How do you calculate zoom times?

[riptorn]

Stupid question from someone with too much money and not enough knowledge...

I just bought a Canon Digital Rebel with the standard lense and a 75-300. Of course I am used to the old fashion p&s terms of how many times optical zoom it has. How do you convert this and how do you factor in the 1.6 times zoom with it being a Digital Rebel. Can someone please give me the formula.

Thanks,

Nathan...

[gsmx2]

Rip,

To calculate the "equivilant to 35mm" for your Digital Rebel, multiply the mm x 1.6. So your 75 - 300 lens would be 120 - 480.

The best way to equate this to a 3x, 6x, 10x zoom on a point and shoot is to find the spec sheet for the appropriate camera. They should list the equivilancy there.

And in case you didn't know, 50mm is equivilant to "normal eyesight" for a 35mm camera.

Scott

[Jim_T]

The zoom is how much the lens moves.. (ie zoom-in zoom-out)

A fixed lens has no zoom. (You can't zoom out or in). A pair of binoculars that can't be changed will have a zoom of zero no matter what their magnification.

As gsmx2 pointed out.. With the 1.6 crop, you've got an effective focal length of 120mm to 480mm..

The zoom ratio is the longest focal length divided by the shortest focal length.

480 divided by 120 = a zoom of 4x Note that this number is the zoom ratio, not the magnifying power. That's calculated differently.

Again as gsmx2 says.. 50mm (on a 35mm camrea) = what an unaided normal eye sees, or in other words 50mm has a 1x magnification. A 100mm lens would have 2x magnification. A 150mm lens would be 3x... Dividing by 50 provides a pretty good estimate of the magnifying power.

To get the maximum magnification of your lens, divide 480 by 50. 480/50= 9.6.

So the zoom of the lens is 4X
The magnification is 9.6X

[agit-prop]

Usually in P&S cameras and camcorders, the "zoom times" indicates the factor you need to multiply the widest focal length by to arrive at the longest focal length, therefore a Canon 28-105mm lens is a 3.75x zoom, while a Sigma 50-500 is a 10x zoom.

telephoto mm / wide mm=zoom factor

The other way to look at it is how many times magnification over a naked eye view a lens provides (as described in a previous post). In the 35mm world, a 50mm lens is commonly accepted as a focal length that most closely matches a naked eye FOV. In the D30 / D60 / 300D / 10D the 35mm lenses provide a very close approximation to a naked eye FOV. A very simplified way to determine the magnification is to divide the focal length of a lens by 35mm to determine the magnification factor. Therefore a 500 mm lens results in a 14.3x magnification.

A more accurate measure of magnification is to check the specs of the lens you are considering and find out it's rated FOV in degrees, and compare that to the number of degrees of FOV of the 35mm lens.

[defordphoto]

I can picture heads exploding all over the planet about now. :)

[JamieAU]

Free China Now!

Sorry bit off the track but numbers just turn me on ;)

[vvizard]

I think this thread was needed. I hear so many people with P&S' tell me: "Seriously? You got that big expensive camera, and it CAN'T EVEN ZOOM??" (with my 50mm). Then another P&S-friend saw my Sigma 70-200mm yesterday, and he wen't like: "WHOLY ****! How many X's zoom is that?" I answered.. Well.. two-point-something. Then he was even more shocked! He lauged at it, stating his 3x-or-so IXUS got more telephoto-"skills".. Then I just laughed back, didn't even bother to try explaining him about aperture and magnification.

_THIS_ is what people should be learning in high-school =)

[Longwatcher]

Others have done a good job of explaining zoom versus 10D, but I feel the need to add.

I always tell people who are into "My P&S zooms more then your P&S" that my 10D has an 85x zoom and Canon has an extender which will allow me to go to 238x* zoom. Try that with your P&S!!!

Although to be honest I can can only go 25x (70x* with extenders) right now. That would be 16-400mm in lenses.


[* = For the small number of confused math persons this is if you mount the 2x and 1.4x extender at the same time - not recommended by Canon]

[robertwgross]

vvizard wrote:
_THIS_ is what people should be learning in high-school =)

Yes, I took a high school course in the latest imaging technique then ... daguerrotype.

---Bob Gross---

[Tin Man]

Oh my god! according to the numbers my 10D is XXX. :D

[morenoar]

My head just exploded. And I was GREAT in HIGH SCHOOL with Math. Maybe the 20 some years that I have been out of school might help. Or that little thing called NEW MATH, should be learned all over again

[Tom W]

vvizard wrote:
I think this thread was needed. I hear so many people with P&S' tell me: "Seriously? You got that big expensive camera, and it CAN'T EVEN ZOOM??" (with my 50mm). Then another P&S-friend saw my Sigma 70-200mm yesterday, and he wen't like: "WHOLY ****! How many X's zoom is that?" I answered.. Well.. two-point-something. Then he was even more shocked! He lauged at it, stating his 3x-or-so IXUS got more telephoto-"skills".. Then I just laughed back, didn't even bother to try explaining him about aperture and magnification.

_THIS_ is what people should be learning in high-school =)

My gosh, you aren't kidding. When the advertizers describe a camera's zoom, they aren't referring to a magnification factor in the same sense that binocular or telescope manufactureres refer to zoom. A 3x zoom on a camera simply describes the range of magnification of a lense from its widest angle view to its most telephoto view.

In order to avoid long-winded discussions, I usually answer the "zoom" question on my SLR as though it had something close to infinity. I mean, I can put a 17 MM lens on it, or I can opt for a 1200 MM lens. That's a pretty wide range (even if it isn't really a zoom range, it is within the range of the camera).

It does give people something to think about... :)

[OviV]

Just use this simple equation:

http://www.main.com/~anns/other/humor/equation.gif

[nosquare2003]

vvizard wrote:
I think this thread was needed. I hear so many people with P&S' tell me: "Seriously? You got that big expensive camera, and it CAN'T EVEN ZOOM??" (with my 50mm). Then another P&S-friend saw my Sigma 70-200mm yesterday, and he wen't like: "WHOLY ****! How many X's zoom is that?" I answered.. Well.. two-point-something. Then he was even more shocked! He lauged at it, stating his 3x-or-so IXUS got more telephoto-"skills".. Then I just laughed back, didn't even bother to try explaining him about aperture and magnification.

_THIS_ is what people should be learning in high-school =)

Zoom is a basic function for P&S. An option to choose "Zoom (and its zoom ratio)" and "Not to zoom" is a basic function of a SLR. Which is better?

[Belmondo]

robertwgross wrote:Yes, I took a high school course in the latest imaging technique then ... daguerrotype.

---Bob Gross---


Don't kid us, Bob. You majored in cave painting, right?

[riptorn]

Just wanted to thank everyone for their contributions (the serious ones that is). I now have to spread the good word and bring charts to illustrate. No seriously, I may take a few hours to calculate the zoom factor (or magnification, better term) but now I can know what it all means.

[riptorn]

Ok just to make sure I got it (and everyone else).

50mm = Normal focal on 35mm film camera
31mm = Normal focal on Digital EOS camera (50mm divided by 1.6)

18-55mm lense = 0.58 - 1.77 magnification
75-300mm lense = 2.42 - 9.68 magnification

Is this correct???

Nathan...

[nosquare2003]

Hi riptorn

As far as I know, they are approximately correct. They are only approximate figures because the FOV of a 31.25mm on Drebel may not be the normal eyesight of a man (diagional angle of view about 47 degree). I cannot prove it as I'm not a scientist.

I did a calculation by FOV and they are approximately:

18-55mm lens = 0.59 - 1.58 magnification
75-300mm lens = 2.28 - 9.04 magnification

By the way, do any photographers care about these magnification figures?

To me, magnification always refers to lifesize magnification which is a total different thing.

Cheers