To review, the NEED test for optical performance (Naked Eye Equivalent Distance) is based on side by side comparison of optics using a standard test target. I use a dollar bill. For binoculars and low power views of scopes I use the little shadow lines under the "O" in "ONE" on the back of the bill. I can just separate those lines at my optimum naked eye distance of about 12-18 inches (or, to be accurate, my corrected naked eye...I wear glasses). I simply place the optics on a tripod and back up from the target until I can just distinguish those lines as separate again. This is not a subtle test. A difference of 6 inches in total distance is critical and very obvious. For high power scope views I have to use finer detail...finer than my unaided eye can see at any distance. I use the finest details of the area around the eagle...or, if I am feeling extravagant, the bars in the railing around the building on the back of a ten.
A reader pointed
out that it might be a more accurate comparison if I divided the
distances I got by the power of the eyepiece used ... converting
everything to a 1 power equivalent. That is a fair observation, so
this time I have provided both figures. As you can see from looking
at the charts, the two methods yield slightly different results. My
own first thought would be that the traditional NEED figures are
fairly representative of my overall impression of the performance of
the scopes at low powers. However I could easily be convinced that
the 1x NEED figures are more accurate. At high power, the 1X figures
are definitely more like what I am actually seeing. The interesting
thing is how close the actual distances come, at high power, to being
exact multiples of the power. You would expect that a 60 power scope
should give you the same view at 60 feet as the naked eye at 1
foot...and that is pretty much what the chart shows. The similarity
of the figures makes me wonder if my eye is the limiting factor for
most of these scopes. It is very possible that all of these scopes
are providing all of the detail I can actually see at any power.
Isn't that a comforting thought. (Doubters might again note how well
the 60mm Fieldscope does in this comparison ...which further
reinforces my contention that most of the time 60mm will get you all
there is to see.)
