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Old Apr 26, 2009, 12:12 AM   #1
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I hope that makes sense. I have a panasonic FZ20 right now that has 12X zoom. I am waiting on my Nikon D90 to arrive in the mail, and am trying to find out how the zoom from my panasonic correlates to the mm on an SLR lens. Anyone know?
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Old Apr 26, 2009, 1:16 AM   #2
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Seems to me that there should be an exact correlation.

The mm markings on a lens indicate a certain angle of view, so that, say, 100mm on your FZ20 should give you the same angle of view as 100mm on the Nikon zoom.

The FZ20 has a range from 36-432mm, but I don't know how the lens barrel is marked. So, I don't know if there's any way to tell the exact mm setting the lens is at at any other than full wide angle and full telephoto except by reading the EXIF information after the picture is taken.

If what you're asking is more that you want to know what the "X" factor would be on the Nikon zoom vs. the FZ20, you just have to divide the highest mm available to the lens by the lowest. Like, if it was a 40-120mm zoom, it would work out to 3x zoom ratio. If the mm measurement with the FZ20 is meant to be the 35mm film camera equivalent, then you'd also have to convert the lens markings on the Nikon to 35mm equivalent (multiply by 1.5) so you won't be comparing apples to oranges.

I hope I got some of this right!

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Old Apr 26, 2009, 8:21 AM   #3
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A non-dSLR model like your Panasonic FZ20 usually includes the "35mm equivalent" focal range in it's specifications. The actual focal length of lenses used on non-dSLR cameras like that is *much* shorter.

Because of the very small sensors used in non-dSLR cameras, you get a much narrower angle of view (more apparent magnification) for any given focal length lens. The actual focal range of the lens on your FZ20 is 6-72mm (which gives you the same angle of view you'd have using a 36-432mm lens n a 35mm camera).

The larger the sensor or film size, the wider the angle of view will be for a given focal length lens. The smaller the the sensor or film size, the narrower the angle of view will be for a given focal length lens. Your Panasonic has a very tiny sensor. That's one reason you can get so much focal range in a small package. The lens on your Panasonic is also very bright (able to maintain f/2.8 throughout it's focal range).

If you tried to duplicate that on a lens for a 35mm camera, you'd end up with a *very* large and heavy lens. That's why you can't find a lens with that much focal range in a lens for a dSLR if you want a lens that bright (since their sensors are *much* larger), and even if you could, it wouldn't be practical to make one that bright (with f/2.8 available throughout the range, which is 4 times as bright as a typical consumer level zoom for a 35mm camera on their longer end).

With a camera using a Sony APS-C size sensor like the D90, you'll need to multiply the focal length of a lens by 1.53x to see how the angle of view compares to the same focal length lens on a 35mm camera. It's usually rounded to 1.5x.

For example, a 100mm lens on a D90 would give you the same angle of view as a 150mm lens on a 35mm camera (100mm x 1.5 = 150mm).

So, if you wanted the roughly same focal range used by your Panasonic in a lens for your D90, you'd need to use a lens with a focal range of around 24-280mm. But, you won't find one that's exactly that range, and the "all in one/super zoom" type lenses available with be very dim in comparison to the lens on your Panasonic. Fortunately, a dSLR like the D90 is capable of much higher usable ISO speeds. So, that helps if you really want a lens with a lot of range from wide to long.

Note that you'll also see Depth of Field differences with a dSLR using a larger sensor for a given subject framing and aperture setting. You'll have a lot less depth of field (how much of the image is in focus as you get further away from your focus point), since Depth of Field is based on the actual focal length, focus distance, and aperture. Again, your Panasonic is using a much shorter "actual" focal length lens to get the same framing for a given subject distance. That makes it much more difficult to help subjects stand out from distracting backgrounds with a non-dSLR model. Sometimes that's a good thing (if you want more of the image in focus), and sometimes that's a bad thing (if you're trying to blur the background with a larger subject, that can be very difficult with a non-dSLR camera model like your Panasonic).. There are pros and cons to both types of systems.

As a general rule, you're much better off using a lens with a more conservative focal range range from wide to long with a dSLR if you want better image quality (i.e., use more than one lens to cover the same range). But, you'll want to consider convenience, too (as you may not want to carry around more than one lens).

There is no one perfect choice in a lens, and any of them tend to be a compromise in one area or another like focal range from wide to long, available apertures (how bright the lens is), distortion, color, sharpness and contrast at various focal lengths and apertures, flare resistance, focus speed, ergonomics, size, weight, cost and more.

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Old Apr 26, 2009, 12:39 PM   #4
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I have the same type of question. I have a Canon Power Shot A 700 with a 6X optical zoom & was trying to compare how the focal lengths related to the ones on my SLR. I took a shot with the Canon without the zoom & it showed the focal length a 5.8. With full zoom it showed 34.8. But on an SLR camera I believe those would be considered wide angle focal lengths so I'm not sure how to know how the actual focal lengths on my point & shoot compare to my SLR. My Canon also has a digital zoom but I don't understand what that is for & the difference between digital & optical zoom & when to use the digital zoom.

Thanks for your help.

Janice
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Old Apr 26, 2009, 12:49 PM   #5
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Answered here:

http://forums.steves-digicams.com/fo...amp;forum_id=9

More info...

If you want to see how angle of view compares, you can multiply the actual focal length shown in an image taken by your Canon A700 by 6x and see what the "35mm equivalent focal length" is (what lens you'd need on a 35mm camera to see the same angle of view).

So, if you take a photo at it's wide angle zoom setting (actual focal length of 5.8mm), you'd have roughly the same angle of view you'd get using a 35mm focal length lens on a 35mm camera (5.8mm x 6 ~= 35mm).

If you take a photo zoomed in all the way with your Canon (actual focal length of 34.8mm), you'd have roughly the same angle of view (apparent magnification) you'd have using a 210mm lens on a 35mm camera (34.8mm x 6 ~= 210mm).

I'd leave digital zoom turned off so that you don't degrade image quality.


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Old Apr 26, 2009, 1:44 PM   #6
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Thanks! I didn't realize that I could find out what length I was shooting at by looking at the photo info. So, I've been looking at my pictures taken with the FZ20 to see what lengths I use a lot. For example, the info onone ofthe photos says "24.6mm (147mm 35mm)". Does that mean that if I use a lens on my D90 that has 147mm in it's focal length range (say, a 70-200mm lens), that that would work? I think I'm starting to get this (I hope). Thanks for all the help!
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Old Apr 26, 2009, 1:55 PM   #7
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ride16 wrote:
Quote:
Thanks! I didn't realize that I could find out what length I was shooting at by looking at the photo info. So, I've been looking at my pictures taken with the FZ20 to see what lengths I use a lot. For example, the info onone ofthe photos says "24.6mm (147mm 35mm)". Does that mean that if I use a lens on my D90 that has 147mm in it's focal length range (say, a 70-200mm lens), that that would work?
Yes, that would fall within the zoom range of a 70-200mm lens. But, you can't use 147mm with it and get the same angle of view with D90, because the D90 has a smaller sensor compared to 35mm film.

In your example using a focal length of 24.6mm with your Panasonic, you'd have approximately the same angle of view you'd have using a 147mm lens on a 35mm camera.

But, if you wanted the same angle of view using a D90, you'd need to use a focal length of around 98mm (you'll have a narrower angle of view for any given focal length on a D90 compared to the same focal length on a 35mm camera)


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Old Apr 27, 2009, 1:27 AM   #8
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When trying to compare mm you would need the crop factor of your sensor and then easy math.
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