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Focus Question


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Hi all, wonder if someone can help.

Its one thing taking images of rockets and I can do images with my DSLR @ prime focus, however...

I have tried to take some wider field images using my cameras (EOS 1000D and EOS 7D) and their associated wider field lenses. In days of yore with old cameras, if you set the lens to infinity you could just about guaranatee that the resultant image would be in focus.

I set my DSLR lenses to infinity and the image is not quite in focus , it seems you need to wind it back a little bit to acheive that but its hit and miss and becoming a pain in the backside!! especially when doing longer exposures just to find they are out of focus. I also find it quite difficult to use Live View for wider shots as you dont seem to be able to zoom in far enough for a star.

Any ideas greatly received as to get pics in focus with a lens attached would be greatly received.

Thanks

Andy

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There is a manual way.. but it needs some "hardware" to allow you to make the minute focus adjustments that are neccesary...

Here's one I made earlier....

4452kp6

Teleskop Service sell a range of these for different diameter lenses...

Here's a link to an earlier thread discussing it...

http://stargazerslounge.com/equipment-reviews/134080-ts-focus-contraption.html

I still find it easier to use the netbook to be honest...

I sometimes use a focus mask... Here's soemthing I have been playing about with...

fobVxT4

Peter...

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Many thanks, the contraption reminds me of the way the guys do it for rocket launches... they find focus and tape down the focus ring. I will give it a go and see what I can get. Thanks again, very much appreciated.

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I nearly always tape the focus rings on lenses and zoom rings when I am imaging.. I find Micropore surgical tape is superb for this... It stops focus and zoom creep and comes of without leaving a mess...

If you haven't tried it have a play with Remote manual focus... there's no going back for me now I wanted a computer free setup but the netbook isn't too bulky and allows you to review images much more easily than you ever could on the cameras display...... I put up with the few pounds extra weight rather than waste a nights imaging...

Another thing to watch is how parafocal the zoom lenses are - or aren't... my 70-200 f4L and 24-105 f4L (which is supposed to be) certainly isn't... I used to zoom to the longest FL , focus then zoom back to the FL I wanted to use for the nights imaging... and lost a couple of mights to softly focused subs... Now I focus at the FL I want to use (locked off with tape).

It's also worth checking focus at the center and edges - especially the corners... and you may need to stop the lens down a few stops to improve any coma

Good luck and clear skies...

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