A question I often hear or read is “should I create one to one previews when I import my images?” And as with so many questions relating to a personal workflow, the answer is… it depends.
What is a one to one (1:1) preview?
When you zoom in to any image to see it at 100% of its size, Lightroom creates a preview image that is full resolution or one to one. If its the first time you are viewing that image you will no doubt have noted the “loading…” icon appear. How long it appears for will depend on the resolution of your image and the power of you machine.
If you’re impatient, this can be frustrating. If you’re not impatient then the answer to the question is probably no.
Where are they stored?
The previews that Lightroom creates are stored in a single file, the Previews.lrcat file. The exact name will depend on the name of your catalog and the size will depend on the number of images in your catalog. But after a short amount of time using Lightroom it will go into the Gigabyte range.
By default you will find the Previews file in the same folder as the catalog. Thats where it should stay. You can of course delete the previews file safely if you need to recover some space on your hard drive but bear in mind the next time you open Lightroom it will be forced to rebuild the previews, albeit not necessarily the 1:1 versions.
Can I delete the previews?
Yes you can. The most immediate way is to delete the Previews.lrdata file but thats rather drastic. Instead, those who ask this are asking if they can delete the 1:1 previews as those will be the largest files stored within the Previews.lrdata file. To do this use the menu item Library > Previews > Discard 1:1 Previews… You can choose to discard one or all.
Lightroom can also delete the 1:1 previews automatically.
This is a useful means of keeping the Previews.lrdata file manageable. You can change it from the default of 30 days to as soon as one day for those who have a high volume workflow but rarely revisit the same file.
Why should I keep them?
Basically it comes down to speed. If you keep the 1:1 previews then you never have to wait for Lightroom to build one each time you zoom in to an image to see or work on detail.
So, should I create them when I import or not?
Now that we understand a little more about what a 1:1 previews is, where it is stored and how that affects our storage needs we are better equipped to answer the original question. But it still depends on your workflow. Sorry, not a one size fits all here.
Note that if you choose to render 1:1 previews at the time of import, your importing session will take MUCH longer. If you have just one card to import, go ahead, knock yourself out. Be prepared to do something else while the import takes place.
If you have several cards to import I recommend you don’t render on import but simply get the images off the cards as soon as you can, choosing the minimal setting, then, in Lightroom you can select them all and choose the menu item Library > Previews > Render 1:1 Previews. This will take some time so maybe go have dinner.
Ultimately it comes down to how much drive space you have and when do you want to spend the time creating the previews.
The defaults are to render 1:1 previews only when you zoom in to 100% and to delete those previews after 30 days.