Rifle Scopes Parallax Error vs Temperature

[lte82]

I noticed something odd today... I took out my S&B PMii to get some zeroes and I noticed I needed to dial more parallax than normal at 100 yards. So I moved to 300 yards and I had to dial the parallax knob to almost to 1000 in order to dial out the error. I could not dial out all of the error at 1000 yards even setting it on infinity. Thinking something must be wrong, I went home, mounted another S&B PMii and drove back to the range. Same exact thing. So I go home, grab my third PMii and just take it behind the house and look at everything from 50 to 970 yards, and parallax is spot on. I leave it outside, grab the first scope I was trying to zero, suddenly, it too is working fine. I scratch my head for a bit, then start looking through them again, and I notice some error. Now, as the minutes tick down, the scopes are getting colder and colder, and as the bodies of the scopes decrease in temp, I need to dial more and more parallax to get the error out at distance. So, I grab an ATACR from the warm house, and immediately go to 970 yards and dial out error. Come back 5 minutes later after the scope has chilled down, and there is error, and I have to dial MORE on the parallax knob to get it parallax free. After 15 minutes, I have to go all the way to infinity to get the error out at 970yards.

Has anyone else noticed that your parallax settings change in cold temps? And by cold I mean it's only 40 degrees out, but the difference between even just 72 and 40 is HUGE! Also, has anyone sent their scope back in to get calibrated for a certain temperature? Seems like some of these are only calibrated for room temp, and when the temps dip you may have an issue dialing the error out...

 

[Subwrx300]

First I've heard of this but could make some sense. If metals expand and contract with heat/cold, then theoretically, the lenses would be shifting slightly also. In turn, focus/parallax would need a different position than normal.

@koshkin do you have anything you can chime in with on this topic?

 

[_Windrider_]

I’m not convinced. I think maybe your eyes are deceiving you. I’m being serious, at 100 yds you barely even need parallax. No way a 30 degree temp change affects that especially given the operating range of that scope as specd by the military contracts.

 

[lte82]

First I've heard of this but could make some sense. If metals expand and contract with heat/cold, then theoretically, the lenses would be shifting slightly also. In turn, focus/parallax would need a different position than normal.

@koshkin do you have anything you can chime in with on this topic?

All of my scopes did it, so its definitely a thing. The S&B is the only one that "runs out" of parallax adjustment before you can dial out the error at distance. All three schmidts are the same, so it's not an anomaly. Interestingly the NF barely had enough adjustment left to dial it out, but the bushnell dmr2 has lots of room left and no problem dialing in perfectly. The image was pretty awful though lol.

 

[Gunfighter14e2]

Your scopes parallax settings change as the scope is changing temp. When the body of the scope dimensions change do to a rapid temp change every thing inside changes as well. I've owned many different brands an everyone of them do this to some degree or another. Even the USO ergo's which are the most forgiving will do this. Once the scope temp stabilizes everything will return to normal.

 

[lte82]

I’m not convinced. I think maybe your eyes are deceiving you. I’m being serious, at 100 yds you barely even need parallax. No way a 30 degree temp change affects that especially given the operating range of that scope as specd by the military contracts.

I wouldn't believe it either, but I literally watched 5 scopes go from room temp to 39 degrees, and all of them needed parallax adjustments once they cooled down. Would've never thought anything of it until I literally couldn't dial out the parallax error at distance with 3x $3000 scopes that all work fine at normal temperatures.

 

[wade2big]

Never noticed. I shoot in all temps.

 

[Gunfighter14e2]

It only happens while the scope temp is changing. I've seen it in as little as a 20* change depending scope mfg.

 

[lte82]

It only happens while the scope temp is changing. I've seen it in as little as a 20* change depending scope mfg.

How long does it take to equalize? I was out there for a while...

 

[Gunfighter14e2]

Depending total max to min temp change, I've had some take 45 minutes, an one took a hour an a half every time from 75* to around +15* degrees. My Mk 4 Leupolds changed the quickest, the USO took a little longer but a few of the Gucci names took longer. If you allow it to ride in the shooting temp to the shooting spot most of the time you'll never see it, or if you place it in the shooting temp an take a long time setting up the targets. If you take it from a warm bed an set it in the cold, just set behind it an watch what they all do. The same thing happens when taking from a cool house an placing in the hot sun, they will change until everything in/on the scope stabilizes temp wise.

 

[Dthomas3523]

So, what we are stating here, that optics spec’d out to perform normally in these temps are not functioning properly?

Not being able to dial all the parallax out at 1k, regardless of temperature doesn’t sound like it’s functioning as spec’d.

I’m not saying any of the above is wrong. Just making sure we are on the same page here.

I get that you might have to turn your knob more or less than normal, but not being able to dial out the parallax at a range that’s well within the assumed capability of some of the systems it may be used on is definitely not functioning properly.

 

[lte82]

So, what we are stating here, that optics spec’d out to perform normally in these temps are not functioning properly?

Not being able to dial all the parallax out at 1k, regardless of temperature doesn’t sound like it’s functioning as spec’d.

I’m not saying any of the above is wrong. Just making sure we are on the same page here.

I get that you might have to turn your knob more or less than normal, but not being able to dial out the parallax at a range that’s well within the assumed capability of some of the systems it may be used on is definitely not functioning properly.

Thats what I'm thinking, yea. The issue may resolve itself once the scope temperature normalizes, but I will find out today. My brain says the cold temps are causing tube shrink which is causing the distance between the lenses to get shorter, which is changing the parallax calibration, so it will only get worse as the temp drops. We will see today.

 

[Gunfighter14e2]

So, what we are stating here, that optics spec’d out to perform normally in these temps are not functioning properly?

Yes but only while in the normalizing processes to the new temp when there is a major change over a short period of time, I've never seen one that won't change, that has a Parallax adjustment. Maybe not to the OP's level but very close. Some mfg's are very little, some are a bunch. My USO Sn 3, 22x ergo has just a shade more than my 20 X Mk 4 but all my 10X MK 4's have way less than both of those. I see it more with higher power scopes than lower no matter the mfg. Fair weather shooters well never see it, but if your one of those that shoot no matter the weather, stores shit in the house, and there's a major temp change outside, then yes. If it rides in the front of the truck to the FFP an your ready to shoot for a prolonged period right from door opening, if you notice small changes you will see it. Depending mfg, power level, an ones ability to see small changes an know their gear many will never see it, but the fact remains all scopes with a parallax adjustment will do it. Think about what happens with any an all devices/items during a major temp change.
Could be the OP's scope has a slight out of spec issue, don't know. However the fact remains if one shoots long enough, has attention to detail, is not a fair weather shooter, they will see it during the items temp change.

 

[lte82]

All three of my schmidts behaved exactly the same yesterday, so it's definitely not a one off thing. I have one sitting in the back of my truck now getting frosty on the way to the match, and one riding shotgun at 73 degrees. I'll be able to test them in a couple of hours.

 

[steve123]

It's commonly known in the Field Target air rifle world that parallax and focus distances change with temperature.

We, the FT shooters are more concerned with focus distance than parallax error because we use the image clarity to judge distance when our side wheels are tuned for distance with ones own eyes - the distance indicator markings on the edge of our big side wheels shows us how far away the target is when it is in focus.

A lot of FT shooters put a temperature tape on their rifle so they know approximately where the scope will focus at whatever temp so they can compensate. I never did this but if I were a national level competitor I probably would.

Some scopes are definitely more sensitive concerning temp changes than others. I do know a guy that complained enough to the place he bought his S&B 12.5-50 FT scope that they took it back for store credit. I had the opportunity to try that scope at the sight in range and it did have a frustrating amount of shift in temps, enough to be off from 50y to 55Y within an hour of the ambient temp change of 10 degrees. That equates to 50% misses even though it's just a 5 yard difference.

Unfortunately it is what it is with you and your scopes, I don't know the exact answer to give you except to make sure your cheek height is perfect so you are staring in the center of the eyebox. You could also try adjusting the diopter to the edges of reticle focus to see how much that would help.

 

[lte82]

Both of my S&bs, as well as all three of my buddies S&Bs out here are all doing it. They have all been outside for hours now and neither of us can dial out parallax error beyond 400-500 yards. The image looks ok at distance, but parallax error is at least .3 mil at 1000 across the board.

My buddies K525i has the same symptom, you have to dial a lot more parallax than normal, but you can still get all of the error out of it.

Not just my eyes, everyone is seeing it.

 

[Gunfighter14e2]

What is the temp an ASL #(above sea level your shooting in?

 

[lte82]

38 degrees F, -1100 DA. Nearly sea level.

 

[Gunfighter14e2]

Never messed with a S&B in cold weather but sounds like they may not be all they are cracked up to be, from what your saying. Good catch BTW. I've USO, Leupold, Bushnell an Hawk and have shot them all them from +110*F -20*F without that issue to-date. Yes they all change during temp transition but once stable they all work.

 

[Subwrx300]

I get the idea that scopes will change focus/parallax with temp (metal has to move) and it's interesting on an intellectual level. But practically, I don't see this as being an issue worth considering when buying scope. As long as the scope is acclimated to the ambient temperature, it will be parallax free when adjusting to the correct distance (forget the numbers on the dial as they don't mean much in the first place.).

So long as the scope has ability to dial out parallax, I don't care if dial says 900 or 700 for an 800yd target. I just need a clear image with minimal parallax shift.

But parallax at long range is pretty damn small to begin with (read: meaningless) when dialing even remotely close to the correct range. See chart below.

If you set parallax adjustment to 9991-1000 yds, the error if shooting to other ranges is listed on far right. At +-300 from dialed distance, .02-.04 MOA ; less than half of a tenth of a minute even when 300yards off dialed parallax.

Count me in the "not an issue" camp. But still interesting in a purely academic way.

 

[koshkin]

Some scope are better compensated for temperature than others. As Steve correctly pointed out, Field Target people have been complaining about it the most, but it has always been around. With significant temperature changes, with some scopes you have to re-adjust both eyepiece and side focus.

I know that earlier March scopes had very significant shift with temperature. I had long talk with Lauren Parsons at SHOT a couple of weeks ago and she mentioned that she had issues with temperature with March scopes, but now that she has switched to Kahles, they are almost gone.

I know Tangent Theta is quite stable with temperature since I tested it for that once.

I do not know about most S&Bs. I have used one of the early 5-25x56 PM II scopes in a wide temperature range and it was quite stable.

I seem to recall that Sightrons that FT people use were reputed to do well with temperature changes.

It must be a common enough issue, since March is specifically callign out better temperature compensation as one of the features on their latest scope.

ILya

 

[steve123]

Some scope are better compensated for temperature than others. As Steve correctly pointed out, Field Target people have been complaining about it the most, but it has always been around. With significant temperature changes, with some scopes you have to re-adjust both eyepiece and side focus.

I know that earlier March scopes had very significant shift with temperature. I had long talk with Lauren Parsons at SHOT a couple of weeks ago and she mentioned that she had issues with temperature with March scopes, but now that she has switched to Kahles, they are almost gone.

I know Tangent Theta is quite stable with temperature since I tested it for that once.

I do not know about most S&Bs. I have used one of the early 5-25x56 PM II scopes in a wide temperature range and it was quite stable.

I seem to recall that Sightrons that FT people use were reputed to do well with temperature changes.

It must be a common enough issue, since March is specifically callign out better temperature compensation as one of the features on their latest scope.

ILya

Kinda OT, but last November Lauren won the shootoff/match in our wildcat FT match here in AZ. There were 12 of us that qualified for this, she won on the 9th shot beating out a friend who is on fire currently. I'm the state champion in my division, and I made it to the 7th shot/3rd place.

Basically, with out shooting aides except a coat, Lauren is capable of putting a pellet into a 1/2 hole at 45Y every time, amazing really!!! I knew I was in trouble when I hit a little 1/2x3/4 target at 30Y offhand and she hitting it also complained it was too big, lol. Anyway, I've seen some awesome shooting in my life but that day she impressed me more than I ever have been.

Actually I've used my S&B 5-25 before and it wasn't too bad for FT. That 30mm tubed 12.5-50 was the worst temp sensitive scope I've seen personally, not sure why???

My cheap Athlon Argos BTR 6-24 doesn't shift much in temp changes.

 

[koshkin]

Kinda OT, but last November Lauren won the shootoff/match in our wildcat FT match here in AZ. There were 12 of us that qualified for this, she won on the 9th shot beating out a friend who is on fire currently. I'm the state champion in my division, and I made it to the 7th shot/3rd place.

Basically, with out shooting aides except a coat, Lauren is capable of putting a pellet into a 1/2 hole at 45Y every time, amazing really!!! I knew I was in trouble when I hit a little 1/2x3/4 target at 30Y offhand and she hitting it also complained it was too big, lol. Anyway, I've seen some awesome shooting in my life but that day she impressed me more than I ever have been.

Actually I've used my S&B 5-25 before and it wasn't too bad for FT. That 30mm tubed 12.5-50 was the worst temp sensitive scope I've seen personally, not sure why???

My cheap Athlon Argos BTR 6-24 doesn't shift much in temp changes.

Temperature sensitivity is a function of both optical and mechanical design. Without opening the scope up, I can't really tell you. Even then, I would need some design information.

Ilya

 

[Denys]

Both of my S&bs, as well as all three of my buddies S&Bs out here are all doing it. They have all been outside for hours now and neither of us can dial out parallax error beyond 400-500 yards. The image looks ok at distance, but parallax error is at least .3 mil at 1000 across the board.

My buddies K525i has the same symptom, you have to dial a lot more parallax than normal, but you can still get all of the error out of it.

Not just my eyes, everyone is seeing it.

Which specific models of S&Bs are we talking about here? Also, at what magnification setting are you seeing this?

 

[lte82]

Which specific models of S&Bs are we talking about here? Also, at what magnification setting are you seeing this?

PMii 5-25. 15-25x, doesnt seem to matter.