DOF as a function of FOV? What am I missing?

[tallahassegreys]

Here's the question: Does it make sense to learn DOF charts as a function of FOV, as opposed to focal length and distance to subject?

Here's the background of my question: I am finally starting to take a close look at DOF charts after realizing that many of my shots may be coming out soft as a result of shooting at wide apertures....which is a bit disappointing since the only reason I bought the 35mm 1.8 and 17-55 2.8 is precisely to shoot wide open!! But DOFMaster is showing me how incredibly shallow the DOF field can be in may circumstances. One option to increase DOF is to back up, but then I need to zoom in to have the same FOV.

I have checked out the Dimensional Field of View Calculator on http://www.tawbaware.com/maxlyons/calc.htm and confirmed that FOV remains constant if you vary focal length (FL) and distance to subject (DTS) by the same factor. So basically any of a number of combinations of FL and DTS can be utilized to achieve the same FOV. So it therefore seems more practical to learn or "memorize" the DOF charts as a function of 1 variable, namely FOV, as opposed to two variables, FL and DTS.

Does this make sense? And if so is there a DOF chart that indexes DOF with FOV?

 

[rosiesphoto]

Here's the question: Does it make sense to learn DOF charts as a function of FOV, as opposed to focal length and distance to subject?

many of my shots may be coming out soft as a result of shooting at wide apertures

I am new to this but doesnt "soft" mean out of focus. if the subject is in focus than why does DOF and FOV have anything to do with the focus problem.
If the area around the focus point is soft would that be due to DOF value?

 

[tallahassegreys]

I am new to this but doesnt "soft" mean out of focus. if the subject is in focus than why does DOF and FOV have anything to do with the focus problem.
If the area around the focus point is soft would that be due to DOF value?

Very good point. I neglected to mention that many of my shots are of my 2 year old girl. So DOF of less than a foot can be tricky as she moves around quickly!!

But to clarify: My main issues are 1) moving subjects when using large aperture in attempt to blur background (at 2.8 and close to subject even the slightest movement can cause out of focus!!) and 2) wanting to learn the DOF charts so I know what aperture to use when I have, for instance, 2 or 3 people at varying instances from the camera who I would like to all be in focus.

So as I mention above, it seems that DOF is essentially a function of FOV. Learning the charts as a function of 1 variable seems more practical than as a function of 2 variables.

 

[sshoihet]

I just try to remember the f stops for the common focal lengths that I use at the distances that I would photgraph a group or an individual.

What I did find interesting is that for 35mm and 10ft, the depth of field is approximately the f number. The dof for the 50mm is quite close to the f number at 15ft. The smaller the aperture, the more it starts to deviate but i find it to be useful at the apertures that would matter to me.

I also have the F8 app for my ipod which i use when i know I'll be photographing a subject at a certain focal length and distance.

Generally though, lenses are much softer wide open; i find my 50mm f1.8 is quite soft until stopped down to at least f4.

 

[uncleskull]

WITH THE SAME IMAGE SIZE

As you mentioned, you sometimes back up and then zoom in. No matter if you use your 35 or back up and zoom in with something longer, DOF will be the same.

What WILL change is perspective. The longer lens will compress things so background objects will appear nearer to the subject. The opposite happens with WA lenses. Again, this is with identical subject image sizes.

This is hard for people to grasp. There some good illustrated articles online. Some googling will find them for you. Some experimenting wil prove it to you.

If you want / need more DOF, use a smaller f/stop. If your pictures are soft, make sure it is not a result of camera or subject movement. Use a tripod or higher shutter speed. If it's subject blur, usually SOMETHING in the picture will be in focus. If it's camera movement, nothing will be in focus. A tripod will not help with blur as a result of subject movement and a slow shutter speed - nor will a VR lens.

--
unc

~ The only things stopping us from reaching our goals are the limitations we place on ourselves ~

 

[Yendawg]

If movement is the issue, try dynamic/continuous focusing if you have it.

 

[tallahassegreys]

Very good points all.

However, I am really looking to confirm that my assumption that learning DOF values for different FOV's makes sense, and if there is a chart like this in existence? If my assumption is correct, then I guess it would be easy enough for me to make one.

Another point (if my assumption is correct that is): although FOV is 2 dimensional, since the ratio of horizontal to vertical measurements is constant for a given sensor size, one could make a chart indexing DOF against a single number, say, the horizontal measurement. Know what I mean??

 

[winparkman]

It makes no sense. Your mind is not quick enough to do the calculation and set up the shot. With experience, your ability to do this sort of thing becomes innate but we are talking about a significant amount of experience.

Rather, your problem is using the lens wide-open when you can accomplish the same results by stopping down. Why use f/1,8 or f/2.8 when f/4 will give you essentially similar results.

I learned people photography by photographing my fast moving children. I applied rules I'd learned in other types of photography to develop a rule of thumb that helped define my style. Most wide-aperture lenses are considerably sharper at f/4 than at f/1.8 or wider.

Do not become so technical that you fail to get the shots you really want to keep. With children, the photos are more to remember a moment in time rather than create an artsy image. With time, your ability to get artistic shots of your children will improve dramatically...just about the time they start slowing down a bit!!

Very good points all.

However, I am really looking to confirm that my assumption that learning DOF values for different FOV's makes sense, and if there is a chart like this in existence? If my assumption is correct, then I guess it would be easy enough for me to make one.

Another point (if my assumption is correct that is): although FOV is 2 dimensional, since the ratio of horizontal to vertical measurements is constant for a given sensor size, one could make a chart indexing DOF against a single number, say, the horizontal measurement. Know what I mean??

--
OK, not so purely a hobby.

 

[uncleskull]

--
unc

~ The only things stopping us from reaching our goals are the limitations we place on ourselves ~

 

[sshoihet]

This is one of those things that I know, yet I continue not to do...a blurry background is great... having more than one eye on your subject in focus is much better

There have been many times where i though "gee, that would be a nice photo if more than 2in of it were in focus".

This is one reason why i think it's not always a great idea to suggest that someone new to SLRs should get a fast prime, esp when it's going to be used to take pictures of their children.

My daughter is 7 and she never stops moving; I'm much better off having 4ft of DOF than 1ft. I just have to keep reminding myself of that

It makes no sense. Your mind is not quick enough to do the calculation and set up the shot. With experience, your ability to do this sort of thing becomes innate but we are talking about a significant amount of experience.

Rather, your problem is using the lens wide-open when you can accomplish the same results by stopping down. Why use f/1,8 or f/2.8 when f/4 will give you essentially similar results.

I learned people photography by photographing my fast moving children. I applied rules I'd learned in other types of photography to develop a rule of thumb that helped define my style. Most wide-aperture lenses are considerably sharper at f/4 than at f/1.8 or wider.

Do not become so technical that you fail to get the shots you really want to keep. With children, the photos are more to remember a moment in time rather than create an artsy image. With time, your ability to get artistic shots of your children will improve dramatically...just about the time they start slowing down a bit!!

Very good points all.

However, I am really looking to confirm that my assumption that learning DOF values for different FOV's makes sense, and if there is a chart like this in existence? If my assumption is correct, then I guess it would be easy enough for me to make one.

Another point (if my assumption is correct that is): although FOV is 2 dimensional, since the ratio of horizontal to vertical measurements is constant for a given sensor size, one could make a chart indexing DOF against a single number, say, the horizontal measurement. Know what I mean??

--
OK, not so purely a hobby.