Re: Faster Glass ...or Image Stabilizer?
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Faster, more accurate Auto Focus.
Another major benefit with using brighter lenses with larger apertures is that the camera's sensor is presented with far more light. This results in faster and more accurate Auto Focus.
How fast AF is depends on more factors than only the aperture. Even with all the light in the world the EF-m 32mm f/1.4 stm isn't focusing fast. Een in low light the Canon EF 35mm f/2.0 IS USM is focusing faster than the ef-m 32mm stm. Furthermore: This lens, and also my sigma 18-35mm f/1.8 is focusing slightly more accurate in low light situations.
In fact the focusing is so slow i returned the lens. And the slight difference in focusing accuracy was especially disappointing. It is not a bad focusing lens, not at all, but when pixel peeping you will find out the other ones are better.
Even with the Aperture set to a narrower size, the sensor still has the benefit of more light when the exposure takes place. The same applies with using darkened filters like Circular Polarizers and Neutral Density filters. It's one of those things that gets overlooked quite often. And it's one of the most compelling reasons to be using fast lenses.
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32mm - accurate AF through glass in a very dark museum. Tack Sharp @ 1/80 sec with ISO 100. Taken at the Sydney Powerhouse Museum... so dark that I can't even use a PowerShot camera in this room.
This picuture would have benefitted more from a stabilizer than a larger aperture as it needs more depth of field. This a an example the EF 35mm f/2.0 IS USM would have been able to give a better result.
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If your facts are different we could save the peace just by calling it copy to copy variation.