photo sharing and upload picture albums photo forums search pictures popular photos photography help login
Type your message and click Add Comment
It is best to login or register first but you may post as a guest.
Enter an optional name and contact email address. Name
Name Email
help private comment
Samir Kharusi | all galleries >> Globular Cluster Messier 13 in Hercules > 1to1_crops Animation
previous | next
1to1_crops  Animation
Samir Kharusi

1to1_crops Animation


Again an animation, so please click on "original" below. For the pixel peepers. 1:1 crops from the 1Ds+1200mm and the 20D+4125mm. Since the pixels on the 20D are smaller than on the 1Ds (6.4 vs 8.9 microns square, factor 1.4x) you are in fact looking at the C14 image at a 40% higher magnification than the Canon lens image. These images were all exposed unguided, one-minute exposures at 1200mm, but ten-second-exposures at 4125mm. Indeed, tracking difficulties increase exponentially with focal length...

Somewhat unexpected: M13 is supposed to have two populations of stars, some more red than the rest. I did not expect good differentiation because of the huge bandpass that my 20D has (Unfiltered, it has a nonsensical colour balance in daylight photography), but in fact it did better than the 1Ds which has a highly accurate color balance. It could also be because the stars in the 20D frames were under-exposed and thus very far from saturation.

Of course, the image scale used for the C14 is a hopelessly over-ambitious 0.32 arc-sec per pixel, 1.55 arc-sec per pixel for the Canon lens. Typical atmospheric seeing is around 2 arc-sec, so going finer than 1 arc-sec per pixel for long exposures, and without Adaptive Optics, very often tends to be an exercise in futility.

other sizes: small medium large original
comment | share