The effects of a circular polarizing filter on a superzoom lens

Note that this testing was not performed on a Canon lens, but I wanted to reach as many viewers as possible:

I'd been recently caught off guard by the lack of sharpness on the long end of my 16-300mm VC lens so I performed a brief test with and without my frequently used 67mm circular polarizing filter. The drop off in sharpness is completely the fault of the filter. At 16mm with my polarizing filter mounted I do get a very sharp image, but at 300mm with the polarizing filter the photos become very hazy. There is no noticeable loss of sharpness from wide to telephoto end without the filter.

The filter in question is a recently purchased Zomei 67mm slim CPL

*Note that none of these photos are intended to be flattering shots, these are uncorrected jpegs in harsh backlighting.


High-resolution results also available on my Flickr page here - https://www.flickr.com …davidraymond/16​387785435/

Well, that is just about the cheapest CPL I've ever seen, so I'm not at all surprised that the image suffers.

tandemhearts wrote in post #17403888
Well, that is just about the cheapest CPL I've ever seen, so I'm not at all surprised that the image suffers.

Yep, it's a cheapie. Interesting that it is still sharp with the filter on the short end though.

It's throwing off the focusing system....which is why its different on the wide vs. telephoto end...focus matters more on the telephoto end.

tandemhearts wrote in post #17403888
Well, that is just about the cheapest CPL I've ever seen, so I'm not at all surprised that the image suffers.

Yep, cheap filters are a waste of time and money. Get a good one, you'll be glad you did. For my CPLs I was able to find a higher end Marumi and Hoya on ebay for relatively cheap and have been very happy with them.

Sdiver2489 wrote in post #17404115
It's throwing off the focusing system....which is why its different on the wide vs. telephoto end...focus matters more on the telephoto end.

Nope.

Camera was refocused for each individual shot, and confirmed via One Shot autofocus. My camera will not take a photo in One Shot AF Mode w/o confirmed focus. In most senses of the phrase this is not a user error....

groundloop wrote in post #17404169
Yep, cheap filters are a waste of time and money. Get a good one, you'll be glad you did. For my CPLs I was able to find a higher end Marumi and Hoya on ebay for relatively cheap and have been very happy with them.

I was using a 67mm slim Hoya, but it got micro scratches on it rapidly, not even sure what caused it.

I had not tested it at various focal lengths, but suspect it was better overall. I've never used a Marumi, but hear good things.

What you just said doesn't refute what I said...the focus system was thrown off. Unless you are manually focusing with liveview then you don't know if its affecting purely the optics or the focus system. Until you do that it could be either cause.

Sdiver2489 wrote in post #17404349
What you just said doesn't refute what I said...the focus system was thrown off. Unless you are manually focusing with liveview then you don't know if its affecting purely the optics or the focus system. Until you do that it could be either cause.

I have similar results from manually focused photos taken at 300mm w/ the filter.

Ok, then you are good...but there have been plenty of examples here of filters causing the focusing system to not accurately hit focus even with confirmation.

Sdiver2489 wrote in post #17404397
Ok, then you are good...but there have been plenty of examples here of filters causing the focusing system to not accurately hit focus even with confirmation.

I've questioned that before too. Had similar problems with Promaster Vari-ND filters. Turns out, it is literally impossible to get a detailed photo through them. Too much degradation through their glass.