Is parallax ajustment really important?

[hack3rpt]

So I bought a Leapers 3-9x40 (will arrive in 3 days) and it doesn't have AO. It has a fixed parallax at 35 yards, and for the most part, I plan to shoot at 30 meters so it's close enough, but if I want to shoot closer, let's say at 15 meters, at the minimum magnification, does parallax have a big effect? I think I can keep my eye centered to deal with the crosshair moving a bit, but will it be too much out of focus, or will it still have great quality?

Thanks in advance.

[Black Beard]

Should be fine at 15 yards. Check it before you attach it to the scope rings (which might mark it) just in case you are not happy. Don't forget to adjust the eye piece to focus the reticule before you check (granny, sucking eggs, I know).

[hack3rpt]

Should be fine at 15 yards. Check it before you attach it to the scope rings (which might mark it) just in case you are not happy. Don't forget to adjust the eye piece to focus the reticule before you check (granny, sucking eggs, I know).

Thanks for the help!

[BTDT]

Maximum POI shift in any direction

O x (P-R) / 2P

Where:

O = Objective lens radius

P = Parallax focus range

R = Target range

Therefore, a 40mm objective focused at 35 yards will give a maximum POI shift at 15 yards of

20 x (35-15) / 70

Or 5.71mm.

You'd only get that sort of shift if you deliberately tried to look through the scope as far from its axis as possible; in practice, shift will be nearer a quarter, or ~1.4mm.

No big deal.

[hack3rpt]

Maximum POI shift in any direction

O x (P-R) / 2P

Where:

O = Objective lens radius

P = Parallax focus range

R = Target range

Therefore, a 40mm objective focused at 35 yards will give a maximum POI shift at 15 yards of

20 x (35-15) / 70

Or 5.71mm.

You'd only get that sort of shift if you deliberately tried to look through the scope as far from its axis as possible; in practice, shift will be nearer a quarter, o1 ~1.4mm.

No big deal.

Thanks for the really elaborate answer! Might use this to calculate some other distances later.

[Portzy]

I have posted this a few times but you may find it useful.

https://www.lelandwest.com/parallax-...6272596b1b5e1f

[Shed tuner]

I have posted this a few times but you may find it useful.

https://www.lelandwest.com/parallax-...6272596b1b5e1f

that's handy.. easy to play with the numbers and see the effective.

Simple answer is buy a smaller objective scope, at set it to the midpoint of your target range.

[Squintykid]

this was the parallax difference with my FAC Rapid with FFP Vortex, it dials down to 25m.
back yard zero was 15yds at 5x mag which should have also been the same as a field zero of 50yds.
The group was shot at 15x at 50yds

[averageplinker]

this was the parallax difference with my FAC Rapid with FFP Vortex, it dials down to 25m.
back yard zero was 15yds at 5x mag which should have also been the same as a field zero of 50yds.
The group was shot at 15x at 50yds

There are a few variables you have introduced there. Wind, different distance (might introduce Cant) and the change in Mag can affect POI on scopes. So the difference may be due to parralax plus other issues etc.
Rich.

[zephyr]

Wow, thank you, I was not aware of this formula or magnitude of the possible parallex error.

Ok I’m getting away from the OP’s original question, but I started thinking about errors in focusing adjustable sights.

I shoot benchrest and try to get the parallex adjusted as accurately as I can, but with the ‘ten’ ring only being 2mm there is little room for error. The depth of field I get at 25m is about 2m. By surreptitious use of the Lelandwest webpage (thanks for the link) I get a possible error spread of 2mm (1mm either side of aim point). With careful focus and head waggling I’m sure I get much less parallex error than that, but even that could compound any bad shooting technique. Ok, it won’t help with the pulled “9”, but the “10” that just miss being an “X” or the “9” that miss being a “10” by a hair.... But as the error works both ways it may have helped with those that are just “10’s” or “X’s”!

Hmm, so while the big objective lens can give bigger parallex error, the smaller objective lens (usually having greater depth of field, due to being lower magnification) can give a bigger error in getting the focus distance correct. I wonder where the cross-over between the two is?

I’m now wandering away in a distracted way, muttering to myself, thinking about this.

I’m sure my shooting technique is a bigger factor than parallex error, but is cant a bigger potential error than parallex?

[Squintykid]

There are a few variables you have introduced there. Wind, different distance (might introduce Cant) and the change in Mag can affect POI on scopes. So the difference may be due to parralax plus other issues etc.
Rich.

yes, have to agree there, I posted and thought..change of magnification; x3 error.
Always made the initial PBR zero in the back yard but with different scopes, a ready reckoner zero.
But if I hadn't put wind speed or direction on the sheet - you woudn't even have raised the point.

However I checked the 50yd zero back on a 15yd card and it was high and left.

[bill57]

There's an excellent animation here which demonstrates how parallax error works in reality. The "shading" is the eye moving out of the centre line of the scope.

https://en.wikipedia.org/wiki/Telesc..._Animation.gif

[32:1]

Ive a few fixed scopes and their set at 30yds, this is great for shooting anywhere from 15 to 45yds, theres more error in my rangefinding than parralax. I like fixed focus and mag too as theres nothing but point and shoot.

I had a 3-9-40 hawke that would hold zero all the time, but touch either the AO or the mag and it went off poa.

Chris

[zephyr]

Well in answer to my question “is cant a bigger potential error than parallex?” After reading stuff that was completely contradictory, I did some experimentation. The result was, at 25m’ish with my gun/scope combination, cant is potentially a bigger error than parallex. At as little as 0.5 degree of cant the error was significant at 1-2mm of error (about the same as the formula calculates the maximum parallex error to be). But, and this is what I found reassuring, I readily sensed 1 degree of cant (2 degrees and above just felt freakish!). Indeed when I bought the gun to my shoulder without any conscious adjustment the cant was a maximum of 0.1 degrees.

How do I know the angle of cant? I put my phone on the gun with a spirit level app displaying and recorded it with my iPad so I could see the cant at the moment of firing.

[Portzy]

For me it helps if the larger proportion of the scope/rifle combination mass is below the level of the forearm resting palm too, gravity takes over and brings the combination into pretty much plumb provided you use a loose'ish hold.