Jared Sinclair gives iOS developers a quick course in Photoshop.
Beware the following caveat: this is an article about tools, not design. If this were an article about ice sculpture, it would teach you how to turn on the chainsaw. It’s up to you to sculpt an angel without losing a limb.
I like the way he hammers this statement. Made me chuckle.
Some designers do all their mockups at non-retina scale and then scale up to retina for final processing. I prefer the opposite.
Any other way just doesn’t make sense to me.
There is also a quick sample project for all your devs to attempt.