Originally Posted by
Bagheera
Thats an unusually worded question. Im guessing you’re looking at a specific scope with 7x magnification and 35mm objective lens ? Thats what the notation would usually mean.
Scopes have a nominal focus distance, where parallax is zeroed out. This is typically 100m to 300m.
Then you have adjustability on some scopes, mainly for parallax but it makes the target image sharp too. This is usually only available on scopes with a too end magnification over 12x. Typical parallax adjudtments are 50m to infinity for centrefire scopes and 10 m to infinity for specialist airgun and rimfire scopes. This gives you 100% sharpness st the range you adjust it to.
Then you have depth of field which is the useable “good enough” focus in front and beyond the nominal focus distance. Lower magnification like 3x can give a lot of depth, say down to 20m for a scope focussed at 100m. High magnification like 20x makes the inage blurry only 10% or 20% from the focus distance. A small objective like 32mm also increases the depth of field while big lenses like 50mm and 56 are fussy.
Then, you have the focussing ability of your eyes (“accomodation”) which is good if you are 20 years old but pretty limited if you are 60. Unfortunately, this does make the reticle go out of focus but the scope can becuseable if thecreticle is a good thick one.
7x would usually be considered good at 50m but getting a bit annoying under 20m for most people.