Crayford Focusers

[Mr. Subatomic]

Hey Guys, Subatomic here,

I am about to buy a GSO 8" Dobsonian and it has a 'Micro 10:1' Crayford focuser.

I was just wondering what the meaning behind that 10:1 ratio is and why it is described as 'Micro' ( I'm guessing that it means you can make fine, 'micro' focus adjustments???).

If anyone could fill me in it would be great. Thanks!

[iceman (Mike)]

HI Sub.

Yep, you're right. The crayfords have 2 knobs, 1 on either side, or a large one and a smaller one on the same side.

The larger knob will be the "coarse" adjustment, where you want to rack in or out quickly. The smaller/fine adjustment knob is the "micro", where it's geared at a 10:1 ratio - so one revolution of the large knob results in 10 revolutions of the smaller knob.

In reverse, it means small adjustments of the micro knob will hardly move the large knob and can be used for very small adjustments in focus to get it "just right". It also helps eliminate the scope shaking around as you focus because it's a smoother action.

By the way, the 10:1 focusers are great! Definitely worth the upgrade if the scope doesn't already come with it.

HTH

[Mr. Subatomic]

Wow! Thanks a lot Iceman!

It all makes sense now. The focuser sounds like a very good feature of the telescope. By the sounds of it, I won't be fiddling around to get the right focus anymore, GREAT!

Also, I thought it was best to ask you, but I may be getting enough money to upgrade to the 10" GSO Dobsonian (practically your exaxct telescope) from the 8". I am still at a good beginner to intermediate level, but do you (or anyone else, feel free to comment) feel that it's best to stick with the 8" and invest in extra accessories? I mean I don't know if I like the idea of having to lug around a 10" telescope and would just prefer one that I could take outside in a manner of seconds. I guess if I do go the next step I'll be a victim of 'apeture fever', wouldn't want that to happen, but what do you think I should do?

Thanks for your help!

[Starkler (Geoff)]

Originally Posted by Mr. Subatomic

I mean I don't know if I like the idea of having to lug around a 10" telescope and would just prefer one that I could take outside in a manner of seconds. I guess if I do go the next step I'll be a victim of 'apeture fever', wouldn't want that to happen, but what do you think I should do?

I dont know that anyone can answer this question for you, but my 10 incher is portable enough given that it lives in my garage and gets wheeled out on a trolley. If I travel with it the tube fits nicely across the back seat.

There is a difference in the views between an 8" and a 10", but the difference isnt staggering. Best advice I can give is to check them in the flesh. Im sure any IIS related star party gathering will have at least 10" dob present

As for spending on accessories vs a bigger scope, what accessories do you already have? Im sure we would love to spend your money for you

[Mr. Subatomic]

Hey Starkler,

I think that's what I'll do. I can just go to Andrew's Communications and compare the 8" and 10" in store. Does anyone know if he displays them in store? If not, I know that the Bintel shop in Glebe have some of heir dobs on display.