In the previous article I addressed the choice based on which focal length you use and whether a single focal length lens might be a better answer.  In this article I would like to talk about the decision from more of a user perspective concentrating on when a prime lens might be a better choice to have on your camera.

From an image quality perspective, a prime lens will almost always be better if you tend to use your zoom lens at either extreme of the zoom range.  The design of zoom lenses are more of a compromise and they generally perform best about 1/3 of the way into the zoom range and worse at the extremes … much worse at the longest zoom range.  In addition, zoom lenses usually have much smaller apertures than primes … at least for us mortals who can’t afford, or carry, a professional F2.8 long zoom.  The small apertures reduce the transmitted light and you have to shoot at a higher ISO setting to achieve reasonable shutter speeds.   This is most important in low light settings inside buildings, etc.   For these reasons, if you want better image quality, the prime is the lens to use.

Another issue relative to selecting a lens is the change in perspective.  It’s really not the focal length but a matter of how far you are away from the subject.  Read the quote below and click on it for a good explanation and demonstration.

“Many will say that focal length also determines the perspective of an image, but strictly speaking, perspective only changes with one’s location relative to their subject. If one tries to achieve the same subjects filling the frame with both a wide angle and telephoto lens, then perspective does indeed change because one is forced to move closer or further from their subject. For these scenarios only, the wide angle lens exaggerates or stretches perspective, whereas the telephoto lens compresses or flattens perspective.”

The main issue is how you wish to view your subject.  With a prime lens it will be consistent, with a zoom lens it will change depending on how much you zoom, and it always depends on how far away you are from your subject.

Another concern is changing lenses.  You have to be careful when changing lenses in the field so that you don’t get dirt on the sensor.  The data aren’t really in yet since the cameras are so new, but this might be a larger problem with the mirror-less cameras since when you take the lens off to change it, the sensor is sitting right up front.  Therefore, if you must change focal lengths frequently in a dirty environment, a zoom is probably a better option.

When traveling, I often visit towns & markets where there are a lot of people and I’m essentially “streetshooting”.   When shooting in those environments, I’m not comfortable having a big long lens mounted on a large camera since I think it diminishes my chances of getting candid shots of people.  One recommendation that I have seen is to try to blend in and not look like a professional photographer.  If you are shooting with a small inexpensive looking camera, people seem to pay less attention to you.

Another feature about prime lenses is that they are smaller and easier to carry in a small “non-camera” bag, either when mounted on the camera or carried separately.  I often carry my camera with a prime lens on it in my jacket pocket thus I don’t even need a bag as long as I also have a spare battery and memory card in another pocket.  But I only carry it this way in between areas where I might be taking pictures.  If I’m planning on shooting frequently I carry the camera around my neck or in my hand.  In addition, a couple of prime lenses are usually lighter to carry and if you have been reading my other articles you know that this is a big requirement for me.

If you consider all of the above carefully, you should be in a better position to decide which lenses to take with you on your next trip.  For me, I’m planning on going to Ireland at the beginning of summer and as of now, I’m planning on walking-about during the day with a 14mm prime lens on my micro four-thirds camera and my 14 – 150mm zoom lens in my bag just in case I need it.  In addition I will use my 20mm lens on my camera in the evening or in any low light setting.  (Don’t forget that there is a factor of 2x for converting these to 35mm camera equivalents.)   When I get to wherever I’m going, I can reevaluate the situation and make changes as needed.  As an example, if I were traveling to Costa Rica I would carry the camera with the 14 – 150mm lens mounted on it.  In that location it is more important to have the versatility a zoom represents relative to focal length.

Good luck with your choices.  In the last year I have been drifting more towards using prime lenses rather than zoom lenses for pretty much the same reasons that Nik stated in his comments to an earlier article.  I’ll let you know what I used in Ireland after I return.  At the moment I’m betting on this one … Olympus E-PL2 with the Panasonic 14mm f/2.5 lens, but I still have to take it out and try it in a similar setting.