For a digital SLR you need a circular polariser (not linear). The auto metering will work fine through it. You will lose 1 - 2 stops of light of course but since they tend to be used in very bright / sunny conditions that's not usually a problem. I took one on holiday with me and really liked using it:.

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Best wishesMike..

Xisquare wrote:.

Hi guys,.

I'm planning a hiking trip next month and thought of maybe getting apolarisation filter for my EOS 10D's zoom lens, in order to protectit but also to maybe get that deep blue sky with no glare that looksso good in other people's photos..

Polarisers are very useful and I would certainly recommend you to buy one, but *not* to keep on the lens all the time. They act as a neutral density filter, robbing you of as much as two stops of light. They have to be correctly adjusted for each shot, otherwise you can get some odd effects - a polariser rotated to it's 'ineffective' position is not the same as no polariser at all..

Inevitably this raises the question of whether you should use a filter to protect your lens at all. What are you protecting it from? Most of the time, it is simply unnecessary, and a cheap filter will be detrimental to image quality. The best protection is a combination of keeping the lens cap on, using a lens hood, and handling the camera sensibly. A lens hood, by the way, can improve image quality while a filter can degrade it..

If you are in a situation where dust, spray etc. are a problem, you may want something on the front of your lens which can easily be cleaned without the level of care that is needed for the lens itself. I do carry a couple of old skylight filters which I have from film days, so I have the option of putting one on if there is just too much cr## flying about. But I rarely use them. Do remember that if you use a 'sacrificial' lens protector, you have to actually sacrifice it occasionally because of the effects of hurried and careless cleaning (if not, you didn't need it, did you?) which all adds to the cost of what is already not a cheap exercise..

Another way to look at this is to treat the cost of 'protective' filters as an insurance policy. But if you check the cost of real insurance, it's less than putting a decent quality filter on each lens..

However I'm not sure whether I should get a circular or a linear pol.flter for use with my camera. I believe the difference is importantfor DSLRs, though not for film..

The need for circular polarisers came with autofocus SLRs, i.e. long before digital SLRs. Linear polarisers can potentially affect both focus and metering, although not all cameras are equally affected..

Also, I've used a circ. pol. filter with my old 35 mm EOS once andsomehow it got the AE all confused, half the pictures got grosslyoverexposed -.

Are you sure it was a circular polariser? That sounds just like what can happen with a linear polariser..

Could it have been the low quality of the filter? (Iremember it was quite cheap).

Probably not, but cheap filters do cause other problems, they are a waste of money..

Or some other issue? Are there any"tricks" one should be aware of with pol. filters?.

- The strongest effect on blue sky occurs at 90 degrees from the sun. Of course, you can't necessarily change your composition to allow for this, but sometimes you can, and sometimes you can come back at a different time of day. At the very least, knowing this will stop you wondering why the polariser sometimes doesn't seem to work properly!.

- A polariser will reduce glare from certain types of surface but not all. They do work on water (that's well-known of course), as well as glass, paint and plastics. They don't work at all on reflections from bare metal..

- At a pinch they can be used as a substitute for a neutral density filter, although they are not as good as conventional ND filter because they can change contrasts. You can even make a variable ND filter by putting a circular polariser on your lens, then a linear polariser in front of that. It has to be that combination and that way round. Rotate the front polariser first to get the amount of ND you need, then the whole assembly as one to control reflections, if applicable...

Inevitably this raises the question of whether you should use afilter to protect your lens at all. What are you protecting it from?Most of the time, it is simply unnecessary, and a cheap filter willbe detrimental to image quality. The best protection is a combinationof keeping the lens cap on, using a lens hood, and handling thecamera sensibly. A lens hood, by the way, can improve image qualitywhile a filter can degrade it..

I'd definitely endorse Steve's point (above): for general-purpose protection of the front element of a lens from bangs and knocks, a hood works very well - and doesn't have to be replaced if it's gets scratched..

Best wishesMike..

Many thanks Steve and Mike for your comprehensive answers & suggestions..

I think I'll buy a circular polariser AND a half-dozen lens caps as I keep losing those Best regards from Berlin,Andrei..

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Retired Navy Master Chief Photographer's Mate. I was a Combat Cameraman, Motion Picture Director, and a Naval Aircrewman. I also had experience in reconnaissance and intelligence photography. I have had considerable commercial photo experience in weddings and advertising photography. I am fully retired now although I dabble occasionally in dog portraiture. I presently use Canon DSLR cameras...