# Focus speed of 50mm lenses and other primes, especially in low light



## TexPhoto (Nov 3, 2013)

I have 2 50mm lenses, the nifty 50 1.8, and the Sigma 50mm 1.4. Neither of these seem to focus very fast or very well in low light. At least my 70-200 f2.8 II blows them away, and my 24-105mm f4 IS is maybe halfway between the 50s and the 70-200.

Now the 50mm does give more light in the photo and lets you use faster shutter speeds, but it usually will not focus. I am talking about a shopping center parking lot (bunch of guys getting their cars together) and things like that. Yes I could use a flash, but that is not what I am after.

Logically it seems like the f1.4 or 1.8 should be a big advantage when trying to find contrast and focus, but it does not seem to work that way. Is the Canon 50mm f1.4 better?

This is with my 5D Mark III and 1D4. I used to have a 5D2 and 7D, and it seemed the same.


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## ajfotofilmagem (Nov 3, 2013)

Canon 50mm F1.4 focuses faster than 1.8 but not much. I do not know any 50mm that do autofocus as fast as 70-200L. Maybe 40mm or the new 35mm F2 IS.


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## Mt Spokane Photography (Nov 4, 2013)

The camera body plays by far the biggest part in autofocus speed. In low light its even more important.


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## Ewinter (Nov 4, 2013)

the canon 50mm 1.4 is terrible at acquiring quick moving targets in very low light. It's IQ is not very good either. 
I actually have more luck with the sigma 35 1.4 and cropping.


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## StudentOfLight (Nov 6, 2013)

My 50mm f1.4 is the same, and I feel a very disappointing lens purchase. It is my least favourite lens (that I still own).

Anyway, I know that you said you don't want to use flash to light your scene but couldn't you just use the AF-assist beam. Flash power set to minimum, point the head off to the side (or behind you) so it won't have significant impact on the exposure?


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## Ewinter (Nov 7, 2013)

StudentOfLight said:


> My 50mm f1.4 is the same, and I feel a very disappointing lens purchase. It is my least favourite lens (that I still own).
> 
> Anyway, I know that you said you don't want to use flash to light your scene but couldn't you just use the AF-assist beam. Flash power set to minimum, point the head off to the side (or behind you) so it won't have significant impact on the exposure?


In the flash exposure menu, you can set flash firing to off. The focus assist will still work


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