Review: Sigma 600mm f/8 Reflex (Part 1 of 2)

Finally, the time has come for my full Sigma 600mm f/8 Reflex review. If you aren't a regular reader of my blog and you'd like the know the back story, check out all the posts marked Sigma600mm.

Of course, if you are too lazy to read the previous posts, let me give you a recap. First, I was looking for a long (400mm+) lens for bird photos and did a bunch of searching on eBay (here are some other lenses I considered). On a whim, I bid on and won a Sigma 600mm f/8 for $78 + $14 S/H. The Sigma 600mm is a well-regarded version of those infamous mirror/reflex lenses (or, officially, catadioptric lenses). My Sigma is an FD lens, so I also purchased an FD-EOS converter (review) for $36 including shipping. I've also described the process, advantages, and drawbacks of adapting FD lenses to EOS/EF cameras.

Sadly, when the lens arrived, it had some fungus on the main mirror, but it wasn't enough to return it and I don't think it is a major detriment to image quality. I did ask the buyer for a $15 refund, so my ultimate price for the lens was $77. Since then, I've shot a decent amount with the lens (maybe 700 shots over 10 hours) and I'm ready to give my review. And, in true backwards fashion, I'll start with the...


Conclusion:

Let me make my advice real simple for you if you are considering the Sigma 600mm for a digital camera (I don't have any experience with it on a film camera, so you're on your own there):

• The Sigma 600mm f/8 does have substantially better image quality than an up -sampled Canon 70-200mm f/4. That's a huge weight off of me, because I was very concerned about what this review said.
• The lens has high build quality but it is still a mirror lens and has plenty of limitations.
• It is VERY hard to get decent pictures out of the lens since it has narrow depth of field, is very sensitive to camera shake (even on a tripod since it has an equivalent focal length of 1000mm), and is relatively slow (f/8). Expect to do a lot of shooting at ISO 400+ and toss a lot of soft images.
  
• If you are strapped for cash but need the reach and you can get a Sigma 600mm for $150 or less (in a mount that fits your camera or can be adapted to your camera), do it. You won't be sorry.
  
• Don't pay more than $200 for one in any mount. Most of the EOS mounts, because of rarity, go for upwards of $250. I don't think it is worth it, because used 400mm refractive lens are available for $300+ without most of the limitations of mirror lenses.

Here's a widget that shows the 600mm Sigma lenses available on eBay right now:





The Minolta version is probably the cheapest and most popular version available (and there are Minolta to EOS converters available). The Canon FD mounts are pretty cheap too. Not all the lenses are black either -- I've seen auctions for at least one white one and one greenish/gray one. There may be different versions of the lens out there, but as far as I know, they are all optically identical and good quality.

Okay, now that I've given you the dessert first, how about dinner...


Physical Characteristics:

The lens itself is built like a tank: metal, well-toleranced, and heavy. Not solid cat heavy or refractive 500mm f/4 heavy, but still pretty heavy. I guess the weight needs to be put into perspective: it is heavy compared to my Tamron 17-50mm, but still under two pounds, and nowhere near the weight of a quality refractive 600mm lens.


The only functional part of the lens (since it lacks both autofocus and aperture control) is the focus wheel, which turns a total of a little over 180 degrees with nice action (smooth and well-damped). The damping has a strange response in the middle of the range (almost like air gets trapped or something) but the effect is only noticeable when you move the focus quickly. I never notice this when I'm actually using the lens. Also, the end of the lens does rotate with the focus wheel, but a front polarizer is pretty unrealistic with this lens anyway!

The Sigma 600mm reflex does include a built-in tripod mount which I really haven't had much use for. Since the front of the lens is so light, the tripod mount isn't that much of an improvement over just mounting the camera on the tripod. In my case, my tripod doesn't mount well at all to the lens mount (it rotates too easy; an issue with my tripod, not the lens mount). If you have a smaller camera like a Digital Rebel, you might prefer the tripod-mount. It allows 90 degree rotation to portrait mode.

The lens does include a filter holder and my package included a case and five 22.5mm filters of various shades. The filters are pretty useless if you are shooting on digital and I'm not sure if a polarizer would even work in the back position. On mine, I actually removed all the filters, including the clear/UV filter. Why put more optical elements in the light path if you don't need them?

My version of the lens has an old FD mount (breech-lock). It mounts securely and has zero interface with the camera since it lacks a diaphragm. Mounted on the camera, it is pretty solid although you can twist it slightly due to the FD-EOS converter. It doesn't cause problems in normal use though, except...

After taking it out a number of times, I started to notice excessive sloppiness when I rotated the lens, to the point where it had a loose feeling even when I was doing fine focus. At first, I thought it was the mount loosening up, but then I realized that the back of the lens (held on by three tiny screws, in the shadows of the image above but easy to see below) was actually loosening up. So, I took it to work where I had some jeweler's screwdrivers and went ahead and took the back off to see what it looks like (and to check for a huge mold infestation). This is what I saw:

I think this is the back of the mirror, but I didn't go any further with disassembly because that seal (which was already pulling out slightly) didn't look like it'd go back in easy. So, I put it back together, screwed the screws back in tightly, and everything works fine now.

So, to summarize, the Sigma 600mm is a really well-built lens. Solid, everything is metal (even the lens hood!) and there's no slop in it at all.


Performance:

The next question, and probably the top question for most people who find this page, is how does the lens perform?

To test performance, I was originally going to go outside and post a target across my yard to get shots and compare them to the Canon 70-200mm F/4 USM. But then it rained. And rained, and rained... So, instead, I just taped a target (something out of a catalog my wife had; as luck would have it I yanked out the religion page) to a cupboard door in my kitchen and set up the tripod on the far side of the living room. Total distance is about 25 feet or so.

To guarantee only a test of optimal lens sharpness, I used a flash to illuminate the target from below, and put the 20D on a tripod with mirror lockup and the self-timer enabled. For each equipment combination I took the best results (focus, etc) of multiple images to really look at optimal performance. All shots were at 1/250s (sync speed), f/8, ISO 100, converted straight from RAW with no levels or sharpening. All Sigma shots used the FD/EOS converter but the optical element is the extra variable (did I include it or not).

The three full frame setups are (click to see them larger, but not the 100% crop):

Full frame Canon 70-200mm f/4 USM (CANON)

Full frame Sigma 600mm f/8, no corrective lens (SIGMA_A)

Full frame Sigma 600mm f/8, corrective lens (SIGMA_B)

As you can see, the Sigma, as expected, has a much smaller field of view. Both versions of the Sigma are darker than the Canon, which may be a result of the FD/EOS converter. And the corrective lens has a smaller field of view and darker image than with the corrective lens removed. I didn't measure the drop in light intensity scientifically but it is probably 1/3-1/2 stop without the corrective lens and maybe a full stop with the corrective lens. Also note the difference in contrast between the Sigma and the Canon, although contrast can be easily fixed in post (with the corresponding increase in image noise).

I did measure the distance between two features, in pixels, on all the images and compute an effective focal length. Assuming the Canon is truly 200mm at full zoom:

• Canon: 200mm (320mm effective on 1.6x crop sensor)
• Sigma w/o corrective optics: 665mm (1064mm effective)
• Sigma with corrective optics: 785mm (1256mm effective)

These rough calculations mean the Sigma is easily over 1000mm effective focal length on a crop body like the 20D. That's intense magnification! It does result in some difficulties when using the camera, which I'll get to in the handling portion of the review.

The Sigma also has a slight vignette to it, even on a small sensor camera like the 20D. I expect the vignette would be much worse on a full frame camera or film, but it isn't objectionable at all for my purposes (I sort of like it, actually). It'd be easy to remove if you wanted to. For example, in the helicopter image below, the blue intensity at the corner is about 85% of the blue intensity in the center.


Next, the real meat: at a 100% crop, how does the Sigma compare to the Canon? Below is a 100% crop from the Canon and the Sigma without the corrective lens:

100% crops: Canon on the left, SIGMA_A on right

The Canon clearly has better contrast and sharpness but the Sigma can resolve finer detail. How about up-sampling the Canon to directly compare at the same resolution?

Left: Upsampled Canon, Right: SIGMA_A 100%

Again, better contrast in the Canon, but the Sigma can clearly make out a lot better detail. Instead of just a rough idea of the words, you can actually read them and make out the edges of the letters. The tiny text at the bottom is a small blob on the Canon but readable on the Sigma.

Overall, I'd say the Sigma's sharpness is probably similar to a decent 400mm refractive lens like the Sigma 400mm f/5.6. Definitely, the Sigma isn't nearly as sharp as the Canon, but the 300+% increase in focal length (and 900+% increase in effective pixels) makes up for the lack of sharpness. The Sigma 600mm f/8 can get shots that you can't get with the Canon 70-200mm F/4. It'd be interesting to try the Canon with a teleconverter, and if I get one, I'll update this comparison.

The final question is whether the optical element in the FD/EOS converter hurts image quality as I hypothesized earlier. The addition of the optical element turns the converter from an effective extension tube to an effective teleconverter (with the accompanying increase in focal length and decrease in aperture). To test, I upsampled the sample without the optical element and compared it to the 100% crop with the optical element:

Left: SIGMA_A upsampled, Right: SIGMA_B 100% crop

Aside from the decrease in brightness, if you look closely you can see the optical element does hurt image quality slightly (the edges of the letters aren't quite as sharp). While the decrease in sharpness is minor, I recommend using the lens without the optical element whenever possible.

The other major conclusion is that the Sigma 600mm f/8 Mirror lens has a substantial advantage over an upsampled 200mm, but probably no advantage (and many disadvantages) compared to the 400mm f/5.6 lenses. So, again, if you can't afford a 400mm+ lens and you can get the Sigma for cheap (<$150) it is worth it. But, I've got to warn you now, the combination of the monster focal length and the catadioptric construction makes the lens really, really hard to use effectively.


To Be Continued...

This post has taken forever to write, and it will take a little longer to be finished. I'm going to split the handling of the lens (along with lots of sample shots) into a separate post to keep this from getting too long. Hopefully I'll get it up in the next day or two!