The cross polarising techniques is a simple one to create. Just place a polarising filter in front of the lens and photograph a stiff plastic object in front of an LCD computer screen. To illustrate the tip I attached a Hoyarex Linear Polarising filter* to the front of a digital camera. 
I then positioned a plastic cereal container in front of my computer monitor (make sure the background is neutral grey and not a screen saver ) and mounted the camera on a tripod. You can hand hold if there’s enough light to get a camera shake free photo.
When you rotate the polariser you will see a rainbow of colour with the background colour of the monitor.
As you rotate the colours will become stronger and the background will go black.
I repeated the technique using a plastic wine glass
* Any polarising filter can be used – linear or circular . We have a selection for sale here in both screw in and system filters. Polarising filters for sale. The system filters are more practical as you can use one filter with a variety of lenses with different filter threads. Just get the filter, a holder, and a range of adaptor rings for the holder to attach to different lenses.
There’s a really interesting article about photographer John Duder going back and experimenting with filters he never got around to using in the 80s over on ePHOTOzine: Experimenting With Filters From the Eighties I Have Never Used – Come Check Out The Results
Also interesting that we’ve got many of the filters he used here on PhotographyAttic. check out our Cokin A-Series section and the Cokin P-Series
The Hoyarex filter system was really good: high quality filters.. Great variety of options in the range. Some glass filters. Solid holder. And a really useful rubber hood. But the Hoyarex System had a big flaw! And that has become evident over the years as more and more filters become scratched.
It’s not due to use either! These scratches occur when the filters are stored in their plastic case. The resin filter catches the edge of the case, which usually bends a bit in the middle. So after being jostled around in a camera bag the rubbing effect causes the resin to mark or scratch. 
So here’s a tip to prevent further wear. Buy a packet of lens tissues and wrap one over the filter at the top end that sticks out of the case. Then the filter wont get rubbed. You can use toilet tissue, but a lens tissue is softer and has no fibres that will come off and cause dust problems. 
View the entire range of Hoyarex filters here
The Hoyarex Skylight 1B filter – cat number 011 – is one of the most valuable filters in the Hoyarex range, yet is often overlooked, because its not a special effect filter.
But this underused filter will do two things to ensure your photography improves.
Firstly, and most importantly, the filter is a lens protector. The Hoyarex system is made so that when a filter is placed in the back slot it removes any possibility of dust reaching the lens. So if the holder is left on with a filter inserted the lens wont get dust falling on the surface or scratches. The skylight is the obvious choice as it has no special effect value. It’s also one of the few filters in the Hoyarex range that’s made from glass so optically very good.
But the filter has another use. A skylight filter has a very slight pink tint that has a warming effect when shooting in hazy days, so landscapes can be photographed with slightly more clarity. 
Using the filter in the back slot near the lens means there still another slot free for a special effect filter when you want to add a graduated effect, sepia tone or spot for example. 
Photographyattic has the Hoyarex 011 Skylight 1B glass filter for sale here
An interesting and under used filters in the Cokin range is the Incolor 061. It’s part of the spot color range, and unlike many of the other colour spot filters this one is very practical and can be used in different ways for different effects. The spot filters with colour can sometime look quite poor if not used well, whereas this one can be adjusted to give a soft focus style effect or a lovely white vignette. This makes it perfect for wedding photography or portraits.
The filter is available in Cokin’s A and P series and has a small hole in the centre. When placed in front of the camera lens the hole either appears small or large, hard edged or soft edged, depending on the lens focal length and aperture used.
To get a large soft edge you should take photos using a longer focal length (around 50-80mm is fine with this filter) and use a wider aperture. If you want a more pronounced circle, use a wider lens and a smaller aperture.
The texture on the filter can be made to look white/grey or neutral depending on how parallel it is to the ccd/film…and if light is reflecting on the rear surface.
You could focus lock on the filter so the subject through the hole is blurred and the filter texture sharp. This makes interesting creative shots.
A longer lens and wider aperture was used here. Notice how soft the edge is and how neutral the filtered area is.
Here the filter was adjusted so the spot was on the face. You can do this if the filter is hand held in front of the camera. The filter was held further away and angled so light reflected on it.
Here’s the filter being used to it’s best. Good choice of aperture and focal length gives a lovely diffused vignette.
Another version with a slightly more defined effect. Using the filter like this is great for wedding photography and romantic portraits.
You can buy the filter here: Cokin A series 061 Spot In color Filter
In the early days of the polarising filter there was just one type – the linear polarizer. The circular type arrived when the cameras with advanced metering (and later focusing) systems became popular. The Canon T90 and Olympus OM4 both had new advanced TTL metering that would be affected by the way a linear polarising filter worked. So a circular polarising filter had to be used instead.
Later, when autofocus came along, some systems got confused by the affect of the polariser. So, as a rule of thumb, use a linear on old manual and semi automatic cameras and circular on newer modern multi menu models.
If you do have a linear filter and a modern sophisticated digital SLR it will still work, but you may get inconsistent exposures. This is easily rectified by looking on the LCD preview and reshooting with necessary compensation applied.
A filter factor is highlighted on many filters as a multiple (or x). It’s simply the amount you need to increase the exposure by to compensate for light absorbed by the particular filter being used.
x2 is a one stop increase
x4 is two stops
x8 is three stops
x16 is four stops
If, for example, you have a x4 orange filter on the lens, the exposure has to be increased by four times – that is two full f/stops or shutter speed increments.
Lets say you have an exposure of f/5.6 (aperture) and 1/125sec (shutter speed) and add the x4 filter. You would either have to adjust the aperture two stops to f/2.8 or the shutter speed two stops to 1/30sec or both one stop so the exposure would be f/4 at 1/60sec.
Fortunately with modern through-the-lens (TTL) metering and automatic cameras the filter factor is taken care of, but you need to make the necessary adjustments when using manual cameras or manual exposure with flash.
To make things a little more complicated, some filters, such as the polariser, have variable exposure factors as you rotate the filter, and others have incremental factors such as 1.3x which makes it hard to adjust if you have an older camera with only full stop increments.
Hoyarex filters were arguably the best filter system made. Optically superb, several made from glass, solid filter holder, brilliant adjustable rubber hood for wide or super telephoto, and a useful range of filters.
Hoyarex was a filter system developed by Hoya. Hoya was the big name in optical filters and then French manufacturer Cokin appeared with a system that would revolutionise the filter world.
Hoya reacted fast but not fast enough. Cokin had soon taken hold of the filter market with serious and special effect filters. Photographers were no longer buying one or two filters they were investing in cases full.
The Hoyarex system emulated what Cokin had done, but in our opinion did it better, some filters were glass, others had frames around them so handling was better. The holder was more flexible and had a more versatile lens hood. The filters slotted in more comfortably and the adaptors clipped in easier.
But they were too late and Cokin won the battle. Hoyarex disappeared as quick as they came.
You can still find remnants of the system sold in the second-hand sections of various photographic retailers, and there are many here on PhotographyAttic.
The illustration above shows the filter holder with an adaptor ring (available in sizes from 43mm up to 77mm) and the wonderful rubber Pro hood that clipped on the holder and had a variable extension.
Two filter holder can be clipped together and rotated when special effect filters were inserted.
Here in numeric order is the entire range with links to buy individual used filters at photographyattic.com
The Multi-purpose UV is similar to the skylight, absorbing the ultraviolet rays which often make scenic shots hazy and indistinct. Moreover, the UV, especially when used with black & white film, increases contrast, reduces haze and generally improves the “sharpness” of your photographs
Many photographers buy a UV filter for each lens and leave them screwed on to protect the lenses’ front elements.
UV filters are available in round type that screw into the lens in ever size imaginable.
UV Filters available here
They were also made by Hoyarex for their square filter system.
Links to buy
Hoyarex 021 Filter
