FF Sharper than crop?

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#2
Robboesan said:
Are there any physical explanations for this phenomenon?
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The main reason - next to various others that also may have some role - the "crop" sensor only uses the center part of the lens. If the edges of the lens are crappy (old/cheap lenses or some ultra-wide) that can be an advantage, but usually it isn't because the 20mp of a 70d sensor are illuminated through less glass than the 20mp of a 6d. If this central lens part is not sharp "enough" this results in the effect you observed... but often it's only visible in test charts, not in real life, and then only if shot wide open and not stopped down.
 
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#3
Marsu42 said:
Robboesan said:
Are there any physical explanations for this phenomenon?
Click to expand...

The main reason - next to various others that also may have some role - the "crop" sensor only uses the center part of the lens. If the edges of the lens are crappy (old/cheap lenses or some ultra-wide) that can be an advantage, but usually it isn't because the 20mp of a 70d sensor are illuminated through less glass than the 20mp of a 6d. If this central lens part is not sharp "enough" this results in the effect you observed... but often it's only visible in test charts, not in real life, and then only if shot wide open and not stopped down.
Click to expand...
and then there is the strength of the AA filter in your particular camera......
 
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#5
The formal answer is that with any lens detail contrast drops as resolution increases. This relationship is illustrated by the lens MTF curve. A lens has more contrast at 10 lpmm then at 20 lpmm. When you frame a scene onto a smaller sensor, the details occur at a higher lpmm frequency and therefore have less contrast.

However, at low to mid ISO it's a meaningless difference because the contrast can easily be restored in post processing, whether in a tool like Photoshop or in camera using the sharpness setting. Detail contrast is not an unlimited good, and at ISO 800 and below it's trivial to make an APS-C file as sharp as an optimally processed FF file. At high ISO FF has a true sharpness advantage because when you apply extra sharpening to the ASP-C file you emphasize noise that's not in the FF file.
 
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#6
neuroanatomist said:
Robboesan said:
Are there any physical explanations for this phenomenon?
Click to expand...

Enlargement. When comparing output of equivalent dimensions, the image from the smaller sensor needs to be enlarged more, and that results in a relatively softer image.
Click to expand...

In the darkroom optical enlargement impacts sharpness again. But this isn't an issue with digital capture. The sharpness difference observed out of camera between APS-C and FF exists at the sensor at the moment of capture and is visible at 100% / pixel view.

Sometimes interpolation to screen resolutions impacts sharpness on its own. But so long as you have sufficient image resolution for the desired print size, digital interpolation or enlargement for printing rarely if ever impacts sharpness today.
 
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#7
Robboesan said:
Hey guys!
So I noticed on the digital-picture website iq comparison tool that FF seemed always sharper than a crop sensor.
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=486&Camera=736&Sample=0&FLI=0&API=0&LensComp=486&CameraComp=0&FLIComp=0&APIComp=0
Are there any physical explanations for this phenomenon?
I am new to this so....
Click to expand...

I believe he also frames the shot the same so you are shooting from a greater distance with a crop camera.
 
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#8
The resolution of the lens used in the Crop sensor needed to have 1.5 time more resolution than the one used in the FF to give us the same sharpness. We are not even talking about diffraction limiting yet.
 
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#12
The main reason full frame is sharper is because its projecting a larger image circle, and there is always going to more detail possible in a physically larger area than there will be in a physically smaller area. Plus the full frame images are sharper because full frame pixels are much larger. Bigger pixels always give better pixel level detail.

Also keep in mind lenses that are optimized to project a full frame image circle are spreading the available detail out more, and using a full frame lens on crop frame means you are discarding a lot of what the lens is capturing, since you are only using the center part of whats being projected. This has the effect of making your full frame lenses longer on crop compared to full frame, because you have to step back in order to shrink the projected image so its fits one crop sensor.

Lenses optimized for crop frame focus the available detail captured by the lens into a smaller area, so there is potential for greater resolution within that area compared to spreading the image out more like full frame lenses do. Take a look at the 22mm lens for EOS M if you want to see a very sharp lens optimized for crop sensor. Thats one of the sharpest crop frame lenses you will find in the digital picture test charts.
 
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#14
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#15
J.R. said:
CropFactor said:
Read this :
http://www.dxomark.com/Reviews/Looking-for-new-photo-gear-DxOMark-s-Perceptual-Megapixel-can-help-you

For the pixel peepers, it's rather worrying the amount of resolution lost in cropped systems.

There is very little to gain by sticking an L lens on a crop body.

(Watch me get mauled to death for this...)
Click to expand...

I wonder why you say that. As far as I have noticed, FF + average lenses = crop with better lenses.
Click to expand...

That is possible yes. But why would you cripple your FF with an average lens?

What I'm saying is the difference is resolution (sharpness) between 'L' and 'non-L' on a crop body isn't that significant.

For example you won't gain 8MP in overall resolution by jumping from a 12MP 450D to a 20MP 70D (crop of course). You might gain 2-4mp. There are losses in any given system. More so for crop.

Even if a crop body makes use of the so called sweet spot of a lens, you just won't get the resolution you expect you would from a high MP crop body :o

If you want real gain in sharpness, go with FF + L ;)
 
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#18
Can we possibly say this :

Lets assume a 20MP crop canon here....

20/1.6 = 12.5

12.5 being the maximum MP you could possibly hope to get.

Add then loss from the AA filter, lens quality and any other attached elements.

Lets say you can realistically get 8 - 11MP from a 20MP crop.

Does this sound far fetched or not? ???
 
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#19
Marsu42 said:
CropFactor said:
There is very little to gain by sticking an L lens on a crop body.
Click to expand...

So what ef-s tele lenses do you use (hint: there are none), or what non-L tele lenses do you recommend at a lower price than for example the 70-300L with the same sturdiness and weather sealing?
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We are not debating functionality but rather sharpness ;)

I was referring to the difference in sharpness (detail) for "CR + Non L" vs "CR + L".

Compare "FF + L" vs "CR + L" even if both bodies are 20MP, the FF will win when it comes to detail.
 
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#20
Marsu42 said:
CropFactor said:
There is very little to gain by sticking an L lens on a crop body.
Click to expand...

So what ef-s tele lenses do you use (hint: there are none), or what non-L tele lenses do you recommend at a lower price than for example the 70-300L with the same sturdiness and weather sealing?
Click to expand...

Actually, there is one pretty decent EF-S tele lens EF-S 55-250mm f/4-5.6 IS STM lens.
 
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