Greater depth of field wanted (1 Viewer)

ronh · May 24, 2009

Henry,
Thank you. Your point about the eye's workings sheds valuable light on this issue.

As to the magnification effect, I would say that due to the more detailed view at higher magnification, it is easier to tell if the image is in focus or not, so focus becomes more critical. Different point of view, same conclusion.
Ron the H

denco@comcast.n · May 24, 2009

ronh said:
Henry,
Thank you. Your point about the eye's workings sheds valuable light on this issue.

As to the magnification effect, I would say that due to the more detailed view at higher magnification, it is easier to tell if the image is in focus or not, so focus becomes more critical. Different point of view, same conclusion.
Ron the H

Good point. I think your explanation is right on and to the point.

Dennis

henry link · May 24, 2009

elkcub said:
Very nicely put, Henry. :t:

Thanks, Ed. Of course I got most of that from you. ;-))

henry link · May 24, 2009

[email protected] said:
Here is a good thread from an Astronomy forum on field curvature and how it relates to DOf. Some good reading:

http://www.cloudynights.com/ubbthre...3155/page/0/view/collapsed/sb/5/o/all/fpart/1

Dennis

I also read that item when it first appeared. It should be noted that Ed goes to some trouble to make clear that "real" DOF is not the same thing as field curvature. DOF and field curvature are completely different optical characteristics and vary quite independently in different binoculars. The article simply points out a handy focusing trick that results from field curvature, provided you don't mind moving an object around in the field to find the best focus.

I use this method mainly on the occasions when I'm carrying an IF binocular, which I do sometimes when walking on the beach. If a shorebird is too close for the central focus I just move it toward the edge until it's focused well enough to determine whether I want to go to the trouble to change the focus on the eyepieces. I don't think it's a very good substitute for a fast center focuser, but it works well enough in a pinch.

denco@comcast.n · May 24, 2009

henry link said:
I also read that item when it first appeared. It should be noted that Ed goes to some trouble to make clear that "real" DOF is not the same thing as field curvature. DOF and field curvature are completely different optical characteristics and vary quite independently in different binoculars. The article simply points out a handy focusing trick that results from field curvature, provided you don't mind moving an object around in the field to find the best focus.

I use this method mainly on the occasions when I'm carrying an IF binocular, which I do sometimes when walking on the beach. If a shorebird is too close for the central focus I just move it toward the edge until it's focused well enough to determine whether I want to go to the trouble to change the focus on the eyepieces. I don't think it's a very good substitute for a fast center focuser, but it works well enough in a pinch.

Good tip and quite useful at times I would think.

Dennis

Swedpat · May 26, 2009

One of the advantages with low magnification is the great DOF. 6x binoculars are very comfortable in this respect when you use the bin at short and varying distances, compared to 8 and 10x. 5x even better: Bushnell X-wide 5x25 has a tremendous DOF. I could easily go from viewing the horizon to 5 meters distance without needing to re-focus. Actually I suspect (due to the exit-pupil size) that the true magnification is ca 4,5x.

Regards, Patric

keithdrengen · May 29, 2009

Maybe a restricted fov makes depth of focus appear deeper. Cascade Porros 8x42 with 50 Degree view has great dof. Just like most 7x bins have ~50 degree EP´s and pleasant dof. I know very unscientific, but just a thought that came to my mind. Wonder how dof is(appears I know!) in zeiss 7x42 (Field: 150m...).

Steve C · May 29, 2009

How typical this is, I don't know, but I have a Nikon Monarch 8x42, which is on the narrow end of fov @6.3*, also seems to have the shallowest dof of all the 8x binoculars I have. On the other extreme, I have some 9.5* Swift Nighthawk 8x40, which while perhaps not the deepest "apparent dof" are certainly superior to the Monarch in dof.

Kevin Purcell · May 29, 2009

keithdrengen said:
Maybe a restricted fov makes depth of focus appear deeper. Cascade Porros 8x42 with 50 Degree view has great dof. Just like most 7x bins have ~50 degree EP´s and pleasant dof. I know very unscientific, but just a thought that came to my mind. Wonder how dof is(appears I know!) in zeiss 7x42 (Field: 150m...).

The AFOV is just a consequence of an eyepiece design choice. Pick a design and it comes with a decent usable AFOV. Combine that AFOV with magnification and you get the FOV of the bin.

How big an AFOV you can use depends on the EP design (how many lenses for a first order approximation then the particular desing) and how much you are willing to trade off aberrations, astigmatism and field curvature for AFOV.

As others point out the "real" DOF depends only on magnification but I think the perceived DOF (which has little relation to the real DOF) depends on may other properties.

Greater depth of field wanted (1 Viewer)

More options

ronh

Well-known member

[email protected]

Well-known member

henry link

Well-known member

henry link

Well-known member

[email protected]

Well-known member

Swedpat

Well-known member

keithdrengen

Well-known member

Steve C

Well-known member

Kevin Purcell

Well-known member

Similar threads

Users who are viewing this thread