Help me understand DOF a little better

DonnieZ · Oct 20, 2015

So I'm trying to understand the relationship between DoF, Focal Length, and focus on DoF - not only to expand my knowledge, but for an upcoming photo project I've got brewing. So I've got my wife somewhat on board with doing a private boudoir shoot in the next month or so.

As a hobbyist and after doing some reading and experimenting - it seems as though I know some about this subject but I get confused a bit when I put it in practice.

For example, I'm trying to get a shot like this:

Pretty much same setup, however the bed in my case is probably 2 feet closer to the door.

I set up the shot to play around with (no wife involved just yet..) and I'm trying to get the door handle in focus, but really blow out the rest of the bedroom - but at least the subject that may be laying on the bed.

I tried with the Sigma 17-50 2.8. AF on the brassiere - and whether I'm at 17mm or 50mm shooting at f/2.8 if I stand 3 or so feet back from the door the brassiere is in focus, but the bed is way more in focus than I'd like. If I get a little closer to the brassiere, I can then get the background blown out as I like - however due to the way the house is configured I'm not sure I can get as much in frame as I'd like without a much wider lens to get the DoF I'm looking for.

My perception that at a reasonable focus distance (3 feet or so) shooting at f/2.8 I should be able to get the subject in focus and the background much more out of focus. However, adjusting focal length had little effect - getting closer to the subject and thus getting a closer focus distance seemed to do the trick. What's more important here - focal length or focus distance? Given the same aperture (say f/2.8) will a shorter focal length or longer focal length give me shallower depth of field?

I didn't bust out the primes, but I have a 35 f/1.8 and a 50 f/1.8 but I think that might be too much telephoto for this. I found out the local photo store rents glass for pretty cheap - I can get a 14-24 from Friday to Monday morning for $35. I might try that, but I'd like to understand this concept a little better.

I can post some samples if requested.

Thanks for any advice!

Don Kuykendall_RIP · Oct 20, 2015

The larger the aperture (!.8, 2.8) the smaller the DOF
The shorter the focal length the greater the DOF 18mm will have more DOF than 50mm.
The closer you are to the subject the smaller the DOF

I think this calculator will help you understand the relationships a lot better. Plug in different numbers and see the results.

Online Depth of Field Calculator
I have this app on my iPhone for finding Hyperfocal distance

Bob Blaylock · Oct 21, 2015

DonnieZ said:
So I'm trying to understand the relationship between DoF, Focal Length, and focus on DoF - not only to expand my knowledge, but for an upcoming photo project I've got brewing. So I've got my wife somewhat on board with doing a private boudoir shoot in the next month or so.

As a hobbyist and after doing some reading and experimenting - it seems as though I know some about this subject but I get confused a bit when I put it in practice.

For example, I'm trying to get a shot like this:
View attachment 183984

Pretty much same setup, however the bed in my case is probably 2 feet closer to the door.

I set up the shot to play around with (no wife involved just yet..)…

Who's that on the bed, then?

DonnieZ said:
…and I'm trying to get the door handle in focus, but really blow out the rest of the bedroom - but at least the subject that may be laying on the bed.

I tried with the Sigma 17-50 2.8. AF on the brassiere - and whether I'm at 17mm or 50mm shooting at f/2.8 if I stand 3 or so feet back from the door the brassiere is in focus, but the bed is way more in focus than I'd like. If I get a little closer to the brassiere, I can then get the background blown out as I like - however due to the way the house is configured I'm not sure I can get as much in frame as I'd like without a much wider lens to get the DoF I'm looking for.

My perception that at a reasonable focus distance (3 feet or so) shooting at f/2.8 I should be able to get the subject in focus and the background much more out of focus. However, adjusting focal length had little effect - getting closer to the subject and thus getting a closer focus distance seemed to do the trick. What's more important here - focal length or focus distance? Given the same aperture (say f/2.8) will a shorter focal length or longer focal length give me shallower depth of field?

I didn't bust out the primes, but I have a 35 f/1.8 and a 50 f/1.8 but I think that might be too much telephoto for this. I found out the local photo store rents glass for pretty cheap - I can get a 14-24 from Friday to Monday morning for $35. I might try that, but I'd like to understand this concept a little better.

I can post some samples if requested.

Thanks for any advice!

Let's see if I understand correctly, as much as you've said so far…

The brassiere, hanging on the doorknob, you want in sharp focus; the bed and the woman thereon, you want out-of-focus. You used a 17-50mm ƒ/2.8 zoom lens to take the picture shown here, and the bed/woman is in much sharper focus than you want.

Am I right, so far?

Much is missing. You mention having taken pictures at 17mm and at 50mm, but have not indicated at which focal length the picture you've shown was taken. I assume this picture represents, more or less, the field of view that you want.

If you get a view that is acceptable with the lens zoomed at 50mm, then your 50mm ƒ/1.8 prime should give about that same field of view, and allow you a wider aperture, with less depth of field. If the 50mm is too narrow, then perhaps your 35mm will be fine.

You also did not say what camera you're using, or what settings you're using on the camera.

For future reference, if you upload a picture that is larger than 1000 pixels on the longest side, this site will scale it down to 1000 pixels,and in so doing, will strip all the EXIF data therefrom. Upload a picture that is 1000 pixels or smaller, and the site will keep it unmolested, EXIF data and all. The EXIF data can help the rest of us to see what settings you used, and to better help you.

In general…

The longer the focal length, the narrower the depth of field.
The wider the aperture (the smaller the ƒ/ number) the narrower the depth of field.
The closer the point of focus, the narrower the depth of field.

First of all, it seems we need to make sure that whatever lens you're using, that you start with it at its widest aperture. Whatever your camera is, however it it takes settings, you should probably set it on aperture-priority exposure, if not full manual; and make sure it's set to the largest aperture setting available. You'll want to make sure that the camera is focusing on the bra, not on the bed/woman. If possible, moving the camera closer to the bra will also help to put the more distant subjects more out of focus, as long as the focus remains on the bra; even if that means going to a shorter focal length (which increases depth of field) you'll still narrow the depth of field by focusing closer, and the distant bed/woman will be farther out of the focus range.

In the example picture that you posted, it appears to me that the lens is stopped down significantly from its maximum aperture, and it looks like the camera was focused somewhere farther forward than the bra. The woman on the bed looks like she is in sharper focus than is the bra.

DonnieZ · Oct 21, 2015

Thanks for the replies

The brassiere, hanging on the doorknob, you want in sharp focus; the bed and the woman thereon, you want out-of-focus. You used a 17-50mm ƒ/2.8 zoom lens to take the picture shown here, and the bed/woman is in much sharper focus than you want.

Am I right, so far?

Read more: http://nikonites.com/photography-q-...derstand-dof-little-better.html#ixzz3pCuFHvqn

.

Yes.

Much is missing. You mention having taken pictures at 17mm and at 50mm, but have not indicated at which focal length the picture you've shown was taken. I assume this picture represents, more or less, the field of view that you want.

I'm unsure as to the focal length of the picture shown - it's somewhat of a sample image I found doing Google image search, and there's no EXIF data embedded.

As for camera settings....

I was shooting in aperture priority with the aperture set at f/2.8. Had camera set to AF on the brassiere. Doing review on the camera screen, brassiere was very sharp and in-focus and bed was somewhat out of focus, but not as much as I'd have liked. Moving closer to the brassiere did provide the depth of field I was looking for, however did not provide the field of view I liked. It may look a little better once I get it on the PC and into Lightroom as well - I'm not sure at the moment.

It was a little late last night, and I made a lazy post without providing sample images I took. I'll have to get the raw files out of the camera and get a sample or two posted tonight when I get home.

Eduard · Oct 21, 2015

Take a look at this reference which may help too: http://nikonites.com/education/24044-reference-chart-shutter-speed-focal-length-aperture.html

skater · Oct 21, 2015

DonnieZ said:
Moving closer to the brassiere did provide the depth of field I was looking for, however did not provide the field of view I liked. It may look a little better once I get it on the PC and into Lightroom as well - I'm not sure at the moment.

You're doing the right thing by having the aperture wide open, but you need to use a lens with a shorter focal length to make it happen. Which one were you using? If it was the 50mm, try the 35mm.

Basically, a wider aperture shortens the area in which something will be in focus. Did that make sense? Imagine a ball a few feet from you. With a narrow aperture, the ball and everything around it will be in focus. With a wide aperture, a smaller part of the picture will be in focus, so presumably you'd focus on the ball and everything around it would be blurry.

I'm not sure if your 18-55 will have a wide enough aperture to create the effect you're looking for. You may need a different lens than you have in your kit (or, at least, than you have in your signature).

Don Kuykendall_RIP · Oct 21, 2015

Also when posting a photo that is not yours please provide the link to it and not just copy and paste. That is a copyrighted photo and belong to someone else

Sent from my iPhone using Tapatalk

DonnieZ · Oct 21, 2015

skater said:
You're doing the right thing by having the aperture wide open, but you need to use a lens with a shorter focal length to make it happen. Which one were you using? If it was the 50mm, try the 35mm.

Basically, a wider aperture shortens the area in which something will be in focus. Did that make sense? Imagine a ball a few feet from you. With a narrow aperture, the ball and everything around it will be in focus. With a wide aperture, a smaller part of the picture will be in focus, so presumably you'd focus on the ball and everything around it would be blurry.

I'm not sure if your 18-55 will have a wide enough aperture to create the effect you're looking for. You may need a different lens than you have in your kit (or, at least, than you have in your signature).

I have updated the signature - I shot these with a Sigma 17-50 f/2.8 in aperture priority set to f/2.8.

I understand the whole exposure triangle conceptually - I know that wider apertures will lead to a shallower depth of field for a given focal length and focus distance.

What I don't fully understand I guess is how focal length and focus distance plays into the equation. From my experimentation, it seems that focusing on something that is closer to the lens seems to lead to a shallower depth of field, or at least a depth of field that is much more out of focus behind the focal plane.

From the information I've been given here, it seems as though shorter focal lengths generally provide a larger depth of field for a given aperture and focus distance - is this correct?

DonnieZ · Oct 21, 2015

Don Kuykendall said:
Also when posting a photo that is not yours please provide the link to it and not just copy and paste. That is a copyrighted photo and belong to someone else

Sent from my iPhone using Tapatalk

Duly noted.

Daz · Oct 21, 2015

DonnieZ said:
From the information I've been given here, it seems as though shorter focal lengths generally provide a larger depth of field for a given aperture and focus distance - is this correct?

Here are 2 photos shot at 3.2 (I thought it was 2.8 but noticed it wasnt in Lightroom but same difference, one at 70mm one at 200mm) you can see the background is blurred the same, it all comes down to where you have the "in focus" item in the shot, the closer to the lens the more the background is blown out:

70mm

200mm

Now bring the controller closer at 200mm and you blow the background out

P.s sorry Exif isnt showing I cant work out why it wont come across from Flickr

Bob Blaylock · Oct 21, 2015

Daz said:
P.s sorry Exif isnt [sic] showing I cant [sic] work out why it wont [sic] come across from Flickr

I think the EXIF is only displayed if the image is uploaded directly to Nikonites, and is small enough (1000 pixels or less on the longest side) that Nikonites doesn't resize it.

Bob Blaylock · Oct 21, 2015

DonnieZ said:
So I'm trying to understand the relationship between DoF, Focal Length, and focus on DoF - not only to expand my knowledge, but for an upcoming photo project I've got brewing. So I've got my wife somewhat on board with doing a private boudoir shoot in the next month or so.
·
·
·
I set up the shot to play around with (no wife involved just yet..) and I'm trying to get the door handle in focus, but really blow out the rest of the bedroom - but at least the subject that may be laying on the bed.

I tried with the Sigma 17-50 2.8. AF on the brassiere - and whether I'm at 17mm or 50mm shooting at f/2.8 if I stand 3 or so feet back from the door the brassiere is in focus, but the bed is way more in focus than I'd like. If I get a little closer to the brassiere, I can then get the background blown out as I like - however due to the way the house is configured I'm not sure I can get as much in frame as I'd like without a much wider lens to get the DoF I'm looking for.

My perception that at a reasonable focus distance (3 feet or so) shooting at f/2.8 I should be able to get the subject in focus and the background much more out of focus. However, adjusting focal length had little effect - getting closer to the subject and thus getting a closer focus distance seemed to do the trick. What's more important here - focal length or focus distance? Given the same aperture (say f/2.8) will a shorter focal length or longer focal length give me shallower depth of field?

I didn't bust out the primes, but I have a 35 f/1.8 and a 50 f/1.8 but I think that might be too much telephoto for this. I found out the local photo store rents glass for pretty cheap - I can get a 14-24 from Friday to Monday morning for $35. I might try that, but I'd like to understand this concept a little better.

You inspired me to try to take some experimental shots, more or less trying to recreate your project.

I first tried using my stock 18-55mm on my D3200, and came to the conclusion that it's not possible, with that lens, to get what you seem to be seeking.

I don't have a 35mm prime, but I do have an ancient 50mm ƒ/1.4 prime, and I next tried using it, starting out with the same fear that you did that it would be “too much telephoto for this.” As it turns out, I was able to get a shot that seems to indicate that what you want to achieve might be possible with such a lens. In retrospect, I should probably have stopped down to ƒ/2 rather than using ƒ/1.4, to better simulate the depth-of-field that you'd get with your ƒ/1.8 lens, but the result is probably close enough.

This is, of course, only a test shot. If this was for real, I would have wanted to remove a lot of clutter from the scene, first; and get a woman to take the place as the background subject, rather than using myself, a bald, middle-aged man. But I think this is sufficient to show that what you seem to be trying to do is possible with equipment similar to what you have. You might have an easier time with your 35mm lens, getting the views to work out the way you want, than I did with my 50mm.

The doorway was approximately six feet from the camera, the brassiere and the nearest corner of the bed were both approximately eight feet away, and my face was approximately fifteen feet from the camera.

One other possible tip that occurred to me is that if you need to get the camera closer to the brassiere in order to get the view and the depth-of-field to work out, use a pair of panties instead of a bra. The panties would take up a smaller space, so you can get the camera closer and still have the entire garment in view. A bra really needs to be shown at full length to show clearly what it is, and I think it would ruin the composition if the frame cut part of it off.

So, in summary, my advice is to try using your 35mm, and consider using a pair of panties instead of a bra in order to allow yourself to get closer to that part of the image.

Bob Blaylock · Oct 21, 2015

Bob Blaylock said:
You inspired me to try to take some experimental shots, more or less trying to recreate your project.
·
·
·
This is, of course, only a test shot. If this was for real, I would have wanted to remove a lot of clutter from the scene, first; and get a woman to take the place as the background subject, rather than using myself, a bald, middle-aged man. But I think this is sufficient to show that what you seem to be trying to do is possible with equipment similar to what you have. You might have an easier time with your 35mm lens, getting the views to work out the way you want, than I did with my 50mm.

View attachment 184075

Having completed this experiment, and posted my result, some part of my brain kept on churning, and came up with a new inspiration based thereon.

I was trying to simulate the OP's idea of a type of a “boudoir” shot, having a few of the elements that he wanted, and having some other elements that really didn't belong, just to stand in for what I didn't have at hand—most prominently, in place of a sexy, skimpily-dressed woman, I used myself, a fully-dressed, shaved-headed middle-aged man.

Now I am thinking of a whole new genre, not really an opposite to a boudoir them, but something that stands at some other side therefrom. Not quite “beefcake” either. Something that suggests an ideal of masculinity, in a similar manner to how the “boudoir” theme suggests an ideal of femininity.

I guess I'll have to try some experiments tomorrow.

The elements that I intend to keep are a bed, with someone on it, and a much closer object in focus. But instead of a sexy, feminine theme, a masculine theme, perhaps not sexy in the same sense, but suggestive of a macho, hard working man. Instead of a brassiere hanging on the doorknob, a tool belt, loaded with the sort of tools that a man would use in the course of working in a manly profession. On the bed, myself, in work clothes, heavy work boots, and a hard hat. I guess there's still much to be figured out about how this theme would actually work. Obviously, a macho working man wouldn't be lounging on a bed while doing such work; but perhaps such a shot would be suggestive of one who has just finished up a day of hard work, and is now resting.

DonnieZ · Oct 22, 2015

So here's about the best field of view I could get with the desired look of the OOF areas using the 17-50. I did a little post in Lightroom with this image. Not entirely what I had envisioned in my mind, but I don't think it turned out horrible. If only I could get the entire brassiere in the frame and keep the OOF areas like they are, I think I'd have what I was trying to emulate. Note that this was taken at night with terrible CFL illumination. I'd hope to get these kinds of shots with window light in the daytime, though the ISO was only 800 on this shot.

I don't hate this, but I think the composition could be a little better with a wider lens.

What I'm envisioning now is that some of the stylistic shots I wanted to take might end up being problematic given the size of the room. I'm not sure I've got enough room to "move around" to get what I want in the frame.

Bob Blaylock · Oct 22, 2015

Bob Blaylock said:
Having completed this experiment, and posted my result, some part of my brain kept on churning, and came up with a new inspiration based thereon.
·
·
·
Now I am thinking of a whole new genre, not really an opposite to a boudoir them, but something that stands at some other side therefrom. Not quite “beefcake” either. Something that suggests an ideal of masculinity, in a similar manner to how the “boudoir” theme suggests an ideal of femininity.

And here is what I've come up with so far along that line.

I didn't really think I wanted the human subject as far out of focus as the OP does in his vision, so I was able to use a shorter, but slower lens—my ancient 28mm ƒ/3.5 instead of my 50mm ƒ/1.4. I don't know whether the idea really works or not, or whether it needs more work and refinement. I guess this can be considered to be a crude prototype or proof-of-concept of what I have in mind.

Daz · Oct 22, 2015

DonnieZ said:
What I'm envisioning now is that some of the stylistic shots I wanted to take might end up being problematic given the size of the room. I'm not sure I've got enough room to "move around" to get what I want in the frame.

If you cant get them at 17mm and you cant go back any further, you may need something like the 10mm 2.8 to get the shot you desire ?

I think if the door was open a little wider (so you can see the top of the bed, lines straightened) then it wouldn't be a bad shot, you would still get the "feel" that you are looking for, the only way to get the shot other than going to something like a 10mm may be to try at a hotel or someone elses house ?

Bob Blaylock · Oct 22, 2015

DonnieZ said:
View attachment 184089

So here's about the best field of view I could get with the desired look of the OOF areas using the 17-50. I did a little post in Lightroom with this image. Not entirely what I had envisioned in my mind, but I don't think it turned out horrible. If only I could get the entire brassiere in the frame and keep the OOF areas like they are, I think I'd have what I was trying to emulate. Note that this was taken at night with terrible CFL illumination. I'd hope to get these kinds of shots with window light in the daytime, though the ISO was only 800 on this shot.

I don't hate this, but I think the composition could be a little better with a wider lens.

What I'm envisioning now is that some of the stylistic shots I wanted to take might end up being problematic given the size of the room. I'm not sure I've got enough room to "move around" to get what I want in the frame.

From your EXIF data, I see that you had the lens zoomed to 34mm. It seems obvious enough that it seems stupid to ask, but did you try zooming out to shorter focal lengths? At shorter focal lengths, depth of field is greater, which isn't what you want, but I think you'd more than make up for that by being able to get closer to the bra.

If you have determined that 34mm is about the focal length with which you want to work, then you might as well switch to your 35mm prime. That way, you should get somewhat better image quality, and you've got more aperture range to work with.

And to repeat a suggestion I made before, consider using a pair of panties instead of a bra. Same idea, same “feel”, but the panties will be more compact, and easier to get entirely in the field of view.

skater · Oct 24, 2015

DonnieZ said:
I have updated the signature - I shot these with a Sigma 17-50 f/2.8 in aperture priority set to f/2.8.

I understand the whole exposure triangle conceptually - I know that wider apertures will lead to a shallower depth of field for a given focal length and focus distance.

What I don't fully understand I guess is how focal length and focus distance plays into the equation. From my experimentation, it seems that focusing on something that is closer to the lens seems to lead to a shallower depth of field, or at least a depth of field that is much more out of focus behind the focal plane.

From the information I've been given here, it seems as though shorter focal lengths generally provide a larger depth of field for a given aperture and focus distance - is this correct?

I wanted to answer this, but I hesitated because...I don't know the answer. I think there are a couple things going on.

Most zoom lenses, especially the less expensive ones, change aperture as you change the focal length. Naturally, changing aperture means that the depth of field will change, so it might seem like the two are related. But, you can buy a lens that keeps the same aperture throughout the entire zoom range (picture me drooling over the f/2.8 80-200), so I'm guessing the depth of field in those would remain constant regardless of the focal length. But I don't know for sure.

This is kind of what I was saying before: I always think of it as taking a picture of a long measuring tape stretching out in front of me. Some part of the tape will be in focus, and it might a full yard long, it might be most of the tape, or it could just be a few inches. The aperture controls which one of those it'll be. With my zoom lenses, that distance will change because the aperture changes as I zoom in and out. I don't know if the focal length alone (on a lens with a constant aperture) would change the depth of field too.

Don Kuykendall_RIP · Oct 24, 2015

skater said:
I wanted to answer this, but I hesitated because...I don't know the answer. I think there are a couple things going on.
so I'm guessing the depth of field in those would remain constant regardless of the focal length. But I don't know for sure.

Nope, It changes. The longer the focal length the les DOF you will get. With my 11mm there is tremendous DOF. With my 300mm I have to be very careful since it has very narrow DOF

Bob Blaylock · Oct 24, 2015

skater said:
I wanted to answer this, but I hesitated because...I don't know the answer. I think there are a couple things going on.

Most zoom lenses, especially the less expensive ones, change aperture as you change the focal length. Naturally, changing aperture means that the depth of field will change, so it might seem like the two are related. But, you can buy a lens that keeps the same aperture throughout the entire zoom range (picture me drooling over the f/2.8 80-200), so I'm guessing the depth of field in those would remain constant regardless of the focal length. But I don't know for sure.

Surely this hasn't always been true, and I don't know that it is now of most lenses, though you're probably right in characterizing it as being associated with lower-priced modern lenses.

Back in the days of manual-only cameras, I think it would have been prohibitively difficult to manage exposure properly with a zoom lens that changed aperture as it changed focal length, in the manner that some modern zooms do. This seems like something that could only be made workable by modern electronics that can keep track of this change and account properly for it.

I do know that the one zoom lens I have from the old days does not have this changing-aperture issue. I'd bet that very, very few, if any at all, from that period, do. But then back then, zoom lenses weren't terribly common. They were generally considered, then, to produce poorer image quality than comparable primes, so they were not terribly favored, then, by serious photographers who cared more about the quality of their images than of the convenience that a zoom offers. And now that I think about it, the convenience that is the advantage that a zoom lens has to offer would be completely negated if you had to manually account for the way the aperture changes on many modern zooms along with the focal length.

skater said:
This is kind of what I was saying before: I always think of it as taking a picture of a long measuring tape stretching out in front of me. Some part of the tape will be in focus, and it might a full yard long, it might be most of the tape, or it could just be a few inches. The aperture controls which one of those it'll be. With my zoom lenses, that distance will change because the aperture changes as I zoom in and out. I don't know if the focal length alone (on a lens with a constant aperture) would change the depth of field too.

A couple of my threads from a while back exist to illustrate this relationship. In each of these threads, with a different lens, I give a practical demonstration of how depth-of-field and other aspects of the image quality change with the aperture setting. It's probably worthwhile for the OP, @DonnieZ, to have a look at them…

Help me understand DOF a little better

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