Linear Polarizing filters on red dots

Jack D · Post by **Jack D** » Fri May 15, 2009 10:12 pm

I have an UltraDot red dot sight on my Savage 24V that came with a (adjustable) polarizing filter. This filter is fantastic and I want to put one on my Bushnell Trophy red/green dot. Tiffen makes one in 30mm, but I'm wondering if it can take the recoil of my 22/45. Has anyone tried this? Tiffen filters are made for cameras, not guns. They are glass and alluminum so I suspect they will. Any thoughts?

5/27/09, edited subject to remove "circular" and add linear.

Post by **Bullseye** » Sat May 16, 2009 9:15 am

Here's an old competition shooter's trick - take a target paster or a little bit of medical tape and place it on the seam of the two lenses. That way you can adjust the filter to reduce background glare and lock it down without having the filters rotate under recoil and blank out your downrange image in the middle of a sustained fire string.

R,
Bullseye

Jack D · Post by **Jack D** » Sun May 17, 2009 2:44 pm

I ordered one. I guess I'll soon know if it will hold up.

http://www.tiffen.com/displayproduct.ht ... emnum=30CP

Of course I didn't pay that much for it. Under $30 including shipping at

http://www.newworldvideodirect.com/prod ... uctid=1798

Jack D · Post by **Jack D** » Tue May 19, 2009 1:14 pm

I just stumbled on this article about red dots and polarizing filters. Very interesting.

http://www.bullseyepistol.com/dotsight.htm

Post by **Bullseye** » Tue May 19, 2009 6:25 pm

The dual filter set up is the one I was referring to with the tape trick. The two lenses work in conjunction with each other to reduce glare. The outer lens is free-wheeling and can be rotated. The tape keeps it from turning under the forces of recoil and totally blotting out your target image down range. The single filter works on the same principle as a pair of polarized sunglasses. You can turn the glasses in your hands and see the glare reducing effects change by their relative angular relationship with the sun's rays.

My old Aimpoint red dot sight came with a set of polarizing filters. Worked great for those bright days at places like Camp Perry. On really bright days you'd have to turn up the dot's intensity so bright that it changes the point of impact. The lower intensity setting is a sharper dot image and toning out the background light helps keep the settings low.

R,
Bullseye

Jack D · Post by **Jack D** » Tue May 19, 2009 8:36 pm

Bullseye wrote:The dual filter set up is the one I was referring to with the tape trick. The two lenses work in conjunction with each other to reduce glare. The outer lens is free-wheeling and can be rotated. The tape keeps it from turning under the forces of recoil and totally blotting out your target image down range. The single filter works on the same principle as a pair of polarized sunglasses. You can turn the glasses in your hands and see the glare reducing effects change by their relative angular relationship with the sun's rays.

My old Aimpoint red dot sight came with a set of polarizing filters. Worked great for those bright days at places like Camp Perry. On really bright days you'd have to turn up the dot's intensity so bright that it changes the point of impact. The lower intensity setting is a sharper dot image and toning out the background light helps keep the settings low.

R,
Bullseye

My Ultradot also has the pair of filters and that's what I'm putting on the Bushnell. The Bushnell came with a single polarized filter and it's too dark for indoor use. I ordered a circular polarized......I hope it's workable. It should be here late this week. It's not clear to me what the difference is between polarized and circular polarized.

Post by **Bullseye** » Tue May 19, 2009 9:24 pm

I had to do a little research on circular polarizing filters as I was not totally up on that technology. Basically the linear filters are two independent lenses that each block out light of a particular phase. When they are rotated independently of each other they work together and combine to block out light of certain phases, like reflected light. For optical shooting scopes this is a good thing, as you can also change contrasts of the image or the background with a linear filter set up. The circular filter is basically one lens with two parts bonded together. These two parts are a linear filter and a plate that blocks out light waves in the quarter wave range. You can rotate this one lens and that can enhance the contrast of the image and reduce reflected glare. The circular polarizer filter is more useful for photography and especially in autofocus and the newer SLR cameras. For shooting optics the benefits of the circular over the linear polarized filters appears negligible.

Hope this helps.

R,
Bullseye

Jack D · Post by **Jack D** » Tue May 19, 2009 9:37 pm

Bullseye wrote:I had to do a little research on circular polarizing filters as I was not totally up on that technology. Basically the linear filters are two independent lenses that each block out light of a particular phase. When they are rotated independently of each other they work together and combine to block out light of certain phases, like reflected light. For optical shooting scopes this is a good thing, as you can also change contrasts of the image or the background with a linear filter set up. The circular filter is basically one lens with two parts bonded together. These two parts are a linear filter and a plate that blocks out light waves in the quarter wave range. You can rotate this one lens and that can enhance the contrast of the image and reduce reflected glare. The circular polarizer filter is more useful for photography and especially in autofocus and the newer SLR cameras. For shooting optics the benefits of the circular over the linear polarized filters appears negligible.

Hope this helps.

R,
Bullseye

If that's the case, I ordered the wrong filter. Dang!.

Post by **Bullseye** » Tue May 19, 2009 9:45 pm

Try it and see how it works. You could always return it if the effects aren't satisfactory. Here is one of the links I used for my research http://www.bobatkins.com/photography/te ... izers.html Perhaps you can get a little more info from it. It sounds like you already had a circular filter if there was just one lens. Did you try rotating it to change the contrast?

R,
Bullseye

Jack D · Post by **Jack D** » Wed May 20, 2009 2:24 am

The one that came with it is fixed. It does change some as you turn it, but not much. Like polarized sun glasses. The filter on the Ultradot turns from clear to almost black in a 90 degree turn. That's what I was hoping for. I'll know soon enough. The circular is on the way.

Post by **Bullseye** » Wed May 20, 2009 6:42 am

Sounds like your Ultradot filter is the linear kind. The two filters will work together to nearly block out all all light if you let it. This is where the advantage is, on a bright sunny day that black ball sitting on a nearly white background will reflect a lot of the sun's glare. Dialing down the ambient light makes the dot more visible at a lower LED intensity setting. The lowering of contrast is really not an issue with a black on white target.

R,
Bullseye

Jack D · Post by **Jack D** » Wed May 20, 2009 5:29 pm

Well.........live and learn. Got the circular today. Was supposed to be black and it came in silver. And it doesn't fit. Apparently a 30mm filter doesn't fit a 30mm tube. Now to figure out what size the threads are. They make the filters in 27mm and 28mm. It's probably one or the other. I can measure, but is it inside (female) or outside (male) that determines the thread size? Probably will have to take the sight to a camera shop to get the right size.

Circular is not what I want. It does darken slightly, but mostly the sky. Might be OK on a shotgun on flying targets, but not what I want. Linear is the way to go. And, yes, the Ultradot is obviously a linear filter.

Post by **Bullseye** » Wed May 20, 2009 10:18 pm

According to the specs for that scope the lenses are 28mm. That should be the size filter you need.

R,
Bullseye

Jack D · Post by **Jack D** » Thu May 21, 2009 11:37 am

Bullseye wrote:According to the specs for that scope the lenses are 28mm. That should be the size filter you need.

R,
Bullseye

Thanks for confirming that, R. I measured it at 27.7mm female and 27.8mm male and assumed that 28mm was correct. Maybe I'll get the proper filter this time. I couldn't find the spec's. on this item. Wasn't packed with the sight and couldn't find it on the Bushnell site. Although I tend to give up early due to dial-up......it takes forever to find anything.

Jack D · Post by **Jack D** » Wed May 27, 2009 1:57 am

Searching for a linear polarizer in 28mm was futile. Best I could do was 37mm and was about to order that and a 28mm-37mm step-up ring when I thought about trying the red dot manufacturers for assessory filters. Found that Ultradot's filter for their 30mm tube is available as a separate item. Ordered one from www.ultradotwest.com (on parts page). Came in today and it screwed right on...just like it was made for it. $9.95 postage paid.

The adjustment ring is a snug (but no too snug) fit so it is unlikely to change due to recoil. Testing tomorrow.