Focal length - magnification?

[AdamK]

Can anyone advise of the magnification being achieved by a 200mm lens on a Canon 40D? Magnification in terms of that I recognise on rifle scope or binocular eg my binoculars are 8x magnification, and scopes up to 18x magnification.
Thanks in advance.

[AdamR]

From memory a 50mm is 45 degree Field of view.
Therefore 100mm is 22.5 degree field of view.
And then 200mm is 11.25 degree field of view.

As to magnification as you mention your on your own. Never heard a reference.

[patrickv]

The "maximum magnification" is something that has another meaning in photography. It's for "macro lenses".
What you are probably looking for is this thread : http://photo.net/filters-bags-tripods-accessories-forum/00FXfK

[AdamK]

Thanks Patric.
So does that mean that a 200mm lens on the APS-C 40D (1.6x) is the equivalent of a 320mm lens on 35mm sensor which divided by 50mm gives a binocular magnification of 6.4x?

[Kieran]

Here is a useful explanation/ http://www.cambridgeincolour.com/tutorials/cameras-vs-human-eye.htm#angle-of-view

If the human eye is around 50mm, then the gun sight at 18x would give a field of view of 50/18 = around 2.8 degrees & 50 X 18 = 900mm

The binoculars at 8x = 50 x 8 = 400mm 50/8 = 6.25 degrees FOV

The C sensor crops the FOV of any lens by 1.6

So you can't think in terms of magnification. A 100 mm lens should have a FOV that is half a 50mm lens. Your sensor reduces this further x 1.6. So compared to your eye or a standard 50mm lens on a 35mm film your binoculars at 8X on your C-sensor should be = to a 250mm lens.
The 18x rifle scope should be = to a 562mm

Of course I could be way off here. Better wait until you can get all this confirmed

Cheers,

Kieran

[OzzieTraveller]

G'day Adam

Some time ago I made up this sketch for the workshops I run ~ it may be useful ...
http://i52.tinypic.com/34fgmms.jpg

Regards, Phil

[ameerat42]

Can anyone advise of the magnification being achieved by a 200mm lens on a Canon 40D? Magnification in terms of that I recognise on rifle scope or binocular eg my binoculars are 8x magnification, and scopes up to 18x magnification.
Thanks in advance.

One problem is that the magnification you get between different optical systems such as you list is subjective.

In a 'scope or pair of binoculars, 8X, for example, can still appear different if the eyepiece they use are different. Some eyepieces can be wide angle and some not (forgot what types).

Also, in a camera, the viewfinder optics may not give the same magnification between camera types, and may not see as much as the sensor "sees".

In other words, you're best to try these things out yourself. The ideas in the posts above are helpful, but there is no "quite right" answer.
Am.

[arthurking83]

And don't confuse higher magnification simply with longer lenses.

While a longer lens will magnify an object than a shorter focal length lens does, this is only really true at subject distances approaching infinity.

You can't simply ask a question about magnification of a lens with a specific focal length, without any reference to subject distance.

The distance to the subject is the important factor in the equation where magnification is concerned.

That is, if the subject is at infinity all lenses have 0 magnification.

If the subject is at a distance that is a long way off(say 100m), it barely has any magnification at all.
While you may see it looming large in your viewfinder(or binoculars, or scope), the reality is that the usually large object is being formed at a sensor at the opposite end of the optical system.

If we take an elephant, which is generally quite a large subject, image magnification in this manner.

you may be 100m away, and we know that the elephant is about 2.5-3m tall and about the same in length and diameter, yet you can squeeze it into an area that is now only 23mm wide and 16mm in height(APS-C) or 36mm wide and 24mm in height(35mm full frame).
You haven't really magnified it in any way have you!
The magnification factor is actually a negative number(something like -0.00200x or more).

As Am said, you can't compare magnifications from one type of system with another.

FOV and sensor size also have nothing to do with magnification either.

While it's common to believe that a longer focal length lens is usually a magnifier of formed image, the opposite as actually true.

In general longer focal lengths have less magnifying power than does a shorter focal length.
The usually doesn't make sense at first, because we haven't made any reference to subject distance, which is the most important aspect of magnification of a subject.
Focal length is also important, but in general only as the focal length gets shorter, not longer.

Think of magnification as a magnifying lens does it. That is you hold the magnifying lens close to the object you want to study, to magnify the subject. The closer you get to the subject the larger it becomes to your eye(with a magnifying lens) or sensor(with a lens).

The other part of the magnification problem has already been commented upon I think, and that was the dioptre of the camera.

Each camera model and brand has a different dioptre magnification factor(see Am's comment about the difficulty of comparing systems).

If one camera's dioptre has a magnification factor of 0.7x and another has 1x, then this will give different apparent magnification effects to the eye, using the same lens!
I'm not exactly sure what each of my camera's tech specs say, but the difference between the D70 and the D300 is noticeable. The D300's viewfinder magnifies the same focal length just a slight bit more than the D70s does.

How this helps the OP I have no idea, but to chase your tail about a subject that has no set reference point is only going to lead to more tail chasing(and no real answers).

[patrickv]

Thanks Patric.
So does that mean that a 200mm lens on the APS-C 40D (1.6x) is the equivalent of a 320mm lens on 35mm sensor which divided by 50mm gives a binocular magnification of 6.4x?

Yes - As a thumb rule approximation though, to "sort of compare", it's pretty valid. Don't call it exact or scientific or a fact though! :) It's more like ... It's going to give you a an idea of how binoculars would compare to a lens. If you look into 6.4x binoculars and then look at the result of a photo taken from the same place with a 200mm lens on a 40D, it should be somewhat similar.

But then again, you better experiment. The human (two eye!) perception is different from a one lens camera perception.