Guidescope Problems

[Matty P (Matt)]

I am finding trying to locate a suitable guidestar in my 70mm guidescope extremely difficult for autoguiding. I am using my DMK as a camera and the only way I can bring it to focus is by using a diagonal and a 2x Barlow. The only object I can get in the FOV is Jupiter and the Moon.

Seeing that there are not many bright stars that are suitable to guide onI have to ask these questions.

Do I need a larger guidescope or am I missing something?

[gbeal]

Must be missing something mate, as I am using a 60 or is a 65 mm guide-scope, and don't seem to have a problem.
I would ditch the Barlow though, I have never used one, and even recently went through a stint of using a converted 8x50 finder objective with the QHY5 in place of the eyepiece. Worked a treat.
The 70mm should be fine.
Gary

[Matty P (Matt)]

I would love the ditch the Barlow but without it, I can't reach focus with the DMK.

Will an extention tube help?

[Ian Robinson]

Without an occular in the train , where does the objective come to a focus for stuff at infinity ?

can you rack in or out that far with your focusor ?

[Babalyon 5]

Howdy.
My brother uses a Stellarvue ED80 as a guide scope and an Orion guide camera, the one they released recently, to which he found that an extension tube was necessary to get focus. Try getting some cheap PVC pipe to do an experimental duct tape rig up to see how it will pan out and may also give you an idea of the length of tube you need to have made.
Definitely ditch the Barlow, you're reducing your field and options heavily. Is your guide scope in rings with adjusting screws so you can line it up where you want it better. Its not a bad idea. Good luck!

[RB (Andrew)]

matty all you need is an extension tube, I use the dmk with the st80 and have no trouble.
I got an extension tube from Bintel when I got the dmk.

[Zuts]

Hi,

You just need to know the FL of your scope. For a refractor just run a tape measure from the front of the lens along the length of the scope for the stated focal length. If this is outside the extended full length of the drawtube then you need an extender.

In any case this will give you a rough idea of where the CCD of the DBK should be placed to get a focussed image.

EDIT, obviously this only works for a simple refractor, which i think you have.

Paul

[gbeal]

Even use a star diagonal, I sometimes do to reduce the length.

[Tandum (Robin)]

I had to put an 80mm Bintel extension tube on mine to focus without the diagonal.

[[1ponders] (Paul)]

Try removing the front lens off your barlow and see if that gives you enough length. If so, you could probably pick up a second hand cheap barlow off the site here. Hell, post a want ad and someone may even give you one.

[ozstockman (Mike)]

I agree with gbeal.

Try just the star diagonal first. All refractors are tricky and to reach focus you must use a diagonal or an extension tube.
I would not recommend to use a barlow unless it does not have its lens like Paul suggested. Once you add a barlow you increase a focal length of your scope and it makes it slower. It means that you'll be able to see only bright stars with the same exposure time.

if using either the diagonal or the barlow without lens doesn't work you can use them both at the same time but remember that the barlow should be without the front lens. It should work and you won't need to buy an extension tube.

cheers,

Mike

[Matty P (Matt)]

Thanks for the advice,

I actually have a cheapo 3x barlow that came with the refractor that I can use, all I have to do is work out a way to remove the lens bit. I tried every combination possible to try to achieve focus and the only way I could do that is with a Barlow in place. So removing the lens part of the Barlow is a great idea.

I'll give it a go.

[gbeal]

Still reckon it is too long, too hard, too prone to flexure, especially if the focuser is as cheap as I suspect. Try a diagonal as well.
Gary

[vash (Ashley)]

it's what I do to focus mine, I use a dsi 2 with a barlow minus lens, works a treat