120-300 vs 300mm prime question

lnk

lnk

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Leigh
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Which of these two lens would take a Canon 1.4 converter better on a 40D

Sigma 120-300mm F2.8 or a Canon 300mm F4L IS.

I know F-stop wise the Sigma will be better but what about focus speeds ??
 
prime beats zoom :)
 
is the sigma f2.8 all the way through the 120-300mm range?

you will cut between 1 and 2 f stops when you put a converter on

the IS of the 300mm Canon will add about 1 f stop

so you need to do the math on where your going to end up apature wise.

the prime will focus faster then zoom and the Canon converter is made with the 300 IS in mind.

Tough call and you maybe need to tell us what your going to be shooting.
 
he already stated he is aware of the fstop and only asked about focus speed. hence why I only answered as i did :)
 
I have the Canon 300mm F4 IS and use it with the 1.4 converter but have the option of getting a Sigma 120-300mm F2.8 (which is a constant 2.8) i generally use the lens for motorsport and even on dullish days manage at 5.6 but sometimes 300mm can be too long.

The sigma sounds good but i am not totaly sure about focus speeds compared with the canon.
 
If your Canon 1.4x converter is the Mk II, I don't think it will fit that Sigma lens due to the seal (it doesn't fit on my Sigma 300 F2.8 prime) but I don't know if the earlier version of the canon 1.4x will fit.
 
I have the Sigma 120-300 and a Nikon 300mm 2.8.

The biggest difference with the TC is in AF speed. It's just noticeable with the Sigma zoom, whereas it doesn't seem to affect the Nikkor at all. That said, if IQ is absolutely critical, the prime wins every time, especially with the TC.

Mind you, I tend to take the 120-300 more for the flexibility. It's a top lens.
 
It is a mkll i have..:thinking:

Flexability is what i have been thinking about but dont want to sacrifice focus speed at all.
 
lnk said:
It is a mkll i have..:thinking:

Flexability is what i have been thinking about but dont want to sacrifice focus speed at all.
Click to expand...

Using an extender will lose you some focus speed.
 
If you dont fancy the 120-300 can you let me know where its at (y)

Been reading up on this lens and from what i can see it is very highly regarded, if a little heavy and takes a 1.4x quite well in terms of IQ, but it can hunt sometimes. Still meant to be a great lens
 
Cannot really comment on the canon comparison, but having owned two 120-300mm sigma's I can confirm that in my opinion it is not a constant 2.8 through the range nor does it focus at anything like the speed of the Nikon 300mm AF-s for example. There are others here who will confirm this.

The Sigma lacks contrast and color rendition compared to the Nikon prime and both examples not only back focused but were very soft at 2.8. Personally I would go for the canon prime every time.
 
When you use IS, you can drop the shutter speed to lower than you could without IS. So.... if your lowest shutter speed with this lens without IS was 1/250 second, switching IS to 'on' will allow you to reduce the shutter speed by one stop and shoot at 1/125 second. (If I remember my stops correctly). IS does not change the aperture but allows you to shoot at a lower shutter speed WITHOUT the dredded camera shakes making the picture blurry.

Adding a teleconverter WILL reduce the widest aperture you can dial in by one stop but increase the reach of the lens. Provided by adding a telecon, you don't reduce the widest aperture available to something around f/5.6 (maybe f/8), you retain autofocus as the lens will still let enough light in for the auto focus sensors to work.

Alan
 
lnk said:
Flexability is what i have been thinking about but dont want to sacrifice focus speed at all.
Click to expand...

You can't have both! You can only have compromise!

Fastest AF will always be a prime, its just got less to do.

Maybe it seems a little inflexible if you havent used one before, but everyone serious from motorsport to aviation to wildlife will pretty much be shooting long primes. Just zoom with your feet, the shot is there!
 
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