a57 v d5100 for first DSLR

Started Apr 6, 2013 | Questions thread
Wally626 Senior Member • Posts: 2,312
Re: a57 v d5100 for first DSLR

123Mike wrote:

If you take away half a stop of light would you expect that the shutter speed to be the same (aperture considered fixed)?

If you religiously obsessively focus on "light taking away, therefore bad", then you will never be happy with an SLT. End of day, the sensor is very sensitive and it is a very good sensor, and it at least partially makes up for it. To me, the loss is not noticeable compared to other cameras, and in fact, it does even better than most of the Canons in its class, and they don't "take away" any light. To me, the evidence of end results is what counts. Plus all the amazing features I'd never want to do without, like full performance non-compromised live view for everything. I hate squinting through a VF, especially with my glasses. I *never* look through the VF, ever.

If it matters to you or not that's another question.

Sony says that it is ISO3200 and uses ISO4800 to achieve the same exposure (shutter speed and aperture). That's why you see this.

First time I heard a claim that Sony is lying about ISO. So you are claiming that ISO 3200 on the dial is more than twice as sensitive (and therefore more grainy) as ISO 1600? Do you have any credible evidence for this? Not saying you're wrong, but I'd like to see a test that proves that.

Sony in the metering system takes into account the 1/2 stop light loss from the mirror. The only way to do this is to adjust the ISO values. So if you have a scene that would require a 1/100 second exposure at f/8 and ISO 800 on the Nikon inputing the same exposure values will also result in a good image on the Sony. Sony cannot play with the shutter speed or aperture and stay consistent with the world of other cameras so they change the ISO values. The adjustment is at most 1/2 stop so if the Nikon is using ISO 1600 the Sony would be using a real-life ISO 2263. This is why the Sports (ISO) rating is about 1/2 stop lower. In practice 1/2 stop usually has little effect, but the Nikon would come out a little ahead in single frame low light shooting.

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