ID function of this Kriegsmarine optic?

My latest thoughts:

Operation: User first sets the density filter wheel to the appropriate setting of the four filter glasses provided. The darkest filter allows direct observation of the sun with no discomfort. The variable-density filters only filter light entering the optical port facing directly to the user's right. The user adjusts each eyepiece separately for focus.

User looks into the larger eyepiece to see a split image formed by two small telescopes of about 4-power magnification mirrored at objective end so their axes point directly to user's right and left respectively, through small round glass windows in either side of the device. The two small telescopes are articulated so their axes may be diverged within the range of -2 to +2 degrees to obtain image coincidence, and the exact angle read-off as described below.

When the images from right and left telescopes are brought into coincidence by the user adjusting the divergence by turning the small black knob, the divergence angle may be read by the user through the smaller eyepiece. The divergence angle scale is graduated in minutes and is read where the black cursor line crosses the -2 to +2 degree scale. The scale and cursor are illuminated by light entering a small, round, frosted glass window in the front of the device, opposite the two eyepieces. The device has no provision for night-time illumination of the scale and cursor, which may mean it is only possible to use it during daytime. That fact may help narrow down the list of possible uses for this device.

Conversely, if the user has a pre-calculated angle of divergence, he may set the angle on the scale, then looking through the large eyepiece, mark the time at which the two target objects' images coincide.

The most striking feature of the operation of this device, as opposed to most other military optics, is that it was designed only for optical targets on opposite sides of the user. Since it was probably designed for use aboard a warship or submarine, the use may involve at least one horizon and perhaps a celestial body at the time of day that it is within two degrees of the horizon. If this was the intended use, note that, for example, the device would could determine the angle between the rising sun to the east and the western horizon. Since eastern and western horizons viewed from a ship in open ocean would be at the same distance, in sextant-user terminology, the sun could be "brought down" to the horizon opposite to the one from which it was rising. The instrument would measure the same angle above the horizon when comparing eastern sun vs. western horizon, as it would if it could compare eastern sun vs. eastern horizon, given that the two observations were made at the same time and date. The device may have been invented to solve a chronic difficulty of observing the exact time of sunrise or sunset with a hazy horizon adjacent to the sun. The sun is only used here as an example; another celestial body's rising and setting may also figure into this. The device may have been developed for use by surfaced submarines where the observer is very close to the water and hazy horizons may have been more of a problem than aboard surface ships.

 

Hmmmmmmmm....

 

My own Latest WAG as to the purpose is that it was used to quickly measure the altitude of a pre-selected star that was close to the eastern or western horizon. That number and the exact time of observation, and some calculations will give the observer his longitude. Knowing longitude would have been particularly important for a U-boat involved in chasing or intercepting enemy convoys in the North Atlantic. A lot of that steaming was probably going mostly east or west. Latitude was much easier if you could see the star Polaris and the horizon, you get the altitude with a sextant and that's numerically about the same as your latitude. There's no provision for night illumination on the device, but if it was intended for taking only one sight, it could be brought into a lighted area inside the boat or ship where the internal scale could be read.

 

Did I kinda say that?

 

I'd like to say u were right all along, or GMTA. Would like to also hear from someone who has read something about this particular machine or someone very familiar with U-boat navigation, so posted the info on a sextant forum and a WWII German collectibles forum, and asked some naval history groups to look into it. Someone on earth has the answer and I'll find them sooner or later.

 

Oh..... Well............it's ok.................go ahead!

 

A reply from Brad on the sextant forum-this is the first one that fits the some of unique design characteristics of this thing!


The +/-2° measuring range, and the fact that the angle is taken between objects 180° apart speaks to a very specific celestial navigation device.

It could be dip meter. The dip of the horizon is normally assumed in celestial navigation. However, the assumed dip can often be wrong, as a function of abnormal refraction.

With a dip meter, one aligns the horizons 180° apart and measures the dip. This accounts for eye height and existing refraction. The measured value is divided by two to obtain the dip to one horizon.

The measured dip is then substituted for assumed dip, yield a more precise reduction of the calculated angle from the observed angle of the sextant.

I have no knowledge of what your device is, only what it 'could be', as the specifics described by you correspond to that detailed herein. This may be just a coincidence.

Brad

 

Article on a Russian naval dip meter, which could have to been inspired by one the Soviet Army captured in Jena. It looks different but functions very similarly.

https://sextantbook.com/?s=Russian+naval+dip+meter

 

The final thing I needed was the proper German name which is abbreviated on the device as "Ktm." After many exchanges on two forums, a German wrote that the names we'd been suggesting were incorrect, and he thought "Kimmtiefenmesser" would work both technically and linguistically. Sure enough that term led me to a much earlier Zeiss version in UK, at the same time validating the name "Kimmtiefenmesser."

http://collections.rmg.co.uk/collections/objects/43306.html

 

Good detective work! Translates as "horizon dip meter?"

 

Here's exactly what the poster (a German) wrote about that:

"The German term for dip is "Kimmtiefe"
Kimmtiefenmesser makes a lot of sense, linguistically ) KTM a meaningful abbreviation

It remains a dip meter, technically.

Regards

Wolfgang"