I don't know if I'm following the latter part of the conversation here.
There were a few things asked. My $.02...
- NEX 5 (or 5N) vs. 7? They are very different cameras in terms of handling, cost, and to lesser extent, overall size/weight, and resolution offered.
- 10mm lens? The widest rangefinder lens I know of is the Voigtlander 12mm (equivalent to 18mm on the NEX). It performs well on the NEX 5N, not as sharp in the corners as the Voigtlander 15, but it also pretty much lacks the color shifting issue that some of these rangefinder lenses have, so it's more user friendly in that it won't require additional processing. I don't have a way to quantify how much better the CV 12 would be vs. the Sony 16/2.8 + wide angle adapter (which effectively makes it 12mm). 18mm equivalent view is pretty darn wide, which is something else to consider - do you really want to work with a lens that wide? The 15-18mm range (22-24mm equiv) is already pretty wide, and of course you can always stitch shots together for wider FOV.
Here are a couple of recent images from the 5N and CV 15...
edit: removed images, put them in next post
- Where to find manual focus rangefinder or SLR lenses? All of Eric's suggestions are good, in addition there are a few forums (and buying from photog comuunity members is always my preference if buying used)... RangeFinderForum.com, GetDPI.com, FredMiranda.com, Photography-On-The.net, Photo.net... eBay prices are usually way inflated on these lenses, especially the rangefinder lenses.
- APSC Lenses... assuming this means for digital APS-C bodies, then not any of them will work, only those designed for Sony E-Mount or (A-Mount + LA-EA1 adapter), unless they happen to have an aperture ring for manual control (I don't know of any that do). When Conurus releases their Canon to NEX adapter the NEX will be able to control the aperture of all Canon EF and EF-S (the latter being specifically for APS-C) lenses electronically. I've almost lost interest in using any SLR lenses on the NEX, but that's just me... and of course I did say "almost" lost interest :)
- Landscape focus at infinity... that might work, then again if you want some foreground objects in the shot to be in focus, it won't work out. Learn the hyperfocal distance for your lenses at the common apertures, or get an app, or make a note :) Which brings me to...
PITFALLS of Rangefinder Lenses
A few things to consider before jumping in without having all of the facts...
- The focus scales on adapted manual focus lenses will not be accurate because of the APS-C sensor (this also applies to SLR lenses).
- Minimum focus distance with most rangefinder lenses is between .7 and .9 meters. This is much more than SLR lenses which can sometimes focus on objects a few inches from the front of the lens. There is a solution, the Hawk's helicoid adapter. It provides the means to adjust the lens-sensor distance on the fly allowing the lenses to close focus. I have not tried it yet as some users have reported problems with certain lenses not focusing properly at infinity with this adapter.
- Many rangefinder lenses 35mm or wider will have some amount of color shift that you'll probably want to fix in some or even all of the photos you take. One way is to use the Cornerfix program, which is free, but requires a separate step in processing each photo. It also requires you to be able to create DNG files (which Lightroom can do, not sure which other processing software can) as it only works with files of that type.
Why bother with rangefinder lenses then?
- Build Quality
- Cost (arguable, some are very expensive, others not so much)
- Beyond 35mm there are no color shifting or corner smearing problems, so the 40-90mm range is full of good performers.