[DeadJohn]

Not to get this topic too sideways, but I've been intrigued by some of the special filters out there. The light pollution filters are one such that have caught my attention:

Light Pollution Reduction Filters | B&H Photo Video

Those wideband light pollution filters are effective for astrophotography. They are unfortunately becoming less effective as LED lighting becomes more common. Here's one of many discussions on the topic How to filter "LED-poisoning"? - Equipment - Cloudy Nights

Narrowband filters do a better job blocking artificial lighting and moonlight, but they are best matched with a specialty B&W (aka monochromatic or panchromatic) sensor. Around 1/3 of the pixels on a color sensor become useless through a narrowband filter.

[clickclick]

For lessening haze, a CPL filter is more effective than a UV filter.

Yep (and I use polarizers a lot too), but don't always want to loose the stops of light and wide angle can be problematic, so just having a high quality UV filter in place is an easy worry free approach for me. I live by the water and seem to have a lot of crap blowing in the air, and it's been kinda mind bending how much dirt seems to accumulate on the front of whatever I am using. I wasn't going to buy a filter for my A50/1.2 or 20-40 Limited, but after a bit, found myself back to having enough visible crud on the front of the lens to decide they too would get some presents made by B+H.

I completely get not wanting to put more glass on the front of a lens. As I mentioned earlier, shooting into the light requires consideration (remove the filter perhaps), and high quality is key. I'd say there isn't a right or wrong answer to this, but only approaches that have different levels of applicability depending on the conditions and desired outcomes. After taking a splash of salt water spray on the front of one of my lenses while out sailing, I'm really happy I had a UV filter in place.

[DeadJohn]

Very true. the photopic response (what we humans see) is skewed to be sensitive to green mostly (for normal color vision) and most sensors would try to mimic that, I am sure. Based on the graph I presented, green is a predominant sensitivity, but WOW, Red really overshadows the green! Maybe we need a cyan filter in there, to reduce the red and bias the sensor toward the blue some!

I think your graph shows the unfiltered pixel sensitivity, as if we were using a B&W sensor. The Bayer filter that gives us color has more green pixels than red pixels so the green to red balance of our cameras is higher than that graph suggests. Corrections welcomed.

[MossyRocks]

Not to get this topic too sideways, but I've been intrigued by some of the special filters out there. The light pollution filters are one such that have caught my attention:

There you are solving a specific problem with a specific filter which is what I state filters are for. Yes light pollution filters work, especially when going after deep sky objects where the light pollution washes away lots of detail. If you don't want to get a dedicated one but want to try one out the Hoya Red Intensifier is a good option. I have a 77mm one that I use with adapter rings on most of my lenses and have a 49mm one installed in the filter holder in my 400mm that was used when capturing this image.

On the subject of UV filters and their possible benefits on digital I have seen some discussion and evidence that there are some circumstances where some specific ones can provide a benefit with purple fringing on some specific lenses. A discussion over in the astro group wandered into that territory a while back and then BigMacKCam had a thread about it when I mentioned it to him. Between those 2 threads there are links to lots of specific cases where it does provide a benefit, but here again it is a solution to a specific problem but also seems limited to specific lenses with specific UV filters.

I actually don't use a UV filter but if I were doing daytime shooting with my 400 I would swap out the red intensifier for one because that lens is at its best with a filter in the holder as it expects on as part of the optical formula which I why I bought one for that lens.

[ZombieArmy]

Lots of forms of UV are blocked by lens glass alone, not even taking into account coatings. It's why uncoated quartz glass lenses and full spectrum cameras are used for UV photography.

So no, UV filters were basically useless back in the film days and they're especially useless now.

[lotech]

That reminds me of those Astronomical Solar filter that has narrow bandwidth to block or enhance a specific range of wavelength to produce those stunning close up shots of the Sun, some such filters are opaque to naked eyes. I've not tried those natural night filters and they are quite expensive.

Let's go further sideways, I took some unplanned shots of partial solar eclipse with the FA 80-320 without any filter, at 5 stops under of 1/8000s F40@ISO125, I shot LV just to protect my eyes, risking to fry the sensor, I even fire the flash to light up the branches but it all wash out due to low flash sync. speed of the K3, thanks God after all that the sensor still works normally. It was an extremely silly thing I to do, if I had a solar filter in place I may get some jaw dropping shots ha !

[MossyRocks]

I've not tried those natural night filters and they are quite expensive.

I haven't either but am considering getting one in 49mm filter size so that I can try it in my big 400. At 49mm they aren't too expensive and are suppose to be a better filter light pollution filter as they are closer to a real light polution filter instead of something that does a good impression like the red intensifier. The NiSi 49mm natural night filter is about $102 and the 77mm Hoya Red Intensifier is about $82 (both checked at B&H just now) so while the natural night is more expensive for a smaller filter it does block more and is multicoated and sticking it in the expensive long lens would provide the greatest benefit.

[BigDave]

Lots of forms of UV are blocked by lens glass alone,

NOT so. UV energy is classified in regions- UVA (aka, near UV) in the 320-400nm range (humans see about 400-700nm), UV B, 280-320nm (the UV that can give sun tans and sun burn) and UV C (200-280nm, aka, biocidal UV, VERY bad for sunbathing and eye health). Below UV are X-Rays then Gamma Rays. As you can see by the attached graph, which ends where the visible spectrum starts, camera lenses can transmit UV down to 310-320nm. Film could be sensitive down to about 360nm (Silver is sensitive to blue light without adding any dye sensitizers), but CMOS sensors are not. So in the film days, the UV filters made a difference. Unless the sensor is designed for UV imaging, UV energy will no longer effect an exposure, however, the reflected UV energy, if high enough, could be reflected into the eye, and cause damage (why you do not look directly at the sun and certainly not during a solar eclipse, when the pupil is dilated open due to the visible light intensity being low, but the UV energy is still high!). Also, any effects of the filter can now be seen immediately in the resulting recorded image.

[lotech]

I haven't either but am considering getting one in 49mm filter size so that I can try it in my big 400. At 49mm they aren't too expensive and are suppose to be a better filter light pollution filter as they are closer to a real light polution filter instead of something that does a good impression like the red intensifier. The NiSi 49mm natural night filter is about $102 and the 77mm Hoya Red Intensifier is about $82 (both checked at B&H just now) so while the natural night is more expensive for a smaller filter it does block more and is multicoated and sticking it in the expensive long lens would provide the greatest benefit.

I will need the 77mm plus some step down rings then

[Lowell Goudge]

Looking at BigDave’s spectra, we could use a violet enhancer in to 400-420nm range!

And the graph also explains how Reds can get over saturated too! Maybe some day there will be a sensor that provides even, or neat even, spectral response. Hey SONY, how about it!

Most of the effect for the UV filter was to protect the lens from debris. It helped a little with cutting off some haze, but a polarizer was always better. The near UV (360-410nm) would contribute to the blue cast. Now there is filtering on both ends (UV and IR) on the sensor. So the filters are not needed, but can still be useful for protection in some instances. Below is a typical CMOS sensor spectral response. We humans see in the 400-700 range +/- a little).

Not to go sideways on this a little, but perhaps the best filter would be a mild red blocking filter at about the wave length of the “spike” in the blue sensitivity in the red range, I am thinking purple fringing here

[lotech]

Wait a minute, I checked many review video on YouTube and found that, the intensifer only works at night time to cut haze from artificial lighting, I don't see any similar filter for day time use to enhance contrast and color, does such thing exist ?

[hypermodern]

Wait a minute, I checked many review video on YouTube and found that, the intensifer only works at night time to cut haze from artificial lighting, I don't see any similar filter for day time use to enhance contrast and color, does such thing exist ?

A polariser maybe?

[lotech]

A polariser maybe?

Here is it but not cheap

LB “Lighter, Brighter” Color Intensifiers – Singh-Ray Camera Filters

[hypermodern]

Here is it but not cheap

LB “Lighter, Brighter” Color Intensifiers – Singh-Ray Camera Filters

How does that work? The examples on the site are difficult to believe.

[lotech]

How does that work? The examples on the site are difficult to believe.

No idea, just a random search to find it.