About coatings...

[jimmyjamjoejoe]

So i picked up a cheap pair of 10x50's at a car boot sale. Collimation seemed fine, views were crisp etc, nice round exit pupils, no rattles...

But ever since the first session with them i couldn't help but feel something was wrong with them, i just couldn't put my finger on it... I checked horizontal alignment and vertical alignment both fine. I noticed there is a slight overlap in views - for instance when an object is on the left edge of the right eyepieces field of view, the same object is about 1/5th of the way into the left eyepieces field of view... Having looked around at guides etc, this is pretty acceptable, and convergence is preferable to divergence, and my eyes have no problem merging the images so i don't think this is the problem.

It wasn't until i used them during the day yesterday, whilst checking alignment tests etc, that i noticed the right eyepiece has a slight blue hue to it, as opposed to the yellower/more natural left. It isn't an obvious blue tinge, only noticeable when compared to the other. I began to suspect this was part of the weird feeling i'd got from them.

I was using them again lastnight, and was yet again comparing the eyepieces, this time against a nice bright moon. The left eyepiece was fine, the right (blueish) eyepiece however, was showing a nice blue band of false colour on the lower half of the moon. All of a sudden it clicked that this was indeed the problem i had been detecting.

So, is this likely to be caused by a misalignment of the prisms? Or could it be that these have been repaired in the past and now sport different prisms in each side?

[Capricorn]

The prisms are not the cause of the different colours. The colour is a consequence of the wavelength at which the coating is intended to prevent reflection.

Sounds like they may have been damaged and repaired and the replacement eyepiece, or at least the replaced lens, had a different coating specification.

Not a lot that you really do as sending them to a repairers to have what would be both lens/eyepieces replaced to match up would not really be worth it.

From the description I would almost guess that the right eyepiece/lens is not the correct one for the binoculars hence the false colour.

Have a search on the net and see if there are any repairers locally, but I would say that they would not have the perfect match for the binoculars that you have.

[jimmyjamjoejoe]

Thanks for that, it's pretty much what i figured. I won't bother getting them fixed since the colour difference at night isn't very apparent at all. I got them for less than £10 at a car boot so i'm not too fussed about them tbh, so long as they give sharp, steady, merged images, which they do.