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  1. #1
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    Lenses Conversion Ratio

    Ok so for digital cameras there is a conversion ratio for older lenses, right?

    That's great for longer lenses, but sucks for the wide angles ones. I'm looking to buy a lens in the 16mm range. But my digital camera its going to be increased.

    I've heard there are some lenses now being built for digital slr's without the conversion ratio. Is there a 16mm'ish lens like that?

    When I buy that lens I'd like to get the full 16mm not 24mm.

    Thanks!

  2. #2
    has-been... another view's Avatar
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    Re: Lenses Conversion Ratio

    One thing to remember is that the focal length of the lens never changes. A 50mm lens on a 35mm SLR is just that, same on a DSLR with a crop factor (example 1.5x on a Nikon). With that crop factor, the 50mm lens will have the angle of view of a 75mm lens - but it still is a 50mm lens. The perspective of a 50mm lens will stay the same. It's almost like making an 8x10 print and cutting a 5x7 out of the center of that print.

    There are ultra-wide lenses made for DSLR's, depending on what camera you have. Nikon has a 10.5mm fisheye and a 12-24 zoom. The third party companies (Sigma/Tamron/Tokina) have some available too. They usually don't work with film cameras because they don't project an image that covers the full 35mm frame, but the Sigma 12-24 works with both.

  3. #3
    MikiShots mikishots's Avatar
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    Re: Lenses Conversion Ratio

    Quote Originally Posted by pgowder
    Ok so for digital cameras there is a conversion ratio for older lenses, right?

    That's great for longer lenses, but sucks for the wide angles ones. I'm looking to buy a lens in the 16mm range. But my digital camera its going to be increased.

    I've heard there are some lenses now being built for digital slr's without the conversion ratio. Is there a 16mm'ish lens like that?

    When I buy that lens I'd like to get the full 16mm not 24mm.

    Thanks!

    You can think of the digital camera as being a different format. An 80mm lens is considered a normal focal length on a medium format, as opposed to a 50mm on a 35mm camera. To get the same field of view for a digital SLR, you'll need something even shorter, like around 30mm, assuming around 1.6X factor.

  4. #4
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    Re: Lenses Conversion Ratio

    So the conversion factor dosen't actually change the focal length?

  5. #5
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    Re: Lenses Conversion Ratio

    Quote Originally Posted by another view
    One thing to remember is that the focal length of the lens never changes. A 50mm lens on a 35mm SLR is just that, same on a DSLR with a crop factor (example 1.5x on a Nikon). With that crop factor, the 50mm lens will have the angle of view of a 75mm lens - but it still is a 50mm lens. The perspective of a 50mm lens will stay the same. It's almost like making an 8x10 print and cutting a 5x7 out of the center of that print.

    There are ultra-wide lenses made for DSLR's, depending on what camera you have. Nikon has a 10.5mm fisheye and a 12-24 zoom. The third party companies (Sigma/Tamron/Tokina) have some available too. They usually don't work with film cameras because they don't project an image that covers the full 35mm frame, but the Sigma 12-24 works with both.
    Does Minolta have one? Or does Sigma make one for Minolta?

  6. #6
    Senior Member OldSchool's Avatar
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    Correct.

    But the digital sensor (CCD or CMOS) is closer to the lens in your DSLR when compared to a 35mm film SLR. Or in other words, the distance to the plane that you focus on is shorter in the DSLR in comparison.

    Does this make sense? Terms like 1.5 crop-factor get thrown about by sales folks or brochures, but it doesn't explain the physics of it all.

    BR,
    Tim
    (someone correct me if I'm wrong here)
    Samurai #17 |;^\

  7. #7
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    Re: Lenses Conversion Ratio

    Ok, so I saw today that Minolta is going to release special digital lenses. But in their press release they give the equivelant focal length on a 35mm. If they are specifically designed for the 7D, shouldn't they be a true 16mm or what ever length?

    Here is the release:
    http://www.dpreview.com/news/0503/05...lta_lenses.asp

  8. #8
    has-been... another view's Avatar
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    Re: Lenses Conversion Ratio

    One of those lenses is 11-18mm. You'll be all set with this one, or if you can't wait for it to be released, check with B&H or any other retailer to see what your options are on a Minolta mount.

    You've got it right - DSLR's do not change focal length of lenses. It's physically impossible - a 50mm lens on a DSLR is a short telephoto; on a full frame 35mm SLR (or something like the Kodak full frame DSLR) it's a normal lens; on a medium format it's a wide angle and on a large format (if you could even find a 50mm) it would be so wide that you could see behind your own ears...

    I'm not sure on this - but don't think that DSLR sensors could be any closer to the rear element than film would be in a 35mm SLR. It doesn't appear to be any different (from seeing the sensor when trying to blow dust off it), and the autofocus system isn't calibrated any differently. All of my lenses focus just fine on my DSLR and 35mm SLR. The sensor is smaller than 35mm film (i.e. not full frame) but the same distance back inside the body from the lensmount. And also, the mirror is the same size at least in mine - so it couldn't be moved forward or it would hit the rear element of a lens on it's way up after pressing the shutter release.

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