ISO, fstop, EV from a different perspective

more light please...

there are lots of entries/articles out there explaining fstop, ISO, shutter speed, and the like. They all are speaking from the camera's perspective. Well, today I want to allude to these from the photographers perspective.

The scenario... My boy is in the dining room having breakfast, alone. The rest of the kids are asleep or otherwise occupied.  I grab the camera for some shots because the light from the window (no other ambient light source) is inviting.

I am using the 70-200mm lens... because it's attached and I really like it for portraits.  I try to compose the shot with mainly his face and his breakfast.  I also want to get some darks just behind his head because I want his exposed face to really stand out. I want to contrast with focus as well, hence the long zoom and wide aperture (more to come).

And mind you, I am not thinking all of the following items prior to first shot. I am thinking, shooting, looking at image, then repeating the process until I start to see what I want... often called "chimping".

First, I put the camera in A mode (aperture priority)- this way I can adjust the fstop, the ISO, and the EV. So ISO first. I have recently set my ISO to full stops... This means when I move my ISO selector, it moves in these increments 100, 200, 400, 800, 1600. If I had a cropped sensor, I would be a little more conservative and put 1/2 steps. This is because the full size sensor looks just fine at ISO 1600. So, ISO 800 is what I choose... [could have gone 1600 in retrospect to allow for faster shutter speed, because about half of my images weren't crisp clear.]  By the way, I have also changed my fstop to full stops too.  This is because when I am working with my Manual powered flashes, it's simpler math.  So ISO 800

Next, fstop. When I adjust fstop in A mode, I am wanting to see what the camera gives my in shutter speed. So I choose f2.8 (wide open). This will give me a really narrow depth of focus, but I may be willing to take it. I try 2.8 and I try 4. I end up using 4 because it gives me a little more playing room of focus distance. See previous blog of depth of field, or depth of focus  If I chose f2.8,  point my camera at my subject, then it gives a shutter speed of 1/125 - that's ok. But I want deeper focus, so I change to f4 and figure the 1/60 will work out.

I end up shooting my subject at 160mm so that my subject more fully fills the frame.
***The rule of thumb to avoid blur due to large zoom is to have the shutter speed match the zoom. So my shutter speed should be around 1/160***   Having said that, vibration reduction allows me to use slower speeds and not get the blur.

So, I've set my ISO to 800 and my fstop to 4.  I turn on the VR (vibration reduction) - don't use this if you are on a tripod.  I shoot off a couple of shots, and my subject is too bright for my taste.  What can I do to underexpose the picture a little, yet not have to change to manual mode and dial in f4 and 1/60th?  The answer:  adjust the EV.  Exposure value (EV) is a nice little tool.  I find I use it when my camera is trying to expose for the darker part of the image, and my subject is overexposed.  This usually occurs when the majority of the frame is dark and I am using matrix metering.
IE:  yesterday I was scouting out a place for some engagement shots I am doing for a neighbor and I had a barn in the semi-shade and the cloudy/blue sky as well.  It appeared that I was overexposing the sky to get the barn in correct exposure.  So I dialed my EV down 1 full stop (to -1.0) and those highlights were no longer blown out.  I can easily go back and add highlights in post-processing.

To recap... ISO 800 due to low lighting
f4 to maintain large aperture but still have good depth of focus
EV -1.0 to allow a slightly underexposed image
Result:  good lighting, not so good composition.

What did the subject think of the image?  --"I am really small... I have volcano hair."
Analysis... my subject is smack in the middle... fix: crop
Also, I am not liking the blue chair in the background... it is distracting.  fix: bw or desaturate just the blue
if bw, then increase the contrast to pop the whites

So, the blue chair becomes gray and is still distracting... bummer.  But I like the image other than that.

Pic of the day:  I really like this pose and composition... in fact most all of her images are impeccable.

Reference

breaking it down - aka "Baby Steps"

Here's the scenario.  I grab my camera, turn it on, adjust some settings, and go to take the picture.  Why is it black?  Yup, even I leave the lens cap on occasionally.

So what steps do I take?  Today, I will start with the first three.  Forgive me if I leave out any steps... this is the first time I have really thought about what I do step by step.

1) Decide which lens to shoot with.  Most of the time, I leave the 24-70mm lens on... esp for indoor shots and outdoor landscapes.  If I am shooting portraits outdoor with more room to shoot or I want to grab some real detail, I grab the 70-200mm.  And on some occasions, I will grab the 300mm.  These are all fixed aperture lenses (f2.8).  If you have a lens with variable f-stop (kit lenses that come with many cameras) no problem - I will address this in the next post

NOTE: Steps 2 and 3 are quite simultaneous

2) Turn on the camera and check the ISO.  If I am shooting low light, I will push it up to between 1250 and 2000.  If I am out of doors it will be set at 200 or lower.  And then you have the in between 400-800 where there is sufficient light indoors, but you are shooting a subject that will be moving quite a bit.

3)  I decide whether or not to use a flash.  The flash will help highlight my subject, create ambient light, or act as a filler for shadows in the outdoor shots.  (Here I also decide whether or not I will grab a second flash to be off-camera)

Oh yah, this is a good time to take off the lens cap so I can move on to the next few steps...

...to be continued...

If you are ready for more of the WHY behind these steps, I have added some additional information here:

Step 1:  lenses... my subject matter and my depth of field are the two major deciding factors for lens selection.  In general, for shooting landscapes (including skies) I want wide angle.  At times, it would be ok to do a single portrait at something less than 35mm.  Remember that distortion on portraits is generally not very flattering. Wide angle gives me large depth of field, so my focus will be infinite most of the time.  As I go longer on my lens (higher mm or ZOOM), the shorter my depth of field or focus will be.  Remember the calculation considers distance to subject, fstop, and mm of lens (remember to consider crop factor).

Step 2: the ISO.  The reason I choose the ISO first is that it is the canvas of the image.  If an oil painter used a napkin to paint on, the results would be sub-par at best... Same with a photographer shooting ISO 64000 on a little point and shoot camera.  ISO 200 on an upper end camera is more like a proper canvas.  The graininess of the image (or pixelation) is determined by the quality of canvas.  Thus, with the newer cameras, they are, in this analogy, trying to make the smaller canvases work like larger or higher quality canvas material so that you can push the ISO more and more with better results.  The size of the sensor is the major determinant in the quality of the image, especially as you begin to shoot in lower light and push the ISO higher. The challenge for camera companies is to have the processors (computers) in the newer cameras do more with less light (thus achieving higher quality images and less noise with the same size sensor).  

Step 3: to flash or not to flash - and to flash on camera only, or off camera as well - this is where we get into the exposure, style, multiple light sources, and much much more... so this is much to large to define here.  

LINKS

Here is a good link to ISO explained

DOF App

IMAGE of INTEREST (Pic of the Day)

Tough image to expose correctly.  Well done with the fill flash.  Obviously off camera flash. 

Shot at 48mm, f8.0 at 1/320 at ISO 400

From the photographers notes:

Lighting -
Alienbee AB1600, camera-left just out of the frame at 1/8 power into large softbox that was threatening to take off like a sail, and would've gone over the cliff that the b/g were standing on if not for an assistant with cat-like reflexes.
Bare Vivitar 283 at 1/16 power camera-right and behind couple.

Reference