CPL for motor racing and/or as a lens protection filter

goinggreynow

goinggreynow

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Am thinking about buying a CPL filter and leaving it on the lens permanently, including when I go motor racing for the day.
Aware of the fact that a CPL will cost between 1 and 2 stops of light but I often want to reduce my shutter speed for panning anyway & so this might not be too big of a deal for me.
Would just be interested to hear anyone's opinions. Do any fellow TP members use a CPL for motor racing photography or just leave one on their camera all the time?
Thanks for any thoughts.
 
I maybe wrong but im pretty sure when people have used them they have made it look like oils been spilt on the windscreen due to the it being persplex screen for safety reasons.
 
Yup I use one so I can get shots of the drivers, or for f1 I was getting the eyes thought the visor, all apart from Hamilton with his iridium visor.
 
danbroad said:
Hoya HD. End of story, best filters in the world.
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^^^ Agreed :)

But not left on permanently! You'll lose 1.2 stops with a Hoya HD, 1.7-1.9 stops with most others.

Polariser is good for motorsport, especially tin-tops where the angles are often just right to reduce reflections and see the driver. You only get the marbled/coloured effect with side windows that may be toughened glass or Perspex. Windscreens are laminated, no probs.
 
You can get more CPL weirdness with racing machinery than just glass though - plastics also can yield unpredictable results with some strange colour shifts and all sorts.

I do use a CPL sometimes, but not for anything really on the cars/bikes but just the usual stuff - to make the skies bluer in wide angles...
 
Just wanted to say thanks to everyone who replied.
Consensus seems to be "yes" to using a CPL at motor racing events, but "no" to leaving it on the lens permanently.
Grateful to you all for your comments.
 
Hope no-one minds me adding a further question to my own post.
Does a CPL only reduce light (by up to 2 stops) if it is in the "polarizing position"? i.e. if I rotate it back 90" so that the polarizing effect is reduced/nil, does the filter still reduce the amount of light reaching the sensor?
I ask because if it does, then I might find it a useful alternative to (say) a 2-stop neutral density filter. Am I thinking along the right lines here?
Thanks
 
It always looses light, I would say 1.5-2 stops dependent on angle.

I wouldn't use it instead of a ND... whilst the CPL will stop the light down, the other things it does might not be what you want?

CPL's are also very expensive compared to ND's...
 
Polarisers have a natural density, like 1.2-2 stops, and you get that reducation regardless. On top of that, any polarised light that it blocks will be reduced by much more.

With a strongly polarised reflection, maybe sun reflecting off a car bonnet, at just the right angle it will vanish almost completely - a reduction of, guessing, maybe five stops or more peak. A strong blue sky can go almost black, perhaps four stops darker?

It all depends on how strongly polarised the light is, your angle to it, and the rotation of the filter.

Some folks use a polariser as a mild ND filter. I much prefer to use an ND filter for ND, and the lightest typre of polariser, eg Hoya HD, for polarising. That Hoya is particularly good for motorsport as you can leave it on and pretty much not know it's there. Minimal reduction of shutter speed. In that application, reducing reflections on windscreens, the angle of rotation is usually close to the same angle needed for darkening blue skies, which is handy. Mark on the rim, if there is one, will be around the top (or bottom, same difference).

Edit: Know your angles. Two to remember with polarisers - 90 degrees to the sun for blue skies, and 30-40 degrees to surfaces for reflections (Brewsters Angle).

For blue skies, make a 'gun' with your forefinger and thumb at right angles. Point your finger at the sun and turn your hand around its axis. Your thumb will scribe an arc in the sky pointing to the maximum angle of polarisation. As you rotate the filter, that area will get darker. This explains why polarisers don't work shooting straight into the sun, as the polarised area will always be above and behind you.

To get a good idea of how polarisers work on reflections, find a dark shiny car and stand 30-40 degrees to the side. Look through the filter (you don't need a camera) and rotate it. Reflections will come and go on the sides/bonnet alternately. Move around the front a bit, in that 30-40 degress zone, rotate the filter for max effect down the side, then walk forward/backwards parallel to the side and the darkest area will move along with you.

Polarisers don't work on bare metal surfaces.
 
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Many thanks to all who replied - especially Hoppy, very informative - thank you.
Based on all replies, I've now taken the plunge & invested in a HOYA HD CPL which has just been fitted to my Tamron 17-50.
Hope no-one minds, but I have a few final questions;
1) How does anyone manage to turn/adjust a CPL with a lens hood on? I'm having no luck whatsoever! Does the CPL negate the need for a hood?
2) Other than light loss are there any negatives if I leave the CPL on the lens all the time (let's say in the "non-polarizing" position). I really would rather not have to keep taking the CPL on & off the lens.
3) How best to clean marks off of a filter - I assume I shouldn't use a lens cloth?
4) At what focal length will I typically start to see colour banding in a blue sky - is 17/18mm too wide to get a consistent sky colour?
Thanks to anyone able to comment on any of the above points.
Regards
 
goinggreynow said:
Many thanks to all who replied - especially Hoppy, very informative - thank you.
Based on all replies, I've now taken the plunge & invested in a HOYA HD CPL which has just been fitted to my Tamron 17-50.
Hope no-one minds, but I have a few final questions;
1) How does anyone manage to turn/adjust a CPL with a lens hood on? I'm having no luck whatsoever! Does the CPL negate the need for a hood?
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CPL does not negate the need for a hood, and there's no easy way to adjust with the hood on. However, while I'm a big fan of lens hoods for various reasons, TBH they don't always do much shading in practise. On your 17-50 for example, the hood will only be optimum depth at 17mm.

2) Other than light loss are there any negatives if I leave the CPL on the lens all the time (let's say in the "non-polarizing" position). I really would rather not have to keep taking the CPL on & off the lens.
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Not many negatives to leaving it on. On walkabout with my 17-40L (on full frame) a CPL is an almost permanent fixture, pre-set to the angle for darkening blue skies which remain fairly constant.

Just be aware of the side issues. One of those is shiny skin, eg suntanned people on the beach. If you think about that, Brewsters angle of 30-40 degrees will be working a lot and can make people look a bit like putty. You can see all this in the viewfinder, and watch it change as you rotate it.

CPL is also a mixed blessing with water I find. Sometimes removing the reflection allows you to see something interesting, or sometimes the reflection itself is the most interesting thing and without it the water just goes black.

3) How best to clean marks off of a filter - I assume I shouldn't use a lens cloth?
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Just normal lens cleaning procedure. Brush or blower for loose bits, then a microfibre cloth and a bit of breath. Greasy finger marks create a lot of flare, but don't be afraid to give it a good rub.

4) At what focal length will I typically start to see colour banding in a blue sky - is 17/18mm too wide to get a consistent sky colour?
Thanks to anyone able to comment on any of the above points.
Regards
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17mm on a crop format shouldn't be too bad, but it varies a lot. With the sun directly above, the band runs evenly 360 degrees around the horizon - looks like a nice mild graduated filter effect. At other times, particularly when the sun is low, it can get a bit patchy with a super- wide but sometimes it looks fine, sometimes it doesn't matter, sometimes it's conceaed by clouds, or you can change the composition, zoom in a bit, rotate the filter to moderate it (also shifts the patch a little) or just take it off.
 
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