Re: S&B pmII questions
Looks like we have to live with it or go somewhere else... Here is more detailed explanation from S&B
Topic:
The "shadowing" effect seen in the field of view of a 5-25x56 PMII.
Thank you for your inquiry into this question about the Schmidt & Bender 5-25x56 PMII. We hope the following explanation helps you better understand this optical issue.
The 5-25x56 PMII was developed to provide 2000 meter capability. In order to achieve this in a first focal plane scope the erector tube must be allowed to move up and down to both ends of its vertical adjustment range. In doing so you will see a "shadowing" affect within the field of view.
This affect is called Vignetting (vin'yed•ing) and is defined as follows:
(optics) Reduction in intensity of illumination near the edges of an optical instrument's field of view caused by obstruction of light rays by the edge of the aperture.
(In this case, when the erector tube is at the end of its adjustment range you will see a distortion caused by the inside edge of the scope tube as it is now visible in the field of view.)
To see this, adjust the power ring to 5x power and set the elevation turret to its lowest setting. Now when looking through the eye piece you will see a "black ring" surrounding the field of view that is off center. The "black ring" will appear to be sitting on the bottom of the tube with a gap at the top. You will also see a shiny elliptical area above the top half of the "black ring" that is a reflection of the surrounding's in the direction you are pointing the scope. This reflective surface is the interior wall of the scope tube. Now if you adjust the elevation turret to its highest setting this view will change. Now the "black ring" appears to be touching at the top and the reflective surface is now visible at the bottom of the field of view. When the power is increased the "black ring" becomes blurred but is still evident even at 25x in the field of view.
Two solutions to this issue would be to:
a) Shorten the vertical adjustment range to eliminate the vignetting which would then also reduce the amount of total elevation adjustment in the turret or
b) install a baffle or ring that eliminates the vignetting, but also cuts down the field of view.
Either solution reduces the effectiveness of the 5-25x56 PMII as a long range scope. So if we remove the vignetting we lose a key feature in this scope which is extremely important to the users of the 5-25x56PMII and allowing this vignetting affect is a compromise Schmidt & Bender is making in order to provide a better product.
Here is the image I found on this forum: