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I used this lens quite a lot before I purchased a Canon 400mm prime lens. Although the Opteka lens is somewhat soft and has some chromatic abberation, the images are quite good if the subject has good contrast. I've used this lens with a 1.4X tele extender as well. The resolving power at 1200mm is about 85-90% that of the Canon 400mm used with a 3X tele extender(giving the same 1200mm). I used a test chart similar to the ISO12233 chart to check the resolving power. Where the Canon shines is that it has next to no color shifts in the shadows or on the edges of images. Small black areas will go deep blue and small bright areas (like an egret against a dark background) will have a litttle blue edge on one side and orange edge on the other with the Opteka, but this not normally noticeable unless the image is blown up. Normal subjects will not usually show the chromatic abberation, except on the edges of an image WHEN BLOWN UP.
The focusing on the Opteka is CRITICAL and gets difficult past 900mm, since the light gets prettty low. I made and put a Vernier scale on my lens and got pretty good focus by splitting the slightly out of focus near and far focus distances. I have some excellent hawk and egret images taken with the Opteka 650-1300 mm lens (email me at
harold-moore@sbcglobal.net for some images if you like). I also made some cardboard STOPS for this lens which work well. It is not practical to go much beyond F22 because of diffraction. A 2X tele is NOT recommended--F32 at max focal length--because diffraction is becoming significant and will blur the image AND, of course, the focus is very difficult. A high quality 1.4X teleconverter will give you 1800mm at f22 with fair images--but the focus is critical and DIFFICULT. If you learn to focus this lens--gets much more difficult past 650mm--then you can get some
pretty good images.
The Opteka is a good starter lens IF you cannot afford the Canon or long focal length Tamrons etc. The main advantage of this lens is its very low cost. The Tamron 200-500mm is close to $1000 and the resolving power is similar. I had fun with Opteka lens and now I don't need it since I have
purchased the Canon 400mm (I can stack 3X and 1.4X teles on the canon to get around 1700mm--again the focus is MANUAL and very difficult past 1000mm since the light levels are so very low (on both lenses). I have also put a Vernier scale on my canon, and it is handy for distant birds that are very far away and must be, therefore, shot at 1700mm. This works well IF THEY WILL JUST STAY STILL.
The Opteka is about 4 1/2 pounds and takes a litle time setting up on a medium sized tripod--this sized tripod will work satisfactory--although I like my heavier duty tripod with Cullmann ball head. Again the
lens is not as sharp as a canon, but similar to that of the Tamron. I compared test chart images of the Opteka at 650mm and my Tamron 70-300mm zoom with a 2X Tamron teleconverter at distances where
the image was the same size. The Opteka resolved as well as the Tamron, but I had to really get it in focus, which I did with the Vernier scale.
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