Depth of Field

[Sturgeon_Catcher 0]

One of the things I hope to see from this forum is a great deal of give and take. Sure looks good so far. I have been taking pictures for a terribly long time. I know what will happen but not necessaarily why. Sure would like to know the technical WHY? Any help along these lines would be greatly appreciated.

 

We have spoken recently about depth of field and its affects on the actual desired image as well as the background. Looking through my trip photos I found an excellent example to demonstrate depth of field.

 

The fly is a crayfish pattern given to me by an Orvis guide in Bristol, Tennessee. I set up and shot this photo to email to someone.

 

Look closely at the first image. The fly is laying away from you. The point where the foreground comes into focus is along the curve of the hook. You can see that the back of the black mount is in focus.

 

 

A crop of the first photo in a larger format. The body of the fly is in good focus. Look closely at the claw in the background. Just starting to go out of focus.

 

 

This view clearly shows both the foreground and background areas that are in focus. This then is depth of field. Think of a rectangle sitting directly over the image with both a front and back element. Objects in the middle are clear and distinct - while approaching the edge...things go a little fuzzy.

 

I might add the depth is determined by the amount of magnification + the fstop + the speed. Digital cameras provide the last two automatically after you set the first element - the magnification.

 

Playing with the last two elements are what will produce in some cases more clarity, more magnification, and stunning effects with the background.

 

Hope this is of some help and provides a little interest.

 

later

Fred

 

 

[Graham 0]

Hey sturgeon catcher, thanks for starting this new topic, you beat me to it… Late yesterday afternoon I took a series of photos to experiment specifically with DOF, and I learned a few things, but I now have new questions….

 

First question is; do lenses have a “sweet spot” f-stop aperture? And if so, can the sweet spot vary? And if so, is this more dependent on light or distance to the subject?

 

For my experiment I used a lens that I want to learn to become very comfortable using, a Nikon 200mm macro lens. For my first experiment I deliberately did not use my lens for close up macro shots, instead had my camera about 4 feet away from my subject, and wanted to see how a static subject changed in relation to the background, depending on the f-stop aperture selected.

 

One thing I was not expecting… At f-32, where greatest depth of field was anticipated, the background and foreground are in good focus, but the subject has diminished focus, and the photo looks flat. The photos with smaller apertures show the subject in clearer focus, the background and foreground are smooth and out of focus, but, to me, this effect seems to have more depth than the flat pic with most of the frame in focus?

 

For those of us new to photography, such as me, an f-stop is basically a setting on a camera or lens that controls the aperture. Inside lenses there are blades that move in unison, sort of like a round curtain, and they can be wide open, letting in a lot of light, all at once, and these wide open settings have low numbers, such as f-stop 2.8 and 4.2. The smaller the number, the wider open the inside of the lens is, allowing it to focus faster and also take a pic faster because the film or digital sensor receives the light faster. A term referred to as "stopping down the lens" means the blades inside the lens are set to not open as wide, in effect letting the light into the camera more slowly which provides greater depth of field focus. A longer shutter speed is then needed to let in the same amount of light as a wide open aperture to get the correct exposure. I guess it could be compared to filling a creel with trout, with the lid wide open you could very quickly fill the creel with 10 trout by tossing them in, but with the lid slightly opened, just enough to slip in a fish one at a time, it would take longer, but you could line the fish up side by side and probably get over a dozen into the creel…. OK, maybe that was a stupid analogy, but from my experiment yesterday it seems appropriate, and now I wonder if stuffing an extra trout into the creel can crush the ones at the bottom…..

 

Anyway, below are four pics from my experiment, a grasshopper fly was placed on a fern, not for a pleasing composition, instead to have a composition with a Z-axis foreground and background, allowing me to see how this changes in relation to changing aperture settings and how this affects the depth of field. I turned off the auto focus button on the lens, focused on the grasshopper and then took a couple dozen identical photos, nothing moved or changed except for the f-stop aperture setting on my camera. I started with an f stop of 4.2, wide open, and continued until I reached f/32.

 

Below are four pics, starting with f-4.2, then 6.3, 11 and 32. Personally I most like the effect with f-6.3 If there are any other f-stop settings from this experiment you want to look at, I can post them. Perhaps I might have resized these pics a bit too large, but I wanted it to be easy to see the differences apertures make with relation to depth of field.

 

f 4.2

 

f 6.3

 

f 11

 

f 16

 

f 32

[Peterjay 0]

Just to (hopefully) clarify a couple of points:

 

Shutter speed has nothing to do with depth of field, but may affect overall sharpness. (as do a lot of things, such as bird droppings or vibrations from the furnace coming on)

 

Lenses are usually rated for edge sharpness and center sharpness - the degree of sharpness varies at different spots on the lens as well as from lens to lens - it's a good way to compare lenses if you can find some test results.

 

The longer the focal length of the lens, the shallower the depth of field - that's why your DOF changes as you manipulate the zoom.

 

As you've already discovered, DOF manipulation is one of the tools photographers use to achieve desired effects. Portrait artists often open the aperture up to reduce DOF, obscuring the background, softening the image and directing the emphasis onto the subject. (like the 6.3 hopper) Landscape guys do the opposite, closing it down to achieve the deepest DOF possible.

 

As a long-time art photographer, it's good to see you guys making an effort to learn the craft - with all the automatic stuff that's built in these days, it's easy to limit yourself to pushing buttons, but all you'll get are average snapshots with the occasional lucky accident - if you understand the process, you can dictate the results, or at least come close. Hope this helps. PJ

 

 

 

 

 

 

[Sturgeon_Catcher 0]

Hey PJ....

If you don't mind my asking what type of art photography did or do you do?

 

To answer your question about sweet spots Graham...

 

Lenses are designed for specific optic distances for best performance. The amount of magnification on the negative or focal plane of the lense with the digital will determine the best lense for the job. Also distance from subject can make a great deal of difference. Graham..what if you used the 100 or the 50? Try the fifty and see what happens. I think you will be surprised.

 

later

Fred

[Graham 0]

Very interesting info, thanks gents...

 

The thing in my pics that got my attention the most was, the little dark fern berry hanging above and behind the grasshopper. The pic I expected to have the greatest depth of field, shot at f/32, looks flat to me. The berry is in focus but it's hard to tell if it’s hanging in front of, above, or behind the hopper. The pics taken at f/4.2 and f/6.3 have much less in focus, but to me the depth of field seems better, because it looks obvious the berry is located a distance behind the hopper. Now, isn't this observation counter intuitive?

 

 

[Sturgeon_Catcher 0]

Graham..

Perhaps this set of photos will help explain the berry. I call it stacking up a photo.

 

Check out what happens when you shoot 100mm at an object in the foreground but still retain focus in the back. The two rocks are almost 10' apart. Look closely in the first photo and you can see a pronounced space.

In this picture it appears the two rocks are almost touching. Yet, they are not.

 

This is a series of photos I shot in Ct with roll film. Did the same shoot as Graham only testing a new 40 year old lense to me. Also, to demonstrate the proper lense for function. The comparison was with a 100mm and an 85mm. Shot the series with both lenses and at different fstops. Combined the digital and roll to complete the survey. Will resize and post soon. Cool location on the Housatonic River, Ct.

[Peterjay 0]

Fred - I do black and white exhibition stuff - my specialty is the urban landscape, but I do botanical studies and when we lived in Idaho, I went through my "Ansel Adams" period - the Rocky Mountains were hard to resist. I use a Pentax 6x7 (and occasionally a Nikkormat 35mm) and by design, limit myself to a normal lens only (105mm for the Pentax) - Most of my prints are 16x20 with the occasional 11x14 - I've done a lot of shows in NE and elsewhere, but I'm mostly inactive these days thanks to limited space and the fact that I lost most of my darkroom gear in a flood - thinking about doing some digital stuff, as the possibilites are endless - About the only (public) thing I've done recently are some action shots for Alan Caolo's book "Sight Fishing for Striped Bass." (that's me on pg. 95) That was more fun than work - got to do a little fishing and took turns with Alan manning the camera - We're moving to a bigger house, so looks like I'll have room to get set up again - listening to you guys reminds me of what I'm missing, and I'm grateful for that - PJ

[Sturgeon_Catcher 0]

Too cool PJ. Thankx for the reply. Do continue to add when you wish. Hope to hear more from you. I'm just a seat of the pants kind of guy when it comes to photography but love to share and at home there is no one to talk to about my cameras or photography.

 

Not everyone is into photography as much as this group.

 

later

Fred

[Peterjay 0]

Fred, some of the best photographers who ever lived were "seat of the pants guys." A lot of folks fall into the trap of concentrating on the technical end of it and worrying about how many gadgets they can acquire, and forget that photography (or any other art form) is really about the finished product. That's why I limit myself to normal lenses and a couple of cameras and concentrate instead on composition, textures, etc. Once you understand the basics, your gut (and a well-trained eye) will take you places that all the technical knowledge in the world won't. PJ

[madkasel 0]

Neat stuff. I understand about a tenth of what goes on here, but I'll be danged if it isn't very interesting. Someday I'll have a camera that can do this cool stuff. Until then, I'll just absorb what I can from you all.

[KVRNut 0]

This is going to be a real interesting topic for me to follow as I go from extreme close up to scenic shots. The more I learn about DOF, how to get the most out of it and use it to the best advantage in a shot, the better.

 

Thanks for starting the topic Fred!

 

Ernie