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View Full Version : D.O.F? "Infront of focus point" vs "behind focus point"



mandonbossi
29-Sep-2011, 05:26
Hello, It has been a while since I have been on here and i am hoping that someone could please explain something to me.. I recently had a chance to play with a friends 8 x10 camera and his Nikon 300mm lens! Holy Moly! Truly an amazing thing to look through! My first time really looking through an 810.. Up until this point i have only ever used a 54.

The look I really seem to like of other photographers is a full body portrait, shot wide open on a fairly normal lens (300mm or so). I recently saw some of Alec Soths prints and they were really amazing! He is mainly who I am talking about with such portraits.. I have tried to achieve a somewhat similar look with 54 and the only lens I found that gave a close drop off in depth was the Xenotar 150mm 2.8 which I guess is similar to 300mm 5.6 on 810 format...

I have really struggled to achieve accurate focus when using this lens at wide open apertures.. I have given up on completely wide open and have settled for around f4 or so.. Still extremely shallow D.O.F. Still find it tricky when shooting people. Obviously when shooting 810, you have a much bigger negative to deal with but was just wondering how others dealt with this. I would presume if focus was off on a larger format, then it also becomes more noticeable as well?

So I'll get to the point raised in the heading.. I noticed in one of his shots (attached) that things seem to be more in focus in front of the focal point and they seem to rapidly drop off behind the focal point. This is all based on the assumption that he had focused on the girls eyes.. I have noticed a similar thing when taking my own photos with the Xenotar and the few I had done on 810. Do people ever focus "slightly" forward of what they are trying to get sharp? Or is that just dumb?

Hmmm, am not sure, would love to hear any opinions on this?

Best Regards

Mandon

mandonbossi
29-Sep-2011, 05:27
Sorry about that, here is the link. You should be able to zoom in on it.

Thanks again.

http://alecsoth.com/photography/wp-content/gallery/niagra/2005_5zL0069_F.jpg

Paul Fitzgerald
29-Sep-2011, 07:16
"Do people ever focus "slightly" forward of what they are trying to get sharp? Or is that just dumb?"

I don't think so. Wide open on 8x10 has so little DOF and DOF that any difference between the GG and film holder will shift the focus enough to throw off the picture. Differences between holders or film bowing can do this also.

Brian Ellis
29-Sep-2011, 08:22
. . . Do people ever focus "slightly" forward of what they are trying to get sharp? Or is that just dumb? . . . would love to hear any opinions on this?

That's a fairly common practice when trying to maximize depth of field. I did it with a 35mm or medium format film cameras (I use a different system of focusing a LF camera). Today with a digital camera I'm more likely to make multiple exposures while focusing at different points from near to far in the scene and then blending and merging the exposures in Photoshop.

johnielvis
29-Sep-2011, 08:39
could be using tilt too.....that's why you tilt..get the foreground in focus

jp
29-Sep-2011, 10:22
In that photo, if Soth aimed the camera down to get the composition, rather than keeping the camera straight and raising the back, the plane of focus would not be perfectly vertical and would be as pictured.

Older lenses like tessar rather than planar, or even triplets (which won't be so sharp) have a smoother in-out of focus range; doesn't drop out quite as fast, but still has a pleasing out of focus area.

Focus is 1/3 in front, and 2/3 in back, so focusing frontwards a bit will improve things in some circumstances. I'd say don't try to shoot it wide open, and find a lens that does what you want with the background.

mandonbossi
29-Sep-2011, 16:41
Hi, Thanks to everyone for all the responses, much appreciated! I feel like I may have confused myself with my last post and now upon readings others thoughts..

If i recall correctly, depth of field is greater in the latter 2/3 of an image (in a typical landscape image), hence the simplified rule of focusing roughly 1/3 into an image..

Does that mean that the latter 2/3 of an image are "sharper" than the first 1/3 or is it the other way around?
I thought it was the first option, is that correct?

In this image, at least in the area where focus initially starts to fall off, it seems the forward part of the image retains a sharper area than the area behind the subject..

If this is the case, I feel like maybe I should be focusing slightly behind the subject (if the area in front of the focus point is holding its sharpness better)

What do you think? Am I way off here?

Thanks again for all your comments and suggestions.

Best Regards

Mandon

ic-racer
29-Sep-2011, 17:12
Do people ever focus "slightly" forward of what they are trying to get sharp? Or is that just dumb?



If the thing you are focusing on is not the sharpest in the negative you have a film plane vs ground glass plane issue. The only reason to purposely focus on a point away from the point of interest is to make it blurry.

cowanw
29-Sep-2011, 17:15
If the thing you are focusing on is not the sharpest in the negative you have a film plane vs ground glass plane issue. The only reason to purposely focus on a point away from the point of interest is to make it blurry.

Unless you are using soft focus lenses, in which case you want to use the space either in front of or behind focu, depending on the lens.

mandonbossi
29-Sep-2011, 22:21
In response to IC-Racer, I have had my camera properly aligned to ensure that this is not the case and have shot stationary subjects with the 150mm Xenotar @ 2.8 and they have been sharp, so I have faith that this is not the issue... I guess the problem is, that I am dealing with people, who of course move.. So that is why I am trying to understand this problem in a way that incorporates this.. I realise that it is really dealing on the extremity side of things but think it must be achievable..

Maybe it is just a matter of more testing, some shot focused on the eyes, others a little behind..

Thanks again for the responses..

Anyone else have any other thoughts or suggestions?

Best

Mandon

Frank Petronio
29-Sep-2011, 22:40
I bet Alec Soth just ever so slightly messed up and she is at the edge of being in acceptable focus. He's not God, just anointed.

Outdoors, without a reference point or a solid wall, I think standing people's heads move 1-2" even when they are trying to stand still. It is like a tall building in the wind, or a tree, there is subtle movement no matter what.

Giving people a wall or corner or a chair helps provide a reference point and a way to physically rest against something static. Even a tree. Or a head rest.

Don't feel bad. Some people think they can shoot an Aero Ektar 172/2.5 wide open and hand held on a Speed Graphic and get perfect focus at portrait distances with that old rangefinder. Funny how rarely you see successful shots actually done that way....

In practice, a portrait done on 8x10 with a 300mm at f/8 or f/11 will still have a very nice shallow depth of field. For that matter a 150/5.6 lens on 4x5 will do well, negating the practical usefulness of those expensive 150/2.8s.

johnmsanderson
29-Sep-2011, 23:56
Does anyone find that rock really distracting?

Anyway, I'm going with Frank's assertion that 8x10 will give you much more shallow DOF in instances like this than 4x5.

-- edit If you look at the very bottom of the image it is slightly out of focus... that negates any tilt, yes?

Frank Petronio
30-Sep-2011, 04:26
That lone rock symbolizes the alienation and despair inherent in this situation, brought upon by the policies of the Republican Bush administration that treats young Mothers and infants as rocks themselves. Soth powerfully and poignantly exposes these subtle truths through out his work and you must be some sort of imbecile Neanderthal not to realize this.

(Thank goodness it's politically correct to still have Neanderthals open to being picked on since we can't use anybody else.)

;-p

I didn't say 8x10 gives you less depth of field. I do break a few laws sometimes but not the laws of optics.

What the original poster is saying, and we concur, is that a 150mm lens at f/2.8 used on a 4x5 camera has roughly the same field of view and depth of field as a 300mm lens used at f/5.6 on an 8x10 camera.

Using the same apertures with the 150mm lens on an 8x10 or the 300mm on a 4x5 -- the depth of field remains identical regardless of the camera size.

Like jp498 said, this is probably all from Soth pointing the camera down. Frankly he probably should have kept the camera level and dropped front standard, which would have preserved her isolation better. But he had one of those Phillips field cameras rather than a professional monorail so he may not have had the full range movements he really needed. Or he might have been in a hurry. Or he didn't care, since it is a minor point in an otherwise great picture of a rock.

johnielvis
30-Sep-2011, 05:44
building verticals are right on...therefore back is straight---lens is tilted.

jp
30-Sep-2011, 05:50
Speaking of Neananderthals.... It could also be a reference to Space Odyssey 2001 where the men learned to use rocks as destructive weapons. This rock has a long history of breaking car windows.

The rock represents her crack-head boyfriend who fathered the child and is missing in the photo. She is turning away from it/him a bit. I'm not going to be politically correct and suggest that this represents all men. Being like a rock is a good comparison in a completely different context.

OK, enough of that....

If the odd plane of focus is indeed intentional, perhaps it's because her feet are distracting; he got the toes in focus, and it would be a lot easier to focus on toes on the ground glass than other parts of the feet.

I'd think he was probably in a hurry as the baby was probably not cooperating, or there were people around outside the frame that were distracting.

Brian K
30-Sep-2011, 07:11
What is so amazing about that photo or the focus technique behind it? It looks like he used a longer lens wide open, probably a 360 on an 8x10. You can tell because the buildings behind her, while easily spaced at distances of 50 to 150 feet apart, don't look like they've shrink much with distance or perspective. What is so hard about that? There's no special technique there. As for focus in front? How does one do that with then adding additional DOF to bring the subject in focus? That would bring the background in focus to a greater degree. No, you focus right on the subject and you shoot wide open.

As for being able to maintain focus wide open using an 8x10, there's no mystery there either. Just make sure that your GG aligns in exactly the same place as the film. You can test for this rather easily. And if you are concerned with 8x10 drooping in the holder, then just tape it in. And focus carefully with a loupe.

And the lens is not tilted. Because if he were to tilt the lens back in order to diminish the focus towards the distance, then the top of the woman, would be in a different plane of focus than her feet, and in order to get both in, he'd again need to rely on greater DOF which would defeat the purpose. In looking at the image I'd say that both the front and rear standards are parallel and level.

Noah A
30-Sep-2011, 07:28
For wider scenes like landscapes/cityscapes, I may manipulate the focus point in order to put the depth of field where I want it. Sometimes I'll focus in front of what is really the main subject so that the foreground isn't too soft.

For portraits, especially ones at larger apertures with big film, I always focus on the eyes.

I don't know why the foreground is sharp in this photo, but I suspect the focus point was a bit in front of the subject (who very well may have moved slightly, she's holding a kid after all). The result is that the subject is sharp but more of the excess DOF is in front of the subject. If you really need to know if it was intentional, you'd have to speak with the photographer. I heard him speak once by the way, he's a nice guy and has a genuine passion for photography.

As Frank said, even a 150/5.6 or 210/5.6 can do the job, there's no need for superfast lenses unless you really want things to get fuzzy. You'd be better off with a sharp f/5.6 plasmat.

This photo doesn't really have all that shallow of a DOF. Check the foreground. But the background is nice and soft since it's so far away. The framing has more to do with the look of the photo than any crazy fast lens. I'd almost guarantee this was shot with a 300mm, and I'd bet it was not wide-open.

Brian K
30-Sep-2011, 07:28
That lone rock symbolizes the alienation and despair inherent in this situation, brought upon by the policies of the Republican Bush administration that treats young Mothers and infants as rocks themselves. Soth powerfully and poignantly exposes these subtle truths through out his work and you must be some sort of imbecile Neanderthal not to realize this.

(Thank goodness it's politically correct to still have Neanderthals open to being picked on since we can't use anybody else.)

;-p

I didn't say 8x10 gives you less depth of field. I do break a few laws sometimes but not the laws of optics.

What the original poster is saying, and we concur, is that a 150mm lens at f/2.8 used on a 4x5 camera has roughly the same field of view and depth of field as a 300mm lens used at f/5.6 on an 8x10 camera.

Using the same apertures with the 150mm lens on an 8x10 or the 300mm on a 4x5 -- the depth of field remains identical regardless of the camera size.

Like jp498 said, this is probably all from Soth pointing the camera down. Frankly he probably should have kept the camera level and dropped front standard, which would have preserved her isolation better. But he had one of those Phillips field cameras rather than a professional monorail so he may not have had the full range movements he really needed. Or he might have been in a hurry. Or he didn't care, since it is a minor point in an otherwise great picture of a rock.

Frank, I'm amazed that people find these types of "portraits" to be of any interest. What is the difference between this image and a snapshot done with a P&S done by someone not making any claims of being an artist? Let's be realistic here, I think there's little doubt that anyone on LFF could do this image, and has in fact already done it hundreds of times before, just most often with small cameras.....

jb7
30-Sep-2011, 08:01
What is the difference between this image and a snapshot done with a P&S done by someone not making any claims of being an artist?

Hanging it in a gallery would be the main difference, I suppose-
I find it engaging, I'd like to see it in the context of an exhibition, or better yet, in the context of a private collection, on display.

It would be impossible to do this with a P&S, but you know that, of course-

Regarding the focus, I'd say it was a little bit of front tilt-
That, or sloppy parallelism...

Brian K
30-Sep-2011, 08:08
Hanging it in a gallery would be the main difference, I suppose-
I find it engaging, I'd like to see it in the context of an exhibition, or better yet, in the context of a private collection, on display.

It would be impossible to do this with a P&S, but you know that, of course-

Regarding the focus, I'd say it was a little bit of front tilt-
That, or sloppy parallelism...

JB the only thing that P&S couldn't do here is the limited DOF. But the content of the image is not exactly a stretch for even the most novice photographers.

aduncanson
30-Sep-2011, 08:41
Focus is 1/3 in front, and 2/3 in back, so focusing frontwards a bit will improve things in some circumstances. I'd say don't try to shoot it wide open, and find a lens that does what you want with the background.

Like many other rules taught in photography classes "1/3 in front and 2/3 in back" should be recognized as a rule of thumb that conveys some useful guidance, but is not technically true.

Consider the familiar situation where one focuses on the hyperfocal distance. The depth of field then extends from half the hyperfocal distance to infinity, so the depth of field behind the subject is infinitely greater than that in front of the subject. As you focus at closer distances (particularly when depth of field is shallow) the depth of field in front of the subject becomes nearly equal to that behind. At 1:1 the depth of field is essentially equal in front of and behind the subject.

What seems to be going on (I have not done the math to prove this) is that the depth of field is approximately equal in front of, and behind the subject when measured by the difference in diopters (1/meters.)

In the case of focusing at the hyperfocal distance (h), this relationship is exact. The focus is at 1/h diopters, the far limit of depth of field is at 0 diopters, the near limit is at 2/h diopters. The differences in focus from the subject to the near and far limits of depth of field are both 1/h diopters.

Computation shows that the equality also holds to within a few hundredths of a diopter at 1:1.

If one makes a bunch of assumptions about the example Soth photo (i.e. 8x10 format, 300mm lens, 3.3 meter subject distance, f/16, CoC = 0.1mm) then the calculated depth of field is 152mm in front of the subject and 169mm behind. Measured in diopters, both limits are almost exactly equally removed from the actual focus point.

Brian K
30-Sep-2011, 10:08
Using an online DOF calculator for 8x10

300mm lens, focused at a subject 20 feet away

at f 5.6 near focus limit is 18.6', far focus limit is 21.6'---- 2.93' of DOF
at f8 , 18.1 / 22.3'--- 4.17'
at f11, 17.5/ 23.4'--- 5.96'

Using a 360mm lens focused at 24 feet

At f8, 22.1/ 26.3'---- 4.15'
at f11, 21.4/ 27.3'---5.92'
at f 16, 20.5 / 29'--- 8.49'

Do we really need tilts or some extraordinary technique for this effect?

ic-racer
30-Sep-2011, 11:04
In response to IC-Racer, I have had my camera properly aligned to ensure that this is not the case and have shot stationary subjects with the 150mm Xenotar @ 2.8 and they have been sharp, so I have faith that this is not the issue... I guess the problem is, that I am dealing with people, who of course move..

Ahh yes. Thus the advantage to those with the twin lens view cameras ;)

So, perhaps the question is to anticpiate subject movement during the time the film holder is placed and the last time you see the image on the ground glass.

jb7
30-Sep-2011, 11:25
I think he's entitled to work whatever way he chooses-
I would also imagine that the focus range would be noticably shallower on a 4' print than those online depth of field calculations suggest.

I think the picture needs to be seen as part of a larger body of work, and for all I know, he might choose a point and shoot when he considers it appropriate.

mandonbossi, thanks for pointing me in the direction of that picture, it made me investigate a bit further-
I'd like to see the show-

http://alecsoth.com/photography/projects/niagra/

Frank Petronio
30-Sep-2011, 11:28
Joseph - Alec Soth is well-known in America as an "artist", not to be confused with a mere photographer. He sells large prints for many tens of thousands of dollars.

Not as much as Peter Lik but to better quality customers ;-p

jb7
30-Sep-2011, 11:33
Thanks Frank-

Was good to get my head out of the sand for a moment...

Very engaging website too, though I've only seen it on my phone so far-
Must have a proper look later

Bill_1856
1-Oct-2011, 10:23
If Ansel and Edward got so bent-out-of-shape about the predominance of Pictorialism, wonder what they would say about THIS crap? Here, even the nudes suck (if you'll pardon the simile)!

K. Praslowicz
4-Oct-2011, 17:56
In practice, a portrait done on 8x10 with a 300mm at f/8 or f/11 will still have a very nice shallow depth of field. For that matter a 150/5.6 lens on 4x5 will do well, negating the practical usefulness of those expensive 150/2.8s.

This photo (http://www.kpraslowicz.com/photo/storm/) was taken with a 150/5.6 stopped down a 1/3rd or 2/3rds from open if you want an example. While I don't think it is as yummy of a transition like you'd see in the works of the 8x10'ers who shoot portraits in this style (Soth, Sternfeld, Greg Miller), it still not too bad.

Brian Ellis
4-Oct-2011, 18:23
"Does that mean that the latter 2/3 of an image are "sharper" than the first 1/3 or is it the other way around?
I thought it was the first option, is that correct? "

It means the circles of confusion become unacceptably large sooner in front of the plane on which you're focusing than behind.

cyrus
4-Oct-2011, 19:13
The effect u see is from tilt

johnmsanderson
5-Oct-2011, 04:18
Really like that example Praslowicz.

K. Praslowicz
5-Oct-2011, 06:34
Really like that example Praslowicz.
Thanks.

mandonbossi
7-Oct-2011, 19:16
Hi everyone, Sorry about the delay in responding, was down the coast for a bit without internet access... Thanks so much to everyone for sharing their thoughts and good to see it has raised some healthy discussion... Thanks to K. Praslowicz for sharing that photo as well, it is great and yes, it is somewhat the look I am going for.. I do really like it when things get really, really shallow and forgot to link to some of Richard Renaldi's work as an example of this...

I especially like it when it is quite evironmental and the figure is fairly small but the background is really quite out of focus... Something I think you can only really achieve with 8x10 and to a lesser extent a fast 5x4..

I am still a little confused as to the rule of D.O.F. It seems that the general rule is that the latter 2/3 in an image are generally sharper than the first 1/3, hence the rule of focusing 1/3 in (for landscapes for example). In these examples, it seems to me that sharp focus is kept better in front of the focal plane (assuming that the camera is levelled, no tilts etc etc).

This has also been my experience in shooting with the Xenotar at anywhere from f2.8 to f4...

Does anyone else see this? If so, doesn't this contradict the general rule?

Apologies if I am missing something really obvious here, it is possible..

Any thoughts or suggestions are once again always appreciated!

Cheers Mandon

P.S Thanks to whoever linked to Greg Millers work, awesome stuff! Although I think by looking at his, he is getting really creative and manipulating the plane of focus for a lot of his shots... Which opens up a whole different discussion..

mandonbossi
7-Oct-2011, 19:20
One more... In this example, it seams to my eye there is a sharp area in front of the subject but it seems to fall off very quickly behind him.. I know it is a bit hard to see with such small images but I have one of his books and it does show this effect a lot better..

OK, thanks again.

Mandon

cowanw
8-Oct-2011, 06:24
I think the 1/3 2/3 rule is
accurate for shots where the subject is positioned at 1/3 of the hyperfocal distance
or is
for shots with Infinity in focus and the horizon high up on your GG: focus 1/3 of the way up the GG.
These are 2 different rules

K. Praslowicz
8-Oct-2011, 07:28
Apologies if I am missing something really obvious here, it is possible..

I think this is the obvious point being missed. In my experience regarding large format, getting everything in sharp focus is difficult. Not trying to squeeze every last bit of DOF out of a lens isn't. You might very well be over thinking this.

http://www.youtube.com/watch?v=SwEAxrmBz64 There is a line in that video where he says the first thing he does is focus on the eyes. I would not be surprised one bit if he puts most of his effort on composing the scene and working with the sitters, then just focuses on the eyes and shoots at a moderate f-stop, and the 8x10 format does the rest.

aduncanson
10-Oct-2011, 06:59
Please look at the two graphs attached below representing calculated data and please do not overlook that the two charts have very different horizontal and vertical scales.

These are an attempt to answer the question of how de-focus of the image changes with object distance, So (that is S sub O). In both charts the horizontal axis is the subject distance and the vertical axis is Circle of Confusion, CoC. CoC here is the size of the actual de-focused point rather than the maximum acceptable CoC that is used as the sharpness criteria in depth of field calculations. However, in both charts there is a horizontal blue line representing the CoC typically taken as the sharpness criteria (negative diagonal / 1780 or 0.176mm per Professor Bigler.)

The first chart was calculated to be typical of the examples you have posted with the assumption that the photo was taken with an 8x10 negative and a 300mm lens at f/8 and focus on the human subject at 12 feet. The second chart reflects the same camera, lens and f-stop, but now focused at the hyperfocal distance, 210 feet.

What is immediately evident and interesting is that the CoC is not symmetric about the point of focus, but goes to infinity on the near side while asymptotically approaching a maximum (the asymptote) on the far side. In the hyperfocal case that asymptote is the CoC sharpness criteria.

Not quite so evident is that if you shift your focus to the near side of the subject, you will gain that bit of depth of field to the near side, and lose it on the far side, but also you will raise the asymptote or maximum CoC approached at infinity.

The first chart also illustrates what I said earlier, that when there is very narrow depth of field, that small part of the subject range where the CoC is less than the chosen sharpness criteria, (that is, within the limits of DoF), begins to be nearly symmetrical about the focus point, and so in that case the DoF is divided nearly equally ahead of, and behind the subject.

I hope this helps.

mandonbossi
11-Oct-2011, 17:49
Thanks so much to everyone who has contributed to this one, it is really appreciated! I must admit some of the more technical information given was a little over my head, so will have to learn it through trial I think.. I will try and absorb all of the information and see if I can crack the code!

Thanks again..

Best Regards

Mandon

K. Praslowicz
1-Jan-2012, 08:06
I would not be surprised one bit if he puts most of his effort on composing the scene and working with the sitters, then just focuses on the eyes and shoots at a moderate f-stop, and the 8x10 format does the rest.

Finally got around to shooting like this on 8x10, just to see. ~15 foot subject distance with a 360mm Fujinon. First one is f/8, second is f/22. I just focused on the eyes and let it rip. 22 seems to much, 8 looks delicious.

http://img.kpraslowicz.com/index5/bwd-8x10.jpg (http://img.kpraslowicz.com/f/bwd-8x10.jpg)

http://img.kpraslowicz.com/index5/bwd-8x10-2.jpg (http://img.kpraslowicz.com/f/bwd-8x10-2.jpg)