Rifle Scopes "Dark" glass

[ranger1183]

I have encountered a problem where two identical scopes of same make, model and reticle have completely different brightness levels at the same magnification, retinal settings, etc.

What causes this phenomenon? Besides passing the darker glass off to someone else, what can be done to alliviate this problem? Will the high end scope makers (S&B in particular) recognize this as a problem and correct it?

Thanks in advance.

 

[TDECK]

Re: "Dark" glass

I will take a stab at it since no one else has. Besides a defect the only other thing I can think of is that the latest produced scope benefits from product improvement that most manufactures make along the way. Was the darker scope produced before the brighter scope?

 

[BobinNC]

Re: "Dark" glass

<span style="font-style: italic">So as through a glass, and darkly
The age long strife I see
Where I fought in many guises,
Many names, but always me.</span>

THROUGH A GLASS, DARKLY
by Gen. George S. Patton, Jr.

It does not answer your question, but I could think of nothing else when dark glass is met....

Poetry of Gen. G.S. Patton

 

[MEDICGORDO]

Re: "Dark" glass

are they mounted in the same way?just a shot in the dark but could one of the rings or mounts be to tight slightly binding the parallax on the darker one just enough to cause a slight difference.

 

[ranger1183]

Re: "Dark" glass

everything is exactly the same on the two scopes. I'm hoping John from USO or Paul from Premier Reticles will jump in and take a shot at this.

 

[dcjs]

Re: "Dark" glass

Very strange, as differences in transmission would have to be significant to even be detectable with the bare eye.

Can you see any differences in general image quality between the two scopes, like more or less CA and generally better/worse sharpness? Does one of the scopes happen to be mounted on an extremely canted base and the other have its erector more centered (flat rail)?

As has already been mentioned, can you exclude the possibility that something is blocking part of one scope's objective due to the way it is mounted? To check, look at the ocular from an arm's length away to see the exit pupil, it should be circular when pointed at a white wall or the sky.

Knowing what make and model you are talking about specifically could also provide some clues as to what might be going on.

 

[ranger1183]

Re: "Dark" glass

then what causes "dark" glass? Are some scopes, even the most high end, subject to a collection of random subtleties that can turn their sight pictures dark?

 

[TDECK]

Re: "Dark" glass

Maybe they have different lens coatings. I believe some military spec glass is darker because of the anti reflective properties of the coatings used specifically for military contracts. Are the lens coatings the same color?

 

[Powerstrokediesel]

Re: "Dark" glass

Reading your post I'm a little confused. Are the scopes you are referring to S&B's or are you mentioning S&B as a hypothetical example? I can imagine someone reading your post and believing that the dark glass problem is with an S&B.

 

[Plange]

Re: "Dark" glass

Hi Ranger1183,
There are a lot of variables to take into account. David S on here is an optical engineer and I see he chimed in.

I can only speak in generalities so lets see what happens:

To answer your question "what causes this"?
Some scope companies offer certain types of filters that are available on the objective lenses. These filters are applied just like a lens coating so it is part of the lens surface. I have experienced these a few times while working on another type of scope but as David said in order to test for this you have to have a photospectrometer as the human eye could never tell (or at least should not be able to tell)a degradation in light transmission such as your describing.

I am going out on a limb here but is it possible that one of your scopes had the erector dialed heavy on the windage and elevation putting the erector so far off of optical and mechanical center the physical location of the erector (being pushed way over to one side or up or down) has caused this dark glass? The reason I bring it up is that I can duplicate that here using our spectrometer- if I don't have the path of light going through the main tube and reticle just right you loose transmission throughout the whole optic. This can even sometimes be seen as a "shadow" on the reticle if the erector is that far over.

As for what they do with the glass I would assume that is up to the company. Most optic companies have certain people that are part of the QC team and these people are used to looking through scopes and would be able to see the difference in light transmission and make the correct call- there are charts that can be used to help with this call-and I would suspect they would remove the offending lens and replace it.

Without having the 2 scopes in a lab condition I would say it might not be a fair comparision if all things are not equal such as erector position, knowing if the scope has a filter coating on the objective, ect.

Sorry I could not of been of more help,
Paul

Edit: What happens if you look through the scope from the objective to the ocular on low power- do you get the same darkness?

 

[ranger1183]

Re: "Dark" glass

David and Paul,

you guys rock! Thanks for your help.

 

[VJJPunisher]

Re: "Dark" glass

not to hijack but this brings up a question to me. Why have there not been scopes using tinted glass, or that glass like in spectacles that gets darker in brighter light? discuss

 

[marduk185]

Re: "Dark" glass

ive known folks thatd probably group better if they had a welding sheild in theyre scope.

 

[Arthur Wesley Williams]

Re: "Dark" glass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: VAJayJayPunisher</div><div class="ubbcode-body">not to hijack but this brings up a question to me. Why have there not been scopes using tinted glass, or that glass like in spectacles that gets darker in brighter light? discuss </div></div>
It would make more sense to add filters to the front of the lens if you wanted to alter it, because they could be removed or changed. Leupold tried to start that with the Alumina filters but they never really went over big like the filters that were used on camera lenses which were big business. To me it would make a lot of sense to have a removable filter over the front lens to protect the lens and if it had a coating like rainguard, or I could see a polarizing filter being useful especially in snow or rain --- that might be somthing worth considering. It probably wouldnt sell to the fair weather target shooters but a military marksman operating in the snow or a hunter hunting in snow could make good use out of a polarized filter and same with heavy rain.