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found the explanat.. by jackill   (Show all posts)
Can give no assist.. by Conor74   (Show all posts)
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)
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)
McCloy
Who'.. by simon3   (Show all posts)
Seen a comment abo.. by McCloy   (Show all posts)
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RECENT CONTRIBUTIONS 1 2 3 .. 19 Next page >>
Track
Lake District: Skiddaw via Ullock Pike
Onzy 10 hours ago.
Classic route in the lakes... walk, Len: 15.3km, Climb: 1062m, Area: Ullock Pike, Lake District - Northern Fe...

  
Track
La Gomera - GR132
GSheehy a day ago.
In 1492, Columbus set out from San Sebasti

  
Summit Summary
Doughruagh: Rocky summit with access issues from Kylemore Abbey
Collaborative entry Last edit by: liz50 4 days ago.
Located behind Kylemore Abbey, it has been reported that access from the grounds is no longer allowed. It is possible to park in a small lay-by at L77637 58711 and walk approx 30m along the road t...

Summit Summary
Doughruagh South Top: Twin of Doughruagh main top
Collaborative entry Last edit by: liz50 4 days ago.
Located behind Kylemore Abbey, it has been reported that access from the grounds is no longer allowed. It is possible to park in a small lay-by at L77637 58711 and walk approx 30m along the road t...

  
Summit Summary
Raghtin More: The smallest Inishowen Arderin
Collaborative entry Last edit by: liz50 5 days ago.
The easiest approach is to park at Urrismenagh viewpoint carpark C317 443 and follow the track to its highest point. From here you can avoid Crockmain and carry on towards Raghtin More to the Nort...

  
Summit Summary
Crockmain: An uninspiring summit with great views
Collaborative entry Last edit by: liz50 5 days ago.
The easiest approach is to park at Urrismenagh viewpoint carpark C317 443 and follow the track to its highest point before heading north over heather to the summit. Alternatively from Mamore Gap c...

Summit Summary
Knocknanacree: Views to Slieve Mish and the Dingle Peninsula
Collaborative entry Last edit by: liz50 5 days ago.
Summit can be approached from the West by parking near Minard Castle V556 992 and following a rough track uphill past a quarry and onto the summit ridge.A shorter steeper approach is possible from...

  
Summit Summary
Currywongaun: Rough and Rocky
Collaborative entry Last edit by: liz50 4 days ago.
Park off road in a small lay-by at L72134 59157 and ascend the spur in a roughly Easterly direction to the summit. Usually climbed en-route to its larger neighbor Doughraugh.

  
Summit Summary
Teeromoyle Mountain: A summit in the middle of a classic Horseshoe walk
Collaborative entry Last edit by: liz50 5 days ago.
This summit is usually accessed whilst walking the Glenbeigh Horseshoe. A shortened version taking in the 4 central 600m summits in the centre of the horseshoe Teeromoyle, Coomacarrea, Mullaghnara...

Summit Comment
Bruse Hill: Bruse
Nekarsulm 6 days ago.
Track up from the quarry is overgrown. I partially walked up a small stream, as it at least cuts its way through the whins. Climbing straight upwards, you will see places where some earlier climbe...

  
Track
Forbidden Keadeen
CaptainVertigo 5 days ago.
Please DO NOT attempt to gain access to Keadeen from the road by following my route. The owner, who is a very decent ... walk, Len: 7.2km, Climb: 487m, Area: Keadeen Mountain, Dublin/Wicklow (Ireland

  
Summit Comment
Coppanagh: Wear Your Wellies
Pepe a week ago.
As of early 2017 the top section of forestry has been felled, making the trig easily visible once you're up. A word of caution: this felling has resulted in a treacherous summit surface; a gazilli...


RECENT CONTRIBUTIONS 1 2 3 .. 19 Next page >>