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Hasselblad Polarizing filter

shawn

New Member
What is the differnce between Radial & Linear polarizing filters? I have 63mm Polarizing filter (Hasselblad # 50482 from my old 2000FCM), but it also seems to fit my H1 80mm (67mm). Do I HAVE to use Radial with Auto Focus lens of H1 or can I manually rotate the filter after the focussing is achived and then take & adjust exposure settings?
 

qnu

Banned
The difference between 'radial' or circular polarizers (i assume you mean those?) and linear polarizers is that circular polarizers let through lineary polarized light (just like a linear polarizer) and then give the polarization of the light let through a twist (quiet literally) so it will not behave like 'regular' polarized light.

A circular polarizer basically is a simple linear polarizer, with a retarder plate behind it.
The polarizer works just like any other linear polarizer.
The retarder plate sets the plane in which the polarized light vibrates in motion, so that instead of the waves vibrating in one plane perpendicular to the direction the light is travelling, they now 'spiral' around the direction the light is travelling.

Some systems inside cameras use light coming through the lens to determine exposure or focussing, and these may or may not be affected by the polarization of that light.
I'm sorry, but right now i don't know the answer to the question what type of polarizer the H1 needs. I'll see if i can look it up and report back.

But you of course can use a linear polarizer even if all the H1 internals need a circular.
You will just have to focus before putting on the filter, or use manual override (very easy to do with the H1).
And exposure you can determine without filter too, apply the appropriate correction (a fixed factor, usually printed on the rim of the filter), lock it, and then mount the filter.
 

shawn

New Member
Yes, I meant Circular & not Radial polarizer. The rim of Polarizer is printed with "Hasselblad/63 2xPola -1". So am I assuming right, the f stop needs to be reduced by 1? But being H1, camera should automatically compensates for the exposure. When I played with it, it looks like it is taking compensation in account, though my Firmware on H1 has not been updated. It is atleast two updates behind. thanks for thorough explanation. I appreciate it.
 

qnu

Banned
The autofocus system in the H1 does indeed need a circular polarizer to work reliably.

Yes, the compensation needed would be 1 stop.

Typically it is about that much, usually a bit more, but never less.
1 stop compensates for the filter removing approximately half of the light trying to go through. Unpolarized light isn't unpolarized, but a mixture of many 'rays', many photons, each having a distinct polarisation. About half of them are stopped.
The polymer used as polarizing material has some density (and colour) of its own, and sometimes dyes are added too to improve the colour balance.
That usually requires a bit more compensation, added to the 1 stop.

Any built-in metering system not 'spooked' by the polarizer will compensate automatically.
None of the metering systems inside Hasselblads and Hasselblad metering prisms care about polarizers, and they all show the correct reading, no matter what type of polarizer.

But alas, the type does matter to the autofocus system inside the H1.
 

lmenzin

New Member
Any metering system relying on a beam splitter (like the H1) requires a circular polarizer. Almost all modern AF and auto-metering SLR cameras use beam splitting. Our "primitive" manual cameras can get by with linear polarizers. Anyone wanting to interchange polarizers with their 35mm (and H1) SLR systems would be advised to buy circular polarizers.
 

colin

Member
Circular polarisers are always "right". Linears may not be.
Circular pols. have been necessary in "primitive" manual cameras for the past 37 years!
When I bought my Leicaflex SL back in 1968, it became necessary to use circ.pols. due to the beam splitting metering system. Sales of such filters have soared ever since.
Colin
 

qnu

Banned
Though circular polarizers are indeed "always right", they sometimes are too much so, and then just are unnecessarily expensive.

The Hasselblad H1 is the first not to cope with linear polarizers (and as far as i know, only the AF system has problems with them, not the metering system).

So i'd say the "always right" circular ones are in effect "not right" for any other Hasselblad.
(Not even for the Hasselblad cameras and prisms with metering systems that use reflecting surfaces. "Beam splitters" do not always make circular polarizers a necessity.)

But then: one could succesfully argue that the simple linear Hasselblad polarizers are more expensive than good non-Hasselblad circular polarizers...
 

simonpg

New Member
Interestingly I was buying polarisers for my Hassey and Leica kits and discovered interesting pricing differences. I nearly fell over when quoted a price on a new Hassey polariser B60!!!

I decided on B&W (MC versions preferred) and discovered that Hassey branded polarisers are made by Schneider (owns B&W) anyway. But, the B&W versions for Hassey lenses were only 20% less cost that the hugely expensive Hassey branded items.

I was told that functionally, there is little difference in performance between circular and linear polarisers; but circular will interfere with most AF systems. Is that correct?

What interested me was that there as only AU$10 price difference between circular and linear versions; and the premium MC Kaesman type (spell??) B&W version was only AU$10 more again. I've read that the foil used in the Kaesman type of polariser has the longest life and optimal optical performance. I wonder if that's true?

Finally, does anyone agree that it is not so necessary to add a lens hood when using a polariser?
 

colin

Member
If by performance one means "what they do", then there is no difference (equipment requirements aside).Circular are required for most AF systems.
The difference in cost between the Lin and the Cir. is becoming less due to the popularity of the latter. My dealer doesn't even stock the Linear type anymore.
Kaesermann filters are more durable and weather resistant...that's all.
In over 50 years of photography I have never taken a picture without a lenshood. With a glass surface close to the end of the lens body, a lenshood becomes even more important!
 

simonpg

New Member
Thanks Colin. I share your view of using lens hoods and logic made me feel that your view of adding "glass" to a lens increases the need for an effective lens hood.
 

rcyoung

New Member
> =46rom Luminous Landscape ( =20 >
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)

Circular Vs. Linear Polarizers

There are two types of polarizing filters available =97 linear or =20 circular. Linear polarizers are more effective and less expensive than =20=

circular ones. But circular polarizers are needed with just about any =20=

camera that has a through-the-lens metering system, or autofocus.

The reason for this is that both of these systems use semi-silvered =20 mirrors to siphon off some of the light coming though the lens. If that =20=

light is linearly polarized it renders either the metering or the =20 autofocus ineffective. This means that you're going to have to buy =20 circular polarizers unless you're shooting with a pre-1970's camera, or =20=

a view camera.
 

rcyoung

New Member
From another source:

Circular polarizers are used in cameras generally when the camera has the autofocus feature. This is because the autofocus feature is sensitive to light levels. Therefore, if a linear polarizer was used, and the camera oriented in such a way that polarized light from the scene of interest was parallel to the polarizer, the light levels would be very high. Turn the camera 90 degrees and the levels would be much lower. The autofocus feature cannot handle this kind of variation, so we compromise by using a circular polarizer. Because the angle of polarization is constantly changing with a circular polarizer, we get the benefits of some depolarization without throwing off the autofocus features.
 

rcyoung

New Member
> And the very last for those who want more details :

Circular Polarizers for Autofocus

Make sure you use a circular polarizer for autofocus cameras. In autofocus cameras, some of the light entering the lens is diverted to the metering cell by a mirror, with the rest directed to the viewing screen. This mirror polarizes some of the light rays, irrelevant in most shooting. Mount a linear polarizer, however, and the combination interacts to absorb some of the light. Hence, the meter receives less than the actual amount, producing an incorrect exposure reading. By the same token, SLRs that use a beam splitter for the AF system can't ensure accurate focus when a linear polarizer is used.

The circular type appears identical, but contains a second element that causes the light to vibrate in a spiral (or circular) direction. The light reaching the sensors now appears to be non-polarized, so the polarizing effect of the splitter isn't compounded. Consequently, exposure and autofocus operation will be more accurate and reliable. Circular polarizers, although more expensive, work nicely with both manual and autofocus cameras.
 

wbulte

Active Member
Well, my 'primitive' Pentax MX (1976-vintage) bodies have no problem whatsoever with linear pol filters.
 

qnu

Banned
The thing quoted, about AF and the amount of light, is rather confusing.
If the direction of polarization of the light hitting the thingy in the AF system is "right", nothing special happens. Even in systems that are "polarizastion-sensitive".
That direction, of course, depends on the orientation of the filter. So sometimes it is a problem, sometimes it isn't.
The real problem is not knowing when it is.

But the real confusion is that there's talk about AF cameras, and then it is mentioned how an exposure meter might be affected.
Meters in non-AF cameras can of course have the same difficulties with polarized light. And, conversely, meters in AF cameras may not have a problem with polarized light at all, even when the AF might.


That line saying "Linear polarizers are more effective" is nonsense.
Circular polarizers are (!!!) linear polarizers. With an addition, yes. But that addition does do nothing to the performance or effectiveness of the linear polarizer bit.


And finally: no. You do (!!!) need to use a lens hood when using a polarizer just as you would without.
Polarizers do not perform any magic tricks that would make using a hood unnecessary.
 
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