Does size of CCD affects DOF?

[stk]

I have a question on Depth of Field (DOF) in digicams.. For different brands/models of digicam, at the same aperture (eg F2.8) and at the same focal length (eg. 70mm), would the DOF be affected by the size of the CCD? The bigger the CCD size, the shallower the DOF?

Someone please enlighten me.. Thanks..

 

[stk]

I'm reading that the Circle of Confusion used to calculate the DOF differs with different film format, which implies that it differs with film size. So I'm guessing the reason why DOF in digicams is not as shallow as 35mm film is due to the smaller CCD.

With the exception of DSLR, most of the CCDs used in consumer digicams are getting smaller.. which means that it'll be harder to get bokeh effect from these newer and smaller CCDs? That means that a Nikon 3100 with 1/1.8" CCD can get better bokeh effect than the Canon A70 which uses a 1/2.7" CCD?

Please correct if i'm wrong..

 

[StreetShooter]

Correct.

If you want razor thin DOF, go for medium or large format.

 

[ST1100]

The actual DOF (ignoring COF) is determined by the absolute size of the aperture. Not the F-stop number - that is relative size wrt to the focal length. The bigger the size, the smaller the DOF.

For example, a 200/f2 has a physical aperture of 200/2 = 100mm. A 50/f1.0 has a 50/1 = 50mm aperture, half the size of a 200/2, and thus more DOF, even though it is a f1.0.

A small sensor indirectly implies a small lens, ie a small physical aperture. Thus a huge DOF. While a digicam may say "35-105" at 35mm equivalent, the actual lens size would be (say) 8mm-22mm. At f2.8, we're looking at 22/2.8 = 7.9mm physical size max. This compared to a real 35mmSLR 105 focal length would be 105/2.8 = 37.5mm. More than 4 times the size.

One simple way to get a digicam with a (relatively/potentially) shallower DOF is just to look at the lens size from the front. The bigger it is (like the Sony 717?), the better your chances.


Try this link for more info:

http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml

 

[stk]

Thanks for the info.. So instead on looking at CCD size, we should calculate the absolute aperture size? Let's see.. if comparing at max zoom and max aperture between some digicams with my C3020..

Oly C3020 - 19.5mm/f2.8 = 6.96mm
Canon A70 - 16.2mm/f4.8 = 3.38mm
Nikon 3100 - 17.4mm/f4.9 = 3.55mm
Nikon 5400 - 24mm/f4.6 = 5.22mm

It would then seem that the Olympus C3020 can achieve a shallower DOF than the other 3? Hmm.. one more point for me to consider when considering a change of camera..

 

[jasonpgc]

The Dof is actually the same. When you use the same lens and same focal length, same aperture and maintain the same subject to film distance. Take D10 and EOS 30 as example. D10 Cmos will capture a smaller angle of the scene than the 35mm film with the same lens. However, if you compare the Dof captured by the CCD and the film for the subject, you would expect to see no difference at all.

On the other hand, if you use a 50mm lens on the D10 and a 80mm lens on the Eos 30. Then, at the same subject to film distance, same aperture, the DOF for the Cmos will definately be greater than the film. This is because 80mm is a telephoto lens and 50mm isn't :bsmilie:

 

[ST1100]

Originally posted by stk


Oly C3020 - 19.5mm/f2.8 = 6.96mm
Canon A70 - 16.2mm/f4.8 = 3.38mm
Nikon 3100 - 17.4mm/f4.9 = 3.55mm
Nikon 5400 - 24mm/f4.6 = 5.22mm

It would then seem that the Olympus C3020 can achieve a shallower DOF than the other 3? Hmm.. one more point for me to consider when considering a change of camera..

The other thing to look out for, assuming you want maximum background blur out of a dgicam, is the minimum focussing distance. For any camera/lens, the closer you focus, the smaller the DOF. A bigger aperture with a much further minimum focussing distance will have poorer background blur (aka bokeh) than a smaller aperture with a nearer MFD.

Here's a site that calculates the DOF for diff parameters:

http://www.shuttercity.com/DOF.cfm

Unfortunately, the smallest sensor it does is 35mm

Your best bet is to look at actually pictures background blur produced from digicams, to know what can actually (vs theoritically) be done. Don't get bitten by the bokeh bug - bokeh is expensive; you may end up with a dSLR and a $10k system.

 

[StreetShooter]

Originally posted by ST1100
The actual DOF (ignoring COF) is determined by the absolute size of the aperture. Not the F-stop number - that is relative size wrt to the focal length. The bigger the size, the smaller the DOF.

For example, a 200/f2 has a physical aperture of 200/2 = 100mm. A 50/f1.0 has a 50/1 = 50mm aperture, half the size of a 200/2, and thus more DOF, even though it is a f1.0.

A small sensor indirectly implies a small lens, ie a small physical aperture. Thus a huge DOF. While a digicam may say "35-105" at 35mm equivalent, the actual lens size would be (say) 8mm-22mm. At f2.8, we're looking at 22/2.8 = 7.9mm physical size max. This compared to a real 35mmSLR 105 focal length would be 105/2.8 = 37.5mm. More than 4 times the size.

One simple way to get a digicam with a (relatively/potentially) shallower DOF is just to look at the lens size from the front. The bigger it is (like the Sony 717?), the better your chances.


Try this link for more info:

http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml

I think that's the best explanation I've seen so far!

:thumbsup: :thumbsup: :thumbsup: