A basic question about focal length

helmarfernandes

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Hi. I'm a Brazilian enthusiast of photography. Forgive my terrible English.

I have a Nikon D5100 and there's something that may be very simple for you, but I still can't understand.

I've bought a 55-200mm lens thinking that with this lens I would be able to reach distant objects, since I've read that what really matters is not the zoom but the focal length in a lens.

So this is my question: I use to take pictures with a zoom camera (Canon SX110is) which is a 10x zoom with a focal range from 6 to 60mm. Since what really matters is the focal length not the zoom how can a 60mm lens can go further than a 200mm lens? Knowing that my crop factor in D5100 is 1.5x it means that I'm really taking pictures in 300mm. But this lens doesn't reach the half of the distance the Canon 6-60mm can reach.

To get the same distance what kind of lens I'll have to buy? I'm a fisherman and I use to take pictures of birds in trees with my old 10x optical zoom lens. What do I do now? Take the Nikon and put it in a box and continue using my old camera? Or do I have to buy a 600mm lens to take the same pictures I use to take before?

I know this is a very basic question for you, but this is confusing me.



I'll appreciate any advice.
Thanks!
 

RCunningham

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You've got a 1,5 crop factor, but your old cameras has an even smaller sensor thus your crop factor gets larger which gives you a longer reach.
 

OLaA

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Well first the zoom and focal length are the same thing. 10x zoom refers to 6mm vs 60 in your old camera. Now to figure out what exact focal length you were using on your old camera you need to find the crop factor for the point and shoot. Multiply and get the optical zoom/focal length you were using.

Now the second part of this equation would be to figure out what amount of digital zoom you were using. Point and shoots often have both optical and digital zoom. Optical being the focal length of the physical lens. Digital being the same as if you took a photo on your computer, and cropped a small part of it to reveal more details. I'm thinking the reason you're confused is you're not factoring this part in, and the "zoom" on your old camera is higher than the 250mm range you're using now. So once you find the crop factor, do the math incorporating the digital zoom, you should have an idea of what focal length you need. I would do some of the leg work for you, but I'm answering from my phone at the moment. Hope this helps.
 

KmH

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As mentioned, image sensor size (crop factor) has a bearing on the 35 mm equivelent focal length of a lens.
a full size 35 mm image sensor has no crop factor

Your Canon SX110is has a 1/2.3" image sensor (6x crop factor) that because of the crop factors to a 35 mm equivalent focal range of 36 m to 360 mm (10x)

Your Nikon D5100 has a 1.5x crop factor APS-C size image sensor, so the 55-200 mm lens has a
35 mm equivalent focal range of 82.5 mm to 300 mm. (200 mm time the 1.5 crop factor = 300 mm).

In other words, the APS-C size image sensor in your Nikon D5100 is 4 times larger in area than the 1/2.3" image sensor in your
Canon SX110is.
 
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helmarfernandes

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Thanks for all your replies!

OlaA. I never used the digital zoom in my old camera. I just keep it disabled. But your explanations were very helpful for me.

KmH. Now I understand why my old camera reachs such a long distance.

But this brings me another question. Considering the classical example of a house and a tree, comparing a full frame sensor and a 1.5x cropped I know what part of the image my sensor will cover. How do I know what part of this same image would be covered in a 1/2.3" sensor?
 

KmH

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The fact the 1/2.3 image sensor has a 6x crop factor compared to the 1.5x crop factor of a Nikon APS-C size image sensor and the zero crop factor of a full frame image sensor..
 

TonysTouch

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The 55-300mm lens will give you a maximum equivalent focal length of 450mm and won't bankrupt you. Your Canon can zoom up to 4/5 this length and the 55-200mm can reach 2/3.
 
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christop

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In other words, the APS-C size image sensor in your Nikon D5100 is 4 times larger in area than the 1/2.3" image sensor in your [/COLOR]Canon SX110is.

An APS-C sensor actually has about 13 times the area as a 1/2.3" sensor: 368mm[sup]2[/sup] for APS-C vs 28.5mm[sup]2[/sup] for 1/2.3". It's almost 4 times the size in each dimension.
 
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helmarfernandes

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In other words, the APS-C size image sensor in your Nikon D5100 is 4 times larger in area than the 1/2.3" image sensor in your [/COLOR]Canon SX110is.

An APS-C sensor actually has about 13 times the area as a 1/2.3" sensor: 368mm[SUP]2[/SUP] for APS-C vs 28.5mm[SUP]2[/SUP] for 1/2.3". It's almost 4 times the size in each dimension.

Thanks a lot guys! Now things are clear for me...
 

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