TSN-82SV vs 663M? (1 Viewer)

[Northman]

I am considering a TSN-82SV or a 663m, with just the 30x occular (32x on 82).

From what I have read, the 82SV uses regular glass, while 663m has XD glass.

And the main difference is less CA with XD.
The 82 has a focal ratio of 5.5 if I remember.
The 663 has a focal ratio of 7 I belive.
Not sure what difference it makes?
82 is cheaper by a couple hundred $.
82 is 1500g compared to 1000g on 663.


Where will I notice the difference between these two optically? At what distance? CA on birds perched on top of tree, with white background is main thing I have read one can spot it, but usually at +35x? What about Ducks across water 100m away? Birds in trees against woodland backdrop? Or on ground? Is Focus knob equal on them?


I am not a serious birder, this is more to dip my toes in the water to see if I can stand one eyed viewing.

 

[jkingrph]

I have a 82, and a 664, the straight version of the 663. Personally I would go the 663, smaller lighter and a bit brighter. I think the larger lens on the 82 narrows the gap, even with glass that is not as advanced as that in the 663.

 

[jring]

Hi,

by all means get the 663. The 82SV is fine with a 30 wide but beyond 35 or 40x things will just get blurry with a fast achromat.

There are two kinds of CA, lateral and lonitudinal. The lateral kind is the well known purple/yellow fringing of hard contrast edges and is often seen far from the optical axis.

The longitudinal kind is also visible on axis and basically means that different colors have different focal points, which means that no point of best focus can be found at higher magnifications and things stay blurry.

Joachim