D7100 High iso samples (100 to 25600)

Started Mar 13, 2013 | Discussions thread
Olaf Marzocchi Regular Member • Posts: 158
Re: Extrapolate...

JimPearce wrote:

The 85mm f1.4 G is a highly resolving lens. dxomark tests this lens at 10 P-Mpix on a D300s, just 11 P-Mpix on a D7000. However, when we move from 12 MP to 16 MP in FX resolution inceases from 12 P-Mpix on the D3s to 15 P-Mpix on the D4. On the 24 MP D3X we're looking at 19 P-Mpix, and the D600 won't be lower. The D800? 22 P-Mpix. What we're seeing here is that as pixel density increases the relationship between pixel count and resolution falls away from 1:1.

Sorry for reopening the thread, but I thought it is worth adding another info.

In general the smallest detail you can get on the sensor has a size (in microns) of about 110% of the f/ value (this does not depend on the size of the sensor). You need two pixels to really extract all the details.

That means that a lens used at f/3.5 has details down to 4 microns. That's a D7100 sensel (pixel). You may still have 24 MPx, if the lens were perfect.

Since lenses are not perfect, the sharpest details (I mean theoretically, disregarding the sensor) are achieved at a higher f/ value.

Now check on DxO the sharpest aperture for a lens. Is it f/8? that means that you have about two pixels for detail and going with higher pixel count won't help at all. That's the divergence you mention.

However, since at f/8 details take two pixels (on each direction, let's say three if you count the surface), that lens will be (on a D7100) equivalent to about 8 P-MPx. I have a Sigma 17-50 F2.8 that gets the best details at f/4, and as result I get about 16 P-MPx.

Now, the same applies to FX, but there the sensels are bigger. That means that the limit is not the lens, but the sensor (minimum details 8 microns? the sensels are about that size!).

FX can still go up in MPx and the actual details will improve even more. DX with 4 microns (24 MPx) is already at the top (unless you consider lenses that achieve best performances at f/1.8, but there are none yet).

 Olaf Marzocchi's gear list:Olaf Marzocchi's gear list
Nikon D7100 Nikon AF-S DX Nikkor 55-200mm f/4-5.6G VR Nikon AF-S DX Nikkor 35mm F1.8G Sigma 17-50mm F2.8 EX DC OS HSM Sigma 50-150mm F2.8 EX DC APO OS HSM +1 more
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