Extension Tubes Review
I am somewhat interested in macro: previously I have done a fair bit of textures / flowers / etc, but something that I have wanted to do but could not do well was larger insects, especially butterflies. I currently have a 60mm f/2.8 AF macro lens, which gives 1:1 magnification. As a flower and still-life lens, it is very good: relatively inexpensive (goes used for about $250 these days), very sharp, just about no distortion, flat field, etc. However, it does not do very well for living things, most notably the larger, skittish, bugs such as butterflies and dragon flies, not to mention the nasty things like wasps.
While the 'correct' approach to this is to get a dedicated long macro lens, such as Sigma 150/2.8 or Nikon 180/2.8. Unfortunately, these are well outside of my budget. Instead, I thought to look into extension tubes. The manual-only eBay specials, sold for $5 - $20, are next to useless (I have tried them before). If anyone is considering them: save your time and money and don't. They fit loosely on the camera and lens, are very difficult to shoot with (even on manual lenses with aperture ring), and generally don't give the results that you would want.
Another option which people seem to have had more success with is the AF-compatible extension tubes. These have electrical contacts, screwdriver AF pass-throughs, and aperture levers (to let you focus wide open and stop down for the shot). There seem to be two main options here: the Kenko brand extension tubes (about $100), and the no-name made in China tubes (about $50). Many people have had good experiences with the Kenko brand, but I have a bit of a problem paying twice as much for the exact same thing (there are no optics in these things, so you don't have to worry about bad glass ruining your images).
Luckily, I recently had the opportunity to borrow a set of no-name AF-compatible extension tubes from a friend. This review tells my experiences and findings from the tests I performed.
Nikkor 300/4 AF + extension tubes
To address the main macro issues I had (not enough working distance), I decided to try out my 300/4 AF with the macro extension tubes. While it would not give as much magnification as the dedicated macro lens, it would give me the working distance needed to get some other insects. My findings with this combination are below:
- Closest focus distance is 103 cm (from the front of the lens), when all three tubes are installed.
- At the closest focus distance, you get an actual 1:2.88 magnification ratio (measured on the first ruler image below)
- With a 1.4x TC added (between the camera and the tubes), I can get 1:1.75 magnification ratio (measured on the second ruler image below). However at this point the combination gets quite awkward; I would not want to use this in the field at all, even indoors on a tripod is difficult at best.
- I did get FEE error a couple of times. The problem was that the stacked tubes, if turned one direction, lost enough of the AI indexing tab distance travel to make the camera think that the lens was no longer in max aperture position. I would think that if this was a persistent problem on my own tubes that I could add a spacer shim to the AI tab on the tubes, to recover the extra 0.5mm or whatever is needed. When the TC is added, the FEE error is even more common.
- When handling the thing in 'real life' (rather than just playing at the office), the entire contraption does feel a bit more unwieldy. You can definitely use it in the field, but I would not want to carry the camera / lens like this. I would put the tubes on when they are needed, and take them off after the fact.
Below are some sample images. The first two are of a ruler, manually focussed at the closest possible focus distance, to show magnification ratio. The first is just the 300/4 + all three tubes; the second is the same, plus a 1.4x TC.
Next are some shots to test the AF of the lens + tube combo. Again, all these shots are from the 300/4 + all three tube combo (68mm of extension). They were shot from a monopod, with flah to keep shutter speed high enough. Aperture was wide open (f/4).
As you can see here, the AF is just about perfect, even with the tubes.
When using the 300/4 plus tubes, the biggest problem is the amount of movement in the tubes. While objectively it is not much, it can be enough to produce the FEE error, and with a 30cm lens-plus-tubes combination, even a small portion of a degree of shift can give noticeable movement at the end of the lens. In the event that I end up buying these tubes, I will seriously consider crazy glueing the tubes together (staying away from the screwdriver AF contacts and the aperture levers, of course). That should reduce radial twisting (which cause the FEE errors), as well as slightly reduce the wiggling of the lens up / down and right / left.
I figured that I may as well take a look at other, shorter, lenses with the tubes as well, since more users will probably be using moderate normal or short telephoto lenses with extension tubes. I have a few options, and will be describing my results with various lenses.
First is the 50mm f/1.4 AI-S. This lens can give you decent macro results with the extension tubes. Below is a shot, from a tripod, at f/1.4:
As you can see, this gives you about 1.48:1 magnification (i.e. larger than life size). The alignment was slightly off, so you can see the DOF plane intersecting the ruler (this may also be partly due to a bit of field curvature: this would probably not be a good lens for recording flat documents or similar). The 60/2.8 (by itself, or with a TC to achieve about 1.4:1) gives better results, but if you already have a 50/1.4 or /1.8 lying around, then you can get decent images out of it + tubes, for a lot less money.
Next is the 60/2.8 AF Micro; with all three tubes attached, you can get a whopping 2.36:1 magnification ratio! Granted, actually using this beast would be so hard that short of noon-day sun and still life shots, I don't think you could really get any sort of usable images (indoors with a south facing window on a bright yet cloudy day, I could not see anything in live view or viewfinder with this combination. I had to stick a flashlight right up to the ruler to see enough to focus, and as you can tell from the slightly OOF shot, even that wasn't enough to focus it well). Even after all that, the exposure was way off:
Both of these lenses handle the extension tubes much better than the 300/4 does: there is no perceived twisting or wiggling, and I didn't get any FEE errors. (Of course they weigh a fraction of the 300/4 too, so that is to be expected!) I would have no issues keeping the tubes on these lenses, even when carrying things around.
I also tried the 85/1.8D, which gave good results as well. I got close to 1:1 magnification, and it autofocused just fine. I don't have any sample photos from this combination at this time.
For shorter lenses (up to maybe 100mm, and not too heavy), I would have no problem recommending the no-name extension tubes. They seem to have decent build quality, and for the shorter lenses work as advertised.
For long, large telephoto lenses, such as my 300/4 AF, it is a bit more complicated. It works fine, but the entire combination feels a bit loose. Plus, it is a bit too easy to twist the lens radially; it is only a few degrees, but it is enough to throw off the AI indexing tab and cause an FEE error. The combination is still usable (and if you are willing to glue the stack of tubes together, it may even be fine), but you should not expect things to work perfectly out of the box.
Now the real question: would the Kenko tubes work any better? As I don't have any here to compare, I can't say for sure, but since the only real problem I have with the cheap tubes is that the entire stack wiggles a bit, it is definitely possible that the Kenkos fit together tighter. Whether it is worth twice the price is harder to say.
Personally, I will likely look into getting the no-name tubes, and possibly just glue them together if extra strength is needed.
Update (August 2 2010)
There are (at least) two versions of the cheap tubes; one has a metal mount, and one has a plastic. The plastic should be fine for smaller lenses, but for using the big guns like the 300mm, I would recommend the metal mount.