Please look at the photos I posted and the accompanying description of how taken?
The EXIF has the information of the lens setting as the OP asked.
"same lens at the same aperture and focusing at the same distance would yield the same dof no matter what sensor was put behind the lens."
If it was your intent to demonstrate that, you did not succeed. The image from the D5100 has less depth of field, because was enlarged more to be displayed at the same size on the screen, as it would have been had the same size print been made. that's why the sensor size matters when determining depth of field, as did film size in the old days.
BBViet, post: 58915140, member: 1713081"]
I went to
http://www.cambridgeincolour.com/tutorials/dof-calculator.htm to try the dof calculator and what perplexed me was that by changing the format from 1.5 crop to full frame and keeping all other parameters the same I get a deeper dof.
I have always thought that using the same lens at the same aperture and focusing at the same distance would yield the same dof no matter what sensor was put behind the lens.
@Great Bustard - you seem to be ignoring the OP's point (bolded above).
Actually, the first scenario given by GB is exactly what the OP asked: same focal length and shooting distance,
relative aperture (aka f-number); with the printed output sized proportional to the sensor size -- in that case the OP's understanding would be confirmed; depth of field would be the same.
The OP stated
same aperture,
not relative aperture. Moreover, the OP did not mention prints.
[/QUOTE]
But depth of field calculators DO account for prints (or for screen viewing; it makes no difference), which is the explanation for why the OP's assumption was incorrect. GB explained that. Depth of field cannot be understood or evaluated without reference to the viewing conditions for the final image. Even when the shooting conditions were the same, a difference in viewing conditions (which includes the size of the output image and the distance from whihc it is viewed) will result in a difference in depth of field.
Your misunderstanding about aperture and relative aperture has been addressed elsewhere.
However, if the print size in both cases is the same -- which is how photos would be typically viewed and how they would be properly compared; and which is the assumption built into the DoF calculator -- then the depth of field yielded by the smaller sensor would be shallower.
GB is pointing out the the evaluation of depth of field requires accounting for all of the variables, including not just the shooting parameters, but all of the steps to producing a final, viewable image.
This sounds like a matter of interpretation and opinion.
Let's agree to disagree.
Um, so you are saying that evaluation of depth of field
should not account for all the variables that influence it? Well, you are entitled to you opinion, but that seems like a difficult one to support.
Can anyone help me understand this?
The easiest way to help you understand what's going on is to tell you that if you took a photo of the same scene from the same position with the same focal length and
relative aperture using cameras with different sensor sizes,
I agree except for the
relative aperture because that deviate from the OP's issue.
The relative aperture is the f-number. Although the OP used the vernacular "aperture" it is best to be clear whether one means the actual aperture size, or the that size relative to the focal length, which is what is more commonly meant. GB was being clear about that.
I go by what the OP wrote, not what I think he meant. Since the OP specified
same lens at the same aperture, how would the the FL change? Why introduce "noise" in the form of
relative aperture to FL?
Because, as explained above and elsewhere depth of field is not, and cannot, be evaluated by stopping at the capture stage. Specifically, you cannot complete a depth of field calculation without using the "circle of confusion" parameter, which includes the ratio of enlargement needed from the sensor size to the print or screen size. If either the print/screen size or the sensor size is different, the CoC will be different, and the resulting depth of field will be different.
printed the photos out at a size proportional to the sensor size (e.g. 1.5x at 12x18 inches and FF at 18x24 inches), and cropped all the photos to the same framing, then the DOFs would be the same.
Why all the fuzz about printing when printing will introduce another unwanted element? Just do a side-by-side (split screen) of
unretouched photos is easier. The two photos I posted above will just do as well. Those are unretouched, not cropped. The filesize was reduced to accommodate DPR filesize upload requirement.
Assuming you mean your earlier post, it isn't clear what point you are making with those. But if images taken with different sensor sizes but identical shooting conditions (including focal length, relative aperture, and subject distance), and are then displayed at the same size and viewing distance, then the one from the smaller sensor will exhibit less depth of field. Is that what you were illustrating?
Again, pictures are worth thousand words. The two photos I posted are the original, no post processing so as to show the effect on the DoF using A LENS on camera with different sensor sizes. You don't have to use the photos I posted. Do your own experiment and decide for yourself.
Yes, as noted above, your pictures demonstrate that when all else is the same except for sensor size, the image from the smaller sensor has less depth of field. If that is what you were trying to demonstrate, you succeeded. Otherwise, not so much.
Alternatively, photos of the same scene taken from the same position with the same framing and aperture diameter (e.g. the aperture diameter for 100mm f/2 is 100mm / 2 = 50mm) displayed at the same size and viewed from the same distance will have the same DOF for all systems.
Aperture diameter is irrelevant for three reasons: (1) almost physically impossible to measure the aperture diameter (2) The lens has already marked aperture ring (3) changing the aperture setting is not in-line with the OP.
I posted your suggestion at least two hours ahead of your posting. Look above your post.
Well here you are kind of off the rails. The actual aperture diameter (not the relative aperture) is what directly determines depth of field. As GB points out, if those are normalized (and everything else,
including framing, is the same), then depth of field will be the same. Understanding that is crucial. Incidentally, one need not measure the actual aperture diameter, is is easy and convenient to determine it from the known focal length and relative aperture, as GB shows.
You keep on insisting "
relative aperture". It is the same lens, hence, the physical FL has not changed. Please do not change the conditions specified by the OP.
Sigh. As GB was originally explaining, if the pictures are taken from the same distance and have the same framing, then the focal length cannot be the same. If that's the case, if the
relative aperture (f-number) is kept the same, then the pictures will not have the same depth of field. But if the
actual aperture is kept the same, they will, if they are viewed under the same conditions. We make a distinction between the actual aperture and relative aperture because they are not the same thing, and the difference makes a difference in things like depth of field. When someone simply says "aperture" it isn't clear which is meant. When discussing things like this, it is essential to be clear about what is being communicated, which is why we keep insisting on "relative aperture" if that is what we mean.
For example, photos of a scene from the same position taken at 100mm f/4 on 1.5x and 150mm f/6 on FF will have the same DOF if displayed at the same size.
Again, using two different Aperture and FL does not address the spirit of the OP.
The OP wanted to better understand how the various parameters work interdependently to influence depth of field, including cases where the depth of field is the same (as he expected) and why they would be different, as he discovered from the DoF calculator. GB's discussion is 100% on point.
Perhaps the OP wanted to know everything about those conditions you stated
BUT the OP did not post what you are suggesting.
It would be ideal for the OP to clarify his intent, otherwise, this loop will never end even if the cows come home.
The OP's subject line was "Help me understand these DoF calculators", which is exactly what GB and other posters are helping him with.
Dave
