Keeping a small dot over one mile distance

[Akiyama]

Actually, the moon really is "that bright".

From the film days of photograph, many professional photographers used the "sunny 16" rule to determine exposure when we didn't have an exposure meter at hand, or were too lazy to use one. That rule said when shooting a scene in bright sunlight if you used an aperture of f16, then the shutter speed on the camera would be the reciprocal of the film ISO. That means that if your film was ISO 200 then you could shoot at f16 with a shutter speed of 1/200 sec.

This rule applied pretty well to shooting the full moon too. Day or night you could get good detailed shots of the moon at that "sunny 16" or equivalent exposure. Sometimes some photogs liked to open up one stop from that exposure but basically the moon behaves just like any earthbound object when determining exposure in sunlight.

Ed

Try to shoot a moon illuminated scene at ISO 200 F16 1/200 and you will discover the moon is merely reflective, and not an emitter. If you took a picture of a rock outside on a sunny day, you'd need to stop your camera down and shoot at low ISO to capture the details on the rock. The same is true of the moon, which is washed out by direct sunlight against a black background. The sunny 16 rule applies to things illuminated by direct sunlight, as the moon is. It does not however apply to things illuminated by moonlight. The moon is not so bright as to require the moon to be an emitter as flat-man suggests. It is no brighter than one would expect.

 

[kcarlson]

Flat-man. i like it. Flat-man has stopped responding to my inquiries:yabbem:

 

[Nordhavn]

I haven't been here in years...

But I will say this, a mile is easy. MM diodes have issues with astigmatism, beam shape and divergence. With one watt you can spare a lot of power using optical beam correction with a larger diameter egress with extremely low divergence. When divergence is known indoors, calculating it over large distances is easy.

By far the best arrangement we used for alignment was a 100 mW Coherent Compass DPSS with expander. The egress beam diameter was the size of a tennis ball (!) but it stayed that way seemingly forever. Those lasers were costly back in the day but you can find them, often in need of some TLC, these days affordably.

Oh and I've spotted things 7+ miles offshore (verified by ship's PPS/GPS) with a "lowly" RPL 450 and Melles Griot expander.

 

[Davidx]

I've been entertained .

 

[Pi R Squared]

Well I certainly missed a lot in my 54 1/2 hours without power, some roads are still blocked due to downed trees. Rumors of my death have been greatly exagerated, am still waiting for the water to come back on.

Alan

 

[Gabe]

Well I certainly missed a lot in my 54 1/2 hours without power, some roads are still blocked due to downed trees. Rumors of my death have been greatly exagerated, am still waiting for the water to come back on.

Alan

Geebus, that's a long time. Must get annoying, on top of unsafe. Y'know, if the earth were round there wouldn't be wind storms like that, since the ground would be curved the wind would just keep on going straight into space. This is actually where the term "solar wind" comes from, these winds help push the sun along in the sky.
[/srow]

 

[kcarlson]

Geebus, that's a long time. Must get annoying, on top of unsafe. Y'know, if the earth were round there wouldn't be wind storms like that, since the ground would be curved the wind would just keep on going straight into space. This is actually where the term "solar wind" comes from, these winds help push the sun along in the sky.
[/srow]

i could make some solar wind for srow by sticking my ass in the air and farting towards the sun.:na:

 

[Pi R Squared]

i could make some solar wind for srow by sticking my ass in the air and farting towards the sun.:na:

Don't do that, methane contributes to global warming and is also explosive.

Alan

 

[Dannno]

I am very new to lasers. I need to be able to fire a laser over a distance of one mile and keep the dot small enough and bright enough to be seen at the other end. I have purchased three lasers two of which didn't have the enough power(1mW) and one 2W(LuckLaser cost £80) which didn't keep a small dot over the distance. The dot became so large after over 100m that it couldn't be seen. Before I buy another laser disaster is there anyone that can help please?

Did you ever get around to performing your experiment? Ive been wanting to do a similar experiment but i have a way to do it on land. Any luck on the laser?

 

[Anthony P]

This is considered a dead thread... no responses since 2015. All the same, here is a link:

 

[hakzaw1]

At least one of the posters has passed away. (Alan)
the 'newest ' post is ~ 4 years old.
IIRC there is one or more threads on this same subject.
MYB try to find a newer one to revive.

 

[RB astro]

I know it's an old thread but I can't resist replying again.....

RB