Sounds like they are talking about depth of field which is the range of apparent focus. If you used older camera equipment the manual focus lenses had marks on them that showed you approximate areas of focus for different f/stops, or the amount the lens was stopped down. The more the lens diaphragm was closed the greater the apparent field of focus. Of course there was only one true point that the lens was in focus, but our eyes and brain compensated to see what was acceptable sharpness, which hopefully translated onto the film image.
Variable magnification scopes do not have diaphragms, but the internal lens elements do move as you change focal lengths, which in turn does affect the light rays as they travel through the scope. The greater the magnification range, the more difficult it is to "correct" the chromic aberrations and light loss, which can cause color shifts and dimming. This is usually accomplished by using more expense glass types which at one time were flourite, but may now be something else. The larger the tube is, the less bending of the light rays occurs, so you are seeing larger tube diameters.
The March scope with a magnification range of 5 to 50 in a compact design is going to much more difficult to engineer than a Nightforce 12 by 42 in a traditional longer design. This is why companies like Zeiss and Leupold have not offered these wide optic ranges, although Leupold is now making a move into this area, but at greatly increased prices.
Hopefully I have not mis-stated anything, as it has been a while since I was heavily into photography and the mind does not retain as well as it used to.
Variable magnification scopes do not have diaphragms, but the internal lens elements do move as you change focal lengths, which in turn does affect the light rays as they travel through the scope. The greater the magnification range, the more difficult it is to "correct" the chromic aberrations and light loss, which can cause color shifts and dimming. This is usually accomplished by using more expense glass types which at one time were flourite, but may now be something else. The larger the tube is, the less bending of the light rays occurs, so you are seeing larger tube diameters.
The March scope with a magnification range of 5 to 50 in a compact design is going to much more difficult to engineer than a Nightforce 12 by 42 in a traditional longer design. This is why companies like Zeiss and Leupold have not offered these wide optic ranges, although Leupold is now making a move into this area, but at greatly increased prices.
Hopefully I have not mis-stated anything, as it has been a while since I was heavily into photography and the mind does not retain as well as it used to.
