Fast lenses, and High ISO

Started 5 months ago | Discussions thread
67gtonr
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Re: Fast lenses, and High ISO
In reply to EinsteinsGhost, 5 months ago

EinsteinsGhost wrote:

67gtonr wrote:

EinsteinsGhost wrote:

67gtonr wrote:

EinsteinsGhost wrote:

67gtonr wrote:

EinsteinsGhost wrote:

Fast lenses, as they are called allow for more light to hit the sensor and in turn allow for fast(er) shutter speeds. The F number provides a relative measure of how much this ability is.

In this age of ever increasing ISO, are fast lenses needed anymore? The only ability I see the fast lenses provide was actually a disadvantage that happened to become a feature, and that is shallow DoF, allowing for separation of subject from the background.

That said, should they be called Fast Lenses or Shallow Lenses

Now, I took some available light family portraits 750ft below ground at Carlsbad Caverns recently using Sony NEX-6. There isn't much light there (in this case, there was some light from the cafe but still too dark to see in person). I had Minolta 50/1.4 on Speedbooster, which gave me an effective 35mm f/1 lens. I used ISO 3200 and still had only 1/30s for shutter speed (could have improved it a bit with spot metering but some of the ambiance would be lost). The scene brightness value was -5EV. This is an example of when just a superfast lens or high ISO capability worked better when combined.

Would I have loved having Sony a7s instead? You bet! Would have gotten same exposure at ISO 6400 which is impressively clean and composed in that camera.

I am confused by this, I thought when a Speedbooster is used on an APS-C sensored camera it essentially negated the crop factor, so instead of your 50/1.4 shooting as a 75/1.8 it shoots 50/1.4, approximately?

It is not an exact compensation (IIRC, 0.71x, so almost). So, using 50/1.4 via speed booster is like using 35/1 without it (the resulting FOV and DOF will be that of about 50/1.5 on FF).

So the Speedbooster gave you a 50/1.5 not a 35/1, if you had used the same lens and Speedbooster on a full frame camera it would have given you 35/1.

No, the lens via SB works as if it is a 35/1 lens. But, if you put 35mm lens on APS-C, you get (approx) field of view of 50mm lens on FF. The DOF equivalence is f/1.5. However, exposure is determined for f/1.

My last reply was being typed as this was being posted. I was initially reading it that the booster was giving an image w/ a 35mmFOV and a F1 equivalent picture and that is not how I understood Speedboosters to work.

So does the auto exposure meter for the f1 correctly or do you adjust it manually?

Auto works (you can use the camera in any mode).

Thanks, good to know.

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