rookie question

[mikebrown]

I’m looking into buying new lens. I have a few things that i needs some assistance on. I partly understand the importance of the speed/aperture thing, but I was wondering for example, I have the canon 40d with the 28-135mm f/3.5-5.6 lens. my question is if i was to get the canon 24-70 2.8l and took a shot at 70mm f5.6 would the image look any different than my existing lens?
my second question is, is the tamron 24-70 2.8 lens as good as the similar canon lens.
The issue that I am running into is that with my current lens I am unable to get the shutter speed/ aperture combination that I desire. The way i currently understand it is that lets say for example I want to take a picture with low light where flash is not permitted. I can bump up the iso or use a slow the shutter speed, the way I think which is most likely wrong, that with a better lens I may not need to bump up the iso, or use a very slow shutter to take the picture. I could use a higher aperture to get the results I need. I know that there is a lot more to it than that but that is the way I understand it so far.

[Thorpeland]

Hey Mike, yeah thats a lot of questions rolled into one. But I'll try to give you my best answers. Although, like most things photography... opinion weighs heavy.

Ok so you have the 40D. I am assuming the 28-135mm f/3.5-5.6 lens is the kit lens? If that is the case, then the 28-70 f2.8L lens WILL look better even at max zoom of 70mm. There is a reason Canon puts that "L" on those lenses. It stands for Luxury and is reflected in its price. What you will get compared to your kit lens is better color accuracy, less of that halo fringe on subjects, much less distortion at all aperture & zoom ranges... and of course the ability to shoot at a constant f2.8 through the entire zoom range. Add in that the L lenses are built like tanks compared to kit lenses too!

Keep in mind, your 40D has a the 1.6X crop factor on its image sensor. So in fact a lens zoomed to 70mm is actually a 112mm telephoto. I *believe* the kit lens is built to compensate for this 1.6X crop, giving you a true 135mm (I could be wrong there).

In your 2nd issue, you complain of not being able to get a fast enough shutter speed in low lighting. Ah, a common battle photographers deal with every day. In this case, again, the L lens will win this battle. Your kit lens will close down to f5.6 as you reach 135mm. This requires you to either crank up the ISO and the grain along with it, or like you said use a slower shutter speed and keep the camera perfectly still. With the 24-70mm f2.8, you could be at max zoom but still shooting at the large f2.8 aperture. That, along with a small bump up in ISO would allow you to maintain a fairly decent shutter speed and get those low light shots.

So yes, your understanding really wasn't far off at all.

[mikebrown]

Thanks for the help !!

[Daniel Bates]

Okay... let me see if I can clear some things up for you.

if i was to get the canon 24-70 2.8l and took a shot at 70mm f5.6 would the image look any different than my existing lens?

Yes. The 24-70L would have better image quality, better sharpness, and better bokeh than the image from your existing lens (though the differences may not be worth the price of the lens - this is where user opinion comes in).

is the tamron 24-70 2.8 lens as good as the similar canon lens.

I assume you're talking about the Tamron 28-75mm f/2.8 here. The answer is: yes and no. The Tamron has excellent image quality and may be a match for the Canon L in sharpness, but it has nothing on the L in build quality and heft. If you prefer smaller, lighter lenses and don't mind if they feel 'cheaper', the Tamron is a good choice. If, like me, you started on old MF film lenses (my first camera was a Pentax ME Super), the Canon will feel much more comfortable. (In my opinion.)



As far as the low light scenario - there are four factors that influence your exposure. They are the shutter speed, the aperture, the ISO, and the light in the scene. Now flash will improve that last factor (available light), but if you can't use flash, you are stuck with the other three options. ISO can get you out of a lot of trouble, and the 40D has pretty good high ISO performance, but when you hit the roof, you're done. Also, very high ISOs will degrade your image quality, possibly quite severely. I haven't owned a 40D so I will not comment on its performance, but I know that maxing out the ISO on any of the bodies I have used (1D, 1D2N, 20D, 10D, D200, D40) results in very poor image quality.

So, you can't use flash and your ISO is up as high as you dare to go, but your pictures are still to dark. What then? Well, the shutter speed can be adjusted, but only so far - camera shake and subject movement will ruin pictures just as easily as underexposure or excessive noise. You can only take your shutter speed down so far before your images get shaky. IS helps, but it doesn't do squat for subject blur, so if your subjects are moving, you need something else. That 'something else' is the maximum aperture of the lens.

At 70mm, your current lens probably maxes out at approximately f/5 or slower. That's not very fast for low-light shooting. The other two lenses you mentioned go up to f/2.8, which is over twice as fast (letting over twice as much light through your lens). There are other lenses out there that are even faster - I own a 35mm f/1.4, which is crazy fast, but you run into other problems at that extreme. The Tamron and the Canon will both give you f/2.8 at 70mm, which is pretty respectable and will let you increase your shutter speed to reduce shake and/or reduce your ISO speed to lighten noise, while still maintaining proper exposure.

(Whew.) Hope this helps!



Also:

I *believe* the kit lens is built to compensate for this 1.6X crop, giving you a true 135mm (I could be wrong there).

Nope. Every lens built for the 35mm format is the same; e.g., 135mm is 135mm is 135mm, regardless of whether it's F mount, EF mount, or EF-S mount. The EF-S lenses just project a smaller image circle.

[Patti Edens]

As far as I understand it, the 28 to 135 is not an EF-S (kit) lens, but even if it was, the Canon kit lenses do not correct for crop factors. They are 35mm equivalent just like any lens.

[Thorpeland]

Originally Posted by Daniel Bates

The EF-S lenses just project a smaller image circle.

Bingo. Thats what I was thinking about.

[toverman]

Thorpe and Daniel have posted great information here.

Zooms are the most convenient, and if you can get one with a constant f/2.8 max aperture, that's a giant leap toward better low light shooting. As Daniel mentioned, prime (nonzoom) lenses can open up even further, and for Canon there are a host of L and non-L (less expensive) lenses that provide excellent results. Primes are also known for their greater sharpness, tendency to be lighter (fewer moving parts) and in some cases less expense to buy. But they take practice to use because you've got to think which lens is best for the situation, and then minor "zooming" can be done with your feet.

I recommend a Canon 50 f/1.8 and 85 f/1.8 for low light stuff. Get better and longer focal lengths if you've got the coin.

[mikebrown]

Thanks for the info. It cleared up the questions I had so far. Now i just have to shoot, shoot, and shoot.
Thanks Everyone

[Thorpeland]

Thats the key man. The joy of digital, no film. Shoot, shoot, shoot, shoot.... repeat. Learn.

Glad we could help.