[time-nuts] A real world project need for timing accuracy...
Bob Camp
lists at rtty.us
Wed Nov 3 11:01:15 UTC 2010
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 <jimlux at earthlink.net> 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 -- time-nuts at febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts
mailing list