Originally posted by Swapnil Okay so no UV filter!
What about Clear filters? I want to protect my front element from dust and in drizzle.
How much I am sacrificing in terms of photo quality if I use a filter?
Any extra layer of glass between subject and frame reduces IQ by some small amount. As we've said, a clear or UV filter WILL protect the front element in grungy conditions -- spraying sea-salt, swirling sand, spurting blood-mud-beer, etc. Absent those situations, a hood provides more protection. When I got my DA18-250 I also ordered a clear filter -- big waste of money, I never ever use it. I should sell that sucker to some clueless newb, er I mean to an anxious novice.
How much IQ loss? That depends. If the light is behind you, then not much. If direct light reflects off a non-MC filter, then a lot. How much does a filter protect? From dust, almost nothing. From drizzle, almost nothing if you have a hood and don't aim the lens upward. From blown abrasive-corrosive gunk I mentioned above? Considerable!
But big hi-quality 'protective' filters are also rather costly. Sure, it's better to waste a US$50-$75 filter than a US$450 lens. But waste a few of those filters, and you're up in new-lens territory, cost-wise. Better to avoid glass-wastage situations in the first place IMHO.
My recommendation: If you plan to be in glass-hazardous scenarios, get some cheap manual 80-200mm zooms for ~US$15 each and waste THOSE instead. If you gotta take your 18-250 into danger, then buy my filter. Otherwise, depend on a hood and your caution.
EDIT: Here is a situation that calls for more than just a hood: