What should you consider when buying a zoom?

Canon EF 70-200mm f2.8L IS USM

Canon 75-300mm f4/5.6 USM

The images above have been taken with the "good lens" above and with the "cheap lens" below.  Click on the image to see the small details on big sizes on Flickr. Compare the details on the leaves of the plants and not on the flowers. This is very tricky because the main subject are the flowers. An untrained eye might not see the differences on a first look!

The other day I was cleaning my closet and found an old lens: a Canon 75-300mm f4/5.6 USM.

I had forgotten about it. Three years ago I bought another long zoom (Canon EF 70-200mm f2.8L IS USM) and tried to sell the old lens but of course, did not succeed (people on this land only buy second hand if it costs 20 bucks).

After all this time using the IS lens, I can write down some points I wish someone would have said to me when I was busy buying lenses...


Aperture

On the north of the planet we have a different light than on the south. On Brazil, even setting the camera to ISO 50, I might need to use some neutral density filter to cut off the light getting into the camera. That also means I might need to set the lens aperture up, missing my blurred background.

On the north, even setting your ISO to 1600, an aperture of f5.6 is not enough on a winter day: you will notice that you won't achieve an acceptable shutter speed (as a rule, shutter speed = 2x focal length). Example: if I am trying to take a picture on a winter day using a focal length of 300mm, I would need a shutter speed of at least 1/500s, which is almost impossible to achieve on a winter day, even with ISO 1600.

 Keep on mind that a zoom lens that has a minimal aperture of f5.6 on his longest focal length (like my old lens) will request you to use a tripod. It won't be useful to take pictures of your baby running around because you won't be able to freeze any scene. If the idea is to use the lens only on beautiful bright days, outside, you can give it a try.

Image Stabilizer (IS) helps a lot. You can still take sharp pictures with a shutter speed around 1/30s!

The use of flash is a little difficult with such a long lens (not impossible): if you photograph with flash, you must be sure you bounce your flash light otherwise you catch the shadow of your own lens!

Weigth

That is another story. My IS lens is gorgeous... but it weights 1490gr! Add to it the camera and you  lift a dumbbell of almost 3Kg! No need to go to the gym.

Sharpness


Sharpness is a very subjective property on a lens: if you are unable to support yourself properly, use a tripod and have an acceptable shutter speed, your pictures won't be sharp, it doesn't matter how expensive your lens is.

But, on the other hand, if you can achieve the three basic points to have a sharp picture, the difference on sharpness will be something subjective: someone that is untrained will look at the picture, will say one might be better than the other but he/she will be unable to say why. Composition will have a much higher importance than the pureness of the glass.

The quality on the glass of a lens will be really visible for the trained eye or when you crop your pictures: details get bigger and then you see fringes and aberrations (blue/violet edges on objects). Lightroom can correct this for you automatically because it has a profile for each lens in the market: just click on "enable profile corrections" and you are done. But even though, sharpness can be quite messy on an entry line lens.

Again, it is subjective. See my flowers above and compare the images!

Conclusion

I still think an entry-level zoom lens can open-up a new world for you. It is exciting to see the world with such a small angle. If you keep the limitations on mind, like not being able to photograph your baby running into the house, you might have lots of fun, specially if going on holidays on sunny places.

I don't regret to have bought my first "cheap" zoom lens but I must say I did not find it very useful in The Netherlands. I have used it a lot during summer holidays but not much here due to the lack of light.

But with light, my cheap plastic 75-300mm  did a very good job! See below!