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Adam Hicks
17th of January 2005 (Mon), 19:02
When I finally save up the money for my 300mm f2.8 IS (have you seen the image quality rating of that thing!?!?) I'm going to play with a 1.4x and probably a 2x TC on it. I'm guessing the 1.4x will still yield excellent images at 420mm, and the 2x will obviously take a hit but would be fun to play with!

Ok so the question... if I lose one stop with the 1.4x and 2 stops with the 2x, what does that put my widest aperture at? I'm a little confused on the stops (seeing that the 1.8 50mm does 2.0, 2.2, 2.8, etc) these aren't each a full stop are they?

Thanks!
Adam
robertwgross
17th of January 2005 (Mon), 19:33
That's correct, don't get confused by fractional stops.

If you start with an f/2.8 lens and add one 1.4x TC, then you have an f/4 lens combo. If you and one 2x TC, then you have an f/5.6 lens combo.

---Bob Gross---
Adam Hicks
17th of January 2005 (Mon), 19:41
Ok thanks... that's what I figured... these half stops throw me off. Is there a chart of standard full stops? I understand that each full stop closed halves the light and vice versa, I'm just not sure what stops are full and what aren't...

Thanks again,
Adam
robertwgross
17th of January 2005 (Mon), 19:51
Standard f/stops are always a multiple of 1.4 times the previous one. Yes, there is a tiny amount of roundoff error.

For example:
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32.

---Bob Gross---
kfong
17th of January 2005 (Mon), 19:52
Each full stop (1/2 as much lignt) would increase the f/number by a facotor of EXACTLY square root of 2.
Each 2 full stop (1/4 as much lignt) would increase the f/number by a facotor of EXACTLY square root of 4.
...etc

Ken

Ok thanks... that's what I figured... these half stops throw me off. Is there a chart of standard full stops? I understand that each full stop closed halves the light and vice versa, I'm just not sure what stops are full and what aren't...

Thanks again,
Adam