Depth of Field...

[troush]

Okay,

I've been going through books from the library and one thing I'm having trouble getting my head around is determining depth of field. I understand what it is - how much of the picture is in focus. Let me see if I can explain more...

I have a Nikon D50. Alas, it does NOT have a depth of field preview button. Also, the lens I have (a kit lens: AF-S Nikkor 18-55mm 1:3.5-5.6G ED) doesn't have the depth of field marks/gear thingy that the books showed in their pictures. And, I prefer to let the camera autofocus, even when I shoot M (I know, I can manually focus it). So, if I want to shoot one of those beautiful scenic pictures with the storm rolling in and the farmhouse on the distant hill and the green grass all in focus, etc (see Bryan Peterson's Understanding Exposure, 2nd edition), on what/how do I focus my camera? The other thing is, I'm terrible at judging distances.

I saw the online tool that someone pointed out, but I'm not making heads or tails of it.

Can someone help my little brain understand this, please?

Thanks,
Trish

[George Favale]

Hi,

I found this link to really help
www.luminous-landscape.com/tutorials/understanding-series/dof.shtml

a very simple way to remember is the lower the aperture number ex f5.6
the less you will be able to see beyond the focus subject. The higher the number ex f22 the more you will be able to see beyond the focus subject.
you don't have to worry about autofocus unless something is in the way of your subject.
I use as a rule of thumb of f22 for landscape's that i want almost everything in focus.
try to remember at that aperture of f22, 1/3 in front of the subject will be in focus and 2/3 beyod the subject will be in focus.
the best way to learn this is go shoot something and vary the aperture and see what happens.... have fun

[MikeH]

Trish,

If you want everything from the immediate foreground to infinity to be in focus, then focus on a point 2 to 3m into the scene and stop down to f/16 or f/22.

Mike

[troush]

George,

I understand I need the larger aperture.. F/16, F/22, F/32.

I went back to the depth of field web site. I think I'll have to read it about 10 times to get my brain around it. (He has good diagrams, which will help).

My problem is I'm no good guestimating distances. I know I'm 5' 6" tall, but guessing how far 10 or 15 feet is away from me to focus on so the picture is in focus from 5 feet to infinity is where my problem is going to be. I guess I'm going to have to put that 12 foot measuring tape in my camera bag :) !

-Trish

[George Favale]

First DOF is a little hard for everyone to understand...

One of the neat things about digital is you can shoot a lot and not worry about cost...
Try shooting something at f5.6, f11, f22 and see difference.
remember the higher the f number the more exposure you will need
which means you may need a tripod.... the only way i learn is doing.
try this exercise and don't worry about distance in the beginning... it will come.... again having fun is what we are all trying to do....:))

[TonyW]

You don't have to be too precise except when you get into macro stuff - I often just take 5 paces and call it 15 ft (or take big paces and call it 5 metres)

Tony

[bwolford]

I have a different problem. My camera has a DOF preview button, but my eyesight isn't keen enough to see the effect in the preview. ;)

Brice

[Chuck S.]

Trish, that 18-55 lens gives you lots of depth of field at the low end. According to the DOFMaster calculator (a free download), at 18 mm with a DSLR set at f8, with the focus point set at 15 feet, everything from about 7 feet to infinity will be in focus; at 55 mm, that shrinks to everything from 13 feet to 17 feet. For those scenics.....use that low end.

Chuck

[troush]

Chuck,

Thanks. I'm going to have to try that. I have a Handspring Visor that runs Palm OS 3.1. I need to see what version that program will run under. (It's 5 or 6 years old - from when I had an easy day job. Now its 24 x 7! ;) )

I was reading all those books, and I really was beginning to understand exposure and everything. And I was feeling really good about taking pictures in modes other than P and A. And then they started talking about "where to focus" and using the lens to calculate it and some other stuff and it went right over the top of my head... Especially since I couldn't do it on my lens. (They were talking about how newspaper photographers just set their focus distance and aim over their heads to capture the shot.)

I'll get the hang of it soon enough. Not like I have time to get out and shoot scenic expanses these days, anyway. Which is a bummer, seeing how I live in the most beautiful state in the U.S. for scenic expanses - not that I'm biased or anything :) . (I'm not draggin' the kids along. I'd need someone to keep an eye on them! My 18 month old boys sure like to wander. My 5 year old daughter would be good... but my, oh my, those boys. Seems amazing that they haven't electrocuted, strangled, or otherwise seriously injured themselves yet!)

-Trish

[Grant]

Depth of field is rather a simple idea that becomes complex because of a bit of confusion.

First off depth of field is just distance between the closest object that is in focus to the furthest object that is in focus.

There are two things that effect the amount of depth of field. the lens you choose and the aperture you select to use.

1) The wider angle lenses have more depth of field than telephoto lenses at the same F-stop. The reason for this is only understood by techno geeks that grind lenses in their sleep. All you have to remember is that if you want more depth of field consider a more wide angle lens and conversely if you want less depth of field use a greater telephoto lens. About now a light should be going off in you head "Ah the reason why modern lenses don't have etched depth of field bars. Today modern lenses tend to be zoom lenses going from wider angle to more telephoto hence different depths of field. So if you start out with this idea in the back of your mind you will become very comfortable with this concept as you take more an more photographs.

2) The larger the lens opening the less depth of field and the smaller the lens opening the more depth of field. Now here is the confusing part, the larger the F-number the smaller the lens opening. So F/16 is a smaller lens opening than F/11 therefore has more depth of field. I think this is were most people get screwed up ...because of how we name lens openings. It is backward from the way we normally think. So how should we think of this? Lets think of your own eyes. You go to the optometrist and he puts drops in your eyes, a trip way better than drugs from the 60s, your eyes dilate and you have no depth of field, in fact you can't see everything is blurry. Later on your eyes have returned to normal and you have to thred a needle but you can't get close enough so you squint increasing the depth of field an now you can see.

Now to Hyperfocusing, that is focusing in such a way to get the maximum depth of field. There are rules and aids for this but the only true way is to manually focus and use charts to be certain. Unless you are using telephoto lenses don't get too bent out of shape on measuring accurately, for example a 24 mm lens, focused at either 10 feet or 1 foot, will have a hyperfocus range of only 9 inches difference.

So to recap the wider angle the lens the more depth of field, the smaller the lens opening (larger F-stop) the greater the depth of field.

[karen donnybrook]

Ah Brice, that catches up with all of us. That is when the auto focus really comes in handy :rolleyes: