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billo

concentric ring sights & the COLD

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OK, so i've got the cash and ready to toss some down for one of Brent's concentric ring sights. The following comments from http://www.brentfinley.com/ringsite.htm concern me though...

Quote

Precision optics were not made to go through temperature extremes very quickly. It induces stresses in the elements and can even crack the crystal. If you jump at a DZ that has very cold temperatures overnight, DON'T leave your helmet in a team room or a car. You are asking for unneeded wear and tear on your sight....
[snip]
My final design is a happy medium between full lamination of all layers and no lamination at all. I laminate the polarizer to the crystal (with a top secret method) to prevent etching of the crystal over thermal cycles that the optic goes through during a skydive



So here's what I'm wondering...how much cold can these sights really take? I can follow the first idea, keeping the sight indoors at night no problem. But what about the cold temperatures briefly encountered at altitude? I'm in the midwest, so in the cooler part of the season we'll be jumping between neg 20 and plus 20 degrees F at altitude.

Can the concentric ring sights handle these brief cold spells without becoming splotchy? Or is it better to hang up the pricey sight during the winter for a cross sight? Please be specific on your winter jumping location if you migrate during the off-season.

Thanks!! :)Bill

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This is a tough one... I don't really have too much data on this.

I know that Mike Skeffington shattered one in Monterey on a particularly cold day on high altitude jumps.

On the other hand, Willy Boekins has had one of my sights in Belgium and probably jumps in some extreme cold there. I just saw him for the AZ challenge and everything seemed fine.

The thing with any extreme temperature shock is you want to do it gradually. If you go from a well Heated plane to standing on the step, it could be disatrous. If you go from 80 degrees to -23 over 30 minutes, like I did on the 300 way in Eloy, you will have no issue.

On some level, it's still a crap shoot. There could be an invisible flaw that will propagate more quickly under seemingly no temperature shock.

I would have to assume that a lack of feedback on sights becoming destroyed would indicate that they hold up rather well, though. (but I cannot make any guarantees, you understand.)

Hope I've reassured you somewhat.

Thanks,

Brent


If you sit by the door
www.brentfinley.com
brent@brentfinley.com

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I've had mine for 4 years and I've made plenty of jumps when the temp has been around 30F on the ground. Granted, the temperature changes were not that rapid, it was just pretty freakin' cold at altitude and the entire way down - never a problem with my sight though. Well worth the cash if you ask me.






Action©Sports

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I have a couple hundred sub-zero-at-altitude jumps on mine with no trouble.

Brent is being his usual modest self. Early morning Arizona in January days are freezing at ground level, let alone at altitude with a 120 mph wind chill factor. I jump there for about a week every Winter, but Brent lives there.

My home DZ in NorCal has a couple months where morning temps are sub-zero at altitude. I wouldn't worry about the concentric in cold temps.

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No issues for the two years of jumping Brent's sight in Russian winters. Thanks Brent for the great stuff!



Dude, I thought Swedish winters were bad enough - what kind of temperatures are we talkin' about here?
I mean, I enjoy skydiving and all but personally, I think the fun starts to diminish with every degree below freezingB|

Just out of curiosity - How do you fit that big furry hat under yer camera helmet?:)
Peace,
Z






Action©Sports

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