Hi Paul,
Welcome to the site...I am only new here myself but have found the place really helpfull. I'm no pro but don't mind learning. Here is my 2cents worth...Basically here is a coppy of what I sent you in PM in reference to the 20X90 I use to own.
The first thing you need to do with Bino’s of this size is obtain a Mount of some sort (even camera mount if necessary) & pick out a bright object like Jupiter and see how much out of collimation they are. My 20X90 were out & I sent them back whereupon the store did not do a very good job at fixing them, so I sold them.
BUT...My binos where considered a cheap set AND large ones of that size have a reputation for arriving out of collimation. However considering all of this, they were excellent when using for DSOs! By this I mean if I wanted to locate something to look at in my Dob but did not want to muck around with star happing or what not...I would pick up the giant binos (3.7kg) and scan the sky. Mind you though...I use to practice with dumb bell weights...LOL. This technique worked well as Most Dim objects in the sky showed up pretty straight away in the 20X90 all be it very small on some objects, which brings me to my next point. Remember you will not be able to magnify the view and DSOs in binoculars are not going to be the same as some object in a telescope. You will pick out globulars in light polluted areas which I never tried in dark skies and would only assume would stand out even more! I was impressed none the less. M31 Andromeda galaxy also was not bad however FOV was maybe a tad to small. Star fileds and open clusters where very good and I am sure I could of done much much more with them...however because of the collimation being out with Jupiter, which I could easily see the moons of, I was upset with the hole purchase and got rid of them.
I miss those Binos now, as I only paid a few hundred “AU” & in many respects feel I sold them far to quickly as for DSO’s they where quite good. I used my sisters camera mount which did give a bit of shake, however did settle down...you need a heavy duty camera/bino Tripod to truly enjoy them.
Binocular astronomy is somthing I intend to fully embrace dowon the track...I enjoy using my 15X70 BUT yes...I really do miss the 20X90. FOV is something to consider with giant binos...I opted for 20X90 becuase I thought the FOV on the 25X100 was smaller....If you could get 20X100 I would go with that, however for the price I think the 20X90 are great for the money. Just don’t expect a cheap set to relove bright objects all the way down into a nice round cerpherical object as when bright objects appear out of collimation, they tend to have a distortion with a shard of light sticking out the side, like when satrs appear to appear like a Q (a tail protruding out of them) when out of collimation...however once again this was not evident on stars or dso’s at all. In a way I really wish I did not sell them now.
I hope some of this helps...just discuss the issue of collimation with whoever you buy them from and remember that if your not paying top dollar and you can live with the fact they binos of this size do make great dso hunters, then you wont be so disapointned if you run into a little distortion on Bright planets and so forth.
Compared to my 15X70 they really showed objects to be much brighter and somewhat more in your face. My 15X70 make a fantastic pair for quick deep field observations and I have become quite good using them to scan the sky with. One way to develope strong wrists for such observing is to double up two 2.5kg dumbell weights and hold them as if using binos...before you know it, you will be able to scan the sky with a set of 20X90. LOL! (my nieghboursI probably wonder what the hell I am doing when they spot me attempting to use such items when looking over thier fence
) I know how crazy that sounds, but yea...works for me. Weight is a consideration...but I am sure you will be using a tripod like any sane person would for DSO...however as I said 15X70 do make an excellent deep field scanner.
Later DaveJ
