Sharper at 6 MP

[Pistnbroke]

On a couple of occasions after photographing items on "small"jpeg  for e bay on a D7100 I forgot to change back to large . Few days later photographed some birds and found the images were sharper than at large.
Testing with a bar code on a box  at large medium and small showed  the small to be sharper with 100% crop...  Now why ?  is it the monitor response or what?
I was using a 300mm f4  .
I also tried this with an 18 mm and the results in small where much softer at small than at large...100% crop

Confused but willing to be educated...no I dont need an eye test !!!

[Bjørn Rørslett]

Sharpness is a perceived entity. Thus magnification of detail, the subject pattern(s),  contrast of light, and the properties of the lens all factor into the final 'deception' delivered by our sensory system.

Short focal lenses magnify less so are at a handicap when sensor resolving power is limited. One need *sufficient* resolution of the imaging chain to make the finer details stand out for the picture of a very complex scene be rendered satisfactorily. If you limit yourself to make pictures of large structures without much detail, even a very short lens will do just fine on 6MPix.

The lenses act as low-pass filters of the optical system. With a longer lens, magnification of detail is greater and thus the chance of details 'getting through' is higher.

[Pistnbroke]

yes I follow that but why is it rendered "worse " at large and medium ?   If its good at small it should be at least as good at large.......yes /no ?

[Ilkka Nissilä]

Each pixel in a large jpg is a smaller part of the whole image. As we go take a look at the image at finer and finer scaled, the contrast of the finer details is reduced. This is due to lens MTF decreasing as a function of increasing spatial frequency. Looking at finer details also reveals slight errors in focus and possible camera shake and movement blur. If you resample the large jpg into the size of the small jpg, it should be comparable (depending on resizing and sharpening methods).

[Bjørn Rørslett]

yes I follow that but why is it rendered "worse " at large and medium ?   If its good at small it should be at least as good at large.......yes /no ?

No, this conclusion cannot be upheld. Good quality at small recorded size does not imply the perceived sharpness will be kept when the capture is done at higher resolving power.

The wider the window the more flies enter the room. To use a metaphor.

[Pistnbroke]

You are wonderfull people and I am the idiot .....because I noticed this in isolated incedents it was not until I did a test at Large then small on the same test object that I realized that in small I needed 200% crop re at large 100% crop to fill my screen .....Once I did this the small was worse ......well we live and learn .......

Thanks every one ...I am not always this stupid !!!