Here are some side-by-side testing results for the Nikon V1 using the Nikkor 10-30mm f/3.8-5.6 and Nikkor 18.5mm f/1.8. This was performed using the Nikon V1 camera, Kowa 883 scope, and 25x LER eyepiece.
I printed out an ISO 12233 Resolution Chart, and set up the scope approximately 8 meters away.
The camera settings were set as follows for both lenses: ISO 100, Auto Focus, Aperture Priority Mode, EV -.7 (this is where I usually have it – perhaps 0 would have been better, but at least it was the same for both lenses). All images were taken using a 2 second timer.
First I used the 18.5mm lens. With the lens wide open, the exposure time was 1/800 sec.
I switched to the 10-30mm lens, and tried to set it to exactly 18.5mm (looking at the EXIF data), but was only able to manage 18.2mm or 18.9mm – perhaps the lens zoom can only be set with a certain resolution. In any case, I saw the same results for either 18.2 or 18.9mm, which resulted in an aperture of f/4.5. For the same image the exposure time was 1/320 sec, or about 2.5 times slower than the 18.5mm lens.
I then zoomed to 30mm, where I sometimes shoot, resulting in an aperture of f/5.6 and exposure time of 1/200 sec.
After cropping in Photoshop Elements, the image histograms were fairly similar, with the 18.5mm image having a mean count of 85.7 with the 10-30mm image showing a mean count of 90.6 – the 10-30mm image is a bit brighter.
The images below are at 100% crop, 2400 x 1800 pixels.
18.5mm lens f/1.7 ISO 100 EV -.7 1/800 sec
10=30mm lens f/4.5 ISO 100 EV -.7 1/320 sec