Which one produces shallower depth of field.....

On the basis that each image will be printed/viewed at the same size for comparison, the APS-C body will produce the shallower depth of field using the same lens. Bit academic really when the fields of view produced are so different.

You statement is not right, especially because you specified "printed/viewed at the same size".
There is an optics law saying that for any focal length, if the subject has same size in the frame, the DOF is the same and depends on aperture only. What changes is perspective, probably bokeh.
The above would be right if both shots are from same distance, thus different subject size.
 
You statement is not right, especially because you specified "printed/viewed at the same size".
There is an optics law saying that for any focal length, if the subject has same size in the frame, the DOF is the same and depends on aperture only. What changes is perspective, probably bokeh.
The above would be right if both shots are from same distance, thus different subject size.

Exactly, therefore the statement is not "not right".
 
I'll put my money on the crocodile.

And I just checked a DOF calculator. I thought it was easier to get a shallow DOF with a bigger sensor, but unless I used the calculator wrong, the APS-C yields a shallower DOF. Now I feel like verything I thought I knew was wrong. Effing great.
 
There is an optics law saying that for any focal length, if the subject has same size in the frame, the DOF is the same and depends on aperture only. What changes is perspective, probably bokeh.

This assumes that the sensor size remains the same for the DOF to be the same. In this case the sensor size changes so the equivalence of DOF between focal lengths does not apply. His statement was correct.

The full version is: DOF will remain constant for a subject shot at the same aperture, subject size and format regardless of the focal length used to take the shot. You missed the bit about the format, which changes in the OP's question.

35mm vs 4/3.

If you stay in the same postion and shoot the same lens and view the image at the same size, the smaller sensor will have LESS DOF as it needs to be enlarged more. But the content of the frame will be radically different and the subject will be a different size when enlarged.

If you move to reframe the shot so the subject size is the same then the larger sensor will have LESS DOF. This is because the movement made by getting further away on the smaller sensor will be greater than the difference in the enlargement amount of the paragraph above.

Gordon
 
The full version is: DOF will remain constant for a subject shot at the same aperture, subject size and format regardless of the focal length used to take the shot. You missed the bit about the format, which changes in the OP's question.

I'm not sure I agree with this part entirely. I think it should state: DOF will remain constant for a subject shot at the same aperture (note: this is about physical aperture size, not f-number), subject distance and equivalent focal length. The equivalent focal length is a function of absolute focal length and sensor format. For instance, an m43 camera with a 25/2 lens (which is 50mm equivalent, with a physical aperture opening of 12.5mm) has the same DOF as a full-frame camera with a 50/4 lens (obviously 50mm equivalent, with physical aperture opening of 12.5mm), provided subject distance remains the same.

Conversely, keeping the physical aperture size, subject distance and sensor format the same while using different focal lengths (for instance, comparing the 25/2 and a 50/4 on the same camera body) will give different results, because the effective focal lengths will be different.

35mm vs 4/3.

If you stay in the same postion and shoot the same lens and view the image at the same size, the smaller sensor will have LESS DOF as it needs to be enlarged more. But the content of the frame will be radically different and the subject will be a different size when enlarged.

If you move to reframe the shot so the subject size is the same then the larger sensor will have LESS DOF. This is because the movement made by getting further away on the smaller sensor will be greater than the difference in the enlargement amount of the paragraph above.

Gordon
This I agree with.
 
I'll put my money on the crocodile.

And I just checked a DOF calculator. I thought it was easier to get a shallow DOF with a bigger sensor, but unless I used the calculator wrong, the APS-C yields a shallower DOF. Now I feel like verything I thought I knew was wrong. Effing great.

The results from the calculator are correct, but the resulting image from the APS-C is cropped so the comparison isn't equal, hence you substitute a shorter focal length lens to get the same angle of view, on which the depth of field is now greater and the planets and stars are all aligned again.
 
See, this is why this question stumped me for a while.

At the most rudimentary level of understanding, a larger sensor will give you shallower depth of field.

On the other hand, a telephoto lens will also give you shallower depth of field.

So by going with a crop sensor you would be increasing depth of field .... but would the increase in depth of field be ultimately cancelled out by the telephoto which is caused by the crop?
 
PS. Some of you cheated by referring to a depth of field calculator.

EWKG6E3.jpg
 
The question in my original post refers to circumstances where you're photographing with your 50mm f/1.4 wide open spontaneously on the street.

In a real world sense if you're on the street and snapping shots on the fly you're going to be snapping these shots from wherever you happen to be standing at the time, perhaps without the luxury of time or space to reframe your shot, ie. you may be observing a spontaneous event unfolding right in front of you that you want to capture asap before the moment passes.

In those circumstances would you tend to see shallower depth of field in the photos from the photographer with (i) the full frame camera or (ii) from the photographer with the same lens on a crop sensor camera?

I refused to use a depth of field calculator, I wanted to work it out conceptually rather than mathematically.
 
My head hurts reading the replies, but here's what I know from experience, and I'm avoiding the DOF Calc.

If you use the same exact lens, and you shoot the subject at the same exact distance, DOF should be the same, but the APS-C will give a tighter crop. It's the same as if you shot it with the FF camera, and then just cropped in LR. DOF does not change just because you cropped the picture.

If you move positions (i.e. getting closer with the FF or moving further away with the crop) to get similar framing, then the DOF should be less on the FF, because you are now closer to the subject. The focal length and the physical aperture size has not changed. If, however, you grabbed a 75mm lens to shoot with the FF and a 50mm lens on the crop (assuming a 1.5 crop), and you kept distance to subject the same, then DOF will be driven by the physical aperture size, so if f/stops were the same (e.g. both 1.4), then the FF should have shallower DOF because 50/1.4=35.7mm vs. 75/1.4=53mm.

That's the way I understand it, but actually don't really care, lol. I have the lenses I have (50/1.4 and 85/1.8 on FF and 22/2 on my EOS-M) and I like the look of these lenses a lot, so if I'm wrong, I'm wrong :)

Also, if "viewing distance" to the picture comes into play here, well then I'll just keep quiet. My viewing distance is just about always 2 feet (distnance from my chair to my monitor) ;)
 
So if I understand you, subject distance is fixed, absolute focal length and physical aperture* are also fixed? Then the smaller sensored camera will have the shallower DOF.

As I said in my previous post, DOF is a function of:
-subject distance [closer = shallower DOF]
-physical aperture size (so not f-number) [larger = shallower DOF]
-equivalent focal length. [longer = shallower DOF]

In your example, the subject distance, physical aperture size and absolute focal length are fixed, but due to the smaller sensor, the crop sensor camera has a longer equivalent focal length and therefore a shallower DOF.

The statement that a larger sensor in and of itself gives shallower DOF is wrong; if all else is fixed, it's the smaller sensor that gives you shallower DOF. Thing is, larger sensors need longer absolute focal lengths to achieve the same field of view; and if you couple that longer focal length with the same f-number, you have by definition a larger physical aperture opening. That's what gives larger format cameras shallower DOF for the same equivalent focal length and f-number.

*50/1.4=35.7mm, regardless of sensor size
 
if all else is fixed, it's the smaller sensor that gives you shallower DOF.

I don't understand this statement. If all else is fixed, then isn't DOF equal, but the crop pic is, well, cropped.

Thing is, larger sensors need longer absolute focal lengths to achieve the same field of view; and if you couple that longer focal length with the same f-number, you have by definition a larger physical aperture opening. That's what gives larger format cameras shallower DOF for the same equivalent focal length and f-number.

This is how I understand it.
 
I'm just thinking aloud now.

Generally speaking, a larger sensor will give you shallower depth of field.

But if you only have one lens, and you want to do some street photography at night where you have to stay wide open, and you don't want to be constantly dealing with razor thin depth of field ... you're better off with a full frame sensor rather than a crop sensor because the crop sensor is going to have shallower depth of field than a full frame sensor.
 
I'm not sure I agree with this part entirely. I think it should state: DOF will remain constant for a subject shot at the same aperture (note: this is about physical aperture size, not f-number), subject distance and equivalent focal length. The equivalent focal length is a function of absolute focal length and sensor format. For instance, an m43 camera with a 25/2 lens (which is 50mm equivalent, with a physical aperture opening of 12.5mm) has the same DOF as a full-frame camera with a 50/4 lens (obviously 50mm equivalent, with physical aperture opening of 12.5mm), provided subject distance remains the same.

Conversely, keeping the physical aperture size, subject distance and sensor format the same while using different focal lengths (for instance, comparing the 25/2 and a 50/4 on the same camera body) will give different results, because the effective focal lengths will be different.

What I stated is correct. Have a read of this thread from mu4/3 this week where the same subject was covered.

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Your statement is also correct. However, I will not get involved in a discussion about absolute aperture. It's just too confusing for most. We've got enough people arguing over the meaning of "bokeh". I'm going to stick to the accepted photographic description of aperture (the relationship between the focal length and the diameter of the aperture blades.

Gordon
 
I don't understand this statement. If all else is fixed, then isn't DOF equal, but the crop pic is, well, cropped.

The smaller sensor will require more enlargement to get to the same viewing size as the shot from the larger sensor (comparisons and DOF calculations are made at a fixed viewing size). So the *apparent* DOF will be thinner due to the greater degree of enlargment. This is why DOF calculators use a CoC value that depends on the size of the sensor,

Gordon
 
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