Newbie needs advise on compatible lenses for the A57

Started Jun 11, 2012 | Discussions thread
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Re: Newbie needs advise on compatible lenses for the A57
In reply to 123Mike, Jun 20, 2012

123Mike wrote:

-The 70-210mm F/4 offers a faster maximum aperture that lets in more light and can put the background farther out of focus for better subject isolation. The 70-210mm F/4 is also much better built, with a metal body, focus distance scale, infrared correction marks, and internal zoom action.

Yes, it's possible that the lens could be made lighter and smaller if it only had to cover the APS-C sensor. The 70-210/4 lens projects an image that is larger and brighter than an image from the 55-200/4-5.6 lens. The APS-C sensor won't use the 70-210mm's entire projected image, but it does benefit from the fact that the 70-210mm's projected image is brighter.

And if you later decide to use a 35mm film or full frame camera, the 70-210mm's image circle will cover the entire film negative or full frame sensor.

However though. That's a full frame (film) lens. Not the entire diameter of the front of the glass is used to collect light from to project onto the APS-C sensor. In essence, part of it is thrown out.

Because what matters is the size of the hole that light can actually pass through....

There might be a small transmission difference between different lenses set to the same aperture setting, but that would be due to how well light passes through the lens elements. Generally, a lens with more elements does not do as well in this regard, although improved lens coatings can minimize the light loss from having more elements.

It's possible that my analogy is wrong on this. I'm currently trying to work through it.

For instance, I currently think that a lens with a larger diameter than another lens, both at the same aperture, will produce a brighter image. Someone is trying to tell me this isn't so, but I can't understand why. In my view, more photons move through that same hole with a larger lens diameter.

When you buy a telephoto lens, you're buying it because you want to zoom in further on small or faraway objects. Basically, you buy telephoto zooms because you want to use the telephoto end. If you find yourself staying mostly at the short end of your telephoto zoom (or at the long end of a wideangle zoom), you've brought the wrong lens for the job...

The OP already has the 18-55 kit lens, which will do a much better job of giving wide coverage than any telephoto zoom.

Your other comparisons, the 55-200 starts at a relatively useful 55. For instance, on a picnic, you can get some useful shots that are not possible with something that starts at 70 or 100.

Can you describe that pizzazz? I don't have the lens, but according to kurtmunger ( ), the 55-200 isn't quite as sharp as the 75-300 at 200mm and bokeh isn't quite as smooth as other Sony lenses in that range.

It does have decent magnification ability (0.29x at min. focus distance), but the kit lens already has decent macro ability (at 0.34x) and the Tamron 75-300 (at 0.5x) does a better job. The 55-200 also lacks the distance scale and metal mount of other lenses.
To me, it seems like the 55-200 lens's biggest advantage is its light weight.

I wish it was wider. I'm considering a super zoom, but I'd hate to see it not have that pizzazz the 55-200 does. Do you know? The Dyxum reviews and forum samples aren't very helpful for that.

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