2x teleconverter vs digiscoping (1 Viewer)

Hi,
I own a sigma 150-500 mm / f 5.0-6.3 lens. That, of course, isn´t enough to photograph for example shorebirds. A Sigma 2x teleconverter would turn it into a 300-1000mm / f 10-13.
I´m much likely going to buy a Nikon ED 82 fieldscope and they offer a DSLR adapter that would turn the fieldscope into a 1000 mm / f 13 lens.
So on my Nikon D3100 both combinations would have 1500 mm / f 13.
Which combination would you recommend? By the way, the prize for the adapter and the teleconverter are pretty much the same.

Thanks for your advise,
Jan

JLS said:

So on my Nikon D3100 both combinations would have 1500 mm / f 13.
Which combination would you recommend? By the way, the prize for the adapter and the teleconverter are pretty much the same.

Click to expand...

Both combinations will be disappointing.
With an open aperture of f13 you will be close to a black-out in the viewfinder that is in most dSLRs anyway not set-up for manual focussing.
Also you will have a hard time with f13 to get shutter speeds that will work with the 1500mm focal length, even if you crank up ISO to the point that it will hurt.
Focal length is priceless, but only for filling the frame not to cover distance. With increasing distance air turbulences and such will prevent good photos. By eye you may not notice those disturbances, but a photo will show them mercyless.

Classic digiscoping with scope and compact camera, and even there don't use much more then 30x on the scope, will likely get you the best results for reasonable investment.

Ulli