In a reply to one of Tony's post below, LD speaks of long sunshades affecting rangefinding abilities,,,,,

how so? is there a single law that covers that or some ratio of scope parameters to amount of inhibition?

Just bought a big  Leapers and thinking of getting another shade. Or I may take the one thats on now and remove it....

 

dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning

a long sunshade may tend to collimate the light therefore increaseing the depth of sharp focus but i bet it is vertually undetectable. on the other hand if you could fit an adjustable aperature onto the eyepiece of a scope it would increase the depth of sharp focus as you make the aperature smaller. incrasing the depth of sharp focus makes it harder to range find. to range find you need vey shallow plane of sharp focus. smaller the aperature, the smaller the circle of confusion untill you reach a point where the light actualy begins to reverse the direction of its bend and the circle of confusion then opens up and makes the image less sharp. bet i told you more than you wanted to know.

If it werent significant, I wouldnt have stopped using long ones. I used to prefer 8" or longer shades when I used 50X scopes, and I was getting away with this. But when I went to lower powered scopes, with their less effective ranging performance, I did some practical experiments and proved to myself that those long sunshades reduced the ranging ability of my rig.

I still use a shade, but its a standard one cut in half ... I would omit it altogether, but I proved in my own tests that the shade DID serve a useful purpose of blocking some sun, hence the name.

i would never have guessed there was an 8" shade out there. at any rate i have never tested it personally nor have i seen a scientific analysis so can only talk about theory. you have a LOT more experience than i do and i take you at your word. i think my shade is at least half the length of what you are talkinbg about so i am not going to worry too much.

i will say that the light collimating properties of a shade probably increase the sharpness of an image over the width of the lense. without a shade you get scattered light that comes from all directions and if your glass is not of the highest quality that will translate into soft image edges and flare in the image that may make it hard to find the sharp focus point. some lense shade length probably is a good idea but i really don't know what is optimum.it would vary from scope to scope. too long and it will probably narrow the field of view by cutting off the edges of the image. we see this in camera lenses all the time. if it does that it definately would act like a smaller aperature and increase depth of field making it less of an accurate rangefinder.

Which is near unigue in requiring use of the scope and guesswork to derive target distance, a long shade IS good because it can reduce glare and tends to sharpen up the image. But with our game, if the light is good, I'm better off with the shortest shade I can get by with, because I'm using a smaller objective and lower mag than many folks, so I want all the light gathering and ranging ability the scope has to give.

is that when shooting out at angeles with the sun behind me i am having a hard time with flare. i wonder of one of those rubber eyepieces helps?

I have definitely found differences between using a long shade and not. I thought it was just me at first, or my sidewheel slipping, or something else, but finally figured it out. Can't say exactly what the quantatative delta was because of changing light conditions over the course of shooting several days, but it was a factor for sure. Just another challenge to throw into the mix!

If one imagined a very long shade, ultimately one would have the equivalent of a pinhole. A pinhole camera has no focal length (everything is in-focus) -- a rifle scope with a pinhole opening in front of the lens would also see everything in-focus independent of distance and, hence, be unable to use focusing to determine the distance to a target.

How long a shade is required before this effect starts to be a factor? My inclination is to respect LD's research (or, at least, use a short shade).

Best,

Joe McDaniel
DIFTA Match Director
AAFTA Webmaster and Chair

Well, I took mine off my Mk2 Big60 sometime ago but for a different reason. Even with the flip-up on, rain still managed to get onto my objective lens from time to time, the Sunshade made it difficult to mop it off & as removing stuff from your rifle is frowned upon whilst on the Course, it had to go.
Interestingly & totally coincidently, our blog tonight touched on sun shades while discussing whether the new Nikko Big 60 took the same size Butler Creek flip-up cover as the previous model. One of our number, an FTer of considerable experience & knowledge, if sometimes alittle difficult to understand had this brief comment to say on the subject of rangefinding with Sun shades;

"Dont need sunshade it throws the rangefinding on every scope encountered.
Best are the honeycomb ARD not the cheapies from China. They dont affect ranging just cut the light down 17%."

I wonder how many shades will be removed before the next match. I know I will be doing some testing in the backyard this week.

Scott

ESP with a "smaller" scope, such as Bushnel Elite 24X or 32X, I wold steer clear of long ones. When I used a Hakko 50X or Big 60 BSA (also Hakko), I felt my ranging was good enough even with an eight inch shade tube.