DOF with FF v DX - is there a difference?

[LuxLuthor]

I suggest you read:

http://www.naturfotograf.com/D3/D3_rev06.html

and look at the pictures, don't take peoples words for the differences but look at the differences or lack thereof in the above reference!

 

[digitalDork]

Thanks for the link LuxLuthor, interesting article which seems to contradict the arguments so far.

I'm not sure whether the 70-180 micro-nikkor, with it's "nominal and effective aperture similar along its focusing scale" behaves differently compared to other lenses operating at portrait distances ?

I'm now thinking the only way I could test my particular scenario is to get hold of a D3, D300, and an 85 f1.4 and try out some portrait shots as described in my post above.

Not sure that's going to happen any time soon though :-(

Cheers,
dD

I suggest you read:

http://www.naturfotograf.com/D3/D3_rev06.html

and look at the pictures, don't take peoples words for the
differences but look at the differences or lack thereof in the above
reference!

 

[tmhw1]

This is for those of you who interested in maths.
You have one lens 85mm.
The lens equation is 1/f = 1/u + 1/v
f = focal length = 85mm
u = distance of object is from the lens.
v = distance of the image is from the lens

for D3, say your object is 3 meter away, then the image is 87.48mm from the lens, for objects say 200mm away from your main object, the image distance is 87.32mm. So the image is focused 0.15mm from the sensor.

For D300, to get the same FOV, your have to go back by a factor of 1.5, so your object distance is 4.5 meter, and the image distance is 86.64mm, for objects 200mm away from the main object, the new image distance is 86.57mm. So it is out of focus by .07mm. To get the same distance out of focus, the object needs to be 475mm away from the main object.

From my previous post, we know that the amount of blur is a function of aperture and the distance the image is focused on away from the sensor. Since your lens is the same and aperture is the same. You can see why D300 will produce larger DOF.

The link from LuxLuthor reaffirmed my previous statement that in real sapce, the blur is the same no matter whether you are doing DX or FX sensor. The signal to noise get better with FX sensor however.

 

[maduhbee]

i would say, since you're using the SAM lens, on your APS-C you're getting a FOV of 85x1.5 = 127.5mm FOV. FF, you're getting 85mm, 85mm FOV.

DOF you're getting is off the 85mm focal length at a given aperture. you would get exactly the same DOF at any aperture, it's just that you're going to get a high MP crop of the 85mm, which makes it 127.5mm

 

[joel9]

Yes, but there is no 135 mm f/1.4 one could put on a D300 to get the
equivalent of a 200 mm f/2 on a D3. Some combinations can be achieved
with both DX and FX, some only with one.

That's exactly the point I was trying to make in the next paragraph--it really comes down to whether you can find the lens you need to get the effect you want in either format. Therefore if Nikon had been more dedicated about releasing DX-equivalents of popular FX lenses, there would be much less incentive for the shallow-DOF lovers to switch.

A 56mm f/1.0 DX should be possible, probably no bigger, heavier, or more expensive than that 85mm f/1.4 you like--same size front element.

 

[Simon Garrett]

The technical answer for this is NO. The same lens with the same
subject to camera distance at the same aperture will produce the same
depth of field.

I don't think that's right. For the same subject-camera distance, same aperture, same focal length there IS a difference.
See http://www.dpreview.com/learn/?/Glossary/Optical/Depth_of_Field_01.htm .
For example: take focal length 50mm, f/8, subject distance 3m.

For FX, DoF=2.07m
For DX, DoF=1.302m

For a subject away from the in-focus distance, the amount of blur on the sensor will be identical, whatever the sensor size. However, DoF calculations assume that the image is enlarged to a standard size and viewed from a standard distance. A DX image has to be enlarged 1.5 times more than FX, so anything out of focus on the DX image is more visible when enlarged than for FX (because it's been enlarged more). This means that the DoF calculations result in a smaller DoF for DX.

However, in situations where you have the same field of view in the image (either by using a shorter focal length lens or by moving moving back for the DX picture) then the result will be a larger DoF for DX.

 

[Thom Hogan]

I suggest you read:
and look at the pictures, don't take peoples words for the

Bjorn and I disagreed about both some of his methodology and certainly his interpretation (wording) when he was first doing these tests and posting his initial findings on nikongear.com.

--
Thom Hogan
author, Complete Guides to Nikon bodies (18 and counting)
http://www.bythom.com

 

[GaySatyr]

I've read the arguments in this and other threads and it seems to me that those who want to argue will continue to do so forever, regardless of the evidence.

The plain simple truth is that, given the constraints of the two differing systems -- DX and FX -- there ARE differences. Testing with zoom lenses, especially consumer zooms with variable apertures, and/or macro lenses with variable focal lengths at various focused distances, is asking for poor results. Using fixed focal length primes of known optical performance is the only way to test effectively.

Based onmy own experience (been shooting since the early '60's), given a 12MP DX body and a 12MP FX body, there is approximately 1-stop difference in the point where the sensor opto-mechanical characteristics (photosite-size, Bayer & AA filters, micro lenses, etc) appear to affect diffraction effects, regardless of the lens in use: f/11 and f/16, respectively (the D200's 10MP DX sensor appears to come in at about f/13). This is assuming that one is examining a top-quality print of the same size (8x12 inches) from both images. This appears to be to be nearly 1-stop worse in each case than similar prints made from half-frame and full-frame 35mm B&W negative material: essentially f/16 and f/22, respectively. However, the onset of diffraction limiting with film appears to be gradual and lens-dependent whereas the onset of diffraction limiting with digital is much more rapid and dependent on sensor physical characteristics.

Also, I agree with Thom: given the same size resulting print of the same image taken from the same distance, One needs a 200mm f/2.0 lens to get the same effective DOF using either a DX sensor and/or half-frame 35mm film as compared to a 300mm f/2.8 lens using either a FX sensor and/or full-frame 35mm film.

 

[paratom]

I can not explain why but I (have) owned several different 50mm Leica lenses for the M8 and the bokeh and even the DOF seems to look different. With the Noctilux the backgropund seems to blur more compared tothe Sumicron when you use both lenses at f2.0.
I cant explain.