I have had eight or more Tento 20x60 binoculars.
None were really sharp to me although other experienced observers liked them.
The reason is that I had one of the dozen made for Jim Hysom specially by hand and selected for experienced astronomers.
Now, one of two things can happen.
Because the normal Tento 20x60s are not very sharp, the in focus image is so so.
Moving out of focus one can perceive that the depth of field is less than the specially good one, or the DOF is greater because the images are still not very good.
However, even the specially made one is nowhere near as good as the Zeiss 20x60S with the stabilizer off.
In my case, none of the Tento 20x60s is as bad as my two Pentax 20x60s.
Then there is actual observation.
Any hand held 8x binocular is likely to be inferior to an 8x IS binocular that works properly.
If a bird is still, then the maximum detail can be seen as one can use central vision for extended periods.
But if the bird is flying the image is a blur, central vision may not be used, only glimpses of good definition might be seen and the resolution may be half or a third of a still bird.
In this case DOF may be all messed up, as nowhere is the bird sharp.
A good IS binocular that pans well may be far more effective.
So, I think that DOF depends heavily on the actual optical quality of the binocular.
I have looked through hundreds of binoculars and the resolution varies enormously.
In some the stars are bloated even in very well made binoculars.
In others the stars are tiny and sharp.
Both the binocular and ultimately the observer influence DOF, and perceived DOF and measured DOF may be quite different.
As said by some above, this is a difficult subject.
Regards,
B.
None were really sharp to me although other experienced observers liked them.
The reason is that I had one of the dozen made for Jim Hysom specially by hand and selected for experienced astronomers.
Now, one of two things can happen.
Because the normal Tento 20x60s are not very sharp, the in focus image is so so.
Moving out of focus one can perceive that the depth of field is less than the specially good one, or the DOF is greater because the images are still not very good.
However, even the specially made one is nowhere near as good as the Zeiss 20x60S with the stabilizer off.
In my case, none of the Tento 20x60s is as bad as my two Pentax 20x60s.
Then there is actual observation.
Any hand held 8x binocular is likely to be inferior to an 8x IS binocular that works properly.
If a bird is still, then the maximum detail can be seen as one can use central vision for extended periods.
But if the bird is flying the image is a blur, central vision may not be used, only glimpses of good definition might be seen and the resolution may be half or a third of a still bird.
In this case DOF may be all messed up, as nowhere is the bird sharp.
A good IS binocular that pans well may be far more effective.
So, I think that DOF depends heavily on the actual optical quality of the binocular.
I have looked through hundreds of binoculars and the resolution varies enormously.
In some the stars are bloated even in very well made binoculars.
In others the stars are tiny and sharp.
Both the binocular and ultimately the observer influence DOF, and perceived DOF and measured DOF may be quite different.
As said by some above, this is a difficult subject.
Regards,
B.