[TEC] Telemeter scale in the german optics

[Hitman]

It seems that I finally found out how the telemeter scale in the german periscope really worked, and as I suspected, the "10" marks do NOT represent 10 degrees, but instead 6.25º. Thus the whole scale is not in the correct size and can't be used in SH3 for proper telemeter readings (Though this won't affect the in-game stadimeter utility)

So why the "10" mark? Well, because at 1.5x zoom you would get the distance to an object which touches that mark simply by multiplying its heigth x 10. Example: A 25 metres mast would mean the object is at 250 metres distance. For other distances you would multiply the heigth by 100 and then divide by the scale marks it covers or use the proportions that follow a 2x sequence (i.e. 10, 20, 40...). This allowed direct use of scale without using the stadimeter (Currently represented in game by the moving line for distance measurements) or in case of a stadimeter failiure. But also allowed a quick and easy speed measurement system when the target presented a zero Angle on the Bow (Precisely those situations where you can't use the fixed wire method).

Here is a sketch I have done for a personal edition of the U-Boot Commander's Handbook I'm working on (Adding sketches and figures in the same style as those seen in german WW2 manuals):



Translation for the speed method:

1.- Measure the time it takes for the masts to double their size in the 1/10 scale.

2. Mast (In Metres) x 10
______________________ x 0,03 = Enemy speed in Knots
Time (In Minutes)

Consider the own submarine's speed while calculating!

Now the question is, can we correct that in game by reworking the graded scale somehow, so that it can be used as intended? :hmm:

[irish1958]

Hitman,
Great observation!
The greatest problem to doing this is when no magnification is used and stability is turned off in the options, it is (to me) impossible to get any accurate readings, unless I am within a few hundred meters in which case, I don't need the data.
If the system could be setup for the GWX 10X scope, it would be useful.

[Pisces]

How certain are you about that 6.25 degrees? Or I should say, I am curious how you derived at that.

When looking at your sketch-a-scope the thought popped up in my mind that the 10 might actually mean 1/10 radians, which is equal to 5.729577951 degrees (0.1*180/pi; and not too far off from your number, but in the ball-park if the SH3 scale is indeed off) If you are not familiar with a 'radian' (though I'm sure you know), it is the angle you get when the radius of a circle is wrapped around that circle. The tangent of one 10th radian is 0.100334672. So if according to your picture the distance E1=Mastheight*10, it could be rewritten the same as as Distance/Mastheight= 1/tangent(radian/10)= 1/ 0.100334672= 9.966644423.

If a contact measures up to be halve-way the 10-mark (and waterline) it is actually 1/20 of a radian, and again halve-way from that 1/40 of a radian. And with those numbers it rounds nicely to 20 and 40 also. The appearant linearity of the telemeter scale puzzles me though. It's not convenient for those 20, 40 numbers.


p.s. playing around with my calculator a bit further I found your number 6.25 is not random. 360 degrees/6.25 degrees = 57.6 .... Hmmm, do I smell something that resembles a radian there????

[Pisces]

I have given what I wrote some more thought. I probably wasn't very clear. It comes down to each small mark being 100th of a radian (0.572957795 deg) and 10 obviously a 10th of a radian (5.729577951 deg). The multiplication factor to use in multiplying mastheight would be 100/scopemarks.

So for the 10 mark : 100/10=10,
for the 5th mark: 100/5=20
for the 2.5th mark: 100/2.5=40
for the 1th mark: 100/1=100

If you zoom the object becomes bigger, so that 100 needs to be adjusted according to the zoom factor difference. So 400 for 6x vs. 100 for 1.5x.

But if actuall ranges in the game don't match, a rescaling of the telemark scale probably is needed.

[irish1958]

Originally Posted by Mikhayl

Something I noticed in SH4 and is probably the same in SH3 (don't remember), the scope marks are "built in" (hardcoded, not a tga), and they always have the exact same size no matter the zoom level and camera parameters (FOV etc).

Bummer!

[Hitman]

How certain are you about that 6.25 degrees? Or I should say, I am curious how you derived at that.

I got it from a german WW2 Periscope Manual The scale there was 10/16 of a degree per mark, and the "100" mark was 6.25 degrees and the example showed a ship at 250 metres. So I investigated a bit why that figure was chosen and soon understood that because tan 6.25 = 0,10 it made sense to get range figures. Actually, 5.75 degrees would be evn more accurat but apparently the rest of the scale wouldn't then be evenly distributed.

When looking at your sketch-a-scope the thought popped up in my mind that the 10 might actually mean 1/10 radians, which is equal to 5.729577951 degrees (0.1*180/pi; and not too far off from your number, but in the ball-park if the SH3 scale is indeed off) If you are not familiar with a 'radian' (though I'm sure you know), it is the angle you get when the radius of a circle is wrapped around that circle. The tangent of one 10th radian is 0.100334672. So if according to your picture the distance E1=Mastheight*10, it could be rewritten the same as as Distance/Mastheight= 1/tangent(radian/10)= 1/ 0.100334672= 9.966644423.

If a contact measures up to be halve-way the 10-mark (and waterline) it is actually 1/20 of a radian, and again halve-way from that 1/40 of a radian. And with those numbers it rounds nicely to 20 and 40 also. The appearant linearity of the telemeter scale puzzles me though. It's not convenient for those 20, 40 numbers.

Actually, the sketch was done in an attempt to make it useful for SH3, therefore I kept the current subdivisions and wanted simply to modify the field of view of the periscope to ensure that the "10" mark matches 6.25 degrees and not 10 degrees.

But the historic periscope reticle looked like this one here (Please see if the subdivisions used make sense for you, your expertise in maths can probably provide a better solution ):




Picture of a real scope (Note that sometimes there seem to be three marks in the same space where there are four on the opposite side of the central cross):

[Hitman]

Something I noticed in SH4 and is probably the same in SH3 (don't remember), the scope marks are "built in" (hardcoded, not a tga), and they always have the exact same size no matter the zoom level and camera parameters (FOV etc).

Actually that could be good for my purpose, because as it currently is, the scale doesn't match the correct proportions

If we can resize the field of view to have the 10 mark subtend 6.25 degrees, that would solve the problem. Could we keep the historic zoom levels 1.5x and 6x and see more detail, the only drawback being we would lose a bit of field of view?

[Pisces]

Originally Posted by Hitman

I got it from a german WW2 Periscope Manual The scale there was 10/16 of a degree per mark, and the "100" mark was 6.25 degrees and the example showed a ship at 250 metres. So I investigated a bit why that figure was chosen and soon understood that because tan 6.25 = 0,10 it made sense to get range figures. Actually, 5.75 degrees would be evn more accurat but apparently the rest of the scale wouldn't then be evenly distributed.

Be carefull there, tan 6.25 is 0.1095, so more like 0.11, not 0.1. Maybe the majority of german officers would not care of the differenc, but a german instrument-maker would not do this! There must be more than meets the eye about this 6.25 degrees value. Some clever reason. As far as I know, (which isn't much more than common sense) for practical use of that scale it doesn't really matter how many degrees it actually is, as long as it matches an easy to use mastheight/distance ratio. I mean, my second post above describes how I would have made it. But I'm not german!

Actually, the sketch was done in an attempt to make it useful for SH3, therefore I kept the current subdivisions and wanted simply to modify the field of view of the periscope to ensure that the "10" mark matches 6.25 degrees and not 10 degrees.

But the historic periscope reticle looked like this one here (Please see if the subdivisions used make sense for you, your expertise in maths can probably provide a better solution ):




Picture of a real scope (Note that sometimes there seem to be three marks in the same space where there are four on the opposite side of the central cross):

This real life scope image shows there is indeed more than meets the eye. Good spotting. On the vertical scale there are 4 spaces above the upper number 10 and 5 spaces below it, which is again repeated (NOT mirrored) below the middle centerline (I do not understand what you mean with 3 marks, did you miss-count?). And those divisions are matched on the horizontal scale. So your (later) sketch isn't an exact match. There must be some special user-instructions on how to use that peculiar division of spaces. I do not see how, other than that the scales could be/had to be rotated to get AOB. But that only explains why horizontal is the same as vertical, it still leaves 4 vs 5 spaces issue. I'm puzzled. Very! ... Maybe I need to sleep.

Hmm, can't you persuade a still living Uboot captain for an interview about this? Just kidding.