Maybe it was just your wording, "That's not what I am saying" as if the comment I made was directed at you, when it was not.
Does Depth Of Field Change Between FX And DX Lenses?
(62 posts) (19 voices)-
Posted 2 years ago #
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??? ok I give up.
Posted 2 years ago # -
I'm not sure what you don't get, sometimes you confuse me too.
In any case look closer at the images, the depth of field is different, although only ever so slightly. That may just be due to movement, if you switched between an FX and DX body, which I doubt you did. Any movement could have caused that slight difference.
Posted 2 years ago # -
Obviously you don't read anything I write. I did not take the photos. I said they were taken from the first link I posted above. It explains that there is NO DIFFERENCE between DOF on a DX camera body and FX camera body at the same distance to the focus point with the same lens at the same aperture. They did switch between an "FX" and "DX" body but they used the same 105mm lens.
Posted 2 years ago # -
for me the DOF is very similar - certainly not a 1 stop different between each photos
Posted 2 years ago # -
nice post of the rulers.. The DOF in absolute terms look almost the same for DX and FX (although on the DX image the digit "1" from "21" can be "seen" more clearly due to the size of it) but relatively to the size of the image the relative DOF is much more in DX. ie about 1/5 if the length of the ruler is "in focus" while about 1/12 for FX. cool! makes much more sense to me now!
Posted 2 years ago # -
The "1" looks the same to me. It's just closer in one photo than the other. Plus there is likely a slight error from moving one camera body to the other on the tripod so it won't line up exactly.
Posted 2 years ago # -
Glad this 'newbie' could be of service Hearty! ;-)
Posted 2 years ago # -
I think some people are more confused now then before they read this thread.
Posted 2 years ago # -
These two pics Niko posted completely confused me.
I thought a larger sensor meant a shallower DOF and I thought that was why compact cameras has pretty deep DOF all the time..
Now can someone tell me why compact have huge DOF if it's not due to the sensor size? is it because you shoot at 6mm to get 35mm? (something like that?)
Posted 2 years ago # -
Confusion is normal when DOF is being dicussed and that's besides the Circle of Confusion:)
At given distance, focal length and and aperture -> DOF will be very similar* between DX and FX but FoV of the picture will be different.
* DOF optically identical but sensor pixel density differences with effects from diffraction may cause some difference in DOF perception.
Posted 2 years ago # -
jbl said:
....Now can someone tell me why compact have huge DOF if it's not due to the sensor size? is it because you shoot at 6mm to get 35mm? (something like that?)Maybe I'll confuse you even more :)
It's all depends on which variables are used :)
For identical framing (subject size on sensor) with given focal length and aperture you need to be closer to the subject with a larger sensor thus get a narrower DOF.
At fixed distance, focal length and aperture the DOF will be similar but the subject size will be smaller on the larger sensor.
It gets somewhat complicated if focal length is the variable.
In close-up photography at a given sensor size, subject size on sensor and Aperture the DOF will be almost identical with different lens focal length.
The ball game changes with increased distance to the subject matter going towards the hyper focal length and there will be more aparent DOF with the smaller focal length as you get closer to its Hyperfocus distance.Posted 2 years ago # -
I think the confusion is that there are 2 different meanings being used for the generic DOF.
* Absolute DOF - which remains the same for any specified focal length and aperture.
* Relative DOF - with includes the FOV + FL + Aperture.Posted 2 years ago # -
Bottom line:
If you took a picture of a butterfly which filled the sensor at 1 metre using a 100mm lens at f16 on a DX then transferred the lens onto an FX camera using the same settings and distance, the butterfly would remain the same size and the DoF the same depth but the FoV would be bigger (so you would see more 'other stuff' round the outside of the butterfly). To then get the butterfly the same size on the FX (i.e. filling the sensor), you would have to use a 50% longer lens so the DoF would be shallower.
Upside of DX? If both cameras are 12MP using the same lens, there are more pixels on the butterfly using the DX and the butterfly is larger on the sensor at a given distance with a deeper DoF. DX best for macro.
Posted 2 years ago # -
jbl said:
is it because you shoot at 6mm to get 35mm? (something like that?)This is exactly why. It's not the sensor size that gives you big depth of field, it's the fact that you are using much shorter focal lengths with compacts than with FX (or DX for that matter). This is why talking about "effective" focal lengths is so confusing, it makes it very difficult to explain how sensor size changes things.
Posted 2 years ago # -
So you're saying if I use an FX camera and take an image with a 200mm lens, then crop the image so I have the same *field of view* the lens would have given me with 300mm (which is what a DX body does), I will also have the same background compression I would have had if I shot at 300mm to begin with on the FX body? That doesn't make any sense. It would follow that taking any image and cropping it changes the background compression.
Posted 2 years ago # -
points said:
So you're saying if I use an FX camera and take an image with a 200mm lens, then crop the image so I have the same *field of view* the lens would have given me with 300mm (which is what a DX body does), I will also have the same background compression I would have had if I shot at 300mm to begin with on the FX body? That doesn't make any sense. It would follow that taking any image and cropping it changes the background compression.No you have got it wrong... Focal length relates to absolute DOF in terms of the number of mm in focus at a given aperture.
If you do a DX crop of an FX image as you stated you get a change in FOV (from 200 to 300 mm lens) but the absolute DOF of the image remains, to all intents and purposes, exactly the same. However, If you had a 300mm lens and took the same picture as the cropped DX they will have the same FOV but the DX(cropped version) will have a greater DOF than the 300mm lens version(as the DOF depends on the Focal lenght)
Posted 2 years ago # -
i'm unofficially confused. . .but I'm unsure if this will effect my photography :-/
Posted 2 years ago # -
OK, I'm going to stick my nose in this. I will claim to understand this, including the math behind it. First a point of terminology that I don't see explained.
Circle of confusion (CoC): this is the amount a point is out of focus. It is an arbitrary value but for 35mm 1/1000 of an inch (40 um) is a common value. Now the point is to enlarge the image! If you enlarge FX, say 8x then you'll need to enlarge DX 12x to get the same size. Therefore your CoC must be 1.5x smaller or 1/1500 inch. So, shoot with a 200mm lens on FX and the same lens on DX keeping distance and f-stop the same, enlarge to the same size, the DX will have 1.5x shallower DOF and a 1.5x tighter crop.
Now what if you change the focal length? This is where it gets interesting. Keeping CoC, distance and f-stop constant DOF decreases with the square of the focal length. So shoot FX with a 200mm and a 400mm, the 400mm shot's DOF is 1/4 that of the 200. Now what if we shoot FX at 300mm and DX at 200mm? They'll both have the same FOV. But FX's CoC is 1.5x larger than DX but the 300mm lens' DOF is 2.25x smaller, (300 / 200)^2 = 2.25. Last 2.25 / 1.5 = a DOF 1.5x greater for DX.
Long story short, for a given FOV, f-stop and enlarging that the same size, the smaller format image gives a greater DOF.
Hope that confuses it for everyone.
Posted 2 years ago # -
Panamon_Creel solved it all for me. Thanks
In the end it all comes down to pixel density.. shooting with a compact is like shooting with a FX that would have the same pixel density as the compact and in which you would only crop the very middle of the frame, in order to make it let's say 12mpx... to do a portrait this way you'd need to shoot with an ultra wide angle lens and stay far from your subject... aka near infinite DOF
I seriously thought that the sensor size had its role... but in fact it affects the DOF only indirectly.
Thanks
Posted 2 years ago # -
@astrophotographer : good stuff .. but if we are going into details, there is another factor that needs to be considered and that is relative distance of the subject against the focal length.
eg if you have a 200 mm lens (on a DX camera) and the subject is 500mm from the front element/hyperfocal it will have a different DOF than for a subject 5000mm away. So for the same subject distance and FOV on FX you will need a 300mm lens for a 500mm subject distance. which will result in a much shallower DOF as the subject distance is now relatively closer. this is also one of the reasons why the tiny P&S sensors and short mm focal lengths produce such great DOF. At say 2m distances on some P&S in effect its like shooting on FX at 50m distances.PS: I had another look at your maths .. and I think you may have taken that in to consideration .. oh well .. maybe... never was very good at maths anyway ! LOL
Posted 2 years ago # -
zhu zhu pets video said:
So you're saying if I use an FX camera and take an image with a 200mm lens, then crop the image so I have the same *field of view* the lens would have given me with 300mm (which is what a DX body does), I will also have the same background compression I would have had if I shot at 300mm to begin with on the FX body? That doesn't make any sense. It would follow that taking any image and cropping it changes the background compression.It's counterintuitive, but this is exactly what happens. You will have the same background compression. Background compression is a result of perspective, not the physics of the lens. If you took a shot at 14mm and cropped out a tiny portion of a distant object in that image, it will also look compressed (assuming you have enough pixels to still see anything).
Here's another way to think about it: your lens is projecting an image onto your sensor. The sensor size has no effect on perspective, aperture, or focal length, all it does is crop compared to an FX sized sensor, this is true for literally any camera, ever. The only thing that changes is your shooting habits and what types of lenses you are likely to put in front of your sensor.
There is also one difference which is only relevant if you are printing to very large sizes, and that is that at 100% view, the size of each pixel becomes the maximum acceptable circle of confusion. Since DX cameras generally have a different pixel size (usually smaller) than FX, this can also affect the depth of field for huge prints that are viewed very closely (have you really ever made a print like this?).
Posted 2 years ago # -
Wait are you saying that printing at various sizes changes DOF???
Posted 2 years ago # -
NikoDoby said:
Wait are you saying that printing at various sizes changes DOF???Yes, absolutely. The bigger you print, the shallower your depth of field becomes, since any point that is even slightly out of focus will no longer look acceptably sharp. On the other hand, on a 4x6 print, you won't notice if something is slightly out of focus. However, this does not change the character of points that are very far out of focus, so for instance the background will look pretty much the same. You are more likely to notice something like slightly missed focus on a large print, though.
This is somewhat of a nitpick, though and is probably just adding confusion to the subject. Depth of Field needs to be defined more rigorously, really. I consider depth of field to be the parts of the photo that are tack-sharp (or at least at the peak of that lens's capabilities). If you focus on someone's eye, but, say you miss by 1cm or something small (maybe the camera focuses on the nose instead). If you view that photo at 100% it is possible that the circle of confusion is bigger than a single pixel, especially if you use a fast telephoto. Thus the depth of field does not include the subject's eye. However, if you print it at 4x6 inches, the subject's eyes will still look sharp, since the print is so small. Thus, I would say that the depth of field does include the eyes in this case.
Posted 2 years ago # -
Don't back down on print size, Shade, because you're right. Print size and viewing distance have to be defined in order to calculate dof—for the reasons you mentioned. It's not a nitpick because circle of confusion depends on those parameters.
BTW, I'm pretty sure this thread would win in a vote for most confusing ever seen on this forum. But I think it's just because it's a complicated subject with a lot of variables to keep track of.
Posted 2 years ago #
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