Depth-of-field conversion with D-SLR?

[Byron Gale]

I understand that the size of the sensor in my D-SLR causes a lens to have 1.5x the normal "zoom"... i.e. a 50mm lens acts like 75mm.

Is there some conversion necessary to use the DOF scale on a lens, when mounted to a D-SLR? Or does the phenomenon not apply to that?

Byron

[Chuck S.]

Byron, I think the depth of field calculator at this website:

DOFMaster (http://www.dofmaster.com/dofjs.html)

would indicate that the answer is "Yes".

For instance, the calculator shows that a 55mm lens set at f/16 on a 35 mm film camera focused to 10 feet would have a total depth of field of 9.39 ft. The same camera mounted on a Canon 30D would have a depth of field of 6.61 feet.

[NMarti]

Thanks Chuck, that's something I absolutely cannot get my mind around. I have tried to understand it but it just doesn't sink into this old brain.:o

[Chuck S.]

Nancy, I don't have it totally surrounded either....:rolleyes:

Upon further thought, it may be that the lens marks are still an accurate depiction of the near and far focus limits, but that they represent different distances when the lens is mounted on a DSLR vs. a film SLR. Guess I'll have to try to do the math......


......NAH!!!!:D

[troush]

I just try to remember if I want more depth of field I've got to have a higher F# - like F22 or F32. If I don't care (using Bryan Petersen's method) - then use F8 or so. Then, if I want the background out of focus, use the lowest number for the lens - like F4. I don't do a lot of landscapes yet, so I'm usually more worried about what's behind my subject being in/out of focus, though..

-Trish

[Byron Gale]

Thanks for that link, Chuck!

Here's a shot of my lens markings, and the calculator's readings for my equipment.

http://www.pixentral.com/hosted/1zM8UjcxQWm9GLXIOYRRzO0IO6nLeU_thumb.jpg (http://www.pixentral.com/show.php?picture=1zM8UjcxQWm9GLXIOYRRzO0IO6nLeU)

It doesn't appear to be too far off, looking at the f22 marks, but when compared to the 35mm values for the same lens...

http://www.pixentral.com/hosted/11wpTmXnTan09tCqEtU6yzoQwV9D_thumb.jpg (http://www.pixentral.com/show.php?picture=11wpTmXnTan09tCqEtU6yzoQwV9D)

...and it is clear that things are different.

The DOF on the DSLR begins farther from the camera, and is shallower.

Byron

[NMarti]

Byron
That's a great demonstration.

Chuck
Me - math? :eek: I'll go for point and luck first!
I do sort of follow Trish's rule of thumb but always have to stop and say smallest number or largest number. I then go with large number - large behind, small number small behind (sort of like clothing sizes) :D

[Byron Gale]

I agree that the general rules apply, as Trish outlines. But if I am manually setting the focus to have my DOF's leading edge coincide with my subject... I guess I'm going to have to come up with a way of calculating things.

Or - I could just run through a few iterations on the web site, and make myself a cheat-sheet!! :p

(I would like to understand what's happening, though)

Byron

[bayhli]

This is all pretty new to me as well, but the DOF Master has settings that you adjust for the type of "film" (digital, film, APS etc) and the circle of confusion (digital, APS, 35mm etc) for your individual camera. My understanding is that there are differences and for accurate DOF calculations you need to be using the appropriate settings.

There is a lot of information at the DOFMaster site that would probably answer your questions Byron, most of which went over my head. :rolleyes:

... and people do indeed carry cheat sheets for their lenses, calculated from gizmos like the DOFMaster.

[Grant]

Oh my DOF is one the most confusing aspects of photography. While it would be nice to say that my camera has 35mm lens conversion of 1.6 therefore ...bla bla bla but it is much more complex than that. The formula is rather scary

f = D*M^2/2C(M+1)

M is in fact the inverse of you lens conversion so for 1.6 M is 1/1.6 or 0.625 but c changes with cameras for a 35 mm camera it is 0.025, for a dSLR it will be about 0.015, and for a itty bitty camera it will be maybe 0.005.

So now you are totally confused and so am I as it is not all that easy to get your head around.

In the old days of fixed lenses they engraved the scale onto the lens. The don't do that now because most lenses are zooms and those engravings wold be worthless.

There are two things you can do.

1) Download a good DOF calculator, there are a bazillion free ones out there for both Mac and PC. Use them to get to know how your camera works.

2) learn these rules.

* Larger F-numbers give greater depth of field.
* Shorter focal lengths give greater depth of field.
* Greater subject distance gives greater depth of field.
* Depth of field is greater behind the subject than in front.

3) (ok I lied there are three things) If you camera has a DOF preview button us it.

--

[lexcell]

Hi Everyone,
Laurie here...I just wanted to jump in, say hi and add my two cents worth. Annie introduced me in the Digital Cameras and Equipment Thread.

What a great discussion on depth of field. Byron, you really stirred things up with your excellent question and I am impressed with all the responses here. It is something that really throws people a curve. It is a great thing to understand but, don't get too bogged down with the technical and be creative. The point is to understand the idea behind depth of field so that you can make creative decisions as to what aperture will best communicate your vision of the world.

The DOF that Chuck posted the link to is an excellent resource so you don't have to do the math and it's a great learning tool. You can enter different aperture values from the same focal length to see how the aperture selected effects the depth of field.

Another way to learn is to use the same distance and aperture and plug in different focal lengths to see how the focal length of a lens also affects depth of filed.

The rules that Grant posted are right on. Depth of field is controlled by...aperture, focal length and distance to subject. Also, as Grant mentioned, you have approx 1/3 in front of the focus point and 2/3 behind depth of field so, you can fine tune depth of field based on where, within the scene, you focus. This rule is not hard and fast...the closer you are to your subject depth of field comes closer to 1/2 in front and 1/2 behind with the range increasing as you "close down" the lens (move towards the bigger numbers).

Whew! Now that there has been some great discussion on depth of field, get out there and test it for yourselves.

[RobertSchuldenfrei]

Hi Everyone,

While a career in the computer industry makes me favor a mathematical approach, the artist in me says "trash the math.":) The DOF preview button is a great boon to seeing what the final image will yield. Also, one of the principal advantages of a DSLR camera is the amount of test pictures you can take. While you can compute the DOF, I would rather "burn film" and pick the final image that fits my need. I am amazed that often the set shot I thought I was taking turns out to end up in the trash bin of my digital darkroom.

Cheers,

Bob

[Elemobe]

Hmm, interesting thread - I didn't even know that I didn't know all of this stuff:D

I use the Nancy & Trish method, I also have to do the chant "big numbers big DOF, small numbers small DOF" I also tend to say it out loud:o

Nancy, I like that, small number, small behind. Think I will be using that one.

[Byron Gale]

Thank you to everyone who responded... let me see if I can "nutshell" what I'm hearing:

- It's possible to calculate the exact DOF, but in everyday practice, exactitude is not vital. A "happy accident" can turn out better than the planned shot.

- The DOF scale marked on a lens is close enough to get "on paper", and subsequent adjustments should be made by using the DOF-preview button, and by "chimping".


Byron

[deedeeO]

Great thread....does this mean that I have start bringing my scientific calculator to my photo shoots now??? LOL!!!

[Chuck S.]

Great thread....does this mean that I have start bringing my scientific calculator to my photo shoots now??? LOL!!!

Denise, nah.....just bring your Palm Pilot with DOFMaster for Palm loaded on it!:D

[lexcell]

Byron,
Almost...however, the more you understand DOF, the more control you have over those happy accidents. As you become more familiar with what aperture does what at a specific focal length and distance, you can quickly get in the ballpark and fine tune by using the rear screen and zooming in to see the result. Of course the best way to learn is to go out and practice using different apertures on the same subject and then reviewing your EXIF data when you review your images.

Not very many of today's AF lenses have the DOF scale so, that is not always the best option but, if yours do, then yes, you can use them as well. I used to set the infinity mark at the next wider aperture than what I was using and this gave me more foreground in focus rather than focusing on the subject and having wasted DOF in the foreground.

The DOF preview button does help to some degree but, the small you close down the lens, the darker it gets and the ahrder to see what is actually in focus.

[deedeeO]

Ah Chuck,,,,I hardly carry a cell phone!! man, I need to start rebuilding my memory....

DOF along with white balance are my BIGGEST challenges right now. Esp. when shooting families and group...AUGH... with the lenses that I'm using (85 f/1.8 and 50 f/1.4) DOF is ultra senstive. I have lenses with f/4.0+ but only if we are outside are they effective. So thanks you'all for the science behind my grieve!!!

[Chuck S.]

DOF along with white balance are my BIGGEST challenges right now.


At some risk of being corrected...I believe DOF is a more serious challenge. You can generally fix white balance with post processing, although you don't want it to be way off. Bringing items back in focus that have been blurred by being outside the field of focus are much tougher.... I'll bet that would even be a challenge for the incomparable Butch! :)

[deedeeO]

Fortunately, my current work around is taking continguous images, finding focus in various parts of the group and photo merging. A big work around, but it works esp. when time doesn't permit changing lenses and babies/kids are involved...

[Chuck S.]

Denise, remind me what camera you're using...?

[deedeeO]

I feel really stupid now....a 40D....I really need to set down and learn to use it because I know that it has all the capabilities of mastering DOF....it is just it's master that is having some problems.

So, my plan was after the first of the year, taking 2 months off to rebuild skills...

[Chuck S.]

Denise, go to page 91 of your instruction manual and read about A-DEP. It may help in some situations like those you're describing

[Elemobe]

This thread may have answered something that has puzzled me for the last year. Below is a photo that I took not long after getting my 350D. I was experimenting with the Aperture priority mode. Here are the numbers:

1/25 at F/3.5 Focal length 18mm and ISO100.

Going along with the "small numbers, small DOF, then this shot should not have been sharp at all:confused: I was attending a night class for beginners photography at the time and was told it was due to the small sensor in my camera. However, after reading this thread I suspect it is due to the short focal length.

Am I on the right track here?


http://www.pixentral.com/hosted/1sqza91IdefeWReJqkNFME56qVwNbv_thumb.jpg (http://www.pixentral.com/show.php?picture=1sqza91IdefeWReJqkNFME56qVwNbv)

[Grant]

Yup you are right or most probably right.

For example with that camera at 18 mm lens and f3.5 if you focused at say 17 feet everything form about 8 feet to infinity would be in focus.

--

[Chuck S.]

Deb, the other factor in depth of field is subject to camera distance. If you were, say, 30 feet from those falls, your camera and lens at those settings would have a sharp focus range of 10.3 feet.....to infinity! How far would you estimate that you were from your subject?

[Elemobe]

Grant, I just had a play with the DOF master calculator and yes, I have a small understanding of it now (albeit a small understanding!). I put in 17ft and get the 8ft to infinity. My grasp of this is tenuous to say the least - but a start.

Chuck, difficult to say how far I was, it was on a regular walk, so I am going back there and going to play with the settings and see what I get. I was stood pretty near that small tree on the bank, so I'm thinking thinking that 30 ft from the fall is realistic.

So not my camera's sensor then!!! Must admit, I never did accept that answer.

Thanks guys.

[lexcell]

Let's recap all this information into a few simple sentences...
-Depth of field (DOF) is controlled by aperture, focal length and distance to the subject.
-The bigger the aperture number (f22), the smaller the lens opening, the more DOF
-The smaller the aperture number (f2.8), the bigger the lens opening, the less DOF
-All things being equal, a wide angle lens has inherently more DOF than a telephoto lens
-The closer you are to your subject, the less DOF you have, regardless of aperture and focal length (although, a wider aperture will still have less DOF than a smaller aperture)

Now, I am going to throw something else into the mix...
-The smaller the aperture (f22)...the slower the shutter speed
-The larger the aperture (f2.8)...the faster the shutter speed
-Slow shutter speeds create a sense of motion, blur
-Fast shutter speeds stop motion, rendering action very sharp
So, you have to keep in mind the effect of your aperture selection on the shutter speed and determine if you can hand hold or if you need to use a tripod.

Something for everyone to sleep on.

[JulieM]

Let's recap all this information into a few simple sentences...
-Depth of field (DOF) is controlled by aperture, focal length and distance to the subject.
-The bigger the aperture number (f22), the smaller the lens opening, the more DOF
-The smaller the aperture number (f2.8), the bigger the lens opening, the less DOF
-All things being equal, a wide angle lens has inherently more DOF than a telephoto lens
-The closer you are to your subject, the less DOF you have, regardless of aperture and focal length (although, a wider aperture will still have less DOF than a smaller aperture)

Now, I am going to throw something else into the mix...
-The smaller the aperture (f22)...the slower the shutter speed
-The larger the aperture (f2.8)...the faster the shutter speed
-Slow shutter speeds create a sense of motion, blur
-Fast shutter speeds stop motion, rendering action very sharp
So, you have to keep in mind the effect of your aperture selection on the shutter speed and determine if you can hand hold or if you need to use a tripod.

Something for everyone to sleep on.

I wonder if I could have that tattooed on the back of my hand??? :D

[lexcell]

I just remembered an excellent website that has an interactive tutorial on DOF.
http://smad.jmu.edu/dof/

[Not4wood]

This is why a baby Telephoto (range 80-105) is a better Portrait Lens then lets say a baby Wide Angle or your normal lens. In this range I would also say maybe up to a 135 which is still a baby Telephoto anyway. In 35mm Photography I always used my 135mm (Not a Zoom) Telephoto as a Portrait Lens.

-You are keeping a good distance away as to not threaten your subject.
-You are close enough to be able to give directions to your subject without being too far away.
-When you are using a good range of Aperture Settings you can even soften the hair and help frame your subject while keeping the eyes in Focus.

Example: There is a great shot on the whats new in the Gallery of a young child by Aussie Nan. Really beautiful little girl with great features. Everything is in focus, what stands out are her great wide eyes which are giving the impression she is looking right thru you. If there was some DOF separation, her eyes would be in focus and the outside of her hair would be soft giving a 3 dimensional aspect for the shot. This works exceptional better with a tight crop like this.

http://www.elementsvillage.com/gallery/files/1/1/9/6/0/chelsea-sfw_thumb.jpg (http://www.elementsvillage.com/gallery/showimage.php?i=602&c=2)


(Aussie Nan, I just wanted to give an example of a great portrait. I hope you don't mind).

Using DOF you can also use it to soften some features of the face instead of doing it with a soft filter or in the Editing Program. I'm sure you can get the same effects in PE5 or PE6 but remembering to do it later after shooting a full portrait session, shooting a Wedding or coming back from a travel adventure will be iffy. Shooting several shots, and giving yourself more to play with as one or two shots (without any effects everything in focus for editing later). Several shots playing with the effects in camera will also improve your shooting skill and it will take less thought and time and eventually end up being a reflex. So this whole rambling on my part wouldn't or shouldn't be necesary. :D

But, now add to this mix something that you all are forgetting in this Digital Photography age!
The Self Auto-Focusing aspect of the camera. Sometimes what you want to be in focus like the scene in the very bottom by Linda makes the water out of focus because the camera will think you want a shot of the tree. If you are setting your camera to the Portrait Programming this will happen. Just be concious of this and the work around it will come naturally. Forget about it and your shot will not be what you had previsualized.

[Chuck S.]

Mark, do you find yourself using the 80 mm end of your zoom lens more now for portraits on a DSLR than you might have on your 35 mm? 80 mm is the equivalent of 120 mm on your D-80, at least in terms of what appears on the sensor. The 135 mm end is more like 200 mm, which strikes me as a little long for a portrait.

[msbrad]

Excellent thread. I will save, print, and read and re read many times.
Thank you.
m

[Not4wood]

Mark, do you find yourself using the 80 mm end of your zoom lens more now for portraits on a DSLR than you might have on your 35 mm? 80 mm is the equivalent of 120 mm on your D-80, at least in terms of what appears on the sensor. The 135 mm end is more like 200 mm, which strikes me as a little long for a portrait.

Good point about the conversion 1.5, I keep forgetting that but since I'm used to it I would frame the shot and not even look at what zoom I'm set at. I would probably bring it down to about a 70 on my DSLR which makes it a 105. Anywhere in the baby telephoto area would be good I guess. You have to just remember that you do want to stay back a little. For a head and shoulders shot you want to stay back a bit to not overcrowd your subject.

Also, you have to keep in mind that a camera is very intimidating to a non-professional model/subject. I've seen a lot of Amatures hide behind there cameras. Or actually talk to there subject while the camera is at there face. Its a normal (if you could call that normal :eek:) thing for beginners to do. If your camera is mounted on a tripod, frame the subject, then move your face away from the back of the camera and talk to your subject to get a good expression and then hit the shutter without looking thru the view finder. If NOT mounted on the tripod, what I've done is frame the subject then while holding the camera still I will then move my head to talk to the subject. It takes some getting used to but not really that difficult considering your exposure will still have a fast enough shutter speed to stop all of the movement anyway.

I want to just remind all of you that everything I've said about what zoom strength is natually what I remember from my old film days. I know that we are now slightly in a more powerful format by conversion to 1.5 times the older version. Remember also, that once you keep in mind these some what standards and try to remember how much of your subject is in the view finder go with it. These rules are never meant to be a written law that you must stick to. You have to understand some of the guide lines to give you an idea of what you can do to get the job done. If it works for you then do it!

I was never a gear head, but a student of Photography. No matter what you know, there is always something new or a change that will make it better. As an apprentice in a small Wedding Studio more then 30 years ago I was always amazed that the owner would remember the standard poses as a place to start then always, always try something new. Always pushing the limits, on lighting, posing and then when we got back to the studio I was the one who ran the Color Proofing Machine and printed these shots.

Even now, I find myself looking around at newspapers or magazines to get an idea of what pose I can try to memorize to give it a shot if I have to pose a subject. Problem is, when I have to remember what I saw I always draw a blank and can't remember beans. LOL

[Chuck S.]

Mark, speaking of weddings, here's a link to the blog for the photographer we commissioned to record our daughter Laura's wedding. I was ordered to leave my cameras at home.... :(

Eclectic Images Photography (http://www.eclecticimagesphotography.com/blog/index.php?year=2007&month=November&id=73)

However, we think she did a really good job and, as you mentioned, trying things different is definitely 'in'. I was also pleased that she used Canon equipment....:D

[Not4wood]

Mark, speaking of weddings, here's a link to the blog for the photographer we commissioned to record our daughter Laura's wedding. I was ordered to leave my cameras at home.... :(

Eclectic Images Photography (http://www.eclecticimagesphotography.com/blog/index.php?year=2007&month=November&id=73)

However, we think she did a really good job and, as you mentioned, trying things different is definitely 'in'. I was also pleased that she used Canon equipment....:D

First, congrats on your daughters Wedding. Don't feel bad about being asked to leave your camera off. It is your party, you should be enjoying yourself not worrying if you got that shot. LOL You can take your camera to someone else's Wedding. :eek:

Great shots, I agree with you she did a lot of very new, unconventional and also old fashioned shots and pulled them off. Everything was in good taste and professionally done - humor. I even like the black and white shot she posted. Great capture of emotions at the house while the girls were getting dressed. I did notice that the before and after shots were there but none of the Ceremony. I have to ask, she did take them and just left them off of the Blog. Correct??? Next question, how many lights did this Photographer use during this Assignment?

Very nicely done, I also have to ask you one more about the equipment. You said Canon right. Now, which format regular DSLR or did she use any of the medium Digital format cameras as well? I am curious if she used the cameras we are using for a Wedding Job, and NO I am not interested in doing another Wedding. One ulcer is enough in my lifetime thank you very much. LOLOLOL

[Not4wood]

Mark, speaking of weddings, here's a .<SNIP>...:D

Chuck;

I can't believe I forgot to ask you. I had mentioned in a post below about moving your face (so as to not hide behind your camera) away from the camera to communicate with and when shooting people.

Did the Photographer at your daughters Wedding do this and how did it look from your perspective being in Front of the camera??

Also, I do know that you had other things in mind but of course you did watch this Photographer anyway. Am I right?? What do you and how do you feel about the way she did her posing and lighting since you have your own perspective of this now?

I am asking these questions not only for myself but for the others reading as well, giving them an insight as to what has happened and also what goes into shooting a monster of a job like a Wedding.

Since this Photographer started in the Brides house with all of the Girls from the Bridal Party, Chuck obviously this is only the start of the job.

Chuck,
My question to you is "How Long was this Photographer at this job till she left and was signed off"?