Well that explains why they won't collimate

[jnb]

Had a quick play with my new toy (revelation 15 x 70) today and first impression is they're horrible! woefully out of collimation. OK I could send them back and see if the next pair are any good or I could just get out the screwdrivers and adjust them (they're only £50 so I'm not too worried).

So screwdrivers out it is. After a bit of investigation I realise that anything I do is having no effect whatsoever so further investigation is called for. Popping the top off reveals the reason, the collimation screws are nowhere near the prisms! a bit of reseating the prisms and suddenly the collimation screws work again and I now have nice round exit pupils, still not collimated and won't be until I can try again in daylight with a suitable target but they're a lot closer. On the plus side each side seems to perform well so if I can get them collimated they should be good.

So the result so far seems to be that they're well made but badly adjusted and getting a good pair is largely a matter of luck or being willing to tinker.

[Naemeth]

Well that does explain it. You'd be perfectly entitled to a replacement pair though .

[jnb]

Now I've had a bit more of a play with them I've come to the conclusion that their quality exceeds their quality control. Potentially they could be very good but there's a lot of evidence that they're put together quickly with good components but little attention to assembly or quality control.

On getting these things I noticed that there was a slight double image which is OK that's easy enough to fix with the collimation screws but more significantly the exit pupil on the left was way off centre and severely far from circular. Well that can be fixed with the collimation but it shouldn't be in that state to start with. At this point I start tweaking the collimation screws and in one direction it gets even worse while in the other there was no effect whatsoever. That's the point at which I start disassembling the binoculars to see what is going on. What seems to be going on is that the collimation on the binoculars was so far out when manufactured that the collimation screws had been put to their extreme limit to compensate for that. Unfortunately they had run out of travel just before they merged the images and any further movement was touching nothing. What I also found was that the collimation screws on the right side appeared to have not been touched at all. I suspect that what is happening is that in the interest of speed of manufacture they make these things and then adjust the collimation on one side only.

So having found that I then collimate both sides and they stay within the travel of the collimation screws and merge the images and even out the imperfections in the exit pupils. The exit pupils are still off circular and a closer examination suggests that the left and right optical tubes are not properly aligned so, making some assumptions again, I would guess that these things are made quickly with little care as to whether the left and right will be aligned on the assumption that collimation of the prisms will fix it which is only partially true. To their  credit they do seem to be made of basically good components, they feel solid and reliable, focussing is smooth and disassembly and reassembly didn't show any crucial cost cutting exercises.

So at the end of all that what I have is collimated 15 x 70 binoculars with slightly flawed alignment and slightly flawed exit pupils. The latter is causing some light loss so they are effectively slightly less than 70mm. On the plus side they were cheap and I have a much better idea of what is going on with collimation and how to assess whether a pair of binoculars is god or bad. Would I recommend them to anyone else? Yes on one of two conditions; one is that you are able to stand in a physical shop and go through the pairs until you get a good pair; the other is that you are willing to take a risk that you might need to immediately void the warranty and hack them about a bit. You could of course repeatedly exchange them via post if you can't get to a shop but is it worth all that inconvenience for a £50 pair of bins?