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Old Mar 4, 2007, 1:23 AM   #1
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I know there is a lot of explanations out there, but I found one thing that was never quite answered.

If I buy a 70-300mm lense for my camera, this means that at the lowest magnification, it's 70mm, and since my eyeball is 50mm, that means the lowest magnification possible is just over 1x (like 1.4x), and the highest magnification (at 300mm) is 6x what my eye sees right? as in if i looked at the bird with my naked eye, itd be 6x closer with this lense? and all this milimeter stuff is the distance the lense is away from the film, or the image sensor on digital cameras. A good way to think of this is how, when you look through a magnifying glass, the thing you're looking at gets bigger as you move it further from it?

sorry if this causes people more confusion :?

Just for reference, how do you know when lenses are being measured by 35mm equivalent, so i can relate it to my eye being 50mm on a 35mm camera?

a good wide angle would be one with a low focal length less than 50mm right, since thatd let me see wider than my eye even can?

*thanks ahead of time

**oh, and if this is all correct, then does that mean a person with a 10-100mm lense, while companies would say it's a 10x zoom, couldnt actually zoom in as far on a bird for example, as a person with a 70-300mm lense, which would be labelled as 4.28x? meaning the x-factor means nothing??

***i think all people that sell lenses should be required to show comparison shots with a reference lense, and how much the image changes with the new lense
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Old Mar 4, 2007, 8:30 AM   #2
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The concept of 50mm as 'normal' in 35mm cameras is more about field of view than magnification. If you want to reference to magnification, as in binoculars and telescopes, the '1x' focal length is more nearly 80 - 85mm. If you have a zoom lens with a SLR or EVF, trn the camera vertical, and look thru viewfinder with your right eye, and keep your left eye open. adjust the zoom until the view is the same in both eyes (normal binocular vision) and then check the focal length. It will vary a little, depending on the VF magnification factor, and you will need to convert to the 35mm equivalent.

You are correct about the zoom factor being more or less meaningless unless it is referenced to a standard. This is why SLR lenses normally give just the actual focal lengths and not the 'X-factor"

brian
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Old Mar 4, 2007, 12:33 PM   #3
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Focal length is a physical measurement that is constant no matter what size sensor or negative you use:

" The focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point, which is located on the sensor or film"

Tom
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Old Mar 4, 2007, 5:58 PM   #4
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Fixed lens digital cameras are confusing as far as I'm concerned. Telling me that a lens is 10X really is meaningless - it just means that the maximum zoom is 10 times the minimum zoom. A lens that is 10mm - 100mm is a 10X zoom, as is a 20 - 200 etc. To make things more complicated, a lens put on a small sensor camera will give you a different field of view than the same lens on a camera with a bigger sensor. So a lens that is physically something like 6-30mm (seeTom's explanation above)might give you the same field of view as a 28-180 mm lens on a 35mm camera. When you are talking about different cameras (especially p&s cameras) it would be impossible to compare them if you refer to their true focal length - putting their field of view in 35mm terms gives you a better idea of what you are getting (comparing apples to apples)

I actually like having lens information stated in 35mm equivalent terms when comparing cameras - I have an idea of what I'll get. But now that I've been using a dSLR for a while, I now have an idea of what a particular lens will get me on the digital camera, and since many of the lenses are ones I use on a film camera, it's just easier to refer to their actual focal length. I've gotten used to it, and for dSLRs, it makes more sense than referring to the 35mm field of view.

Are you totally confused now?
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Old Mar 4, 2007, 6:26 PM   #5
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not totally, but how much magnification would I get compared to the naked eye on my k100d with the lense 300mm away from the sensor?



**would I be correct in assuming that a 70-300mm lense would show a wider angle shot at full zoom, as opposed to a 100-300mm? or would they be the same?
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Old Mar 4, 2007, 9:19 PM   #6
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xfxgeforced wrote:
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**would I be correct in assuming that a 70-300mm lense would show a wider angle shot at full zoom, as opposed to a 100-300mm? or would they be the same?
The 70-300 lens at "full zoom" (300mm) would be exactly the same as the 100-300 lens. The difference would be at the other end - 70mm would have a wider view than 100mm. Also, to confuse things further, there's a difference between "magnification" and "field of view." To give a rather exteme example, if you were to look at a panorama that was stitched together from 3 different frames, you would have the same magnification as one ofits frames, but a much wider field of view.

You've given me an idea for how to spend tomorrow's lunch hour - think I'll visit some place, sit down and take pictures at various focal lengths. I can cover from the 18mm where the kit lens starts to 300mm. Would that be useful? This way you can get an idea of what you might see at various focal lengths, and it won't matter how much is "magnification" and how much is "field of view." Besides, I'm always looking for an excuse to take pictures!
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Old Mar 4, 2007, 10:16 PM   #7
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mtngal wrote:
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xfxgeforced wrote:
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**would I be correct in assuming that a 70-300mm lense would show a wider angle shot at full zoom, as opposed to a 100-300mm? or would they be the same?
The 70-300 lens at "full zoom" (300mm) would be exactly the same as the 100-300 lens. The difference would be at the other end - 70mm would have a wider view than 100mm. Also, to confuse things further, there's a difference between "magnification" and "field of view." To give a rather exteme example, if you were to look at a panorama that was stitched together from 3 different frames, you would have the same magnification as one ofits frames, but a much wider field of view.

You've given me an idea for how to spend tomorrow's lunch hour - think I'll visit some place, sit down and take pictures at various focal lengths. I can cover from the 18mm where the kit lens starts to 300mm. Would that be useful? This way you can get an idea of what you might see at various focal lengths, and it won't matter how much is "magnification" and how much is "field of view." Besides, I'm always looking for an excuse to take pictures!
that'd be great if you could do that, then make a new thread, and just link to it in this. It would help a lot of people in the future im sure. Now I understand how the mm's work, but cant wait to clear it up with your pictures!
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Old Mar 5, 2007, 12:57 AM   #8
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VTphotog wrote:
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The concept of 50mm as 'normal' in 35mm cameras is more about field of view than magnification.
Actually it is BOTH..... frame constrained field of view, but at ZERO mag diference when you take your eye off the VF or actively look through both eyes separately.

ON a 35!!!.... On but the few full frame DIGITAL (most of us don't have) 50mm is a 75mm.... and as to the the OP's question no that 70-300mm is going to start out as effective 105mm not 70mm. ... and at far end be 450mm.
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Old Mar 5, 2007, 2:12 AM   #9
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xfxgeforced wrote:
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that'd be great if you could do that, then make a new thread, and just link to it in this. It would help a lot of people in the future im sure. Now I understand how the mm's work, but cant wait to clear it up with your pictures!
Take a look here:

http://www.tamroneurope.com/flc.htm

You can use the slider to see what your FOV would be for just about any practical FL, ad compare 35mm against a cropped sensor. It's pretty neat.

Scott
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Old Mar 5, 2007, 8:04 AM   #10
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Great link! What a wonderful tool for showing the differences between cameras.
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