Depth of Field questions..

[Village Idiot]

Here's a DOF calculator that give you an idea of how much DOF you'll have in a given situation. You pick your camera, your focal lens, your f stop, then your subject distance. You can also experiment with other lenses you may want to purchase.

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

*POP*

That's the can of worms opening.

(Notice I said same focal length and not apparent field of view )

 

[Designer]

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

I think you are confusing DOF with FOV.

 

[Village Idiot]

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

I think you are confusing DOF with FOV.

Edit:
Well, no.

The focal length of the lens doesn't change. An APS-C Canon camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .45'. A FF camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .71'. It's a wider DOF at the same focal length. Where the confusion comes in is that the APS-C camera with a 50mm lens is giving you an apparent field of view of 80mm. If you have a FF camera with the same FOV as the crop, you will have a DOF of .21', which is less.

The confusing part is that the focal length of the lens never changes. A FF camera will give you a wider DOF with a similar lens. It's when you use an equivalent FOV on the same cameras that the FF camera gives you a shallower DOF.

 

[wfooshee]

Using same lens on crop-sensor and FF, I don't see how the depth of field changes just because the sensor size changed.

I shoot a FF image with a 50mm lens at f:4, subject 5'. In post I crop that image to use the center section of it. There is no way my DOF changed by cropping an image in post, and cropping an image in post is the EXACT same effect of shooting with a crop-sensor camera.

DOF is linked to focal length, subject distance, and aperture. Crop factor can't figure in to it in any way, shape, or form.

 

[Village Idiot]

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

I think you are confusing DOF with FOV.

Yes. Duh...

Using same lens on crop-sensor and FF, I don't see how the depth of field changes just because the sensor size changed.

I shoot a FF image with a 50mm lens at f:4, subject 5'. In post I crop that image to use the center section of it. There is no way my DOF changed by cropping an image in post, and cropping an image in post is the EXACT same effect of shooting with a crop-sensor camera.

DOF is linked to focal length, subject distance, and aperture. Crop factor can't figure in to it in any way, shape, or form.

IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens. But this should correlate to what you post. You have to crop the image down. An uncropped image with the same lens on both cameras at the same distance with have different DOFs, but it will also have different FOVs.

 

[Braineack]

that's not why--not even close. It's the CoC part of the DOF equation.

 

[Overread17 5]

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

I think you are confusing DOF with FOV.

Yes. Duh...

Using same lens on crop-sensor and FF, I don't see how the depth of field changes just because the sensor size changed.

I shoot a FF image with a 50mm lens at f:4, subject 5'. In post I crop that image to use the center section of it. There is no way my DOF changed by cropping an image in post, and cropping an image in post is the EXACT same effect of shooting with a crop-sensor camera.

DOF is linked to focal length, subject distance, and aperture. Crop factor can't figure in to it in any way, shape, or form.

IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.

I don't think that is the reason at all. Far as I know the selection of the middle of the lens only affects the distortion and sharpness - the middle of the lens indeed being flatter and thus distortion at the edges is reduced - further the optical properties tend to be best near the middle. That's why on lens test setups they show middle and edge sharpness because it can vary (sometimes quite a bit on some lenses).

 

[Village Idiot]

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

I think you are confusing DOF with FOV.

Yes. Duh...

Using same lens on crop-sensor and FF, I don't see how the depth of field changes just because the sensor size changed.

I shoot a FF image with a 50mm lens at f:4, subject 5'. In post I crop that image to use the center section of it. There is no way my DOF changed by cropping an image in post, and cropping an image in post is the EXACT same effect of shooting with a crop-sensor camera.

DOF is linked to focal length, subject distance, and aperture. Crop factor can't figure in to it in any way, shape, or form.

IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.

I don't think that is the reason at all. Far as I know the selection of the middle of the lens only affects the distortion and sharpness - the middle of the lens indeed being flatter and thus distortion at the edges is reduced - further the optical properties tend to be best near the middle. That's why on lens test setups they show middle and edge sharpness because it can vary (sometimes quite a bit on some lenses).

Derp. Correct, sharpness. It would relate to the subject to camera distance and the crop camera having the FOV of a longer focal length. A crop camera with a 50mm will have a wider FOV and wider DOF, but if you zoom in to have the same FOV as a 50mm on a crop, the DOF should be shallower.

 

[pgriz]

Using same lens on crop-sensor and FF, I don't see how the depth of field changes just because the sensor size changed.

I shoot a FF image with a 50mm lens at f:4, subject 5'. In post I crop that image to use the center section of it. There is no way my DOF changed by cropping an image in post, and cropping an image in post is the EXACT same effect of shooting with a crop-sensor camera.

DOF is linked to focal length, subject distance, and aperture. Crop factor can't figure in to it in any way, shape, or form.

Check out DOFMaster - the sensor size DOES make a difference.

 

[wfooshee]

.....An APS-C Canon camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .45'. A FF camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .71'. It's a wider DOF at the same focal length......

....IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.....

So which gives the wider DOF, FF or crop?????

Still trying to wrap my synapses on this, because it conflicts with what I've read elsewhere, and with discussion with knowledgeable photog friends.

Going back to my shooting example, print my picture I shot with the crop-sensor. Print the full image. Put the lens on a FF camera and shoot the same subject, same conditions. Print that picture to the same scale. Completely different FOV, obviously. FF image will be larger, covering a wider view. Now cut the FF print down to match the crop-sensor image. Now you have two identical images of the same subject shot with the same lens. I simply do not understand how they can have a different DOF.......

(I'm old and my brain thinks it's through learning.....)

I will say that the Circle of Confusion concept is something I've not been introduced to before, and I simply don't understand it.....

 

[Village Idiot]

.....An APS-C Canon camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .45'. A FF camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .71'. It's a wider DOF at the same focal length......

....IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.....

So which gives the wider DOF, FF or crop?????

Still trying to wrap my synapses on this, because it conflicts with what I've read elsewhere, and with discussion with knowledgeable photog friends.

Going back to my shooting example, print my picture I shot with the crop-sensor. Print the full image. Put the lens on a FF camera and shoot the same subject, same conditions. Print that picture to the same scale. Completely different FOV, obviously. FF image will be larger, covering a wider view. Now cut the FF print down to match the crop-sensor image. Now you have two identical images of the same subject shot with the same lens. I simply do not understand how they can have a different DOF.......

(I'm old and my brain thinks it's through learning.....)

This is what I meant to post in the earlier post:
Online Depth of Field Calculator

 

[pgriz]

.....An APS-C Canon camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .45'. A FF camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .71'. It's a wider DOF at the same focal length......

....IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.....

So which gives the wider DOF, FF or crop?????

Still trying to wrap my synapses on this, because it conflicts with what I've read elsewhere, and with discussion with knowledgeable photog friends.

Going back to my shooting example, print my picture I shot with the crop-sensor. Print the full image. Put the lens on a FF camera and shoot the same subject, same conditions. Print that picture to the same scale. Completely different FOV, obviously. FF image will be larger, covering a wider view. Now cut the FF print down to match the crop-sensor image. Now you have two identical images of the same subject shot with the same lens. I simply do not understand how they can have a different DOF.......

(I'm old and my brain thinks it's through learning.....)

I will say that the Circle of Confusion concept is something I've not been introduced to before, and I simply don't understand it.....

"Acceptable sharpness" depends on the medium on which the image is recorded. The less resolution the medium has, the less you can distinguish clearly between what's in focus and what is not. That's what the circle of confusion concept is about.

Assuming perfect optics, and extreme resolution, then the only place where things are in focus is at the point of focus. Anything behind or in front of that plane of focus will be blurred, the amount proportional to the distance away from the plane of focus. This blur can be considered the circle of confusion. Now, getting slightly more realistic, the recording medium resolution is not infinitely fine, but has some resolving ability (say, 2 microns per cell or sensing element). Now the zone over which everything is perfectly sharp becomes slightly thicker, because the circle of confusion (the out-of-focus element), has to be larger than the sensing element for it to start appearing blurred (ie, start affecting the neighbouring cells). If the sensing element is larger, say 20 microns, then the depth of field is much higher, because a lot more blur can be accomodated by the cell. In other words, a point in front of or behind the plane of focus will appear in focus if its circle of confusion is less than the resolving power of the medium.

Sensor size factors into this because larger sensors usually have larger cells, and smaller sensors have smaller cells. The larger cells are usually more sensitive, give a cleaner signal (less noise), and are more uniform in terms of response. So FF cameras generally have better dynamic range, sensitivity and noise characteristics compared to crop sensors and P&S sensors.

 

[qleak]

.....An APS-C Canon camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .45'. A FF camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .71'. It's a wider DOF at the same focal length......

....IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.....

So which gives the wider DOF, FF or crop?????

It depends on what you change. DOF can be the same, less or more depending on the focal length, focal distance, f-number and format.

If you know the focal length multiplier of a camera you can use it to figure out equivalences.
For nikon crop sensor FLM=1.5 for canon FLM=1.6

You can multiply the FLM by the focal length of a lens and it gives you the equivalent field of view (FOV) FF focal length.

A little bit less known is you can multiply the FLM by the f-number to get the equivalent DOF.

So a 50mm at f/1.8 on a nikon crop sensor has an equivalent FOV and DOF to a 75mm f/2.7 on FF. Most people would round that to f/2.8 since tenth stops are not usually used for apertures.

 

[Ysarex86 80]

.....An APS-C Canon camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .45'. A FF camera with a 50mm lens at f/4 and a subject distance of 5' will give a DOF of .71'. It's a wider DOF at the same focal length......

....IIRC, a crop sensor uses more of the middle of the lens which is flatter and less curved than the outside, therefore produces a wider DOF on the same lens.....

So which gives the wider DOF, FF or crop?????

Still trying to wrap my synapses on this, because it conflicts with what I've read elsewhere, and with discussion with knowledgeable photog friends.

Going back to my shooting example, print my picture I shot with the crop-sensor. Print the full image. Put the lens on a FF camera and shoot the same subject, same conditions. Print that picture to the same scale. Completely different FOV, obviously. FF image will be larger, covering a wider view. Now cut the FF print down to match the crop-sensor image. Now you have two identical images of the same subject shot with the same lens. I simply do not understand how they can have a different DOF.......

(I'm old and my brain thinks it's through learning.....)

I will say that the Circle of Confusion concept is something I've not been introduced to before, and I simply don't understand it.....

There's a basic logic flaw in you're example. When you crop the image from the FF camera to compare it with the crop sensor camera then you're comparing a crop sensor camera with a crop sensor camera. To make an appropriate comparison you have to take the same photo with the two different format cameras. When you do that you'll discover that the format size does factor into the equation.

It makes no sense to compare two different photographs and then claim they share a characteristic nor does it make any sense to alter the function of one of the cameras (making them the same) and then claim they're the same.

To take the "same photograph" with two different format cameras you must use both cameras from the exact same position so that perspective remains the same. You should then equalize the FOV between the two systems and this will require using different lens focal lengths. At the same f/stop then the smaller format camera will produce more DOF.

The smaller the recording format gets the more DOF the system will produce as a general rule and vice versa.

The easiest way to look at that mathematically is to look at the formula for hyperfocal distance.

...........f ^ 2
H = ----------
...........NC

(H)hyperfocal distance = (f)focal length squared / N(f/stop) * C(circle of confusion). The value for circle of confusion is variable with the recording format. As the sensor or film size decreases the CoC decreases and that formula produces a different result moving the hyperfocal distance closer to the camera -- more DOF.

Joe

 

[Designer]

You can also see how a full frame camera with the same lens on it will give you a wider depth of field at the same focal length.

I think you are confusing DOF with FOV.

Village Idiot; the question was about depth of field, not the field of view.

If you adopt a more easily-understood terminology, yoiu would see that your answer confounds the original question and leads one down the wrong path.

Instead of using a term like WIDER to describe the DOF, use either DEEP or SHALLOW to describe the DOF. That way, the issue of lens focal length and sensor size will not enter the conversation needlessly.