Can filters ruin the quality of an image?

I just bought the 70-200L f/4. I added a polarizer just the other day. I shot some cars this afternoon (first shoot with the polarizer on) and the picture quality seems about as good as my cheapest lens. Can this mean I bought a bad filter? Its a COKIN circular polarizer 67mm

You'll lose some lens speed with a CP filter, and you might kill some of the highlights. Whether or not it is the problem with your photos is hard to say. I use a CP only when I need a CP. Otherwise, I use UV or daylight filter, and only for lens protection.

well, I heard that the cokin polarizers are'nt good. but thats only what I heard. Have you tried a normal "screw on" CP?

Peter

Yeah, its a screw in type. I only use it to remove the glare of the windscreen and reduce reflections in the car's paintwork. I was shooting at about 1/40 - 1/60 handheld with the ISO right down to 100 on a very diffused overcast day. I seemed to have lost all detail. I would have liked to post an image, but I was so upset that I deleted them all first.

I use a Jessops own screw in CP filter, its pretty good quality, got some nice results from it!

I would say " I was shooting at about 1/40 - 1/60 handheld with the ISO right down to 100 on a very diffused overcast day." would have more to do with it than anything else.

Shooting handheld at aht speed, yeah, I would say you'd lose some details, you'd probably need a faster shutter to really get some good details.

I mainly use a CP for bringing out the blues in the sky and such like, makes it look a lot deeper and warmer!

John_T wrote:
I would say " I was shooting at about 1/40 - 1/60 handheld with the ISO right down to 100 on a very diffused overcast day." would have more to do with it than anything else.

What he said, thats much too slow for that lens.

I have circular polarizers that cost more than many lenses. Good 77mm filters are not cheap. Hopefully you will have multiple lenses that you can use them on.

Thanks for all your advice, I really do appreciate it. I think you maybe right about the speed. I always thought that overcast conditions were ideal for shooting cars. Am I terribly mistaken?

No, I don't believe you are mistaken. It's the CP that's the problem. It requires you to use the slower speed. Besides, on an overcast day I don't think you need it much. Simply removing it would give you maybe 2 stops. Then there's ISO100. You could easily use ISO200-400 to allow for another stop or two. That should bring your shutter speed up to around 1/180.

These were made outdoors on a bright hazy day at around 1/100s @ f2.8 and no filters. I worked more with angles that gave reflections I wanted and avoided blow outs.

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OK, there are probably two factors at work here;

1. (as has been mentioned) you probably needed to use a higher shutter speed unless you have very steady hands. Remember the old rule that the shutter speed for hand holding should be (as a minimum) the inverse of the focal length and don't forget the crop/multiplier factor. So for 70mm you need @ 1/100th or faster and for 200mm you need 1/320th or faster.

2. Quality of the polariser. There is absolutley no point in putting a cheap polariser (or indeed any other kind of filter) on a good lens. If you do that, you may as well have just bought cheap glass in the first place.

As to the other points, I don't think that overcast is necessarily better for car photography. Even lighting is the key.

Polarisers are wonderful devices for car photography. Used properly they can turn the glass transparent and minimise unwanted reflections allowing you to see the detail of the cars. Stick one on the front of the lens and then twiddle away until you get a result you are pleased with through the viewfinder. KennyG did a great example post on this subject a few months ago.

For some examples of my own http://2004.ukmotorspo​rtpics.com/c215223_1.h​tml all of those static car shots on the first page were taken in awkward early morning light using an EF 17-40mm f/4.0L and a Hoya 77mm Super HMC-Pro1 Circular Polariser. Whilst by no means perfect, I wouldn't have got them without the polariser.

Oh man, I thought I just had this figured out. I thought the crop factor only meant to show what equivalent frame filled picture and that the image is actually the same, except since the sensor is smaller then 35mm film that only a "cropped" part of the image coming through is recorded. In another thread I thought it was explained to me this way and therefore the DOF calculations are not with the added crop factor but of what the lens actually is. Wouldn't this be true for the inverse focal length rule as well? I mean it's the same image and distance coming through the lens as it would on a 35mm format, just cropped. I would like to know, I'm not saying your wrong since I don't know for sure.

No, I think you still have it figured right. The inverse focal length rule really relates to the Field of View which of course narrows with longer focal lengths. The narrower the Field of View, the more apparent vibration from hand holding becomes. The crop factor has the effect of narrowing the field of view so it needs to be taken into account in the calculation.