Just to add some tips to the above list:
When you first get your Camera make sure it is equipped at all times. Pressing RB will take you back to the previous weapon you used.
Equip Tonics to increase your score. Tonics stack so Equipping Photographers Eye 1 & 2 giving a total bonus of 25%.
Which = you completing this achievement 25% quicker. (Remember to unequip when earned)
The quality is determined by a number of factors: How centered the camera is on the enemy, proximity to the player, whether enemy is in combat or not (if they are, the player gets an "Action Shot" bonus) and whether there are multiple enemies in the frame or not ("Multiple Subjects" bonus).You can zoom the Camera simply by pressing down
Some enemies will not appear in later levels so backtracking maybe needed.
If you have not got Rosie by the time you reach Fort Frolic then dont worry you will encounter her in the later levels. Nitro Splicers become less frequent after you leave Neptune's Bounty although there is the occassional one in later levels
When photographing machinery eg Bots/Turrets make sure you take a picture before you hack as friendly pics dont count. However if an enemy triggers your hacked security camera then you can take pictures of those security bots.
If you accidentally kill an enemy you are allowed to take one picture of its corpse (maybe more on lower difficulties)
A great tactic is to shoot an enemy with an electric bolt then run up close and get a pic. You should get an A rating every time.
If by the final boss this has not popped then you will need to backtrack. It is likely that you will need Rosie or Little Sister particularly if you have not found them all.
This achievement will pop as soon as you 100% research all items. You do not have to wait until the end of the game.
Researching Enemies gives some fantastic bonuses and if playing on hard is a must. So dont think of this as a chore, it really helps with the gameplay.
Hope these tips help