focus and depth of field

tlittleton

I was taking some shots of wildflowers today and I ran into a problem. The AF on my camera can't quite focus in on something as small as some of these flowers, even in macro. I'm using a S5100, and it does have a manual focus. The problem is on small detailed items like the ones below, it's hard to get a sharp focus because the viewfinder is electronic not optical. I know the leaves and stems came out pretty sharp, and I did have a small f stop set. If I increased the f stop, would that help with the focus since I'd be increasing my depth of field?

David_S85

tlittleton wrote:

I was taking some shots of wildflowers today and I ran into a problem. The AF on my camera can't quite focus in on something as small as some of these flowers, even in macro. I'm using a S5100, and it does have a manual focus. The problem is on small detailed items like the ones below, it's hard to get a sharp focus because the viewfinder is electronic not optical. I know the leaves and stems came out pretty sharp, and I did have a small f stop set. If I increased the f stop, would that help with the focus since I'd be increasing my depth of field?

The point 'n shoot cameras, due to their smaller/more compact optics and tiny sensors, have a fairly deep Depth Of Field compared to the larger cams; sometimes too much if you want the background to blur away for composition's sake and near foreground subject emphasis. This can be a boon or a hindrence, depending on what you're trying to convey in the pic.

Yes, a smaller aperture (higher f-stop number) will help to increase the DOF, with the downside being that background probably coming even more into focus.

Manual focus (in fact manual everything) might help, in that the camera won't be hunting for focus on a sometimes narrow object like a flower stem or petal. The key is in knowing your camera and having a good feeling of distance from the lens to subject. No substitute for real trial and error and practice here. Shoot lots of shots to get it down. Practicing by taking pics at an angle to a ruler might help too knowing just what will and won't be in focus at short manual focus lengths at given f-stops.

If your camera can accept one of those macro type add-on lenses, you might be able to increase your camera to subject distance, but with a loss of usable DOF as the tradeoff. They have their purposes, but ease of handheld focusing isn't one of them.

DOF is also affected by the focal length chosen. A longer focal length will compress the DOF (shallower), while a wider focal length will increase DOF.

A DOF summary for all types of cameras:
For the least DOF... use longer focal lengths, wider apertures (and faster shutter speeds) with the subject in the very nearby foreground. And you might need further help from a neutral density filter to get the f-stop open enough on bright sunny days.

For the most DOF... shorter focal lengths, smaller apertures (and slower shutter speeds).

jthomas

tlittleton wrote:

I was taking some shots of wildflowers today and I ran into a problem. The AF on my camera can't quite focus in on something as small as some of these flowers, even in macro. I'm using a S5100, and it does have a manual focus. The problem is on small detailed items like the ones below, it's hard to get a sharp focus because the viewfinder is electronic not optical. I know the leaves and stems came out pretty sharp, and I did have a small f stop set. If I increased the f stop, would that help with the focus since I'd be increasing my depth of field?

This problem is exactly why I finally bit the bullet and bought a DSLR. :

bfjr

I have those same flowers in my backyard
They are extremely hard to get right Why?, I don't know but there's something about the way they move in the slightest breeze, or the tightness and depth of the bloom
Still don't have a keeper :cry

I was happy to see your's, makes me feel less inept

bkriete

Is it possible you might be closer to your subject than your camera and lens will allow focus at all?

willow56

flowers

bkriete wrote:

Is it possible you might be closer to your subject than your camera and lens will allow focus at all?

i also have a file full of bad pics of those particular flowers.. the combination of brilliant green and multiple pastel colors have always attracted me.. have finally decided to just give up on them.

Jekyll & Hyde

Yup, manual focus is the way to go.
J: I use Manual focus for all my macros (Sony F717).

H: What I do though, is set the focus on Minimum distance and leave it there (minimum distance gets me the largest Image Size).

J: I find it almost impossible to focus using the LCD screen (or EVF) while turning the focusing ring. The resolution is just not fine enough.

H: So I leave the focusing ring alone and rock back and forth until the area that I want in focus is sharp. This at least can be determined using the display.

J: It can be really tough at times (esp. when it's very bright out or very dim). What helps is that on my display, the areas in sharp focus will start to shimmer slightly.

H: It takes practice (I still get less than 50% of my photos focused exactly where I want). It's due more to camera movement as I sway (I rarely use a tripod or even a monopod).

J: BTW, it's easier to focus when the aperture is wide open (so don't half-press while you're focusing). And like the others said, the smaller you set the aperture, the more DOF you'll get.

H: If you still want to use AF, then set the smallest focusing frame possible, focus on the desired part of the subject, recompose, and shoot.

Good luck,
J&H

wxwax

1/ In Macro you have such a narrow depth of field that if you don't properly grab focus on the thing you want to shoot, it will be out of focus. In fact, the front tip of the petal could be in focus, and the back of the petal be blurry.

2/ Setting a smaller f-stop will help. But it's no guarantee you'll get the depth you want. So be very careful and precise about what you grab for your focus. Lots of testing, I reckon.

3/ As you say, manual focus with most of our cameras, especially for Macro, is incredibly difficult.

4/ Personally, I would center focus and recompose. But at the shallow depth of fields you'll be working with, you run the risk of losing your sharp focus point when you move the camera to recompose. Fish had a good post about that here. The camera movement seems tiny, but at narrow depths of field it can be enough to throw off the focus.

5/ If a breeze even slightly moves your flower, your macro focus is gone with the wind. That's why they sell little arms that attach from your tripod to the stem of plants, to hold them in place for macro photography.

6/ Don't discount the possibility that your lens is too close to the flower to be able to focus - even in macro mode, it can happen.