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Monday, June 18, 2012

Lens Review: Opteka 500mm f/8 Mirror Lens


What kind of lens can you get for $95? How about a 500mm f/8 manual focus lens, that's compact, lightweight, and produces darn good images? If that sounds too good to be true, then read on -- it's not.

A couple of weeks ago we had a rare opportunity to photograph a transit of the planet Venus across the face of the sun (see my original post here). I had planned to have my Canon 5D Mk II on a tracking telescope to photograph it, but wanted a backup using my Canon T2i camera. I decided to risk $95 on the Opteka 500mm f/8 mirror lens sold by Amazon . It worked out just fine, and I decided to do a full review of this lens, especially since there's so much misinformation about it on the internet, and so few sample photos.

Mirror or catadioptric lenses have been around for quite some time now -- at various times, Minolta/Sony, Vivitar, Nikon, and others have offered versions of this same design. Basically, a mirror lens uses specially curved mirrors to "fold" a 500mm focal length light path into a very compact shape, by bouncing the light around inside the lens. The basics are illustrated in the image below:


Light enters the lens through a shaped glass "corrector" element, bounces off a parabolic primary mirror at the back of the lens to a central secondary mirror in the center of the corrector, then out the back of the lens through a hole in the primary mirror. The design is the same basic one used in Schmidt-Cassegrain telescopes, and it's a good design for folding a long focal length into a short physical length instrument or lens.

There's one big downside to this design: a central obstruction (the secondary mirror in the front corrector) reduces contrast in the formed image. The greater (by percent of the area of the corrector) the obstruction, the greater the reduction in contrast. It's a given that a catadioptric lens will have lower contrast than a "normal" lens of the same focal length, and it's simply a design trade-off.

The Opteka 500mm f/8 uses this same design. When you first open the box, it might be hard to believe that a 500mm lens can be so small and light -- it's only about 4 inches long and less than 3 inches wide, and weighs less than 0.8 pounds (360 grams). That's the benefit of the mirror design.

The fit and finish of the lens are amazingly good, especially for the $95 price. The lens is mostly metal, with a bit of plastic up front and a plastic lens cap. The rubberized focus ring has been changed since previous versions, and is no longer the knurled rubber we're used to on lenses -- but the textured rubber surface used now is easy to grip and I had no problems with it slipping. Focus action is smooth and well-damped, and *amazingly* long -- it turns about 300 degrees from beyond infinity focus to the stated close-focus distance of 1.72 meters (about 5 feet).

The lens itself has a t-thread mount on the backside, and is mounted to various cameras by use of an included t-mount adapter, which you specify for your camera brand when ordering. Screw the lens onto the t-mount adapter, then mount the adapter to your camera's bayonet mount in the usual way.


So how does it perform? Above is an image of the 2012 Venus Transit of June 5th -- the reason I got this lens in the first place. With a home-made solar filter attached to the front of the lens, images of the sun and little Venus crossing it were sharp and very well-defined. Contrast of the images was a little low, as expected from the design of the lens, but a little bump of contrast in post-processing produced very nice images.

Focusing a manual-focus lens at f/8 can be challenging (see below for some tips to make this as easy as possible)...the best way to go about it is to find a high-contrast edge to look at, and then gently move the focus ring back and forth while you look for the highest contrast on that edge. Using the edge of the bright sun against the nearly black sky, I had no problems getting good focus using this lens on my Canon T2i DSLR.

That f/8 aperture, by the way, is fixed -- it can't be changed. There's no aperture ring to open up or stop down, it's f/8 or nothing. The lens does come with two neutral-density filters which screw onto the *back* of the lens -- one a 2X ND filter, the other a 4X ND filter -- so you can get effective apertures of f/11, f/16, or f/22. Keep in mind, however, that these don't give you ACTUAL apertures in those ranges, and the depth of field of the lens doesn't change.

And speaking of depth of field...there isn't any. That's simply a function of focal length and aperture, and at 500mm depth of field is for all intents and purposes non-existent. Calculations show that at 10 feet, depth of field is a total of 0.03 feet -- about 1/3rd of an inch or 12mm. Things don't get much better at 100 feet of distance, giving you only about 2 feet in front of and behind your subject (3.65 feet, or about 1 meter, of total depth of field). If you want a lens that will give you very narrow depth of field and blurred backgrounds/foregrounds, this will do. If you're looking for everything in an image to be in focus, this isn't it. The image below (taken about 5 feet away) gives you an idea of the very shallow depth of field with this lens.

I used the edge of the orange to focus on, and there the image is sharp and in focus -- but the front curved surface of the orange less than 1 inch closer is already getting out of focus.
Another unique feature of mirror lenses is the donut-like shape of out of focus highlights; the central obstruction of the secondary mirror gives such highlights a bright ring with a dark center. Some people like the odd and unique quality of these, some people hate them. You can make up your own mind. The image below shows what these look like, taken at a distance of about 30 feet.



If you read the reviews on Amazon from some people who've purchased this lens, unfortunately you'll get a lot of misinformation. One big "complaint" there is that the lens isn't hand-holdable -- poppycock. Every shot (except the Venus transit image) in this review was hand-held. The same "rule of thumb" that applies to every other telephoto lens applies to this one: keep your shutter speed at about 1/focal length and you won't have shake issues. That means you'll want to shoot at between 1/500th and 1/800th of a second to avoid camera shake ruining images. If you do so, the lens is *very* hand-holdable, and as you can see from the sample images here, you can get very good results. Here are a couple more sample images, taken at our town's annual parade in late May right after I got the lens:



In conclusion, for $95 you get a 500mm lens with very good build quality, that is capable of some very good images -- as long as you understand what it's good at and what it's not. I have the Sigma 50-500mm "Bigma" zoom lens, and use it often; however, at 500mm the Bigma is about two feet long, and weighs over 3 pounds -- and operates at f/6.3. Hand holdable it's not. This tiny, lightweight lens is an inexpensive alternative that, when used within its capabilities, produces some very good images. If you don't have a lot to spend on a long lens, it's certainly worth a look.

Adjusting the Lens Orientation on the Camera

When you get the lens and mount it on your camera using the supplied t-mount adapter, the top (focus mark) of the lens may not line up with the top of your camera. This won't affect operation or focus of the lens, but if you'd like to line it up correctly, it's easy to do so.

The t-mount adapter has three set screws recessed into its side -- one of them is shown in the image above. Using a small jeweler's flat screwdriver, you can gently loosen the three set screws (only a little bit!), and turn the inside ring of the adapter until the top of the lens lines up with the top of your camera. Once it lines up, tighten up the set screws again, and you're done.

39 comments:

  1. Good review Paul, I think I'll buy one!

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  2. Thankyou for the review Paul. I have just ordered this lense and will use your tips. Thankyou for supplying them.
    Diane

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    1. You're welcome! Please post back after you've had a chance to use it and let me know how you like it.
      Paul

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    2. Hi Paul, I am planning to get "Opteka High Definition 500mm f/8 Preset Telephoto Lens" and was wondering if all of these are the mirror lenses or not.

      Regards

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    3. Hey Paul, the review was helpful. I am using this lens on a sony a3000. I have tried it and for the cost and my limited with changeable lens is good. too many negative reviews but none showing how to better use it until I read your review. I did however find out it can be used in auto mode as well as manual mode on camera. I hope to get some good wildlife shots while here in Africa. where might I send a photo to show u my results. Jeromemundy@yahoo.com....jerry mundy

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  3. Hi Paul I have just brought one and I have a Pentax Kx camera and I put the Opteke lens on and my photo are really dark, is there something I am doing wrong?i am a real beginner

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    1. The only "automatic" exposure mode that will work is "aperture priority" mode. So be sure you're either in aperture priority mode, or using manual exposure mode and setting the shutter speed yourself.
      Your viewfinder image will certainly be "darker" than you're used to, since the lens is fixed at f/8.

      Set your camera to aperture priority mode, set your ISO to 400, and give it a try -- you should get correctly exposed photos. Let me know if you're still having problems after trying that, ok?
      Paul

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  4. Thanks for the advice I will give that a go and let you know how I get on :~}

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  5. Hi Paul I tried that but the photo's are still pretty dark definitely not like the ones you have been taking.... Any other advice I would really like to be able to take half decent photo's

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    1. Hi Phoenixfairy,
      Can you e-mail me one of the photos, in JPG format? I'd be happy to have a look (including the EXIF data in the file) and see if I can offer any suggestions...lefevrephoto@gmail.com

      Paul

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  6. This comment has been removed by the author.

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  7. Thanks for the review! I definitely was having trouble deciphering the babble on Amazon (as is often the case) and what I really wanted was some freaking sample shots (preferably with metadata!) to get a good sense of what the lens's limits were. And I really appreciate that you take into consideration the lens's design characteristics when addressing the contrast, because reflex mirrors do have that "issue," which all the reviews I've read thus far haven't been willing to concede.

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  8. Hi. Thanks for the review. It was really cool. I specially liked the screw alignment comment lol I confess I was a bit bugged by the misalignement. I'll try that!
    Well, for a super ultra mega plus telephoto (with the 2x adapter :) the pic are great. Wobbling is the big prob. Live view definitely help a great deal specially on low-end cameras with no mirror lock-up (tip for the readers unfamiliar with it. If your camera has no mirror lock-up - like mine doens't - but has the live-view mode, the camera keeps the mirror locked up so the live-view works :)

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  9. The bokeh is a matter of taste. I like it. The built is great. Solid. I confess I'm not really happy with moon shots but for very distant close-ups it's fantastic. I can get really close to objects 1km away. Well, at infinity, the lens is limited to at most 12cm os resolution (at best), so you can resolve lamp post, windows and people (but not enough to recognise their features).
    One thing that drives me a bit crazy is that 'post-infinity' focus turn. Past the notch of infinity there's still a good way past it the lens lets you turn/focus, but nothing comes into focus when you do it. And that I cannot twig out!

    cheers

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  10. I finally got around to testing "cheap mirror lens" against "real Canon L lens". There is still the matter of ~$200 vs $1,400, but... Vivitar (although it came with Opteka paperwork) 800mm/8 mirror lens vs Canon 100-400mm.

    Testing at: http://www.flickr.com/photos/tenesmusphyre/sets/72157632502482635

    Feel free to remove if you think it's inappropriate, but I wish I'd seen some more testing before I bought the lens.

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  11. I'm contemplating this lens to take to a soccer tournament - I currently have a lens that goes to 200mm and wanted something a little larger but can still be handheld. Would you suggest this lens instead of buying another "cheap" lens that goes from 75-300mm? Also, one deal on Amazon has this with a 2x zoom extender -- is that worth the extra $30 or is it just a piece of crap that I'll regret?

    Thanks for the input!

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  12. Thank you for the great review. I just bought the Opteka 500mm HD lens to use it in nature photography. Your review has bee very helpful including the tip on the screw allignment. I still use my manual equipment from 30 years ago and they work great. I just use them in the A/V mode on my KX.

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    1. Anonymous: you didn't say if you liked the Opteka 500mm. Is it any good?

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  13. Hi, what a great web blog. I usually spend hours on the net reading blogs on various subjects. And, I really would like to praise you for Photographs and pictures of sun

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  14. Good review. I am relatively new to photography (but learning fast). This lens sounds like a good addition, particularly since I have a Panasonic G1 micro 4/3 format. I am fairly sure I can get an adapter but please tip me the wink if this is not the case.

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  15. I purchased this lens and was told it would operate on my Nikon D3100 if the camera is set on Manual Focus.
    As instructed I pressed the 'i' button on the camera twice but found I was unable to engage MF and whenever I attach the lens the screen says lens not fitted.
    I am not good with technology, what am I doing wrong.

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    1. Are there any more MF/AF selection sliders on your camera? If so, they should be on MF as well as the program selector. That is how it works on my Sony A380

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  16. Am so glad I ran across this blog. Paul it is like you were reading my mind. I saw this lens when I was looking for one of those long lenses on Amazon and thought this might work on my moon projects. Bought it, and while I haven't used it much, weather is very bad, I have found some interesting things just playing with it in the house.
    Your blog, better explained it's primary purpose and gave me a couple of ideas for some intentional out of focus shots. Thanks much

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  17. Great review! I just bought this lens. It needs some theory and practice to get good images.
    You have to keep in mind setting up high ISO, small shutter speed, and sometimes it's necessary to use compensation +2, +3 etc.
    Very narrow depth of field is a great area for experiments, though!
    I just adore donut bokeh!

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  18. Hi Paul.
    Great information in your review. I just received my lens today and have a question. The instructions say to use the ND skylight filter. What is the purpose of a skylight on the back of a lens. Thanks

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  19. Hi, I bought one of these based on this review, and you know what? Opteka's 500mm lens DOES NOT FOCUS. It's just not lack of contrast either, it simply does not have a point of focus. After being unable to get a single focused image handheld, I mounted it on a tripod, pointed it at a bright star and tried to focus. The best it will give is a fuzzy oval. Twist a bit more and it knots into a fuzzy oval going the other way. There is never an actual point of focus. By a great deal of processing and colour decomposing I can get an almost only half bad image from this lens. Bokeh I don't mind, but a lens that does not focus is not much good!

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    1. sounds like there is a problem with your lens. I can quite easily focus with mine.

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    2. I have the exact same problem. Mine won't ever achieve a sharp focus.

      I emailed Opteka some sample images and they said that the performance I was seeing was about right for that lens.

      Did you ever get your lens fixed or exchanged?

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  20. Thank you ..i bought the lens before reading all the bad reviews...after reading the reviews i could not see pass the reviews ...but then i read your info ...thank you ...hugs for bringing my awesome birthday/mothers day gift back to happiness.I will not give up on this beautiful lens ...now that I understand it ...thank you thank you thank you

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  21. It would be much easier to understand what the lens can do if you would provide a few full resolution images from your 5D for us to evaluate. None of the small JPG's appear to be in focus.

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  22. Thats a more realistic review..thanks so much for posting

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  23. I got the lens but I am unable to click any pic.....I am using this on canon EOS M.....i just cant click on the button to take the photo.....is this becos I am not using a tripod?
    please advise in what mode can i use this lens......
    Thanks
    PV

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    1. Your camera should be set to M mode, as this lens provides no electronic communication to your camera body.

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  24. Finally, a no nonsense, factual, intelligent review. I am so over the "hacks" whop go buy a DSLR, see a BIG lens, and think they can have fun shooting nudey pics of neighbours or the like, and then complain it isn't working for them.

    You have shown this lens is useable, in the right hands, in the right manner, and the right setup/conditions. Thank you.

    I am seriously considering this lens, for wildlife and moon shots. Taking the parade photos into account, it may also work nicely for sports shots (motor racing).

    Again, many thanks for a real review and well done on your blog.

    Feel free to visit my website and have a browse around and you will see where I am at with my photography.

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  25. I am pleased with this lens. On my Sony A380 I do the following:
    Set AF/MF slider (beside the lens position red dot) to MF and the Program Selector to M. Set ISO selection to 3200. You can now set the shutter speed on the thumb wheel with your right index finger, while you are focusing. Use the view finder and not the LCD display. Under sunny circumstances I have to use speeds shorter than 1/1000, so movement blur does not occur. After the first shot I look immediately at the result on the LCD using the > button on the right bottom. You can now modify the speed for the optimum setting. I have by now taken incredible shots from foxes and their fast moving cubs, deer and birds.

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  26. Very nice review. Any chance that you can share full-size of the images?

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  27. I have asked Santa for a solar filter for my Nikon 500mm Reflex (N) and have been wondering how big the sun would appear using my Nikon D7000. Thanks to Paul I now know. I have used my mirror lens many times to photograph the moon which can be seen at http://spaceweathergallery.com/indiv_upload.php?upload_id=99510.

    Thanks again Paul,

    Sincerely Frank Jr.

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