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Thread: Recommendations for filters, please

  1. #1
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    Question Recommendations for filters, please

    I just got myself a Panasonic NV-GS400 at a good price from eBay and I want to kit it out.
    Specifically I want to get a UV filter (to protect the lens), Circular Polarizer and a couple of Neutral Densities.
    I have some basic Jessops filter for my first cam (JVC GR-DF420) and have suffered often from relections.

    Now, the Panny, which has a 43mm filter thread has come with a nice 43-55mm step-up ring which is pretty useful as stacking filters or (when I get one) a WA lens shouldn't result in much of a vignetting problem. So I'm looking for 55mm filters.

    The thing is there is a vast range in price and presumably quality.

    Some manufacturers have a number of ranges - Hoya for example seem to have uncoated, coated, very coated and incredibly professionally coated. I'm not after perfect. I don't want to spend double the money on something where I won't even notice the difference, but equally I don't want to cut corners when a few bob more would have made a noticable difference.

    Does anone have any specific recommendations on manufacturers/ranges?
    And where's a good place to buy in the UK?
    Would I be right in assuming that eBay items from Hong Kong which seem to have B+W filters for less than half the usual price are likely to be fake?

    And does anyone know where I can get a rectangular lens hood that'll fit over a 55mm ring?
    Tim

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    The answer for me is clear, get the very best filters you can, and the very best way to protect your lens is a lens cap, don't put anything else in front of it unless you 'need' an effect imho, I only use UV or 1A filters as protection if I've got a cam mounted on a vehicle.

    Multicoating is a must for the best quality, but unless it's changed you won't find a MC polariser (must be a 'circular' polariser as linear ones confuse metering systems, even then it's best to check exposures).

    But, that's all very well, but any 'reasonable' filter usually does in most circumstances, if your fond of contre jour you'll need decent coatings though.

    A 'sound' quality budget filter I've used is 'Kood', not brilliant, but good value for money. Penny to a pound you'll not notice the difference in most circumstances

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    Thanks Jerry. Kood eh? Searching now.....
    Tim

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    Quote Originally Posted by Jerry Hill View Post
    The answer for me is clear, get the very best filters you can, and the very best way to protect your lens is a lens cap, don't put anything else in front of it unless you 'need' an effect imho,
    I'm not so sure. IIRC you come from a stills background where, although expensive, if you do happen to damage a lens, you can replace it. In my world of consumer cams, this just isn't possible - it means a new cam, and whilst I am pretty obsessive about putting the lens cap on between every click of the rec button, I simply don't trust bad things not to happen It never ceases to amaze me how dirty the filter gets just in a normal outside environment. I'd rather keep cleaning that (and in extremis replacing it) than trying to clean the lens all the time)

    Anyway, I had a quick look at the Kood filters - they do seem VERY cheap, but there's little info about what "coatings" are involved. I'm quite happy to go up in price to say 30 for a UV or 81A filter to keep permanently in place (other than if I'm using another filter) if it has decent anti-reflective and hard wearing (so I can clean it) coating. On the other hand I could simply buy 5 or 6 Kood UVs for the same price and throw them away as the coating gets worn.
    Tim

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    Quote Originally Posted by TimStannard View Post
    I'm not so sure. IIRC you come from a stills background where, although expensive, if you do happen to damage a lens, you can replace it.


    That's a sound thought Tim, but let me enhance my reasoning some more.

    I'll start with the main potential indicator.

    If putting a filter in front of the lens purely for protection was a firm and irrefutable thing to do, why does no one make a plain glass 'protection lens'?

    The problem is one of distortion. I'm guessing that most folk have an understanding of 'refraction', the effect where as light passes through a change in density that it is bent if it enters at an angle, something specified in 'Snell's Law'. This we see as the thing where if you put a straight stick into water at an angle it appears to bend where it enters, and it's also responsible for why we see the 'mirage' effect, where as light comes from above it passes through differing densities of air, and this bending can be at such a degree that it can be deflected back upwards, so on the horizons of land in hot places we see blue sky 'on' the land, the usual source of the 'mirage'. Different materials that transmit light have what's called a 'refractive index', which when included in a simple calculation you can find out by what degree the light is bent.

    It is this action of refraction that makes a lens a lens, by curving the glass in varying degrees we can adjust the distortion in a controlled manner.

    So, all of that is about degrees. To expand on my thoughts the concept is that people spend their hard earned cash on cameras with decent lenses, feel compelled to protect them, not realising that they are messing up a lot of the work that the lens manufacture has put into the optics that you've paid for.

    In one sentence - The fitting of filters in front of lenses causes distortion of the image in ever increasing amounts towards the edge of the frame because the filter is flat.

    The wider the field of view, the more pronounced the problem, as at these wide settings the light at the edge is hitting the filter at an ever increasing angle.

    Lens makers have to draw a compromise to minimise this.

    Unfortunately zoom lenses are the biggest area of concern, as the shape of the outside of the front element on a fixed lens will be married to the field of view. The idea is that we want the light to hit the glass perpendicular to the surface. The lens' rear surface then bends it again, and the aim is to make the bending of the light proportional across the lens' area, so that the image remains consistent.

    On a zoom lens we are adjusting the focal length, therefore the field of view, and our problem is how to we account for the changing field of view and the consequential change in need on the curvature of the front lens element?

    There are two forms of zoom lens.

    The early types physically extended the entire lens body. The problem with that is the whole of the front element surface is in use in all settings, so they have to plump for a curvature somewhere in the middle of the scope of zoom. at either end there will be distorion of the image, but they tend to err on the side of the longer settigs being closest to desirable, as wider settings are distorting the image anyway, so the problem is less noticeable.

    Arguably better zoom lenses have an internal 'group' that move within a fixed lens body. This is better in prinicple because we are using the whole of the front element in wide angle settings, and only the centre of it when zoomed in. This means then that the front element can be made to match the field of view in infinite degrees between wide and tele. The problem however is that as we are now only using a tiny bit of the front element when on maximum zoom that element has to be made to nth degrees of accuracy, as in proportion to the diameter of section being used the accuracy error ratio becomes more critical. This is why on cheaper camcorder lenses the full zoom seems to lose sharpness. We may only be using a few milimeters in the very centre of the lens.

    So with all of that in mind, put a parallel piece of glass in front of it and you are upsetting the whole thing. That's a simple optical fact.

    Now, let's look at motive. I've been lucky possibly? I've never damaged a lens, but lets look at what are the possible causes of lens damage.

    There are only four things to be concerned about really:

    Impact:
    The hitting of the lens by external objects.

    Abrasion:
    an external object rubbing across the lens.

    Fluid ingress:
    Water or other liquid entering the lens.

    Contamination:
    The presence of matter resting on the lens surface

    (Continued in next post due to character limit)
    Last edited by Jerry Hill; 10-10-2008 at 09:00 PM.

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    (Continued)


    The way to prevent something hitting the lens is simply by being careful. If you think about what object might end up doing this it's pretty hard to think of anything that won't be the consequence of bad handling or storage. An easy way to provide some protection is to use a lens hood, and in particularly aggressive environments use a rubber one, as these fold over the lens front when hit.

    Abrasion can also be resisted by using a lens hood, but here probably the most common cause of this form of damage is poor cleaning. Lens cleaning is something that folk often don’t give enough attention to in my view. There are a number of things that need to be done to minimise risk:

    1) Always dust off the lens before rubbing any cloth over it. Any dust particles will be rubbed into the surface no matter how fancy the cloth you’re using is, the dust will also contaminate the cloth and become a further risk. Compressed air cans are the best way to remove this stuff, but for more stubborn particles a lens brush will be needed. ‘Blower Brushes’ can be useful for intermediate things. This brush needs to be natural hairs, buy a quality large artists brush and cut the handle down, cheaper and better than purpose made ones, in fact some quality makeup brushes for face powder are really nice for our use. Do not blow on the lens yourself unless you’ve ‘test blown’ first, as tiny particles of acidic saliva can get on the lens. Do not breath on the lens to apply moisture for the same reason.
    2) Lens cloths were revolutionised in the late seventies when Pentax introduced the microfibre cloth. However I find they have a greasy feel and are generally too small. The size thing is a problem with them because the micro-weave sucks up liquids very effectively, and this means every time you handle them they suck oils of your skin, again these oils are acidic. So I prefer to use domestic microfibre cloths available from Tesco’s etc. wash them in clean water repeatedly before use. They are big enough to allow them to be handled so that their centres are not touched at all, and of course they should be regularly washed.
    3) Keep your lens cloths and brushes in plastic bags, replace the bag regularly.


    Moisture getting into the lens is pretty difficult, but it can happen. Most front elements are hermetically sealed, but not all, and if you have to shoot in the rain, or in my case near sea spray, then this is a reasonable case for using a filter to protect the lens. A lens hood is obviously a good way to help in the rain, I prefer to use an old Hasselblad bellows hood I have in the rain as you can adjust it’s length to max it out without vignetting.

    Things simply getting on to the surface of the lens, like dust, will be covered by the cleaning operation. These must be removed as many dust particle are abrasive. For instance if you’ve just filmed a car driving over a dirt track, that cloud that comes up from the wheels is made up from rocks, just very small rocks. Don’t underestimate the problem that pollen can cause in some environments. Have you ever cleaned your lens and ended up with a streak across it? This it likely to be pollen particle that squidges across the surface when you wipe over it. Sadly it needs liquid to remove them, otherwise there will be an excess of lens cloth rubbing. A microfibre cloth slightly dampened with clean water is ok for this. Our water in the South West is top notch, use distilled water or filtered water if you live in an area with poor water quality.

    So in conclusion then my position is that protecting lenses with filters is a need created by lack of care in most cases. I accept that sometimes it’s a must, but I refuse to put things in front of the work that has been put into the lens by the maker to make it as good as possible. Clinical cleanliness and attention to handling and storage are the only way to protect a lens for me. I will only use a UV filter in extreme conditions, or if I want to filter UV.

    And here’s the evidence. This un-retouched image focussed on the lens surface shows an Olympus Zuiko that came with a camera that cost a full eight weeks of wages from my first full time job, it has been is regular use since new, and still is as the lens for a DOF adaptor, it was bought in 1976.




    Last edited by Jerry Hill; 10-10-2008 at 09:02 PM.

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    Quote Originally Posted by Jerry Hill View Post


    If putting a filter in front of the lens purely for protection was a firm and irrefutable thing to do, why does no one make a plain glass 'protection lens'?

    Actually they do:

    Tiffen Filters - UK Online Shop

    But nevertheless you make your points very well, as usual. And I rather enjoy the fact that your comments fly in the face of perceived wisdom on most camcorder forums.

    You may even have convinced me only to use a UV filter where I know there's going to be a risk of materials flying about.
    I feel some experimentation coming on - it'll be interesting to see how much the filter distorts.

    Your comments are very much appreciated - together with your tips on cleaning lenses. You don't mention lens papers though - any thoughts?
    Tim

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    The first thing you should do is get a decent UV or skylight filter and screw it onto your lens... and leave it there.

    Over the past few years I've had to replace UV filters due to scratches but I've never had to replace a lens... because the UV filter protects it. The front element of your lens will almost certainly be coated, this is very delicate and even rough wiping with a tissue can damage it. The filter costs about 10 and will save you hundreds.

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    Quote Originally Posted by TimStannard View Post
    Actually they do
    I guess if I'm not looking I won't find

    Lens papers are ok, but too small for me, as I've found they also suck moisture from the skin and you can end up transferring that to the lens. If you ever find yourself spreading a greasy mark around the lens it's probably skin oils you put there. To prevent this the tissue needs to be scrunched up, and for me there's not enough material there to do that, basically you end up with a tiny area of the tissue being useful and the rest used for holding it. They are cheap enough though, so if folk get on with them then fine, not as absorbant as microfibre cloths though, so any damp cleaning takes a few to dry off. I have found lint amongst them sometimes in spite of the claim that they have none, with is a bit against the whole idea.

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    Quote Originally Posted by The Guru View Post
    Over the past few years I've had to replace UV filters due to scratches ......................... tissue can damage it
    So you're telling us that you must be pretty clumsy when handling your cameras if you've had to change them that often, where did the scratches come from? Is this not resignation to failure?

    Regular tissue will damage lenses, yes, celullose fibres are abrasive.
    Last edited by Jerry Hill; 10-11-2008 at 04:35 PM.

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