Getting What You Pay For

Disclaimer:

This is a very casual "field test" review of the Opteka 500mm f/6.3 mirror lens kit for the Canon EOS system. I don't have a lab. I didn't use a heavy tripod. I didn't use a color chart or handheld exposure meter. Please don't expect pixel-level comparisons, or MTF charts. This is just me, unboxing the kit and taking it out on a test run. I've uploaded out-of-camera JPG files with no tweaking for your amusement.

Reality Check:

This kit, which includes a lens, T-mount to EOS adapter, and 2x teleconverter (not tested in this session), sells for less than $200. Usually much less. Anyone who expects it to perform like Canon L glass that costs over 20x as much needs to get their head examined. Ditto for even thinking about comparing it to the Tamron or Sigma cheap super-telephoto zooms. These are still over 5x the cost, and their performance clearly justifies the difference.

The purpose of this review is to see just what you DO get for your money.

Unboxing:

The Opteka kit comes in a plain brown box with a label which advises that the contents are sold as a kit, and not to be marketed separately. Inside the box are retail-packaged individual components, the lens itself, a T-mount 2x converter, and the EOS adapter - as well as a "bonus" lens cloth:

Everything was nicely packaged in a single box (bubble wrap removed for photo)

Although labeled to not individually sell, each component was in full retail packaging.

Once I got the boxes opened, I found the pieces themselves to have quite a substantial feel, with full-metal construction, and nice finishes overall. The lens and the teleconverter also had naugahyde (vinyl) carry-pouches.

Front of the lens with the cap removed. Note the large disk for the secondary reflector.

The Technology:

So, just what is a mirror lens, anyway? And what is this "T-Mount"? Some camera lenses, especially telephotos, tend to make you think you are mounting a telescope to your camera body. While this is true in some sense, the optics of even the simplest "regular" camera lens are far more complicated than a typical telescope. Not so in the case of a mirror lens. In this instance, you actually are, essentially, mounting a "Schmidt-Cassegrain" telescope to the front of your camera...

Optical path of a reflecting telescope  lens, essentially identical in concept to a "Mirror Lens", with your camera body in place of the eyepiece.

As if the optical path weren't enough to convince you, Telescopes have long had a standardized connector for adding cameras and other imaging systems. This is called the T (for Telescope) Mount. The Opteka lens uses such a mount. This is a threaded screw system, which then needs to be "adapted" to the actual imaging equipment. In our case, a simple mechanical T-mount screw to EOS bayonet mount is provided. Again, this is a metal part that feels very solid.

The T-Mount to EOS converter. Simple but effective. Also usable on any T-Mount equipped telescope you might happen to buy later.

The T-Mount adapter screws onto the small end of the lens, and Voila! You are ready to put it on your camera and take pictures!

The screw-on T-Mount for the Opteka 500mm lens.

Let's Make it Go!

The camera I'm using for this outing is an EOS Rebel T6s, or 760D.

There are some key things you need to understand about using a mirror lens. There is no auto-focus. You have a fixed aperture. There is no electronic feedback to the camera.

The manual focus on this lens is different from any lens I've used before. The barrel has a nice wide rubber ring, but when you turn it, the whole barrel turns, and essentially starts unscrewing from the base (it is limited, so it won't come off). While there is a lot of movement from "lock to lock", I still found it difficult to focus to precisely the right spot.

The fixed aperture means that you have zero control over the depth of field in your image. Since this is an f/6.3 lens, that DOF is actually fairly narrow. This means you need to be spot-on in order to have the part of the image you want appear sharp. It might also mean that even if you are perfectly focused, you may not have enough DOF to provide critical across key components of the image. You will see this manifest in several (most?) of the test shots posted.

Finally, since there is no communication with the camera, you can't use P, or any of the full auto modes. You can't use "Av", either since although it is fixed, you have no way to tell the camera what it is fixed at. I got my best results with Tv, setting my shutter speed to 1/800, and using Auto ISO.

Example Shots and Scenarios:

Here is an example where the fine control over the focus ring is lacking. Even a fraction of a millimeter of rotation would knock this guy even farther out of focus. This "best" shot was achieved using live view and 10x magnification.

Rufus Sided Towhee.

Birds in flight are even harder. No focus tracking by the camera, and as noted, the focus ring isn't precise enough for constant manipulation.

I have to think this Osprey's sharpness is at least partially attributable to the diffraction from the leaves in front of him.

Another shot of the Osprey. I was actually pretty close to its nest, though I didn't see any signs of offspring.

One thing that this lens might be good for is pseudo-macro photography. It has a close enough minimum focus distance that moderately sized flowers and insects can fill your frame. Again, of these shots are handheld, so with a solid tripod, and a good dose of patience, you should be able to produce some very attractive images, provided you can live with the shallow DOF and "distinctive" bokeh patterns.

Although the background here is a bit distracting, this is probably the best focused of the dragonfly shots.

Notice how hard it was to achieve critical focus, and just how shallow the DOF is. Of course, if I had WANTED the tail to be the focal point, this would have been perfect!

Nicely lit, pretty close on focus, and a quite nice background. But my shutter wasn't fast enough. Camera shake is the enemy.

Conclusion

The Opteka 500mm f/6.3 Mirror lens kit for Canon EOS is a very affordable package. At an order of magnitude cheaper than other telephoto kits, you have to expect some limitations. What I have found, though, is that even though I need some more time to acclimate to its unique characteristics, I actually had a blast shooting with this lens. While I wouldn't expect to regularly produce award winning images with it, given sufficient time and effort, it certainly is capable of producing some pleasing pictures.

Generally speaking, you get what you pay for. This lens definitely falls into the "cheap thrills" category. But I have to say, I was not disappointed for its price.