13th August 2009, 11:44 PM
Lens Filters - UV/skylight *and* a circular polarizer?
Hi All! First time post :-)
I recently acquired a Sigma 170-500mm lens from EBay. This has two filters attached; the first is a Visico 86mm CPL, and the second is a Kood 86mm Skylight. This is my first super zoom lens, so I've a couple of queries....
The first is this, do I need both filters attached? I've looked on the net, and all I can see is people for and against them. I've already done some test shots, and they're coming out a little dark.... It is a little cloudly where I live at the moment.
Whilst I can un-screw the Kood, being as the lens cap clips on that, I can't remove the Visico at all; it just goes round and around. There does appear to be something else betweent the Visico and the body of the lens, a 3 or 4 mm groved ring. I don't want to put too much pressure trying to remove the Visico, but want to remove it to compare test shots with no filters attached. Second question then, how to I get the Visico off???? Or is it wise to visit my local camera specialist?
Thanks in advance.
14th August 2009, 01:36 AM
Welcome to CiC - great to have you with us.
Different filters perform different functions ...
UV filters originally were for removing the negative effects of UV on film (mostly at high altitudes) - these aren't necessary on a digital camera (in terms of UV removal), but many (myself included) like to use them as a form of cheap insurance ... they're a lot cleaper to replace (and a lot easier to clean) then the front element of your lens, because accidents do happen. Normally they don't degrade image quality ("IQ"), but can cause ghosting and flare in extreme contrast situations (eg shooting lights at night), and are best removed for these types of scenarios (but kept on at other times).
CP filters remove polarised light - and come in two halves ... the first 1/2 screws into the lens (and then doesn't move) whilst the 2nd half is rotateable ...
... so you won't be able to remove it by trying to unscrew the bit furthest from the lens - you need to grip the bit between the lens and the bit that rotates. Filter removal can be a MAJOR challenge; try to grip the ring using even pressure on at least 4 equidistant points - if you grab it with only 2 fingers they'll distort the ring and it'll jam even tighter. Sometimes a rubber band helps, although CP filters are trickier. I jammed mine on so tight the other day I had to pull the two halves apart to get the inner ring out! (temperature also plays a big part).
In terms of CP filters, I'm not a big fan of them, some some people shoot with them often. You won't want to leave them on all the time though because they cut the light passing through to about 1/4 of what it was originally meaning you'll have much slower shutter-speeds and get more camera shake. It shouldn't affect the metering though (so it shouldn't make your images darker - the camera should compensate automatically) (assuming in an automatic mode).
Does this help?
Last edited by McQ; 25th August 2009 at 04:15 AM.
14th August 2009, 08:18 AM
Just a small clarification on what Colin wrote that might help if you're new to what these CP filters do.
Originally Posted by Colin Southern
They can make blue skies darker, or remove glare from reflective surfaces (water, glass, cars, etc.) and increase saturation on foliage, hence making these things appear darker, even allowing for metering. However, these effects depend upon the relative angles of sun, camera and surfaces, that's why the filter rotates. Just look through the lens at a puddle reflection at 45 degrees and twist it through 360 degrees, every 180 degrees, you will see the effect repeating. Then try it looking at a clean, shiny car, and finally, if one arrives by now, a blue sky
I agree you won't want to leave the CP on all the time and can't really add anything to the getting it off advice. Except possibly if it has notches, maybe they make a tool to assist getting it off, but that's more expense. Just be careful with any tool near a lens!
14th August 2009, 08:26 AM
14th August 2009, 09:46 AM
Honestly, I could have made an extended-length documentary out of my efforts! The funny thing was that I deliberately didn't screw it on tight, so I'm really not sure what happened; perhaps a change in temperature.
Originally Posted by Dave Humphries
I tried a normal removal - a normal removal with extra-grunt - rubber bands - did a search of the net for additional tricks ... heated one side, cooled the other - nothing worked. In the end I was past the point of caring and just prised it apart ... and (interestingly) at that point the remainder unscrewed easily, so it was something to do with the forward assembly that was causing the thread to jam.
In the end it all popped back together pretty much none the worse for wear, apart from a few screwdriver marks around where I seperated the rings.
21st August 2009, 06:24 PM
I had a similar problem a short while ago, try as I might I could not unscrew the uv filter off my kit lens and gave it up as a permanent fixture.
A couple of days later I tried again with the same result.
Once the temper had cooled down I tried again and it unscrewed so easily it was totally mystifying.
I then screwed it back on and only slightly nipped it up, and found I could not unscrew it again, a bit strange I thought..... or words to that effect.
Then I found what the problem had been, I had been gripping the lens near to thread where the filter screwed to it too tightly, when I only put gentle pressure on it the filter unscrewed very easily.
It just may be a thought to keep in mind, or it could just have been my particular lens, being a kit lens.
Last edited by Keith; 22nd August 2009 at 05:58 AM.
22nd August 2009, 12:29 AM
That reminds me of the time I was changing the brakes on my car. The rear axle had drum brakes. When I tried to take the drums off, nothing I did would let me pull them off the car. I pulled and pulled and backed off the star wheel that moved the brake shoes off of the drum but no avail. My brother-in-law, who is quite a motorhead and apparently something of a magician, walked up and offered to try. I swear he seemed to barely touch the drum and pulled it right off the car! After finishing with that side, I went to the other side of the car and, yes, I had the same problem trying to remove the other drum. My BiL again happened by and magically touched the drum and easily pulled it off.
It turns out that removing the drum had more to do with the how it was held than how much force was used. The machined tolerance of the brake drum on the hub was so tight that the sag of gravity on the drum had to be compensated in just the right way. I suspect the same might be true for stuck filters. I suggest trying to grip the filter at different points and see if one works better. There might be a 'sweet spot' that allows you to readily unscrew it. If so, try to notice where that is on the filter so you can go back to it every time.
22nd August 2009, 07:57 AM
For a minute there John, I thought you were going to say your brother-in-law went inside the car and released the handbrake!
But clearly your not as daft as ...
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