[CMG]

I use Marumi SHG Protective filters on my lenses for, you guessed it, protection. I haven't noticed a difference in the rendering, that's not a conclusion about the effect of the filter rather just a statement of what I see. Many say it is a good idea to use a protective filter particularly on high end lenses like FA ltds and DA ltds, some say use them on all lenses, some say never ever use them. OK, this debate is ongoing and will likely go on forever. But here is where I'm confused, lots of people shoot with CPL and ND filters. Now, I realize that these and other such filters are used to achieve a certain specific compositional objectives whereas the protective filters are not, unless you consider a pristine front element ato be compositional objective and it may well be. So, if the argument goes that using a filter such as the Marumi will negatively impact the lens IQ and cause an inferior rendering, shouldn't the same argument hold true for CPL and ND and other filters? It seems to me that the argument against a protective filter can be distilled down to the idea that no additional glass should be placed in front of the front element because it degrades the IQ of the lens. So how do we reconcile this with the use of "compositional" filters. Do you concede the loss of IQ in order to gain the effect of the filter? Even if you answer yes, you still must address the IQ degradation issue. I read some very passionate pleas in opposition to protective filters of any quality (and I agree, you should get a good filter which does not necessarily mean it must cost 1/2 as much as the lens), but never in opposition to any other kinds of filters. Thoughts?

[Docrwm]

They do degrade the image quality but the impact the image positively in a predictable and desirable way too. It is a tradeoff and there are times when the benefits from a CPL or ND outweigh the negatives. There are no visual pluses on dSLRs for UV or Protective filters other than their physical protection (which as you stated are debatable) of the lens.

[jatrax]

Any additional glass in front of the lens degrades the IQ to some degree. Whether that is detectable by you in any given image depends on a lot of factors, including the quality of the filter and the angle of the lighting.

CPL and ND filters provide a modification of the image that is difficult or impossible to achieve without the filter. So when you need those effects you use the filter and accept that the image quality will be somewhat less than without the filter. But since you could not achieve the desired effect without the filter then the image quality loss is immaterial.

[Docrwm]

Going back to this issue because I just bought two Marumi CPL filters (49mm and 62mm) to help avoid the need for step-down rings (which jam occasionally).

The reason that the UV and Protective filters are the only ones that get the rants is that they are unnecessary for "getting the shot" because they add nothing to a dSLR. UV filters were necessary back in film days but not now as the sensor screens out UV itself (or has a built in filter).

All filters involve essentially the same trade-off - they ALL degrade the image quality (yes, good ones do so less - sometimes significantly less - than cheap ones but they still degrade the IQ some) but some add to the range of the camera. The UV and Protective have all the negatives but no positives from an image capture standpoint, however the ND and CPL filters, while having the negatives too, bring very distinct positives to the cameras ability to capture certain images that without those filters would not be anywhere near the same (or even possible in some cases).

Hoods.