Lens question, please educate me

[ahmads]

ok, so i have been exploring the concept of exposure and have a question. Lets say I have two different quality lenses. If set to the same focal length and same aprature, will the both achieve the correct exposure at the same shutter speed. My guess is no. So what I am getting at is, Is it possible for a really good quality lens with max aprature of 4 to be just as fas as a poor quality lens with max aparature of 2.8.

[Dante King]

ok, so i have been exploring the concept of exposure and have a question. Lets say I have two different quality lenses. If set to the same focal length and same aprature, will the both achieve the correct exposure at the same shutter speed. My guess is no.

Sure they will. Exposure should be the same. IQ might be different: Sharpness might be different. Color and contrast might be different. Unless there is a mechanical problem, the exposure should be the same.

So what I am getting at is, Is it possible for a really good quality lens with max aprature of 4 to be just as fas as a poor quality lens with max aparature of 2.8.

No speed is relative to max aperture. A f/4 $1000 lens will NOT be as fast as a $200 2.8. In fact it will be slower by a stop.

[ahmads]

Doesn't the quality of the glass matter. One type of glass can potentially let more light through and thus be able to expose the same at a faster shutter speed?

[The Zman Abides]

No, the aperture is going to be the biggest factor in speed, like Dante King said.

[tsaraleksi]

A really really bad lens might have problems that block light, but that would only be the case in very rare instances.

[lostdoggy]

Exposure Value is a standard. If you take an EV with a photometer it will not ask what lens you'll be using just what ISO it will be set at and it'll gve you the Tv and Av values.

[dontblink]

Different lenses may expose differently at the same aperture, but I've never heard of any being off by a full stop. Usually 1/3 stop or less. And its not really an indication of lens quality, for example the 85 f/1.2 and the 85 f/1.8 both set to f/2.2 and 1/125 will likely expose slightly different images in the real world, but not because one is crappy just because no 2 things are ever identical.

[mxwphoto]

But on the other hand, the color reproduction of surperior glass will make it seem as if the cheaper lens really did do a bad exposure job! :)

[jra]

Just to add another voice to the choir....Exposure is exposure, doesn't matter if you're using an expensive lens or a cheap lens.