Scope sunshade question.....
- Thread starter NDAR15MAN
- Start date
USMCDOC
Silver $$ Contributor
I have seen the target literally dancing around in the scope from barrel heat on my 22lr br rifle..
Heat waves - look over a hot engine block and observe heat wave refraction near the surface of the engine, should be similar for a hot rifle barrel. The refraction is caused by light waves traveling through media having different densities. My fix was to stretch a black elastic suspender band over the barrel hooked onto the front sight and to the scope mount base on the receiver ring.
Stray light hitting the surface of the objective lens - this causes light flaring inside the scope. The fix is a sunshade long enough to prevent stray oblique light from hitting the lens surface.
Light waves tend to travel in straight lines and I think it would be unlikely to have a situation where light waves would pass through different media densities inside a sun shade. Threading on a bunch of sunshades would likely block heat radiating from a hot barrel causing media density changes and resulting refraction - unless the sun shades got real hot like the barrel.
What would be the effect on light transmission from a distant image though a really extended sun shade some yards long and an objective scope lens. If the straight line traveling light waves passed through on a super long sun shade having uniform density air the amount of light, brightness being a function of amplitude, should be, in theory the same. How much light might be absorbed by the anti-reflective inner surfaces on the sun shade? Looking through a highly polished reflective inner surfaced tube, regular dark bands can be seen (interference rings) my guess is that some light is reflected and scattered by shiny surfaces forming the bands. If the inner surface were to be light absorbing it might result in less light being transmitted through the sunshade. If I screwed all my like threaded sunshades together might be able to get a 1.5 foot long sun shade.
Stray light hitting the surface of the objective lens - this causes light flaring inside the scope. The fix is a sunshade long enough to prevent stray oblique light from hitting the lens surface.
Light waves tend to travel in straight lines and I think it would be unlikely to have a situation where light waves would pass through different media densities inside a sun shade. Threading on a bunch of sunshades would likely block heat radiating from a hot barrel causing media density changes and resulting refraction - unless the sun shades got real hot like the barrel.
What would be the effect on light transmission from a distant image though a really extended sun shade some yards long and an objective scope lens. If the straight line traveling light waves passed through on a super long sun shade having uniform density air the amount of light, brightness being a function of amplitude, should be, in theory the same. How much light might be absorbed by the anti-reflective inner surfaces on the sun shade? Looking through a highly polished reflective inner surfaced tube, regular dark bands can be seen (interference rings) my guess is that some light is reflected and scattered by shiny surfaces forming the bands. If the inner surface were to be light absorbing it might result in less light being transmitted through the sunshade. If I screwed all my like threaded sunshades together might be able to get a 1.5 foot long sun shade.
The only way to block 99.999% of stray light from entering the scope is to have the shade cone shaped at least as long as target range and as wide at target range as the field of view.
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Black sun shades heat up from sunlight. Just like so many other things heating up from direct sunlight that are hot to the touch. Therefore, so does the air inside them; unevenly, just like air outside the shade.
Black scopes' insides heat up more than silver ones.
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Good question.
Only the light rays from the scope's field of view is unobstructed going into and directly through all the scope's lenses. All other direct light rays beyond the field of view are blocked or reflected at some place. They can be reflected inside the scope and sunshade some small amount to cloud or reduce target image contrast. How much light is reflected off the inside if shades is probably less than 5%. It depends on the surface angle and quality.
BoydAllen
Gold $$ Contributor
As far as I am concerned the only reason to use a sun shade on a scope is to prevent the sun from shining directly on the front lens of the scope. All of the ranges that I shoot on have covered firing lines and the direction of fire is north, so there is not going to be any direct sun on the front element of a scope. If the wind is light enough that it does not blow away the barrel mirage, a mirage shield is the best way to handle this problem. If you have not shot a 36X or higher power scope, you probably have an imperfect understanding of the magnitude of the effect from ground generated mirage that those who do experience...but you can still experience issues with barrel generated mirage. IMO the reason that many shooters do not use barrel mirage shields is not that they are impractical for their application, but rather that they do not want to look different when shooting at the range...which of course is their perfect right.
I use my sunshades to prevent direct sunlight from shining on my scope objective lens and thus preventing image flaring. My scope objective lens is the only portal where light can enter my scope and the "field of view" may vary as magnification changes. The internal surfaces of both scope body and sunshade are designed to essentially remove light reflection that might cause light flaring or image degradation. Internal air temperatures inside my sunshades are very uniform as compared with a hot rifle barrel and surrounding cool air, essentially removing the air density refraction effect inside the sun shade. Light waves travel in straight lines though the tunnel like body of my anti reflective inner surface sunshade are protected from greatly differing air densities would result in light wave refraction inside the sun shade. Finally, the light waves contact the anti-reflective outer coated surface of my objective lens to be transmitted and refracted to provide an image of the target.
The black stretchy suspender might look goofy but worked even at 1X (no glass).
The black stretchy suspender might look goofy but worked even at 1X (no glass).
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The reality is, sun shades and light ray tracing into and through scopes ain't a simple thing.
If it is to you, why didn't you point out that one simple thing I overlooked defining a shade dimension to block stray light from entering the scope?
Please!! Tell me what I forgot to mention and compensate for. Then I'll correct that post.
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Relax. You are going to blow a vessel in your head. LOL You didn't overlook anything. Hell NASA could use your posts to land on Mars. My post was a joke in that it's a small tube screwed to the end of a scope that blocks some sun going into the scope and secondarily gives the objective some protection. A simple thing. Sorry the post bothered you. Proceed....
Yes I did. But thanks for the accolade anyway.
The shade inside diameter has to be enough larger to not block light from field of view when adjustments move line of sight off the scope axis a few dozen MOA. I forgot about that.
So did you.
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A description -- a black stretchy suspender is cut to length to provide tension and prevent sagging between the front sight and a scope base attached to the receiver ring.
A "D" shaped loop with a projection wide enough to fit around the front sight is fashioned from coat hanger wire (small diameter welding rod would work) and fit inside a loop sewn into the front part of the suspender.
A "D" shaped wire loop is fashioned but has a modified stripper clip soldered onto the wire loop and is fitted inside a loop sewn into the rear of the suspender; the modified stripper clip fits over a scope base screwed into the top of the receiver ring. The base was intended for an external adjust Unertl scope (this is old stuff), but now using sheet steel, a clip could be made to fit over some Weaver type base.
No more or real difficult to find wire coat hangers. The suspender flaps and vibrates when it is windy. Barrel vibes don't seem to be affected by the relatively weak suspender tension.
Sorry to not have a picture, I quit using the entire rig some years ago but remember it as an attempt to avoid "rocket science".
Brians356
Gold $$ Contributor
If you happen to be shooting close to directly at the sun, stacking sunshades (i.e. doubling the length) allows you to point a bit closer to the sun but still avoid any direct rays impinging on the objective lens.
Several places I shoot ground squirrels afford steep uphill shots, and it's possible to have aims that are in the general direction of the sun even in midday hours.
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Several places I shoot ground squirrels afford steep uphill shots, and it's possible to have aims that are in the general direction of the sun even in midday hours.
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I was at a score match a couple years ago early in the year and about 3pm the sun hit us in the face,,,I couldnt see the rings on the targets at 200 yards much less my bullet holes,,,I rolled a target up and duck taped it around the front of my scope,,at least I could tell where the bulls were at and kept them all on the target,,
they moved the 200 yard targets after that,,
they moved the 200 yard targets after that,,
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