The Human Eye

[Dr Nurburg]

After being explained how the efficiency of gathering light in a telescope is equally as important as its magnification, I began to ponder and asked myself this question:

How much more would we be able to see in space if the human eye was:

a) 25% more efficient at gathering light

50% more efficient at gathering light

c) 75% more efficient at gathering light

Just to the naked eye, no magnification involved, just light gathering efficiency.

Since I'm not a scientist I can't really begin to work it out.

Any ideas?

[iamjulian]

I think the answer is not much. Aren't a basic pair of bins something daft like 50x more sensitive to light than the human eye... or am I just making that up!?

[John]

I'm not a scientist either but I guess the light gathering capacity of the eye depends on i) the diameter of the fully dilated pupil (effectively the aperture) and ii) how sensitive the optical nerves are to low light / contrast.

I'm told that my pupil will dilate to around 6mm - 7mm (I'm 49 years old) max so that's my aperture. Assuming that optical nerve sensitivity is constant (which I'm sure it's not) if I could achieve a 14mm pupil dilation (I hate to think how I'd do that )

my eye would be 4x more sensitive to light .... I think

John

[iamjulian]

Just found a table... 50mm aperture = 51x light gathering power of human eye fully dilated/dark adapted (presumably average pupil size whatever than may be?) while 150mm aperture = 459x and 355mm = 2500x.

[pvaz]

Interesting question. I googled the formula for limiting magnitude and did some free thinking. I have no idea if I'm right or not but here are my thoughts.

1st I need to explain magnitude: Objects brightness in the sky is measured in magnitude. The lowest number the brighter it is. Example: a 0 magnitude star is 100x brighter then a 1 magnitude star.

This is the formula for the limiting magnitude where D is the aperture in mm.

ML= 3.7 + 2.5 * Log10(D^2)

One eye haves an average 6mm diameter. So our current limit magnitude is:

ML= 3.7 + 2.5 * Log10(6^2) = 7.59 (It's a bit over the usual 6.5 estimated mag for humans maybe because this formula is made for telescopes).

Adding 25%

ML = 3.7 + 2.5 * Log10((6*1.25)^2) = 8.02

We would see objects that are 43x fainter then the ones we see now.

Adding 50%

ML = 3.7 + 2.5 * Log10((6*1.5)^2) = 8.47

We would see objects that are 88x fainter then the ones we see now.

Adding 75%

ML = 3.7 + 2.5 * Log10((6*1.75)^2) = 8.81

We would see objects that are 122x fainter then the ones we see now.

I may be completely wrong...

Edit: Corrected the text. It was leading to misunderstanding.

[Dr Nurburg]

I'm not sure I follow, pvaz. Why would see stuff fainter? If we had better capability of gathering light, surely we would see things sharper?

You might have meant 43,88,122x magnification but fainter, but we're not supposed to be magnifying, just adding light...?

You've lost me.

[pvaz]

I meant the other way around. At 75% you would see stuff that are 122x fainter then the faintest objects you can see now.

Magnitude values are in reverse for some odd reason. The sun is -30 mag (if memory doesn't fail), the brightest stars are -1 or 0 mag, and the fainter objects you can see now in perfect dark skies are around 7 mag.

Magnitude is a measure of the apparent brightness of an object. Magnification is the amount of times you enlarge an object. They are different things. Aperture affects Magnitude not Magnification.

PS-> Maybe "dimmer" wasn't the best English word to explain what I meant.

[Tim]

Sadly, even if I had 300% more light gathering eyes, the only thing that would be brighter would be the light pollution

Interesting question though. I often wonder about animals like Eagles etc, and wonder what sort of detail they would be able to discern on say, the moon.

[michigander]

If you increase the pupil area by 25% you get 1.56X the light gathering power.

At 50% you get 2.25X

At 75% it's 3.06X

Each magnitude is 2.512X brighter or dimmer than the next, so to see a magnitude fainter you'd have to increase the pupil area by about 55% to 9.5mm

Dana

[Breakintheclouds]

There's another oddness about our eyes which make them less sensitive that they could be: all the nerves that carry signals around on the retina lie on top of the photoreceptors, and get in the way of the light. You really wouldn't design the eye that way if you were starting from scratch (hem hem). Interestingly, the evolution of the octopus did a much better job, and led to an eye with no impediments in front of the photoreceptors - see here: New Page 0

[Kit-Fox]

Size and focussing power isnt the only consideration. Eyes are made up of two different types of receptors to light.

One set that we call 'cones' can see colours & the other set we call 'rods' can only see in black & white.

To see more in darkness and therefore in the night sky we would need to possess more rods in our eyes that we currently do.

[iamjulian]

Breakintheclouds posted an excellent primer on rods and cones and the eye:

http://stargazerslounge.com/primers-tutorials/90030-primer-understanding-night-vision-averted-gaze-telescope-tapping.html

[Dr Nurburg]

You guys are coming up with some lovely responses. Thanks.

So at 75% I guess the sky would be quite covered with loads more stars than we see now, and we'd possibly be able to just make out pin pricks of the moons of Jupiter!

I like what if's.