Re: practice practice practice


Message posted by lone wolf on February 01, 2005 at 18:35:49 PST:

One way to practice using a telescope with a camera is to photograph money. Money has lots of fine detail on it. My set up is to mount a dollar bill about 250ft away (a bit less that a football field). Tape the bill to a dark piece of cardboard so that the edge of the bill is easy to see. Obviously, you need to tape the bill to something to hold it up, i.e. telephone pole,etc. The bill should have decent front lighting. From the photograph of the bill, you should be able to at the very least read the serial number. If you focus well, you can read the "legal tender" print and see some engraving.

Vary the magnification, either by using different power barlows, eyepiece projection with different focal length eyepieces, or with a barlow and varying the distance to the focal plane with tubes. Eventually you will find how much magnification is useful. I find that on a 3 inch APO telescope, the limit is a factor or 4 to 5 in multiplication of the focal length, or about 3000mm equivalent focal length.

Lastly, you can judge your ability to focus by using focus bracketing. That is, focus to the best of your ability. Take the photo, then move the focus as slightly as you can in one direction, and take a photo. Refocus, then move slightly in the other direction. If the "out of focus" images are better than your target focus, you are doing something wrong. First timers should bracket there exposure as well.


In Reply to: practice practice practice posted by lone wolf on January 30, 2005 at 19:11:41 PST:

Replies:



[ Discussion Forum Index ] [ FAQ ]