Parallax vs Focus

[Wild Bill G]

Great article I nevver knew the info about the side mounted paralax knobs. How ever I think Landtosea never did get the right answer. I beleive he probably still has his infinity at 400yds. Catshooter tried to explain again but but LtoS still never caught it. He should have gone back and done as CS said and found a far off object anywhere and used it. As long as that object was 1000 plus yds away to set his infinity and turned until the knob quit moving then set it. I think that was the correct info from what I read. We are to always start that way with our side focus/parallax adjustment. If I am wrong please correct me.

 

[xdHammar]

Thanks for the clarification.

 

[Buckys]

Thank you CatShooter

 

[Orange Dust]

Proves you are never too old to learn something. I never knew you always have to come down from infinity to adjust parallax. Love this site and the shooters here. None of us know everything, but each of us know something someone else may not know. Great job guys and I feel blessed and thankful.

 

[Danehunter]

Wild Bill,
What do you mean by "setting" a parallax knob?
The factory "sets" the parallax knob for infinity and we scope owners live with what the factory has given us, and in a quality scope that is virtually always correct.

Yes many parallax/target focus knobs do have yardage of meter numbers on them and those are almost always "ballpark" numbers and not exact. And many parallax knobs only have dots on them, the manufacturer realizing the numbered knobs always lie a bit.

As the OP stated, parallax target focus adjustment is to get the reticle and target in the same focal plane. This means when the parallax knob is set properly you get no "parallax effect" (of the reticle moving around on the target) by moving your head slightly back and forth or up and down when viewing the target.

As I stated earlier, to be sure you are not having a parallax problem (misplaced reticle on the target) keep a perfect circle of shadow around the edge of the scope. This means you eye is centered.

Eric B.

 

[Bart B]

Stumbled onto this thread looking for something else, then read Catfish's words again on scopes having three image planes.

Why do scope patent drawings showing light rays focusing on only two image planes? Front/first one at objective lens focal point and the rear/second one at the reticle plane.

https://patents.google.com/patent/US4643542A/en

 

[WildBillG]

Litehiker it was explained on this thread that some scopes have set screws on the parallax adjustment knob. Now as you said alot of scopes are juat we get what we get. If your scope does have a set screw though you can set your parallax knob to stop at infinity. The article is in this thread not sure where give it a read I found it interesting. How ever most of my scopes can not be changed and turning screws that look like plugs on a scope kinda scares me a bit.

 

[Bart B]

The definition of parallax is basically one thing is not visually aligned with two other things.

If your aiming eye is on the scope's optical axis and the reticle is on the target, there is no parallax regardless of where the objective lens system is set at to focus the target image at. That knob on the side could be set anywhere and it matters not

 

[WildBillG]

Bart B you are missing the fact that the parallax dial is also used to focus your scope at a certain distance. If the image you are aiming at is bluury you can not pick an exact aiming point. This to is explained very clearly in this thread. When shooting long range or for a very small group the smallest inconsistency in head placement makes a huge difference at the target. That is why parallax adjustment was created because we can not do some thing exactly the same every time. Bart I am not sure what you have for scopes or if they have parallax adjustment but if you do and have a 25x scope try this. Go out to the range and set your scope on 25x and the parallax at infinity now aim at your target at 100yds. It is my guess you will be lucky to male out the bulls eye or center of the page. Now set your parallax at 100yds and see the difference. After this test let us know if the parallax/focusing dial works.

 

[Bart B]

WildBill, how was parallax adjusted on scopes before that knob opposite the windage knob was added? It's been done for over a century.

My two target scopes don't have a parallax adjustment knob. Don't need one. That knob does nothing more than focus the target image in the reticle plane and makes no angular adjustment to the line of sight in the scope. Exactly the same as a single lens reflex camera lens focusing subject image on the ground glass in the viewfinder and on the image sensor.

 

[WildBillG]

Bart B do your target scopes have an adjustable ring on the objective bell. I am not a historian so I have no idea when the first adjustable parallax scopes came into being. I do know that all of my target scopes have an adjustable parallax whether it is on the objective or on the side. What power are your target scopes and at what distance do you use them. These 2 questions could explain why your target scopes work well for you.

 

[Bart B]

My Weaver model T scopes compensate for (adjust) parallax effects by twisting the objective bell back and forth to focus the target image in the first image plane. Exactly like the first adjustable objective lens scopes made a century or more ago. Their focal length is about 7.2" and move about 2/10ths inch forward changing range focus from infinity to 50 yards to focus the upside down target image in the first focal plane. Erector tube lenses invert it to right side up to focus again in the reticle plane.

As long as my aiming eye is on the scope optical axis, there is no parallax error regardless of the range the objective lens is set to focus on. Its easy to center the eye on that axis when it's at maximum eye relief plus a fraction.

That knob on the left side doesn't adjust anything other than where the target image is focused in the line of sight inside the scope. Exactly the same as adjustable objective lens barrels. Worst thing scope companies did was claiming it adjusted parallax instead of focusing for target range.

 

[WildBillG]

The adjustable objective of your Weaver model T is an adjustable parallax. The only difference in the 2 set ups is how they are to be adjusted. The one on your Weaver does not have to be turned to infinity first then adjusted down to your target distance. The dial on the left side has to be turned to infinity first and adjusted down to target distance. Both styles clear up your sight picture when adjusted correctly. It is just 2 different ways of doing yhe same job with different names.

 

[Bart B]

The dial on the left side has to be turned to infinity first and adjusted down to target distance.

Name one whose instructions say to do that. Never heard of that. Physically impossible based on all the scope patent drawings I've seen such as the link in my post #76 in this thread. Not a requirement stated in Nightforce benchrest and competition scope manual.

All the mechanical drawings of such scopes show both lens elements move back and forth as the knob is turned starting anywhere in its range. Their lens mount has pins whose diameter is the same as the spiral slots in the outer tube that the adjustment knob twists. The lens mounts stay in position until the outer knob is turned. Those two lenses move.the same as the two lenses that change magnification on variable power scopes that don't have to be set to one extreme before changing it to another.