FF Lenses on the A77?

Started Apr 27, 2013 | Discussions thread
Allan Olesen
Senior MemberPosts: 2,555
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Re: FF Lenses on the A77?
In reply to Graham Best, May 17, 2013

Graham Best wrote:

Allan Olesen wrote:

Graham Best wrote:

Allan Olesen wrote:

Graham Best wrote:

APS crop factor doesn't increase the lens magnification.

It increases the magnification of lens flaws in the final photo.

I always think relative to final photos. That is the only "common ground of comparison" which tells what will happen in practical photography when comparing different camera/lens combinations.

How so? If one looks though a window 2 x 3, then looks though an adjoining window 1 x 2, is one able to discern greater detail in the view though the smaller window?

Now you are assuming that we use the same lens at the same distance on two cameras with different sensor size.

That would result in very different photos because of the different framing, so these would not be comparable situations.

Instead think of tho FF lenses with equal resolving ability in lp/mm. One is 75 mm focal length, and the other is 50 mm. Take two photos from the same distance with 75 mm on FF camera and 50 mm on APS-C camera. Both cameras have the same number of MP and the same AA-filtering relative to pixel width. Enlarge both photos to the same output size.

Which one of these two photos will contain most detail?

I'm assuming exactly what you stated, and what I originally responded to in this thread. To refresh your memory, I'll paste your statement.

"That is twisting the truth a bit. You avoid the less sharp outer parts of the image circle, but all unsharpness in the image is blown up 1.52x more than if you had used the same lens on FF."

Nothing is "blown up". My point was there's no magnification factor involved when moving from full frame sensors to APS-C sensors, only a field of view crop.

You don't need to refresh my memory. I know exactly what I wrote, and it is still correct.

All unsharpness is blown up 1,52 x more, because you will have to blow up an APS-C photo 1,52 x more to get the same final output size.

If you print a FF photo at 24x36 cm, one mm on the sensor corresponds to 10 mm in the print.

If you print an APS-C photo at 24x36 cm, one mm on the sensor corresponds to 15.2 mm in the print.

So in the latter case, a lens flaw with a given size on the sensor is magnified 1.52 x more.

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