The Human Eye

[Kyle72]

Hi

I have been trying to find out what focal length does the eye see at compared to a lens

i.e If i was to focus on a balloon across the room, what lens would i use to get the same focal length to produce the same size photo on what the eye sees

or maybe i should ask what lens comes close to what the eyes see, or what is the focal length of our eyes.

Sorry if im confusing you, im just trying to work out what is the best method to explain this,


Thanks
Kyle

[anon]

Hi,

From what I understand the human brain does some amazing stuff from the info it gets from the eye,
sadly this implies that the eye doesn't produce as great an image as we would think,
(or camera's would probably work more along the lines of the human eye)

Some of the tricks and things I've heard about include,

Causing the eye to constantly make tiny movements and then using the information from current and previous images to effectively increase the resolution,

Remembering detail and filling in your mental picture from stored detail, when your eye isn't focused on that detail,

Colourising parts of the image where the eye does not perceive color well,

Filling in the blind spot located where the nerve exits the eye,

A mental version of HDR,

And all this while you're unaware of all the post processing it's doing... and in real time too...

Amazing stuff.

And yes part of your effective field of vision (and probably depth of field) is dependent on your processing power,
which is why people with Alzheimer's often have a sort of tunnel vision limiting what they see to things closer to the center of their field of vision than most people.

Sadly what this means for you is that even if you could find out the Focal length and Aperture for the human eye,
the resulting shot would compare very poorly to what he think we see.

Furthermore, the experience is different for everyone,
Try the following experiment,
Hold your arms out away from your body, at eye level and with your hands as far apart as possible,
(IE with your left hand pointing to your left and the right to your right)
start wiggling your thumbs,
slowly move your hands forward until your thumbs come into your field of vision,
(you could use this to calculate the effective focal length of your eyes)
Now get some friends to do it, and you should quickly notice that different people have
different fields of vision. (younger and more mentally alert tending to have wider fields of view)

To calculate your effective focal length,
Work out the angle your arms make,
*grin* using this system I have about a 180 degree field of vision on a good day, which I'm told is rather good...
now find out the angle of view by comparing this to a chart,
search for something like "lens angle of view chart"

Some basic figures based on that search ...

8mm fish eye - 180 degrees full frame - 175 degrees 1.6 crop
15mm fish eye - 142 degrees full frame - 92 degrees 1.6 crop

12mm - 112 degrees f full frame - 87 degrees 1.6 crop
17mm 93 degrees full frame - 67 degrees 1.6 crop
28mm 65 degrees full frame - 44 degrees 1.6 crop
35mm 54 degrees full frame - 36 degrees 1.6 crop
50mm 40 degrees full frame - 26 degrees 1.6 crop
70mm 28 degrees full frame - 18 degrees 1.6 crop
200mm 10 degrees full frame - 6.5 degrees 1.6 crop
300mm 6.9 degrees full frame - 4.3 degrees 1.6 crop

I hope this helps

Regards,
Anon.

[etherial]

I have heard that the human eye is something close in terms of perspective to what you would see with a 50mm lens on a full frame camera. I suspect it is much more complex that that though.

Check out Wikipedia which has some interesting info on it. The dynamic range stuff is particularly interesting. http://en.wikipedia.org/wiki/Human_eye

[ameerat42]

Just eyeballing it, wouldn't it be in the order of an inch or so? Say 25-30mm?
Am.(Sample only.)

[ricktas]

depends..on your sensor! Sensors come in different sizes so the resultant photo at a setting of 50mm gives a different 'field of view' depending on the size of the sensor in the camera. I am not talking MP here, but the physical sensor size. APS-C, APS-H, Full frame, medium format, camera phone, point and shoot all offer a different field of view. So if you (could) put a 50mm lens on each of these camera's the result would be different for each.

To understand sensor sizes and the 'field of view' look at this as an example. :

http://www.ausphotography.net.au/for...ctor_w_example

http://www.ausphotography.net.au/for...vs_Crop_Factor

[Film Street]

this subject relates to the distance between two objects. It has nothing to do with width. So you have a balloon across the room. Now put an apple half way across the room. Looking at the distance between the two - that is what you want to replicate with your camera - a human focal length.

Using a full frame 35mm camera, a focal length of about 43mm will give you that.

Using an APS-c sized sensor, a focal length of about 43mm will give you that.

Both are 43mm, why is that? Because the size of the sensor does not change the focal length.

The smaller sensor just means that (over) half of your picture has gone missing compared to the larger sensor.

The 43mm focal length gives the same distance between objects regardless of what sensor it's being used on.

Kyle you are using a 50D, an APS-c sensor. Use a 40mm or 45mm to get what you are after.

The Sigma 50mm 1.4 actually is a 45mm.

This is the very reason I use a 40mm lens.

[anon]

Hi Kyle,

Given the variety of answers you're getting I'm guessing at-least some of us aren't quite getting exactly what you're asking,

Could you please post some feed back on the answers posted to help narrow down what you're looking for?

Thanks and regards,
Anon.

[Kyle72]

Hi All

Sorry for the delay in reply but work has been keeping me busy, As for the replies i have been getting, its a wealth of information which all makes for an interesting read. A discussion i had with a few family members, which made me ask the question what lens on a camera does the eye actually see. 50mm seems the most common answer. But as written up there are a number of factors that need to be considered, such as sensor size. So Anon to answer your question, what i was try to acheive or compare is the eyesight to a lens, and if my eyes were focused on something at 1 meter away, then focused on something 15 meters away, what lens would come close to what i see at these distances. The other part to this was the width the average person can see. now if i focus on something such as a monitor sitting at a desk with a distance of approx 70cm and look straight ahead the picture in front is focused clearly, but i know that i can still see more in this picture out wide but its blurred. So keeping everything in focus, would this be compared to a 50mm lens of a full frame sensor. and without keeping everything in focus would the focal length be a lens 8mm - 50mm. then the next part would move on to what colour the eye is actually seeing to compare of what is actually being captured with out editing.

Anon i have learnt a lot from just your post alone and i thank you for that, along with everyone else that has left a reply, its amazing to get such a great response and ideas on how everyone perceives this.

Thanks again

Kyle

- - - Updated - - -

Film Street, i just saw your post, thank you very much, that was basically what i was trying to achieve and have even tried on the night of the conversation. I did not have my camera with me this night but a family member just bought his new canon 660d out to show, so what we were trying to do is using the camera to capture the same view of the camera. we would put up our hands and create a box just focusing on the ballon, we would try to capture the same with the camera, and we almost had it to about 70mm to capture the same on what we were seeing. now i dont know if the lcd at the back is what you can use to judge this as this is what we were trying to do, or should it have been transfered first onto a larger screen to get a more realistic approach.

Once again, i thank everyone for there input

Cheers

[Film Street]

Hi Kyle.

The method I use is to just forget about the width. Width can be achieved by walking backwards.
The distortion of distance between objects is a better way of looking at it I find.
I look at the subject. If I want the objects behind the subject further away than what I actually see, I use a lens wider than 40mm. I use a lens longer than 40mm for the opposite effect.
People often confuse a 50mm lens in terms of width instead of depth.

[Film Street]

Just found a video explaining this.