Strodav Loc: Houston, Tx

Sensitivity is different than Auto Focus.

CHG_CANON Loc: the Windy City

You haven't told us what EOS body and EF lenses you're considering. Although not "cheap" in that the cost is nearly $2000 combined, but the 100-400L II and a 1.4x III combination is a great balance of cost to performance yielding an extended 560mm at f/8. If you have a body that can drive the AF, whether at 1 point or across the entire AF array, the image results are (can be) excellent. The AF performance can be a challenge in responsiveness, depending on the EOS body, where you might get better results in AI SERVO than using single-shot or AI FOCUS.

Other options around the same price are the EF 300 f/4L IS and the EF 400 f/5.6L, where the 300 can be doubled to 600mm, still with IS, with an EOS body that can AF at f/8.

You can balance these options against a 3rd party 150-600, comparing the cost, the IS performance and image quality, particularly in the 500mm to 600mm range.

The next step up are the 300 & 400 f/2.8L IS models and the 500 & 600 f/4L IS models. You might shop for used lenses and / or discontinued v I or the older non-IS models, where the older primes are wonderfully sharp, work great with v III extenders, but have size and weights that are much larger / heavier than the current v II / v III models.

bleirer

I just got a eos rp with a rf 24-105L. I have an old 75-300 but not sure I'll be happy with that. The rp is supposed to be good with older ef lenses so i thought maybe a prime 400 or a 100-400, someone said the nano was good, and maybe an extender.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

The answer is in your question:

"huge cost in image quality between the two"

And add the impact on autofocus performance requiring manual assist or full manual AF, and the need for higher ISO. Unless you are using a 2X extender with a fast (an F2 or F2.8 200, 300, or 400mm) prime telephoto lens, you are not going to be happy with the results.

CHG_CANON Loc: the Windy City

The Canon extenders cannot be physically connected to a Canon L-Series lens until you get to a 135L prime or a 70-200L zoom. I wouldn't bother with a non Canon extender nor a third-party extender with a non-L lens, although there was a discussion last week that made it seem almost 'acceptable' to use a 2x with a 75-300 and an RP as a method to get to 600mm. I'd expect the AF would be too slow for practical / useful purposes. The RP does seem to "up" the limit for the smallest aperture for AF support when extenders are involved. Here, I don't yet have my own hands-on experience.

jerryc41 Loc: Catskill Mts of NY

Cheaper and possibly slightly less reduction in quality, although quality reduction hasn't been an issue with my Kenko.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Even Nikon, Canon, and Sony 2X extenders do NOTHING to improve image quality, actually using this type of extender diminishes image quality of any fine lenses. The 1.4 is all I will put on my lenses and that is only in an emergency. To say that 2X extenders makes no perceptible difference just ain't so.

Szalajj Loc: Salem, NH

Watch for sales of used 1.4 converters.

I stumbled across a like new Canon v3 one a couple of months ago, when I wasn't even looking for one, and the price was low enough that I couldn't pass it up.

It was listed for sale by Hunt's Photo, which is where I've bought most of my equipment. I got on the phone and placed the order with my sales rep, who had a devil of a time tracking it down in their inventory, buy he finally found it.

I haven't had enough time to run controlled tests on it yet, the weather hasn't been cooperative on any of the days that I had time to go out to shoot. But on the one outing that I did shoot with it, I did have to push my ISO higher than I like to shoot at, and I was shooting at a slower shutter speed than I'm comfortable with hand holding the camera and my 100-400 lens.

The Canon 100-400 v2 shouldn't be hand held at anything lower than 640 without a converter mounted. The minimum shutter speed that you need to shoot at with the converter mounted is 896, which is higher than I had set it that day.

You have to weigh the need for the additional distance against the loss of light, and the potential loss of quality if you are not shooting with a tripod and a shutter release. But tripods are not always the answer when shooting birds in flight, or sporting events.

gwilliams6

The old truths about 2X are going away. The best of the modern 2X extenders are excellent. Pro Sports and wildlife shooters are using them on the top=quality lenses and getting wonderful image quality. An example the Sony 400mm f2.8 comes with both the 1.4X and 2X extenders in its case and pros love it. Here is a shot I made with my Sony A7RII camera, Sony 70-200mm f2.8 G-Master with Sony 2X extender giving me a 400mm f5.6 lens. In this shot of a squirrel along the National Mall in Washington DC, you can see every hair, with excellent image quality, contrast and color.

(CLICK ON DOWNLOAD TO SEE THE FULL RESOLUTION AND COLORS)

The two stops of light difference is not a problem when you start with a f2.8 lens.

(Download)

Rayban

I have the Nikon Z6 which I use for telephoto work with a Tamron 70-200 F2.8 G2 and sometimes a Tamron 2x Teleconverter.

Images are very sharp, with the converter on sometimes a little slower to autofocus but no noticable image degradation.

As has already been said it will all depend on the lenses that you are using with the converter.

CHG_CANON Loc: the Windy City

The EF 2x III extender has limited compatibility, although the mirrorless EOS bodies appear to be changing this situation. I use the 2x tool only with an EF 300 f/2.8L IS II. This link is a post I put together in 2018 that gives a collection of examples for the purpose of showing this combination. In my work filling the frame with a subject at 600mm is far superior to cropping from 300mm. https://www.uglyhedgehog.com/t-559412-1.html

I also use the EF 1.4xIII with all the compatible lenses, although typically only with the compatible primes and only the 100-400 zoom. Given your interest in the 100-400L II and a 1.4x, there a link with specific examples: https://www.uglyhedgehog.com/t-559960-1.html

joer Loc: Colorado/Illinois

There are a few good lenses that the loss of image quality is not noticeable with a 1.4X. Always noticeable with a 2X.

Additionally, extenders impact focus speed, auto focus, loss of auto focus, and stability, especially the 2X.

Over the years I've tried different brands and lens combinations and concluded that all things considered cropping is a better option, and it costs nothing.

Blair Shaw Jr Loc: Dunnellon,Florida

Your point is very well made and I agree with your explanation and most recent testing of the two devices.
And the fact that you have tested on 3 different cameras of the same brand as your tele-converter were designed for, illustrates this perfectly.

As with any system, one must practice and test before running out to do a critical shoot and hoping to get desired results especially in awkward lighting conditions.

Thanks man.

CatMarley Loc: North Carolina

It is just common sense. For every "tweak" there is a penalty, and the bigger the tweak, the bigger the loss of quality. You are forcing an additional bend to the light that that lens was designed to do. The more you distort what the lens optics were designed to do, the greater the loss of quality. 2 is greater than 1.4. Common sense.

MountainDave

I use the 1.4 III quite a bit mostly with a 5D IV and 100-400 II. I've also used it some with a 77D. The results are excellent, especially with the 5D. But there a few caveats. Accurate autofocus is more difficult in lower contrast situations and, if you are hand holding, practice being steady. I can live with F8 as a maximum aperture but F11 with a 2X would be difficult. Like others have said, the 2X is probably best used on primes with big apertures. I sure would like to see what one could do on a 600mm F4. A 1200 F8 could be fun!