Diffusion

[Edd]

Hi All,

We had a thread going a while ago where we spoke briefly about "Diffusion" where a small aperture can cause an image to soften instead of sharpening as we normally expect.

I was out yesterday and and decided to try and see this effect. Have a look at the images below, both are crops of the same scene, the first was taken at f22 and looks sharper and the second taken at f40 and looks blurred/soft. Both images were taken from a tripod with cable release and mirror locked up.

F22 Image




F40 Image



Do you think this is "Diffusion" ????

Thanks

Ed

[gldiana]

Hi Ed,
not sure what that is but actually the image will be sharper around f/5.6 - f/11 depending on the lens. After those value images soften up again. That's why usually calendar companies usually never except photos shot at more than f/18.

[bob_r]

Ed and I were sending PMs to each other about this test and I suggested a different test. I'm not sure if Ed had a chance to try it, but I did.
I took my Canon 30D and a Canon 200L f/2.8 (probably my sharpest lens) and put it on a tripod and used a remote shutter release.
I took shots with the ISO set to 100 at every full F stop from f/2.8 to f/32 (this lens only goes to f/32).
I'm not going to post all the shots, but here are 3 to show you some results.
These shots are all 100% crops and resized to allow easier "pixel peeping".
This just proves that diffraction does exist as the aperture closes to the smallest settings.

[gldiana]

Bob,
what setting are you using other than the f/stop? I'm actually really surprise at how soft that image looks at f/8 with that lens.

[bob_r]

Luca,

These are 100% crops and then the images were resized - both steps reduced the I.Q.
No processing was done to the images and all the originals at the normal size looked much better than these.
I blew these up just to allow easier comparisons. My copy of the 200L is probably my sharpest lens.

The exif data was not deleted from the images if you want to see it.

Bob R

Here's a shot taken with the 200L wide open (f/2. just to show how sharp it is.

[gldiana]

was it RAW or JPG ?

[bob_r]

It was a jpg.

[gldiana]

Not sure why then. Was the camera on a tripod? Remote Release? and mean no offense but I don't find the Gorilla shot particularly sharp either.

[bob_r]

Bot sure why then. Was the camera on a tripod? Remote Release? and mean no offense but I don't find the Gorilla shot particularly sharp either.

I assume you didn't read my previous post and I'm not sure what any of this has to do with the topic.

[gldiana]

I assume you didn't read my previous post and I'm not sure what any of this has to do with the topic.

I sure did, just forgot about the tripod/shutter release part. You said: just to show how sharp it is.
To which I replied that I didn't find it particularly sharp. Sorry but if my post has nothing to do with the topic then I'm not understanding why the gorilla photo does. There are a lot of factors that influence the softness/sharpness of a photo, not just Diffusion. At this point I don't understand why the gorilla photo is so soft with that lens at f/8.

[Edd]

Thanks Guys for your input.

Bob, unfortunately to date I haven't been able to conduct the trial you recommended but hope to try it out this weekend.
Thanks for taking the time to do this and demonstrate "Duffusion" to me/us.

I was just curious to learn what "Diffusion" may look like so that I could try to find the sharpest point on my lenses. With the mast images posted above I did take one at f11 which looked identical to the f40 image. It was just a quick experiment whilst I was out.

Cheers

Ed

[bob_r]

I assume you didn't read my previous post and I'm not sure what any of this has to do with the topic.

I sure did, just forgot about the tripod/shutter release part. You said: just to show how sharp it is.
To which I replied that I didn't find it particularly sharp. Sorry but if my post has nothing to do with the topic then I'm not understanding why the gorilla photo does. There are a lot of factors that influence the softness/sharpness of a photo, not just Diffusion. At this point I don't understand why the gorilla photo is so soft with that lens at f/8.

The orangutan photo was shot at f/2.8.

[Edd]

Okay so would I be correct in saying that if I make the size the the aperture smaller then I increase Depth Of Field, but the image becomes less sharp ?????.

Ed