[EricB (Eric)]

Hi there,

I have indicated previously in a couple of posts the difficulties I have in using a Barlow in conjunction to my DMK 41 CCD camera when taking AVIs of the Moon (I have an off-the-shelf SW Flex 10" Dobsonian).

Basically, without the Barlow, I get data I am really happy with, and when I attempt to use my GSO x3 Barlow all I seem to get is a grey picture completely out of focus. A far cry from what I can get without the Barlow (and I far cry from the great Moon close-ups I see on the web).

Yesterday, I had possibly the best seeing I have experienced in my 8 months of photographying the Moon. The AVIs were of high quality and I gave the Barlow another shot. The resulting data was better than usual; however, it was still unfocussed. What I mean by unfocused is that there is focuser travel on each side of the picture, but this is the best focus point I can get.

I have attached a picture without Barlow and with Barlow of the Theophilus and Cyrillus for comparison.

My question are:

Is my Barlow low quality, therefore I can't achieve focus when added to a CCD?

Are Barlows only usable in exceptional seeing conditions and I should only bother fitting it on those few days a year?

Or, as I suspect, is it a bit of both? In which case, I should invest in a better Barlow (eg a TV Powermate x 2.5).

Am I missing anything obvious ?

I would be very grateful for your comments. Thank you.

Eric