hagerman@friday.DEC (what is hip?) (08/29/84)
x This is in response to a recent question about coated filters. First I want to apologize in advance for being a Leica fanatic. The basic point was that some filters are coated and others aren't. The reason for coating an optical glass surface is to reduce reflection at that surface by using destructive interference. But on a filter that is going to have a 100% to 400% change in exposure anyway, saving another 8% by coating is pretty insignificant. But another comment was that a UV filter was being used to protect the front element of the lens. I'm not sure that that is a good idea. For one thing, the front (and rear) elements of all camera lenses are made of glass that is tough, and the coatings are selected specifically so that they can be cleaned; abiding by this limitation is part of the lens design process. Unless you are a real klutz and put your thumb on the lens every time you pick up the camera, I think you're better off avoiding the extra two surfaces to get dirty. There are also optical effects. For example, the curvature of long focal length lens elements is small relative to that of short lenses. Clearly a non-flat filter will have a greater detrimental effect on a long focus lens than on a shorter lens. Can you justify spending a couple of hundred bucks on a telephoto lens and then putting a $6 filter in front of it? Also it's questionable whether a UV filter is desireable. This is a quote from an informational (read: sales) booklet on Leica Reflex Lenses: "...UV rays are invisible to the eye, but affect the film... Ultraviolet light must therefore be filtered out. In the past, this was done with a UVa filter on LEICA lenses. LEICA lenses of the current generation (from about 1965 onwards) absorb ultraviolet rays throught the use of certain types of glass and above all through a certain method of cementing the lenses, so that basically a separate UVa filter is unnecessary." "...slightly tinted UVa filters were in the past recommended for colour photographs of subjects with exceptionally high UV and blue content of light, such as subjects in the shade or distant views through a slightly blue haze. Their use with the current LEICA-R lenses is discouraged, because they will make the colour rendering unnaturally warm." "...It must, however, be mentioned here that even high-quality filters may create problems in certain situations. At high contrast, for instance during sunsets, in night shots including powerful light sources in the picture and when bright objects are photographed through a dark arch, the risk of reflections even from optically flat and coated filters is very great. Double images or a general degradation of the contrast or partial lightening through stray light are relatively frequent. In such photographic situations all filters, including the UVa filter, should be removed. With ultra-wide angle lenses, too, filters may lead to inferior results. Owing to the wider angle of field the marginal light rays must traverse a slightly longer path through the filter in front of such lenses than the light rays in the center. This may often adversely affect the picure quality, and is one reason why, for instance, no filter is offered for the 19mm ELMARIT-R f/2.8 lens." So I only use a filter when there is a specific need for it, and buy big-buck glass filters, or gelatine filters. DHagerman
aws@ncvet.UUCP (08/30/84)
I disagree about using UV filters for lens protection. If you use you camera often it is better to put something in front of the lens to prevent the chance of it being damaged. The loss in exposure is a good trade off against buying a new lens. A. W. Sapp at NC State Vet School decvax!mcnc!ncsu!ncvet!aws
jans@mako.UUCP (Jan Steinman) (08/31/84)
[good greif, charlie brown! golden ears comes to rec.photo!] > But another comment was that a UV filter was being used to protect the front > element of the lens. I'm not sure that that is a good idea... I think > you're better off avoiding the extra two surfaces to get dirty. DIRT is not the issue, MONEY is! > Can you justify spending a couple of hundred bucks on a telephoto lens and > then putting a $6 filter in front of it? Now you're talkin'! Can you justify spending a couple of hundred bucks on a telephoto lens and then spending another $125 to have the front element replaced? > Unless you are a real klutz and put your thumb on the lens every time you > pick up the camera... ...or unless you like to take your camera rock climbing, skiing, bicycling, to the beach, in short, if you like to use the durn thing instead of pampering it... need I go on? I've shot professional assignments, taught photo seminars, won contests, and have many good action shots under my belt. I don't use a case or a lens cap. I've got a respectable bit of brass showing through and I'm sure the resale value is nil. (Leica owners, especially <antique> Leica owners, shudder in your shoes!) I've fallen on my camera, buried it in snow, banged it against rocks. I've <broken> two 1A's while they have been on the lens, and I have a stack of dead ones that I use only with vaseline now, for softening effects. Perhaps some of my shots are not as rock-crystal clear because of the filter, but I HAVE THE SHOTS! And I find myself taking more and better shots when I'm not constantly worring about what I may be doing to the lens. Maybee this article belongs in net.flame. Then again, maybee DHagerman's article belongs in net.golden-eyes! -- :::::: Jan Steinman Box 1000, MS 61-161 (w)503/685-2843 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::
gino@voder.UUCP (Gino Bloch) (09/01/84)
>> But on a filter that is going to have a 100% to >> 400% change in exposure anyway, saving another 8% by coating >> is pretty insignificant. As is hinted at in the quotes from E. Leitz later in the article, the main problem with reflections (these days) is light ending up in the wrong place, as in scattered light or flare, not lost light. >> Clearly a non-flat filter will have a greater >> detrimental effect on a long focus lens than on a shorter lens. And a flat filter is worse for wide-angel lenses. Again refer to the quoted material. (I made a typo above, but I like it so much that I won't correct it). >> First I want to apologize in advance for being a Leica fanatic. NEVER apologize for that!
dmmartindale@watcgl.UUCP (Dave Martindale) (09/01/84)
I realize that using a filter will inevitably degrade the image from a lens. But in some situations, it doesn't matter much. For example, I do a lot of shooting of people in available light, and I haven't the time or the finder brightness to focus extremely critically (and people move continuously anyway). And for me, leaving on a filter by default gives me some peace of mind that is worthwhile: 1) though I've not done this yet, several friends have had impacts to their lenses hard enough to bend the filter ring or break the filter glass. These would have been much more serious accidents without the filter. 2) I have a permanent fingerprint on the lens of a pair of binoculars where someone touched it and I didn't notice it for several months. By that time, fingerprint oils had attacked the lens coating. If this ever happens to my camera, I'd rather it happened to the filter than the front element of the lens. 3) (irrational reason): I don't feel very guilty using Kleenex or my shirt or whatever is at hand to clean the filter when it gets grundgy. If I scratch it inadvertently, that's life. I can't be quite as cavalier about my new $250 lens. If your Leica manuals specifically warn about not using skylight-type filters, I'd tend to heed them - they should know what they are talking about. But my manuals seem to suggest that using UV or 1A to protect the lens is generally OK. When I'm worried about getting the greatest possible contrast and resolution, I won't use a filter unless I absolutely have to. But then I'll also use a fixed lens instead of a zoom under these conditions. And I suspect that the presence of a filter (at least if it's a good one) matters less than the choice of lens.
darrelj@sdcrdcf.UUCP (Darrel VanBuer) (09/01/84)
Personally, I don't use filters to protect my Nikkors, but I do scrupulously
use lens hoods (which is a good practice anyway). Less protection than a
filter, since a pointy object can still get in, but stops walls, baseballs,
flare.
Spiratone used to make a nonfiltering glass opticap (i.e. a #0) for use as
a clear lens cap.
--
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
!sdcrdcf!darrelj
VANBUER@USC-ECL.ARPAdmmartindale@watcgl.UUCP (Dave Martindale) (09/03/84)
In some circumstances, I'd be happy to use a (rigid) lens hood instead of a filter for protection, particularly for long-focal-length lenses where the hood would be long enough to provide a fair protective zone. However, all of the non-original-equipment lens hoods I have are the folding rubber type, since that is all I could find. Anyone know of a source of good metal lens hoods which screw into filter threads?