Off-axis sharpness Trinovid 8x32 (1 Viewer)

The consensus seems to be that Leica gets soft away from center. However, although my BN 8x32 is not "sharp to edges" (not that any glass is), it actually performs quite well off-axis. Is there a significant variance from model to model concerning such? I am particularly interested in the relative "sweet spot" sizes of the Trinovid BN 8x32 and the Ultravid BR 7x42.

Thanks, APS

Much of this is discussed on the thread earlier, on the Ultravid HD.

APSmith said:

The consensus seems to be that Leica gets soft away from center. However, although my BN 8x32 is not "sharp to edges" (not that any glass is), it actually performs quite well off-axis. Is there a significant variance from model to model concerning such? I am particularly interested in the relative "sweet spot" sizes of the Trinovid BN 8x32 and the Ultravid BR 7x42.

Thanks, APS

Click to expand...

APS,
The pictures in the attached PDF might help. Top is 8x32BA, bottom pre-HD Ultravid 7x42. Sorry, could not get full FOV.

Best
Ron

EDIT: I may have the whole FOV shown. The specs are 7.7 and 8 degrees.

Ron,
Thanks, a photo like that ought to take a lot of the subjectivity out of it. But there is something that may keep it from being so simple.

We understand that one's focus accomodation influences how much field curvature softens the view at the edge. A camera also has a kind of "focus accomodation", in its depth of field. Do you take these photographs at fast or slow focal ratios, and do you think it matters?
Ron H

ronh said:

Ron,
Thanks, a photo like that ought to take a lot of the subjectivity out of it. But there is something that may keep it from being so simple.

We understand that one's focus accomodation influences how much field curvature softens the view at the edge. A camera also has a kind of "focus accomodation", in its depth of field. Do you take these photographs at fast or slow focal ratios, and do you think it matters?
Ron H

Click to expand...

Hi RonH,

I really don’t think it matters. I may be wrong but will cite a few reasons for the assumption.

The objective portion of the optic converts a flat wavefront to a curved wavefront by virtue of convergence. The eyepiece then converts the curved wavefront back to a flat (hopefully) afocal or collimated image for the eyes or other detector to use. See image.

Concerning the camera, the target is at a fixed distance, infinity, no depth of field. The curvature blur comes from the optics alone. The eyes may have enough accommodation to correct this but the camera will show worst case, so most may see the view better than the strict test results.

As a test to answer this question, see the method in the post http://www.birdforum.net/showpost.php?p=1560531&postcount=26. These checks were done by different methods.

I use a dioptometer to measure on the bench and it has 4.7x to sharpen focus and reduce any accommodation effects. I have very little accommodation anyway, but see the attached explanation from an Optics book. BTW, the D sub c in the equation is the user accommodation.

Best
Ron

Surveyor said:

APS,
The pictures in the attached PDF might help. Top is 8x32BA, bottom pre-HD Ultravid 7x42. Sorry, could not get full FOV.

Best
Ron

EDIT: I may have the whole FOV shown. The specs are 7.7 and 8 degrees.

Click to expand...

Wow! Thank you Surveyor, for such fascinating information. Very, very interesting - not only the comparison at hand, but also the test format. This is useful in comparing the powers, FOV, etc as well, perhaps brightness too. Seems like this could be refined/expanded to study all sorts of parameters, and also standardized for use as reference material.

It would be nice to see something like this for so many glasses, really any glass under consideration, or being discussed. One has to wonder, would the differences be glaringly obvious, or do they all look fairly similar?

That said, I'm still studying the images. It would appear that this particular 7x42 model holds up just a tad better than this particular 8x32 model - but it's really quite close. I need to think about this some more now.

Thanks much, APS