway and see if I can sort it out.

[slice of heaven]

Phil
Plate glass is green.That I know.
Bk7 is frosty. I think. Maybe someone else can confirm.
Hope it works out for you.

Slice

[ballaratdragons]

Yes Phil, Slice is right. Plate glass has a green tinge to it. BK7 is clear frosted.

Also the Inside of the 12" 'Deluxe' OTA is supposed to be Painted Matt Black! If not, ask Andrews about that too.

Here is a pic of my Crayford focuser on my GS Deluxe. Same as Geoff's.
Compare it to yours. Heaps different. On yours you can even see the 'Rack'.

[iceman]

Howzat, you definitely need to contact andrews - you have the standard rack n pinion there.. you definitely want the crayford - I tried it out on froggy's scope at the last mini star party, and it's a 200% improvement on the standard r&p. It's a very nice focuser (the crayford, that is).

[h0ughy]

how did things end up with Andrews?