Tag Archives: iris

May ’11 Review

A small group of us from the GNPC went on a photowalk to RHS Hyde hall on 1st May, with the intention of doing some macro flower photography. However, we were somewhat thwarted by the fact that it was VERY windy! Never mind, I did manage a few reasonable shots, and this rather splendid purple Iris (complete with added fly) nearly made it on Day #1217:

Purple Iris
Purple Iris
Hanging Crystals
Hanging Crystals

After my stint at the BBC finished, I had a couple of days to draw breath before I went out with the Upminster Camera Club to judge their Shoot Maldon Live competition. I had a great time, despite the weather being rather variable. One of my own favourite images from the day was this detail [right] from the chandelier in the pub dining room – it would have been picture of the day had it fitted one of the six themes we were supposed to be shooting!

The Chelmsford Photowalk Flickr group had an early outing this month to visit the Essex Young Farmers’ Club Show in Roxwell. Plenty of photographic subjects to see, and there was an excellent turn out. Again, it was very windy so some shots were a bit limited by the conditions (the sun was in and out all afternoon). My multi-shot composite of the mad motorcylists had to be picture of the day, but if I hadn’t have had such a good image, then this rather striking (and clean!) picture of one of the old tractors on display would have been my choice:

Orange With Blue Nuts
Orange With Blue Nuts

Ingatestone Camera Club had their first summer photowalk on 31st May, where we had the free run of the grounds of Ingatestone Hall to ourselves. My macro shot of water lilies in the pond was ultimately what I chose for the day, but it was nearly this mono image of the Hall and pond. It had taken innumerable goes and oodles of patience to get all of the elements in the right place – when the sun was out, the swan had invariably swum off!

Ingatestone Hall And Pond
Ingatestone Hall And Pond

 

All About Apertures & F-numbers

Background
What is meant when referring to the “aperture” (or f-numbers) of a lens?

Photographic lenses contain an iris, made up of solid vanes, built in a similar pattern to those on the left. The vanes can move in and out, thus making the central hole larger or smaller – and so letting more or less light through the lens. This is what’s called the aperture, and is a guide to the speed of the lens.

The f-stop, (f-number) or aperture is not an absolute number, it’s also related to the physical diameter of the lens. So we can compare the relative apertures of a small compact camera’s lens with that of a large telephoto, and still get a sense of which is better at gathering light.

Theory
The main series of f-numbers goes as follows (a sequence of root 2): f/1.8, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32

This seems rather complicated and counter-intuitive at first, but the basic thing to remember is this:

lower f/number = larger hole = faster lens = better in low light
higher f/number = smaller hole = slower lens = better in bright light

Most SLR lenses will have their maximum aperture written on the side. This is the largest size of the hole, when the iris is fully retracted.

More expensive lenses will have a lower f-number, such as f/2.8, which means they have a larger maximum aperture – and will be better for taking photos in low-light conditions.

Things get complicated with zoom lenses – which often have a different maximum aperture at each end of the zoom range, eg. 28-105mm, f/4-5.6. This is saying:

at 28mm end, max aperture is f/4
at 105mm end, max aperture is f/5.6 (ie smaller than f/4.5)

How this affects your pictures – Depth of Field
The other thing which needs considering at this point, is something called Depth of Field. This means what proportion of the image is sharp, in front of and behind the actual point where you focus. I will cover depth of field more fully in another post, but for the purposes of apertures, in general, we need to remember the following:

lower f/number = smaller depth of field = less of image in focus
higher f/number = larger depth of field = more of image in focus

Examples
Let’s compare the effects of using two extremes of f/number:

f/2.8

  • Large aperture
  • Good in overcast or low-light conditions
  • Will tend to require using faster shutter speeds
  • Smaller depth of field – less of the overall image in focus
  • Better for portaits or closeups, because backgrounds become blurred and do not intrude

[large aperture – in low-light conditions, giving small depth of field (only the first couple of blooms are in focus). The background is unobtrusive]

f/16

  • Small aperture
  • Good in bright, sunny conditions
  • Will tend to require using slower shutter speeds
  • Larger depth of field – more of the overall image in focus
  • Great for landscapes, where you want everything, from a few meters to infinity, to be sharp

[small aperture – in sunny conditions, giving a large depth of field (almost everything is sharp), great for landscape work]

As good practice, why not turn your camera to AP (aperture-priority) mode and take a few pictures of the same subject, but using different aperture settings. This will show you exactly what the effects of controlling the aperture can do for your photographs.