Depth of Field numbers in the viewfinder?

[AEForber]

I hope someone at Canon can help with this.

I have an R5 and an R6 as my working cameras and a 90D as an emergency backup, and five L-Series lenses. Particulary with the 24-105 and the 70-200 f2.8 it would be really useful to have a digital display in the viewfinder saying what the depth of field is. The camera has all the data: stop, focal length, focus distance and of course the camera's CoC. Why can't it give me a number saying that the current DoF is 6 inches, or 15cm, or whatever, and update it as I change parameters? It sounds like a trivial thing to do, and much more solid than depending  on a mental guess or the DoF button. Why should I have to whip out PhotoPills when the camera can do the work? Sometimes I just want to know for certain that my subject's ears are going to be in focus once I lock onto their eyes.

Also, why can't the coloured MF focus peaking happen in AF mode? That would be almost equally helpful.

End of rant/suggestion. 🙂

Andrew Forber

[stevet1]

Andrew,

From what I understand, your depth of filed is going to remain constant, depending on the f/stop that you have chosen. It's only the apparent depth of filed that has changed. There is an article in Complete Digital Photography that explains this:

https://completedigitalphotography.com/2018/08/focal-length-and-depth-of-field/

Obviously, changing your shutter speed or ISO can't affect your depth of field, only your focal length can, and that's only your perception of it. If you take two photographs at two different focal lengths, and blow them up so that your subject is the same size, you'll see that the depth of field remains the same.

Your second question about focus peaking is a good one. There are the lights in the bottom corner if you are in One Shot fpcus, and the beeping that you can use, but the peaking would be a nice touch.

If you're in Servo, that wouldn't help, because you can take a shot in Servo, even if you're not in focus.The constant peaking and beeping as you are constantly achieving focus as you hold down the focusing button as you move would probably drive you mad.

Steve Thomas

[normadel]

Depth  of field also varies with magnification changes from distance changes. Having a camera be able to tell you the DofF for any constantly changing situation seems like a dream, not a do-able feature.

[AEForber]

With respect, no. I saw the link, read the articles, and watched the video. They're incorrect. I understand both the physics and the mathematics of depth of field, which is a linear function of focal length and aperture diameter. Becauses it's a linear function of diameter, it's also a function of the square of the focal length for a given f-stop.

You can't use an example that says "look, these photos are equally out of focus at infinity" and say that proves the focal length isn't a factor. The only thing you can do is photograph an actual distance scale and see what range of distances is in actually in focus. To claim otherwise would be to say that all of the math, all of the DoF calculators on the market, and my own direct experience are incorrect. If you like, you can google anywhere the formula is given online and do the algebra, or if you'd rather you can use a calculator, or actually experiment with photographing a tape measure. You'll see the results very clearly.

[AEForber]

I don't believe that's true. The calculations are quite straightforward, otherwise a dozen iPhone apps couldn't do it. Might the numbers change rapidly if you change settings? Sure. Would that be fatal? No. As it is, the cameras all show the current focus distance. There's no reason they couldn't show a range in the same slider in the viewfinder.

[johnrmoyer]

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@AEForber wrote:

I don't believe that's true. The calculations are quite straightforward, otherwise a dozen iPhone apps couldn't do it. Might the numbers change rapidly if you change settings? Sure. Would that be fatal? No. As it is, the cameras all show the current focus distance. There's no reason they couldn't show a range in the same slider in the viewfinder.

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Which depth of field do you want?

Practical depth of field depends upon how the photo will be viewed. Standard depth of field assumes a print size, assumes a viewing distance, and assumes the visual acuity of the person viewing it. 

Many Canon cameras will put into the meta data "Focus Distance Upper" and "Focus Distance Lower" which are based upon an ancient camera standard. Would subtracting those two numbers be useful to you?

If you down scale the image, or print to a small size, the depth of field will be larger. If you zoom in to 100 per cent on a computer screen, then the depth of field will be smaller.

https://www.cambridgeincolour.com/tutorials/depth-of-field.htm 

https://www.cambridgeincolour.com/tutorials/dof-calculator.htm depth of field calculator 

In order to calculate the depth of field, one needs to first decide on what will be considered acceptably sharp. More specifically, this is called the maximum circle of confusion (CoC), and is based on the camera sensor size (camera type), viewing distance and print size. The default is to say that features smaller than 0.01 inches are unnecessary, when viewed in an 8x10 inch print at a distance of 1 foot (~25 cm). However, people with 20-20 vision can see features 1/3 this size. This calculator therefore also has the ability to adjust for parameters such as viewing distance, print size and eyesight — thereby providing more control over what is "acceptably sharp".

https://www.bhphotovideo.com/explora/photography/tips-and-solutions/depth-of-field-part-i-the-basics 

[normadel]

Depth of field can be boiled down .....

In the most basic  terms, there are two things that affect depth of field. All the formulas in the world do not change the principle.

They are:(1) Aperture size, and (2) Magnification. 

Now, the things that affect Magnification are: focal length change at a given distance from the subject, and changing distance to the subject at same focal length (lens or zoom setting).. You can get the same magnification by changing your distance and/or changing your lens length or zoom setting. Depth of field doesn't care which way you get there if magnification is the same.

[kvbarkley]

I am sure the same calculation they used to put DOF scales on lenses should be fine. To request this go to the canon USA home page and look for the little (+)feedback button. 

[Waddizzle]

“I hope someone at Canon can help with this.”

They probably won’t. The forums are a social media platform. There is a link on the main home page to provide feedback and suggestions.

As for your suggestion, I fail to see the benefits.  I don’t feel that you have thought this feature all the through.  Nothing is ever easy.  The implementation seems far more complicated than you might think.

First and foremost, where in the viewfinder would you display the DOF.  As previously mentioned, the camera reports a focus range, two distance values in the EXIF. 

Even if you display the difference, just a single value, again where should it be displayed?

What value(s) should be displayed when your intended subject is not in focus?

Hiw many times per second should this DOF readout be updated?  How much CPU load would this real time display present to the camera?

Maybe the information could be displayed along the bottom of the display, replacing exposure info, while DOF Preview is active.

But if you don’t know what the actual distance is to your subject, then what good is there in knowing the min/max focus range? 

Have you considered the heavy lifting that would be required to update the User Guides and camera menus?

” Having a camera be able to tell you the DofF for any constantly changing situation seems like a dream, not a do-able feature.”

I too fail to see the benefits.

[stevet1]

From my T8i manual:

Theoretically, I suppose this could be expressed as a range of numbers instead of areas of smaller or larger areas of darkness.

Steve Thomas