Focal Length vs Sharpness Photo Gallery by Jacky Lee at pbase.com

Focal Length vs Sharpness

In my camera test for some of the top compact film cameras,

https://pbase.com/middlehill/contax_t3_vs_contax_g2g35_vs_leica_minilux_vs_minolta_tc1_test_1
https://pbase.com/middlehill/contax_t3_vs_contax_g2g35_vs_leica_minilux_vs_minolta_tc1_test_2

I receive some comments about the fairness of the test. What is suggested is that the longer the focal length, the better the sharpness. From this assumption, Minilux MUST be the winner in the tests because it has the longest focal length (40mm) when it is compared to Contax T3 (35mm) and Minolta TC-1 (28mm).

I do agree with this assumption to a certain degree, but is it REALLY true that a camera with a longer focal length must have a sharper image than that with a shorter focal length? The below test was therefore carried out aiming to find the relationship.

All the below pictures were taken with Canon EOS 5D. One zoom lens and two primes lens were used. All pictures were captured in RAW. Only resizing and levelling was applied to the images.

Let's see the results.

24mm	24mm cropped	35mm	35mm cropped
50mm	50mm cropped	70mm	70mm cropped
100mm	100mm cropped	135mm	135mm cropped
50/1.4	50/1.4 cropped	200/2.8L II	200/2.8L II cropped
Tamron zoom lens comparison	Canon primes lens comparison

comment |

Jacky Lee		06-Mar-2009 17:32
Wenqing, Yes, I do agree that it is not an absolute fair to compare pictures taken from 28mm and that from 40mm if the object distance is kept unchanged. But what I would like to point out is whether the increase in focal length (i.e., in your case, from 70mm to 200mm) contributes a large amount in the increase in sharpness in pixel term. From your test, 200mm image is "sharper" than 70mm image, right? But by how much %? Let me assume it to be an 20% increase in sharpness. However, when you compare my images taken by TC-1 and Minilux, by how much % of increase in sharpness you can notice between the two shots? I believe that it must be greater than 20%. Bear in mind the following figures: 28mm = 75 degree 40mm = 57 degree 70mm = 34 degree 200mm = 12 degree A 40mm image has to be reduced to 30% linearly in order to have the same image size of 28mm; while a 200mm image has to be reduced to 66% linearly in order to have the same image size of 70mm. This means that the increase in sharpness from 70mm to 200mm should be double that from 28mm to 40mm. If that's true, image taken by Minilux should not be so sharper than TC-1 if we compare it with the 70-200 Nikon lens shots. My conclusion is that there must be another factor contributing to the increase in sharpness, which should be the different optical design of the two cameras. I do agree that the test would become more "fair" if we step back the Minilux further in order to have the same image contents as TC-1. But my test should also show a certain degree of logical comparison. Thanks for your comment again.

Guest		05-Mar-2009 23:55
The link ishttp://www.pbase.com/wqdeng/lens_test

Guest		05-Mar-2009 23:53
Jacky, I did a test also with Nikon D200 with 70-200mm/2.8 VR lens. Mount on tripod, VR OFF, MLU, AF on center and remote control. All I changed is changing the zoom from 70mm to 200mm, resizing 200mm image to about 35% to compare. This Nikon lens has better MTF and resolution at 70mm than 200mm. But you can still tell the difference than rezised 200mm is better than 70mm. Here is the link.http://www.pbase.com/wqdeng/lens_test. I include the full size images also. I didn't say a longer focal length must have a sharper image than that with a shorter focal length. If the focal length difference is not much, better lens with shorter focal length might outperform the so so lens with longer one when doing resize comparison. But I don't think 50mm will outperform 200mm. I noticed the DOF of 200mm image is much samller than 50mm. Can you do the test with 50mm and 200mm against some test chart without angle like mine, and post full size images also? Finally I still said it's unfair to test different focal length lens by taking pictures at same spot and resize it. The fair game should be stepping back with longer focal length lens and take picture by keeping object is the same size in frame.

click on thumbnails for full image

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