This is an interesting conversation.
I also use a Barlow and ADC for planetary imaging (VB > Barlow > ADC >Cam). I have a Tele Vue 2x, by the way, which I am very happy with. Don't put anything but quality in your optical train. YMMV.
I was surprised to see FireCapture calculate my FL as 6000 the night before last! I had never noticed this in the txt file generated with my AVI, so I was a bit shocked since it should have been closer to 4700. Since my pixel size is 3.75, I should be shooting for f/18.75 or so, 20 would be fine, but at 6000 FL I am closer to f/25.5! Based on what I've read, that would be way over the "theoretical" Barlow bump that I should be pursuing (pixel size x 5). It seems pretty clear that the ADC is driving up my magnification due to the additional separation between the Barlow and camera chip.
So, the next time the bloody smoke from the Apple Fire clears, I am going to try a few modifications; 1) I will push the barlow into my visual back all the way to the rear of the SCT plate to reduce the magnification, 2) I will swap the ADC and the Barlow to see what effect that has on magnification as well (presuming that placing the Barlow after the ADC will still put the Barlow lens within the focal plane).
I am curious to see what numbers I get. I'd hate to have to buy a 1.5x Barlow to get better images. But logically, Barlows should be closest to their specified magnification at the top of the Barlow tube.
Edited by KTAZ, Today, 06:01 PM.