[Wavytone]

Adrian I have the 311k encoders on my AZ8, thats 4 arc sec per step. They are quite simply a game-changer.

With SkySafari, there are a few interesting tricks:

- I can leave a high power eyepiece in my mak (9mm, 300X) and it will locate objects spot on every time. Forget finders - and forget swapping eyepieces. In the first night under dark skies it pulled in more DSO's than I've seen in a very long while.
- in suburban sydney skies it makes it possible to reliably find DSO's where there are simply no bright stars to use for star hopping.
- it is possible to distinguish between individual stars in a cluster. Simply impossible with 6k encoders !
- trying to find a nova in a busy star field you can be quite sure you have the right star if you reference a known star nearby.
- you can be quite sure of what is (or isn't) a moon of Saturn or Jupiter,
- you can measure the relative positions of things quite accurately, such as reasonably wide doubles - directly from the encoder positions - allowing for constant offset each time.

Lastly, and this one is a special trick - at 4 arc seconds resolution the position will update so frequently and precisely I was able to let a friend look through the mak at Saturn at 300X, while I had Sky Safari zoomed in to the maximum and used that to manually track Saturn using the image on the iPhone (this mount has manual worm drives on both axes). With low-res encoders that would simply have been impossible to pull off.

The accuracy is inherently only as good as your calibration on reference stars so frankly you really do need a large finderscope with 20X magnification and decent cross hairs to nail the reference stars to a minute of arc or better - eyeballing out-of-focus circles is simply not good enough to show what this can really do. Using a zero-power finder, RDF or Telrad etc is simply letting yourself in for disappointment later.

Admittedly there a few unknowns - the mechanical errors in the mount (the axes wont be precisely perpendicular), plus the effects of flexure in the tripod, mount and scope. The latter are significant in dobs as well as cheap metal mounts like the EQ5/EQ6. The other unknown at this level of accuracy is atmospheric refraction and so far I do not know whether SkySafari or the Nexus DSC are compensating for this. Maybe, maybe not. So far I've only had it out a few nights and not long enough to really test these aspects but what I do know is that it does reliably locate objects to better than 10 arc minutes with the AZ8. And it will do this all night from the initial calibration. No resetting, no recalibration required.