<p>You have the idea right! The amount of light collected is indeed proportional to the area of the collecting surface.</p>

<p>Now, if you want to take it a bit further, try to think about the following:</p>

<ul>
<li><p>Binoculars have one lens for each eye, does this mean you get twice the amount of light in the end?</p></li>
<li><p>Reflecting telescopes almost always have a secondary mirror which results in part of the light being masked and not collected by the primary mirror. Now imagine you have an 8-inch telescope with a 2-inch secondary mirror, can you calculate again the light collection ratio compared to the naked eye?</p></li>
</ul>

CC BY-SA 3.0
2018-02-01T14:02:38.983Z
The amount of light that **can** be collected is proportional to the entrance aperture area.  However, unless you account for lens systems aberrations, vignetting, etc.,  the amount of light that **is** presented to your Official Mark-I Eyeball will be less than that.
Carl Witthoft
CC BY-SA 3.0
2018-02-01T05:17:41.133Z
2018-02-01T05:17:41.133Z
Romain P.
<p>The amount of light collected for a period of time is proportional to the area of the collecting aperture. We use our eyes -pupils have diameters of approximately 5 mm-, binoculars and telescopes. How much more light can we collect with a 50mm pair of binoculars compared with our eyes? And with an 8-inch telescope? If we could have access to a 10-meter class professional telescope, how large would the gain be?</p>

<p>50^2/5^2= 100 times more light</p>

<p>8in = 203.2 mm</p>

<p>203.2^2/5^2= 1652 times more light</p>

<p>10000^2/5^2= 4000000 times more light</p>

<p>Did I solve this problem correctly?</p>

CC BY-SA 3.0
2018-02-01T14:49:05.133Z
This is basically right in terms of total light from one small area of the sky that fits within the telescope's field of view. But remember when things (extended objects like nearby galaxies and nebulae) are magnified, the brightness is spread out to a larger area on the retina, so brightness per unit area has your aperture square term, but then divided by magnification squared.
uhoh
<observational-astronomy>
Comparing Light Collection Between Pupil and Telescope?
Roceofiron
# Comparing Light Collection Between Pupil and Telescope?

(Asked by: username_0 on 2018-01-31)

The amount of light collected for a period of time is proportional to the area of the collecting aperture. We use our eyes -pupils have diameters of approximately 5 mm-, binoculars and telescopes. How much more light can we collect with a 50mm pair of binoculars compared with our eyes? And with an 8-inch telescope? If we could have access to a 10-meter class professional telescope, how large would the gain be?

50^2/5^2= 100 times more light

8in = 203.2 mm

203.2^2/5^2= 1652 times more light

10000^2/5^2= 4000000 times more light

Did I solve this problem correctly?

**Tags:** observational-astronomy
> **Comments:**
> **username_1**: This is basically right in terms of total light from one small area of the sky that fits within the telescope's field of view. But remember when things (extended objects like nearby galaxies and nebulae) are magnified, the brightness is spread out to a larger area on the retina, so brightness per unit area has your aperture square term, but then divided by magnification squared.  

---

## 1 answers

### Answer by username_2 on 2018-02-01. Score: 1

You have the idea right! The amount of light collected is indeed proportional to the area of the collecting surface.

Now, if you want to take it a bit further, try to think about the following:

* Binoculars have one lens for each eye, does this mean you get twice the amount of light in the end?
* Reflecting telescopes almost always have a secondary mirror which results in part of the light being masked and not collected by the primary mirror. Now imagine you have an 8-inch telescope with a 2-inch secondary mirror, can you calculate again the light collection ratio compared to the naked eye?

> **Comments:**
> **username_3**: The amount of light that **can** be collected is proportional to the entrance aperture area.  However, unless you account for lens systems aberrations, vignetting, etc.,  the amount of light that **is** presented to your Official Mark-I Eyeball will be less than that.  

---

