I have managed to compare the Kowa and RSPB 6.5x32 bins, here are some very brief observations.
Field of view on the Kowa is better leading to a larger AFOV which makes the image more immersive. The brightness is also better on the Kowa and the colours seem more neutral. However there is an issue with the size of the sweet spot and in particular the drop off in focus towards the lower part of the image - focus is lost much more quickly than toward the upper part of the image and this is noticeable virtually all the time. In addition the Kowa seems to suffer more in challenging light conditions, for example when the sun is low or the street lights are on, and a significant amount of flare and veiling is visible a lot of the time, particularly in the lower part of the image.
The RSPB binoculars have a slightly smaller FOV (9 degrees) and the colouration of the image is a bit yellower to my eyes. Although brightness is good I do find it to be slightly less bright than the Kowa, more noticeable early morning and late evening - during daylight hours the difference is not so apparent. One area where the RSPB model does excel is in edge of image sharpness. Whilst both binoculars are very sharp on axis the RSPB model is also sharp virtually to the edge, a slight drop off in maybe the last 5% or so. In fact overall image sharpness is not a million miles away from my Swaro 8.5x42 FP and the size of the sweet spot is certainly much larger than the Kowa.
The Kowa is a smaller binocular and the overall build quality is very good with large oculars, a large smooth focus dial and good quality eyecups and armour. Eye placement is very easy and with 17mm eye relief I can see full FOV with my glasses on.
The RSPB model is a bit larger and has a softer feel rubber armour which seems thicker and may offer more protection. I'm not sure if the body is magnesium as in the Kowa, possibly not. The advertised 22mm eye relief appealed but in reality I get a lot of kidney bean effect with my glasses on. After adding a couple of rubber O-ring spacers this has virtually gone so I feel 22mm is too much ER even with specs, at least for my face shape. In addition the eyecups don't have any stop points which is annoying and they are made from a harder rubber than the Kowa so aren't as grippy on my glasses which makes eye placement a bit more tricky.
In summary I think that these are both good binoculars with individual strengths and weaknesses. Providing you are prepared to put up with flare, veiling and a smallish sweet spot the Kowa provides an excellent FOV, bright image and neutral colours. The RSPB still has a great FOV and has a much larger sweet spot which is equally as sharp. I prefer the overall image quality of the Kowa but wish it had the sweet spot/edge sharpness of the RSPB model. They would then be the perfect compact large FOV bin in my opinion.
The RSPB model has had a recent price drop and if you are after a large FOV, low mag sharp image binocular it's definitely worth a look. I would love Swarovski to consider making a 6.5x32 with a 9-10 degree FOV as I feel this would be a great 'A class' option for birding in woodland or if you have unsteady hands. With both the Kowa and RSPB I have not really noticed the drop off in magnification when it comes to ID, but I have noticed a steadier image which really helps.
I can't keep them both so now have to decide which one to get rid of........
