Struggling mightily with focal length and effect it has on dof

[Icee258]

The OP said he was using the 18-150 lens, so I trusted that.

I agree that the factors you listed could also be an issue given the subject of a bird on a lake.

 

[PGH423]

The OP said he was using the 18-150 lens, so I trusted that.

I agree that the factors you listed could also be an issue given the subject of a bird on a lake.

In the original message, yes, but the posted image was at 214 mm.

 

[chutestrate]

The OP said he was using the 18-150 lens, so I trusted that.

I agree that the factors you listed could also be an issue given the subject of a bird on a lake.

Sorry about that. My mistake

 

[FingerPainter]

A measurable depth of field only exists in the image projected by the lens.

That is incorrect. The depth of field is a property of the displayed image. Like a print.

You say that Bill's statement is incorrect. Then you repeat Bill's statement in slightly different words, but meaning essentially the same thing!!!

No, it was not a repeat in almost the same words. An image projected onto a sensor is not a displayed image.

And actually, a DOF is a property of a viewed image, not merely a displayed image. A displayed image may have multiple DOFs, for instance if it is viewed by the same person at two different distances. If nobody looks at the displayed image, it has no DOF.

What sort of nit-picking are you doing?

Nit-picking?! This is the basics.

Indeed!

DOF is not "burnt" into the sensor data.

Correct.

If you crop the image, the DOF will decrease.

Yes.

Same pixel data displayed differently = different DOF.

Yes, and also displayed the same way but viewed differently - at different distances or by people with differing visual acuity.

How do you think Bill eneded up telling us that 70/2.8 and 200/8 give the same DOF on full frame for the same focus distance? Any DOF calculator would disagree.

You said "The depth of field is a property of the displayed image. Like a print." That statement is no more precise than Bill's statement. If you want to be precise, then spell out the factors that need to be taken into account to work out the DoF.

Subject distance, focal length, f-number, displayed image size, viewing distance and viewer's visual acuity.

Instead, you seem much more intent on criticising what others have said.

 

[Dem Bell]

A measurable depth of field only exists in the image projected by the lens.

That is incorrect. The depth of field is a property of the displayed image. Like a print.

You say that Bill's statement is incorrect. Then you repeat Bill's statement in slightly different words, but meaning essentially the same thing!!!

No, it was not a repeat in almost the same words. An image projected onto a sensor is not a displayed image.

And actually, a DOF is a property of a viewed image, not merely a displayed image. A displayed image may have multiple DOFs, for instance if it is viewed by the same person at two different distances. If nobody looks at the displayed image, it has no DOF.

What sort of nit-picking are you doing?

Nit-picking?! This is the basics.

Indeed!

DOF is not "burnt" into the sensor data.

Correct.

If you crop the image, the DOF will decrease.

Yes.

Same pixel data displayed differently = different DOF.

Yes, and also displayed the same way but viewed differently - at different distances or by people with differing visual acuity.

How do you think Bill eneded up telling us that 70/2.8 and 200/8 give the same DOF on full frame for the same focus distance? Any DOF calculator would disagree.

You said "The depth of field is a property of the displayed image. Like a print." That statement is no more precise than Bill's statement. If you want to be precise, then spell out the factors that need to be taken into account to work out the DoF.

Subject distance, focal length, f-number, displayed image size, viewing distance and viewer's visual acuity.

Thanks FP! Shall we add the sensor size to this list?

 

[FingerPainter]

A measurable depth of field only exists in the image projected by the lens.

That is incorrect. The depth of field is a property of the displayed image. Like a print.

You say that Bill's statement is incorrect. Then you repeat Bill's statement in slightly different words, but meaning essentially the same thing!!!

No, it was not a repeat in almost the same words. An image projected onto a sensor is not a displayed image.

And actually, a DOF is a property of a viewed image, not merely a displayed image. A displayed image may have multiple DOFs, for instance if it is viewed by the same person at two different distances. If nobody looks at the displayed image, it has no DOF.

What sort of nit-picking are you doing?

Nit-picking?! This is the basics.

Indeed!

DOF is not "burnt" into the sensor data.

Correct.

If you crop the image, the DOF will decrease.

Yes.

Same pixel data displayed differently = different DOF.

Yes, and also displayed the same way but viewed differently - at different distances or by people with differing visual acuity.

How do you think Bill eneded up telling us that 70/2.8 and 200/8 give the same DOF on full frame for the same focus distance? Any DOF calculator would disagree.

You said "The depth of field is a property of the displayed image. Like a print." That statement is no more precise than Bill's statement. If you want to be precise, then spell out the factors that need to be taken into account to work out the DoF.

Subject distance, focal length, f-number, displayed image size, viewing distance and viewer's visual acuity.

Thanks FP! Shall we add the sensor size to this list?

Duh! Of course. How did I forget that? I think I'll take a nap!

 

[chutestrate]

Thank you Thank you everyone for taking the time to respond to my questions. I'm taking a break from this. I've been chasing this concept for a couple of weeks, and it's just not clearing up. I'm ok with the aperture/fstop part of dof. The other ones I'm hitting the wall. Maybe I've just backed myself into a corner and don't see the explanations for what they are.

At the suggestion of a few people I did do an experiment of setting up small objects and trying different distances, I kinda get that. Buuuuut, the focal length. Fugeeet about it...I saw more dof changes with different apertures than anything with the focal length which probably means I was doing something incorrectly when I was setting up my test shots. Dang this whole concept has shaken my confidence on taking pictures. Beginning to question every decision now.

 

[BackToNature1]

Thank you Thank you everyone for taking the time to respond to my questions. I'm taking a break from this. I've been chasing this concept for a couple of weeks, and it's just not clearing up. I'm ok with the aperture/fstop part of dof. The other ones I'm hitting the wall. Maybe I've just backed myself into a corner and don't see the explanations for what they are.

At the suggestion of a few people I did do an experiment of setting up small objects and trying different distances, I kinda get that. Buuuuut, the focal length. Fugeeet about it...I saw more dof changes with different apertures than anything with the focal length which probably means I was doing something incorrectly when I was setting up my test shots. Dang this whole concept has shaken my confidence on taking pictures. Beginning to question every decision now.

Depth of Field, Part I: The BasicsBy Todd Vorenkamp | Tue, 07/28/2015

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www.bhphotovideo.com

 

[Michael Fryd]

Thank you. I"m shooting in raw and jpeg and no cropping. I had it at 400mm but couldn't set the image as I wanted. I wanted to capture the reflection, and bird on the log. Just seemed a cool composition. I am definitely learning about needing to check images before I leave a site. I took one today that I am unhappy with the focus. It was a good shot, and I can't use it.

You might want to try manual focus. Put the camera on a tripod, and using the rear screen, zoom to point you want in focus. Then manually adjust the focus until it appears sharpest. If you are not sure, take a few shots varying the focus just a little bit for each.

A others have mentioned, in your same image, it looks like the camera is focused on some leaves in the background. When focused on the background, your depth of field is not deep enough to cover as much of your subject as you would like.

I think you need to resolve the issue as to why the camera is not focused where you want it to be (possibly on the bird's eye). You may also wish to stop down a little to increase depth of field. To compensate you may need some combination of longer shutter speed, and/or higher ISO.

If you can estimate how far you were from the bird, and the range of distances you want in focus, an online depth of field calculator will help you determine what sort of f/stop will give you your desired depth of field.

.

There's been a lot of talk of how focal length affects f/stops (all other things being equal). The answer is that it depends on what you mean by keeping all other things equal, as it literally can't be true. For instance, if you keep the same f/stop, then you have changed the aperture diameter. If you keep the same subject distance, then you have changed the framing. When you change the focal length, other things always change, and reasonable people can disagree on what should be kept equal (and often the answer depends on context.

For instance, consider a 50mm lens on a 2X crop body vs. a 100mm lens on a full frame. If you keep the same f/stop, the full frame will have a shallower depth of field (and less noise). If you keep the same aperture diameter, both yield the same depth of field (and same image noise). One can make a reasonable case for either one being the obvious choice for "everything else being equal".

The autofocus is excellent with this camera. It’s not a $200 old DSLR. My approach with the R7:

Plan A: Input the right settings and let the AF do its work.

Plan B: (rare instances where plan A isn’t working): Use single point focus without subject tracking and tell it where to focus.

Plan C: Manual focus.I’ve never needed to resort to this. I have taken only about about 10K photos in the the 3 months I’ve been using the R7. So I say this with a moderate (not huge) amount of experience.

From what I have gathered (and I could be wrong), the OP wanted the camera to focus on the bird, with enough depth of field to get the foreground and background also in focus. The OP had the aperture set to f/8 in the belief that it would give him sufficient depth of field.

The first issue is that the camera did not focus on the bird. I agree that this could easily be the result of various camera settings. It is quite plausible that fine tuning the camera settings would have gotten the camera to focus on the bird.

As to the belief that f/8 should have resulted in everything in focus, that can be chalked up to a misunderstanding of how depth of field works. Depth of field is based on many factors, Aperture is just one of them. One cannot blindly assume that f/8 will always yield a deep depth of field.

 

[Nick on the Baltic]

If you've got aperture, that's the most important parameter (IMO) . Put the rest on the back burner in your mind and take some photographs. Maybe think a bit more about composition generally. Sooner or later you'll have an "aha" moment about DoF. Main thing is have fun taking photos.

 

[FrancoD]

The OP said he was using the 18-150 lens, so I trusted that.

I agree that the factors you listed could also be an issue given the subject of a bird on a lake.

If you are using a computer (not a phone...) you can put the mouse pointer over the photo and you will see the data right there.

 

[Michael Fryd]

Thank you for replying. To be honest much of the discussion is way over my head. Aperture vs f-stop, formulas, etc. Really doesn't make any sense to me. Hell, I'm struggling with the idea of a forward and rear zone of dof. How does one take that into account when taking a picture.

The calculators aren't really helping yet. I don't know how the data im getting translates back to an image to help me make better decisions.

Forget the formulas, but remember that depth of field is based on many factors, not just aperture.

The general rule is that if you stop down, you increase depth of field. However, stop down too much, and nothing looks sharp due to diffraction blur. Stopping down also reduces the light reaching the sensor. This results in a noisier image (unless you compensate by using a longer exposure (which increases motion blur.) Photography is often a balancing act.

Another rule of thumb, is that with long telephoto lenses, depth of field is often not nearly as much as you might like.

Someone suggested that you embrace this. Make the artistic choice of shallow depth of field. This may give you a good looking shot, although not what you originally had in mind. Sometimes you need to go with the image you can get, rather than the image you want.

.

In terms of forward and rear depth of field, this refers to the fact that the depth of field (the range of distances that appear to be in focus), are often not centered around the focus distance. You can ignore that when working out ballpark figures of depth of field. Frankly, at this point you might be more concerned with whether the depth of field is on the order of inches or feet, not how close it is to being centered around the focus difference.

.

Basically, you just need to get a feel for general size of depth of field. I still suggest you start with the online calculators.

.

When you took your sample photo, about how far were you from the bird? 10 feet, 50 feet, 100 feet? You don't need to know exactly, just something close (the closer the better).

Next you need to think about what range you want to be in focus. Assume that this will be centered on the focus distance. Do you need a foot in front/behind the bird? 5 feet? 10 feet?

You should know what kind of camera you have and what focal length you used.

Now you have enough to use the calculators. Enter the focus distance, focal length and camera type. Now you can play around with the f/stop setting, and the calculator will tell you how much depth of field you have. If the calculator tells you you have 12 inches, and you need 12 feet, then you know you need a smaller aperture.

By trying different apertures, you will find what aperture is needed to get your desired depth of field. This will be an approximation, as the values you entered were estimates.

If the calculator tells you that f/32 is required, then you know that f/8 won't get you what you want.

Yes, this is a pain, but then photography is not trivial. Getting sufficient depth of field does require a little bit of playing around to get a fell for what you need.

 

[chutestrate]

Thank you. I"m shooting in raw and jpeg and no cropping. I had it at 400mm but couldn't set the image as I wanted. I wanted to capture the reflection, and bird on the log. Just seemed a cool composition. I am definitely learning about needing to check images before I leave a site. I took one today that I am unhappy with the focus. It was a good shot, and I can't use it.

You might want to try manual focus. Put the camera on a tripod, and using the rear screen, zoom to point you want in focus. Then manually adjust the focus until it appears sharpest. If you are not sure, take a few shots varying the focus just a little bit for each.

A others have mentioned, in your same image, it looks like the camera is focused on some leaves in the background. When focused on the background, your depth of field is not deep enough to cover as much of your subject as you would like.

I think you need to resolve the issue as to why the camera is not focused where you want it to be (possibly on the bird's eye). You may also wish to stop down a little to increase depth of field. To compensate you may need some combination of longer shutter speed, and/or higher ISO.

If you can estimate how far you were from the bird, and the range of distances you want in focus, an online depth of field calculator will help you determine what sort of f/stop will give you your desired depth of field.

.

There's been a lot of talk of how focal length affects f/stops (all other things being equal). The answer is that it depends on what you mean by keeping all other things equal, as it literally can't be true. For instance, if you keep the same f/stop, then you have changed the aperture diameter. If you keep the same subject distance, then you have changed the framing. When you change the focal length, other things always change, and reasonable people can disagree on what should be kept equal (and often the answer depends on context.

For instance, consider a 50mm lens on a 2X crop body vs. a 100mm lens on a full frame. If you keep the same f/stop, the full frame will have a shallower depth of field (and less noise). If you keep the same aperture diameter, both yield the same depth of field (and same image noise). One can make a reasonable case for either one being the obvious choice for "everything else being equal".

Michael, what do you mean by this statement? I'm not that well versed in the teminology. If I'm changing the fstop in my mind I'm changing the the hole in the lens, and I also call it an aperture. At this point in my confused my peabrain aperture and fstop are the same thing.

 

[Nick on the Baltic]

If I'm changing the fstop in my mind I'm changing the the hole in the lens, and I also call it an aperture.

correct. But decreasing the f-stop (e.g. f/4 -> f/2.8) increases the aperture.

At this point in my confused my peabrain aperture and fstop are the same thing.

They are related, but not the same. The f-stop is the focal length of the lens divided by the aperture diameter. Looking at it another way, the aperture diameter is the focal length divided by the f-stop:

f-stop = f / d

f = d x f-stop

d = f / f-stop

So at a given f-stop, a 200mm lens will have a larger aperture than a 50mm lens (four times the diameter).

 

[chutestrate]

If I'm changing the fstop in my mind I'm changing the the hole in the lens, and I also call it an aperture.

correct. But decreasing the f-stop (e.g. f/4 -> f/2.8) increases the aperture.

At this point in my confused my peabrain aperture and fstop are the same thing.

They are related, but not the same. The f-stop is the focal length of the lens divided by the aperture diameter. Looking at it another way, the aperture diameter is the focal length divided by the f-stop:

f-stop = f / d

f = d x f-stop

d = f / f-stop

So at a given f-stop, a 200mm lens will have a larger aperture than a 50mm lens (four times the diameter

I don't understand where the one term stops and the other begins and how that would relate to anything I'm doing as I'm trying to figure out dof. I do appreciate the attempt,

 

[FrancoD]

This is how Adobe explains the two :

"The f-stop explained.

F-stop is the term used to denote aperture measurements on your camera. The aperture controls the amount of light that enters the camera lens and it’s measured in f-stops. Along with shutter speed and ISO (sensitivity to light), aperture is the third fundamental component that makes up the exposure triangle in photography.

Not only does your f-stop setting or f-number, help you to get a proper exposure, it also helps establish the look and feel of your photo by determining the depth of field. “Unless you’re working with a whole lot of light or in very low light, your f-stop is usually more about style and how you want the photo to look than about necessity,” says photographer Nicole Morrison.

All things aperture.

The “f” in f-stop stands for thefocal length of the lens. While focal length itself refers to the field of view of a lens, f-stop is about how much light you allow to hit the sensor via the aperture opening. The aperture is the hole in the middle of the lens, made up of rotating blades that open to let in light when you press the shutter release. The diameter of the aperture determines how much light gets through and thus how bright your exposure will be."

Keep in mind that some here will disagree because they know better...

Note that most cameras have an A* (for aperture) setting but that of course is to set the f stop on the lens you are using.

* Canon calls it Av for Aperture value

 

[chutestrate]

This is how Adobe explains the two :

"The f-stop explained.

F-stop is the term used to denote aperture measurements on your camera. The aperture controls the amount of light that enters the camera lens and it’s measured in f-stops. Along with shutter speed and ISO (sensitivity to light), aperture is the third fundamental component that makes up the exposure triangle in photography.

Not only does your f-stop setting or f-number, help you to get a proper exposure, it also helps establish the look and feel of your photo by determining the depth of field. “Unless you’re working with a whole lot of light or in very low light, your f-stop is usually more about style and how you want the photo to look than about necessity,” says photographer Nicole Morrison.

All things aperture.

The “f” in f-stop stands for thefocal length of the lens. While focal length itself refers to the field of view of a lens, f-stop is about how much light you allow to hit the sensor via the aperture opening. The aperture is the hole in the middle of the lens, made up of rotating blades that open to let in light when you press the shutter release. The diameter of the aperture determines how much light gets through and thus how bright your exposure will be."

Keep in mind that some here will disagree because they know better...

Note that your camera probably has an A (for aperture) setting but that of course is to set the f stop on the lens you are using.

I ran across that explanation as well, and I just thought that Adobe explained aperture in a very poor way. Guess I was wrong, but I still see fstop as a way to measure aperture. You can't see the hole to say, " yeah that looks about right".

Ok, I finally have a specific question and if it's been covered already I apologize. Aperture/fstop of 2.8 on 2 different lenses is still 2.8 right? Will it let in the same amount of light in regardless of the focal length.

And if I am wandering away from my original question I'll stop. I'm trying to assemble this big jigsaw puzzle that all the responses have given me.

 

[FrancoD]

Take a look at this article :

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www.sulasula.com

this is about what I tried several time to explain , oh yes I did try....

 

[chutestrate]

Take a look at this article :

https://www.sulasula.com/en/wide-angle-wildlife-photography/

this is about what I tried several time to explain , oh yes I did try....

Is this related to your advice about how to approach a bird not looking directly at it?

 

[chutestrate]

i wish I could get close enough to some of the wildlife around here to use a wide angle.