Home Forums Hunting & Shooting Hunting Optics School Me on Parallax Adjustments

I have my first scope with a parallax adjustment, a Zeiss V4 4-16. I've only been able to play at a 100 yard range so far, but I can see the benefit. The Zeiss's parallax adjustment doesn't have any yard markers on it. I was playing at 100 yards and found a sweet spot. Ultimately I'd like to put some markings on the adjustment for repeatability so I don't always need to find that sweet spot...especially hunting. Does the parallax vary on different magnifications? Assume I was on the highest power and found that sweet spot, would parallax change at a lower magnification? That would moot the point of marking unless I considered them at a particular magnification only. Most scopes I've seen with a parallax adjustment have distances. Why not the Zeiss and is this good or bad. Looking to get a little informed and get the most out of this scope.

I am the optic dummy of the world, but will share my limited experience. I have a couple of old Bausch & Lomb 6 x 24 with AO. The approximate yardages are marked...but I have discovered that the diopter movement negates the parallax yardage marks much, much more than power ring changes. This was checked with the rifle clamped solidly and the scope crosshairs on a grid target at 300 yards. My conclusions are, marked yardages on the parallax adjustment may be true with the diopter set at zero. If because of your eyesight, the diopter is set far away from zero, then, the yardage marks are almost useless. Perhaps that is why Zeiss omitted them. Still, with the rifle clamped solid, moving the power ring to extremes and bobbing your eye around in the "eyebox" to detect parallax error, I have found that the power ring does not induce any detectable significant error. Keep in mind, 2 different brands of scopes, mine also being 40 years older than yours.
Also, I'd like to add that after a lot of varmint shooting at varying mid ranges, I find myself increasingly refraining from twiddling adjustments. Barsness pointed out in one of his books, that if you need to reduce parallax quickly, just move your eye to the very rear limit of eye relief (where you see a black fuzzy donut around the crosshair intersect). I shoot ground squirrels between 100 and 400 yards generally, about the size of a playing card, using that method, and still getting a satisfactory hit probability. I leave the parallax alone, set on a real life 250yds as opposed to the actual yardage marking which is moot because my diopter setting is to the minus end of the scale. Hope I haven't confused you.

Let me see if I can answer your questions.

First off, let's make sure we have the nomenclature straight. The parallax adjustment of which you speak is essentially a focus knob used to set the focus of the image projected by the objective onto the first focal plane of the riflescope. There are two ways of doing that: an adjustable objective, which is where the objective lenses are adjusted by twisting them (much like in a camera lens); and a side focus knob the turning of which causes an extra lens in front of the first focal plane (in front of the erector) to go back and forth thus shifting the focus. The Zeiss Conquest V4 4-16X44 is a side focus model.

Parallax issues occur when the image of the target is not focused exactly on the same plane where the reticle resides. First of second focal plane is not important here, the underlying principle is the same; have the image of the target be focused on the same plane as the reticle.

Now, let's define "in focus". In optics, there is a concept called Depth Of Field. This is an area in front of, and behind the exact focus point where the image still appears to be in focus. There are some rules, like everything else in optics. The higher the magnification used the smaller the depth of field. The closer the target it, the small the depth of field. So a high magnification scope focused on a close target has very little depth of field and focus is critical. Conversely a low magnification scope focused on a target pretty far away has an immense depth of field, meaning most everything appears to be in focus, from the boulder near the target 400 yards away to the clouds in the sky 4 miles away.

Now, are some rules with which you might not be familiar; the bigger the objective lens, the higher the parallax error at the same magnification, distance and setting. The parallax error is not influenced by the magnification of the scope. And of course, the further away from the focus your target it, the larger the parallax error. Finally the parallax error we are discussing here is the maximum displacement possible due to not being properly behind the riflescope. If you are lined up perfectly, parallax errors do not arise. That's why they say to move around to see if there is a parallax error.

Ok, let's move on.

Fixed focus riflescopes are usually set at 125yards or so and take advantage of the depth of field for that distance and their relatively low magnification. These riflescopes usually have smaller objective lenses so the parallax error is smaller.

Now even though the reticle is set on the plane where the objective projects precisely the image of the target 125yards away, the reticle is still useful for objects 250 yards away because the parallax difference is rather small at low magnification, especially with smaller objective lenses.

Now with your bigger objective lens, the parallax error will be bigger. The neat thing about a side focus (or an AO) is that you can get pretty close to focus quickly and that reduces the parallax error. But the issue is that with a large DOF you can be quite a bit away from perfect focus, yet it still looks good enough and you don't think about the parallax error that exists between being focused at 125 yards while the target is at 200 yards and in decent focus.

Here is a site that has a parallax error calculator.
https://www.lelandwest.com/parallax...nid=84303a04d18b0ce869e35b1e395473364069
If you put in 44 for your objective, 125 for the focus, a starting and ending range of 100 and 500 with a 50yard increment, you will see that your maximum parallax error is a half inch (quarter MOA) at 200 yards. Not much to worry about.

Now we know that parallax error has nothing to do with magnification, but on the other hand we know that focus is more critical at higher magnification due to the reduced DOF. I like to focus at high magnification and then reduce the magnification from there, knowing that my focus is the best I can make it.

The parallax error will not change as you reduce or increase the magnification.

Lastly, the focus of a lens if a logarithmic scale so the closer the target the greater the movement range to obtain focus and as the target is further away the less adjustment is needed on the lenses.

I hope this was helpful.

Very helpful. Thanks for taking time for so much detail.