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Post details Post   (Contract pics)
Wife wants to go t.. by Conor74   (Show all posts)
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simon3
2011-08-16 13:17:29
"Laser Beam" from simon3 Contract pics
Picture: Laser Beam (Contract pics)

Lasers in the mist
On the top of Stumpa Dúloigh jackill did his usual thing of assessing where the highest point actually is. MountainViewers have tended to use the Abney Level as a way of assessing this. In this case the highest point appears to be some metres from the junction of two fences. jackill was assessing the distance from this junction to the highest point where I was with the camera. He has a handy little laser rangefinder gadget for this which showed the fence junction to be 21m from the highest point.

The laser light shows up nicely, being scattered by the misty air. Shows up that is except when it was getting near to the camera - something that begs explanation. As anyone knows who takes photos in the Irish mountains, mistiness is a huge issue. In this case the mistiness is Mie scattering caused by water droplets. These are rather large compared to the scattering caused by small particles that causes blue skies (Rayleigh scattering). Mie scattering also has another important quality. Most of the scattered light goes forward close to the original line of travel. So when viewing the droplets in the beam from a distance you see them because you and they are nearly in line. However, nearer, the angle is different and you can't see the beam.

It's all beautifully explained here:
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html

And the relevance? Well knowing about the two types of mist and what, if anything, you can do about them is really useful for upland photographers. For example, because of forward Mie scatter the sun or the moon tend to get a whitish halo around them when there are large particles in the air. The same doesn't happen for Rayleigh scattering - you don't see a blue halo around the sun. This laser beam is a great example of the physics.


RECENT CONTRIBUTIONS 1 2 3 .. 21 Next page >>
Summit Comment
An Bhinn Bhuí: Benwee Loop walk towards Portacloy.
ucampbell 20 hours ago.
The Loop walks here are well signposted, it's a great idea to go out onto each headland.

  
Summit Comment
Doonvinalla N Top: Coastal Hill
sandman a day ago.
On 26/4/2014 i spent a very enjoyable afternoon walking this area visiting the army observation hut and the stone constructed EIRE marking as part of an addition to the Benwee Head Loop walk but i...

  
Summit Comment
Doonvinalla N Top: Flat topped but hard to get to.
simon3 a day ago.
View from the west.

Track
Circuit of Dirkbeg Lough - easier ascent
simon3 2 days ago.
The purpose of this walk is to reach the Maumtrasna plateau and Maumtrasna NE top (MNET). The lattter is quite possib... walk, Len: 11.6km, Climb: 564m, Area: Maumtrasna North-East Top, Partry/Joyce

  
Track
Near Galtybeg, Galty Mountains (Ireland)
caiomhin 2 days ago.
walk, Len: 11.3km, Climb: 663m, Area: Galtybeg, Galty Mountains (Ireland) Galty...

  
Track
Benwee Coastal Walk
simon3 2 days ago.
The walk starts at a small carpark and Wild Atlantic Way sign just west of Benwee. In fact some of the local rock has ... walk, Len: 8.1km, Climb: 245m, Area: An Bhinn Bhu?, North Mayo (Ireland) An B

Summit Comment
Benwee NE Head: Jagged summit
simon3 a day ago.
View from the east.

  
Forum: General
Riddle of the Spinc
BleckCra 3 days ago.
I was at Glendalough yesterday and on the Spinc for the first time. I cannot imagine there haven't already been a thousand hours debate on the boardwalk and and that there won't be a thousand hour...

  
Summit Comment
Benwee NE Head: Jagged summit
simon3 a day ago.
Picture from the west.

Summit Summary
Kid Island: Steepwalled island.
Collaborative entry Last edit by: simon3 a day ago.
Kid Island is very visible from Benwee Head.

  
Track
Lenadoon Coastal Walk
simon3 3 days ago.
walk, Len: 2.5km, Climb: 8m, Area: Mayo Coastal Hill (Ireland)

  
Summit Comment
Buckaun East: Cliffy north edge.
simon3 a day ago.
This is a picture of Buckaun East taken from the valley below.. Obviously the safest way to go up and down this is to the left or south of the ridge.


RECENT CONTRIBUTIONS 1 2 3 .. 21 Next page >>