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Author Topic: DSLR Magnifaction Factor  (Read 2984 times)

SRW

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DSLR Magnifaction Factor
« on: July 26, 2006, 10:33:02 am »

On July 25, 2006 I sent the following message to a photo pro:
>
> I want to buy a "normal" lens for my Canon 30d and
> read your article with great interest, but must add that I am now thgroughly
> confused.
>
> I thought that those who said a 300mm lens on a
> digital camera actually performed like a longer lens,
> say 450mm were wrong.  That the truth was the 300mm
> lens on DSLR provided the narrower field of view of
> the longer lens, because the sensor on the DSLR was
> smaller than 35mm format, but did not actually equate to a 450mm lens.
>
> Then I read where you said that a 30mm lens on a DSLR
> equaled a normal 50mm lens on a 35mm
> camera.
>
> I know that you know what you are talking about and
> will be able to clear up my confusion.
>

I received the following reply and being very dense I am now more confused then ever:

cheap digital SLR -> film
30 -> 50
300 -> 450 or so

How can a 30mm lens act like 50mm lens on a DSLR camera?

SRW
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Ray

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DSLR Magnifaction Factor
« Reply #1 on: July 26, 2006, 11:26:09 am »

Quote
How can a 30mm lens act like 50mm lens on a DSLR camera?

[a href=\"index.php?act=findpost&pid=71771\"][{POST_SNAPBACK}][/a]

If you crop the image that a 30mm lens would project on a full frame 35mm sensor to the same size as your 30D sensor, you would get the same FoV, the same picture essentially, as you would get with a 50mm lens on a full frame 35mm camera uncropped. The differences would relate mainly to lens quality differences. A cropped image from a 30mm lens might not be of the same quality, in the center, as an uncropped image from a 50mm lens, but probably as good or better around the edges. Good wide angle lenses are very expensive.

It goes without saying, the total number of pixels on the sensor also affects resolution.
« Last Edit: July 26, 2006, 11:29:34 am by Ray »
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SRW

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DSLR Magnifaction Factor
« Reply #2 on: July 26, 2006, 12:54:11 pm »

Quote
If you crop the image that a 30mm lens would project on a full frame 35mm sensor to the same size as your 30D sensor, you would get the same FoV, the same picture essentially, as you would get with a 50mm lens on a full frame 35mm camera uncropped. The differences would relate mainly to lens quality differences. A cropped image from a 30mm lens might not be of the same quality, in the center, as an uncropped image from a 50mm lens, but probably as good or better around the edges. Good wide angle lenses are very expensive.

It goes without saying, the total number of pixels on the sensor also affects resolution.
[a href=\"index.php?act=findpost&pid=71776\"][{POST_SNAPBACK}][/a]
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SRW

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DSLR Magnifaction Factor
« Reply #3 on: July 26, 2006, 12:58:54 pm »

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[a href=\"index.php?act=findpost&pid=71781\"][{POST_SNAPBACK}][/a]

OK.  Got it, and thanks for the response.

Next question:

I understand that a 300mm lens on a DSLR "crops" to provide an image equal to a 450mm (or so) lens on a 35mm film camera, but does it magnify the image or not?

SRW
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DarkPenguin

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DSLR Magnifaction Factor
« Reply #4 on: July 26, 2006, 01:24:55 pm »

No.  300mm is still 300mm.
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Jonathan Wienke

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DSLR Magnifaction Factor
« Reply #5 on: July 26, 2006, 02:11:44 pm »

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I understand that a 300mm lens on a DSLR "crops" to provide an image equal to a 450mm (or so) lens on a 35mm film camera, but does it magnify the image or not?

While it is true that the DSLR does not "magnify" an image more than a 35mm film camera, magnification still does occur. If you shoot the same subject with the same framing with both, the film camera (and full-frame DSLRs like the Canon 1Ds) will record the image the lens projects over a 24x36mm rectangle, while the recording area of the 20D is 15x22.5mm. So if you make an 8x12" print from each camera, the 20D image is magnified more than the 1Ds image, but the magnification happens during the printing process, not in the camera. Does that make sense?
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