Henry,
Sorry for the delay in getting back to you. Many thanks for the additional data and observations, I found it very useful. It's a pity you didn't get the stopped down reading but there's plenty in your comments to suggest the HT might have have produced an extraordinarily poor value for a binocular of this status and price.
I'm not particularly familiar with the resolution x D way of expressing resolution performance but I see it's a useful way of making comparisons across different apertures. Like you, I've found an apparent limit using a home printed chart of about 125/D which doesn't sound unreasonable as about midway between the Dawes and Rayleigh values. I've now found 4 binoculars better than 130/D when stopped down to 20mm, but at full aperture they ranged between 160. and 220/D. All seemed equally 'sharp' to me but more about that later. The 189/D for the HT doesn't seem exceptionally good or bad for binoculars, but as you mention eyesight is pretty poor in low light so probably unimportant for hunters and the like. I often choose to relate the resolution to acuity and I'm uncomfortable guessing the eye's pupil diameter as 2.5mm in bright conditions. Your 90” VA gives would give a guestimated discrimination threshold of 90x2.5 or 225/D for bright light but that would considerably worse for low light. The reality might be something different of course.
I'm not sure why you concluded that the HT might have been around 6.2 arcseconds at 22mm. The difference between the FL and the HT in the centre cross photo resolutions look a great deal more than a fraction of an arcsecond, it looks like the equivalent of several steps on the USAF chart to me? That would be consistent with your observations unboosted where the HT reduced apparent acuity to 11.4”. Perhaps not the most accurate method of estimation but that would put the stopped down resolution at almost double your guess and gives a value of 228/D. From my limited stopped down chart testing, 11.4” might be reasonable for a compact model but it's at the bottom end of the usual range for full size for mid range and premium models. The 20/15 user will see a differences in sharpness when compared to better models in very good light conditions. It's entirely consistent with your comment that normally you don't see apparent resolutions difference in high quality binoculars. I'd judge the majority would have stopped down values far better than that. It just highly suggestive that the middle of the HT objective appears to be seriously bad.
Naturally some users will have visual acuities somewhat better than the average and they will be able to see differences between higher performing models. One thing I have become particularly aware of is how critical the light level is to being able to discriminate between models and particularly for getting consistent results for a chart. My peak acuity is around 400cd/m2 and I try to get close to that level for testing and comparing. In poor light my VA drops like a stone and the results are rubbish. Do you think varying light levels might explain your inconsistencies using the chart?
I mentioned at the start that the 4 binoculars with <130/D values stopped down appeared equally sharp. My results suggest that my visual threshold would usually be140-150/D in good light. I'd say that plenty of demonstration samples from the big players don't reach that standard. I've only briefly tried a couple of HT x42s at BirdFair and they looked pretty good to me at the time unlike some notable others.
I know Kimmo and yourself are very keen on the star tests and you mention that they might predict the resolution performance of the HT. Maybe I'm doing something wrong, but I've not been able to find any relationship between the patterns, apparent sharpness or stopped down resolutions. A spikey mess might be 125/D and something resembling text book might be 180/D. (stopped down). I'm sure it's telling me something, but I've certainly haven't figured out what... but I'm willing to learn.
“It appears that the oddities of the aberrations in this binocular create a rare instance where the resolution visible on a lp/mm chart at low magnification is poorer than would be predicted by the true resolving power of the instrument.”
Henry, I've only estimated full and stopped down resolutions for 15 binoculars so far, and found that the instrument resolution (full aperture) is a very poor predictor of how sharp the view is going to appear, or indeed the stopped down result. The HT x54 appears to be an exception in the range of the difference but moderate relative shifts, both improving and deteriorating, appear to be the rule rather than the exception.
Of course the above includes a lot of speculation, but you've convinced me there is a problem with the HTs you and Kimmo tested and I really appreciate both your efforts. I hope to have a look for myself, but it probably won't be until the UK birdFair in August now.
Best regards,
David