24M pixels vs 24M pixels

[yauman]

Help - I think I'm confused or missing something really important. I am looking at the Nikon D600 with a Full size FX 36x24mm sensor at 24MP and comparing it with the D7100 with a cropped DX size 23.5x15.5 mm sensor, also at 24MP. So, if my maths is right, shouldn't the DX (smaller) sensor be better - it packed 24 Mega Pixels into a smaller sensor which would require them to make each photo site smaller or at least pack them more tightly, the result would be a sharper image and ability to resolve finer details. Yes, with smaller photo site, less photon will be captured and thus less sensitivity resulting in lower ISO. So, all other fancy features being equal or not important to me, shouldn't the D7100 with smaller sensor be better? (FYI, I remember my grad student days in the 1970's ordering a thumb nail size 4K (yes 4,096) pixel sensor from United Technologies for an experiment in Femi lab that cost $8,000 !!!! Yes, I'm old!)

[PhotomanJohn]

Yauman - The short answer is not really. Remember you can frame the image so that it covers the full sensor in either case giving you the same resolution of the final photo. As you said, the larger provides other benefits like improved low light capability. In addition, the larger sensor will make better use of the lens's resolving power. The D7100's sensor exceeds the resolving power of all but the best lenses that Nikon makes. Also the D7100 will be more sensitive to camera shake because of the reduced angle of view with the same lens (larger distance to the subject for the same lens and framing). So all in all, the larger sensor should provide a higher resolution end result than the smaller sensor all else being equal.

John

[Shadowman]

I read of a comparison of sensors and it went something like this...

The larger the photosite, the more light it can capture and the more information can be recorded.

[NorthernFocus]

Everything already said is accurate. One thing that hasn't been mentioned is the fact that the D7100 has no anti-aliasing filter so is somewhat sharper. The relevance of the differences in the two is dependent on what you shoot. If you shoot a lot of wide angle and/or portraits and/or family photos and/or high ISO work, then the D600 is a good choice. Recognizing however that FX lenses are more expensive.

If you shoot wildlife and typically don't need higher than ISO800, 1600 occassionally, the 7100 is an awesome little camera. With adequate light and good glass there is nothing out there that produces a sharper image.

[yauman]

Thanks for all the great info. I'm upgrading from a D90 so I have DX format lenses. I will be shooting mostly models and portraits for web posting and seldom need any printouts. So I guess the D7100 more than fit the bill - there's a US$800 difference between the D600 and D7100, which given what I learned here, I will spent it on a high quality portrait lens.

[NorthernFocus]

If you're doing model type work you may want to look into the possibility for moire effects caused by some patterns (e.g.knitted sweaters). The anti aliasing filter is intended to prevent moire and the 7100 lacks said filter. It occurs rarely and I believe there is software out there to correct it. But worth a few minutes on the web to investigate. Hasn't been a problem to date with fur/feathers

[Harrie]

On the Cambridge Colour site are beautifull explanations about sharpness of sensors. All to do with the pixel size blur-circle, lense quality and so on. It even explains about pixel size and possible noise. It was very helpful for me. I use a D7000 (16 Mpixel) and found my lenses do not perform as well as they could on a full frame sensor. DxO optics, can tell the same and explain why.
When you use a DX camera with 24 Mpixel or a FX with 36 Mpixel, you only benefit from the posible sharpness, when you use very good lenses and a tripod.
Even the best zoom lenses are not good enoug to exploid the real sharpness these sensors could deliver. Only the best prime lenses can do that.

Don't think you can find more sharpness in more megapixels. The reason why I would love to have a FX camera (still too expensive for me) is the posibillity to play with the depth of field. The bigger the sensor, the more you can play with depth of field. Not only will the perspective of a lense on a DX camera look like a lens that is about 1,5 times longer (cropfactor) The DOF will look like a apeature setting that is about one step bigger so 1,4 looks like 2 and so on.
So there is more, than just mega pixels and sensor sizes.