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Mountain Rescue Te.. by simon3   (Show all posts)
Thought I'd post s.. by paulca   (Show all posts)
found the explanat.. by jackill   (Show all posts)
Can give no assist.. by Conor74   (Show all posts)
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:

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)
Something in which.. by khkk   (Show all posts)
McCloy. Shome mish.. by Bleck Cra   (Show all posts)
Jim is a key organ.. by McCloy   (Show all posts)
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RECENT CONTRIBUTIONS 1 2 3 .. 12 Next page >>
Glenbeigh to Galway's Bridge
GSheehy less than an hour ago.
I?m putting this one up because it was a club walk and I was thinking about the other day. There aren?t too many clu walk, Len: 40.5km, Climb: 917m, Area: Glenbeigh Horseshoe (Ireland)

Summit Comment
Knockchree: Knockcree
Biker 11 hours ago.
On the way up.Looking East down onto Attical Flying Club. Notice the manicured Runway and spot the Plane sitting on it. The Dwellings are nestled into the side of Aughrim Hill on the Ballymageough...

Summit Comment
Knockchree: Views
Biker 12 hours ago.
More pictures Not Quite at the top yet. Foreground slopes of Knockcree above the treeline , looking on to Aughrim Hill and the Blue Peaks in the distance

Summit Comment
Knockchree: Knockcree. The Hillock in question.
Biker 13 hours ago.
The Hillock in question Itself, looking at the western side .

Peak bagging in The Sperrins in autumn
peter1 23 hours ago.
Again, the use of a mountain bike is highly recommended for this route, if you are a solo walker. I left my bike in a... walk, Len: 16.2km, Climb: 1048m, Area: Mullaghclogha, Sperrin Mountains (Irela

Summit Comment
Trostan: Longer but More Scenic and Enjoyable Approach
dr_banuska a day ago.
This was my 4th visit to Trostan: 1st was via neighbouring Slievenanee and 2nd and 3rd were via the perpetually wet Moyle Way/Ulster Way approach to the west. On the 3rd visit we did the entire MW...

Forum: General
Cable Car to the Hellfire Club - 20/10
cave-dweller 2 days ago.
Hello, There is a meeting being held in the Yellow House Pub in Rathfarnham in Dublin 14 tomorrow night at 8 pm about some proposed "redevelopments" in and around the Hellfire Club/Montpelier Hill...

Slieve Foye
Onzy 5 days ago.
Sunday route over Slieve Foye and along the ridge for a bit... walk, Len: 9.9km, Climb: 439m, Area: Slieve Foye, Cooley/Gullion (Ireland) Slie...

Summit Comment
Esknaloughoge: Good parking available Oct 2016 at V 63582 65203
melohara 4 days ago.
Good parking available Oct 2016 at V 63582 65203 Followed Kerry Way until it emerged from wood at 62811 65060 where a rough track ascended NW towards Esknaloughoge. Track descends into pool at one...

Summit Comment
Coomnahorna: Good parking available Oct 2016 at V 63582 65203
melohara 4 days ago.
Good parking available Oct 2016 at V 63582 65203 Followed Kerry Way until it emerged from wood at 62811 65060 where a rough track ascended NW towards Esknaloughoge. Track descends into pool at one...

Ox Mountains: Knockalongy & Annatoran
Onzy 5 days ago.
Route taking in Knockalongy, its 2 satellites, and Annatoran.Parking is as suggested by Mountainmike in track 3166, a... walk, Len: 17.1km, Climb: 370m, Area: Knockalongy North-East Top, Ox Mountains

Forum: General
Quad bikers in the Mournes
mcrtchly 2 weeks ago.
Whilst out in the Mournes on Sunday 2nd Oct, at about 8.30am we were shocked to see a group of half a dozen quad bikers powering up the track from the Banns Road towards Lough Shannagh (below Doan...

RECENT CONTRIBUTIONS 1 2 3 .. 12 Next page >>