Focuser Issue With 10" Dob.

Suzy · #1 14-07-2010, 05:23 PM

Hi everyone,
As some of you'll know, I have recently purchased a 10" dob, but my 2 inch barlow doesn't fully fit into the focuser (there is silver showing on the barlow, that should normally go fully in (did in my last 6" dob). There is a step inside the focuser on the tube which doesn't allow the barlow to go in any further.

I have concerns about the performance ability so I rang the store from where I got it from, and he said that's normal, perfectly fine and will not affect the image providing the screws lock it in (which they do).

I was wondering if this is in fact normal and nothing to worry about. Hubby is annoyed and can't see how this won't affect the image, and wants to machine it down.

Thank you for taking the time to help me,
Suzy.

bmitchell82 (Brendan) · #2 14-07-2010, 05:28 PM

yep they are right,

Sky watcher in their infinite wisdom decided to make a not 2", 2" focuser... don't ask me why.

It will not affect the "performance" in any way apart from push back the focus point by how ever much the silver ring is showing.

I have done the modification before for machining the collar down until it just fits a 2" ep though. Though i would just get a 10:1 focuser either moonlight or FT, and be done with it that way its accurate, and easy to focus at high mag.

Ian Robinson · #3 14-07-2010, 05:33 PM

Can take some photos and maybe make a sketch so we can all get a good picture of the extent of the problem ?

You might need to get a Dremel and a Dremel grinding wheel and do some grinding and polishing on the inside of the draw tube, or maybe replace the focusor.

torana68 (Roger) · #4 14-07-2010, 06:34 PM

Ive seen this and wouldnt stress as long as it al locks in place ok , me I'd grind it off but youll have to take it off to do that, not worth the effort really

bmitchell82 (Brendan) · #5 15-07-2010, 10:31 AM

http://www.iceinspace.com.au/forum/s...ad.php?t=56773

Like i said, all done before!

Suzy · #6 15-07-2010, 03:45 PM

Thanks Roger & Ian for your input.

Thankyou Brendan for all that info as well. Interesting! So they giveth, and then taken away...

A wannabe 2" focuser.

That was an interesting read and see he ended up getting it machined. I don't plan on doing photography as the guys were talking about in the link you gave me, but my concerns pretty much lay with my 2" barlow. Do I understand it is going to take longer to focus, and once it does, the image will be fine? Would there be any good reason why I shouldn't go ahead and get hubby to machine it (he is good at it)? Or might this come back and bite me later? Thanks Brendan, really appreciate your help so far. The bit I'm talking about isn't the 2" adaptor, but the actual focuser that's screwed on to the tube.

torana68 (Roger) · #7 15-07-2010, 05:22 PM

yep just a matter bringing it to focus, all good UNLESS you find you dont have enough focuser travel , then you might have to do the machining thing. but I would say youll be ok.

erick (Eric) · #8 15-07-2010, 05:34 PM

How far is the barlow from seating fully, Suzy? Sounds like a cm or less?

If so, that will be no hassle at all.

Suzy · #9 15-07-2010, 06:41 PM

Hi Erick,
It's 12mm.

astro744 · #10 15-07-2010, 07:40 PM

If you seat your Barlow 12mm further in then that is 12mm more you will have to rack out to get to the same focal plane. Will you have this extra 12mm available to you in the focuser travel? If not you may have to pull the Barlow out a bit.

If you can reach focus with your Barlow and any eyepiece you intend on using with it the leave it alone.