I don't think the filter has an effect on depth of field. All the filter does is restrict some of the wave lenghts of light. Closings the f-stop restricts all the light, forces the lens to bend and then unbend the immage (for lack of a better term), in order to get it correctly focused on the film or immage sensor.

http://www.cambridgeincolour.c...s/depth-of-field.htm

quote:

Originally posted by NikonUser:
maladat, curse you for making me thing further on this.

I also just noticed I got it backwards - you'd get more DOF if your pupil was less dilated, not more dilated (not sure how significant this effect actually would be). Every now and then I get mixed up with smaller numbers meaning larger apertures.

Hey, I totally get that, and it doesn't get better with age.

That's why when one examines these concepts, it's great to talk about it in a group just to keep someone (me!) from getting tripped up.

I'm quite fond of saying "I'm never quite so stupid as when I'm being brilliant." Shorthand for "when I have a great idea, that's when I can't even add 2 and 2 to get 4."

Well, that was quite the weekend. I have not seen this much wind over a 3 day period in a long time. On Friday, we had the team match with the wind predominantly from the south switching back and forth between the left and the right. We shoot due north so the wind came from behind us and just messed up everything. We had 4 relays of two shooters each. I shot the first relay strictly on flags and we did ok. The next three relays were strictly on mirage but it was ever so faint. We discovered that when the mirage was going from left to right, it had double the effect on target than when it was going right to left, yet it appeared the same from either directions. I also saw times when the mirage shifted direction without a pause or boil. One second it's going right, then it's going left. At then end of the day, I tried with the CPL, but the clouds were already rolling in and I did not discern much difference with or without the CPL. And then I ran out of time as the cloud cover became complete and mirage was gone.

On Saturday, there was no mirage anywhere. Total overcast and windy as all get out. Steady wind at 12-15 with gusts to 30mph. The scores suffered. On Sunday, total wind reversal. It was coming in from the north-northeast and I put 3 MOAs left and 1.5 MOAs up one the gun and did everything on flags. The wind was epic and it was cold. When I finished my two matches, I put away my equipment and sat in my chair for the next 2.5 hours visiting with some of my friends. At one point the Sun came out and I heard mirage was out in force. I looked at the firing line and it was totally crammed with shooters, scorers, officials and observers I didn't feel like going back up there to play with my spotting scope that was already packed at the bottom of my cart. Anyway, I was fretting about scores as I was hoping that I had won match #5 and didn't want to see the other relays destroy my hopes and dreams. Especially now that they had mirage, not just the crazy flags.

I do have a match next weekend and the CPL is now part of my standard equipment so I will see if I get anything then.

Today we had another match and I actually had more time to play with the CPL and observe the mirage, with and without the CPL.

The first observation was that when I screwed in the CPL in front of the objective lens, I had to play with the focus. Then I discovered that I could not quite get a good focus and realized the CPL filter was crap. When I just observed the mirage, it seemed to knock off some scintillation but the mirage was very apparent.

I called another shooter over to go through the same observations. I did not tell him what I was doing, I just said: look at the mirage and then tell me what you observe. While he was looking through my Kowa, I added the CPL. I saw him reach for the focus knob and then play with it, hunting for a proper focus. He reported that it was a little darker but he was not seeing much difference in how the mirage appeared. I removed the CPL, and he focused quickly and said again, there was no real difference.

Going forward, I would have to buy a top quality CPL for the Kowa and that's going to be expensive. I may do it at some point, for now my focus is the Worlds this summer, so no more playing until the fall.

Thanks for trying. Even this little experiment helps. Good luck in your shoots.

Will wonders never cease? While going through my equipment in preparation for the coming Worlds, I found two CPLs one is 62mm and the other 77mm. The 62mm should fit on my March-X riflescope and the 77mm will fit on my 18-300mm lens for my Nikon DSLR.

These are quality CPLs, not like the apparent junk I got for the Kowa. I'll do some playing around, especially with the camera.

I finally got around to checking the effect of the polarizing filter on the appearance of “mirage” (heat wave effects). I don’t know if the total range distance would make any difference, but when focused about 100 yards on a 200+ range, there didn’t seem to be any significant difference in looking at the target. The distortion caused by the mirage didn’t seem to vary regardless of whether I was looking through the filter. At the out of focus distances in front of and behind the target, though, the filter seemed to reduce the apparent distortion effects. Without the filter the mirage seemed to move faster and with less amplitude (if that makes sense). I.e., the waves were quicker and seemingly smaller.

Because those effects were not at the image focal point I don’t believe that there would be much of an advantage in using or not using the filter except if the shooter wanted a clearer picture of what was happening with the mirage.