That cleaning issue sounds like a horrible pain!
As for the telephoto thing I understand where you're coming from. I'm sitting here contemplating the Nikon 180-600 or the same Tamron you have now for Z for myself for Christmas. I just keep looking and saying how huge they are. I knew getting out of m43 was going to impact that significantly weight wise, but I definitely needed to prioritize low light with indoor sports my kids are doing. For proper exposure and shutter speed to freeze action I'm regularly at ISO 12,800 + in the gymnastics gym with an f2.8.
I definitely miss some of the Olympus features, but my main use cases didn't rely on them primarily.
If you do end up back in m43, I adored the 40-150 2.8 Pro. However if you're looking to to be as satisfying with the MC20 to get out past 500mm equivalent, I don't think you'll be happy after having 500 built into a lens with no TC. It really compromised the AF speed and accuracy and IQ took a big hit too. For pure wildlife/birds you'd probably be better with a 100-400.
Good luck with your decisions! I've thought about just an OM1 and a 100-400 for birds only, but I can't justify 2 systems.
-Eli
Thanks. Despite the automatic close shutter when the camera is off there still seems to be dust on the sensor even after I literally just cleaned it and turned it on. On a suspicion I started cleaning all my lenses on their mount every time I clean the sensor too. I think the shutter makes enough draft that it can pull dust from the inside of the lens and onto the sensor... But that's just a hunch, I have no way of proving that.
The Tamy lens is an absolute gem for what it is. The focus accuracy is very good but very dependent on the camera AF system. Th AF speed improves when you use the AF limiter because it has such a great AF range. I am always amazed how close you can focus, at 1:4 throughout the range you can get very good images of small-ish subjects. Works great with butterflies and dragonflies, it lets you have really good working distance at 500mm with 1.8 minimum focus diatance. The IQ at MFD is really really good, often I shoot wide open because there's not a lot of sharpness improvement.
The size is pretty okayu for transport, I can fit it in my Crumpler Quick Escape 800 which is my most used camera bag. The zooming takes a bit of effort compared to internal zoom and the weight balance shifts a bit frontally. It feels more balanced and comfortable at 150mm then 500mm. The zoom lock clutch is brilliant and I use it quite often because it can help me stay within a certain aperture brightness. So what I did is put 3 small vinyl labels at:
*250mm for f 5
*420mm for f 5.6
*485mm for f 6.3
And I often think of it as 3 point prime lens, mostly when I need to be careful about shutter speed in lower light. For its size it's amazing that it can be a 250mm f 5 and a 420mm f 5.6 lens.
I have test the histogram at 485mm f 6.3 and 500mm f 6.7 and there's literally no exposure change and all colour channels have the same levels, meaning the lens is optically a f 6.3 at 500mm but because of the math of glass opening and length of the lens Tamron advertises it as f 6.7
Luckily the tripod collar is completely removable which sheds quite a bit of weight to be at 1.7 KGs, with it on its so close to the Sony 200-600mm that you are better off with the Sony. I almost never use it, as I almost never take the lens hood with me either. Unless it's raining or I'm expecting it to rain I keep the lens hood at home because BBAR coating makes it almost impenetrable to flare (you can make it flare if you try hard enough but its very rare to get that at such a narrow angle of view).
Image Stabilization is good but not great (not even compared to IBIS only on Olympus), it can hold on to the view of 500mm for a few seconds but after about 5 seconds it starts wobbling before it can settle again. I trust it to about 2 stops in general and 3 stops if I'm very careful and not to tired to get my body in a more stable platform. And dont trust the panning mode of the IS, it doesn't work great especially at 10 FPS or lower, you are better off with IS turned off (which is lucky dead easy as it's a separate switch to IS modes).
The lens has given me some amazing images, cropped and uncropped, and I still love it:
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I am just not taking it out with me as often as my Tamron 70-180mm f 2.8 and if I have to chose between the two I pick the smaller lens if I don't have hopes for some awesome birding moments.
I am curious to see what OM System is cooking with the 50-250mm f 2.8 and f 4 but I'd the rumours are true about the f 4 not being compatible with teleconverter it's going to be less appealing as a birding lens.
A lens and camera combo under 2 KGs would be great and at 1.5 KGs would be awesome (but that's possible only with the Panasonic Leica 50-200mm f 2.8-4)
I understand your conundrum of action in low light. The fastest longest lenses Micro Four Thirds has are:
*Olympus 45mm f 1.2 PRO,
*Olympus 75mm f 1.8,
*Panasonic Leica 200mm f 2.8
They are relatively affordable compared to larger formats, for FE:
*Sigma 105mm f 1.4 DG HSM ART,
*Sony FE 135mm f 1.8 G Master,
*Samyang AF 135mm f 1.8,
*Sony FE 400mm f 2.8 G Master
For my low light action it would have to be the Samyang because it's what I could afford ... Maybe the Sony 135mm GM used for about 1.000 £ for th best possible AF.
I can't justify 2 different systems either, that's why I tried so hard to find a way to switch back to Olympus/OM System but I just can't right now. Maybe in spring when bugs come back to life I can try for the most portable combo ever: E-M5 Mark III + Oly 60 Macro + Meike MK320.
