Isopropyl alcohol has water in it which is left behind when the alcohol quickly evaporates.
A lens cleaner like Zeis pads from Walmart or any optical store, places that sell glasses or drug stores usually have them as well, these work best. They’re made for AR coated glasses so of course a lens is a lens. 
^
+1 on the Zeiss lens cleaner from WalMart. :+1:
Either the individual foil wrapped pads or the spray & microfiber cloth work great. 
aha! Thanks a thousand! Had fun cloud bouncing… and spotting party balloons of all things with it!
no probs with my tn42
here it is doing what it likes to do 
Nice pic! Really shows what this bad boy does, love it!
Edit: One of very few reflectors I’ve seen that puts out a column of light that doesn’t cross over, most make an “X” pattern where the optimal focus point crosses over and flares back out, reducing effective distance. This one makes over a mile because of the great collimation of this awesome reflector, ya just gotta love it!
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Nice!!
casting shadows on the clouds and fog
Fun light, isn’t it?
sure is 
glad im not alone with this light problem ! lol !
lol!!! Somebody is borrowing[stealing!!] pictures.
A guy on CPF[hahoo] posted the same picture and claims he took it!
It might be him, it might be you or maybe BOTH of you are claiming this is your light!
See link below with his post! Post #510 and post #531 where he claims to have taken it!
Or maybe…. ‘nodoubt’ (BLF) = ‘hahoo’ (CPF) … :question:
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man, dont you have better things to do ?
i bet you were a tattletail back in grade school.
Hi Dear, I have used 99,9 isoprophyl alcohol and window cleaner (blue liquid) none of those were harmful to the AR coating (purplish or greenish) I guess the traces you see when you use 70% isoprophyl is due to the residue left of almost 30% water content. Hope this help you.
I have to smile when I see you post nodoubt… we had a good friend named Winston that worked in an Automotive parts store who used to say No Doubt! all the time! lol [ie: “These parts are EXPENSIVE!” “No Doubt!”] As such, your tattletale response above elicited an immediate “No doubt!” in my mind, making me laugh at the double entendre. (all this instead of simply saying …)
no doubt… No Doubt!
Where is your sense of humor “hahoo”? Not only disrespectful to me on CPF,no sense of humor either!
I’m thinking of getting a 2nd TN42, would the CW be better at cloud-lighting than the NW? After all it is a cooler temperature beam that works wonders at illuminating fog than a warm one.
Cooler tints tend to have more backscatter in general, and so probably would illuminate the surface of a cloud more. When trying to illuminate solid objects to view them, this is a disadvantage, but it might well work better for that.
CW has the most throw and lumens, NW loses some ground on it in sheer power and downrange punch. It was the CW that I tested at a mile.
Thanks for the advice. Was torn between the personally better tint of the NW and the cloud-lighting and power of the CW. Guess i’ll be having a CW this time!
Thanks for the advice. How about 95% denatured ethyl alcohol? What’s denatured even mean anyway?