Any hope for an extender?

Started Aug 24, 2020 | Discussions
David Franklin Senior Member • Posts: 1,542
Any hope for an extender?

Does anyone have a truly informed opinion as to whether Canon could and, therefore likely will, make a 1.4x, 1.7x, or 2.0x tele extender for the RF 70-200 lens, given the fact that the lens design has precluded any room at the camera mount end of the barrel for an extender to intrude inside the lens, as do other Canon extenders? Is it possible and is it likely? I really don't want to invest another $2,700.00 in the 100-500 lens right now, and because just a really good 1.4 extender would meet my needs almost completely, I would love not to have to think about it at all.

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tkbslc Forum Pro • Posts: 16,540
Re: Any hope for an extender?

It's definitely possible. While all of Canon's past TC seem to have that protruding design, most third party TC do not. Take a look at the design of a Kenko  TC for example.

However, given that Canon just barely released new RF TC with the protruding elements, I'd say that's your answer from Canon. Your only hope will be once more companies start making RF compatible lenses. Maybe Tamron or Samyang can bail you out in a couple years.

OP David Franklin Senior Member • Posts: 1,542
Re: Any hope for an extender?

Anyone else? Someone with optical expertise?

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1Dx4me
1Dx4me Forum Pro • Posts: 11,791
Re: Any hope for an extender?

David Franklin wrote:

Does anyone have a truly informed opinion as to whether Canon could and, therefore likely will, make a 1.4x, 1.7x, or 2.0x tele extender for the RF 70-200 lens, given the fact that the lens design has precluded any room at the camera mount end of the barrel for an extender to intrude inside the lens, as do other Canon extenders? Is it possible and is it likely? I really don't want to invest another $2,700.00 in the 100-500 lens right now, and because just a really good 1.4 extender would meet my needs almost completely, I would love not to have to think about it at all.

i am not sure about RF but i regularly use my 1.4 III TC on my 100400 II with very good result. in fact, my TC 1.4 is attached to my 100400 II all the time. here is a sample of EF 100400 II+TC 1.4x III:

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Tony D Senior Member • Posts: 1,019
Re: Any hope for an extender?

I doubt they will make one as it would lower the optical quality - it protrudes in order to contain the required number of element to maintain optical performance. And the RF 70-200mm design as it stands is shorter than the original EF design so limits the ability to make it work with the RF 70-200, no space to make the space to allow for the extender protrusion, probably too many design constraints to make it work.

Also the EF 1.4/2.0 extender did not work with certain lenses, if I remember correctly the 70-200mm L was one it work with. No longer have mine to check.

Other manufactures could make one without this protruding design at the cost of optical quality (less element or less well balanced elements). Without the exact lens design details it is difficult to predict if it can be done, it may not be possible with the RF lens distance/mount size. These are all generated by reverse engineering the Canon lens/extenders to generate a design, so always likely be optically inferior.

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OP David Franklin Senior Member • Posts: 1,542
Restated: Any hope for an extender?

Thanks to those who have replied so far.

As I think I might have implied but didn't outright previously state, I fully realize that the lack of room in the lens mount barrel end of the RF 70-200 f/2.8 lens to fit Canon's previously designed protruding EF lens extenders, makes using extenders of that design impossible for use with the RF lens.

What I have been asking is, is there someone out there with true experience in and/or knowledge of professional optical design, who knows whether a completely new type of non-protruding designed RF extender of very high quality can or would likely be made by Canon, so that it would be useful on my RF 70-200 f/2.8. I know this is probably a difficult question, with few people really qualified to give an answer, but I'm hoping to get lucky here, in order to understand my lens choice options.

Thanks to all again.

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Tony D Senior Member • Posts: 1,019
Re: Restated: Any hope for an extender?
1

You want a straight answer?

It will be Canon will not for a number of reasons.

Just look at the EF situation Canon has never made one for any of their own lenses which don't allow the extender to 'extended' in to the lens body, for a good optical reasons. To do otherwise will compromise image quality (and cut sales of their better higher cost lenses). It is also optical difficult to do with no separation between last lens element and the extenders elements (check the Canon extenders and the lenses they are compatible with and you will see the last lens element is some distance from the first extender element, there is a gap). Also with the RF600, 800 and RF100-500 out there (all compatible with their own extenders) where's the logic for them?

Optically the extender is another lens element in the optical train, it magnifies the image, losing the field edges (much like EF lenses do on cropped sensor bodies). To do this they need to magnify and move the image plane back on to the sensor.

Another manufacturer may try but the optical design will need to introduce a gap. They would need to introduce a separation between last lens element and the first lens in the extender, in a place were they can achieve the correct magnification and still have the image plane on sensor but just magnified & correctly in focus. The space will be need to find a place where the light path is at the required size/magnification and then refocus it to the sensor. A simple light ray path diagram can show how these work and why a separation is needed.

When I get I chance I could contact some Zeiss engineers I know (my day job involves working with Zeiss on more specialized lenses, the several million dollar type) but I know they will say similar or would want to know the exact element parameters for the current Canon lenses so they can model this and give a good answer.

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OP David Franklin Senior Member • Posts: 1,542
Re: Restated: Any hope for an extender?

Tony D wrote:

When I get I chance I could contact some Zeiss engineers I know (my day job involves working with Zeiss on more specialized lenses, the several million dollar type) but I know they will say similar or would want to know the exact element parameters for the current Canon lenses so they can model this and give a good answer.

If you could ask, then please do ask, as it might help to finally settle the issue for me. But, I do wonder, why would introducing a gap in the extender be such a bad thing? You make it sound like that would be quite bad, and I don't quite understand that. Plus, even if a gap were, per se, a negative, could there be a way that with special optics that such as gap could be greatly minimized?

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sobrien
sobrien Senior Member • Posts: 1,665
Re: Any hope for an extender?

I don’t understand why they didn’t make the RF 70-200 be able to safely take the extenders when zoomed out to 200mm or thereabouts, in a similar way that the RF 100-500 can only take them when zoomed out to 300mm or more. It sure looks like there’d be enough space to do that.

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OP David Franklin Senior Member • Posts: 1,542
Re: Any hope for an extender?

sobrien wrote:

I don’t understand why they didn’t make the RF 70-200 be able to safely take the extenders when zoomed out to 200mm or thereabouts, in a similar way that the RF 100-500 can only take them when zoomed out to 300mm or more. It sure looks like there’d be enough space to do that.

Good question.

By the way, do you know how that process, by which the 100-500 only works in its longer focal length range with the extenders, actually works? What happens if you put the extender on the camera and then try to fit the lens to the extender when it's not zoomed out to the "acceptable" focal length range. Does the extender then actually collide with the glass in the 100-500, or is there some mechanism, other than human caution, to prevent this from happening? It seems highly unlikely that Canon would design something that would't avoid the users from damaging their optics if a simple and likely mistake were made by fallible people, but I can't easily imagine the mechanism for preventing it.

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sobrien
sobrien Senior Member • Posts: 1,665
Re: Any hope for an extender?

David Franklin wrote:

sobrien wrote:

I don’t understand why they didn’t make the RF 70-200 be able to safely take the extenders when zoomed out to 200mm or thereabouts, in a similar way that the RF 100-500 can only take them when zoomed out to 300mm or more. It sure looks like there’d be enough space to do that.

Good question.

By the way, do you know how that process, by which the 100-500 only works in its longer focal length range with the extenders, actually works? What happens if you put the extender on the camera and then try to fit the lens to the extender when it's not zoomed out to the "acceptable" focal length range. Does the extender then actually collide with the glass in the 100-500, or is there some mechanism, other than human caution, to prevent this from happening? It seems highly unlikely that Canon would design something that would't avoid the users from damaging their optics if a simple and likely mistake were made by fallible people, but I can't easily imagine the mechanism for preventing it.

There’s a mechanism though I’m not sure of the precise details. Something in the lens barrel to prevent colliding glass as I understand it. Deliveries of RF 100-500s expected any day now so we should get the details soon enough.

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Tony Defriez Regular Member • Posts: 192
Re: Restated: Any hope for an extender?

Even if you get the answer what, other than say o well its not going to happen, will you do with it? Are you going to make your own or push someone to make it for you?

It would make the extender larger for one (not an optical reason but).

One reason for the RF mount (detailed by Canon) lower lens distance to sensor distance and the larger flange - more complex designs and better designs possible (reason they can now make an f2 version of the 24-70mm lens). The design of the RF 70-200mm is such that the last lens element almost sits in the flange, so the angle of the cone of light must have steep angles (more than the earlier EF70-200 where the last element is some way forward of this, ergo the angle was less). This make any optical design for an extender harder.

Tony D Senior Member • Posts: 1,019
Re: Any hope for an extender?

Two things:

  • Just check the RF70-200 and there is not enough clearance when full zoomed (set at 200mm for the current RF 1.4 extender to fit so the RF 2.0 extender certainly will not.
  • You are assuming it is a physical constraint with RF100-500 lens, until we see one in the wild, we are only speculating, it could be an optical limit not a physical limit
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OP David Franklin Senior Member • Posts: 1,542
Re: Any hope for an extender?

I'm not exactly assuming anything yet, I'm just questioning, based on what another poster here said. What I really want to know is whether a good quality extender, no matter what its construction would be, is optically possible, and likely to be made by anyone.

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R2D2 Forum Pro • Posts: 23,268
Re: Any hope for an extender?

David Franklin wrote:

I'm not exactly assuming anything yet, I'm just questioning, based on what another poster here said. What I really want to know is whether a good quality extender, no matter what its construction would be, is optically possible, and likely to be made by anyone.

I’d say there’s a possibility 3rd party manufacturers might produce (non-intruding) RF tele-extenders, just as they did for EF.

R2

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sobrien
sobrien Senior Member • Posts: 1,665
Re: Any hope for an extender?

Tony D wrote:

Two things:

  • Just check the RF70-200 and there is not enough clearance when full zoomed (set at 200mm for the current RF 1.4 extender to fit so the RF 2.0 extender certainly will not.

Hi, have you physically tried this? Or measured? What are the measurements for the protrusion of the RF1.4x and RF2x extenders, respectively? Thanks

  • You are assuming it is a physical constraint with RF100-500 lens, until we see one in the wild, we are only speculating, it could be an optical limit not a physical limit

I have read about a physical feature that prevents contact of the elements.

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Tony D Senior Member • Posts: 1,019
Re: Any hope for an extender?

I only have the 1.4 extender - physical you can’t even mount the lens on it. The physical construction of the lens prevents this ( there is a moving tube which has a smaller radius then the extender) - so it physical does not fit

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Tony D Senior Member • Posts: 1,019
Re: Any hope for an extender?

Was talking about 70-200 awaiting delivery of 100-500

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JackiePan Regular Member • Posts: 129
Re: Any hope for an extender?

1Dx4me wrote:

David Franklin wrote:

Does anyone have a truly informed opinion as to whether Canon could and, therefore likely will, make a 1.4x, 1.7x, or 2.0x tele extender for the RF 70-200 lens, given the fact that the lens design has precluded any room at the camera mount end of the barrel for an extender to intrude inside the lens, as do other Canon extenders? Is it possible and is it likely? I really don't want to invest another $2,700.00 in the 100-500 lens right now, and because just a really good 1.4 extender would meet my needs almost completely, I would love not to have to think about it at all.

i am not sure about RF but i regularly use my 1.4 III TC on my 100400 II with very good result. in fact, my TC 1.4 is attached to my 100400 II all the time. here is a sample of EF 100400 II+TC 1.4x III:

Did you use extension tube?

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OP David Franklin Senior Member • Posts: 1,542
Re: Any hope for an extender?

Thanks for all the replies so far.

Well that bit about the current RF extender not possibly fitting the RF 70-200 seems to take care of the question I didn't really ask, but was nevertheless curious about.

And another response here was optimistic about possible 3rd party companies making a non-protruding extender; this was the closest thing to good news so far.

Anyone else with a more (optically) technical background, someone involved in lens or optical design here, who can wade in?

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