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Nikon D800


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#1 sharky1961

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Posted 08 April 2012 - 04:58 AM

Hi,
Ad s far as I understand has a FX sensor a smaller DOF as a DX sensor, correct??
Wenn I switch the D800 from FX in DX mode will I get the same DOF as a normal DX sensor?? or will the D800 just crop the image and will the cropped image have the normal FX DOF??
just wondering, because if we will get real DX DOF it would make sense to switch from FX to DX sometimes if you really need the extra DOF.

Rob

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#2 loftus

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Posted 08 April 2012 - 05:41 AM

Hi,
Ad s far as I understand has a FX sensor a smaller DOF as a DX sensor, correct??
Wenn I switch the D800 from FX in DX mode will I get the same DOF as a normal DX sensor?? or will the D800 just crop the image and will the cropped image have the normal FX DOF??
just wondering, because if we will get real DX DOF it would make sense to switch from FX to DX sometimes if you really need the extra DOF.

Rob

When you switch from FX to DX you are simply cropping the sensor in the camera. DOF is related to angle of view. So when you switch from FX to DX you effectively have to have a wider angle of view to get the same image in the frame. Just like switching to a wider angle lens or moving backwards to make the subject smaller in the viewfinder. All will change your DOF accordingly.
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#3 Glasseye Snapper

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Posted 08 April 2012 - 09:12 AM

It is like Loftus wrote but with a little correction to the rationale. Cropping to DX format actually changes the angle of view without effect on DOF while changing the subject distance leaves the angle of view untouched but changes the DOF. What determines the DOF is not angle of view but the solid angle captured by the lens. Think of it as the angle between two lines emanating from a single point on your subject to opposing points of your aperture opening. The wider that angle the shallower your DOF. So, cropping to DX has no effect as long as you don't change aperture or subject distance.

DX cameras are said to have shallower DOF than FX because you have to either shoot from a larger distance with the same focal length lens to make the same scene fit on the sensor (same field of view: FOV), or shoot from the same distance with a shorter focal length lens. Both approaches reduce the solid capture angle and thus lead to broader DOF (a shorter focal length lens has a smaller aperture diameter than a longer lens set to the same aperture value). These are the practical points Loftus raised.

As a logical continuation, you can get equal DOF and FOV on DX as FX by simply using a lens with shorter focal length (by a factor or 1.5/1.6 for nikon/canon) and shoot at a wider aperture (again by the same factor). So a 100mm lens on Canon FX at F16 should give very similar results to a 60mm lens on Canon DX at F10 when shooting the same scene from the same distance. The solid angle captured is also directly related to the optical resolution of the image while the actual recorded resolution is either the optical resolution or sensor resolution, whichever is lower. This adds a little twist. For the in-focus part of the image resolution tends to be limited by the sensor and sensors with smaller pixels can capture more detail. For pixels in parts of the image that are increasingly out of focus the image resolution decreases correspondingly and when the image resolution falls below the sensor resolution you start to notice the out-of-focus blur in the image. For small pixel sensors this will happen earlier so DOF may appear to be a bit wider on a sensor with larger pixels. This latter effect is related to the fact that you can typically stop down FX cameras more than DX cameras because the former have larger pixels. As you close down the aperture you decrease the solid angle captured and the image resolution. You start to observe "diffraction effects" when the image resolution drops below the sensor resolution. The larger the pixels the further you can stop down before you notice the effect.

OK, that was a way to long answer to a simple question but it was a useful exercise for myself and hope others may find it helpful. In the end, for your D800 DX vs FX cropping case none of this matters and cropping to DX has no effect whatsoever on the actual image.

Bart
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#4 sharky1961

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Posted 08 April 2012 - 11:53 AM

thank you Bart,

now I understand.

Rob

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#5 nathanm

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Posted 08 April 2012 - 07:13 PM

A couple additional points.

One way to explain what Glasseye Snapper says is that depth of field depends on image size. If you resize an image so the subject is the same size in the frame (which is a different way to say same solid angle) then all lenses have the same DOF if they are at the same aperture - from fisheye to 600mm super telephoto. That always surprises people but it is true.

Of course you would have to crop the hell out of the fisheye, or move WAY far away with the 600mm to equalize the same field of view. Here are example shots that demonstrate this on Luminous Landscape.

So when people ask about DX versus FX (or FF) formats, the fact is that the same thing is true - at the same aperture and if distances are adjusted so the subject field of view is the same, and the image size is the same, then the DOF will be the same. Normally the way to achieve same subject size in the frame is to use a different focal length.

Here is an excellent page that explains how diffraction hurts resolution if you stop down too much: diffraction page .

#6 Tom_Kline

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Posted 08 April 2012 - 07:37 PM

Hi,
Ad s far as I understand has a FX sensor a smaller DOF as a DX sensor, correct??


Rob


You are correct. DOF is inversely proportional to format size. This is better seen when comparing formats with a larger difference than DX vs FX. For example compare 35mm (24 x 36mm) format with 4x5 inches. The normal lens for 35mm format is 50mm whereas the normal lens for 4x5 is 150mm. Shoot a picture with the same aperture such as f/8 on both formats. There is a lot more DOF with 35mm. One has to stop down quite a bit more with large format to get the same DOF.

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#7 Glasseye Snapper

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Posted 09 April 2012 - 07:23 AM

The link to the "diffraction page" that Nathan gives is a very good one, including nice illustrations to clarify the concepts and a diffraction calculator that lets you get an idea at what F-stop diffraction starts to set in for your particular camera. It is also not dogmatic about exceeding the diffraction limit, in the end it is the photographer that needs to come up with the best camera settings to capture the intended image. Understanding diffraction effects just helps you do a better job at that.

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#8 garyyoss

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Posted 09 April 2012 - 08:17 AM

How about the viewfinder?
Will putting the D800 in DX crop mode will you reduce the viewfinder view?
Thanks,
Gary
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#9 Alex_Mustard

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Posted 09 April 2012 - 08:58 AM

The areas of the viewfinder not being used are shaded dark grey. I've not checked - can someone confirm that in DX mode the RAW files are DX sized. I know if you alter image dimensions (resolution) - the RAWs are unchanged - but I think Image Area does change the RAW files. Alex

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#10 PeteAtkinson

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Posted 09 April 2012 - 04:53 PM

NEFs shot with the 12-24 DX are 4800 pixels by 3200 and about 18.3MB with compressed lossless. Otherwise they are 7360 by 4912 and around 40MB compressed lossless.

#11 Alex_Mustard

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Posted 09 April 2012 - 10:16 PM

Thanks Pete.

Scene needs to be pretty simple to get full res RAWs to just 40MB. Most of mine are about 10% larger than that.

Alex

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#12 Alex_Mustard

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Posted 10 April 2012 - 01:15 AM

Pete - if you are still there - what is the fastest synch speed of the D800. Is it 1/320th or 1/250th (assuming an UW strobe). Alex

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#13 dava

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Posted 10 April 2012 - 03:25 AM

If you took exactly the same photograph with the same lens and the same settings at the same distance with a d7000 and then with a d800 set on DX mode would the DOF be the same

MD

#14 Paul Kay

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Posted 10 April 2012 - 06:28 AM

Wenn I switch the D800 from FX in DX mode will I get the same DOF as a normal DX sensor??

You will get the same DOF field as a DX sensor with similar pixels.

or will the D800 just crop the image and will the cropped image have the normal FX DOF??

It will crop the image, and the cropped image will have identical characteristics to those of any image from the FX sensor.

just wondering, because if we will get real DX DOF it would make sense to switch from FX to DX sometimes if you really need the extra DOF.

No it doesn't work like this - unfortunately.

Depth of Field is a complex subject and varies depending on many factors. It can only be strictly calculated if you know both output image characteristics and size AND viewing conditions and distance. Most Depth of Field scales and tables make varied assumptions - as have you here. Cropping the sensor does nothing other than lose the outside of the image. enlarging this cropped section to match the size of an output image which might be expected from the full FX sensor changes the Depth of Field characteristics of the image because, whilst the sensor and the image are identical, its output magnification has increased and this needs to be taken into account. There are lots more nuances to Depth of field too........ its difficult to be really quantitatively specific when comparing Depth of Field from different sensors and formats and I have yet to see a really good explanation regarding the interaction of the lenses projected image and differing sensors (or even film).
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#15 loftus

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Posted 10 April 2012 - 07:51 AM

If you took exactly the same photograph with the same lens and the same settings at the same distance with a d7000 and then with a d800 set on DX mode would the DOF be the same

MD

I think what I was trying to say earlier, that it's really not possible to get the exact same image with a D7000 and a D800 with the same lens, at the same distance.
You would have to back up or move forward to get the exact same framing of the subject if you use the same lens. In other words, to get the exact same photograph, you have to keep the same field of view from the camera. Hence DOF changes according to FOV, but also remember the relative distance between subject, camera and background will change
It goes back to the old discussion if you take a portrait with a long telephoto lens that blurs the background, then change to a wide angle and go so close that you fill the exact frame with the portrait.
So there are a lot of variables. Overall if you back up with a DX camera using the same lens to get the same shot, you will get more DOF.
There's a Wikileaks entry here on this, 5th paragraph down talks about changing formats
http://en.wikipedia..../Depth_of_field
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#16 Viz'art

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Posted 10 April 2012 - 08:28 AM

If you took exactly the same photograph with the same lens and the same settings at the same distance with a d7000 and then with a d800 set on DX mode would the DOF be the same

MD



If I understand correctly your question, the answer is yes.

When the D800 is set in DX format, if using the same lens at the same distance with the same depth of field, you will gets the same images as the D7000 which is a native DX format. Resolution will differ slightly but that is beside the point.

When you switch to DX on the D800 you transform the camera into a D7000 on steroid, but just to complicate matter more :P even the D800 in full frame at the same distance, using the same lens on the same subject would yield the same depth of field as the D7000, but the image surface taken in FX mode would be larger than the DX

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#17 Paul Kay

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Posted 10 April 2012 - 09:13 AM

.....but just to complicate matter more.....

Please don't Jean. If there is a topic which is guaranteed to start a heated photo forum debate, it is depth of field. :P
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#18 loftus

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Posted 10 April 2012 - 10:33 AM

Hmmm....will someone please explain to me why this is any different from someone conceptually just physically cutting the sensor down to DX size, or removing the FX sensor and sliding in a DX sized one, or for that matter just masking off the sensor with tape.
So when one is using a full size sensor it behaves like FX, and when one crops it by whatever method, the effect is identical to a DX camera.
To get the same image you would have to change the lens accordingly, just like you do now if one shoots two separate cameras.
So I think cropping a D800 to DX, and changing the lens accordingly for DX, would give you identical characteristics to a D7000. (Even the pixel pitch is similar enough)

Edited by loftus, 10 April 2012 - 02:00 PM.

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#19 Paul Kay

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Posted 11 April 2012 - 12:24 AM

Hmmm....will someone please explain to me why this is any different from someone conceptually just physically cutting the sensor down to DX size, or removing the FX sensor and sliding in a DX sized one, or for that matter just masking off the sensor with tape.
So when one is using a full size sensor it behaves like FX, and when one crops it by whatever method, the effect is identical to a DX camera.
To get the same image you would have to change the lens accordingly, just like you do now if one shoots two separate cameras.
So I think cropping a D800 to DX, and changing the lens accordingly for DX, would give you identical characteristics to a D7000. (Even the pixel pitch is similar enough)

Sounds fine to me - but the OP's question ended with:

just wondering, because if we will get real DX DOF it would make sense to switch from FX to DX sometimes if you really need the extra DOF.

which assumes an increase in final output image magnification.........
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#20 Alex_Mustard

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Posted 11 April 2012 - 12:42 AM

So I think cropping a D800 to DX, and changing the lens accordingly for DX, would give you identical characteristics to a D7000. (Even the pixel pitch is similar enough)


And better AF. Alex

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