Birding with a 500mm F4 or 600mm F4

Started Feb 1, 2014 | Discussions thread
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Dr Bob
Dr Bob OP Senior Member • Posts: 1,118
Re: I'd be interested to learn more about this test Andy...

JimPearce wrote:

It seems to me that the laws of physics must have been suspended. The D800 at DX crop has 15.36 MP. The D7100 has 24 MP. At ISO 1600 the SNR of the D7100 is 30.5 dB. Correcting the D800 for DX crop we get 30.6 dB. The DR of the D7100 is 10.72 Ev, the D800 corrected is 10.51 Ev. Call IQ a wash. Then let's look at the lens resolution. The D800 with the 500 scores 16P-Mpix. At DX crop that would be 7 P-Mpix. With the D7100 it scores 9 P-Mpix. Taking the square root, this suggests that the actual linear resolution advantage with the D7100 is about 13.3%. In other words, the D7100 has about the same reach as a 566mm lens on a D800. This is just over half of the 25% reach advantage we'd expect from simply taking sqrt(24/15.36). But it is not nothing.

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I can't really help with the laws of physics here. In a previous life I was an expert on quantum mechanics (the Dr ..Bob has to come from somewhere!) but optical electronics are not my speciality. There have been a myriad of threads here comparing FF and crop bodies and the majority of respondents quote the theory.

In September I wanted to get a 2 body to back up my D600 and so scoured the internet for input. Most was just theory (so not much help) so I did a quick and dirty test in the field to compare the D600 with the D7100 to see if was worth buying a D7100 rather than a D800E. Price wise I would have saved a lot getting the crop frame. I did the comparison side by side with two 80-400G lenses on the 2 bodies, shooting a range of ducks in what was poorish light giving iso's of 640 -1200 along with a 'more expert' shooter and birder than me.

The test was for me to see the difference in IQ performance so I could make an informed decision. I was reluctant to share it with others as I didn't want to mislead the less informed. I am happy it is a good comparison and gave me a good input for the decision. I am sure many on here would moan about methodology etc. I am sure Leonard would object to the targets not being 'as per Nikon' (the targets though were real ducks, swimming round and quacking – which is what I normally take pics of).

The test was a wash. For some of the birds, the best images came from the D600. For others the best came from the D7100. From this I considered at these light levels the D7100 did not give me an advantage. Instead I bought a D800E a few weeks back at significantly more expense.

There was also another thread a few weeks ago comparing the 7100 with the 800E but I couldn't find it again. I remember shots of a 'blue' bird but they had not been resized to give similar sized birds. The conclusion from many was that the 800E was a bit better (difficult to comment given the sharpening behaviour when re-sizing on this site).

Perhaps the 7100 is better in good light and the FF's better in poor light. We rarely see the sun here. Some of us can't tell the difference between the sun and the moon - it is usually so cloudy.

….how this all fits with the law of physics, I have no idea. Perhaps sub-space anomalies are shrinking the photo sites when the shutter button is pressed?

Take care

 Dr Bob's gear list:Dr Bob's gear list
Nikon D800E Nikon D600 Nikon AF-S Nikkor 500mm f/4G ED VR Nikon AF-S Nikkor 24-120mm f/4G ED VR Nikon AF-S Nikkor 28mm f/1.8G +1 more
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