# Real lens sharpness



## chrysoberyl (Feb 10, 2016)

When testing FF lenses, LensTip consistently shows the APS-C edges to be sharper than the FF edges. TDP’s ISO 12233 Test Charts show the opposite. Please explain this seeming inconsistency. Thanks!


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## takesome1 (Feb 10, 2016)

TDP's ISO 12233 tests are normalized for the exact same field of view. The crop body will be 1.6x farther away than the FF camera. Because of this the crop body shots will actually have less pixels covering the entire ISO target than the FF body. It is the camera's resolution not the lens you are seeing.

I didn't see side by side comparisons on LensTip, only charts depicting resolution.
You would need to find out how they arrive at the data for their charts.


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## Mt Spokane Photography (Feb 10, 2016)

chrysoberyl said:


> When testing FF lenses, LensTip consistently shows the APS-C edges to be sharper than the FF edges. TDP’s ISO 12233 Test Charts show the opposite. Please explain this seeming inconsistency. Thanks!



Testing methods and cameras used will make a comparison invalid.

Lens Tip still uses a 20D or sometimes a 40D to test lenses. The results are only valid if you use one of those. Don't bother trying to compare results with those from other high mp bodies, they just do not compare.


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## AlanF (Feb 10, 2016)

takesome1 said:


> TDP's ISO 12233 tests are normalized for the exact same field of view. The crop body will be 1.6x farther away than the FF camera. Because of this the crop body shots will actually have less pixels covering the entire ISO target than the FF body. It is the camera's resolution not the lens you are seeing.
> 
> I didn't see side by side comparisons on LensTip, only charts depicting resolution.
> You would need to find out how they arrive at the data for their charts.


You are quite correct. TDP put Crop at a disadvantage by having it further away. Lenstip just marks off where the edges are at the same distance away.


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## neuroanatomist (Feb 10, 2016)

AlanF said:


> TDP put Crop at a disadvantage by having it further away.



We're talking small distances, e.g with a 50mm lens, 1.8 m for FF and 2.9 m for APS-C. With long lenses, he uses progressively smaller charts – they are Applied Imaging QA-77 charts based on the ISO 12233 standard, and they come in four sizes (of which I have three). 

It's not the distance, per se. Rather, it's the fact that framing is the same (which is how ISO 12233 charts are designed to be used), and the chart crops are displayed at the same final output dimensions. That means the images from the APS-C sensors must be subjected to a greater enlargement, and _that's_ why they appear less sharp than FF images with the same lens.


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## takesome1 (Feb 11, 2016)

neuroanatomist said:


> AlanF said:
> 
> 
> > TDP put Crop at a disadvantage by having it further away.
> ...



If i understand you correctly you are saying the shots are resized. I looked at a few charts at TDP earlier and noticed the 5Ds R file was not downsized. So really the ISO shots on TDP are great for comparing lenses, but for comparing cameras you really need to know the specifics of the test if several different charts are used when testing crop bodies.


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## neuroanatomist (Feb 11, 2016)

takesome1 said:


> ...but for comparing cameras you really need to know the specifics of the test if several different charts are used when testing crop bodies.



First, the charts are functionally identical, that's why it's an ISO _standard_. There are aspect ratio-specific framing guides, and feature resolutions are matched to the framing (i.e., you fill the frame with the chart, and the same camera+lens will yield the same resolution measurement/estimate with different size charts at the frame-filling distance). Second, I have no doubt that while different charts may be used for different lenses (you need a big chart for a 16mm lens, a small chart for a 600mm lens), for a given lens the same chart would be used with all bodies. So, it's perfectly valid to compare bodies as long as you're comparing them with the same lens. The smaller sensor looks softer because it needs more enlargement. 

Ever printed film? An image from a 4x5" negative vs. an equivalent image on a 35mm negative, put them in an enlarger and print both at 8x10". The MF negative needs much less enlargement, and thus will yield a sharper image.


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## takesome1 (Feb 11, 2016)

neuroanatomist said:


> takesome1 said:
> 
> 
> > ...but for comparing cameras you really need to know the specifics of the test if several different charts are used when testing crop bodies.
> ...



A fair comparison if you understand you are comparing an equally framed identical subject.



neuroanatomist said:


> *and the chart crops are displayed at the same final output dimensions. *



It appears that the 5Ds R is not resized to the same final output dimension in this comparison;http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=458&Camera=963&FLI=0&API=0&LensComp=458&Sample=0&SampleComp=0&CameraComp=979&FLIComp=0&APIComp=0


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## takesome1 (Feb 11, 2016)

Since were talking about TDP's test, this is TDP's explanation of the tests;
http://www.the-digital-picture.com/Help/ISO-12233.aspx


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## neuroanatomist (Feb 11, 2016)

takesome1 said:


> neuroanatomist said:
> 
> 
> > *and the chart crops are displayed at the same final output dimensions. *
> ...



In all the other FF vs. APS-C comparisons you can make, the APS-C sensor has much smaller pixels and that somewhat compensates for the the enlargement. When comparing the 5DsR to the 7DII, the pixels are approximately the same size, and thus there are many more of them covering an identical physical dimension of the chart. That's why the 5DsR crops look so much larger.


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## 9VIII (Feb 11, 2016)

chrysoberyl said:


> When testing FF lenses, LensTip consistently shows the APS-C edges to be sharper than the FF edges. TDP’s ISO 12233 Test Charts show the opposite. Please explain this seeming inconsistency. Thanks!



Are you talking about the Lenstip lp/mm graphs?
In a graph showing resolution across the width of a full frame image, sharpness falls off from center to edge, just as you would expect.
If they were to show the lp/mm numbers of a high resolution crop sensor using the same lens in the same graph, the numbers from the crop sensor would be much higher, because it has more resolution.

What a graph doesn't tell you is that the crop sensor is going to enlarge all the flaws of a lens every bit as much as any desirable details, for example, Chromatic Aberrations will always cover more of the image frame with a smaller sensor of equal or higher pixel density. Fuzzy edges are going to be twice as fuzzy when viewed at native resolution if you have twice as much pixel density.

The larger your sensor and the lower your resolution, the less demands are placed on the lens.
Thus all the hubbub about high resolution lenses lately, given how many people are using 24MP crop sensors (higher pixel density than the 5Ds)


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