Polarizer Vampires!

[Craig Markham]

I have been puzzled at the slow speeds, wide apertures and high ISO’s I’ve needed with my 500mm f/4.0. And I have been having a hard time stopping action and eliminating excessive evidence of microvibration in my rig. At last the mystery is solved! The other day, someone mentioned in passing that using a polarizing filter causes a 2 f-stop loss [more or less, depending on the effects of polarization in a given situation]. I have known this for years, since I bought my first polarizing filter. However…

While I was photographing chickadees off my back deck today, and having the usual frustrations with low Oregon winter light and a slow lens, it suddenly hit me: that fancy $200 Canon drop-in polarizing filter has been living in my 500mm since I bought it, stealing 2 f-stops of light from every one of the thousands of images I have made with this lens for the past 2 years! Duh! Believe me, I whipped that p-filter out of the slot and replaced it with the original haze filter in the blink of an eye. I confirmed that the filter was indeed taking 2 stops by simply taking a reading and then pulling out the filter for a comparison reading.

So let my hard lesson be a reminder to any of you that may be forgetful about your own p-filters: They are specialized accessories intended for specific situations where polarization is beneficial. They should not be left on the lens for general purpose photography unless you have so much light that you want a couple of stops of neutral density filtration.

That drop-in filter is especially easy to forget, since it’s out of sight. But just because it cost you an arm and a leg doesn’t mean it deserves to cause a lens that cost 25 times as much to underperform 90% of the time. Not only do you needlessly lose light, it is likely it also slows AF acquisition by your camera. With a polarizer, your camera only sees f/8 light when your lens aperture is f/4. I cringe at the number of otherwise good images I have made that were compromised by this one simple-to-fix, no-brainer oversight. I finally found the wooden stake!

Viola! More light at last!

[Mike Tracy]

Since you have gotten more use out of it then you ever bargained for do you want to sell it ?

[Alfred Forns]

Craig there is one other point to consider regarding drop in filters.

The one in the lens "needs" to be cleaned periodically I have seen some that are right down filthy !!

[Craig Markham]

Since you have gotten more use out of it then you ever bargained for do you want to sell it ?

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Mike, at this point it has probably cost me more in optimal images than I paid for it. So I have some work to do with it for redemption. On the upside, this should help me stay more vigilant in being aware of conditions under which it would be useful. I do like it sometimes when working at right angles to the sun to tone down the brightness of the sky, cut glare, or dramatize background clouds, among other things. So it's not for sale, sorry.
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Al, thank you for the reminder about periodic filter cleaning. That little space in the drop-in slot does "breathe" and can collect condensation and dust.

[Ed Cordes]

Craig there is one other point to consider regarding drop in filters.

The one in the lens "needs" to be cleaned periodically I have seen some that are right down filthy !!

Alfred - Thanks for the reminder! I haven't cleaned mine since returning from FL!!!

[Sabyasachi Patra]

Alfred,
Thanks for the reminder. I have to check it. I had last checked I think a couple of months back, when I had used the polariser. In our dusty forests, I think twice before I put the polariser.

Craig,
Yours is an extreme example. I wish you had accidentally touched the polariser thread and roatated it, so that you would have known. The good thing is you could discover it now. Just imagine, you could have taken many more years to discover this as well. It is better that you atleast discovered it.