What Barlow can I use?

[brucen]

Having just got my first scope - Skywatcher 130P AZ GOTO - I have been dabbling with imaging using a modified webcam from Morgans. I have not been able to focus on Jupiter just using the webcam but can do so when using a 2x Barlow. I believe that this gives an effective magnification of around 210 which seems to be about the maximum for this scope. I have, however, seen on other threads that 3x or even higher strength Barlows have been suggested for similar size scopes. If I do get a 3x am I likely to see any improvement or am I at the limit already?

[Cornelius Varley]

Don't get confused by the practical maximum optical magnification of a telescope, usually about 50x per inch, and what can be acheived when imaging. For most telescopes when planetary and lunar imaging you need to be aiming for a focal ratio of between F20 and F30 to get the best imaging resolution. For a 130/650 you could use a 3x or maybe a 4x barlow.

Peter

[datman]

Hi

Assuming you have an spc900nc, you should be able to focus without any trouble. Is the focus tube not coming out far enough?

If so move the webcam out of the tube a little bit.

It could be that the barlow is conpenstating for this.

I have to do this with one of my cheaper eyepieces to bring it into focus

[brucen]

Don't get confused by the practical maximum optical magnification of a telescope, usually about 50x per inch, and what can be acheived when imaging. For most telescopes when planetary and lunar imaging you need to be aiming for a focal ratio of between F20 and F30 to get the best imaging resolution. For a 130/650 you could use a 3x or maybe a 4x barlow.

Peter

Thanks Peter. I hoped this would be the case but was confused by the practical maximum issue. I will now buy with confidence!

[brucen]

Hi

Assuming you have an spc900nc, you should be able to focus without any trouble. Is the focus tube not coming out far enough?

If so move the webcam out of the tube a little bit.

It could be that the barlow is conpenstating for this.

I have to do this with one of my cheaper eyepieces to bring it into focus

I do have a a spc9oonc and have tried moving it out of the tube - but perhaps not far enough. I also made an extension tube by canabalising an old plastic barlow but still no joy. I was trying whilst observing Jupiter which was probably not a great move, I suppose, as it's not that easy to find in the ccd anyway. Better to wait and try it on the moon which is a bit harder to lose! At least you have confirmed I should be able to focus which helps no end. Thanks.

[datman]

Hi

You should be able to focus without major mods. Have you tried it in daylight? You need a very distant object to focus. I cannot get a long view in daylight, best I can manage is about 100-150 metres at this distance I have to space the camera out about 50mm.

The webcam is about the equivalent of a 5mm EP

[brucen]

I haven't tried in daylight yet but will give it a go at the weekend if it is dry! I am hoping that I will have better luck with the moon although I won't know for a while as the house next door is in the way at the moment.