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Hello Simon,My nam.. by simon3   (Show all posts)
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simon3
2011-08-16 13:17:29
"Laser Beam" from simon3 Expand pics
Laser Beam (Expand 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.
Can anyone explain.. by Dessie1   (Show all posts)


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User profile
magicstep
magicstep 10 hours ago.
A leisure climber, I take it easy. If I climb something big then in a good weather only and spend lot's of time on top of the hill picnicking, enjoying the views and taking pictures. Mostly I walk...

  
Summit Comment
Gortnagan Beg: A worthy 500
thomas_g 13 hours ago.
Gortnagan Beg turned out to be my 500th peak. The bog was dryish, the rain threatened but waited until I got back to the car and the midges had other targets; what more could you ask for.The peak ...

  
Summit Summary
Gortnagan Beg: Small hill with great views
Collaborative entry Last edit by: thomas_g 13 hours ago.
Gortnagan Beg might be diminutive in stature but has fine views and some steep ground.The best approach is from the NE where there is a stile on the roadside. Parking is scarce so the best option ...

Track
Gortnagan Beg from Cappanlea
thomas_g 13 hours ago.
walk, Len: 5.0km, Climb: 219m, Area: Gortnagan Beg, MacGillycuddy's Reeks (Irel...

  
Track
Galtymore & Galtybeg from King's Yard
conrad1179 2 days ago.
run, Len: 11.8km, Climb: 670m, Area: Galtymore, Galty Mountains (Ireland) Galty...

  
Summit Comment
Kirikee Mountain: Kirikee from the NW.
simon3 2 days ago.
From the ridge south of Derrybawn there is this NW view of Kirikee.Courtesy of siteviewer_comreg.ie we can find the owner of this mast: Three Ireland.The amusing conjunction with the cairn below t...

Summit Summary
Camaderry South East Top: Steep climb, sorry trail, great views.
Collaborative entry Last edit by: simon3 2 days ago.
There's a number of ways to reach the top such as starting from the main, paying, carpark near the Glendalough lake at around T1115 9635. Going straight up from here more or less north there is an...

  
Summit Summary
Brockagh Mountain SE Top: Flattish height NW of Laragh with views, boggy paths a
Collaborative entry Last edit by: simon3 2 days ago.
Situated at the south eastern tip of a spur from Tonelagee it therefore commands wonderful views out over Laragh to the south east and Glenmacnass valley and waterfall to the north. Glendalough is...

  
Summit Comment
Carrickarede: Island.
sandman 4 days ago.
Carrickarede island is connected to the mainland by the world famous Carrick-a-Rede rope bridge. One of Northern Ireland's top tourist attractions it is operated by the National Trust but unfortun...

Track
BRANDON HILL - THE QUICK WAY
David-Guenot 4 days ago.
A steep but quick ascent along the forestry on rocky terrain, along what I believe has been dug as a firebreak rather ... walk, Len: 5.0km, Climb: 305m, Area: Brandon Hill, South Midlands (Ireland) B

  
Summit Comment
Inishmeane: The concrete road thru the village
magicstep 5 days ago.
Part of the village, about 10 houses in total.

  
Summit Comment
Inishmeane: Not much to do, a tranquil place.
magicstep 5 days ago.
Visited in 2014. There's a sandy beach and a solid pier with slipway and a picnic table facing the mainland. The road from the pier all the way thru the village is a robust concrete one, but it's ...


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