For American gunsight it seems that there existed range-knob, which has to be twisted to obtain "correct range"
It seems I was slightly wrong about the working operation of the gunsight!
http://www.lonesentry.com/blog/k-14-gunsight.html
Before engaging enemy, presumably the enemy wingspan will be chosen as necessary.
Minimum range setting is = 182.88m
Maximum range setting is = 731.52m
I am unsure if it is possible for the pilot to know exactly, which range positions are chosen, EXCEPT for the max and min ranges (those are always same according to factory specifications)
Therefore, the gun convergence should be between those min and max ranges.
The pilot could either, choose the shortest range setting, and move it further, until the enemy target fits into the diamonds indicator...
Or he could use the fixed-and-gyro-mode, and calculate the necessary diamonds indicator wingspan(you simply imagine that diamonds indicator is already enemy fighter, when compared to fixed circle.)
This way he can choose to engage at convergence distance vs fighter for example, without any gunsight-fiddling with fingers, during the heat of battle.
If he changes target between bomber and fighter, then the sight must be recalibrated of course...
This way, the necessary range can be obtained. (imagine you're flying in a straight line at home territory doing this when flying). Works well enough for most purposes.
Then you can recalibrate gunsight when enemy fighters are destroyed, then you can switch into bomber-engagement-mode with gunsight. You could even calculate before battle, which gunsight positions would be most suitable for you, for either bombers or fighters...
Germans very rarely used heavy bombers as such, I think for most purposes it could be useful just to calculate only two cases of enemy aircraft, for instance 10m fighter wingspan, and 20m medium bomber wingspan. German side, could encounter American heavy bombers with 30m wingspan.
Then with K14 gunsight, you select either focke-wulf or heinkel target, and choose the range setting into correct distance, when you compare diamonds into fixed gunsight. Then you know, when the enemy enters the "killing zone" distance...
This kind of estimation works well enough for the standard German REVI in most cases. I can't bother calculating the distances properly for each and every slightly different enemy aircraft wingspan. The lead will not be that much different, unless the difference between wingspans is drastic large... Always aim for the nose of the enemy, this helps mitigate small number of wrong aiming. (you still hit the middle fuselage and tail, otfentimes)
The K-14 gunsight does NOT calculate lead based on enemy aircraft speed.
According to historical documents, the principle only takes note of your own aircraft angular velocity and all kinds of fancy calculation, to arrive into an eastimation of correct lead.
Radar based gunsights do, on the other hand, calculate accurately on the basis of enemy speed, and enemy angle. K-14 is not radar-based, only gyroscopic.
Therefore, the choice of enemy target type, should only be for purposes of narrowing down the wingspan of enemy. For the purposes of more accurate estimation of lead and range.
If you calculated with Fw-190 setting, the stuka out in the distance off your cockpit, will appear too far, for the gunsight, when you use fw-190 setting.
Reason being, that fw-190 wingspan is smaller than stuka?
When you compare me-109 setting into fw-190 out in the distance off your cockpit, the lead and range will be almost exactly same (because wingspans are basically the same) Choice of target type would be unnecessary in this case when engaging me109 or fw190, assuming you make boom and zoom attacks and you have a medium distance convergence. You have to climb outside your convergence, and dive back into attack curve, and fly into convergence range again...
When you compare heinkel wingspan into stuka, the stuka is too close.
But I'm not sure how much error exists in reality, when you compare fw-190 wingspan into stuka out in the distance off your cockpit. Probably the stuka will still be destroyed if you shoot a good sized burst into him!