Originally Posted by
Colin Southern
Generally anything you CAN do in ACR you SHOULD do in ACR. The main reason is that whilst you're in ACR you're still in linear gamma so all the data is still intact. Once you pass the image through to Photoshop you're in gamma 2.2, so tonal ranges have then been compressed and stretched (ie a lot of information has been thrown away). Once you get into Photoshop "proper" you can still adjust tonal ranges, but it's best practice to only make small tonal range adjustments; if big ones are needed then they should have been done in ACR.
What many folks don't realise is that ACR tailors the single conversion no matter how many things you tweak, eg some folks worry that adjusting too many things will have a cumulative effect on image degradation in ACR, but it doesn't. It's a bit like taking 10 steps forward, 7 steps back, 2 more back, then 14 forward followed by 9 back - when the image has been converted in ACR you haven't taken 42 steps; ACR works it all out an only makes a single adjustment of "6 steps forward" Once you get into Photoshop "proper" then edits to a single layer are all counted as "individual steps". Hope that made sense.