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DOF difference between DX & FX

BCinDC

Sterling, US
179 posts

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BCinDC Registered since 01st Nov 2007
Mon 07-Jul-08 01:17 AM

I am sure that if I dug around online or in some of my books I could find this/figure it out, but...I'm lazy and others might want to know this too, so here goes:

Many have mentioned Depth of Field and Field of View differences between the DX and FX sensors. I am wondering if, when the crop factor is accounted for, are DOF and FOV the same? (i.e. comparing a 200mm @ f/2.8 on a DX to 300mm @f/2.8 on an FX, is there a difference?)

Bob

"Something really clever or profound should go here...I have nothing "

mwhals

Winfield, US
1664 posts

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#1. "RE: DOF difference between DX & FX" | In response to Reply # 0

mwhals Silver Member Nikonian since 18th Apr 2004
Sun 06-Jul-08 11:43 PM

The DX lens would have more depth of field in your example at the same aperture, because the focal length dictates the depth of field. The FX camera would allow less DOF at the same aperture, which actually gives you more control over DOF in my opinion. To get the same DOF with the 200 and 300 mm lenses, the FX lens would need to be about 1 stop different on the aperture meaning 200/2.8 on the DX and 300/4 on the FX.

This is the way I understand it.

Shoot nature with respect and don't trample it or startle its inhabitants. :)

BCinDC

Sterling, US
179 posts

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#2. "RE: DOF difference between DX & FX" | In response to Reply # 1

BCinDC Registered since 01st Nov 2007
Mon 07-Jul-08 01:11 AM

Thanks for the quick response. Of course, as soon as I posted my question I got a little less lazy and started actually trying to find info on this .

FWIW, two good references are:

Depth of Field and the Small-Sensor Digital Cameras, by Bob Atkins

and

Online Depth of Field Calculator

Playing with the calculator confirms your guidance about needing to add one stop, even with lenses with equivalent FOV.

This all adds greater relevance (and clarity now for me) to the point many have made about getting an FX camera to "regain the DOF" their FX lenses originally had. I had always assumed that if I got the DX equivalent lens, the DOF would also be the same.

Bob

"Something really clever or profound should go here...I have nothing "

BJNicholls

Salt Lake City, US
10095 posts

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#3. "RE: DOF difference between DX & FX" | In response to Reply # 2

BJNicholls Gold Member Awarded for his contributions to the community and the Resources Charter Member
Mon 07-Jul-08 03:28 PM

Specifically the folks who look to FX DOF want the shallower depth of field that's a creative tool for subject isolation. If your shooting benefits from more DOF, the DX has the advantage.

BJ

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Len Shepherd

Yorkshire, UK
12722 posts

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#4. "RE: DOF difference between DX & FX" | In response to Reply # 2

Len Shepherd Gold Member Nikonian since 09th Mar 2003
Mon 07-Jul-08 07:49 PM

>the point many have made about getting an FX camera to "regain the DOF" their FX lenses originally had. I
>had always assumed that if I got the DX equivalent lens, the DOF would also be the same.
Actually the Nikonians poll implied it is the few (under 10%) who want FF for less dof.
One challenge of going for minimal dof is many lenses have a significant optical quality reduction especially on 24x36 at or near full aperture needed for minimal dof.
Just about all sports, PJ and wildlife photographers want either extra dof or the option of a faster shutter speed with the same dof - the main reason many pros prefer cropped sensors to FF.
The ideal is to take advantage of the unique features of each format by using both - something many Canon users have been able to do for years

Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.

Len Shepherd

monteverde_org

Monteverde Cloud Forest, CR
1283 posts

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#5. "RE: DOF difference between DX & FX" | In response to Reply # 2

monteverde_org Silver Member Nikonian since 16th Nov 2007
Tue 08-Jul-08 06:53 AM

Check DOFMaster's Digital SLRs and Depth of Field article for concise explanations & illustrations about DOF & crop factor.

BCinDC

Sterling, US
179 posts

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#6. "RE: DOF difference between DX & FX" | In response to Reply # 5

BCinDC Registered since 01st Nov 2007
Tue 08-Jul-08 11:46 AM

That's a good article. The article I posted previously gives a more technical explanation, that is also interesting, but the DOFMaster is an interesting and more intuitive approach. I had not thought about there being two components to the difference: crop factor and subject distance.

Since an FX camera isn't in my near future, this isn't immediately applicable to me. However, I did learn something that had never occurred to me before that will be: adding a TC decreases depth of field. I had always assumed that the increase in f-stop offset the additional focal length, but that isn't true. I still have about one stop less DOF when adding a TC.

Bob

"Something really clever or profound should go here...I have nothing "

Budi


1 posts

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#7. "RE: DOF difference between DX & FX" | In response to Reply # 6

Budi Registered since 03rd Jun 2006
Tue 08-Jul-08 12:00 PM

As I understand it (I shoot a D3 and a D200), if the angle of view and aperture remains the same between the two cameras, the dof difference is negligible. If I'm taking a picture of a person filling the entire frame with her face, I'll need a longer lens or move towards the subject with the D3, and conversely, I would need a shorter lens or move away from the subject with the D300. Since the objective here is to frame her face, there will be a difference in focal length and/or distance from subject. If we are enforcing a constant distance to subject, as well as focal length, in addition to aperture, then dof differences will be apparent.

I'm doing a really poor job of explaining it. Bjorn does a far better job than I can ever dream of doing. He even has pictures to back it up.

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

In summary, for me, I'll just pick up a camera and shoot. I never seem to get tripped up with the different formats when I shoot.

-budi
http://ignitecreative.com/photography

monteverde_org

Monteverde Cloud Forest, CR
1283 posts

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#8. "RE: DOF difference negligible?" | In response to Reply # 7

monteverde_org Silver Member Nikonian since 16th Nov 2007
Wed 09-Jul-08 03:08 AM

"the dof difference is negligible" - when shooting a bird from 50 ft for example, not being able to get closer because of the circle of fear, the difference is enough to make a difference in which parts of the bird will also be in focus.

As per the DOF calculator link in post #2, with the same frame:
- D3 (or D700) from 50 ft with a 600mm lens @ f/4 = 0.49 ft DOF
- D300 from 50 ft with a 400mm lens @ f/4 = 0.74 ft DOF

OTH with the extra ISO capability of the D700: from 50 ft with a 600mm lens @ f/5.6 = 0.69 ft DOF.

The real difference in this example is that according to B&H today, the D300 + 400mm combo is $10,150 while the D700 + 600mm is $12,500 & 1.3 lb heavier.

G