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

Fat Dragon wrote:

Wally626 wrote:

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.

Is this claim based on your own observations or is it verifiable by some means?

I think I read that Sony was playing with the ISO setting to get the camera to match other types of light meters when the A77 came out. I do not recall the exact article and it is possible the author was also speculating. If the camera is going to match other cameras and external light meters that is really the only way to do it. In any camera the ISO setting is nothing special, it is just a value used to adjust the sensor output so that under specific circumstances the image will be properly exposed. Sony just makes the final adjustments on the ISO setting with the mirror in place. Canon and Nikon of course do the same thing, the amount of light hitting their separate light sensor arrays is also adjusted to represent real life values. In that case the light is also split by mirrors between the PDF focus arrays and the light meter arrays. It is of little importance how they do it as long as you can use an external light meter to set your exposures. I have never actually check to see if the A77 really matches a incident meter, but perhaps I will this evening.

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