Determining Aperture Value w/TC

[Zamora3]

I will soon purchase the Sigma 70-200 F/2.8 (wanted the Canon L, but too much $$$). I was thinking of also buying the 1.4x Teleconverter. How do you figure out the aperture value with a TC, do you just multiply 2.8 x 1.4 to find the value?

[Scottes]

A 1.4 TC adds a stop of aperture. f/4 -> f/5.6, f/5.6 -> f/8, etc.

Which is the same as multiplying the aperture by 1.4.... 4 x 1.4 = 5.6, etc.

Funny how that works, huh? :-)

[jbradc]

I think you mean a Sigma 70-200 F2.8 (they don't make a 1.8 ). I am not sure I understand the rest of your question, the 1.4x TC causes a 1 stop loss, so the lens will be F4 wide open. If you are asking about focal length on the Drebel it would be as follows

70-200 Lens on Drebel (1.6 crop factor) = 112-320mm
with the 1.4 TC it would = 156.8-448mm (112-320 x 1.4)

I hope that helps.

[Andy_T]

I will soon purchase the Sigma 70-200 F/1,8

WOW :shock:

I also want that lens. Where can you get one ;)

Best regards,
Andy

[Zamora3]

Yes, it was typo, I'll fix that. And yes you guys answered my question..thanks.

[Zamora3]

I think you mean a Sigma 70-200 F2.8 (they don't make a 1.8 ). I am not sure I understand the rest of your question, the 1.4x TC causes a 1 stop loss, so the lens will be F4 wide open. If you are asking about focal length on the Drebel it would be as follows

70-200 Lens on Drebel (1.6 crop factor) = 112-320mm
with the 1.4 TC it would = 156.8-448mm (112-320 x 1.4)

I hope that helps.

That would be the same w/ the 20D, right. Once I sell my dirt bike, I'll have the 2.8 and the 20D..I can't wait.

[jbradc]

That would be the same w/ the 20D, right. Once I sell my dirt bike, I'll have the 2.8 and the 20D..I can't wait.

Yes, the Drebel and the 20D both have the same size CMOS, so they both have a 1.6 crop factor.

[Adam Hicks]

So real quick... if I'm using the 200mm 1.8 this weekend (which I will be) with a 1.4x, that multiplies out to about f2.5 which doesn't seem right. What will it be?

Ashamed,
Adam

[robertwgross]

So real quick... if I'm using the 200mm 1.8 this weekend (which I will be) with a 1.4x, that multiplies out to about f2.5 which doesn't seem right. What will it be?

Yes, f/1.8 plus one stop is f/2.52.

Why doesn't that seem right?

The f/1.8 is not an even f/stop, so if you add one stop, the result is not an even one either.

---Bob Gross---

[steven]

I don't know about the Sigma TC but for the canon 1.4 TC I have the electronics in the TC take care of the added stop e.g. the display shows the correct apature with the added stop included. So for a 2.8 lens the largest apature that would show is 4.

[CyberDyneSystems]

Steven,

The same is true of the Sigma TC.

[Zamora3]

Can you use a Canon TC w/ a Sigma lens or vice-versa Sigma TC with Canon Lens.

[robertwgross]

I've stacked a Canon 1.4x TC along with a Tamron 1.4x TC, but the Tamron unit does not change any data passing through it like Canon does.

---Bob Gross---

[Zamora3]

so is that a yes? I don't plan on stacking them, only when I need that extra little distance.