i was just wondering... as i have a canon 50mm 1.4... how does the tamron 17-50 2.8 compare to it in low light?



With both at maximum aperture, in theory the Tamron lets in one quarter the light of the Canon. Two stops is a lot.


if i just set the canon to 2.8 i'll get a precise idea?



Not really. A rough idea exposure wise at best.



i'm going to shoot a feature film with lots of night street scenes, available light... i would hate to get them with only one focal length!



It's always hard to get a clean image at night with only available light, even with a f/1.4 lens. You need all the light you can get for best results


i'm going to get the tamron anyway, but i'm thinking if i should or shouldn't add a sigma 30mm 1.4 for the night street scenes...

Depends how important the results. If you don't mind higher ISO's you might get by with a f/2.8 zoom.

The problem your going to have shooting at 1.4 is that very little of your frame will actually be in focus. 1.4 with a 50mm lens will give you a sliver dof that is pretty much unusable except for cool little detail shots. I've noticed tons of people trying to shoot this way and having an overly out of focus image just isn't appealing. To be honest it looks pretty amateurish to me.

BTW to all... don't know if anyone noticed that sigma released a 17-50mm with image stabilation (OS) a couple months ago. I prefer sigm to tamron for build quality so I would give that one a look if you're in the market. Unfortunately it doesn't have full time manual which the expensive canon does.

You're right Scott. There is a lot of stuff out there that demonstrates the fashion for out of focus DLSR shots.

Your point about shooting at f/1.4 is correct, but let's look at the numbers. Taking a 50mm lens, a subject at 10 feet from the lens at f/1.4 has a depth of field of 0.69 feet. Stepping up to f/2.8, you have 1.29 feet, roughly double.

Both depths of fields are difficult to manage without looking, as you say, amateurish. However, working with half the depth of field yields quadruple the light, which looks like a good trade off. At least you have the option of splitting the difference and shooting at f/2.

The point being, you can never have too fast glass, especially for the stated goal of shooting at night using available light. Also worth bearing in mind that typically, lenses start to become sharper when stopped down a couple of clicks. In other words, if you do decide to shoot at f/2.8, the f/1.4 lens will typically be sharper than the native f/2.8 lens.

Interesting insights... the thing with high iso is that it gets very color noisy! Not nice...

Found a review on the Sigma, not favored when compared to the Tamron!

Sigma 18-50mm f/2.8 EX DC Lens Review (http://www.the-digital-picture.com/Reviews/Sigma-18-50mm-f-2.8-EX-DC-Lens-Review.aspx)

That's interesting... I wonder if the reviewer got a crap copy of the sigma... It seems I've rarely read a review where a tamron has siginifigantly outperformed a sigma... good info though...

Hey James,

Would love to know where I can learn that math...calculating dof based on aperture and lens would be a great thing to know... Does your calculation take into account the sensor size? My understanding is that the same lens used at the same aperture and focal length on a t2i and 5d will yield a shallower dof on the 5d due to the 5ds enormous sensor. Is this correct?

Hey James,

Would love to know where I can learn that math...calculating dof based on aperture and lens would be a great thing to know... Does your calculation take into account the sensor size? My understanding is that the same lens used at the same aperture and focal length on a t2i and 5d will yield a shallower dof on the 5d due to the 5ds enormous sensor. Is this correct?

Yes sensor size is part of the calculation. As you say, the bigger the sensor the shallower the DOF, other things being equal.

I don't think the maths is that hard to learn, but why bother when you can get a computer to do the work? Here are two useful online calculators that will enable you to pose as a ninja photo nerd:

Online Depth of Field Calculator (http://www.dofmaster.com/dofjs.html)

Field Of View Calculator (http://www.howardedin.com/articles/fov.html)

you... rule...

What do you think about getting "the three Canon low-light primes"?

I mean...

28mm 1.8
50mm 1.4
85mm 1.8

... and maybe cheat in a Tokina 11-16 for ulta wide shots.

Do you think that set would work?