In the video linked below the employee of a precision rifle manufacturing company and long range competitor stated that prolonged heating of a riflescope’s internal components by sunlight shining through the objective lens could cause a zero shift.

On the one hand the claim seems plausible because high quality scope sights are precision instruments built to very tight tolerances. We know that temperature shifts can cause dimensional changes, so why couldn’t the claim be valid?

On the other hand, though, I have read countless accounts of military sniping and other long range shooting, and this was the first time I recall seeing the claim or even any discussion of temperature effects on a scope’s settings. I would think that if the problem were going to occur, it would be during long exposures to the large temperature swings in the desert conditions that military snipers have experienced in recent decades.

So, what do the knowledgeable members think? A genuine effect and something to at least be aware of, or nothing to be concerned about?

https://www.youtube.com/watch?v=Soo8UCjPOsw

Personally I think that would be mighty tough to measure without other factors being more of a problem.

For example, I'd be more worried about sunlight causing a temperature difference in the environment from dawn to dusk. Maybe at really long distances a shot at 6 am would be different from one at 1 pm?
Aside from the air getting thinner/heavier over time, temperature changes are also a big factor in wind speed in some cases right?

Not an expert by any stretch though, so take this for the ramblings of an every man.

I think any thermodynamic shifting of the components inside the scope are going to be far less significant than a 10 or 20 degree swing in the temperature/density of the air that you are shooting through.


I suppose if you intentionally positioned a scope where the objective lens was pointed directly into the sun you might warm up some internal components.


I have competed in 3 gun matches with a rifle where I never touched the zero from February and below freezing to August in Kentucky where the guns get so hot sitting in the sun that we started throwing damp white towels over them so that they weren't too hot to touch, and never had a zero shift in my scope. I even considered painting my competition rifle and shotgun white to reduce the solar heating.


I do plug in the current temperature into whatever ballistics solver that I am using because density altitude matters quite a bit at longer ranges.

quote:

Originally posted by IndianaBoy:
I have competed in 3 gun matches with a rifle where I never touched the zero from February and below freezing to August in Kentucky where the guns get so hot sitting in the sun that we started throwing damp white towels over them so that they weren't too hot to touch, and never had a zero shift in my scope.

All right, thanks. That’s the sort of voice of experience response I was hoping for.
I am, however, also curious whether anyone knows if scopes are designed and manufactured with consideration given to the question of temperature effects on the components.

And although I didn’t think it would be necessary, I’ll say it now: Assume for my question that I was referring to mechanical changes within the scope that would affect the zero, not external environmental factors affecting ballistics that the ignorant wouldn’t think of and adjust for.

You should have stated in advance that the comment on scope temperature occurs around 16:50 into the video. I did not and will not listen in detail to his droning on. It took me a bit of bouncing around to cut to the chase on the scope zero issue. He stated that sun coming directly into the objective heats up the scope parts, causing the zero to shift. I seriously doubt that, at least on a quality scope. Other factors will be in play. As in staring into the sun and trying to keep one's eye in the sweet spot of the eye box.

I've never seen any issues with temperature and changing scope zero. None.

NF 5-25x ATACR on a 6.5CM bolt action
- Shot it over the winter at casual matches in the town of Rifle, CO. One morning started at -7 F IIRC. Zero was fine.
- Without adjusting zero, I shot the same setup in June at the Steel Safari in NM. Temps were around 100 F on two days. Zero was fine.

NF 7-35x ATACR on a 6.5CM bolt action
- Similar situation of Rifle, CO in the winter, although temps were a balmy +10 F IIRC. Zero was fine.
- The next June on to the Steel Safari, with two days around 105 F. Zero was fine. There's very little shade at the Steel Safari, so my rifle was often hanging out in the direct sun.

I've shot every one of my bolt actions and ARs in Colorado across 4 seasons. When it's my choice to shoot, I don't practice below 20-25 F. I regularly shoot in the summer with temps of 85-90 F. Never had a problem with zeros changing in this temperature range. This is across the full line of Nightforce scopes and a couple of the middle range Vortex scopes. Never saw it with my older Leupolds -- and they were nowhere near the league of my NF scopes.

His one statement about a changing zero from scope temperature means I won't take the time to listen to the rest of his presentation.

Thanks, fritz, for your comments. Again, your experiences help answer the question.

The video was mostly about his Vudoo setup and I could have just said that I had heard the claim and what did we think of it, but some people appreciate links to the original sources.

Didn't the original EoTech have a thermal drift issue? I could have swore I read that somewhere.
Personal experience from hunting in the Winter and then shooting again when it was warmer was that I had no issues. Most optics that I have on hunting rifles are Leupold.

Years ago when I elk hunted a lot, my 338 had a Redfield scope. Year after year it NEVER needed re-zero for any reason for weather, or removal for cleaning. No mater what I did the zero was always the same, hot, cold, wet, or dry, snow, rain nothing affected it in the field.
The rifle was a long magnum action Model 70, Douglas premium barrel. Mounts were Redfield. Loads were 225 Hornady, fully processed Winchester brass, 215 primers and 74gr 4831. I had the barrel made with some freebore. And it shot under 1" at 100yds. And it kicked like a mule so groups were only 3 shots. I named the rifle "Big Oney" Long story.
Now older, if I go for elk again, I will use my 300H&H

Everything expands and contracts with heat fluctuations. The questions is how much and at what distances?

To test any theory, you'd need to clamp a scope on a solid test bench and zero on a target a long ways away while it's cool. Then you'd have to heat the scope or let the sun bake it. By then, it would be hard to tell how much the crosshairs would have shifted due to heat waves/mirage.

You could, in theory, limit thermal shifting if you changed the color of your scope body to a brighter color, like coyote brown, or silver.

I work in the laser industry and everything has to be thermally stable to be accurate. We calibrate our linear stages with a glass accuracy grid and we let the grid "bake" on the work surface for a few hours before calibrating the system. If we don't, the system will fail to meet accuracy specs. Our machines are accurate to within about 5 microns over a 630mm x 530mm work area. If we don't let the glass bake on the work surface, we'll fail with about 12 microns of error.

I'm willing to bet he's right, but the amount of shift is minuscule, when considering all the other components that are affected by heat (ammo, barrel temp).

Tony.

quote:

Originally posted by joatmonv:
Didn't the original EoTech have a thermal drift issue?

It did, but although I could be wrong, it was my impression that the zero shift was due more to an electronics thing than mechanical dimensional changes. It would be interesting to know what the cause was, but I imagine the company hopes that memories of the problem will just fade away.

And thanks for your comments, benny6. It is good to learn about other experiences.

I have no way of knowing whether that experienced competitor made the comment based on valid experience or it was something that occurred to him as a theoretical possibility. I do, however, find such issues interesting and that is the reason for my questions.

If you really want to dive down the rabbit hole, look up the term "Thermal Lensing".

https://www.rp-photonics.com/thermal_lensing.html

Thermal Lensing Outside of a Laser:

Thermal lensing can also be significant outside a laser resonator when a laser beam with high average power is sent through a transparent optical device such as a lens, a beam splitter or a protection window, or a Faraday isolator. As a result, the position of a focus behind such an element may depend on the optical power level. This can happen e.g. in high power laser cutting heads.

While the context is always discussed in lasers, the concept is the same. As a lens absorbs heat, the image becomes distorted or the focus changes.

In my business, I "collimate" a laser beam, or remove convergence/divergence over a set distance at a set beam diameter. To do this, I use a beam imaging profiler or a beam camera. To use this, I have to take a laser beam from watts to milliwatts to view it in a camera without destroying it.

15 years ago, we would install an attenuator mirror (a clear pieces of glass) on a mirror mount to dump 99% of the power into the mount, while sending 1%, or simply a leakage beam, to the camera. We would use this image to set/check collimation over a set distance. But our spot size at the work surface was unreliable or didn't match up to the mathematical calculations.

After a while, we discovered that the heat dumped into the mirror mount was heating up the mirror, causing image distortion when using the camera. We changed our method to use an open-back mirror mount and we'd dump 99% of the beam into a ceramic beam dump that was separated from the mirror and mount. We are now able to get cleaner and more accurate results since we eliminated the heat absorption/distortion.

And a slight thread drift here...

In researching thermal lensing, I found this gem about light shades that you might find interesting...



Tony.

quote:

Originally posted by benny6:
In researching thermal lensing, I found this gem about light shades that you might find interesting...

Yes, thanks.
I ran across that some time ago myself and made note of it. The man does a nice job of proving that his hypothesis was true, and demonstrated that not all unusual ideas are promoted by crackpots.

Unless you're testing under laboratory conditions, removing as many other variables as possible, how would anyone ever know?

I can't say I've ever taken a rifle to the range and had the bullets hit slightly off from where I expected and thought "It's probably due to heating conditions of the scopes internals."

No, I didn't think about it at all because I assumed it was caused by the dozen other things that could have and probably did cause it.

quote:

Originally posted by sigfreund:

quote:

Originally posted by joatmonv:
Didn't the original EoTech have a thermal drift issue?

It did, but although I could be wrong, it was my impression that the zero shift was due more to an electronics thing than mechanical dimensional changes. It would be interesting to know what the cause was, but I imagine the company hopes that memories of the problem will just fade away.

Electronics drift is a very real thing and difficult to get around.

I spent several years as the Chief Electronic Engineer of the Scales section in R&D for Friden Alcatel, and we designed and marketed postal scales, which are extremely regulated by the feds for accuracy, drift, repeatability and a bunch of other things.

We found that electronic components are going to drift, even if you buy the very best thermally stable components on the market.

Even so, as the scale warmed up, the components warmed up and the output drifted. Very slowly, and small amounts, but it still drifted enough that we had to design an algorithm that would look at the drift and decide whether it was something on the scale or temperature drift and tare it accordingly.

It's an interesting balancing act and you probably won't see an optic company putting the kind of time and money into it that a postal scale manufacturer does.

quote:

Originally posted by Flash-LB:
Electronics drift is a very real thing and difficult to get around.

Okay, thanks. That was my belief, but it is good to get confirmation from an expert.

Well, I'm no "optical expert" but I thought I would contribute here a little bit.

I watched a little bit of the video, thanks to fritz for pointing out the location of the statement on the video. Saved me a lot of time because I really didn't want to watch the entire video.

The statement should be disregarded. The Sun's rays will not heat up the insides and cause the zero to shift; I just don't see how that is possible.

However, that said, temperature changes can have some effect on a lens, but definitely not in the way the video purports to be reality.

As we all know, the magic material for glass for lenses is something called fluorite crystals. This material is virtually immune to chromatic aberration, the effect we also know as color fringing, etc. This is due to the fact glass will not refract the various wavelengths of light on the exact same point. This effect is magnified the more you refract, or bend, the light. Lenses made from fluorite crystal glass do not have that issue. One of the multiple problems with fluorite glass is that it is affected by temperature shifts and that manifests itself by change in focus. I am only aware of one riflescope made with this ultra-expensive glass, it's an Hensoldt of some type costing north of $7000. Fluorite crystal glass is also fragile, and doesn't like the repeated shocks of a riflescope.

There are many camera lenses and spotting scopes made with pure fluorite crystal glass; Nikon, Canon, Kowa... These offerings are all very expensive, but their owners report excellent IQ and superb contrast, as you would expect in the absence of any CA.

If you're still with me, let's go further. In the 1960s, Nikon invented a type of glass that the termed ED for Extra-low Dispersion. This glass was an attempt to get the optical qualities of pure fluorite crystal glass, without the downsides (cost, fragility, temperature sensitivity, etc.)

ED glass does not suffer from temperature-induced shift in focus. ED glass is not pure fluorite crystal glass, but it's a big step in that direction in terms of CA reduction. Some years later, Nikon invented Super ED glass as the next evolution in optical glass and currently there is only one riflescope maker that uses Super ED glass in riflescopes. Right, you got it; that riflescope maker is indeed Deon with their March riflescopes. Some years back it was discovered that the Super ED glass was subject to temperature shift in focus when you hade fast temperature changes and this was due to the high fluorite crystal content in Super ED glass.

A solution was found and they have been using temperature anti-drift Super ED glass in some of their top end, high magnification offerings.

You can read more about it here:
https://marchscopes.com/column...ch-scopes-by-lenses/

And here is a more technical one:
https://marchscopes.com/news/5171/

I've heard of benchrest and other long range shooters keeping their ammo a consistent temperature, but never worrying about scope temperature.

I am not much of a long range shooter, but I have never noticed this phenomenon. I would also suspect other factors that might vary with temperature would be much larger considerations. Mirage, wind, ammo, the gun, etc.

Back in the day, I have seen a shift in zero among Remington 700 PSS and Leopold scopes. It was minimal, but the zero would differ slightly from 10 degrees to 100 with high humidity.

It was a click or two here and there. But it wasn’t enough to worry with until the swing was greater than 50 degrees.

Basically, my zero was the same on 50 degree days as it was 10. Once we hit steady 70 degree with, I would reconfirm and make an adjustment here and there.

But, to be fair, I was really in tune with shooting the rifle and would often notice deviations in switching lot numbers on ammunition. I could also tell you in my sleep the mil hold overs in 25 yard increments out to 300. We shot a lot.

How much of that was the optic versus rifle tech and exterior ballistics I can’t say.

quote:

Originally posted by jljones:
Back in the day, I have seen a shift in zero among Remington 700 PSS and Leopold scopes. It was minimal, but the zero would differ slightly from 10 degrees to 100 with high humidity.

It was a click or two here and there. But it wasn’t enough to worry with until the swing was greater than 50 degrees.

Basically, my zero was the same on 50 degree days as it was 10. Once we hit steady 70 degree with, I would reconfirm and make an adjustment here and there.

But, to be fair, I was really in tune with shooting the rifle and would often notice deviations in switching lot numbers on ammunition. I could also tell you in my sleep the mil hold overs in 25 yard increments out to 300. We shot a lot.

How much of that was the optic versus rifle tech and exterior ballistics I can’t say.

I have an easy answer for you. The vast majority of the "deviation" was due to atmospherics and a little bit perhaps to the temperature of the ammo. Nothing for the optic.

I might have mentioned a time or two, that I shoot competitively at 1000 yards year-round. From about 32F to 100F and from 20-30% humidity to 110% humidity. My 1000-yard zero varies from match to match throughout the year and will even change during the day as it gets warmer.

Great additional information. Thanks to everyone who contributed.