Depth of field in a flower garden

Changing aperture and focus settings.

My wife and I recently visited the Auckland botanic gardens.  We quite enjoyed the walk and marveled at the wide assortment of plants and flowers present.  There was one area which grew a variety of spring blooming annuals which made a perfect setting for this depth of field blog.
Depth of field is controlled by a number of factors, but the three which the photographer has direct control over are focal length, aperture, and point of focus.  I shot three images of Kathryn, seen above, using my 150 - 600 mm birding lens.  Set at the 150 mm mark, it had a relative focal length of 225 mm on my Nikon digital crop sensor camera.
The first image would be the one I would normally go after, with foreground and background both blurred so draw your attention to the subject.  The key here is a longer focal length lens with a small f/number (wide aperture).  Larger sensors produce images with less depth of field given the same relative focal length, so using a full frame camera will produce narrower depth of fields than a compact camera will.  Focusing on the subject renders most other objects out to focus.
The middle image used all the same settings except that the point of focus was changed to the red poppy indicated.  The wide aperture and closer point of focus led to a very narrow depth of field, causing my subject to be very blurry.  If you notice though, your eye goes to the poppy without much prompting - this is a terrific way to draw your eye.  I will go into this in anther blog.
The last one used a small aperture (large f/number).  I increased the ISO so that my shutter speed would not be too slow.  The lens had vibration reduction, and I was three stops under the recommended hand held shutter speed without vibration mitigation technology.  Since I had this turned on, I was within its effective range, as long as the subject wasn't moving.  Point of focus placement is important, and I chose a spot about 1/3 of the way from the front poppy to the person.  You can see that depth of field was increased significantly.
This is one of the reasons I suggest shooting in aperture priority instead of program or an auto mode; you have much more control over aperture.  As you become more familiar with your camera its many controls you will be able to make better choices regarding the composition of your images.

Using a polarizer filter

A house in Russel, New Zealand.  The left was taken without a polarizer; the right used one.

Two shots, same building, same exposure.  The difference is the polarizer filter.  If you have never used a polarizer filter, you will be surprised by their usefulness.  It is an essential part of any well equipped photographer's arsenal.  And the good news is, they are not very expensive.
To really appreciate the difference in the two shots, I will take time to point them out.  The first is obvious; the sky.  Notice how the clouds stand out better in the second image.  Also the blues are darker and much more saturated.  This is not because it is blue, it is because of what the polarizer is doing.  We will get to that.
Take a look at the red roof.  The house had a vibrant red roof which starkly contrasted with its walls and windows.  The image without the polarizer does not capture that, but the one with the polarizer does.  Again, it is not a function of colour or hue; it is a function of what a polarizer does.
Another difference, more subtle, is the polarizer's effect on white balance.  Notice the right image appears a cleaner white.  The image on the left is flatter in contrast and has a certain hue of colour associated with it.  Polarizers remove some of the colour cast associated with blue skies.
OK - so it works.  The question is, "Why?"  The answer has to do with light coming in from the open blue sky.  Light from the sun vibrates in all planes, and they are not polarized.  That means that each ray of light vibrates at a random angle.  Polarizers do not let light pass though it that vibrate at a particular plane.  It will remove some light, which is why polarizer filters appear grey.  You have to give up about a stop of light.  But their benefits greatly outweigh this disadvantage.
Light reflected from open sky has a decidedly blue colour associated with it.  When it comes to earth it throws a colour cast on everything.  Whites and greys appear bluish, greens are much darker and the skies are brighter.  Put on a polarizer and look what happens.  That blue light gets pulled out so skies darken up, blue shades get removed, and colours appear the way they are meant to be.
Polarizers don't work all the time; they only work in situations where there is polarized light.  I take mine off indoors or during events which do not benefit from it.  There are times though, that it is great to have.

A lake near Hobart, Australia - with and without a polarizer

Lake near Hobart, Australia - Polarizer used.

Lake near Hobart, Australia - No polarizer used.

Anyone interested in doing the best job they can when capturing landscape images should think seriously about acquiring a polarizing filter.  They can be expensive, especially for lenses with large filter sizes; but a polarizing filter for your basic kit lens shouldn't set you back very much.  I have a 77 mm polarizer that I use for my ultra wide angle lens and my 28 - 300 mm lens.  I always travel with it because it just makes such a difference.

Notice the difference between the skies in the two images.  Even the boat and the sand are affected.  The grass is also changed.  This is because of what a polarizer does.  It filters out light traveling along a particular plane.  If there is no polarized light, it makes no difference other than acting as a bit of a neutral density filter.  However, on sunny days it can make an enormous difference.

The trick with a polarizer is to put it on only when it can make that difference.  Inside it has very little value, and cloudy days typically are without merit.  The place where it shines though is on sunny days, partly cloudy days, or in situations where you have annoying reflections coming off things like water or other shiny surfaces.

The best way to experience a polarizer is to get one.   Start off with a small one so you don't have to make too much of a sacrifice expenditure wise.  Borrow one if you can.  Play with it for a while and come to your own conclusion.  You will find that it is well worth the purchase and the time needed to attach it and play with its properties.