topic Re: Canon extender with Tamron lens question in EF & RF Lenses

Canon extender with Tamron lens question

Pauly_6_String — Tue, 09 Jun 2020 02:30:01 GMT

Hi all. I just picked up a used Canon EF 1.4x II extender and attached it to a Tamron G2 70-200 f/2.8 lens.

The camera displays f/5.6 to f/45???? Exactly two stops high on each end. Is that a compatibility/communication issue between the two brands?

Also was disappointed to find that it won't fit my EF 17-40 or my EF 24-105 lenses.

thanks

Re: Canon extender with Tamron lens question

kvbarkley — Tue, 09 Jun 2020 02:38:37 GMT

Canon extenders are only designed to work with Canon lenses.

You should only lose 1 stop.

Re: Canon extender with Tamron lens question

Pauly_6_String — Tue, 09 Jun 2020 03:32:34 GMT

Thanks. Is the stop loss supposed to be from a reduction of light entering the lens or physically not being able to select the largest aperture?

Re: Canon extender with Tamron lens question

Tronhard — Tue, 09 Jun 2020 07:22:57 GMT

@Pauly_6_String wrote:
Thanks. Is the stop loss supposed to be from a reduction of light entering the lens or physically not being able to select the largest aperture?

There is a fair amount of glass in an extender and the optical algorithms required to render the resultant extension will lose about 1 stop on the 1.4x and 2 stops on the 2x extender. There are tables available from Canon defining what lenses extenders will work with what lenses and the resultant performance of those combinations. Furthermore different camera models give different performance results when used with extenders, especially in terms of autofocus and f-stop values for shooting.

If you want to invest in extenders, some serious research is in order to avoid disappointment.

Re: Canon extender with Tamron lens question

kvbarkley — Tue, 09 Jun 2020 13:27:05 GMT

It is an optics thing, and has nothing to do with the physical aperture. Since you are effectively increasing the focal length, the ratio of the max Aperture to focal length goes down.

Re: Canon extender with Tamron lens question

ebiggs1 — Tue, 09 Jun 2020 14:16:02 GMT

" I just picked up a used Canon EF 1.4x II extender and attached it to a Tamron G2 70-200 f/2.8 lens."

It makes more sense to get a ~~Sigma~~ Tamron tel-con for a ~~Sigma~~ Tamron lens, doesn't it? The Canon 1.4x tel-con only works with prime lenses except for a very few zooms. The 17-40mm and 24-105mm are not one of those few.

Question, why would anyone want to put a tel-con on a WA lens like the 17-40mm? It seems that concept is contrary.

Edited sorry for the mustake!

Re: Canon extender with Tamron lens question

Pauly_6_String — Tue, 09 Jun 2020 14:07:36 GMT

"Question, why would anyone want to put a tel-con on a WA lens like the 17-40mm? It seems that concept is contrary."

Thanks for th e reply. I tried to put it on those lenses because I wanted to see if the same thing happened (aperture display issue) with a Canon lens. Also I though maybe for traveling using it on the 24-105 may lighten the load, THEN I went to their website and found which lenses it is compatible with.

I was unaware of the proprietary nature of the extenders. I did get a Tamron lens for a Canon camera and figured (wrongly) that extenders were compatible in the same way.

Re: Canon extender with Tamron lens question

kvbarkley — Tue, 09 Jun 2020 14:11:31 GMT

You have to be especially careful with Canon Extenders. Sometimes the elements protrude a bit and can rub against the elements of the target lens.

Re: Canon extender with Tamron lens question

ebiggs1 — Tue, 09 Jun 2020 14:19:11 GMT

"I did get a Tamron lens for a Canon camera and figured (wrongly) that extenders were compatible in the same way."

I know that seems logical but even Canon tel-cons are not compatible with most Canon lenses. Buy yourself a Tamron extender.

Re: Canon extender with Tamron lens question

RobertTheFat — Wed, 10 Jun 2020 00:43:50 GMT

@kvbarkley wrote:
It is an optics thing, and has nothing to do with the physical aperture. Since you are effectively increasing the focal length, the ratio of the max Aperture to focal length goes down.

And to make it go down by one stop, you have to increase the focal length by the square root of 2. And what is the square root of 2? Almost exactly 1.4, which is why they make "1.4x" extenders.

EDIT: For maximum clarity, I should have said "multiply" rather than "increase"..

Re: Canon extender with Tamron lens question

ebiggs1 — Tue, 09 Jun 2020 14:47:06 GMT

Keep in mind, using a tele-con does not change the physical aperture. You are magnifying an image that is already projected by the lens. The physical aperture is unchanged so the depth of field is unchanged.

Re: Canon extender with Tamron lens question

kvbarkley — Tue, 09 Jun 2020 15:50:47 GMT

Since the "circIe of confusion" is changed, I think that the DOF is changed too, just like the fact that the DOF changes when you use the same lens on FF vs APS-C.

ETA:

This is wrong, the change in depth of field is entirely due to the effective increase of the focal length.

Re: Canon extender with Tamron lens question

ebiggs1 — Tue, 09 Jun 2020 16:05:55 GMT

You are talking sensor. I am talking lens.