Do I Really Need An f2.8 Lens to “Cook” the Background In My Photos?


This is a really hot topic of discussion right now. It applies to me nearly all the time because I am a big fan of outdoor or location portraits. I’ve read really heated discussions on this and there are strong arguments for both sides, but I’m going to do a little “show and tell” about what I found out about my gear in my gear bag.

I recently had a friendly conversation with my friend Tom at Calumet Photo here in San Diego. I was talking to him about how a lot of folks are selling or trading glass to get Sigma or Tamron f2.8 zoom lenses. I explained that I have the Nikon 16-85mm VR and 70-300mm VR lenses for zooms and what he thought about those lenses compared to the Tamron and Sigma zooms. What he said may (or may not) shock you.

Tom told me that as a friend, he would tell me to keep the Nikon glass unless I really needed to shoot in low-light situations ALL THE TIME. Notice I emphasized those last three words. He said that for the work that I do that I would get no increase (and maybe even a slight decrease) in optical quality with a Tamron or Sigma lens.

Cooking The Background

This is a term or phrase used to describe dialing in a large aperture (small f-stop number) into your camera in order to keep your subject in focus and throw your background out of focus. This is directly related to Depth of Field. A shallow depth of field will allow you to “cook” the background (great for portraits), while a deep depth of field keeps everything in your image in focus (great for landscapes).

Small aperture setting (large f-stop number, like f22) = deep depth of field
Large aperture setting (small f-stop number, like f4) = shallow depth of field

There are a couple of other things that affect this as well, like focal length of your lens, subject to background distance, and focusing distance.

The image you see above I shot with my D90 and Nikon 70-300mm VR lens at f5.6. I had the lens racked all the way out to 300mm and I was about 6 feet away from the hummingbird feeder. My background was about another 10 feet away and I was able to really throw my background out of focus, which draws the viewers eye to the bird.

Many pro photographers say that the sweet aperture for shooting portraits and throwing the background out of focus is f4, which I can’t do at all with that lens, at any focal length. It’s maximum aperture is f4.5. However as you can see above, f5.6 looks pretty good and I probably won’t have any trouble cooking the background on an outdoor photo shoot.

So after saying all that, I hope you got my point. If not, my point is that you don’t necessarily need f2.8 glass to be able to cook the background in your images. Pay attention to your ratios that I mentioned above and you’ll be fine. I really don’t need f2.8 glass because I don’t shoot in low light situations very often and even if I did, I can get very useable images out of the D90 even at ISO 3200. If I really need some fast glass, I’ll probably just rent a really good Nikon lens like the 70-200 f2.8 or the like. Although, there are definitely some more Nikon prime lenses in my future!

If you have questions or comments, feel free to leave them below and I’ll answer them as quickly as I can. Have a great day and I’ll see you tomorrow for a little lesson in macro work.


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2 thoughts on “Do I Really Need An f2.8 Lens to “Cook” the Background In My Photos?

  1. Pingback: links for 2009-03-04 | Steve G. Bisig Photography

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