Ultra-wide ideas

You (soon) have Samyang 10/2.8 also  
http://www.bhphotovideo.com/c/product/1039937-REG/rokinon_10m_mft_10mm_f_2_8_ed_as.html

 

Definitely doesn't take filters...

 

If you're going to go with a cheapo focal reducer, then I'd advise to skip the Sigma. You're going to want more resolution than that.

Either of the Olympus 9-18mm's are great lenses. You wouldn't be going wrong with either of those.

 

I like that idea, but don't skimp, get the metabones speedboster. Also there is a thread somewhere taking about how many of the APS-C dSLR lenses will still cover the 4/3 sensor with the use of a speed booster.

In this digital age, whats the importance of taking filters?
Unless you just like having filters on your lens , or you are worried about being clumsy and damaging the front element and wish to put a protective filter on.

 

There are even some APS-C lenses that will cover an APS-C sensor even with the speedbooster--e.g. the Nikon 35mm f/1.8.

 

I'd pass on the Sigma with the cheap focal reducer, though if you're really not that concerned about resolution, you might be okay with it. The Metabones focal reducer will do a credible job, but that puts you well over budget.

You don't say how wide you want/need. If 11mm is sufficient, there's the 11-22/2.8-3.5 and 4/3 adapter as well. The 11-22 has long been popular for interiors due to relatively low distortion and fast(isn) aperture. The 9-18s are probably the most practical choice though. The m4/3 occasionally appears on the Olympus refurbished site for $400. With manual focus lenses you're not going to do any better than those lenses optically or price-wise.

 

polarizers don't work well with ultra wide lenses.

 

If resolution is a concern for the landscapes, what about just doing a pano and stitching? You can use whatever lens you already have, and get more resolution than ou ever can with a single shot.

 

Original 9-18 can be had for $300 shipped quite often on eBay and other sites. I just sold mine in excellent condition for $300.

 

Makes sense.

The only lens that you mention that I've used is the native 9-18, and even though I've had it for around a year, I haven't used it too much. Just haven't done the kind of traveling where I'd use it a lot, but what I've done has been pretty good. I think that it has shown up from Olympus as a refurb in your price range (looks like it was $399 not too long ago, might be back to that when they get stock back in).

 

I believe the m.Zuiko 9-18 will be your best bet.

1. It not only takes filters but they are relatively small (52mm) and less expensive compared to the other options.
2. it is also very small which means smaller kit which is why you bought Micro 4/3 in the first place, yes?  
3. Being native m43 you will likely use it more - no adapter to attach and carry.
4. Did I mention it is very small?  

It is my favorite lens for hiking.

 

OLY MZD 9-18 is not bad. You can get full 16MP pixel level resolution under the right circumstances (aperture, exposure, composition, ISO, etc.) and with proper post processing. I got mine during Oly 20% off reconditioned sale for only ~$320. There are plenty of good deals on ebay. Definitely fits your budget.

 

I think going wide with m4/3 is not a good idea, just get a bigger sensor camera + an ultra wide lens and call it a day, you can probably get a canon 5d and a sigma 12-24, that's less than 1000 bucks and you have a FF camera to play with.

 

I suggest that your criteria are too arbitrary and will result in dissatisfaction if you follow them. Just get the mZuiko 9-18, even if it ends up costing a bit more than your $500 limit. The other options are kludges that you'll eventually abandon for a native mFT solution. (Personally, I would go with the P7-14, but that would require you to abandon yet another of your criteria.)