The Teleconverter's Lament - UPDATED
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Canon’s 2x RF Mount Teleconverter. Looks simple. Because it is.
Hi folks. I know that teleconverters don’t actually have feelings, but you could understand that if they did they would be depressed.
In the words of Rodney Dangerfield, “I don’t get no respect” could be the motto of the humble teleconverter. Let’s look at why this is unfair and wrong.
What Is a Teleconverter
Back in the ‘80s, the photo world was awash in teleconverters from all manner of labels. To be blunt, most were junk, optically similar to those horrible screw on close up filters. Camera makers had a few, Nikon being a great example of a company that built excellent teleconverters, but for the most part this was the space of the questionable names.
A teleconverter works with telephoto and telephoto zoom lenses, the “tele” part. They do not work with wide angles, wide angle zooms, wide angle to short telephoto zooms and are most impractical on shorter focal length lenses. The “converter” part is the focal length change or conversion that they impart.
Modern teleconverters typically come in 1.4x and 2.0x options. If for example, you have a 70-200 lens, using a 1.4x teleconverter would make it behave like a 98mm to 280mm lens. If you use a 2.0x teleconverter on that lens, it behaves like a 140mm to 400mm lens.
The Cost in Light
Teleconverters are optical instruments with multiple internal lenses. Consequently, as in any lens, a certain amount of light enters but does not exit. Teleconverters must also fit between the lens and camera body, so maker’s cannot do anything to avoid this loss. Modern cameras, and even older cameras do through the lens metering, so you see the light impact automatically but as some folks want to hear numbers, here they are as approximations.
A 1.4x teleconverter will consume approximately 1 stop of light. In our 70-200 example, let’s say with a maximum aperture of f/4 natively, that lens now behaves like the 98-280 with a maximum aperture effectively of f/5.6
A 2.0x teleconverter will consume approximately 2 stops of light. With our 70-200/4 example, it now behaves like a 140-400 lens with a maximum aperture of f/8
How Bad is This, Really?
When we were shooting film and higher ISOs quickly took us to Noiseland, this was a concern. With today’s sensors, in my opinion, higher ISOs are a significantly less important consideration, with most of the noise about higher ISOs coming from Internet media rather than images. We also have superb noise reduction algorithms in the post processing world, so my personal take, is use whatever ISO you need to make the image, and so long as you don’t spend your time pixel peeping (don’t there is no point in the real world) you are well and done.
So how bad is it? Not at all. The concern is hypothetical in reality.
Can I Get a Teleconverter for My System
Here’s a quick results check of vendors who make teleconverters for their current line of cameras
Canon - available for both DSLR and Mirrorless
Nikon - available for both DSLR and Mirrorless
Fujifilm - available for Mirrorless
Olympus, other Micro 4/3 - available for Mirrorless
Pentax - nothing listed on website
So if you own one of the top four selling brands in the marketplace, you have teleconverter options in the 1.4x and 2.0x versions across the board.
But, I Hear That There is Quality Loss
Anytime, you add more air/glass/air surface interchanges you will lose some quality and some contrast. That’s the reality of optics. Pixel peepers will tell you that a 2.0x converter will increase softness towards the edges and at 300% magnification, with your nose against the display, it is true. Viewing the image at a normal viewing distance does not show this degradation, so I am calling it a tempest in an irrelevant teacup. Moreover, if there is some nominal contrast loss, we have at our disposal numerous editing tools that have this thing called a Contrast slider. Hence, this is not an issue. If you think that you are losing sharpness that you can actually see, there is this slider and process called Sharpening that you are probably doing right now. Moreover since most images these days are viewed on low resolution computer displays or very small smartphones, I will state that any losses, real or imagined are unseeable.
What Happens to Depth of Field?
I want to thank regular reader and subscriber Dave, for the reminder to update the article to touch on depth of field. Fortunately the use of a teleconverter and it’s impact on depth of field is very simple.
Whatever the effective aperture becomes once the teleconverter is in place, that is what aperture determines the depth of field at a given camera to subject distance. Let’s look at a simple and clear example.
You have a 70-200 f/2.8 lens and use a 2x teleconverter with it. So it delivers the field of view of a 140-400mm lens with an effective maximum aperture of f/5.6 Good so far? Now consider that without the teleconverter your selected aperture was f/4 with a camera to subject distance of 10 meters with the zoom ring at 200mm. You could then use a tool such as Photopills to find that the depth of field on a full frame camera would be 0.59m with a close point of 9.71 m and a far limit of 10.3m. When you add the teleconverter, the focal length becomes 400m and that f/4 aperture becomes an effective aperture of f/8. Again consulting Photopills we discover that the near limit is now 9.86 m and the far limit is 10.15 m for a total depth of field of 0.29m , or roughly 1/2 Without getting into deep math, this makes sense. We have doubled the focal length, which would reduce the depth of field, and made the aperture smaller which would increase the depth of field. The two together produce the new effective depth of field.
Conclusions
Let’s say that you want longer reach on a few occasions that do not justify the cost, the weight and the extra kit needed to support that super long lens. What if you just want a little more extra reach before you could <horrors!!!> crop in post? I have bought teleconverters for every system that I have shot, including my Hasselblad. I have never regretted the investment, because they solve a problem for a fraction of the cost (and weight) of a super long lens and get the job done. Even the Hasselblad converter fits in a vest pocket. Small, efficient and useful. That’s a teleconverter. You should try one. Since this post publishes on Boxing Day 2021, that could be seen as a hint!
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I'm Ross Chevalier, thanks for reading, watching and listening and until next time, peace.
