Originally posted by gatorguy Essentially he's arguing (with backup evidence) that 2.8 on a full-frame lens ends up as something lower than that on a crop sensor since much of the light-gathering ability is wasted, unusable. I'm really waiting for one of our lens experts here to comment. I agree with some of the other posters that on the surface it doesn't sound right, but Northrup is not exactly a newbie either.
For most photographers the biggest attribute of Aperture is not light gathering ability but depth of field.
And I've said a bazillion times, You set the FF camera to F4, the APS-c camera to ƒ2.8 and the same ISO and Shutter speed collect the same amount of light. It's the same old hogwash folks like Tony have been publishing for years. They keep restating it with different takes, because they don't really understand it. Tony is the perfect example of a self proclaimed expert, that doesn't have the technical background to really understand a lot of the stuff he talks about.
You can't compare 2.8 on FF with 2.8 on APS_c because the DoF is different, they are different pictures. It's just a little tricky because most people assume 2.8 produces the same image on all systems. That one litlte difference seems to have turned 95% of the internet into disseminators of incorrect information.
It's a case of those who understand being yelled down by all the ignorant fools who assume they are right, because everyone else and the Tony Northrups of the world don't understand either, so as far as they are concerned the consensus of the internet is on their side and folks who say different are wrong.
That Tony would still be posting this nonsense is completely disappointing.
An FF lens used on APS-c produces twice the size of image circle it needs to, but that is not a disadvantage photographically speaking. The only possible disadvantage would be if the APS-c camera didn't have internal baffles to block the extra light and keep it from reflecting around in the inside of the camera body.
Looking at the inside of my K-3 and my wife's K-5, I see the necessary ballers. These cameras were designed to us FF glass. Something Tony neglects to mention.
Tony makes money from his website, spreading his version of photo reality, none of us get paid for correcting him.That the way of the world. If you can come up with a logical sounding half truth that draws people to your webpage, people will send you money and watch your videos. The truth is so boring (and obvious) , nobody ever thinks they should send you money.
If you benefitted from this explanation send 5 bucks to the room.
I'm partly kidding... we are volunteers here.
But partly not kidding, it cost to keep the site running.