a77 resolution

Started Nov 19, 2012 | Discussions thread
philbot Contributing Member • Posts: 846
Re: A77 picture of a ruler, 50 mm lens, 6 meter distance

sagarmatha wrote:

So in my case with Sony 16-105, Tamron 90 and Sony 70-300G it is the lenses that sets the resolution, not the camera?

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Simplifying things a little,

a Camera's resolving ability is usually measured in LP/PH (Line Pairs per picture height), for the A77 DPReview state this is 3400LP/PH (out of a possible theoretical 4000) (A 16MP APS-C seems to be around 2400 LP/PH out of a possible theoretical of around 3200)..

So that is what the camera can resolve, and we know the A77 is very good for it's MP rating..

Of course lens performance is far more of a problem, as their 'resolution' is very variable, often depending on focal length (in the case of Zooms) and Aperature (Can be lower resolution wide open, and also diffraction can limit resolution when venturing north of f/8)..

I am no expert, but have just done a little reading around, and this may be a rough guide..

(Using this page as a guide, http://image-engineering.de/index.php?option=com_content&view=article&id=483 it lists conversion factors for various resolution measures..)

MTF-50 ( a normal lens sharpness value) is in LW/PH (Line width per picture height), and using the above linked conversions you need to multiuply this by 2 to get LP/PH

So 3400LP/PH = 1700 LW/PH, so you need to look at where your lens produces more then 1700LW/PH (MTF-50) in order to know it's not a limiting factor..

For reference, looking at the new Nikon 18-300 (I know it's a nikon, it's just an example!) according to DPReview's tests, http://www.dpreview.com/lensreviews/nikon-af-s-18-300mm-3p5-5p6-vr/3 you can see that it can only achieve > 1700LW/PH in a very limited amount of the frame, focal length and aperture..

And that's the thing, it's more then feasible you lenses are only going to not be the limiting factor if you get them in their sweetspots..

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