extender?

[chewiebakka]

is it possible to get a 2x extender for canon 28-135is?
what brand is ok?
tamron, sigma, canon????

[50/1.4]

Kenko's 1.5X TC and Kenko's and Tamron's regular line of 1.4X and 2X TC's will work. Do not get the better PRO version if you are going to be using it at less than 90mm focal length, according to Tamron the PRO extenders will actually degrade the image at less than this focal length and they say the regular TC will work better. The PRO series is also recommended for use with 2.8 lenses or faster. Check out Tamron's web site for details. The Sigma, as the Canon, is not compatible with most lenses, it's not even compatible with their 170-500, for example.

[dbarthel]

Be aware that autofocus goes bye bye with either of these alternatives.

[50/1.4]

Not completely. My Kenko 1.5X will AF with my 28-105/3.5 at all focal lengths, so I assume it will with the 28-135 up to ~100mm and it AF's through some of my 75-300's range, but then becomes very erratic, so I don't use it above ~135mm. But, dbarthel's point is well taken, don't count on it. I read somewhere someone else with a 28-105 and Kenko 1.5X could not get good AF above just 50mm, that's why I even tested it on my 28-105 at all, I normally just use it on my 75-300IS.

[50/1.4]

Make that 28-105/3.5-4.5 and my 75-300IS is 4-5.6.

[chewiebakka]

anyone tried this combination? a 28-135 with extender? is it right that if i have 5.6 and use a 2x ext. it will become 11(5.6*2)? and if i have an 1.4ext. it will become close to 7.5(5.6*1.4)???

[robertwgross]

You have your math wrong. You really ought to get over to your local community college and sign up for a photography class. They will teach you fundamentals, like how f-stops work.

f 5.6 plus 2 f-stops equals about f 7.6

---Bob Gross---

[Slow]

robertwgross wrote:
You have your math wrong. You really ought to get over to your local community college and sign up for a photography class. They will teach you fundamentals, like how f-stops work.

f 5.6 plus 2 f-stops equals about f 7.6

---Bob Gross---

I may be a new member but feel that it is not Chewie that needs to venture back to college as f5.6 plus 2 f stops is very near f11! Or at least it was when I was at Uni! My 2 cents........

[robertwgross]

I found the flaw.

My teleconverter says to increase the aperture by two f numbers. Not two f stops.

Two whole stops up from f 5.6 is f 11.

Then I looked to see why my teleconverter says only two f numbers and not two f stops. Because it is not the x2!

---Bob Gross---

[robertwgross]

More.

If you start with a good fast aperture, like f 2, and if you have lost two f-stops, then that gets you up to f 4. So, that looks like two f-numbers as well as two f-stops.

If you start with a smaller aperture, like f 5.6, and if you have lost two f-stops, then that gets you up to f 11. That makes an excellent case for why many people recommend to start with the fastest lens (small aperture numbers) in the first place, if you can afford it. You can shoot lots of subjects with f 11, but you just want to know what you are getting into, and what you can or can't do with depth of field.

My teleconverter only drops one f-stop, so the numbers for it are not relevant to your two-stop teleconverter. Plus, I always think starting from f 2 or f 1.8.

I had to use a x3 teleconverter one time, and the loss of three f-stops was staggering. Fortunately, I had one f-stop left to shoot in, and there were no depth of field issues with that at all (since I was shooting a solar eclipse).

---Bob Gross---