Lesson number 2: The lens


posted on 11th of july, 2012

Continuing on from my first post on camera bodies (camera bodies - lesson 1), here is a bit of extremely basic information on camera lenses, in plain, simple English. As before, I am writing this with novice photographers in mind; those who are new to the world of SLR and stock and want a bit of basic, easy to digest information.

When I opened the box of my first SLR, I found a shiny 18-55mm lens sitting inside. I asked myself, ‘what does the 18 – 55mm actually mean?’
Those values are the measurement of the lens's focal length; in layman's terms, its ability to zoom. The mathematics of lenses are fairly complex (and therefore beyond me). Put simply however, in this instance, 18mm is zoomed out whereas 55mm is zoomed in.

So as I rotate the lens towards the 18mm setting, I am setting it to a wider angle and I can take in more of what is in front of me (however objects appear further away). When I rotate it the other way towards the 55mm setting, I am zooming in so as to be able to see objects close up. Of course, I will then sacrifice being able to see more of the area surrounding the object.

Put more accurately, a lens has the effect of bending light rays. Therefore parallel rays of light emanating from an object and passing through a lens will bend so as to converge on a point (in the case of a camera, the sensor). The distance from the lens to this point is called the focal length.
That’s the basics taken care of. Obviously when choosing a new lens, focal length range is one of the biggest considerations. So what else do you need to consider, and why not just stick to the kit lens?

• Quality of the glass is what really counts! The optics are what make your photo crisp and vivid. There are plenty of sites out there reviewing the various lenses, but be sure to take into account customer reviews such as those on amazon and other forums, I can’t recommend this enough. I started out with a canon kit lens (18 – 55 mm) and swapped for a Tamron 17- 50 and I noticed the difference in quality straight away.

• The greater the focal length range of a lens, the worse are the optics. To illustrate this: a 50mm prime lens (one which is fixed at 50 mm and can’t ‘zoom’, will generally have good optics because everything about it is designed to work at 50 mm (and it’s cheap). Prime lenses can produce some stunning images. An 18 – 300 mm lens will generally have poorer optics because the glass is having to compromise in order to work at the greater ranges. The loss of quality is more marked towards the extremes (i.e 18 mm and 300 mm). This is why I replaced my kit lens with one of similar focal length range. 17 – 50 mm can retain good quality in terms of optics and I have rarely needed anything outside of that range anyway. If I wanted a greater zoom level, I would be better off going for an additional 50 – 130 mm lens (for example), rather than going for a replacement 18 – 130 mm lens. The trade off in having two lenses is having to swap between the lenses every now and then. Here is a tip. Don’t rush into replacing your kit lens. Take plenty of photos, play around with it in the studio and out and about. Then sit down, and really look at the type of photos you actually take (not what you think you take). Lightroom is great for this as you can sort your photos by focal length and gain an insight into your photographic habits. For example, I always thought that I desperately needed a powerful zoom to take photos of distant deer, birds, elephants etc. It turns out that I very rarely take such photos, and there are no elephants where I’m from anyway. So when choosing a future lens, I knew that I tended to take more wide angle shots, and that around 50mm is close enough for nearly all the photos I take.

Here is on of my wide angle shots of Tokyo:




And a close up shot:








• The next factor to think about is image stabilisation (IS). Having a stabilised lens will allow you to take photos at a slower shutter speed without suffering from camera shake. I went through a period of being obsessed with having image stabilisation. I suffered from severe lens jealousy until I finally got my hand on a friend’s stabilised lens. In the end I wasn’t that taken with it, and had aged ten years through stress all for nothing. IS certainly does work, but bear in mind that it does not help when taking photos of moving objects. For the conditions in which I usually take photos, I just found it to be unnecessary, so I decided not to make image stabilisation a factor when choosing future lenses; there are other things to think about.

• Aperture is also a consideration. It is worth remembering that some lenses are able to work at a wider maximum aperture than others. This becomes important in low light and those shots requiring a nice blurred background – all to be explained in my next blog post.

Thanks for reading and happy shopping. Please browse my portfolio or check out my site hiblaze.comuf.com

Comments (7)

Posted by Montylola on July 17, 2012
That is one of the reasons for the large apertures, they are the ones that give one the ability to create Bokeh effects and have part of ones image in sharp focus and the background or foreground out of focus.

David May
Posted by Martingraf on July 14, 2012
I hadn't the money to buy good new lenses = so I bought very good used ones - also exceptional good zoom teles. I rather have a small scratch or a dust corn in or on the lens than a lens which has miserable optics from the beginning.
Posted by Kimdeadman on July 13, 2012
Absolutely, David, I completely agree. My kit lens was indeed 3.8 at its largest, and I upgraded to a fixed aperture 2.8 (tamron) which I love. It does pretty much everything I want and is good in low light. I have a question though - I have never taken photos with an aperture larger than 2.8. Do you not sometimes find that you actually get too much out of foucs at these apertures?
Posted by Montylola on July 12, 2012
Very helpful and plain english explanation, just as important as focal length is the speed of the lens. I would think that the 18-55 lens you got with your system would be quite slow ie the largest fstop would probably be 3.8 or even 4.5. I learnt very early on that a fast lens, one that has an aperture greater that 2.8 are ones to aim at purchasing, so my prime 50mm lens is a 1.4 gives one my more latitude and flexibility.

Regarding zoom lenes I think unless you are shooting objects or animals at a distance, more than 100mm is a waste of money because unless you spend a HEAP of money on the lens, it will suffer from being a very SLOW lens ie it's largest aperture will not be a very small number.

The lenses I use most are 17-35mm 2.8 and a 24-85mm 2.8 and a 50mm 1.4.

Just my thoughts
David May
Posted by Mike2focus on July 12, 2012
Thanks, great info! I'm going to step up my lens quality in the future and this is some good reference material. M
Posted by Laurasinelle on July 11, 2012
Interesting blog, thanks for sharing!
Posted by FabioConcetta on July 11, 2012
Interesting lesson, congrats!



Comments (7)

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Photo credits: Kim Deadman.

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