Depth of field

[Whubee]

Attempting to get a good depth of field. How can I improve a shot like this?

[fotodog]

Depth of field is affected by three things,

focal length, lens to subject distance, and aperture.

The smaller the aperature the greater the depth of field. (for example f/22 will give you a greater depth of field than f/8)

A wide angle lens will give you greater depth of field than a telephoto lens (for example a 28mm lens at the same distance and aperture will give you greater depth of field than a 200mm lens)

The farther away you are from a subject the greater the depth of field at any given aperture and focal length. (for example a macro shot at 1 foot will have an extremely shallow depth of field even at f/22. A shot with the same lens at 12 feet and f/22 will give you a greater depth of field but not the same composition).

Two ways to get this shot with more depth of field. (macro shots are extremely difficult to get any depth of field)
1) Shoot with a wider lens with a bit more distance and a smaller aperture
or
2) Shoot multiple shots (on a tripod with a cable release with manual exposure settings) focusing on different planes and then combining them in photoshop.

Best of luck!

[Whubee]

If im understanding you correctly, using a smaller aperture (higher ƒ/number) will in turn give me a more gradual change in the depth of field.

The shot was taken using a 40-150mm at 40mm ƒ/5.6

If I decrease the aperture, I should get a better effect?

I dont have a wide angle lens or telephoto lens. I using what came with the kit. I would like to, in time, get more lenses.
Thanks for the help.

[Politik]

That is correct whubee.. If you want to and are bored, try this:

Setup a tripod and attach your camera

Put an object, ideally something that wont fill the frame on a nearby table with a busy background.

Start at f/3.5 (or however wide you can go) and increase the then move on to f/5.6, f/11, f/14 ect ect until you hit f/22.

Never move the tripod nor the item, just switch the aperture.. you should notice a huge difference as you close up the aperture. the big blur in the background will slowly disappear and come into focus as you hit f/22.

actually, i have a sample of this from my outing the other day.

This first one is f/3.5


this next one is f/14



So even a few stops makes a huge difference when it comes to background focus. f/22 it would have all been in focus (but also the SS would have gotten very very slow)


hope this helps a bit.


BTW - to answer your question, macro shots you want to isolate your subject which you did a pretty good job at

[Hardy]

Little thing I learned years ago at college to understand depth of field (well it was actually the reciprocal relationship but its all the same thing!) was this:

Imagine a ball of dough as the amount of light that needs to get to your film/sensor to take a picture.

The diameter of the ball relates to the apature of your lens so as a ball the apature is at it's widest wetting (smallest f number). The depth of the ball relates to the amount of a given scene that will be in focus (ie the Depth of Field).

If you reduce the apature (increase the f number) it has the same effect as rolling out the ball into a sausage shape. As the apature gets smaller, so the sausage gets thinner and the length longer so your depth of field increases.

I'm not sure I explained that very well but it's stuck with me for about the last 30 years!!

[Whubee]

Politic,I may try this over the weekend. Should I try shooting this in aperture priority mode or manual?

Hardy, thats a great analogy! You explained it perfect.

Thanks for the help.

[Politik]

use aperture priority because of this:

When the aperture gets smaller, more light is needed to reach the sensor than when its wide. If you think of it as an bucket you are trying to fill with water the wider the bucket top, the quicker it will fill. So makiing the top smaller (goinng towards f/22) it will take a longer shutter speed to equal the same amount of light to hit the sensor as it would at f/2.8. Thus, taking the bucket longer to fill up.

(umm for the bucket thing lets assume the water's diameter coming into the bucket is always larger than that of the bucket's diameter so the analogy actually works )

So f/2.8 you may get a SS of 1/320 but at f/22 you be looking at a 1 sec exposure to get the same photo.


So use aperture mode to save you the trouble of having to adjust the SS for proper exposure. Besides, we are learning DOF , let the camera deal with the exposures.




[Edited on 5/22/2008 by Politik]

[Pasta_Al]

I think the other thing that could have improved the shot is the lighting? There isn't enough light on the flower you are concentrating on... a bit of fill flash would have helped in tandem with the DOF. It is possible the flash would have darkened the background a bit... Or changing the point of view so the sky wasn't a feature, I find the big white bits just a minor distraction from the main subject...

[Whubee]

Al, from what I have been reading, it is not encouraged to take shots of flowers with a flash. Unless it was referring to on camera flash. I'll have to go back and look it up. The best suggested time is on overcast days to get an even soft light (which it has been here for almost a week. The rain held off for most of the day I took the shot).

I see what you mean by distracting, I'll keep it in mind for future compositions.

Thank you all, I can't stress enough how great full I am for all your advise.