That is simply because I don't know how much those transmission rates really matters in real use. I haven't owned too many binoculars in my life. Sapphire is my first full size binocular which I can call really good one. But I can see quality differences between my pocket Zeiss and my Hawke. Full size Terras are made in China and I suppose that those are not so good, maybe...so they say.I think you worry too much about the transmission values. They are already good enough in modern mid-range binoculars. I'll tell you a little story I've experienced myself: I ordered the Hawke Frontier EDX 8x32 (FoV = 135 m) and the Kowa BDII XD 8x32 (FoV = 154 m) at the same time and tested both binoculars immediately one after the other. Then I wanted to know how the binoculars would fit my husband because of shadows, kidney beans. First I gave him the Kowa's, then the Hawke's: "What kind of tube is that?!" Because of the relatively smaller field of view from Hawke's. "And which binoculars show the better image?"; "The Hawke's, the tube." (Tube means here a view how in a toilet paper roll). It was a grey day with overcast skies, ideal for testing the colour representation. The image was dull, sad with low color saturation and low contrasts. Further research revealed that another forum member (German forum) also reported a dull, sad image from the same Kowa BDII XD series, but 10x42 format. At street lights at night, the Kowa's shows extreme spikes, the Hawke's almost none. Both binoculars were returned, the Hawke's with relative small eye cups only because of shadowing due to my individual physiognomy. Bigger eye cups of Kowa's fits better to me. Too bad.
And now let's look at the transmission curve of the Kowa BDII XD 6.5x32 with high transmission values of 90% (pages 7 and 11):
What do I conclude from this? Besides the already sufficiently high transmission of modern mid-range binoculars, there are more essential quality criteria for optics in praxis: Quality of the grinding of the lens surfaces, glass quality, uniform and appropriate thickness of coatings, quality of prisms, etc. With the test for spikes, I can at least check the quality of the roof prisms. I also look carefully in the objectives under different angles of illumination against brown and green backgrounds in front of oculars. Without flash light. Visible roof edges also indicate poor quality. I really wanted the Kowa's because of its impressive field of view and tested and returned 3 units. I found visible roof edges on 2 of them. The Kowa's with to me good fitting eyecups shows also extreme veiling glare, false light, flashes under overcast sky. (The Hawke's I don't test in this regard because eyecups are not fits to me, a test is meaningless.)
And now read carefully my technical-dry review again. I also assessed the mechanics. ;-)
Best wishes and good night. JessieHello friends of nature and optics, I have been reading the forum, learned a lot and selected my Nikon Monarch HG 8x42 based on your posts about 1 year ago. Now I have purchased a new binocular Hawke Frontier APO 10x42 to complement the Nikon 8x42. I want to give something back to the members...www.birdforum.net
You have given lots of valuable information, Thank you!