Fleet Submarine Periscopes

[LukeFF]

I want to know if I am understanding something here correctly about the periscopes used in fleet submarines:

The diameter of the exit pupil for both the attack and observation periscopes is listed as being 4mm. Now, if I'm reading the description of exit pupil diameter correctly, (such as from this link), the brightness of an image viewed through a lens will increase as the exit pupil diameter increases.

Now, with that said, given that both fleet sub periscopes had the same exit pupil, does that mean the brightness of the image was the same in both periscopes?

[JMV]

A tad too technical for me, but see following link if that can be usefull in any way :

http://www.maritime.org/fleetsub/pscope/index.htm

[Jan Kyster]

"Brightness" is a matter of how much light your system gathers = first lense. The Mt. Palomar telescope probably have the same pupil exit

[Rockin Robbins]

Actually, Jan Kyster is incorrect. The brightness of the image is only partially determined by the diameter of the objective lens. It is possible to put enough magnification on a larger objective lens to make the image dimmer than a lower power view through a smaller objective lens, so objective diameter alone is not responsible for image brightness. The other factors are light transmission efficiency through the system (clarity of glass, number of optical elements, dirt and foreign matter in the system) and the magnification.

The exit pupil is the diameter of the total field of view that your eye is looking at though the eyepiece. The image will appear brighter until it reaches the diameter of a fully dark-adapted eye pupil, about 7mm for a young adult and decreasing to about 5mm for an older adult. Any image of over 7mm exit pupil will not look any brighter to your eye than a 7mm or whatever is the diameter of your pupil at the time.

The way you calculate the exit pupil is to take the diameter of the objective lens (the first lens in the system at the top of the periscope) and divide that by the magnification. For instance, have you ever wondered why 50x7 binoculars are such a popular size? 50mm/7x=just a hair over a 7mm exit pupil. Personally I own a 50x10 pair of binoculars because for me a 5mm exit pupil is just as bright and I can use the extra magnification.

So exit pupil equals diameter of objective lens/magnification. Brightness at the same exit pupil will be greater for a larger diameter objective lens because there is more light condensed into that little diameter.

[Fish40]

Very interesting topic. I have a question concerning scope useage. In reality, was the Obs. scope ever used, or could it even be used to conduct an attack? I know the attack scope had a higher magnification and smaller profile for the obvious reasons. What about the range markings? Did the Obs. scope have similar markings as the attack? I think you know where I'm headed (at least I hope you do). In case you don't, It's my feeling in the interest in realism, that if the Obs. scope was and could only be used as an observation medium, it should be portrayed as such by removing (if possible) the fire controls and associated TDC inputs from the screen. I'm thinking along the lines of what OLC did for his GUI Mod in SH3.

[Munchausen]

Originally Posted by Fish40

In reality, was the Obs. scope ever used, or could it even be used to conduct an attack?

See Calvert's "Running Silent," page 79 of the hardbound copy, for a discussion on how (and why) he used the observation scope to conduct a submerged attack.

[LukeFF]

Originally Posted by Fish40

Very interesting topic. I have a question concerning scope useage. In reality, was the Obs. scope ever used, or could it even be used to conduct an attack? I know the attack scope had a higher magnification and smaller profile for the obvious reasons. What about the range markings? Did the Obs. scope have similar markings as the attack? I think you know where I'm headed (at least I hope you do). In case you don't, It's my feeling in the interest in realism, that if the Obs. scope was and could only be used as an observation medium, it should be portrayed as such by removing (if possible) the fire controls and associated TDC inputs from the screen. I'm thinking along the lines of what OLC did for his GUI Mod in SH3.

In short: yes, the observation scope had the same magnification and markings as the attack one. One big difference was that it did not tilt as high as the attack scope.