Trouble focusing after adding a Barlow lens

[richardgawthorpe]

Hi everyone,

Brand new to the site but have already picked up some great tips so I'm hoping someone might be able to help a newbie with a question.

My other half bought me a Skywatcher Mercury 607 refractor telescope for Christmas and I'm really enjoying getting into astronomy. It has a 60mm lens diameter and a focal length of 700mm (f/11.66).

I've managed to focus the telescope during the daytime (and at night today while looking at the moon) using the supplied 20mm eyepiece and the 10mm eyepiece.

My problem is that as soon as I add the supplied  2x Barlow lens 1.25" between the triangular mirror (sorry, don't know the correct term) and the eyepiece, I can't get it to focus despite adjusting the focus as far as it will go in either direction. I've tried during the day having focused the 20mm eyepiece on items roughly 2 miles away, and then added the Barlow and tried to focus but it just never seems to focus on anything in view.

I've also managed to focus at the same time using the 10mm eyepiece without the Barlow, so I believe that is the same magnification as the 20mm and the Barlow (?) so don't think I'm going past the practical magnification of the telescope as far as I know?

Many thanks in advance for any help!

Richard

[JamesF]

The barlow is possibly moving the point of focus too far out for the amount of travel in the focuser.  If the barlow was supplied with the scope that suggests something else might be wrong somewhere.  Does it help if you don't insert the eyepiece all the way into the barlow?

James

[paul mc c]

It may be too much power for your scope,ideally you would have 30x per inch of apperture,your 10mm would give you 70x which is roughly your ideal limit,using the barlow would give you roughly 56x per inch.

[Peter Drew]

The only time I would expect focusing travel problems to arise when using a Barlow in a refractor is if the barlow had been placed before the diagonal ("triangular mirror") instead of after it.

[richardgawthorpe]

Thanks JamesF,

I’ll try not inserting the eyepiece all the way into the Barlow and give that a go. Not ideal but I wonder if there’s something wrong with the supplied Barlow as all the other accessories seem to work ok.

Hi Paul Mcc, thanks for the reply. I have tried with the 20mm eyepiece and the Barlow, which should be the same magnification as the 10mm, and therefore within the ideal power if I understand correctly? The only thing that makes me think that it’s something to do with the Barlow rather than the practical magnification is due to the fact that the moon was really clear last night just using the 10mm EP so I hoped that trying the 20mm + Barlow would have been ok magnification-wise?

Richard

[m37]

Hi mate

Wasn't sure from your post whether you have nothing at all in view when using the barlow, or if you have something but it is out of focus.

Are you aligned correctly? By this I mean how are you locating the moon? If you have a finder scope or a red dot thingy and it's not in line with the main scope then you could be 'pointing' at the moon with the guider but your actual scope is missing it. This might only happen with the Barlow as the image will effectively be twice as 'big' and with there not being that much moon at the moment it might just be out of view.

Just another thing to consider.

If you can snap a picture of the business end (how the eyepiece, barlow etc are placed) someone can probably spot what it going on.

cheers

Chris

[StevieDvd]

On some barlows you can unscrew the lens and use that like a filter on your eyepiece. Or put the eyepiece/barlow into the scope without using the diagonal (triangular mirror) as that shortens the light path as well. Those may help if you have insufficient in focus.

If it's a lack of out focus then as you say don't put the barlow and/or eyepiece all the way in (just to try not a permanent stable option).