Batteries from the Mk II will most definitely work in the newer Mk IV, but they will not like doing so. They might send you error messages or run out of power sooner than expected, but they do work. If you stop to think about this you will realize the Mk IV is a power hog compared to the Mk II. The AF system utilizes it's own computer which uses power. The touch screen on the Mk IV uses lots of power. The Mk II is a power miser by comparisons. Most of the adjustments made on the rear LCD of the Mk IV are done on the top LCD of the Mk II, a feature that uses far less power. Try this, open the manual for the Mk IV and start reading the nomenclature section. Look at every button and ask yourself if the system using that button is using power and how much. You will quickly realize how efficient the Mk II is. I carry a Mk II in my car. I looked at the battery charge this morning and found it to be full, and it's been that way since Thanksgiving. My Mk IV goes through 2 batteries a day just shooting birds out the window. That body with large lens eats batteries whole. I am just greatful that I am able to use the Mk II batteries at all in the Mk IV. They can still be used for back up. The card situation in the Mk IV is sort of funky, to me. I dislike SD cards and got one 64gb card for it. I use this card solely for backing up the RAW files on the CF card. It never comes out of it's slot. Best of luck to you and the new Mk IV, it is one great experience. Wait until you see it work at ISO 12,8000!

From what I can tell, lightroom's catalog has a copy of every image that adds to the images on my hard drive.

I backed up the images on my hard drive to an external and to the cloud and deleted them, then emptied the recycle bin, but my hard drive is still half full.

Are the images in the catalog taking up all that space? How do I create more room on my hard drive?

I have a wedding with two other shooters tomorrow and I have a feeling the RAW images will take up more space that I have. I have 221 GB free. The hard drive is only half a TB.

How to clear the catalog if this is the problem? Is this advisable? Should I get a 256gb flash drive to store the images for the wedding tomorrow?

Yes, the RAW images from 3 photographers shooting from 8:30 to 7pm may be upwards of 256gb.

I continue to plan my long awaited River Cruise on the Danube - Prague to Budapest next August. Ideally, I'd like to bring my desktop and all my photography equipment!
However, Lufthansa and TSA have suggested I pair down. Most UHHer's have suggested I travel with lighter equipment than my Canon 5D MIII and three lenses. My concern, in addition to making the trip enjoyable, is image quality. I'm leaning towards the Sony RX10 IV, either renting or purchasing.

Here's my concern: Will the 24 mm be sufficiently wide to capture the grandeur of the castles and scenes?
Thanks,
Mark

I have been using Canon printers for many years and should never have used non OEM ink. This is the second printer I've had to replace because non OEM ink ruined the print head (I'm a slow learner). I researched how to clean the print head and followed all the instructions and now a printed page comes out in PINK type! The black ink tanks are full, although the colors are low, so that doesn't explain why it doesn't print text in black. I ordered one set of Canon ink for a last ditch effort to resurrect this $60 printer.

I already have a Canon Pro 10 dedicated to picture printing, although I may occasionally print a picture on the all in one.

That being said, I could be swayed to switch brands for my office work printer. It needs to scan, copy, & print and not put me in the poor house buying ink!! I've even considered a color laser printer. Replacement toner cartridges cost more than the printer, but that is true for ink jet printers too. The difference is the number of times they need to be changed for best results.

I've looked at so many options that my head is spinning and would really like to hear what you all like.