Extension Tube Questions

[jwkramer]

I have a couple questions regarding Extension Tubes:

1) Is there any quality difference between the Kenko Brand, and the Canon ones? If memory serves me, they don't actually have optics...

2) Will the 100mm f2.8 Macro Lens still Auto Focus with the extension tube(s) installed? I can't find any documentation regarding f-stop loss from the tubes.

Thanks!!!!

-Jim

[Belmondo]

1. You're right --- extension tubes are just tubes. They're hollow.

2. I have the 100mm f/2.8 macro, and it autofocuses with my Canon extension tube (EF 12 II).

Tom

[jwkramer]

belmondo wrote:
1. You're right --- extension tubes are just tubes. They're hollow.

2. I have the 100mm f/2.8 macro, and it autofocuses with my Canon extension tube (EF 12 II).

Tom

Tom,

Is there any kind of light loss when you use the tube? I figure there has to be at least a little....

Thanks!
-Jim

[robertwgross]

What Tom just stated is correct. There is no loss of light.

My EF 12 tube allows autofocus to work on most lenses, but autofocus gets pretty squirrelly when you are working at such close distances (like 4-18 inches).

I use mine for shooting the inside of flowers that are less than an inch in diameter, and it works well.

---Bob Gross---

[w10d]

jwkramer wrote:
Is there any kind of light loss when you use the tube? I figure there has to be at least a little....

Yes, as a lens moves away from the film/sensor an increase in exposure is required. Haven't got any tubes for my 10D yet, but often the smallest tube requires an extra 1/4 or 1/3 stop, and the largest 1 stop.

[teddynet]

There will be a loss of light because the light has to travel further, some will be absorbed by the black sides of the extention tube. If you want to find out how to calculate this then look up 'bellows extention' in google or read some large format technical sites.

The camera's internal metering will take care of it for you assuming that the extention tubes work in auto and you're not using non-TTL flash.

Rich.

[robertwgross]

My D60 can measure in 1/2 stop or 1/3 stop steps. How do you measure 1/4 stop?

---Bob Gross---

[Belmondo]

robertwgross wrote:
My D60 can measure in 1/2 stop or 1/3 stop steps. How do you measure 1/4 stop?

---Bob Gross---

Very carefully, Bob.