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  #11    Top
Old April 25th, 2012, 11:20 AM
pixeldawg's Avatar
pixeldawg pixeldawg is offline
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Re: Okay now I'm confused

Quote:
Originally Posted by WHolmes View Post
Notice the difference in the size of the red car. The small sensor D300s shows a larger car than the D700 so I would say there is some change in the Crop as well.
Bill H.
Bill,

If you crop the 2nd image identically to the first, and enlarge it to the same width and height, the vehicle will be the same size. There is NO "magnification" in crop factoring.

Cordially,

Mark Lent
  #12    Top
Old April 25th, 2012, 11:56 AM
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Re: Okay now I'm confused

Next test Jerry, the first is my 16-85mm @85mm from the D300s, the Second is from the same lens @85mm in the D700
D300s


D700



Bill H.
  #13    Top
Old April 25th, 2012, 12:14 PM
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Re: Okay now I'm confused

Since the 16-85 is a DX lens your illustration shows the guy on the other forum is dead wrong. I could have done the test myself comparing the 18-200 DX to the 70-300 FX at the same focal lengths if my 18-200 had not been stolen.

Jerry
  #14    Top
Old April 25th, 2012, 01:21 PM
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Re: Okay now I'm confused

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Originally Posted by Jriepe View Post
Thanks Bill,

I guess Di for Tamron and DX for Nikon are the same. So the FOV is definitely different even though you were using a Di lens. Am I correct in assuming that the 70-300mm Tamron Di lens is a lens designed for cropped sensors?

Jerry
Jerry, just to confuse things a bit more; if that Tamron were designed for an APSc sensor, the field of view RECORDED from both cameras would be exactly the same.
That's because the D700 would crop the full frame sensor to match the lens' image circle.
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Old April 25th, 2012, 01:34 PM
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Re: Okay now I'm confused

The problem with Bill's test is that he recorded the entire sensor on the D700, getting severe vignetting of course.
I don't own a Nikon full frame camera, so I don't know, but it appears that to avoid the vignetting, the camera must be set to record on a APSc size area. And then the two images will be alike.
Canon won't play with anyone's mind like that. The lenses, for APSc sensor cameras will not fit on any full frame Canon camera.
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  #16    Top
Old April 25th, 2012, 01:55 PM
RABaker RABaker is offline
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Re: Okay now I'm confused

Jerry,

As already stated, your original understanding was correct. The lens focal length is a feature of the lens and is not affected by what camera it is attached to. A 50mm FX lens on a DX camera will give a "cropped" image with a more narrow angle of view than the same lens on an FX camera. If you put a 50mm DX lens on a DX camera it provides the same "cropped" angle of view as given by the FX lens. This is because angle of view is determined by lens focal length and the size of the recording medium (whether it is film or digital) - it is a relatively simple mathematical calculation. As long as the focal length is the same, the resulting angle of view with a given size sensor will also be the same. If you want to obtain the same angle of view on a DX camera as a 50mm lens on an FX camera, you must divide the lens focal length by the crop factor: 50mm / 1.5 = 33.3mm. (or 31.25mm for Canon APS-C sensors).

Also as mentioned, DX lenses are designed to project a smaller image circle that will completely cover up to a DX sensor but will, at best, exhibit severe vignetting if they can be used with an FX sensor (or 35mm film). This allows the lens to be smaller and lighter than it would be if it had to cover a "full frame" FX sensor. The best wide angle DX lenses are also designed to provide a projected light path that hits the corners of the sensor at a higher angle (closer to 90 degrees). This is because the photosites on digital sensors have a physical depth (kind of like very small buckets) and light at an acute angle results in less light making it to the bottom of the photosite where it can be detected. By altering the angle that the light hits the sensor edges/corners, more light reaches the bottom of the individual photosites and there is less light falloff in the image with better signal to noise ratio in those areas.

Good luck,
Richard Baker
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  #17    Top
Old April 25th, 2012, 03:14 PM
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Re: Okay now I'm confused

On the other forum someone else has jumped on board bringing to attention the misinformation that was given.

Jerry
  #18    Top
Old April 25th, 2012, 03:40 PM
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Re: Okay now I'm confused

Didn't mean to start "problems" Janos, just trying to help Jerry...
Bill H.
  #19    Top
Old April 26th, 2012, 12:15 AM
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Frank B Frank B is offline
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Re: Okay now I'm confused

50mm is 50mm, and so on. A lens designed for DX (such as one of the Nikons) can be smaller since it doesn't have to cover as big of an image circle. But it's still 50mm (or whatever length we might be talking about).

Pentax makes a bunch of lenses that they call the DA Limited series. They are designed for an APS-C (aka DX) sensor. That design allows them to be very small compared to similar focal length full-sized lenses. You still get the crop factor when you put them on an APS-C camera. For example, DA21 has the same field of view as a 32mm lens would on an FX sensor (about 1.5x crop). Just like the Nikon AF-D 20 looks about 30mm equivalent when it is put on a D7000. I happen to have both of these lenses - the Nikon is well over twice as big as the Pentax, maybe even more. Huge difference (but pretty much same field of view on the two APS-C cameras).
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