Rifle Scopes March Scope Temperature Anti-drift lens

[JB.IC]

I’ve notice some scopes are extremely parallax sensitive to temperature. *cough* NF (I still use two 7-35x ATACR anyways).

anyone else notice sensitive parallax with temp changes?

Below is from March scopes Facebook post about their glass:

Effect of Temperature Anti-drift lens in March Scope 10-60×56 High Master-----------

We have received inquiries regarding the effect of Temperature Anti-drift lens. Our top lens designer, Nishikubo-san calculated with March Scope 10-60x56High Master. Temperature Anti-draft Lens is incorporated in the High Master lens system of 10-60×56, 5-42×56, 4-40×52, 6-60×56 so that it will create a more stable lens system that naturally adapts to changes in temperature to maintain focus and clarity over a wide range of conditions. This was originally developed to meet the requirement of Field Target shooters who are sensitive to subtle temperature change. (*Fixed 40-60x52High Master and 48x52High Master do not incorporate Temperature Anti-draft Lens in their High Master lens system as they have less lenses and therefore less susceptible than other High Master models.)

Comparison with March Scope 10-60×56 High Master
(1) Before : High Master lens system without Temperature Anti-draft Lens
◆Temperature change : 35 degrees Celsius difference
25 degrees Celsius (77 degrees Fahrenheit) → minus 10 degrees Celsius (14 degrees Fahrenheit)
◆Change in focal point
∞(infinity) → 350m (about 383yard)

When there is a 35 degrees Celsius difference,
focal point first set at ∞(infinity) will be shifted to 350m (about 383 yard).

(2) After : High Master lens system with Temperature Anti-draft Lens
◆Temperature change : 35 degrees Celsius difference
25 degrees Celsius (77 degrees Fahrenheit) → minus 10 degrees Celsius (14 degrees Fahrenheit)
◆Change in focal point
∞(infinity) → 1.3km (about 1422 yard)

It may be easy to see the change between infinity and 350m,
but it is very difficult for a human eye to detect the difference between infinity and 1.3km and some people may not feel any focal difference at all.
The newly developed High Master lens system with Temperature Anti-draft Lens incorporated within 10-60×56, 5-42×56, 4-40×52, 6-60×56 High Master models is way less sensitive to temperature difference than ever !! This new system will naturally adapt to changes in temperature to maintain focus and clarity over a wide range of conditions. (*Above is an example based on calculation. When inputting different values, there will be a different result.)

You can also enjoy Nishikubo-san's story in this article.

Meet the March Scope’s Top Lens Designer – Nishikubo | MARCH Scopes | DEON Optical Design CorporationMARCH Scopes | DEON Optical Design Corporation

MARCH Scopes Official Site

marchscopes.com

March Scopes passionately support serious shooters so that they can continually enhance their performance

 

[Denys]

It is my understanding that this has to do with the material used in the lens. The best material for making lenses that do not suffer from chromatic aberration is fluorite crystals. The challenges of making fluorite crystal lenses are many; expensive, fragile, and subject to temperature variations, among others. These issues is what prompted Nikon to first develop ED (Extra low Dispersion) glass in the 1960s for camera lenses. ED glass goes a long way to control CA, but it's not as good as fluorite crystal lenses. Around the turn of the century, Nikon introduced Super-ED glass, which very much approaches the capabilities of fluorite crystal glass, but without the drawbacks. It is my understanding that Super ED glass contains fluorite crystal material.

Now, March was the first riflescope maker to use ED glass about 14 years ago. They are currently the only riflescope maker that uses Super ED glass. They upgraded the Super ED glass to use the one they mention in their article so all High Master scopes use that material. That goes for March-X 10-60X56 HM, the two Genesis models, the March-FX 5-42X56 wide angle and the upcoming March-FX 4.5-28X52 wide angle riflescopes.

I do not believe that regular ED glass is as sensitive as regular Super ED glass to wide, abrupt temperature changes, but on the other hand, the scope body may be affected by rapid swings in temperature and that's conjecture on my part.

At any rate, I have a March-X 10-60X56 HM and I have not noticed any parallax issue related to temperature changes, but then again, the only time I would see something like that is getting the rifle out of my air conditioned SUV and taking it to the 105F line. Long ago, I learned to uncase the rifle and put in on my cart or the rifle rack to let it acclimate before the match starts.

 

[steve123]

I didn't know about the why, thanks JB.

One time a guy I knew bought a brand new S&B 12.5-50 FT scope, the old 30mm version. Man that thing had the worst temp shifting any of us had seen in a FT scope. He brought it back to the Co he bought it from and got store credit.