Observatory 8

Since the 17th April we have had rain and more rain, and, as of 11 May, this was the only break in the weather. Seeing was average at best and I tried to get another shot of Saturn, this time with a barlow lens. Since the image was ‘boiling’ rather a lot, I think the mistake I made was to assume that a short exposure, albeit dim, would be superior to a longer exposure that might suffer from atmospheric distortion. The brighter ‘no filter’ images below seem to produce a slightly better result. Saturn is quite low and the light pollution from nearby Royston doesn’t help. Here is a composite RGB image taken with a x2 barlow through the VX14 (although the blue image was so faint I did cheat and use the green image again at 50% instead of the blue one – it does have a greenish tinge – oh well).

And then brightened a bit …

and then with no filter, so monochrome, but brighter …

 and slightly more processed …

This just underlines to me that the seeing conditions are, of course, paramount, and that getting a short exposure in the video images appears to be counter productive and does not out weigh any atmospheric losses incurred from a longer frame exposure time.

I took a number shots of Saturn (which was at opposition 2 days ago on 15 April). Its not very high in the sky so I took the shots around midnight to get the maximum altitude. The computer disc was filling up with large AVI files and, in my sleepy state, managed to accidentally delete the images I took with a x2 and x5 Barlow lens. So the image below is at prime focus and therefore somewhat small -but what’s the magnification? Magnification is really concerned with the angular view of the object when seen with the optical aid compared to the unaided view. A rough guide is to consider a 50mm lens produces a magnification of 1 when used with a camera (or ccd sensor). So at prime focus, a rough guide is the telescope focal length (mm) divided by 50 (mm). So for my VX14 with  its 1600mm focal length this is about 32 at prime focus. Saturn at about 20″ arc would cover approximately 1/30 of the width of my DMK21AU04.AS chip.

I am waiting for the next clear night so I can try this again with a x2 and x5 Barlow lens and this time I have plenty of disc space 🙂