Hello, I wanted to share with y’all some results of a test I did measuring the maximum parallax error in 6 rifle scopes that are set to be parallax free at a fixed range. I first noticed the magnitude of these errors when looking through a Zeiss Conquest 3-9x40 scope at a target 300 yards away. I found that without touching the rifle I could move the cross-hairs completely off the 8 1/2 x 11 sheet of paper just by slightly moving my head, all while maintaining a perfectly clear sight picture. I have shot targets to 500 yards with moderate regularity with and decent success but only with scopes with adjustable parallax and have never really qualified most of my “hunting guns”, most of which have 3-9x40 scopes, beyond 100 yards. Searching across the internet I found countless posts regarding parallax errors and an often quoted formula which goes something like this: (1/2)*D*abs(l-f)/f = PE D = objective diameter f = parallax free distance l = distance where parallax error is being measured For typical objective diameters this yields very small parallax error at the ranges in question. For a 40mm scope this should be around ~1.5 in. Since this didn’t match the error I was seeing I decided to go through my various different hunting scopes and try to measure their parallax error. I once again stuck a target on a 8 1/2x11 sheet of paper and set it up at exactly 300 yards. I put my rifles in a rest and adjusted them to aim at the center of the target and then, without touching the rifle, moved my head as far left and right and up and down as I could and still keep a sight picture. Using the sheet of paper as a reference, I recorded the maximum parallax error to the nearest inch as best as I could resolve. The results are as follows: Scope .......................................................PE Zeiss Conquest 3-9x40 .............................. ~8in West German Zeiss Diavari-C 3-9x36.............~2in Leupold VX-II 4-12x50.................................~8in Schmidt Bender Zenith 3-12x50...................~4in Zeiss Victory Diavari 3-12x56.......................~7in Nikon Monarch 2.5-10x42............................~2in As you can see, a few of these scopes have a huge parallax error. The difference seems to be not only related to objective diameter as the formula suggests. I suppose this equation comes from some thin lens approximation that doesn’t hold up to these modern complex optical systems. I was really impressed with the Nikon here, as it costs a fraction of many of these scopes. The West German Zeiss (I wish I had more of these great scopes) belongs on a hunting rifle that I have practiced with extensively to 400 yards in preparation of an Idaho elk hunt last year. The gun and scope both performed excellently and I noticed no problems due to parallax then. The Zeiss conquest bothers me the most. Its objective is only 40mm. I have loved these scopes for there clarity ( which side by side makes the VX-II look like crap),long focal lengths, and affordable price. I have about 10 of them now and I checked several to make sure I didn’t just pick a lemon. I would image these are popular scopes. Does anyone here have them and have you noticed the same problem? I invite and encourage anyone who possesses any of these scopes to try this on their own. This amount of error makes them almost unusable at this range. The rifle that I first noticed this with does not have a straight comb, and with such a forgiving eye relief you can move your head forwards and backwards several inches which is all the while moving the cross hairs. Well that kind of got winded. I hope someone made it down this far and I hope to hear back from some folks.