Long Tele Lenses and Bins.

zeugma

zeugma

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Colin
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Q.
Is there a formula by which you can compare the magnification factor offered by a telephoto lens of X mm to that afforded by a pair of bins of YxZ?

For example: 400mm prime on a 1.3x crop body vs a pair of 8x32 bins?
Just an odd question that occured to me tonight.

Sorry if the idea seems daft!
 
Hell, I struggled with that for longer than is healthy...:(
 
I'll give it a go.

For starters, I'm going to go along with the old (and possibly incorrect) adage that a 50mm lens on a full-frame camera approximates the field of view of the human eye. We can easily tweak the calculations later if you prefer a different value.

Then it appears to be quite simple: a 400mm lens on a 1.3x crop camera gives you a magnification of 400 * 1.3 / 50 = 10.4x. So that's a slightly higher magnification than the 8x32 binoculars, which have a magnification of 8x.

(Incidentally, I assume you know that the 32 has nothing to do with the binoculars' magnification? It's simply the diameter of the front elements, in millimetres.)

Can anyone confirm that my reasoning is sound? Or am I barking up the wrong tree?
 
I got a little lost when the 1.3 crop factor came in....how does the crop affect lens magnification? Surely the mag is exactly the same whatever sensor you have and it's only the image as seen on the monitor that becomes magnified

Bob
 
zeugma said:
Q.
Is there a formula by which you can compare the magnification factor offered by a telephoto lens of X mm to that afforded by a pair of bins of YxZ?

For example: 400mm prime on a 1.3x crop body vs a pair of 8x32 bins?
Just an odd question that occured to me tonight.

Sorry if the idea seems daft!
Click to expand...

TBH. You're comparing 'apples with oranges' The bins are 8X mag with a 32mm optic, therefore the magnification is 8 X..... The bins use an eyepiece to magnify the image you see when looking through them :thinking:

The lens doesnt actually magnify anything it only sees a smaller area of the image! Then when you add the crop factor of the sensor you're doing the same thing again :shrug: at 1.3X So, arguably :thinking: the magnification is zero if you view the reultant image at the same scale as the sensor size. When you upload the image on a computer or print it! then you start to magnify the image and the magnification depends on the size you view it at (effectively the eyepiece)?

Well, at least it's something like that.....I hope....Oh damn, now I've confused myself :D

Basically the eyepiece of bins magnify the image, but that doesn't happen in camera. Or put it another way, if you used a magnifying glass to look through the camera view finder you would be doing the same thing as the bins :D ....Hope this has cleared it all up for you :)
 
^^^ You're confused?....I certainly am.

How about simply dividing the focal length by 50?

400mm equates to 8x mag

Bob
 
If it's any help, 400mm on my 1.3x 1D, is pretty much the same as a pair of 10x15s I have! This would mean Stewart's maths are plausible!
 
Canon Bob said:
^^^ You're confused?....I certainly am.

How about simply dividing the focal length by 50?

400mm equates to 8x mag

Bob
Click to expand...

Canon Bob said:
Maybe this'll be a pointer in the right direction

http://www.the-digital-picture.com/Canon-Lenses/Canon-Lens-Magnification-Value.aspx

Bob
Click to expand...


No problem at all with both of those :D Except?... To compare the two examples of bins and lens consider the exit pupil size of the bins (effectively the sensor size of the camera, sort of....? ) Anyway, If you took a shot through the eyepiece of the bins with a 1.3X camera would it actually change anything? would the magnification increase?.... I doubt it as you would just be making a larger image of the same view! but the resolution would decrease significantly :thinking:

Sorry zeugma I think Bob and Stewart have answered your question :thumbs: but I really love discussions like this......Thanks for asking the question..:clap:

Steve
 
Comparing eyes and lenses is very difficult. They work completely differently. As you read this text, your eyes are scanning a very tiny angle, something like 2 degs or so, yet you are simultaneously aware of an angle of view around 180 degs. It is quite possible to put forward a plausible argument for the human eye's angle of view to be anything between those extremes.

However, it is 'generally accepted' that a 50mm lens on a full frame camera has a magnification of 1x. If you accept that, then a 400mm lens will have an 8x magnification, and if you're using a crop camera, multiply that by 1.3x (or 1.6x or 1.5x etc).

So on that basis, I agree with Stewart :)
 
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