Migrant Songbirds

Started Sep 29, 2012 | Discussions thread
Lions
Regular MemberPosts: 315
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Re: 7D crop factor + 1.4TC = 1120mm.
In reply to John Sheehy, Oct 7, 2012

John Sheehy wrote:

Lions wrote:

Beautiful photos and excellent composition. Any PP cropping to achieve composition? Any PP noise reduction? Bokeh is buttery smooth!

It's easy to get excited by high "equivalent" mm through crop factor, but it is really not a value in and of itself.  The 7D has smaller pixels than any FF Canon, and that is where the real benefit lies.  Had he been using a 3MP Canon D30 from 2000, would you really try to quote the crop factor as some kind of benefit?  It would have given far less detail than a 5D3 with the same lens and subject distance, and a lot more subject noise at higher ISOs.  You could have cropped the 5D3 tighter, and your resulting equivalent focal length could have been even higher than 1120mm.  There is no more validity to a crop factor that is limited by sensor size, than there is in not using the full sensor of a larger sensor.  You could take a 562x374 pixel crop from the center of a 5D3 and say the equivalent focal length is 7000mm, but is that really any great achievement?  It /might/ be, if the FF sensor were 200MP or more.

I use a Pentax Q with a so-called crop factor of 5.5x with my Canon lenses.  I still think of them as the focal length written on the barrel, because that /is/ the focal length, and determines the DOF at any given f-stop.  The pixel density is the real value here; not the crop factor.  If this were a 1MP 1/2.3" sensor, it would not be worth the effort of adapting the Q to EOS lenses.

Well John, here's the way I see it.

DX has the "Reach" advantage over FX. To achieve 1120mm on FX you would need an 800mm +1.4TC. Secondly, a 5d3 + 500f4 +1.4TC=700mm, your suggestion of cropping tigher, would result in lower PIXEL DENSITY. The 5D3 image (700mm), to the equivalent 1120mm of the 7D would require a 62.5% crop. In doing this you reduce the PIXEL DENSITY of the 5d3 image from 22.3 down to 13.94, compared to 18 mp of the 7D.

Ken

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