Hocus Focus

[DCBarner]

Okay, so today I found out that if you shoot at a higher F-stop you will be more in focus. Who knew? I didn't. So next question. How can you shoot low light situations and attain a sharper focus? Must you use a flash? I can't imagine that there would be any other way, but you all are smart.

I really had no idea that smaller openings gave you sharper focus...I can't believe I missed that.

Dane

[Nicole]

You can (1) use more light (for example a flash), (2) use a higher ISO, or (3) use a slower shutter speed. That's why it's important to understand the exposure triangle. As you increase or decrease one of the parts (ISO, Aperture, or Shutter Speed), it effects all of the other factors as well. You can read about the exposure triangle on the DPS Blog: Learning about Exposure – The Exposure Triangle

[natek313]

Originally Posted by DCBarner

Okay, so today I found out that if you shoot at a higher F-stop you will be more in focus. Who knew? I didn't. So next question. How can you shoot low light situations and attain a sharper focus? Must you use a flash? I can't imagine that there would be any other way, but you all are smart.

I really had no idea that smaller openings gave you sharper focus...I can't believe I missed that.

Dane

Well, that's kind of right, and kind of not. I guess it depends on what you mean, though. All lenses have a "sweet spot" (i.e., certain f-stop range) that will produce the sharpest image for said lens. But, from how you put it, it seems like you're confusing "depth of field" with "in focus/sharp." Correct me if I'm wrong, though.

Using a smaller aperture (higher f-stop number) will increase the depth of field, or, in other words, what is in focus in the frame. Anything outside of the depth of field will be out of focus. On the contrary, using a larger aperture (lower f-stop number) will decrease the depth of field, minimizing what is in focus in the picture.

Shooting in low light situations can be challenging. It requires a knowledge of how aperture, shutter speed, and ISO affect exposure. If this is new to you, I would kindly recommend reading this. There are links to more information in that article as well.

A flash is not required to achieve an image that is in focus in low light. A lot of times, if the shot is posed, photographers will use manual focus because auto-focus sometimes struggles finding the proper focus due to poor lighting. Or, if you need the speed of auto-focus, try focusing on an area that is clearly defined and has some contrast so that the camera is not "hunting" to achieve focus.

EDIT: It looks like Nicole and I linked to the same article. Oh well.

[kencaleno]

Concerning exposure:

Exposure

Thanks to digital cameras, exposure has never been so easy and simple to achieve, for general outdoor photography. (Studio work still requires a hand-held meter and grey card for its more exacting demands on the photographer) Most of the time matrix (evaluative) metering, will do a great job. For portraiture, centre-weighted is preferred, and where high contrast separates dark from light, spot metering comes into its own. Considering stock photography, we need to also keep in mind the element of noise, the biggest reason for rejection in the business- noise can be reduced in post-processing, to an extent, but if we can avoid excessive noise when making our images, the better our chances of approval, and less time at the computer. Correct exposure is how to control noise at the making/taking stage- and correct exposure is simple-By studying the histogram on the camera’s monitor screen, we can adjust our exposure compensation to ensure that the bulk of the graph is just to the right of centre, and each end is just touching bottom corners.- If left-hand side of graph climbs left screen edge, the shot will be under-exposed, with no detail in the shadow areas: If the same thing happens to the right-hand side, highlights will be blown, rendering the shot totally useless. For a second opinion, we can use the highlight flashes, also on the monitor screen, which flash black and white when highlights are blown. NOTE: If you can, get hold of a hand-held exposure meter, and you will be amazed at the difference it will make to your images

The advantages of a hand-held flash/exposure meter

A flash meter can give exposure reading in reflected light and incidental light and can detect a one-tenth of an F-stop difference in light levels-A digital sensor has less dynamic range than negative film, and resembles slide film-If you get the exposure just a little bit off, the resulting images are less than desirable. Although software such as photoshop etc,. can correct exposure via curves and levels, by needing to redistribute tonal qualities in an image, valuable detail suffers in the process. If you look at the histogram of an image that has been manipulated in this manner, gaps will be apparent, to show that there are no pixels present in those tones. By using a hand-held meter, to gather exposure information, your image will need little, or no tonal correction in photoshop.
When you need to measure flash exposure, you can either set meter to flash, (Lightning symbol) for use with pocket wizards, or corded flash, (lightning symbol with C) when using a pc cord which plugs into the meter itself.

To use a hand-held meter, first you set the ISO rating, by pressing a button. Then you set the mode (ambient- just a sun symbol) flash, or corded flash. These also from a button push or wheel spin, depending on the make of meter. Your meter will either have a sliding opaque semi-sphere, (Like Half a ping-pong ball) or one that can be attached. For reflected readings ,detach, or retract this semi-sphere from the metering cell. Pointing meter slightly downwards, to avoid too much light from the sky, press the measurement button to get a reading. Readout will display shutter speed/aperture combination for correct exposure. you can then use either a wheel or up/down buttons, to cycle through the different combinations to suit speed of subject or aperture for desired depth of field, and transfer these settings to your DSLR. When you want to take an incident reading, use the semi-sphere over the metering cell, stand within the subject’s plane, and point meter to where photo is to be taken from, and adjust buttons accordingly

Your camera uses reflected light readings for exposure-light reflected from different subjects, will result in a range of tones, which your camera’s meter will try to average to give an overall exposure. It may not matter sometimes, but because any little deflection of lighting will give a different reading, and if you are photographing a wedding, for instance, it could look as if photos were taken on different days!
You may have noticed, at weddings, the pro photographer will hold a meter at the bride’s face, pointing to where the camera will be-This is taking an incident light reading - which actually measures the light falling on the subject, not affected by the tonal differences of the subjects coloring- as the light falling on any subject in the frame will be constant, so the incident reading will ensure that there will be detail in the black tuxedo, and the white of the wedding dress will not be blown out. .
Sometimes you will find a scene will be beyond the camera’s 5-stop dynamic range, so if you meter using ,Matrix (Evaluative) or Centre-weighted, you will lose some detail in either highlights or shadows. A split-graduated neutral density filter (ND Grad) is recommended, But if you don’t have one: Try Dynamic Range Increase: With camera on tripod: meter for highlight, take a shot-then meter for shadows, take another shot. In Photoshop, add lighter image to darker as a new layer, then: Select> Color Range-click highlights ,check “invert”, click “OK”. Add layer mask. Filter> Blur> Gaussian Blur 250 pixels. Flatten and save. You will get detail in highlights and shadows.







How zoom lenses can affect metering

There are two distinct types of zoom lenses
a) Constant aperture zooms, that maintain a fixed aperture when zooming
b) variable aperture zooms, where the aperture changes as you zoom

Therefore metering with a type b) zoom lens, is trickier than a type a) where the aperture remains constant, when in manual mode
So when you zoom away from the original metered scene, you will need to change the settings, because the aperture will have changed while zooming
So, with an 18-55 zoom lens, which aperture varies from F3.5-F5.6 as you zoom, If you get a meter reading at the 55mm (F5.6)setting, then zoom back to 18mm, your aperture will have changed to F3.5 .
Those two stops difference in exposure will make a noticeable effect on the final image



Manual Exposure Metering


Your camera uses reflected light readings for exposure-light reflected from different subjects, will result in a range of tones, which your camera’s meter will try to average to give an overall exposure. It may not matter sometimes, but because any little deflection of lighting will give a different reading, and if you are photographing a wedding, for instance, it could look as if photos were taken on different days!

Incident light-light falling on the subjects is always constant.
Start using your in-built Incident exposure meter- Your eyes!

This is how us oldies who started in the late 1950’s/60’s learn to read exposure: You will often hear the term “The sunny 16 rule”, or Basic Daylight Exposure” here it is explained:

Basically four apertures are used: F16; F11; F8; and F5.6

Shutter-speed is based on Equivalent ISO#

Watching the shadows, the base settings are: ( for ISO 200)

Hard-edged shadows …………………….1/200 sec @ F16

Soft-edged shadows………………………1/200 sec @ F11

Barely visible Shadows…………………..1.200 sec @ F8

No Shadows……………………………….1/200 sec @ F5.6


Remember, these are the base settings: so variants would be:

1/200 @ F16
1/400 @ F11
1/800 @ F8
1/1600 @ F5.6
These all give the same exposure (But with different depths of field)
The other 3 settings use the same spatial relationship, the settings you choose are based on subject movement and/or depth of field desired. For instance If you want to keep the Aperture at F8:


Hard shadows……………………………1/800 @ F8
Soft shadows…………………………….1/400@ F8

Barely visible shadows…………………1/200 @ F8

No shadows………………………………1/100 @ F8 (As shadows fade, more light is required)
Heavily overcast…………………………..1/125 @ F8

Deep Shade………………………………1/60 @ F8

Pre-thunderstorm…………………………1/30 @ F8

Brightly lit store interior……………………1/15 @ F8

Well-lit stage/sports arena…………………1/8 @ F8
Well-lit house interior……………………….¼ @ F8

(Of course you would vary the F stop and shutter speed combinations to whatever would be most appropriate. )


To get more exact exposure readings, you may want to bracket exposures. As you can’t use exposure compensation button when in manual made, this is what I do on my Nikon, your Dslr will have a similar action:

I set aperture to F16, and shutter-speed to 1/200, ( for Hard shadows) Take a shot, then:

2 clicks of the thumbwheel to the left-take a shot- this gives me a + 2/3 exposure
1 click to the right now, gives me + 1/3 exposure

1 more click to the right brings me back to the basic (meter as read) setting, then:

1 more click to the right gives me -1/3 exposure, and finally ,
1 more click to the right gives me - 2/3 exposure-so I have 5 exposures from 2/3rds over, to 2/3rds under exposure.

Looking at these, I choose the one that gives the most detail in the shadows and also in the highlights, without blowing the highlights-and after a while you will find you are able to guess just about right with your exposures-It is all very simple, and I hope I have explained in words that make it easy to understand.

Regards, Ken

[nathanbarlow]

that comes in handy for wide angles in particular. Literally, you can not not worry about focusing, as the DoF is so large, its sweet as, so you can just set the distance scale to approx (optional!) and FIRE!

Apparently NASA did this in space: used wide angles, and point and shoot it, no need for focus [remember the 60's had no(?) AF cameras]

[DCBarner]

I started to type a response that explaining that I wasn't talking about exposure, I was talking about focus. Then, I set to finding examples and then I started looking at EXIF data and THEN I found out I have no idea what I am talking about. So! New question: Take a look at these two photos, both are at the same f-stop number (5.6). One looks in focus and one looks OOF. Why?



1/50
400
30mm

And:



1/50
400
30mm

I do appreciate your help

[natek313]

To me, it looks like the focus in the first photo fell on his shoulders and the neck line of his shirt. This was either due to the photographer not focusing properly if he/she was using manual focus, or it was due to the auto-focus, if used, being fooled. The focus in the second picture looks good to me.

The aperture, as it relates to focus, is only going to influence the depth of field. Now, there are other factors that influence the depth of field, but that's another story. The size of the aperture is virtually arbitrary if you do not focus properly.

[OsmosisStudios]

Originally Posted by natek313

To me, it looks like the focus in the first photo fell on his shoulders and the neck line of his shirt. This was either due to the photographer not focusing properly if he/she was using manual focus, or it was due to the auto-focus, if used, being fooled. The focus in the second picture looks good to me.

The aperture, as it relates to focus, is only going to influence the depth of field. Now, there are other factors that influence the depth of field, but that's another story. The size of the aperture is virtually arbitrary if you do not focus properly.

Bingo. The first is OOF and the second is in focus. That simple. Its hard to nail focus with kids. The first could also be motion blur: the 1/50 shutterspeed is usually quick enough, but with moving kids it can be tricky.