I wet-clean my sensors whenever they need it, but something like tree sap might prove to be difficult to remove completely. The methanol you dampen the swabs with should dissolve the sap, but could leave a smeary mess. As others have said, take it to a lab and let them use a pile of their $wabs to clean it up.
Terrific review, Dustin. Thanx so much for putting forth the time and effort to produce a review that can really be trusted. Another plus for this lens is that it plays very nicely with infrared, unlike the 2.8, which is horrible. I traded off my 2.8 for it primarily for that reason, but the f/4 is so good I've been using on my unconverted body all the time.
I have discovered that just tucking a leg of my TVC-24L into my Think Tank belt works fine. If you keep it behind your hip it doesn't hit your legs, and is easily accessible. Would get uncomfortable with something a lot heavier, tho.
If your lenses look clean and the dirt pattern is roughly the same with different ones, then it's on the sensor.
You can check directly by following the manual sensor cleaning procedure with a full battery and looking at the sensor with a lighted loupe or flashlight + magnifier. Dust is visible but usually pretty tiny. If it's not sticky, like drops of lube, you might be able to carefully blast it away with a rocket blower. Good luck.
I have come to the point that I want to upgrade from my current tripod. I have a Manfrotto 190CXPRO4 with an 054 head converted to A/S that is getting pretty beat up. I use it primarily for landscape and night photography. Heaviest rig is a 5D3 and 100-400. I am a 5' 4" older lady, and don't need a bunch of height or weight.
So I need advice from the RRS gurus out there. What height of legs should I consider? I like the travel-friendly TVC-24, but am afraid that it would be too short even for me on uneven ground. Would it?
What RRS [or other] ballhead? I used to have a BH-40 but it seemed to have a lot of creep. Maybe I was too afraid of over-tightening. A screw-knob clamp might be better than a lever for me, since I have plates and L-brackets from everybody.
I have used the Op/Techs and Storm Jacket during some pretty heavy rain w/o harm to my 5D3. I stuff the little Op/Techs in all my bags; great insurance for unexpected rain or dust. I have the Kata, too, but it's so bulky I've never brought it anywhere.
I am seriously considering trading in my 16-35II f/2.8 on the new f/4 IS, simply because the f/4 reportedly plays very nicely with IR [unlike the miserably awful 2.8 in IR]. I don't expect to miss that stop, and will get a dual-purpose UWA.