Lemming51

The bright light sources in the lower-right-center are being reflected as bright spots in the upper-left-center.  Typcial when using "protective" filter.  Take it off and the reflection should be ...

Assuming only with this lens, Aperture blinking to F00 and the AF mode jumping to M tells me this lens's internal wiring is bad.  Have it serviced. IMHO, YMMV.

Hard to make any kind of conclusion when comparing completely different lenses, both of which are third party and not as likely to perform as well as Canon or Nikon's own. IMHO, YMMV

Yes, set the Drive mode for Continuous and the AF mode to One Shot. That does not sound like a situation in which you would want focus lock.  Sounds more like you would want active focus to track ...

bingo. Canon's marketing copy pretty much says that. https://www.usa.canon.com/internet/portal/us/home/products/details/lenses/ef/wide-angle/ef-s-24mm-f-2-8-stm

Seems like you'll be in the best position to give us the answer to that question. I think it is also heavily dependent on the lenses being compared.

which speedlite? For example - the default for Canon's 580EX II, 600EX RT, 600EX II RT is to cancel after the third FEB shot, but they have a custom function (C.Fn-03) to disable the auto-cancel.

congrats! maybe, how did the seller represent it? maybe.  If so, virtually the same as getting a new camera (leaving aside condition of other parts). I'm sure it's theoretically possible, but would ...

Clarifying ... (edit - sorry to repeat what others have already said) The AF modes and the Drive modes have similar names and can be confusing. AF modes: (1) One Shot - half-press of the shutter button ...

I have the original EF 70-200 f/2.8L USM. The model was intro'd in 1995. In "bench tests" its optical performance is still 2nd best in the Canon line of 70-200 f/2.8: EF 70-200 f/2.8L IS II USM > ...

I could be wrong (I often am ;-) ) but in my limited experience: The shutter count maintained internally and read from 3rd party apps I would guess would start with 0 or 1, but wouldn't surprise me ...

"On the cheap", I'd trade the EF 2x for the EF 1.4X.  Would give much more usable 140-560 f/6.3-8 instead of 200-800 f/9-11. IMHO, YMMV

It sounds like you'd be able to tell us.   Do your non-default settings remain with the batteries removed?

Assuming the EXIF is correct, these 2 pics were taken 11 years apart, thus accounting for the vastly different atmospheric effect and foliage colors.  The primary reason you have stars "off focus ...

Can't speak to the specific EF 135 f/2L USM + ET-78 combination.  But have several other Canon lenses with hoods by Canon and clones by Vello with no issues at all.

Set to 1/2 stop increments you get ... 1/30 ... 1/45 ... 1/60 Set to 1/3 stop increments you get ... 1/30 ... 1/40 ... 1/50 ... 1/60. As a practical matter, for your purpose there is virtually no ...

Time was when a photojournalist worthy of that professional title used a 4x5 or medium format SpeedGraphic. But that was supplanted by 35mm SLRs, trading away the higher resolution and DOF control ...

Is that one of "his high production value videos"?  I quit after 30 seconds it was so annoying.

First EF mount body, the EOS 650, was released in March 1987. November 1988 the EF 600 f/4L USM was released.

Nope, but watch me rationalize it. ;-) I look forward to Canon reviving their old tag-line, "So advanced, it's simple."  Simple would be full auto flash exposure always.  Non-dedicated flashes need ...