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Author Topic: Crop factor impact on maximum magnification?  (Read 1309 times)

glowsplint

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Crop factor impact on maximum magnification?
« on: August 17, 2012, 07:54:44 AM »
Not sure where this should belong but...

Does crop factor have an impact on the maximum magnification (MM) of a subject? I heard before that if you use a 2.0x teleconverter to increase the effective focal length of a lens the minimum focusing distance (MFD) stays the same and you effectively increase the maximum magnification.

So does shooting 1:1 with true macro lenses actually give you more than 1:1 magnification on APS-C crop bodies?
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Crop factor impact on maximum magnification?
« on: August 17, 2012, 07:54:44 AM »

neuroanatomist

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Re: Crop factor impact on maximum magnification?
« Reply #1 on: August 17, 2012, 08:21:10 AM »
Technically, no.  Maximum magnification is a property of the lens.  A 1:1 macro lens will project an image on the focal plane that is 'life size' when focused at the MFD (i.e, a 10mm wide object will be projected as a 10mm wide image), and a macro lens with a 2x extender behind it will project an image that is 2x life size (2:1 magnification, the 10mm object would cover 20mm at the image plane).  That's true regardless of the sensor size (or film frame) that happens to be sitting at the focal plane.

But...practically, maybe.  It depends on the resolution of the sensor. 

For example, consider using the 100L macro lens at 1:1 on a 1D X vs. a 7D - both 18 MP sensors, one FF and one APS-C.  Imagine you're taking a picture of a US quarter, which is ~24mm in diameter.  On the 1D X, you'll get the entire quarter in the field of view, at 1:1 magnification.  On the 7D, you'll cut off Jefferson's neck and the top of his head in the image.  But, if you view both images at 100% size on your computer, Jefferson's face will be bigger in the 7D image, because the 18 MP of the 7D's sensor are packed more tightly - higher resolution.

Now, say you repeat the above example, but this time with a 5DII and a 20D.  The FoV's will still be the same - larger on the 5DII.  But now you're comparing a 21 MP FF sensor with an 8 MP APS-C sensor, and both sensors have approximately the same pixel density.  This time, when you view both images at 100% on your computer, Jefferson's head will be the same size in both images, you'll just see more of the field with the FF sensor.

When comparing dSLR's of similar generations, the APS-C sensor usually has a higher pixel density than the FF sensor (that's even true with the D800's 36 MP sensor - an 18 MP APS-C sensor 'upsized' to FF would be 46 MP).  Because of that, practically speaking an APS-C sensor will generally deliver a higher apparent magnification than a FF sensor, when comparing contemporaneous bodies.

Hope that clarifies...
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LetTheRightLensIn

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Re: Crop factor impact on maximum magnification?
« Reply #2 on: August 18, 2012, 03:28:24 PM »
Not sure where this should belong but...

Does crop factor have an impact on the maximum magnification (MM) of a subject? I heard before that if you use a 2.0x teleconverter to increase the effective focal length of a lens the minimum focusing distance (MFD) stays the same and you effectively increase the maximum magnification.

So does shooting 1:1 with true macro lenses actually give you more than 1:1 magnification on APS-C crop bodies?

no crop factor does not itself

Although crop sensors are often more dense so it might toss more detail on the bug so you might be able to print a larger print of the bug with the same detail per area of print and you would effectively get more magnification in the end result that counts compared to a FF than happened to have a less dense sensor. But a 5D3 FF would give more than an APS-C 10D would so it's not really about the crop factor at all.

One thing to keep in mind though is DOF and diffraction.

neuroanatomist

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Re: Crop factor impact on maximum magnification?
« Reply #3 on: August 18, 2012, 03:48:51 PM »
One thing to keep in mind though is DOF...

Indeed.  Many people claim that a crop sensor is better than FF for macro, because of the deeper DoF.  But that's false - a crop sensor has deeper DoF only for the same framing, because you're further from the subject. If you're shooting at 1:1, you're at the same distance with APS-C or FF, and in that case, the APS-C sensor is actually giving a shallower DoF than FF.
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pharp

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Re: Crop factor impact on maximum magnification?
« Reply #4 on: August 18, 2012, 04:22:48 PM »
One thing to keep in mind though is DOF...

Indeed.  Many people claim that a crop sensor is better than FF for macro, because of the deeper DoF.  But that's false - a crop sensor has deeper DoF only for the same framing, because you're further from the subject. If you're shooting at 1:1, you're at the same distance with APS-C or FF, and in that case, the APS-C sensor is actually giving a shallower DoF than FF.

Sure, but we shoot based on framing, not magnification. If you need a macro shot - would you use your 7D or 1DX?

neuroanatomist

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Re: Crop factor impact on maximum magnification?
« Reply #5 on: August 18, 2012, 05:34:08 PM »
My 1D X, usually, because at 1:1 I can frame a larger area.
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Re: Crop factor impact on maximum magnification?
« Reply #5 on: August 18, 2012, 05:34:08 PM »