Binoviewer prisms - is this normal?

[Andrew*]

My binoviewers' prisms do not seem to be symmetrical and I'm wondering if this is normal or if they're faulty.

As you can see, in the left one, there is a sliver intruding on the light path, whereas the right one is perfectly circular.

I have already had a look with a high power eyepiece and it focuses and merges fine, and views appear the same through each (however, there seems to be a warmer cast to the left side, but I think this is unconnected). Nothing appears to be moving or rattling about.

Andrew

[Jamie]

Andrew

I am sure there should be no obstruction in the view path.......I had a pair of Revelation bino viewers and there was no obstruction on them...

[Merlin66]

What you see is not uncommon. If the prism(s) used inside are on the small side or not absolutly positioned in the support cradle you can get this effect.

Can cause a bit of light loss; if everything else is OK collimation and FOV, you can live with it.

( I checked out some binoculars in a shop recently and three out of four - all the same make, same design etc showed prism cut-off. So you never, never know unless you check them before purchase)

Ken

(EDIT: Just re-read your post! Binoviewers not Binoculars...Doh! -Similar problem though.)

[Peter Drew]

At least the slightly obstructed aperture appears potentially round. The cone of light through the prism at this position probably falls within the obstructed portion. All the other characteristics you mention seem fine so not to worry. The difference in the brightness between the two sides is probably due to the beam splitter, these often have transmission ratios in the order of 40%/60%. Unfortunately, the brain does not make a summation of the two, hence the overall brightness would be based on the 60%, this is the main reason why binoviewers are not ideal for faint DSO's.

[Andrew*]

So you reckon it's not a problem?

[themos]

Andrew, perhaps the vignette section in this will help

http://www.cloudynights.com/item.php?item_id=2407