I use an iMac at home - currently with Aperture for RAW editing. However, I travel frequently and have a PC laptop for that. SO I am thinking of moving to LR4 and install it on both machines.
However, How easy is it to do editing on the laptop while I am travelling and then to merge these edits / RAW files onto my primary system at home?
It can be done but you need to have a very controlled workflow and stick to it meticulously.
Lr stores everything done to photos in its data base, called the "catalog". Without this catalog Lr on computer A "knows" nothing of your edits done on computer "B".
So you need to make sure that when you switch computers and want to continue working that the other computer has access to the latest version of the catalog.
This can be done by
a) copying the catalog to an external hard drive (or an USB stick) before switching computers and then connecting this hard drive (or USB stick) with the second computer.
b) having the catalog on a dedicated external hard drive that is connected to your computers alternatively, so that Lr reads and writes to and from this onecatalog. The disadvantage of this method is that the connection to external hard drives is may be slow which would slow Lr down. Remember that Lr constantly reads and writes to and from the catalog.
In version a) the catalog would be on internal drives of each computer.
Alternatively: You can have Lr write (metadata) changes to file. For Raw files the metadata will be written into an xmp sidecar file. For other files (JPG, TIFF, PSD, DNG) the metadata will be written into (the header of) the original files. By saving to file your edits done on computer A would be available on the computer B even if this computer did not have access to the latest version of the catalog. BUT there is a trade off with the saving-to-file method. Certain things done in Lr (Collections, Virtual Copies, Stacking) are only stored in the catalog and not saved to file. These things would be accessible for computer B only via the latest version of the catalog.
This can be done very easily with the help of synchronizing/backup software. I use SmartSync Pro (at $50 or so) to keep my work and home computers fully synchronized at all times, so that I can work from either one without missing a step.
You also need an external drive that will hold copies of all the folders you want to keep synchronized, as well as the Lightroom catalog.
The software copies new or modified files from machine A to the external - including a copy of the catalog. Then you bring the external with you, and on machine B, you do the reverse. This can be set up as a one-click operation and is very quickly done because it only copies new stuff, the rest just sits there.
This way you have very solid backup, and the working catalog is on the machine, not a slow external. In fact it doesn't really matter if the external is slow, once you have copied everything over. I use a 1 TB 2,5" drive that I simply slip into a pocket.
There's just one little gotcha: For this to work with the Lr catalog the drive letters and names have to be the same on the two machines - naturally, since this is used to reference the images in the catalog. But the external is just for transport so it doesn't matter there.
So I've no idea if this could work between Mac - Win. But on my two Windows machines it works perfectly.
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