Johndbr said:
This site may explain it better then I can.
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Thanks Johnbr, that's very useful especially with the calculators :^)

Johndbr said:
This site may explain it better then I can.
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Cool link, very accurate.
To make things simpler it is like this, on DX you gain DOF by walking away from the subject (and increasing the distance) or by using the wider lens to get the same crop.
I hope this is clear enough ...

This site may explain it better then I can.
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

heartyfisher said:
Are you sure are not confused about that? LOL :-)

Well DOF calculators will use a larger COC (COF) for FX than DX.

Panamon_Creel said:
Well in DX crop mode the DOF would be more shallow because of the smaller Circle of Confusion or so they say :).

Are you sure are not confused about that? LOL :-)

alphanikonrex said:
Exactly!

Think about it this way: if you switch an FX camera to DX crop mode, does you DOF actually change? No!

Well in DX crop mode the DOF would be more shallow because of the smaller Circle of Confusion or so they say :).

Years ago depth of field was explained to me like this: DOF depends mainly on reproduction ratio and F stop. Focal length of the lens doesn't have anything to do with it. Now, before you say wide angle lenses have more DOF, think about reproduction ratio. If the subject covers the frame exactly the same with a 35mm lens as with a 300mm lens then DOF will be the same. Perpective will be differant. And you have to back away from the subject with the 300mm to get the same coverage. Check it out. It does work this way.

ShadeofBlue said:
Actually at the same distance and aperture, the DOF is exactly the same. The difference is that for the same angle of view (not the same focal length), DX has more DOF, so you need a narrower field of view to get the same subject isolation you can get on FX.

As an example, a 50mm f/1.8 on FX will have shallower DOF than a 35 f/1.8 on DX, even though the field of view is almost the same.

Exactly!

Think about it this way: if you switch an FX camera to DX crop mode, does you DOF actually change? No!

Actually at the same distance and aperture, the DOF is exactly the same. The difference is that for the same angle of view (not the same focal length), DX has more DOF, so you need a narrower field of view to get the same subject isolation you can get on FX.

As an example, a 50mm f/1.8 on FX will have shallower DOF than a 35 f/1.8 on DX, even though the field of view is almost the same.

mb said:
You do not gain DOF in DX format, if shooting with the same lens from the same distance measurable DOF is actually better on FX.

I don't understand...could you expand on that?

alphanikonrex said:
The DOF you gain in DX format allows you to use a bigger aperture, however in FX format though you would stop down you have the high ISO advantage.

You do not gain DOF in DX format, if shooting with the same lens from the same distance measurable DOF is actually better on FX.

The actual physical size of the pixels is the factor that means DX will always be less sensitive (noisier) than FX, and 4/3 always less sensitive than DX, for the same pixel count in the sensor. At what point this noise becomes significant resulting in noticeable variations in image quality, I'm not sure, but it seems to me that there are real variations between DX and FX right now that are fundamental to the physics of imaging that can't be processed out.

The D3 sensor has about 14,000 pixels per square millimeter.

The D3x sensor has about 28,000 pixels per square millimeter.

The D300 sensor has about 33,000 pixels per square millimeter.

The Coolpix 6000 sensor has about 300,000 pixels per square millimeter. A square millimeter is pretty small - that seems pretty dense to me.

Will there ever be an FX sensor with 300,000 pixels per square millimeter? A 250 megapixel FX sensor? I'm guessing not, at least in cameras for general use.

With more pixels per square millimeter, you lose uniformity of physical characteristics between pixels in manufacturing (which can be corrected to some extent by a pixel sensitivity map for each individual sensor used to prepare the raw data in the data flow), you lose processing space on the sensor to process the info, and you lose average number of photons per second per pixel at any exposure level. As you lose average number of photons per second, you get greater variation of photons per exposure (fundamental image noise, not sensor noise which is subject to at least some improvement with technological change), particularly in the darker areas of the image - absolute increases in noise per pixel that cannot be processed out except by methods that lose some of the real data in the image (e.g. if you average over either time or adjacent pixels, you don't know for sure whether you are processing out actual data or noise).

While I don't know the number of photons per second per pixel we are dealing with on the Coolpix 6000 sensor (I don't have my physics textbooks in my library any more, but somebody here can probably figure it out), I suspect that in dark areas of the image we are getting to the point where the statistical variation from one 1/1000 second exposure to the next is quite significant. At some point not too far away, Moore's law will reach limits imposed by the size of molecules and with sensors by the number of photons per second per pixel.

Wait what? What do you mean by 1.2 hearty?

I wouldn't want DX to take over, but I'm just saying that in the end sensor size doesn't really do anything unless you're a specialized photographer (like a portrait photographer would benefit from low noise, shallower depth of field, and corner issues).

Alpha.. you are right.. but there is still a slight edge about 1.2 against the DX sensor. Thats why the dx system is so going to own the FX system in the future! ie for 1.2 times the benefit you need to pay 10 times the cost. well I exaggerate a bit as we are comparing systems and not sensors. System wise I think its about 1.8 to 2 times.

I'm sure you understand that a DX sensor merely crops the image rather than actually extending the lens. Basically, the only thing you gain from using a DX sensor rather than cropping an image from an FX sensor is pixel density (number of pixels per area), and that's only because manufacturers choose to make them that way. Technically, the D3x shouldn't have better low-light capabilities than a 10MPix DX sensor. I assume that it actually does, but that's due to the way Nikon handles the sensor's output. If you cut a D3x's sensor to DX size, it would have the same amount of noise.

This does mean that for a given number of pixels, the physical size of each pixel on the sensor is bigger, and that is what provides most of FX's benefits. The sensor receives more light, and you are dividing it between the same number of pixels, so each pixel receives more light.

So, in the end, DX really just represents a mandatory 1.5x crop on your image, which is undeniably a bad thing. The thing is, you can make a DX sensor with the same pixel density for something like 10 times less cost than an FX sensor. So if you expect to need to crop your image (wildlife and sports generally do), then DX can have benefits in resolution.

It is always a matter of cost. If cost were not a factor, there really would be very little reason to use a DX sensor. We'd all have 27 MP FX sensors (becomes 12 MP when cropped to DX size) with very powerful chips that will maintain that 10 FPS despite the huge image files.

I was thinking about sensor size, and then I realized that everything seems to cancel out. Except for $$$ of course. But that's a different story. But I think I'm missing something.

What I mean by cancel out:

Fast telephotos are easier to get for DX format, but the light you gain from the lens you lose in ISO.

The DOF you gain in DX format allows you to use a bigger aperture, however in FX format though you would stop down you have the high ISO advantage.

Corner issues/vignette on DX are rare (compared to FX), yet you need a sharper lens to get a good image out of DX (compared to FX).

So what am I missing here?