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This weekend I followed my own advice, and rented a lens to try out before deciding whether or not to buy it. As I suggest in my post Why You Shouldn’t Buy the Kit Lens, if you are considering purchasing an expensive lens or want to compare a couple similar lenses to decide which one to go with, rent one or both of them for a day or a weekend, and see how you like using them. Check with camera stores near you, or look into online lens rental sites that mail the lens to you, like I went to Calumet to rent, since there is a store near me and it’s pretty cheap for the weekend rate.

(click on any product links in the text to view the lenses on

I rented the Canon 24-70mm f/2.8L since I’m curious how it compares to the Canon 24-105mm f/4L IS. While they have a similar focal-length range and can each serve as a great walk-around lens for everyday use, they have some differences that make it difficult to choose between the two. The 24-70mm is larger, significantly heavier (2.1 lbs. vs. 1.48 lbs.) and extends externally as you zoom. The 24-105mm has an internal zoom mechanism, and also has image stabilization (IS). But a major difference is the maximum aperture: f/2.8 vs. f/4.

side by side bokeh
click here to view these images larger on Flickr – from the garden at the Longfellow House, Cambridge, MA

The wider maximum aperture of the 24-70mm makes it a “faster” lens, allowing it to be used in lower light, although the IS of the 24-105mm can make up for that shortcoming. Visually, the wider maximum aperture allows for shallower depth of field (dof) which provides more dramatically blurred backgrounds, or bokeh. While I have resisted using the term bokeh in my writing, I can’t really avoid it in this discussion because the difference between f/4 vs. f/2.8 is all in the bokeh. The above image demonstrates what that means. It refers to the “circles of confusion” of the out-of-focus areas of an image – their size, shape, edges, and quality. Both of the images are taken with the 24-70mm lens – at f/4 on the left, and f/2.8 on the right. You can see that while they both demonstrate dramatically shallow depth of field and background blurring, the image taken with the aperture set at f/2.8 shows a smoother blend of the background colors and contrasts. The images are from the garden of the Longfellow House in Cambridge, MA.

When I got my Canon 70-200mm f/4L IS lens, I chose the f/4 version rather than the f/2.8 IS version because it was smaller and significantly lighter, and I knew I would not dread using it on a long day of shooting as I feared I would with the 3.24 pound f/2.8 IS version. Three and a quarter pounds! (According to the Canon website. I’m not sure if that is right – Amazon says it is 2.9 lbs.) Anyway, that kind of weight might be an important consideration for someone traveling with a lens or using it for consecutive full days of shooting. I know it is a consideration for me. So, even though I got the f/4, I’ve wondered what I have been missing image-wise by not being able to open up to f/2.8. So I took these two images with the 24-70mm to see the difference, and it is more considerable than I had thought it would be.

I was very pleased with the 24-70mm. I had been concerned that I would want more range on the telephoto end, and I did end up with a lot of images taken at the 70mm focal length, but I didn’t usually feel like I needed or wanted to zoom in any closer. It really is a great range for everyday use. It is a big lens, but other than the weight, it feels great and is comfortable to use. You can’t deny its image quality, the bokeh is wonderful, but the weight is still a consideration and may dissuade me in the end.

Here is a great site at to compare lenses, side by side. You can compare test images taken at various focal lengths and apertures. I will leave all the pixel peeping and debating of the merits of the 24-70mm vs. the 24-105mm to the forums, and just share a few photos I took with the 24-70mm at the Harvard Museum of Natural History and the adjoining Peabody Museum of Archaeology and Ethnology. All the images are hand-held, without flash, in very low lighting. The leaves and flowers in the images below are from the world renowned glass flower collection. Yes, they are made entirely of glass! Even those fall leaves. It is mind boggling, especially when viewing them in person.

If you are considering buying any of these lenses from, please use the links above, and I will get a little something for referring you. Or use this link to go directly to I appreciate your support!

HMNH cat

HMNH bird-hawk

HMNH bird-dove

HMNH autumn leaves
glass leaves above, glass flowers below. yes 100% made of glass!
HMNH purple flowers

HMNH snake

HMNH fish fossil

HMNH Peru map

HMNH Mayan stones

HMNH Indian diorama

HMNH Indian diorama 2

I responded to a comment on one of my posts, and my response ended up being the size of a blog post, so I’m just going to turn it into one! Please note that the title of this post should actually, technically be “Fixed Maximum Aperture vs. Variable Maximum Aperture,” as I will explain in a second.

If you are getting into dSLR cameras and lenses, you may have noticed that some lenses have a fixed maximum aperture, while others have a variable maximum aperture.  This is spelled out in the name of the lens.  For example, the Canon EF-S 17-55mm f/2.8 IS USM lens has a fixed maximum aperture of f/2.8 at all focal lengths, while the Canon EF 28-135mm f/3.5-5.6 IS USM has a variable maximum aperture which ranges from f/3.5 to f/5.6, depending on which focal length you are using.  (the EF vs. EF-S means that EF lenses can be used on any Canon dSLR, while EF-S lenses are designed for, and can only be used on Canon dSLRs with 1.6x cropped sensors, including all Rebels, 50D, 60D, 7D, T2i/550D, but not the full frame 5D.  IS means image stabilization.  USM means ultrasonic motor, and means the lens has a high quality, rapid, and quiet motor for auto focusing.) The term fixed aperture usually does not mean that the lens only has one aperture setting you can use, but rather that is a common way of saying it has a fixed maximum aperture. So you can change the aperture of a “fixed aperture” lens and set it anywhere from its maximum aperture, possibly f/2.8, to its minimum aperture, perhaps f/32.

Barbes drummer face
Barbes, Brooklyn, NY

With variable aperture lenses, the largest, maximum aperture you can choose when you zoom to the telephoto end will not be as wide open as the largest aperture you can choose at the wide angle end. For example with the 28-135mm f/3.5-5.6, with the lens set at the focal length of 28mm (the wide end), you can use the f/3.5 aperture setting. But with the lens zoomed to 135mm, the widest aperture you can use is f/5.6. This will slightly affect the amount of background blurring – or foreground blurring in the image above, and will decrease the amount of light entering the lens.  Wider, larger apertures like f/2.8 or f/3.5 blur the background the most, which helps to create dramatic images.  The reason not all lenses have fixed apertures is that they require more sophisticated internal parts and mechanisms, such as more lens elements, which thus makes them very expensive (and heavy), so variable aperture is a compromise in order to offer more reasonably priced lenses.

Barbes sax hands
Barbes, Brooklyn, NY

Also, the wider apertures (f/2.8, f/4) are best for low light situations because they allow more light to enter the camera and thus allow you to select a fast shutter speed that won’t blur the image while hand-holding the camera. If you are typically working outside, this shouldn’t be too much of a concern, but if you work indoors or in low light, lenses with wide apertures like f/2.8 or f/1.4 are desirable.

Now, why is f/2.8 called a large aperture and f/22 a small aperture?  2.8 seems like a smaller number than 22, right?  No, f/2.8 and f/22 are fractions.  So if f were to equal 1, a slice of pie that is 1/2.8 of the pie is a bigger piece that a slice that is 1/22 of the pie, right?!  So f/2.8 is a large aperture, which means a large opening, which lets in lots of light all at once, but which then causes objects not in the plane of focus, such as the background, to be blurry.  f/22 is a small aperture, a small opening which lets in just a little light.  But everything from near to far is in focus, like when you squint to see a street sign clearer!  (The letter f in the fraction stands for the focal length of the lens.)

Please leave a comment, ask a question.  Let me know what has been helpful, and what you’d like to read more about.

For additional posts about lenses see Best Lenses for Travel and Humanitarian Photography and Why You Shouldn’t Buy the Kit Lens.

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