Another Titanic question

[Rocketeer]

@Leo_Bloom

I was happy re-reading this on the drift I kicked off on full speed ahead (we’re now on other drifts…).

A little late, but:
“clear the bar”?

The sandbar at the mouth of a river. Clearing the bar means you’re moving out into the open sea.

[Daylate]

Quote:
Originally Posted by Daylate View Post
T&C, your analysis of the effect of binoculars is pretty much spot-on, except for the idea that they reduce the amount of light received by the eye. Actually, the amount of light they receive is governed by the area of the objective lens. In other words, a binocular with a 50mm objective, having an area of 1963 square mm, will gather in a bundle of light of that area. Then when it effectively condenses that the diameter of that bundle down to 7mm (an area of 51 square mm), it is increasing the amount of light to the eveball by a factor of 1963/51 = 51 times.

Then from Tired & Cranky,
Again, I’m not really an expert, so perhaps I’m wrong, but I don’t think I am. I believe that binoculars don’t deliver more light to your eyes – they just deliver the light you want to see the most in the center of your field of view. Optimizing the exit pupil just means the binoculars will do it without also making the view appreciably dimmer.

You seem to have accepted my general idea above that the exit pupil is critical. So let’s think about this for a moment. Assume we are dealing with hypothetical 3x50 binoculars. The objective lens is the same size, so under your theory, it should collect and deliver to your eyes the same amount of light as the 7x50. But the exit pupil on 3x50 binoculars would be about 17mm. That is more than twice the diameter and five times times the surface area of your dilated pupil. So how does the 3x50 binocular get the rest of that light into your eye? It doesn’t. It would go to waste. It would deliver less light to your eyes than is collected by the large lenses.

In fact, I understand that’s basically what happens with the extra light you are talking about that is collected by the 7x50 binoculars. It gets thrown away because only light collected from within the binoculars’ narrow field of view gets delivered to your eye. The rest is thrown away. The light coming from within that field of view won’t be any brighter than the rest of the lighted objects. The light coming from outside that field of view is irrelevant. So the amount of light delivered by binoculars to the eye is reduced by a little because of dispersion and other effects in the lenses and prism, and perhaps more if the exit pupil is too small. It doesn’t increase. But the light that the binoculars do deliver is more useful to you.

I found a good dissertation on the internet about low light binoculars and how they function, and even learned a few things. Those of you who may be interested will find it clear and interesting.

http://www.notpurfect.com/main/optics.html

I will say that binoculars on the Titanic may not have been as much use as they would have been 30 years later, primarily because they would not have had coated lenses which would have significantly reduced their clarity at night. Whether or not they would have been enough to give the Titanic that extra few hundreds of yards to miss the berg is something we will never know.

And now IMHO this binocular business has been threshed to death, and I officially announce that I’m dropping the whole subject! On to better things!

[Snnipe_70E]

@DrDeth

Are you saying that the captain is not in total command of his ship?

The captain is not in command of the engine or boiler rooms. My dad saw a captain picked up by the seat of his pants and tossed out of the machine shop by the ships 2nd assistant engineer.

I was on a ship where the captain ordered 130 turns (RPM). We were in a storm and the storm was beating up the ship. The Chief only wanted to slow down for the safety of the ship. There was a heated argument in the officers solon. The captain would not back down. The Chief Engineer went down into the engine rooms and wrote in the night order book that the maximum turns was 110 turns until further notice. There was no way the captain could over ride the Chief Engineer orders in the engineering spaces.

I was on a ship we were tied up in the middle of the bay. The bridge rung up stand by engines. I went to the EOT and rung up STOP followed by Finished with engines.;

A captain can not get underway without permission of the Chief Engineer.

Normal deck officers have not studied engineering and do not know anything about the engine room.

In the days when Merchant Officers wore uniforms, The captain is a 4 stripper and the chief engineer is also a 4 stripper.

[Snnipe_70E]

@Leo_Bloom

I was happy re-reading this on the drift I kicked off on full speed ahead (we’re now on other drifts…).

A little late, but:
“clear the bar”?

The bar is where sediment builds up outside the port. After crossing over the bar the pilot is dropped off.

[DesertDog]

@Daylate

This is why the 7X50’s are the best type to use in low-light conditions. For instance, by the same analysis a pair of 7X35 binoculars (another popular size) would increase the light by only 19 times, while at the same time producing the diameter of the exiting light bundle to only 5 mm, thus wasting a large part of the eyeball’s capacity to receive light.

As T&C stated, the combination of 50 mm objective and 7 power, results in what is the best match with the size of the night-dilated pupil. 100X14’s would do the same, but would be to heavy and bulky for handheld use.

Besides the weight, even 10x binocs have too much magnification to be only hand held* never mind 14x They are much more useful on some kind of mount.

7x50s hit the sweet spot between portability and light gathering ability for night use. Daytime you’re better off with 7x35s because they’re about half the weight.

Once when I had them available under dark skies, I compared the view among a 7x50, a 7x35, and my Mk I eyeballs. The difference was astonishing.

*My brother has a pair of 12x36 image stabilized binoculars by Canon. Those you can hold by hand but they were $850