Help with collimating binoculars

[mrsnipey]

I bought a pair of 10x25 tasco binoculars from e-bay (no warranty - yeah, I know - slap self on side of head - hard) for my daughters for christmas. I didn't expect much from them but I was pleasantly surprised at how much I could see with them.

Then I was reading one of the messages in the forums and it made me go and check both pairs. And unfortunately, one of the pairs is out of alignment.

The right side is perfect, the left side however shows a ghost image to the top right. I pulled the binoculars apart (as you do) and put the prism from the right side into the left and it was perfect. So ... I have narrowed it down to the prism from the left side but I have no idea how to re-align a prism.

Has anyone had this problem before and do they know if it was fixable.
Or have I done my dough and should I just buy another pair. :sadeyes:

Please help. :prey:
Denis.

[chris lewis]

This may help - it does get technical however .http://rchamon.iies.es/collimation_methods/sun_images_method.htm

[saberscorpx]

If it can't be aligned with adjustment screws, tinkering or elbow grease and isn't cost effective to be professionally collimated then you're pretty much stuck with two monoculars.

Local hunting and department stores should have something similar that can be tested on-site.


SJS

[erick]

Yes Denis

Tinkering carefully with the adjustment screws is your best approach. I wouldn't be concerned about such tinkering, given you have already pulled the prisms out!!:scared: If you read up on collimation you'll see that there is a full and proper collimation which holds across interpupillary distance (IPD) adjustment (ie. between different people), and conditional collimation which holds only around a particular IPD (say, your daughter's).

Just work on adjusting one screw on one side to align the images vertically, at your daughter's IPD. (Read the literature on the internet to identify which screw.) If you can reach that alignment, that should get them sufficiently functional. :)

[Suzy_A]

A few hints on collimating binocs....

Get a few different people to check them as well. I found that quite a few people are a bit cross-eyed and will look through some binocs and say that they are fine but they are not at all!

I remember once when I was a uni stewed ant, someone (not me!) dropped the physic's dept binocs (25 x 80) onto concrete and they were way, way out - every star was now a double! And doubles were now quadrooples.

I gave the binocs to the physics technician and he had a look through - bad idea. One of his beady eyes would be pointing straight at you and the other would be looking at the roof. I had a few problems convincing him, without offending him, that the binocs were actually really out of collimation.

The other time I had a similar, although not as bad problem, was when I had my Carl Zeiss 7 x 50's professionally cleaned. The guy that did it cleaned it very well, but once again, his eyes were a bit out and I had trouble convincing him that the collimation was out - not enough to be a problem for normal daytime use, but certainly for astro use.

[saberscorpx]

Very true Suzy.
One persons aberration can be anothers elation.

I remember one starparty visitor who brought his own 7x50 binocular which he insisted was easily revealing the four separate main component stars of Orion's Trapezium (a feat requiring the visual acuity of the Bionic Woman).
A suspicion was confirmed as I looked through the horribly misaligned barrels. Everything had separate components.
The kaleidescopic view made me nauseous, but the excited man was perfectly content to continue with his 'bonus' abundance of stars.


SJS

[mrsnipey]

Thanks for the advice everyone.

Thanks for the link Chris.
It is very technical but it looks like what I need.
Lucky I'm on holidays. It's not the sort of article you can knock over
in a lunch break at work. Well, not if I wanted to get any work done
after lunch anyway.

Suzy_A
I'll get my missus to check out the binos tomorrow morning (this morning?)
when she wakes up just to be sure it's not me. :D

Erick,
I'll keep trying with the screws. I did improve it quite a bit but still not to
a usable level. And after three hours of using one of those tiny screw
drivers, I think I might have been going cross-eyed.

I'll let you know how I go.

[saberscorpx]

Exact collimation of roof prisms is a tall order anyway.
Angle tolerances of something like 2 arcseconds (1/1800 of a degree).
Porros can allow 5-10 arcminutes of leeway.


SJS