Scope Parallax Max. Error calculations

[kenl]

This spreadsheet is the result of wanting a different scope on the .22 mag CZ455. It now wears a Sightron 4-12 SiH-TAC AO. Great scope, except it has non-locking target turrets, and the rifle was bought for field use. I’m a klutz, and have already accidentally moved the settings. Easy enough to fix, if I notice it, but don’t want to have that problem when hunting.

I have a Sighton Sii 3-12 that I’d like to use, but was concerned about the parallax error. It's parallax is fixed at 100yd. Digging into it, found a lot of information describing P error, but almost nothing on how to compute the amount of error that you can expect at a certain range. Then found the formula

Max. Parallax Error = 0.5x ObjectiveDia. X (RangetoTarget – ScopeParallaxRange)/ ScopeParallaxRange.
It’s important to use the same units (mm, inch, yard, parsec, rod, etc) in the formula.

Below are 2 excel spreadsheets that details parallax errors from various scopes from short to very long ranges, one metric, one standard. Yeah, the ScopeParallaxRange on the metric sheet is in yards, because that’s what’s in the spec sheets.

_Perror std.jpg
_Perror metric.jpg

Edit: Sorry, couldn't figure out how to attach a legible image of it, so it's uploaded as a PDF.

parallax error in inches.pdf

I hope someone smarter than me can attach an image of it. PM me if you want a copy of the excel sheet. Go to https://www.lelandwest.com/parallax-...calculator.cfm (not my site) if you just want a simple fill-in form.

BTW the Sii will work with the CZ IMHO

And please tell me if you find any errors

[smoothy8500]

If people take the time to analyze your data they would see that parallax error is more influential (based on total MOA/MILRAD) at shorter distances rather than longer distances.

[kenl]

If people take the time to analyze your data they would see that parallax error is more influential (based on total MOA/MILRAD) at shorter distances rather than longer distances.

Agreed, but I was surprised how usable a scope is when you look at inches of error.

[smoothy8500]

Unless it is serious benchrest competition, parallax error is greatly overblown. For the "average shooter" parallax error can be less than their shooting capabilities.

[kenl]

^ after looking at the numbers, I agree with you.

[HK Dave]

Hmm this calculator looks like it assumes fixed parallax scopes. Try putting 10 yard parallax with a 56mm objective in the calculator. With your parallax set to 10 yards and aiming at 1000 yards, you have 3 mils or 109" of potential parallax error.

At a fixed 50 yards parallax, you can have a potential of 21" error at 1000 yards. Easy miss. Course wind probably has more of a factor at this point.

I don't know that parallax error is overblown. If it were, every manufacturer would fix their parallax at a certain yardage and be done with it.

I do agree however that the average shooter can't shoot within the limits of most scopes parallax error. So I suppose in essence I agree with smoothy. :P

[kenl]

Sorry, I should of specified that the spread sheet, and it looks like the calculator, are for fixed parallax scopes. AOs are entirely different animals. It also is for the theoretical maximum P error of that lens system. A shooter can reduce the error by consistent cheek weld/eye placement. The manufacturer can increase it by sloppy design, machining, or assembly.

I don't think I'd use a fixed P scope for a 1000yd target. Never attempted to shoot that far, but IMHO that calls for good glass, large lenses, and adjustable optics. What this also tells me is that a good hunting scope doesn't need the weight or complexity of an AO system, even if it's used on a lowly .22mag rifle.

[HK Dave]

Keno, you’re an engineer huh?

[kenl]

no, just a data geek with some optics background from a LONG time ago

[smoothy8500]

I don't know that parallax error is overblown. If it were, every manufacturer would fix their parallax at a certain yardage and be done with it.

I should clarify that I was referring to scopes with a fixed parallax, usually set at 100yd up to 300yd depending on mfr.

[HK Dave]

I should clarify that I was referring to scopes with a fixed parallax, usually set at 100yd up to 300yd depending on mfr.

They need a like button so we don't have to respond and just say we liked it. lol