need a hoya polarizing filter explanation

Discussion in 'Photography Beginners' Forum' started by htomas, Jul 22, 2009.

  1. htomas

    htomas TPF Noob!

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    Dear photographers,

    I consider myself as a rather newbie in the dslr photography, so I am sorry in advance for some meaningless questions coming from my side.

    I would like to buy the fastest possible (in terms of light transmission) 82mm Hoya circular polarizer for my f2.8 sigma lens, such that I could keep this filter fixed during the most (if not all) shooting situations. But after some research I left quite perplexed with several things - and I hope that you guys might explain them to me.

    1a) on the hoya website

    HOYA FILTERS - The Difference is Clear

    an 82mm S-HMC circular polarizing filter is advertized. As I understood from the hoya website, a SHMC means a 99.7% average light transmission, which would be a perfect (fastest) circ. pol. filter for me. But I have never (ever) found this filter on any of the internet shops (unlike SHMC UVs, which are plentiful).

    1b) So I wrote to one of the hoya resellers to ask for this filter and they told me that the fastest available Hoya circ. polarizer is HD (heavy-duty), which, according to them, transmits 99,35% of light.

    My first question is then - what is actually available on the market from the higher-end of hoya circ. pol. filters? And which of them is the fastest in terms of the average light transmission?

    And my second question is really a newbie one (in case the previous one wasn't):

    2) When I read a 99.35% of the light transmittance, I understand that almost all light - and certainly more than half of it - will go through the filter into the lens and camera sensor. I was then surprised, when I read on this website

    Hoya HD Polarizers
    [FONT=Helvetica, Arial, sans-serif]
    that a HD polarizer stops more than a half of the coming light:

    > Light loss (filter factor), HD Polarizer: 1-1/6 stops (2.2x).

    Could you please explain me what do I understand wrong? How can a 99.35% light transmission end to a more than a 1-stop loss?

    Thank you all for any comments, hints, or links, I am in a process of learning and be happy for every explanation!
    Regards,
    Tomas
    [/FONT]
     
    Last edited: Jul 22, 2009
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Welcome to the forum.

    Those are certainly questions that I would not consider to be on the 'newbie' side. I don't think I've ever heard anyone ask about it before.

    My personal thoughts are that you shouldn't use a CP filter on your lens at all times. As far as I know, they do block up to a stop & a half of light, so if you are concerned about speed, you will want to keep it off when you are not specifically using it.
     
  3. htomas

    htomas TPF Noob!

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    Big Mike many thanks for welcoming me and the fast reply. So there is indeed a general substantial light reduction from the CP to lens.

    I looked again into Hoya website and what they state is that the coating "reduces light reflections off the filter surface to an average of 0.3%" (for SHMC types). So then the "99.7% light transmission" would actually mean the remaining fraction of light passed between the outer coatings onto the filters' polarizing glass (and not between the filter and lens as I thought previously).
    Then, of course, the polarizing glass transmits only a (perpendicularly) polarized light, while absorbing the rest. This absorbed light would then most probably account for the resulting stop-down.
    But even then, the amount of blocked light would vary depending on the shooting conditions (metallic surfaces reflecting the light, sunny/cloudy day, etc.) and not be a fixed value.
    But all this may well go bananas, as I really have no idea if this was close to reality.

    Anyway, it seems that the difference between SHMC and HD (in case of Hoya) can not be (that much) due to the light transmission and that both types will stop-down the lens.
     
  4. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    You're dealing in the realm of physics, and not photography; I suspect that the answers to your questions will need to come from someone with initials after his (or her) name. Certainly they're beyond my rudimentary understanding of light transmission, BUT if you want a CPOL which blocks less light, than that's easy. Spend more money. B+W, Singh-Ray and Heliopan CPOLs can reduce the light by as little as a single stop.
     
  5. KmH

    KmH Helping photographers learn to fish Supporting Member

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    No 1 to 1.5 stops is not "a general substantial light reduction."
    Any filter will reduce the light to some extent. There are situations it's prudent to use ND (Neutral Density) filters that reduce the amount of light by 3 or more stops.

    Don't get to hung up on all the little technical details unless you have an abiding interest in the light transmission properties of glass and glass coatings......

    Otherwise, slap one of those polarizing suckers on your lens, go take some pictures and look at the results. Re-load, adjust, and fire again if necessary.
     
  6. htomas

    htomas TPF Noob!

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    Thanks guys for the comments. I only wanted to understand the numbers and differences between some of the hoya filters - there are so many types. I have a large lens (82mm) so many of the CP filters are quite expensive (well, at least for me), so I wanted to know what I am buying (without any prior experience with CP filters whatsoever).
    The reason why I started with all that light transmission thingy was that at the beginning I thought I could replace my UV filter that I use always on the lens, by some fast CP filter that can be mounted always as well (including indoors) and thus serve as a lens protection at the same time. But now I see that this is not the case and it probably wasn't a good idea anyway.

    I think I will go for the Hoya HD CPOL that I can get on ebay for $140. It blocks the light only by 1 and 1/6 of a stop, which now I think is a fast option (after tirediron's comments). Anyone has any experience with this filter on sigma lens?
     

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