Can someone explain ACR camera compatibility to me please?

Although I have had CS5 installed on my PC for years, I have never had to use ACR within it. I went from DPP straight to LR5 (upgraded yesterday to LR6) for raw processing. In fact, I have barely ever used CS5 at all because of LR's remarkable functionality. So my question could be chalked up a lack of familiarity with Adobe's compatibility policies but here goes:

I needed content-aware fill for an image yesterday so after making general edits in LR, I tried to transfer it to CS5 (Edit In > CS5). LR popped up a warning stating the ACR in CS5 isn't fully compatible with the raw file from my 5DM3 and said I should download ACR 9.1 instead. However, when I chose the option to transfer the image anyway, it transferred without an issue and I was able to continue working there before bringing it back to LR.

Today, I downloaded and installed ACR 9.1 but when I checked CS5, it still showed ACR 6.7 as the most-recent version installed. Looking online, it quickly became clear that 6.7 is indeed the last version of ACR compatible with CS5: https://helpx.adobe.co​m …patible-applications.html. I know of Adobe's policy to stop releasing updates for previous versions of their software so it makes sense.

I then checked camera models and their compatibility with ACR and Adobe says ACR 7.1 is the minimum version required to work with 5D3 raw files: https://helpx.adobe.co​m …ug-supported-cameras.html

This has me confused because even if I open a 5DM3 .CR2 file directly in CS5 (instead of transferring from LR), it opens up just fine within its ACR. So how can ACR 6.7 suffice in this case when 7.1 is supposedly the lowest version required for such raw files?

The link you posted for camera support in ACR is in error. 6.7 supports the 5D3. See here:
http://blogs.adobe.com …ailable-on-adobe-com.html

However, because LR 6 and ACR 6.7 are not parallel versions, the older ACR can't do all the editing that LR 6 (any version) can do, so when sending an image from LR to PSCS5 you should pick the option to send a copy (tiff or psd) with LR edits.

Ah...that's quite the typo by Adobe. Thanks for explaining. In the warning dialog, LR did notify me that I could use it to render the image in PS. I chose not to, and it didn't seem to affect the LR edits. I will give it a try next time.

As well as camera support you also have to consider functionality questions. Updates to ACR can feature both camera updates as well as feature updates. When you ask LR to edit in PS what it does depends on which version of both LR and ACR you are using. If your version of PS supports ACR at the same or higher level, then LR passes the details of which file to open, as well as all of the editing instructions to ACR for it to process. ACR does all this processing without actually opening the ACR window. When ACR then passes the image to the main PS edit window it is opened as an RGB raster with all of the properties that you had specified in your LR preferences. Once you have finished editing in PS you use the Save command (Ctrl+S) and PS creates the new file for the image, again using the options in your LR preferences for file name and type etc. LR then also imports the image to the catalogue for you. The advantage that this has is if you change your mind about editing in PS, since if you decide it just isn't going to work you can close PS without saving the image, and you have no file to worry about.

So if your version of LR is newer than the version of ACR that PS supports, it may have new functionality that ACR doesn't understand. Now if you were to use an xmp file from a newer version with those unknown commands ACR won't crash, it will just ignore them. The thing is that you might get a little annoyed if you suddenly lost some of the processing that you did in LR, simply because you passed the image to PS. Especially if you could export the image from LR as a file with all the editing complete.

So what LR does in this situation is say OK you are using an old version of ACR, give the user a choice, allow them to have ACR render the image anyway, and chance losing edits made with new functionality. Or have LR render the image itself, create the file, and then open the file in PS. It is this second option that I would usually recommend, since you know that what you get in PS will match what you had in LR. In this scenario LR imports the file to the catalogue when it creates it, before passing it to PS. Depending on how quick your system is you will probably see LR going though the render and import stage before passing the file to PS, since it makes the new file the selected image.

Once in PS when you finish editing, you again save the image just as you did before, since you are now just working with a normal file of that type. The difference comes if you change your mind, since now when you discard the changes in PS and close the image, you still have the file. So you will have to go back to LR, change to the folder view, if you are say viewing the image in a collection, and then delete the file from both LR and the filesystem.

Although this sounds convoluted it is not bad in practice, since you have a remember this/don't show again option in the "error dialogue" so that you can set the default option for all future edit in PS calls. Other than the changing your mind situation, the time at which the file is created seems to be of very little importance, and usually one is working with older versions of PS with newer LR, and not the other way around.

Alan