Is always good to have a curious mind, because it keeps you young :bsmilie:
It depends on situation and location. If you are shooting indoor, it is okay to shoot without filter.
The picture quality difference is almost non visible if you use a good filter.
If shooting outdoor, especially in a dusty environment, a filter will keep your front element clean, so you do not need
to clean it. It is best to avoid cleaning the front element, some people will say it will damage your lens coating. My own opinion is
the coating will not be so easily damage, if you use the proper method and be careful.
Only, one kind of shoot, I will confirm remove my lens filter. That is shooting sunrise or sunset direct.
Removing the filter may help to reduce the flare. But again is subjective. Some people love the flare and it makes the picture more interesting.
back in film days, as a stupid student, i followed what people were recommending - putting filter.
Back a few years ago, i found that the filter creates softness, lack of sharpness, increase chances of flare on your pictures, etc, etc. With the talk about filter protecting the lens, i have never experienced it in 20-30 years of photography.
Now, i rather not put a filter on than to reduce the sharpness of lens
The older long telephoto Canon L lenses have a built-in protective meniscus glass on the front.
The front lens element is behind this built-in protective meniscus glass. That explains why those old long telephoto lenses have no filter thread at the front. A drop-in filter holder for smaller filters is situated at the back of the lens.
Recently, Canon has not included this built-in protective glass on the front. Perhaps due to cost cutting exercise.
Of course, Canon will say the reason is to make a lighter lens.
They won't claim that without the front meniscus, the lens is sharper - because that would imply their old lenses are not sharp.
If your purpose is to protect the lens from damaged, then put on a hood! Some people use filter to protect their lens in corrosive environment, such as salt spray, dusty place etc. FYI, filter will degrade the image quality, unless u die die have a good reason to put it on.
For those who were offended by my post, sincere apologies. For those who posted your views, a big thank you!
Confirms what I intend to do...take off the filter from my telephoto lens.
I declined purchasing a filter when I got the Sigma 35/1.4, used it without filter for the past 3-4 months, truly amazed by the IQ. Starting to have the opinion that NC/UV protective filters may degrade IQ or cause some color cast. That's the reason I started this thread to understand the general practice out there.