Stacking UV, Cir Pol filters

I keep a UV filter on my lens at all times, mainly for protection

(as I'm sure many of us do). I want to start experimenting with a

circular polarizer. Can I screw one on top of the other, or should

I remove the UV first for best results?

For best results you should remove the UV. There are two things to consider, first you have an extra piece of glass with two surfaces in your optical system, even if these two surfaces are coated with good anti-reflection coating they WILL transmit less light than no glass at all (physical fact) thus increasing stray light and the possibility of flare (plus extra surfaces for dust, dirt and grease to stick).

 

Second, when stacking filters you might find that the filter threads are visible and vignette. They might not be much visible for this effect to take place. How many filters you can stack depends upon which lens and how large the filters thread are.

Of course, Peter, you can srew as many filters on top of one lens as will hold. Guiness book of records, anyone? Any idea how many that will be? 20, 50, 1000?

 

That apparently is not your question, right?

 

So: for photographic best results: no more than 1 filter. For really knowledgable people, maybe two in tuff situations, such as 2 NDs for 1600 film on the beach or for special effects etc.

Hoya makes a UV/Circularpolarizer combo. I think B&W may as well not cheap in either case.

Ignore the foregoing, here's the bottom line: if you use a B+W MRC "Multi Resistant Coating" UV filter you can forget about any negative effect of the UV filter including ghosting or flare. Therefore putting a C-POL or any other filter on top of it is the same as if the UV wasn't there, so the only issue remaining is whether the added thickness will cause vignetting in the corners. This is most likely with wider lenses and zooms.

Peter,

 

for _best_ results you should still remove the UV prior to attaching the polarizer. Jay is correct in that sense that using a good quality filter the effect will be minimal, but it will still be there. And don't pay attention to the specific brand name of the coating. B+W calls its prime coating MRC and Hoya Super HMC or S-HMC, pay more attention to the transmittance of the coating (should be around 99.5% for a really good coating). Depending upon what requirements you have, you might prefer to leave it on or remove it. In your original post you said best results though...

 

With good coating only about 0.3-0.5% of the light will be reflected. This is a lot better than the 4-9% uncoated glass will reflect, but still it won't transmit 100% of the light. And you have another (previously) exposed glass surface with dust and possible grease, so again, for best results, remove the UV.

 

If you aren't _that_ concerned with flare, keep it on, by all means, as long as it doesn't vignette. Personally I always remove the protective UV when attaching another filter. But I also make sure that my front glass is protected from direct rays of light to prevent flare (using a hood or a large piece of cardboard to shield/shade the lens). One does not exclude the other.

The UV filter is redundant.

Alex,

 

Do you mean that the POl filter cuts out UV light?

On my 70-200 IS, I can stack a UV, CIR POL, and 81B with no ill effects or vignetting. Though the light loss is 4 stops, which gives me shutter speeds of 1/60 - 1/100 in the daytime with Reala and adequate DOF. Though an optically clear piece of glass will reduce the light transmitted, this is hardly a concern with TTL metering.

A couple of different perspectives on this. The first is that with a

decent polariser in place the UV isn't performing any useful

function therefore why leave it on?

 

The second is more general. The people who say you can't have

more than one filter on a lens don't know what they're talking

about and are just repeating oft-stated claptrap rather than real

experience. So long as you know that you're not causing

vignetting , and check in the viewfinder carefully for flare , there's

no reason at all why you shouldn't use a polariser and warm-up.

a polariser and grad ND or whatever together. Just make sure

the filters are clean and are of respectable quality - they don't

have to be the best money can buy.

The polarizer isn't intended to filter UV, so stacking the two isn't redundant.

<P>

But filter stacking is still ill-advised. Which is why warming polarizers and UV polarizers are made.

<P>

The very best coated filter STILL has two glass/air interfaces; and worse, you're combining that with two more; and putting two of those interfaces in very close proximity, and parallel.

<P>IF you have no strong light sources entering your lens hood (You are using one, right?) the detrimental effects can be expected to be negligible; but if you do have a light source entering the lens, it can be expected to give you the 'hall of mirrors' effect as it reflects back and forth in the air gap between your two filters.

<P>Of course, if you're taking a picture, that means you've got light entering your lens; so this effect is going to be unavoidable. As noted however, unless it's a strong light source, it probably won't cause that much of a problem.

<P>As others have noted, I likewise always remove my UV filter when using a polarizer.

The polariers that I have definitely cut UV light. Additionally as much of the UV light which we encounter is polarized, rotation to darken the skies will block UV even more. To see what I mean, take photos of the high altitude mountainous sky with no filter, a UV filter only, a CP only, and with both. Aiming at the north sky should give the most UV. While this is best done with either ortho, or non-color-sensitized B&W film, any film should show the effect of UV blocking. You can get 35mm film which has its strongest sensitivity in the UV (like 103-O emulsion), though it really isn't needed.

 

But don't take my word for it. Try it. (That's what I did many years ago with Kodak Spectrum Analysis #1 that has almost no sensitivity outside the UV. I respooled it to fit my Leica.)

I have UV filters for all my lenses but ordinarily I remove them unless I am afraid I will miss the decisive moment in which case I at least have a picture that I would not have had i taken the time to remove the filter. <p> A properly used polarizer will filter as much, or more, of the UV than a UV or skylight filter, thus the UV filter is redundant if the Polarizer is in use. Any glass, depending upn its refractive index, will refract to a greater or lesser degree, any light rays that enter the surface at any but a perpendicular angle, therfore several layers of glass, irrespective of their reflective coatings (or lack thereof) will accumulate slight angles of refraction depending upon the number of glass to air surfaces. Thus it would stand to reason that stacking of filters cannot improve and may degrade the quality of light entering the lens. <p> The foregoing is my considered opinion predicated on my understanding of basic physics, and represents no presumption of authority other than the force of reason. Dissentions therefrom, based upon commonlogic are therefore welcomed and encouraged.

Screw the polarizer on top of the UV and check for vignetting, for instance by shooting a blue sky at the widest setting (if a zoom). If there is no vignetting, and both filters are good quality (multicoated), then I say stack 'em and save yourself the hassle of having to remove and reinstall the UV filter every time you want to use the polarizer.