I am the OP for this thread. Thank you for all comments. I had NO real information on an MP. I spoke with a "Leica" user and he suggested an MP. After everyone's kind comments, it seems that there are better buys than an MP. What is the best "BUY" in a used Leica, and which lens or lenses would you recommend? I have no problem buying used. Also anything I buy used, will go to a Leica person, for a CLA. Like a Hasselblad, it is a mechanical system and needs maintenance. The camera will be used for fun, not professionally. I do sell some of my work, but do not see it as that use.
Now we are talking!
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I would divide M film Leicas in few groups by the way they feels (mostly).
1. Classic German. M2, 3 and 4. They have most solid build and best build quality.
2. M5 is weird shape and larger size for just one reason to accommodate metering. "Strange" battery.
3. ELC (Ernst Leitz Canada) M4-2 and M4-P. They feel cheaper than group 1. But they are black.
4. M6, M7. Not so new M6 (TTL) (chrome feels like plastic) and M7 with aperture priority mode (only one film M made like this, if I'm not mistaken). Again, "strange" batteries.
5. German reincarnation of classics from group one. MP and M-A. Available new and this is the only reason to buy them. Well another reason to buy is to support Leica!
All M film cameras are capable to be used for decades. Not so many, but currently enough independent repair services are available. They will do same CLA as Leica do, but under much reasonable price.
Which M to choose is the matter or personal preferences. The only way to find out for sure is to hold and feel particular M in your hands, operate the shutter and see if you like different styles of film loading. Well, not exactly like, but to deal with... And too look at all frame lines in VF.
Lenses are plenty. UWA will need external VF. 28mm lenses will work with 28mm frame-lines starting from M4-P. Starting from M6 VF has different "magnifications". Scroll down in this link:
http://lavidaleica.com/content/overview-m-system
35mm will have frame lines starting from M2. If you like 50mm lens, M3 is the best for it to take pictures with both eyes open.
Lens groups, not in particular order.
1. Leitz and Leica.
It is started with Leitz in Germany and continued with Leitz in Canada. Earlier Leitz German lenses are severe prone to fogging, fungus and separation. Lens coatings and lens glass is chalk soft. The bad quality of old Leitz glass doesn't match the brass bodies, which build to be in use forever and very smooth to operate. If old Leitz lens still has undamaged optics it will provide lovely bw images with hint of Leica rendering which no other lenses has.
LTM and M mounts. LTM needs M adapter. Adapters are gamble if buying cheap MiC, but more expensive original or quality manufactured ones are available. Main difference with LTM, most of the lenses will only focus at 1 meter. Most of old Leitz glass is overpriced, over glorified, IMO. But some lenses are good bargain. Like Elmar 90 f4 (LTM and M under 200$)
2. FSU 20, 28, 35 and 50mm LTM lenses. Those are copies of Zeiss in general. Totally opposite to group one. Most of the glass is in perfect condition, coating and material is good. Bodies are soft aluminium, with extremely small screws. Main problem is aligning of FSU LTM lenses with M Leicas. Shimming is required, but it is not going to be adequately sharp on all distances. But miracle is often happens and some FSU lenses will work fine on film M. FSU is cheap to get.
3. Old Japanese LTM lenses. Canon, Nikon and some exotics. Not expensive, well made. Optics might have fungus and fogging. I have little knowledge of lenses in this group. Most of them are boring lenses to use and to print from, IMO. But Garry Winogrand made it with Canon 28 3.5 and 2.8 lenses. And Henry Cartier Bresson used Nikkor 50 lens for a while as well.
4. Leitz Canada made, designed lenses. Mostly Summicrons 35 and 50. Well, Elmarit-M 28 and some others, as well
Most are black, M mount, not so expensive as modern German ones. Very good build, fine glass for film. The only thing which bugs me is plastic focus tabs on them.
5. Konica and few others from eighties made lenses in Japan. OK lenses, but became overpriced. Some have optics issues.
6. Leica Germany lenses after Canada and before ASPH. Slightly improved optically and in the build Canadian lenses. More expensive, not so different from Canadian in results.
7. Leica Germany current offerings.
ASPH versions of group 6. Clinical sharpness wide open, more contrast. Expensive. If obsessed with sharpness and Leica rendering - those are good choice.
APO - if you have ten thousands dollars to spend per lens...
Summarit-M 35, 50, 75 and if I'm not mistaken 90. f2.5 series are bargain in terms of current Leica pricing. Rendering is compromise between clinical ASPH sharpness and classic rendering. f2.4 Summarit series came after f2.5 series and have better build.
8. Made in Japan current offering. Cosina Japan manufacturing two types under old German names. Voigtlander (owned by Cosina) and Zeiss (German are still involved, they say). If you don't have money for lenses from 4, 6 and 7 or even 1, but want modern, no bad surprises (almost) lens - Viogtlander is great option. non-ASPH and ASPH lenses are available. Cheaper prices claimed to be due to non Leica label, but some are saying what Leica has better build and more interesting rendering. But even modern Leica lenses (some) will fail apart.
Zeiss (Cosina made) is offering more prestige, different build (which doesn't always makes sense). Lenses are modern copies of old original optical formulas. (Old, original Zeiss lenses for Leica are also possible to find). Modern contrast and sharpness (with most models).
MS Optics is one person company, who makes very tiny lenses with not so impressive optics in them. Little quantities dictates higher prices.
9. Lomography made by Russian (they say) lenses. Reincarnation of old FSU lenses. 20mm Russar, 32 Minotar and Jupiter 3. New Leica mount lenses with not so crazy as the rest price (for new).
10. Made for losers conversions. Where are some kits or build to order conversions from lenses which are taken from broken film cameras.
Disclaimer. I'm not 100% precise in details, but I'm 100% biased.