Extender+extension tube anomalies

[atkinsonphoto]

I recently added a refurb 2x III extender and a used 1st gen Canon 25mm tube to my kit and have been stacking them with a 200 2.8L, 85 1.8 and 35 2 IS on a 5d III. The 85 and 35 need to be 2x>25mm>lens to clear the 2x's protruding element. The 200 can be stacked either way.

The 25mm>2x>200 gives a 400mmF5.6 and a focus range of about 2 feet and no infinity. The 2x>25mm>200 gives a 400mmF2.8 and a focus range of about 6" and no infinity.

The 85 combo yields 170mmF1.8 with a similar focus range as the 200. The 35 stack gives an error01, no communication with lens/clean contacts. The 35 works with the 25mm alone, with a tiny focus range right next to the lens.

I understand that some combos just don't work, like the 2x>25mm>35, but what's going on with the 85 and 200 max aperture with the 2x>25mm stack? The 2x should double them, right? The resulting images really seem to be at 1.8 and 2.8.

 

[Mt Spokane Photography]

Is it with the extension tube that you get a wrong aperture? If so, the signal is not getting to the camera thru those extra joints. I'd use alcohol on a soft cloth to wipe the contacts clean. and try again.

http://cpn.canon-europe.com/content/education/infobank/lenses/extension_tubes.do

 

[Loswr]

With the 2x TC, the max aperture is reduced by two stops, regardless of what is recorded in the EXIF or how it appears. The behavior you describe is normal, and it will make sense if you count the pins/contacts. On the camera mount, there is a set of five pins and another set of three, with a slight space between them. The front end of the extension tube duplicates this 5+3 arrangement. Most lenses (with specific exceptions mentioned below) have a set of five contacts for the five pins, and a set of two contacts for the three pins (one of the two is double-wide). So, cameras, extension tubes, and most lenses have that 5+3 setup.

However, look at the front of the 2x TC (extender), and notice the arrangement is 8+3 – those extra three pins are specific for communication of the lens with the TC (the rear mount of the TC is 5+3, and the TC 'converts' the information to the same 5+3 on the camera). On the mount of your 200/2.8, and on all Canon lenses that are compatible with TCs (70-200 zooms and L primes 135mm and longer). there's a corresponding 8+2 set of contacts.

So, the only way the TC information is communicated to the camera is if the TC is mounted directly behind a compatible lens.

 

[Mt Spokane Photography]

With the 2x TC, the max aperture is reduced by two stops, regardless of what is recorded in the EXIF or how it appears. The behavior you describe is normal, and it will make sense if you count the pins/contacts. On the camera mount, there is a set of five pins and another set of three, with a slight space between them. The front end of the extension tube duplicates this 5+3 arrangement. Most lenses (with specific exceptions mentioned below) have a set of five contacts for the five pins, and a set of two contacts for the three pins (one of the two is double-wide). So, cameras, extension tubes, and most lenses have that 5+3 setup.

However, look at the front of the 2x TC (extender), and notice the arrangement is 8+3 – those extra three pins are specific for communication of the lens with the TC (the rear mount of the TC is 5+3, and the TC 'converts' the information to the same 5+3 on the camera). On the mount of your 200/2.8, and on all Canon lenses that are compatible with TCs (70-200 zooms and L primes 135mm and longer). there's a corresponding 8+2 set of contacts.

So, the only way the TC information is communicated to the camera is if the TC is mounted directly behind a compatible lens.

Right, I assumed that the tube was between tc and camera. using it between lens and tc will not let aperture info pass thru.

 

[midluk]

I would expect the exact effect of the TC to be different depending on the distance to the lens. The 2x factor only results when it is placed exactly where it is designed to be. If you place it further away (extension tube between lens and TC) the magnification will likely be less (and I would also not be surprised if significant vignetting occured).

 

[atkinsonphoto]

Thank you all for the info. The number of contacts makes sense.

 

[Don Haines]

With the 2x TC, the max aperture is reduced by two stops, regardless of what is recorded in the EXIF or how it appears. The behavior you describe is normal, and it will make sense if you count the pins/contacts. On the camera mount, there is a set of five pins and another set of three, with a slight space between them. The front end of the extension tube duplicates this 5+3 arrangement. Most lenses (with specific exceptions mentioned below) have a set of five contacts for the five pins, and a set of two contacts for the three pins (one of the two is double-wide). So, cameras, extension tubes, and most lenses have that 5+3 setup.

However, look at the front of the 2x TC (extender), and notice the arrangement is 8+3 – those extra three pins are specific for communication of the lens with the TC (the rear mount of the TC is 5+3, and the TC 'converts' the information to the same 5+3 on the camera). On the mount of your 200/2.8, and on all Canon lenses that are compatible with TCs (70-200 zooms and L primes 135mm and longer). there's a corresponding 8+2 set of contacts.

So, the only way the TC information is communicated to the camera is if the TC is mounted directly behind a compatible lens.

Interesting..... good to know!