topic Re: Is there a teleconverter available that will mount to a Canon EF S lens? in EF & RF Lenses

Is there a teleconverter available that will mount to a Canon EF S lens?

Birdog638 — Wed, 02 Apr 2014 20:47:57 GMT

I have a new Rebel T5i with EF S lenses but I Alamo have a Kenko 2X teleconverter. As I understand the Kenko will not mount to the EF S lens. Are there teleconverters available that will mount to EF S lenses?

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

cicopo — Wed, 02 Apr 2014 20:58:44 GMT

You may find something to physically fit but depending on the lens you'll most likely loose AF or drastically limit it.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

ebiggs1 — Thu, 03 Apr 2014 13:23:28 GMT

Yes, not a stellar idea. Don't do it.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

TCampbell — Thu, 03 Apr 2014 15:25:43 GMT

The "S" in EF-S stands for "Short backfocus". The rear-most element on an EF-S lens sits farther back than it does on an EF lens... and typically proturdes just slightly beyond the lens mounting flange. The lens is designed to mount on something with a hollow cavity to accomodate the short backfocus. Teleconverters aren't unlikely to provide enough space.

But that's just the "tip of the iceberg".

When you use a teleconverter, you have to multiply both the focal length AND the focal ratio by the teleconverter factor. It's the focal ratio that can be a problem. I'll use an example to illustrate why.

Suppose you have a Canon EF-S 18-135mm f/3.5-5.6 lens and, hypothetically, you found a 2x teleconverter for it. This would convert the lens into a 36-270mm (that part makes sense) lens with an f/7-11 focal ratio range. Notice how I had to multiple the focal ratios?

The "problem" with this, is that camera generally cannot auto-focus at high focal ratios. The Canon 1D X and 5D III can both auto-focus at f/8... but that's it. No other Canon camera can do this (and it's the same for Nikons... most cannot). They're designed to auto-focus up to f/5.6 and there are 3rd party lenses where f/6.3 might be the best you can do... and AF works on them -- but you're really pressing the limits at that point. This means you might get the lens to focus at f/7... but that's only available when you're zoomed all the way "out" to the 36mm end. As soon as you zoom IN (and the whole point of the teleconverter is to let you zoom in more becuase the lens would have provided 36mm natively without using the 2x teleconverter) you're jumping up beyond f/8 where there's absolutely no way the AF system is going to work.

The focal ratio limits for the AF system aren't arbitrary. If I hand you a 35mm film camera with manual focus and a split prism focusing aid in the viewfinder, but dial the focal ratio down to f/8 and have you try to focus with it, what you'll discover is that you can get one half of the split prism "moon" to show the image but the other half will be black. Barely move your eyeball and they'll reverse... the other half is visible but the first half is now black. It's near impossible to get both halves visible at the same time to allow focus because of the way the prisms work (even manually).

Teleconverters work best on lenses that have low focal ratios to begin with... e.g. f/2.8 lenses when using a 2x teleconverter (which turns it into an f/5.6 lens) or f/4 lenses if using a 1.4x teleconvert (which also turns it into an f/5.6 lens).

But even after all of that... the teleconverter will noticeably degrade your optical quality. It's never as good as if you didn't have to use a teleconverter.

I have a Canon EF 300mm f/2.8L IS USM lens... that was a pretty expensive piece of glass (I think it was around $4k). If I put a 2x teleconverter on it (and I can -- it works)... I get optical quality out of it that looks like I bought a $200 lens.

Part of the reason this happens is teleconverters are a bit generic. They aren't tuned for one specific lens. Canon makes an $11k lens with a built-in 1.4x teleconverter and it's remarkable. But that built-in TC was optimized and tuned for that one lens only.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

Birdog638 — Thu, 10 Apr 2014 14:37:25 GMT

Tim,

Thanks for the technical response to my question. Based on your response I will rethink my approach and may ulitmately purchase a suitable lens to accent my equipment that will not rely on a teleconverter.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

ebiggs1 — Fri, 20 Feb 2015 14:18:54 GMT

Kenko makes a converter that will "mount" to a consumer (EF-S) level lens. But I still say it is a bad idea and not recommended by me. Plus the fact it isn't a Canon product.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 01:12:57 GMT

Hi, I was looking for a TC too but there isnt any, but I got a solution, you can modify the EFS mount by taking it off the lens and cutting away the pretruding plastic, its not the best solution but if your careful you should be ok, it worked for me and I have a Canon EFS 55-250 STM IS on a Kenko 2 x TC and its pretty amazing considering, there are web pages which show you how to do the mod, it will obviously void ny warranty but I love this lens and now its even better, Its now a 110 to 500mm lens on a crop sensor like mine that equates to approx 800mm on top end, Pete

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

ebiggs1 — Fri, 20 Feb 2015 14:24:49 GMT

And now you have a f8-11 very marginal lens! I hope you have plenty of light, like manual focus and nothing is moving.

BTW, never mount a "modified" EF-S lens directly on a FF camera. Nothing good will come from that.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 17:03:40 GMT

F8 yes it aint the fastest and its manual focus which i dont mind. I already had the lens and a TC for my Magic Drainpipe, It produces very good results even in average conditions, the lens is really well balanced with the weight of the camera so its easy to hold it very steady, I have some very good pics shot at 1/8 second , What i am saying is it is possible to get this lens workinf with a TC, there are better options out there but the results are as good as my Tokina ATX 80 - 400 and my Sigma Fixed 500mm, thanks

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

ebiggs1 — Fri, 20 Feb 2015 17:12:43 GMT

Could you possibly post one of your "good results"? Especially the hand held one at 1/8th. I am very interested in seeing it.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 20:25:22 GMT

All photos taken the day after I modified the Canon EF-S 55mm - 250mm with Kenko x 2 TC, Just test shots, The Upright Bass was taken at FL 110 wide open with exposure of 1 second in very low light conditions, The outdoor photos were taken at 500mm or 2 x 250mm at 1/25th wide open hand held on a very overcast dull day, The Vase was 1/25th with low energy lamp to the right, Not my best work but was just making sure everything was working ok, Its obviously not as bright as my L series with a F2.8 aperture but ok for a budget solution, thanks, Pete

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 18:43:32 GMT

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 18:47:53 GMT

These have been reduced in qaulity 3 times too so lost a bit of clarity

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 19:03:44 GMT

Here is the modded lens on the Kenko 2 x converter, EF-S 55 - 250 STM IS on a Kenko EF 2 X Converter

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 19:13:30 GMT

This is the EF-S without the Kenko TC, obviously faster and more clarity

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 20:22:13 GMT

some more photos around 1/25th the specs shot at 1/20th

Canon EF S 55 - 250 with Kenko 2 X Converter

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

ebiggs1 — Fri, 20 Feb 2015 20:54:14 GMT

Thank you.

I guees it is, all in what you want and expect from your equipment. I might suggest (the bird) you lay off the sliders in LR just a bit.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 21:05:50 GMT

the bird was taken before light room installation, and has had basic balancing with the Canon software and it was more or less like this off the lens, anyway i am only trying to be helpful and we all know a 2 x TC and a cheap canon STM lens will never be as good as a Fast Prime or Top end zoom but for a few hyndred dollars (or Pounds) it does a job better than some more expensive low end lenses, I was only answerie question which I have answere yes you can use an EFS on a EF TC if you are prepared to void your warranty and possibly risk damaging it, It worked for me and the lens is light even with TC attached, it will never compare to an L lens , most things dont but its a good carry everywhere soluion, I will use it until I can afford the Canon 800mm F5.6 fore price of a new vehicle, Pete

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

ebiggs1 — Fri, 20 Feb 2015 21:12:43 GMT

Pete,

I appreciate your reporting back as to what can be done. Each has to decide the best course for them and not worry about what others say or think. Kudos to you. I would have never thought to do what you did.

I might add, while on the bird subject, I think the converter imporved the lens if you didn't adjust the photo in LR.

Re: Is there a teleconverter available that will mount to a Canon EF S lens?

riffman2015 — Fri, 20 Feb 2015 23:47:56 GMT

It was before I purchased the TC, it's a reasonable lens for price, a good travel lens but too fragile for any pro use