Hi I have indeed seen people try to do this with 18 ~ 24" aperture optics. They don't seem to do a lot better than the smaller stuff spotting holes at distance. They do get a nice bright image though.
Bob On Nov 3, 2010, at 12:15 AM, jimlux wrote: > Robert Darlington wrote: >> Hi Jim, >> This doesnt' look right to me. > > you're right.. I forgot inches/feet.. divide my 0.08 by 12.. > .007 mrad.. > > Now we're talking big, big aperture.. instead of 2-3 inches, 2-3 feet. > > I'm getting roughly 2.3 inches at 2400 feet >> is 0.08 miliradians. 0.01 miliradians (1*10^-5 radians) at 2400 feet is >> 0.288 inches (roughly 30 caliber). Wikipedia says that to resolve 0.01 >> miliradians you need: >> R (in radians) = lambda / diameter (of scope) (aka, Dawes Limit if you use >> 562nm light) >> 1 * 10^-5 radians = 562nm (green) / X >> X= 5.62cm aperture or 2.2". This is what it comes to on paper, in >> practice you'd probably need something bigger because of atmospheric >> effects, lens quality, and the like. >> That being said, I can't see my holes at 300 yards with my Leupold scope >> with an opening greater than an inch. I can just barely make them out at >> 200 yards. See http://en.wikipedia.org/wiki/Angular_resolution - Also, >> somebody please double check my math. >> -Bob >> On Tue, Nov 2, 2010 at 7:28 AM, jimlux <[email protected]> wrote: >>> Bob Camp wrote: >>> >>>> Hi >>>> >>>> Ok, I mis-understood the question. >>>> >>>> In my experience, you can have big buck (as in many thousands of dollars) >>>> optics and not see .2" holes at 800 yards. The bull's eye is a *lot* bigger >>>> than the hole the bullet made. >>>> >>>> 0.2" at 2400 ft is about 0.08 milliradian.. or 0.3 minutes of arc. Your >>> eye can resolve about 1 minute of arc... I'm not questioning your >>> experience, but it seem that even a moderate power scope should allow you to >>> see the holes. As I recall, the Rayleigh limit for resolution is something >>> like 0.7 milliradian/mm of aperture, so 10-15 mm aperture would be in the >>> right ballpark.. >>> >>> I can imagine needing more aperture than 3", though.. you're not interested >>> in resolving a star, but something more akin to separating dots. >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
