Drop In Filters (1 Viewer)

First Thanks to those of you that replied to my previous thread
"Upgrade from 350 & 100-400 "

This question is about drop in filters

I see that Canon's prime lens of longer focal length and larger physical size use a drop in filter.
I am used to using a UV or Skylight filter on the front of the lens to protect it from accidental damage.
I don't use any other filters perfering to use photoshop.

What is the idea behind the drop in filter?

I presume it is smaller diameter and therefore cheaper to produce / purchase ?

Is it used as well as or instead of a filter on the front? if instead off is it "just" a case of take extra care not to damage the front of the lens?

My main lens has a drop in filter, to be honest in two years using the lens I've never thought about changing it. I think you are right the drop ins mean you can use smaller, cheaper filters, but in the digital age far few people actually use them.

I don't use filters on the front of any of my long lenses, as in my experience they degragde image quality. I rely on lens hoods and being careful to keep my front elements safe.

THE very front element is just hi quality glass on the long primes and act's as a protection so the main glass wont get damaged.
Rob.

I must admit I had never dreamed of not placing a filter infront of my lens until

1. I realalised I would have to if I purchased a lens with the drop in system
2. I read on this forum about the IQ loss of a filter on the front that is contained in several threads.

I am extremely happy with my 1-400 but it is slow to focus (especially on moving objects) is this because it has a filter or it?
I thought it was a combo of the fact that the 350D is slow to focus and so is a zoom lens rather than a faster prime lens.

I am not always as pleased as I could be with the focused image. (Photoshop can work wonders but a sharp image to start is so much better)