The point I was trying to make sure the images are sharper at low f stop
They are less "ill defined" then.
Let´s have a closer look on the term "ill defined".
"Ill defined" basically says . . . . : nothing at all
. I don´t know where you read this term regarding photography - it´s non-specific and isn´t related to sharpness only.
"Sharpness" needs to be understood! To understand "sharpness" you need to understand "circle of confusion" and "airy disks" - and
some other things.
That´s why i suggested to read carefully the links i postet. The images you postet clearly show that the issue is a wrong focusing.
Set the focus wrong results in a faulty set DOF. To get the background AND the foreground sharp you would have needed to not set the focus on the flowerpot but a calculated distance some meters behind it. In that case you would have achieved the optimal DOF.
You simply misunderstand DOF here! No problem: most people do
but.. When attempting to stitch a sequence of fisheye images, a compromise has to be made against sharpness and fewer issues with stitching using a higher f stop. Since the fisheye image have about a 30% overlap, its far better to have APG detect well defined pixels rather than ill-defind pixels captured using a low f stop..
In photography it´s ALWAYS preferable to have "well defined" pixels - which usually simply means "sharpness" . . . .
I would expect that images captured using a 16mm FX full frame would work better with a slightly lower f stop than using a DX 10.5 fisheye..
Why would you expect that?
Therefore I would suggest that f8 would be equal to about f11 using a 10.5..
Why would that be?
I do not have a 16mm to test this so I am only guessing... If I were to capture a pano using f5.6 with a 10.5mm fisheye, using my D800, I would have stitching issues..
Most unlikely due to "ill defined pixels" by aperture, sorry . .
However, if I used f11 to f16, depending on the situation, I would do better with my stitching.... Also, if I used f5.6 I would notice some blurred patches in my pano.. Sometimes very noticeable but sometimes not so much...
If you have "blurred patches" in your pano they definitely do not result from stopping down to 5,6 or 8.
I know the 10.5mm Nikon FE very well - used it for about a year when i started shooting panos about 7 years ago.
Used it here: http://360impressions.de/Tower/
It shows it´s optimal performance @f5,6/f8. It´s performace weakens from f11 on. That doesn´t mean it becomes really blurry - but the resolution of details becomes softer. Which is the opposite to "well defined pixels".
The same is with the 16mm Nikon FE and the Canon 15mm FE: stopping them down to more than f8/11 softens the detail-resolution.
Diffraction is a major theme with lenses - it´s related to ALL kind of lenses. It results from the light ray´s dispersion which occurs on the rims of the aperture´s blades the smaller the opening becomes.
Fisheyes have the advantage of no need to being stopped down more than two or three steps - which usually means 5,6 or 8 on a 2,8 lens - because due to their kind of projection they´re DOF is very big stopped down two steps already.
Now what does that mean in terms of stitching?
A) set your focus carefully
- that´s most important. Learn about "hyperfocal distance" and how to calculate it.
B) choose an appropriate
aperture. Diffraction often is over-estimated. It softens the performance of a lens - ANY lens.
Softening the performance of a lens means less definition of details. That influences the "clearness" of pixels in a way it makes it harder for the stitcher to identify details in images and finding the correct place to set a CP.
A real problem rises with long tele-lenses. Here you usually need to use a small apetrue for achieving an appropriate DOF.
The point is: APPROPRIATE.
Appropriate means to set the focus accordingly to the situation and regarding your DOF.
Hyperfocal calculation also here helps a lot.
A camera like the D800 - and much more extremely a digital MF camera - due to high resolution is much more critical in the way it is handled. It reveals any kind of wrong handling without mercy.
Conclusion: anyone who uses a high-resolution camera needs to get used to what "resolution" and "sharpness" mean in detail
So i again sugest to read the links i postet:http://www.cambridgeincolour.com/tutori