When my article on field curvature was published a while ago, where I talked about how one could do a quick analysis of lens MTF data and determine if it exhibits any field curvature, some of our readers expressed interest in understanding how to read MTF charts. Since we talk quite a bit about lens performance and MTF data here at Photography Life, I decided to write a detailed article on the subject and do my best to thoroughly explain everything related to MTF curves, charts and all the verbiage that comes with them.
A fellow photographer recently asked me how much image degradation one would see with each Nikon teleconverter. As a nature photographer, I have been wondering myself about this for a while, but never had a chance to actually quantify what the image degradation figures would look like when using the TC-14E II, TC-17E II and the TC-20E III with Nikon lenses. I have been relying on field use and my vision so far and here is what I have thought about each teleconverter.
The Nikon TC-14E II is excellent. I have not seen it degrade image quality on any Nikon lenses to the level where I could see obvious loss of contrast or sharpness. I have used it with the 105mm VR, 70-200mm f/2.8G VR (the old one, as well as VR II), 300mm f/4 and pretty much on every expensive super telephoto lens. I take it with me everywhere and mine stays pretty much glued to my favorite Nikon 300mm f/4 AF-S the majority of the time – that’s what I use primarily for birding. When shooting with my Nikon 200-400mm, I don’t hesitate to use the TC-14E II, because it does a very good job sharpness and contrast-wise and AF stays accurate and fast. It is obviously the smallest and the lightest of the three.
The Nikon TC-17E II is a mixed bag. It works with many Nikon lenses, but it slows down AF and impacts AF accuracy. Not as good of a TC to be used with slower f/4 lenses, which includes the 300mm f/4, 200-400mm f/4 and 500mm f/4 lenses. I tried to use it with my 300mm f/4 and it makes the lens hunt a lot, especially in anything but good light environments. The same thing with the Nikon 200-400mm f/4, even with the latest camera bodies like Nikon D4. Because of this, I rarely use mine. On fast f/2-2.8 lenses, however, it does pretty well. It works great on the Nikon 70-200mm f/2.8G VR II and it does not disappoint with the 200mm f/2, 300mm f/2.8 and 400mm f/2.8 lenses.
The Nikon TC-20E III is much better than its predecessor (which was very disappointing with many lenses). I was pretty shocked to see it perform very well with the 70-200mm f/2.8G VR II (stop down to f/8 for best results), because the 2x TC was always known to be bad with zoom lenses. It works like a champ with the 300mm f/2.8 and 400mm f/2.8 lenses. On slower f/4 lenses, however, it is still pretty disappointing. It is unusable on the Nikon 300mm f/4 and 200-400mm f/4 lenses and while it will work with the 500mm f/4 and 600mm f/4 lenses, you will have to stop down to f/11 to get anything reasonably good and you will need to use one of the latest Nikon DSLRs like D4 that can handle f/8 lenses. Not a great setup for fast action, but could work for large animals from a very long distance.
A couple of weeks ago I had an opportunity to visit Norman Koren, founder of Imatest, LLC. I have been fascinated by his software for a while now and after evaluating the software, decided to purchase it to use in our lens reviews. When I found out that his company is right here in Boulder, Colorado (where I lived for over 5 years), I gave him a call and asked if I could come over and interview him. Despite his busy and hectic schedule, he was able to accommodate me for an hour during his lunch time. Below is the text version of the interview.
Nasim: Thank you for giving us the opportunity to visit your office and learn more about you and your company. Let’s get started with your background, your company and how it all started.
Norman: You are most welcome Nasim. I grew up in Rochester, NY, about a mile from the George Eastman House, which I visited frequently. Both the technical and artistic exhibits made a deep impression on me—it was there that I first saw the beautiful prints of Ansel Adams and Edward Weston. I had a long career in magnetic recording technology, where my job involved simulating the performance of read, write, signal processing and detection in disk and tape drives. It started back in 1967 at Honeywell in Boston. I then worked for a number of companies including, curiously enough, Kodak in San Diego. Kodak at the time— we are talking 1985— believed that very small tape drives would be used in digital cameras. Well, it didn’t turn out to be a winning technology, but I had an interesting 12 years there. At the same time, I’ve always been a passionate photographer.