Filters and F-Stops

[PJcam]

As a beginner just getting used to the basics, I have a question that to you guys is so obvious but, I always say if you are not sure ask.

I read that if I add a filter to my camera it can reduce the light coming in, that I understand. Then I read a polarizer filter cuts down light by 2 stops. More than I thought but I can understand this far.

The bit that I am not sure about is, if I look through my camera and at this stage say it is set on auto, doesn't the camera work out the settings based on reduced the light entering the camera?

Some of these things would all make sense when I try them out but the weather is so bad at present, the light so dull and winds so strong I just can't get out. Roll on spring, it won't be long.

Thank you in advance for your replies and help.

 

[tirediron]

Yes; if you have a filter attached your camera's light meter will determine the exposure based on the reduced light entering the lens.

 

[PJcam]

Yes; if you have a filter attached your camera's light meter will determine the exposure based on the reduced light entering the lens.

Thank you tirediron, then I wonder, why do I read that we should allow for the loss of light by 2 stops? Bit confusing, maybe the statement in the books are considering the situation from manual settings with an external light meter.

 

[Designer]

Yes; if you have a filter attached your camera's light meter will determine the exposure based on the reduced light entering the lens.

Thank you tirediron, then I wonder, why do I read that we should allow for the loss of light by 2 stops? Bit confusing, maybe the statement in the books are considering the situation from manual settings with an external light meter.

It depends on what mode you are using; auto, using the built-in internal light meter, or manual, using either an external light meter, or none at all.

 

[astroNikon]

Yes, polarizers stop light by 2 stops normally. There's also 1 stop versions.

Also, ND filters (Neutral Density) come in a wide array of various stops to compensate for what you are looking for. ==> Neutral-density filter - Wikipedia

 

[PJcam]

Yes, polarizers stop light by 2 stops normally. There's also 1 stop versions.

Also, ND filters (Neutral Density) come in a wide array of various stops to compensate for what you are looking for. ==> Neutral-density filter - Wikipedia

I have also purchased a ND2-ND4 variable filter, I have not used it yet, but can see the difference from the minimum to maximum with this filter. Not sure how many F-Stop the variances are but I would be using the in camera light meter to meter should it should not be a problem.

Thank you for your comments.

 

[astroNikon]

Yes, polarizers stop light by 2 stops normally. There's also 1 stop versions.

Also, ND filters (Neutral Density) come in a wide array of various stops to compensate for what you are looking for. ==> Neutral-density filter - Wikipedia

I have also purchased a ND2-ND4 variable filter, I have not used it yet, but can see the difference from the minimum to maximum with this filter. Not sure how many F-Stop the variances are but I would be using the in camera light meter to meter should it should not be a problem.

Thank you for your comments.

If you check that Wiki page and the chart.
ND2 in the column "NDnumber" is 1 stop in the column "f-stop reduction"
ND4 is 2 stops

 

[Christie Photo]

Hi!

The 2 and the 4 on your neutral density (ND) filters is called a filter factor. If you have a filter factor of 1, there is no loss of light. A filter factor of 2 will cut the light in half... so a loss of one full stop. Going to 4 will cut the light in half again, making a loss of 2 stops in comparison to no filter. I hope this all makes sense.

But, yes... while your meting system will take care of compensating for the loss of light, things change. So with you polarizer, your system will either slow your shutter or open your aperture automatically.

I hope this all makes sense.

Good luck.
-Pete

 

[TCampbell]

Neutral Density filters get really confusing because there seems to be lots of standards on how they are marked.

Some manufacturers mark them based on the number of stops they block (e.g. 3 stops of light... or 10 stops of light).

Others mark them based on the "optical density" factor where an optical density of "0.1" represents one-third of a stop. So a "0.3" density would be 1 stop. "0.9" would be 3 stops. "3.0" would be 10 stops.

Others mar them based on the percentage of light this allowed to pass... so an "ND 25" means 25% of the light will pass (which works out to 2 stops. ND 13" means 13% of the light will pass (really a round-up of 12.5 which means 1/8th of the light can pass ... in other words that's a 3 stop filter.)

The "Filter Factor" that Pete mentions above is a new one to me... most of my filters are based on optical densities (that's what B+W brand uses as well as my Lee slide-in filters) but I have a few from other manufacturers that use other notation methods.

Confusing? Absolutely. I wish the industry could agree on a notation that every manufacturer would agree to use.

 

[dxqcanada]

why do I read that we should allow for the loss of light by 2 stops? Bit confusing, maybe the statement in the books are considering the situation from manual settings with an external light meter.

Correct, it is specifically for those that do not use Through The Lens (TTL) metering.

 

[PJcam]

Hi!

The 2 and the 4 on your neutral density (ND) filters is called a filter factor. If you have a filter factor of 1, there is no loss of light. A filter factor of 2 will cut the light in half... so a loss of one full stop. Going to 4 will cut the light in half again, making a loss of 2 stops in comparison to no filter. I hope this all makes sense.

But, yes... while your meting system will take care of compensating for the loss of light, things change. So with you polarizer, your system will either slow your shutter or open your aperture automatically.

I hope this all makes sense.

Good luck.
-Pete

Thanks Pete, I understood it as ND2 being 1 stop and ND4 being 2 stops equivalent, but I hadn't checked it out and on what I had read there did/does appear to be different methods of categorising them.

 

[PJcam]

Neutral Density filters get really confusing because there seems to be lots of standards on how they are marked.

Some manufacturers mark them based on the number of stops they block (e.g. 3 stops of light... or 10 stops of light).

Others mark them based on the "optical density" factor where an optical density of "0.1" represents one-third of a stop. So a "0.3" density would be 1 stop. "0.9" would be 3 stops. "3.0" would be 10 stops.

Others mar them based on the percentage of light this allowed to pass... so an "ND 25" means 25% of the light will pass (which works out to 2 stops. ND 13" means 13% of the light will pass (really a round-up of 12.5 which means 1/8th of the light can pass ... in other words that's a 3 stop filter.)

The "Filter Factor" that Pete mentions above is a new one to me... most of my filters are based on optical densities (that's what B+W brand uses as well as my Lee slide-in filters) but I have a few from other manufacturers that use other notation methods.

Confusing? Absolutely. I wish the industry could agree on a notation that every manufacturer would agree to use.

Thanks Tim, I had seen variations in the way the ND Filters are categorised, it is as you say confusing. I purchased the gradient one, thinking initially of shading maybe a little like that for a polarizered filters. I can see how they can be used, but have not done so yet.

I have since read about them and there is a good example of using the gradient ND filter in 'Understanding Exposure' by Bryan Peterson, a good book, thanks for recommending it to me.

 

[Overread]

Yes; if you have a filter attached your camera's light meter will determine the exposure based on the reduced light entering the lens.

Thank you tirediron, then I wonder, why do I read that we should allow for the loss of light by 2 stops? Bit confusing, maybe the statement in the books are considering the situation from manual settings with an external light meter.

The suggestion is there both for those using external light meters and thus them having to account for the loss of light entering the camera system; but also to keep in mind even if you are using through the lens metering. This is because if you're in challenging lighting you might well weigh up the filter effect against the light loss for what you want; thus being aware roughly how many stops of light your filter is losing you is important in such a situation.

It also stops people just putting something like a circular polarizer on their lens all the time.

 

[PJcam]

Yes; if you have a filter attached your camera's light meter will determine the exposure based on the reduced light entering the lens.

Thank you tirediron, then I wonder, why do I read that we should allow for the loss of light by 2 stops? Bit confusing, maybe the statement in the books are considering the situation from manual settings with an external light meter.

The suggestion is there both for those using external light meters and thus them having to account for the loss of light entering the camera system; but also to keep in mind even if you are using through the lens metering. This is because if you're in challenging lighting you might well weigh up the filter effect against the light loss for what you want; thus being aware roughly how many stops of light your filter is losing you is important in such a situation.

It also stops people just putting something like a circular polarizer on their lens all the time.

Good point Overread, I had to go out the other day, to take wife to dentist, it was a terrible day, very dull, very low cloud and raining, the sky and the water looked the same dull grey. I parked up in an area near water (not meaning the rain) to try the camera with the polarizer filter on), I soon realised the reduction in light, removed the filter and I could see the difference. I wasn't shooting anything in particular, being a total newby I was just trying out the camera in bad light, testing different conditions, later I read more in Bryan Peterson's book, 'Understanding Exposure', that Polarizer lenses always work best with sun at 90 degrees to the shot being taken, whether to either side or directly above. This is another reason I think for not leaving the filter on at all times. Learning daily.

 

[petrochemist]

Yes, polarizers stop light by 2 stops normally. There's also 1 stop versions.

I've always thought that this is a great over simplification. If most of the light in the scene is reflected off a window or water etc, then the effect of the polarizing filter will depend very much on it's orientation. In one position it will pass most of the reflected light, while in another it will block most of the reflected light. There could quite easily be 5 or more stops difference just from rotating the filter. In more everyday scenes where a polarizers are useful a 1 stop variation is easily achievable.

Off course with TTL metering &/or today's instant review options this is no longer a real issue for most photographers.