Welcome to MountainViews
If you want to use the website often please enrol (quick and free) at top right.

General Whatever you want to say that doesn't fit under the comments about mountains or another forum.
Sort by >

More controls

<< Prev page 1 .. 167 168 169 170 171 172 .. 369 Next page >>
Post details Post   (Expand pics)
Hello Simon,My nam.. by simon3   (Show all posts)
THIS SATURDAY AUGU.. by Bleck Cra   (Show all posts)
I'm speaking at a .. by ahendroff   (Show all posts)
Interesting accoun.. by khkk   (Show all posts)
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)
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 D˙loigh 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)


RECENT CONTRIBUTIONS 1 2 3 .. 18 Next page >>
User profile
HoschIchenheim
HoschIchenheim an hour ago.
I'm a Hillwalker from the South-West of Germany near the French town of Strasbourg. I'm mainly walking in the Alps, Vosges and Black Forest mountains. So far on two occasions I have been to Kerry,...

  
Forum: General
Picture test
simon3 an hour ago.
Picture Test

  
Forum: General
Feeling Blue
mcrtchly 2 hours ago.
This is one of the most famous mountain views in Norway of the fishing village of Hamn°y, Lofoten islands with Fellshelltinden mountain (428m) in the background. The rust red cottages are old fish...

Summit Comment
Knocknacusha: Nice end to a day out.
muddyboots 20 hours ago.
Similar to the other contributors, this is not a single summit day out. I did it after Colly. It's an hour or so with a coffee break. Start at the Ballaghasheen pass (spectacular drive in & out) a...

  
Summit Comment
Meenteog South-East Top: Really...when is a mountain a mountain
muddyboots 21 hours ago.
I am sure like many of you, especially simoburn, that the addition of the Arderin Begs while technically needed, added loads more summits to climb. This one is, well, a real hard sell. I was tryin...

  
Summit Comment
Colly: Double entendre?
muddyboots 21 hours ago.
This is a great quick summit- follow the farm track from the end of the road at Coomnaspeara. I met 2 farmers (one on the way up and the other on the descent. There are 2 farmhouses at the end of ...

Track
Keeper Hill from Silvermines (Knockanroe Carpark)
caseyc481 2 days ago.
Wanted to climb Keeper Hill from the Silvermines side. Parked at Knockanroe carpark, walking downhill on fire road unt... walk, Len: 14.9km, Climb: 763m, Area: Keeper Hill, Shannon (Ireland) Keeper H

  
Summit Comment
Shehy More: Try a new approach
muddyboots 21 hours ago.
A nice 2 hour 7.5km loop including Shehy More and Loch na mBreac Dearg. The loop starts at W13435 60417 (room 2 cars) and follows a farm track up onto Shehy More. Also for those including Shehy Be...

  
Forum: General
MountainViews Gathering 2017
simon3 3 days ago.
The event on Feb 17, 2017 had Peter Walker as MC with two main speakers.Gareth McCormack spoke about the vision and technicalities of modern landscape photography.Paul Clements discussed the Wild ...

Summit Comment
Meenavally: A pleasant walk to theTower
BigFly 4 days ago.
Lovely pleasant walk

  
Summit Comment
Two Rock Mountain: Red Grouse near the summit.
BarnaneGoat 2 weeks ago.
I climbed here a few days ago from the east along the Dublin Mountains Way. The summit was shrouded in mist and we went astray at one point. I later discovered this was the result of a way marker ...

  
Summit Comment
Sgurr a'Choire Riabhaich: If Allt a' Choire Charnaig in spate there's a small
melohara 2 weeks ago.
If the Allt a' Choire Charnaig is in spate there is a small footbridge, wires and planks, a little upstream


RECENT CONTRIBUTIONS 1 2 3 .. 18 Next page >>