Points in Focus Photography

Some Thoughts on Extension Tubes

I like macro photography. I don’t shoot a lot of it mostly because it’s a pain in the rear and requires specialized equipment to do well. I do own a macro lens, a Sigma 150 mm f/2.8 EX DG APO HSM, but the problem with a macro lens is that it’s a whole lens. Don’t get me wrong, a purpose built macro lens is the best possible quality solution for macro photography.

Of course you don’t need a 1:1 macro lens to do really nice close up work. There are plenty of reasonably good close up but still general purpose zooms on the market. A lot of the 3rd party lenses top out of 0.25x magnification, which isn’t great but it’s better than nothing.

Canon has done some interesting work on that front, with their EF 24–70mm f/4L IS USM, which on its own is decent range for a general purpose walkabout zoom, but can zoomed into macro mode where it gets a very respectable 0.7x. Likewise, the EF 100–400mm f/4.5–5.6L IS USM II, gets a pretty respectable 0.31x magnification at 400 mm and does even better at 0.44x and 0.64x with a 1.4x and 2x teleconverter respectively. In fact, the 100–400 mark II with the relatively huge working distance of 3.2 feet, makes a really nice lens for those little critters you don’t want to or can’t get that close to.

Don’t get me wrong, I don’t have a beef with using a purpose built macro lens per se. My problem mostly comes down to what I can pack in my bag when I’m going somewhere. Sure if I know I’m gonna be in a macro rich environment, sure I’ll pack the macro. But more often than not though, taking the macro means leaving some other lens behind, and that can be a tough pill to swallow.

The other macro option is to use an add-on to modify another lens; extension tubes. Tubes aren’t the only option, there are also close up lenses, and each have their strengths and weaknesses, but it’s tubes I’m talking about because it’s tubes I’m giving a whirl.

Extension tubes work by moving the lens away from the camera. This has the effect of reducing the close focusing distance and thus increasing the magnification.

Of course, like everything in photography, this doesn’t come for free.

To start with, by moving the lens away from the body, you lose the ability to focus at infinity. I don’t really see this as a problem when shooting macro, but it is if you want to quickly transition between macro and non-macro modes.

However, the problems don’t stop there. The increase magnification is related to the focal length and amount of extension. Which is a long winded way to say the longer your lens’s focal length, the less effective the extension tubes are at increasing the magnification.

Put a 25 mm extension tube on a 70 mm lens like the EF 24–70mm f/2.8L USM II, which has a max magnification of 0.21x natively, and you get a maximum magnification of 0.74x at 70 mm with a working distance of 229 mm. Put the same 25 mm extension tube on an EF 70–200mm F/2.8L IS II USM, which has a magnification of 0.21x natively, and you only get 0.31x magnification at 200 mm at a working distance of 862 mm. In fact, due to different minimum focus distances, even if you use that EF 70–200mm f/2.8L IS II USM at 70 mm, you only get a maximum magnification of 0.48x.

Oh but wait there’s more. Image quality, at least in the corners, can degrade significantly if you push a lot of extension for high magnifications. Remember, we’re using regular lenses. Having really well controlled optical performance at very high magnifications wasn’t part of their design goals. Using better quality lenses, does help, but even then there are limits. The first place I see my images degrade is in the corners and along the edges, even when the center stays quite sharp.

With all these downsides, why would I bother to want to use extension tubes at all?

For me, the biggest consideration ends up being size and the functionality I get for the size. A 12 mm tube is long enough to get my 24–70 to 0.45x magnification. That’s generally close enough that I can shoot pretty much anything I want with it. But the kicker is it’s only 12 mm thick. Even with caps, a 12 mm tube is thin enough I can toss it in just about any pocket and not worry about it. Heck, it is half the thickness of a 1.4x Teleconverter, or a 40 mm f/2.8 pancake lens.

Compounding matters, extension tubes are pretty rugged. There’s no glass in them that can break or become misaligned or get dirty. In fact, you really don’t even need caps on them to protect them unless you’re really concerned about the electrical contacts.

Of course, there’s still that point about image quality. Well, the good news, is that in my experience, at 12 mm of extension there really isn’t a noticeable degradation in it. And honestly, even if the corners are a bit soft, for most subject matter, there’s enough novelty in being able to present something in a way that isn’t readily seen that it doesn’t really matter. This is even more true if you’re not photographing a flat subject where the corners will likely be out of focus anyway.

One final thought…

There’s a lot of math out there for calculating the magnification and working distance for any given amount of extension on any given focal length lens. Normally I’m all down for math stuff, but this is a case where I’ve found it’s generally more practical to just measure it with a ruler.

Canon does publish in their manuals the magnifications and working distances for their lenses, with their 12 mm and 25 mm extension tubes though, so if that’s what you use you can just reference that. Nikon, however, doesn’t.

Whether or not extension tubes are the right tool for you is, well, a personal choice. I like the flexibility that is offered in something that’s both small and rugged. And honestly, they’re not all that expensive as far as camera stuff goes, so it’s hand to have if you have an extra couple of bucks to drop. Canon’s 12 mm tube(Affiliate Link) is $75, and their 25 mm tube(Affiliate Link) is $129; but both of those are quite expensive for what they actually are.

My extension tubes are made by Keno and come as a set of 3 12, 20, and 36 mm(Affiliate Link) which runs $130 for the set. Kendo also makes the set for Nikon, and Sony Alpha, as well as sets (10 and 16 mm) for Sony E mount and Micro 4/3rds.

Even cheaper alternatives can be had, all the way down to $10–15 dollars per tube. However, I would offer a word of caution on those. While there aren’t any optics in an extension tube to worry about, the two mounting surfaces do need to be parallel to keep the lens parallel to the film plane and not create tilt effects. Really cheap tubes, may not be parallel, or parallel enough not to cause a noticeable problem. Of course at the same time, they might just be fine. Of course at less than $20, it might just be worth it anyway.


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