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Elastic bands with filter wrenches?

Discussion in 'General Equipment Chat & Advice' started by ChrisNewman, Apr 16, 2019.

  1. ChrisNewman

    ChrisNewman Well-Known Member

    It’s me who should apologise to you for not being clearer, Geoff. I fully understood that you were referring to physical distortion, although I doubt it’s relevance. In fact my protector filter is stabilized by its glass insert, whilst the screwed ring of the polarizer is only a simple ring of, I believe, aluminium, loosely interlocked with the slightly wider ring stabilized by the glass support for the polarizing film.

    As you might expect, during this correspondence I’ve been taking more notice of the filters than usual. On Wednesday evening, I found that the polarizer was only loosely screwed into the protector, such that if I turned the polarizer in the unscrewing direction, part of that movement was achieved by the polarizer rotating as intended in its screwed mount, but part by unscrewing the filter bodily from the protector. I wore the camera and lens around my neck on a walk on Thursday morning. I rotated the polarizer (carefully using the direction that would tighten loose threads) and took a single set of photos while it was still fairly cool, although it became quite warm by the end of the walk. On Thursday evening, after my camera bag had been standing in our bedroom for hours, I checked the filter again. It was then locked tightly into the protector, although I didn’t bother to apply my full hand strength to investigate how tightly, never mind using filter wrenches. Since then I’ve used other lenses, but not my 24-70mm, although it’s been carried around in my camera bag. Just now I tried again, and once again the filter is loose enough that rotating it in the wrong direction is likely to remove it accidentally. I can’t think what, other than thermal movements, might be causing these changes, but also I don’t think conditions in our bedroom are much different this lunch time to what they were on Thursday evening!


    Chris
     
  2. GeoffR

    GeoffR Well-Known Member

    I think we have different measures of distortion, I am thinking 2 or 3 hundredths of a mm, you can distort a filter that much just by gripping it and it doesn't matter which filter distorts the effect is the same.

    In your case I think the two filters expand differently when heated, only when they have stabilised at the temperature at which they were fitted together will the come apart easily, at least that is what your comments suggest. A little dry film lubricant may help but you only need a very tiny amount.

    I stopped using protective filters back when I had an Olympus OM system, partly because of the difficulty in removing filters and/or separating them, and only used polarisers with my Nikons, since going digital I haven't even used those (that! my most used lenses share a 77mm filter).
     
  3. ChrisNewman

    ChrisNewman Well-Known Member

    The reason I don’t think physical distortion is relevant to my problem is simply that the polarizer will go from loose to locked in tightly and back to loose without any external forces (other than the weight of the lens along the lens axis in my camera bag) being applied.
    I’m pretty sure differential thermal movement is behind the filter sticking. The situation would be relatively straightforward with most types of filter (if I wanted to add one or more high-density filters for long exposures, for instance). But the complication with a polarizer is that using it requires adjusting its angle, which will inadvertently take up any slack between the threads at times when thermal movement has created it. And I still can’t understand why the filters were locked when my kit was at a stable temperature on Thursday evening, but loose when at a very similar stable temperature this lunch time!
    I’ve just looked up, and read that “Graphite and molybdenum disulphide are the predominant materials used as dry lubricants.” As I commented to Roger Provins earlier, I’d be scared to use graphite for fear of getting particles on my sensor. Does solid molybdenum disulphide shed particles in the same way? And is there any reason to think it would be a much more effective lubricant than light machine oil, or silicone grease, which I know from experience is far from a complete answer. My suspicion is that lubricant enables the filter threads to engage even further when conditions allow, so that the subsequent tighter fit tends to counteract the advantage of the lubricated unscrewing.

    Chris
     

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