Star testing the Canon 14mm and 17mm TSE

Well - my visit with the two Canon L series lenses from CPS is going to end tomorrow - have to send them home. But - before I do I have to give them the ultimate test for any optical system capable of focus at infinity - the star test. The most severe test one can perform on a telescope or lens is to see how it handle point sources across their field of view - especially in the extreme corners of the field.

So - I took them with me up to mount Lemmon Observatory last night. I had to help the CSS astronomers Steve Larson and Ed Beshore work on their new 1 meter telescope and decided to take a few portraits of the new scope with the 14mm . . .







When it finally got dark I setup the camera and lenses on a tripod and made a couple of short exposures at high ISO and the lowest f ratio for each lens - doing critical focusing on a star near the middle of the field using the live view mode of the 5D mark II body I employed for these final images. I then examined the stars at the corners of the field of view (highlighted in the full frame image.) Note that coma is apparent in both lenses - not unexpected and not as bad as other lenses I have. All in all the 17mm performed best and it is most likely my next lens purchase.


The 14mm . . .





The 17mm TSE . . .