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Crop factor

 
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Harald



Joined: 13 May 2011
Posts: 290
Location: Steinberg, Norway

PostPosted: Sat Jun 20, 2015 12:54 pm    Post subject: Crop factor Reply with quote

Hi there,
I have an EOS 7D with crop factor 1.6.
Used with 180mm macro the focal length is 288mm.
Does this count for the magnification as well ?
1:1 x 1.6 = 1.6:1?
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Harald

Lier Fotoklubb / NSFF
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TheLostVertex



Joined: 22 Sep 2011
Posts: 287
Location: Florida

PostPosted: Sat Jun 20, 2015 1:22 pm    Post subject: Reply with quote

No.

The "1:1" description of the lenses magnification is a ratio, of the objects actual size, to the size that it is projected on to the imaging plane as.

So if you photograph something that is 10mm wide, at a magnification of 1:1(1x), that means the object will cover a 10mm width on the sensor. If you photograph the same 10mm wide object at 2:1(2x) it will cover a 5mm width on the image sensor.

Changing the size of the sensor does not change this value at all. We are only concerned with the projected light from the lens, rather than how the final image appears.
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Harald



Joined: 13 May 2011
Posts: 290
Location: Steinberg, Norway

PostPosted: Sat Jun 20, 2015 1:30 pm    Post subject: Reply with quote

Hi there Steven,
Thanks for the quick response.
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Harald

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rjlittlefield
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Joined: 01 Aug 2006
Posts: 17516
Location: Richland, Washington State, USA

PostPosted: Sat Jun 20, 2015 2:45 pm    Post subject: Re: Crop factor Reply with quote

Harald wrote:
I have an EOS 7D with crop factor 1.6.
Used with 180mm macro the focal length is 288mm.

This is not really true. The focal length is still 180mm.

What is true is that if you're focused at infinity, the image captured by your 7D using the 180mm lens will cover the same area that a full-frame 35mm camera would capture using a 288mm lens (1.6*180 = 288).

But really your "crop factor 1.6" camera is literally just cropping the center of the image.

The same thing is true for all other focus arrangements.

Quote:
Does this count for the magnification as well ?
1:1 x 1.6 = 1.6:1?

It depends on whom you're talking with.

Here at photomacrography.net, we will say No, you're still at 1:1. With your 22.3 mm wide sensor, you'll be imaging a subject area that is 22.3 mm wide also.

But if you're talking to a diehard fan of 35mm cameras -- somebody who was raised with film and feels compelled to translate everything into terms of that format -- then he'll say Of course it does. You'll be imaging a 22.3mm wide field, and 36/22.3 = 1.6 so you're obviously working at 1.6:1 .

You just need to recognize that the diehard's "1:1" and our "1:1" actually mean different things, despite their identical spelling. He uses "1:1" to mean imaging a 36 mm field; we use it to mean optical magnification onto sensor.

Does that help?

--Rik
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Harald



Joined: 13 May 2011
Posts: 290
Location: Steinberg, Norway

PostPosted: Sat Jun 20, 2015 3:23 pm    Post subject: Reply with quote

Hi there Rik,
This is great. This is in fact what I thought.
I just love this forum. You can ask almost anything in the range of macro and micro photography, and you´ll get an answer. There are so many people here with a lot of knowledge.
Thanks a lot!
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Harald

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AFIAP / CPS
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