Lemming51

The XSi is 11 year old technology, the T1i only 10. ;-) The XSi does not shoot video, but the T1i does.  The T1i also has greater resolution (15 mp v. 12 mp), and greater ISO range of 100-3200 (and ...

Per your comments, I think you're going to find FF lenses too heavy and too pricey.  Especially when you try to reproduce the wide-angle you currently have with a 16-35ish full frame lens.

I'd first suspect that the 2-3 yr old batteries are degraded (p. 370 of the instruction manual). You might check how they register in the camera's Battery Info. menu ("wrench 3" menu, p. 348 of ...

"Hope is a good thing, maybe the best of things, and no good thing ever dies." Me, I'm a cynic. It is not going to be a size-and-cost-be-damned L series, like the EF 28-300, which was 2x the size ...

If the plan is to sell the 2.8L II, then YES it's a no-brainer. Smaller, lighter, greater zoom range, trade one stop max aperture for IS, and cash in your pocket are the clinching arguements "for ...

Agree, but just to clarify:  2nd curtain sync "works" with any shutter speed longer than the x-sync.  The effect on the image becomes more apparent with longer shutter speeds.

This. That's what's indicated in the "leaked" RF 70-200 f/2.8 patent: https://www.canonnews.com/canon-patent-application-canon-rf-70-200mm-28 (1) Focal length: 72.00 135.00 194.99 [mm]

+1. Even less if go for a third-party clone for either the wired -E3 or the bluetooth remote.

600D is kind of an old model (2011), how old is the battery? Overtime they lose the ability to deliver the power the camera wants to draw, may need to replace it. [edit] Upon further review, that's ...

MLU was an option on better SLRs in the film era.  There's some vibration associated with the mirror slapping up that could affect the image when shooting extreme macro or tele with slower shutter ...

Samples with much more info would be helpful in diagnosing your problem. The 5D III has 4 different metering modes to choose from in P Av, Tv, and M while Auto has only 1. Exposure Compensation may ...

Sigma 18-250 is 3.5" long very similar to the EF 85 f/1.8 USM, the EF 100 f/2 USM is also just under 3".

Sounds like it is set for Mirror Lock Up.  Which menu this setting is in depends on the model.  MLU only applies to those "Creative Zone" modes.   1st press of the shutter flips up the mirror, a ...

YES.

[Edit - never mind.  Wrong answer in 1st draft.]

Same reason Zeiss and Nikon don't.  Because it solves a problem more prevalent in long teles. https://global.canon/en/imaging/l-lens/technology/fluorite.html

Sounds like you've inadvertently set Mirror Lock Up.

Have you tried using the 6D II's AFMA? Doubtful. Another thought - could be it's the reason you got it at such a discount. Pay for calibration and you're still money ahead.

(1) Canon's own BG-E21 grip, or a third party clone? or (2) note on p. 158: " Under ['wrench' 1: Wireless communications settings] , if [Bluetooth function] is set to [Smartphone] , remote control ...