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I assembled a collection of widefield images I have taken over the
past few months using Pentax medium format lenses of various focal lengths (90mm, 150mm and 200mm) with slight variations in the system configuration. All but one of them were shot using my ST10XME camera. The first configuration tried used a separate guide scope and guide camera mounted on a Losmandy side by side dovetail plate arrangement. I used an AP80/900mm guidescope which is longish and because of that there was noticeable differential flexure in that system that manifested itself in elongated stars in the corners. the next configuration tested was the same setup but with self guiding used via the ST10XME camera. So long as the camera is self guided that is a potentially workable solution but I found with Halpha and other emission line filters that the attenuation of the guide star was so great that sometimes guidestar integrations of 15 to 20 seconds was needed. at a short focal length that is OK except for the time lost in reacquiring the guidestar after image download and aiming dithering. It usually takes 4 to 8 cycles of guiding to reacquire good tracking and that was taking several minutes in some cases. Still I managed to take a few nice images with that arrangement, one of which was selected as an
APOD
on Feb 14th of this year.
the third configuration tried was using a custom made frame that permits a solid mounting of the guidescope and will also allow the imaging camera to be rotated to any angle from horizontal to vertical. This gave the functionality I needed to use a separate guider without introducing differential flexure and also let me optimally frame my object by rotating the camera to an optimized angle. One of the first targets taking advantage of this camera angle adjustment was the Antares/Rho Ophiuchus area I arranged the images in order of most recent first (they are the better ones) to oldest last. http://www.narrowbandimaging.com/widefield_page.htm |
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