Compare to point and shoot camera , what is the equivalent optical zoom (3x, 5x or 10x) of EF 75-300?

Question

how about the 18-55mm?

Answer 1

The answers above are both correct, but perhaps you are a visual learner.

There is not a lens-to-distance equation.  If we are talking about a "35 mm equivalent," a 50 mm focal length is approximately "normal" view without any magnification.  For most DSLR's, the lens factor of 1.5-1.6 means a "normal" focal length would be about 31-33 mm.  If we go back to a 50 mm "normal" lens then, a 100 mm lens would be a "2 power" lens, 200 mm would be 4X, and so on.

Just divide the smaller number into the bigger number and you get the "X" power of the lens.  For instance, a 35-80 mm lens is 2.3X zoom.  Divide 80 by 35 and you'll get the result. 35-80 mm lens is 2.3X zoom.  Divide 80 by 35 and you'll get the result.

It is usually better to know what the focal length of a lens in "35 mm equivalent" is and judge by that, rather than relying on the "X" power of the lens.  For instance, most point and shoot cameras start at about 35 mm and have either a 3X or 4X zoom.  This would make it a 35-105 or a 35-140.  I've seen some that start at 28 mm, though.  A 3X starting at 28 mm is 28-84 and a 4X is 28-112.  Neither one is a particularly strong telephoto lens and the 4X is just about the same as the 3X that starts out at 35 mm.

It's also important to realize that tradition dictates that lens focal lengths are usually expressed in terms of "35 mm equivalent," where "35 mm" refers to a 35 mm film camera.  This is because of the relation between the sensor size and the actual focal length of the lens and the resultant angle of view of the lens.

I have one point & shoot that is actually a 5.8-24 mm zoom.  This is a 4X zoom.  The 35 mm equivalent is 28-116 mm.  The sensor is 7.2x5.3 mm. (1/1.8")  (And I wish I knew someone who could explain how the heck they came up with sensor size terminology!)

I have another point & shoot that is actually a 5.7-17.1 mm zoom.  This is a 3X zoom.  The 35 mm equivalent is 34-102 mm.  "How could a shorter focal length give a longer 35 mm equivalent?" you might ask.  It's because the sensor is only about 5x4 mm. (1/2.5")

I have a few Nikon DSLR's and - thankfully - they all have the same size sensor.  They all have a "lens factor" of 1.5.  This means that you just multiply the actual focal length of the lens to get the 35 mm equivalent and then you can make comparisons accurately from camera-to-camera.  Most Canon's, for instance, have a lens factor of 1.6.  On a Nikon DSLR, a 28 mm lens is the "35 mm equivalent" of a 42 mm lens. On most Canon DSLR's, the same 28 mm lens is the equivalent of a 45 mm lens.

These example are just to show you how freaking confusing it can all become if you try to make sense of the "X" power of a zoom lens.

Bottom line...

Check the 35 mm equivalent specifications for the lens.  This way, you will be leveling the field and comparing apples to apples.  More or less.

Here is a mini-tutorial I made myself to compare focal lengths. This is NOT a lens test or a camera test!  It is merely intended to show the difference between various focal lengths.  The lens was the Nikon 18-200 VR lens, which is (by definition) an 11X lens, but that 11X does not tell you what the final image will look like.  I added one more frame taken with a 300 mm lens.  The camera was a Nikon D200 so there is a 1.5X "crop factor," "lens factor," or "focal length multiplier."  There is further explanation on the image itself.  It would help if you click on "All Sizes" above the image.

http://www.flickr.com/photos/7189769@N04...

This was done with two different lenses: the Nikon 17-55 and 70-300:

http://www.flickr.com/photos/samfeinstei...

Answer 2

Optical zoom for that brand is nearly always 4X or higher.

In addition, this is because of the amount of sensors the camera carries compared to other brands which state they have equivalent quality. Sensors give the camera its power, and you need a wide or nicely sized viewfinder to truly have a powerful camera.

http://www.flickr.com/photos/samfeinstei...

Wide Angle uses 24-35 Medium Telescope uses 85-135, and Super Telescope normally always uses 400-600 or above.

http://www.parsonsfoto.com/canon_ef_lens...

http://seattle.craigslist.org/tac/pho/78...

Answer 3

Ok, here's the deal: zoom has nothing to do with how close you get to the object. Zoom is the ratio of the highest focal length to the lowest. As said before that makes the 75-300 a 4x zoom (300/75 = 4). However, you could also have a 10-40mm lens and it would be 4x (40/10 = 4). While these lenses are both 4x, what you see through the lens will be vastly different.

The human eye sees at roughly 50mm. That means that the 75-300mm lens will get you way closer to the action (it's what's known as telephoto). The 10-40mm will show you much more than your eye (it's known as wide-angle).

What this means for you is that if you're getting an SLR you need to abandon the zoom talk that you hear so much about with P&S cameras. What matters now is focal length, not zoom.  

Answer 4

http://www.usa.canon.com/app/html/EFLens...

Most lenses on an SLR arent measured in the multiplication factor that point and shoots use. Most point and shoots start around the same spot, so if you have a camera that sports a 7x lens compared to another camera with a 3x lens you have a fair comparison. But since SLRs have interchangeable lenses you have a much wider range, you just have to switch lenses. The widest that I know of for a Canon is 4.5mm. Thats pretty dang wide. The most telephoto lens that I know of is 1200mm, but then there are adapters for using telecopes so the sky's the limit, literally.

http://www.fredparker.com/vislize.htm this may actually be of more help to you. The only thing that you would need to visuallize what any given focal length lens is on your Canon camera is your hands.