How to properly compare RX-100 and NEX-6 kit high ISO noise?

Started Apr 29, 2013 | Discussions thread
GaryW
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Re: How to properly compare RX-100 and NEX-6 kit high ISO noise?
In reply to CosmoZooo, May 2, 2013

CosmoZooo wrote:...

If you can explain how more overall light would impact the image quality I would like to hear it.

Here's is what I assert hypothetically:

If you took the RX100 lens at f1.8 and mounted it on the NEX-5R and took a picture you would only see a small crop of the sensor - the resulting image would be black all around except some area in the middle.

Say then you crop that area into a clean rectangle. You then take a 1.8 NEX lens take the same photo and crop out the same exact rectangle from the center of your image.

I assert that assuming both lenses are equally sharp and perform similarly on their respective systems the quality of those rectangles would be nearly identical. I can not think of any reason why that would not be the case.

True, but you end up with a small 3mp or 5mp crop or some such.  It's hardly using the resolution of the Nex.  Then when you open it up to use the full Nex sensor, you see that you have a lot more to work with.  But yeah, if you force the Nex user to only use digital zoom, then the two cameras are exactly alike!  

Think about how legacy FF lenses work on APS-C. They do not produce lower quality images and their speed doesn't change...but you're cropping the image...there is less overall light hitting the sensor but not per photosite - that stays the same assuming the photosite on your FF and APS-C sensors are the same size. You loose bokeh and field of view in the process but not quality - not if the two sensors perform similarly.

If the number of photosites (MPixels) is the same, then the smaller sensor has smaller photosites.  Each photosite then must receive fewer photons.  You have to lose quality.   Or, you keep the size of the photosites the same, and then  you have much lower resolution on the smaller sensor, like in the earlier example above.

Now think about how the speedbooster works - it condenses the light of FF into an APS-C area actually increasing the amount of light hitting each photosite and making the lens faster. The overall amount of light coming through the lens is still the same but it is being concentrated into a smaller area - of course the difficult part here is not to distort the image or introduce another issue so you can only condense things so much...but you see my point here.

But this has nothing to do with these two cameras.  It's not as if you are taking a Nex lens, putting a speedbooster behind it, and then attaching it to an RX-100.  That would be the equivalent scenario.

I say total light doesn't matter

Sure it matters.

- light per photosite does matter and the performance of each photosite does matter.

That matters too.

I'll let others chime in if they disagree...

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Gary W.

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