What is Depth of field? (Explained)

[Poseidon]

Depth of FIELD (or Focus)!!!!

Most simply stated depth of field is term used to describe how much or how little of your picture is in focus. There are several factors that determine the depth of field, but none is more profound then the aperture used to capture the image. A large aperture will result in LESS depth of field then a small one will. There are other factors as well, focal length, and the distance from the camera to the subject, but neither of these are as dramatic as aperture. Aperture along with ISO directly impact the shutter speed as well, so you can't change one without changing at least one of the other 2, but for this demonstration, I will only talk about the aperture.

So what is the difference between getting an image like this:
http://PerfectPix.smugmug.com/photos/339219936_WZAG9-L-1.jpg
And this:
http://PerfectPix.smugmug.com/photos/339219707_T8vra-L-1.jpg

APERTURE!!!!

Those of you that keep your SLR camera on the GREEN SQUARE, or the "P" mode are really losing out. If you use the camera "program mode" you are allowing the camera to decide what results you are going to get, you are giving control to the camera rather then keeping control for yourself. Aperture is the single most dramatic control we have over the finished result of our images, once you learn to control the aperture, you can decide what the finished image will look like. In some cases you may want to have as much of the picture in focus as possible, in other cases you will want to isolate the subject from the background by using the largest aperture you can.

Okay... enough typing! Here is a progression of images from the largest aperture to the smallest, meaning the least in focus to the most in focus.

http://PerfectPix.smugmug.com/photos/339219936_WZAG9-L-1.jpg
2.8

http://PerfectPix.smugmug.com/photos/339220144_Z6kUm-L-1.jpg
4.0

http://PerfectPix.smugmug.com/photos/339220407_6swDe-L-1.jpg
5.6

http://PerfectPix.smugmug.com/photos/339218611_hqMx4-L-1.jpg
8.0

http://PerfectPix.smugmug.com/photos/339218865_iCVD4-L-1.jpg
11

http://PerfectPix.smugmug.com/photos/339219123_DeRgU-L-1.jpg
16

http://PerfectPix.smugmug.com/photos/339219421_W2HeT-L-1.jpg
22

http://PerfectPix.smugmug.com/photos/339219707_T8vra-L-1.jpg
32

The scale from 2.8 to 32 are the "standard" f stops available on most cameras. Each stop allows in TWICE as much light as the next one, so from 2.8 to 4 is half the size. This is where the relationship between aperture and shutter speed is most evident, but that is topic for yet another thread!

As always, I hope you find the information presented here useful, and if you have any questions, please post them here!

-Mike

[BlueCorn]

The sticky at the top of this forum contains detailed information on this subject as well.


http://www.reefcentral.com/forums/showthread.php?s=&threadid=333197

[Poseidon]

So a link to luminous landscape is better then my example?

[BlueCorn]

Did I say anything about "better?" I find that many folks learn best when presented with information from many sources. I apologize if you were threatened by that.

There's a ton more information in there than just "a link to luminous landscape." I'm just pointing out resources that are already here but people frequently miss.

Like this, also from that link:

http://reefkeeping.com/issues/2004-11/gr/index.php

[Poseidon]

Nope, wasn't threatened, I am insulted. I took the time to take the images, and write the text, and the very first response is a redirect to another thread. That response in effect says to me that I wasted my time posting it here, cause it is all already covered.

[drparker]

Enterprise nice visual examples of DoF.

Beerguy good links but that Dof Calculator is lacking in the Canon end of things:p All digs aside here's a calculator that has a greater selection of camera bodies and lenses.

DoF calculator (http://www.dofmaster.com/dofjs.html)

I'll try to cut through all the tech talk that is in most tutorials on DoF.

Dof is the total distance that will be in focus when you take a shot. Part of that is in front of the focus point and part behind. As a general rule there is less in focus distance in front of the subject than behind. Camera body, lens, aperture and distance to subject all play a roll in the DoF you will get.

As an example with my Canon 5D if I use 100mm lens and focus on something 10 feet away with an aperture of f/4 then my total in focus distance is 8.5 inches, with 4.1 in front and 4.4 behind. But the same lens and settings on an XTi only gives a total of 5.38 inch DoF

Using the 5D 100mm lens but focusing on something 12 inches away with an aperture of 2.8 gives me a .04" total in focus distance.

I run the calculator for all my lenses at typical distances for tank shots, people shots and landscapes. This gives me a rough idea for when I'm out shooting.

[Poseidon]

Thanks drparker! I had fun putting the thread together, I hope that is found to be useful by many.

[melev]

Thanks for the samplings. I usually shoot at f/2.8 exclusively, but it was really interesting to see how much it changed. I didn't expect it would be f/32 would be all in focus, but rather f/11. You must have a great camera to have such a degree of DOF.

I'm still using a Fuji with a built-in lens.

[Poseidon]

Thanks Marc!

It is the lens that has everything to do with DoF. The size of the image sensor also plays a role, but it is certainly not as easy to demonstrate that! (I would need at least 4-5 different cameras!)

[H@rry]

Mike - thanx for the excellent example of different aperture settings. I recently bought a D40 and have spent the past two weeks trying to learn how to use it, especially with taking shots of my corals. I've been looking at some of the pics posted by others who really seem to have mastered the art and have been trying to learn it as well.

If you don't mind, I have a couple of questions.

You mentioned that as the aperture changes we need to also alter the shutter speed. I tried looking at the Exif data to see that but it was missing. Do you think shooting in aperture priority mode and allowing the camera to adjust shutter speed will yield good results or is that something I'll need to manually adjust as well?

What about ISO settings? What are the benefits of the various setting? I know that a higher setting can result in "grainy" pics.

I'm using the 18 - 55 mm kit lens now but realize that I want a macro lens. Others have suggested the 105 mm lens as one that will take excellent macro shots. I understand that it is not adjustable as far as zoom is concerned and I'll just have to move the lens closer or farther away to adjust that. Is there anything else that may yield a good macro pic and have some zoom capabilities?

Thanx for allowing a newbie to ask all these dumb questions.

[Poseidon]

You are welcome! I don't mind the questions at all.

Aperture priority is a great place to start! With my camera, I have to use exposure compensation with it though. Usually this is an EV scale that goes from -2 (or -3) to +2 (or +3), what this does is allows you some control of the exposure. Depending on your lights, this may work for you.

Set your camera to Av, then set the aperture for 8.0, ev to -1, and ISO to 400. You will most likely need a tripod, as the shutter speed may be very slow.

I have an ISO thread as well, I will send you a link.

[H@rry]

Is adjusting exposure compensation the same as adjusting shutter speed?

[Poseidon]

Kinda.... It forces the camera to either increase the shutter speed, or decrease it, based on if you want to overexpose the image or underexpose it. I find that most of the time in Av mode, I have to underexpose what the camera thinks by 2/3 to 1 stop.

[d4a2n0k]

Thanks for the thread Enterprise! I got my first DSLR (Rebel XTi) about a year ago and your threads really help. Ive read a bunch of websites and feel I'm in the same position as when I first bought the camera, clueless. :) Its frustrating because I'm very into electronics and I have to say I cant remember the last piece of electronics I bought that I actually read the manual.

After picking up the XTi I, it was a kick in the pants because this is not something thats easily learned by yourself so your threads are priceless. Especially since the camera websites never touch on coral photography. Your pictures are worth 10,000 words!

I also have the Canon 100mm Macro lens and found that F11 - F16 seem to give a good compromise between DOF and sharpness. Is that a fair assumption? Is that about where I should be shooting corals at?

Keep up the good work and I look forward to more threads from you.

[Poseidon]

Thank you d4a2n0k, I am glad you find this helpful!

You are correct, F11 and 16 are great places to be for a compromise in sharpness, DoF, and shutter speed. As far as if that is where you "should" be at, only you can answer that. If that is what you like as an artist, then YES! If you prefer to create an image with only a single polyp in focus, then that is RIGHT too. There are certain times when more DoF is required, for ID purposes as an example, but there are times where you as the artist have complete freedom as well!

[BlueCorn]

Something to keep in mind is that for most DSLRs you're going to start seeing diffraction once you go above f/11. Don't let that stop you from going above that if the shot calls for it, just don't automatically think that if f/11 is good then f/16 is better.

Camera's with a full-frame sensor can generally go up to f/13 without diffraction since there is more room between pixel sites.


Cheers

[Aadler]

Enterprise what lens is that? Maybe I need a true macro lens, but I feel my DOF is nowhere near that narrow, even with the cannon 50mm at 1.8 i still feel like im shooting 4-5.6 or something.

Cannon 30D.

[Poseidon]

These are an exaggeration, I used my 70-200 2.8L WITH a 500D diopter attached, just so I could make the difference more drastic over the aperture range.

I am sure a 100mm Macro will have a similarly shallow depth of field. With such a sort focal length, it is hard to get this type of bokeh.