Astrotrac first test run results

Started Jan 14, 2013 | Discussions thread
just Tony Senior Member • Posts: 1,713
Re: Astrotrac first test run results

Team Thor Expeditions wrote:

Zeiss 28mm M-mount lens at f2.8, 3.9m exposure, ISO 400, manual focus. Full frame.

I examined the photo above using LR at full pixel level and there is no evidence of motion slurring of the star images.

Zeiss 28mm M-mount lens on Oly OMD-EM5 Iso 400 235 sec exposure.

What I do to assess the quality of my results is to examine the dimmest stars for evidence of trailing, and the brightest stars in the corners for evidence of lens aberrations. When I view the image above at original scale there is very slight evidence of trailing which disappears at the smaller scale default view. I think the first image looks superb.

Oly OMD-EM5 with Canon FD 300mm fully manual lens. 235 second exposure.

Note in the last image that there is substantial star trails. My alignment o the pole was either fully wrong for this long shutter speed. More precision is needed. The mount is up to the task, but the operator needs better pointing skills.

This image was captured at nearly 11X higher optical magnification (relative the the first image), and it is likely to be a similar amount of trailing when you think of it as the angle of the drift. It comes down to the error in polar alignment and the length of the exposure.

One challenge that may face Accutrac users if they are using a standard photographic tripod as the support, there are often no fine adjustment controls available in the tripod head for the elevation or azimuth adjustments. Sometimes the fine polar alignment adjustments can be accomplished more precisely by raising, lowering, or shifting a tripod leg rather than unlocking the head, hoping for the best, and then re-locking the head. On medium-quality and better astronomical mounts there are geared motions available for those axes which allows you to make the fine adjustments with confidence.

I will eventually get better.

That is very likely! Keep it up.

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