A crit cap or crit-factor cap is the point at which having any more crit factor is a detriment to your DPS potential. That part is pretty straight forward. The rest of the post will explain how the crit cap works, what influences the specific numbers, and how you can achieve a specific crit factor number at different stages of your gameplay.
How Your DPS is Affected By Your Crit Factor
Non Critical versus Critical Skill Damage
Your skills have a non critical skill damage amount, say 1000, and critical damage amount. The critical damage amount is based on your non critical damage times your crit power. If your crit power is 2.0 then your critical skill damage is 2000. If your crit power is 2.84 then your critical skill damage is 2840.
How Crit Factor Impacts The Percent of Hits That Crit
Whether or not your skill crits is random based on a formula that causes a percentage of your skill hits to crit. To keep things simple, if your chance is 100% then all your hits will crit. If the chance is 50% then only half your skills will hit. If you only hit 2 times, there's a chance that neither of those 2 hits will crit. At a 50% crit rate, if you hit 240 times in a fight, then roughly 120 of those hits will crit.
What Crit Caps Actually Mean
Your total damage will be affected by how much your individual skills do in damage, and that is dependent on how often they crit. The "crit cap" is the point at which your crit factor is high enough that a given skill with crit 100% of the time. Your class crit cap is the point at which you get key skills to crit enough to maximize your damage. In some cases, the key skills may not be able to reach 100% and you have to settle for something lower that gives you a decent crit rate in exchange for flat damage.
What Do You Do After You Reach The Crit Cap?
Build your power stat. You usually have to give up 1 power for every 2 points of crit factor (roughly) when you are picking between two versions of the same accessories, buffs, and etchings. Once you have enough crit factor, you can convert everything else to power, resulting in a flat damage percentage increase overall.
Given A Crit Cap Number, How Do You Reach It?
There are several methods for adding power and crit factor. You usually have to pick one or the other and the tradeoff is usually 1:2, power to crit factor.
Unless your class uses attack speed crystals, you can add up to 12 power or 24 crit factor with Powerful and Keen Vyrsks.
Accessories - Rings, Earrings, Necklace
These comes in pumped and carving versions. The stats on both are the same except for either increasing Power or Crit Factor. If you need to change from carving to pumped or vice versa, you can use an accessory morpher from a general merchant. This will let you change the type without losing any etchings or item xp. Note that at higher tiers, these accesories will give you high amounts of power and crit factor. This is why players with Best in Slot accessories don't need as many carving pieces to reach the crit cap. Note that on the necklace, don't try to get extra crit factor with the extra selectable line. It isn't a 1:2 tradeoff for power so you're better off just taking the power line.
Accessories - Circlet
There's only one version of the circlet but you can pick 4 power or 8 crit factor, which is a fair 1:2 trade.
Accessories - Halidrom and Relic
The two extra slots below your innerwear and belt are the Halidrom and Relic spots. You can equip them after level 66. They come in three tiers and they can also be upgraded by combining multiples of the same tier. The tradeoff isn't quite 1:2 but it's a decent way to bump up your crit factor and power. You can also keep a set of power and crit factor pieces to more easily adjust for your healer. More on that in the next section.
For your weapon and gloves, if you don't need to use energetics, you can choose to use a power or crit factor etching. You can also use power and crit factor etchings on all your other gear. The point impact is relatively small, but it can add up. This is more of a "I'm already best-in-slot, got a ton of gold, and nothing else to work on" kind of thing though. Read more in the etchings post.
There's power and crit factor innerwear. It comes in a few different tiers and the highest power and crit factor options are 14 and 28. If you are using new gear, the magic and physical amplification may be more useful for you, depending on your total amplification. Or maybe in general / all cases. Not sure.
The energetic mask is usually preferred unless you are using the new gear mask, in which case the appropriate amplification mask for your class is best. But there are crit factor and power buffing masks that you can use for a few points. With masks usually obtained at random from dungeon drops, this is more of a luxury to choose rather than a normal part of gearing.
Note that there's magic and physical amplification food, and this is probably preferred if you are using new gear. Otherwise, you can use a Feast or a Lamb Bulgogi to get +20 crit factor for 15 minutes. There's power food but I can't recall it at the moment and it seems to be rarely used.
This is only really for +9 crit factor from an uncommon Crayfish card. But it's more than nothing.
What Factors Influence the Crit Cap?
There are a few components to the crit factor formula as well as some typical modifiers that will come up during a fight.
Boss Level versus Your Level
The difference between the target and your level will adjust how much crit factor is needed for your skills to crit. It might be an impact on how much crit resist the boss has but the important part is the higher you are relative to the target, the lower amount of crit factor you need.
Healer and Boss and You
The healer in your party can debuff the boss and buff you. The boss debuff is a reduction in their crit resist, but only if the healer has that talent maxed out. This is the same for both priest and mystic. The buff on you is a crit factor increase and is only caused by the mystic Aura of the Merciless. This is generally conveyed as a +60 crit factor difference. This is why the crit cap with a priest party is higher than with a mystic party.
You and Your Own Skills
Depending on your class, you will have skills, glyphs, and talents that will impact your own crit factor. For example, being in Assault Stance as a warrior will increase your Crit Factor. The crit cap for your class is probably assuming that you are using your class specific buffs, but you need to check whether or not the buff is taken into consideration.
But How Does Crit Cap Actually Work?
Wouldn't you want all your skills to crit 100%? Why not just have all power and play the RNG? This last bit will try to illustrate how the difference in damage contribution, hits per minute, and crit power change how important an optimized crit factor can be.
There's going to be an interactive form here soon(tm). Gotta think about how to lay it out in a way that makes it easy to understand and manipulate.