[Kendra59]

My definition of a hybrid camera system is to use a DSLR camera body with old school MF lenses; it might not match other people's definition.

generally know what to use with a DSLR and a digital era lens: circular polarizers, UV Haze filters, etc. My confusion appears when I consider what filter to use on an old MF film era lens attached to my Pentax K-50 camera body.

Do you still need to use a circular polarizer, rather than a regular polarizer? Is it okay to use a modern UV-Haze filter, or should I stick with a skylight 1A, or simple Haze filter?

I appreciate any insight on these matters...

[tonezime]

My understanding: use the filters that make sense for the medium (sensor or film).

[ramseybuckeye]

You don't need to use the UV filters on digital, some people use them as a "protective cover" for their lens, but the only thing they can do for your image is degrade it.

[UncleVanya]

Polarizers:
Linear Polarizer vs Circular Polarizer: What's the difference? - Lindsey Optics

I disagree a little with the statements about generic mirror issues. However autofocus systems in most dslr and autofocus SLR systems can be negatively impacted by linear polarizers.

So with manual lenses you probably won’t see any problem but there’s also no reason not to use a circular polarizer if you have one. UV filters are typically not needed since they coat the sensor glass and the light allowed to reach the sensor isn’t really affected by common UV filters. Digital “protection” filters are available and some people love them others hate any glass added. On non-telephoto lenses the debate is pretty religious. On telephotos there are several published threads showing serious degradation on sharpness but despite my own bias I’d say you would need to test for yourself.

[Kendra59]

You don't need to use the UV filters on digital, some people use them as a "protective cover" for their lens, but the only thing they can do for your image is degrade it.

That is what I hoped would be the case. The circular polarizer... is it needed because of the digital sensor, or because of digital specific lenses, or...?

[UncleVanya]

That is what I hoped would be the case. The circular polarizer... is it needed because of the digital sensor, or because of digital specific lenses, or...?

See above. We were posting stopping the same time.

[AstroDave]

Do you still need to use a circular polarizer, rather than a regular polarizer?

That's a good idea - so you don't mess with metering and/or focusing.

[Michail_P]

Use cpl when it’s available. Polarization can’t be done without one, when you need it. I’d only use circular.

[othar]

That is what I hoped would be the case. The circular polarizer... is it needed because of the digital sensor, or because of digital specific lenses, or...?

In my opinion the only filters of value on a DSLR are CPL, ND filters and IR filters, because in general you can't recreate the effects they have on the image in post (yes, there are techniques to simulate some of the effects (stacking multiple exposures to simulate a long exposure with a ND filter, or using presets in post processing that create a look similar to IR images), but those techniques don't always work and they might look similar but not 100% the same.)

That said, you don't need any filters on your lenses in general, only if you want or need a certain effect they create (CPL filters to see through reflective surfaces like water or to strengthen the saturation of some colors, ND filters to expand your exposure time (either to capture motion in a different way, or to use a lens with wide open aperture in full sunlight where you would otherwise max out with your possible exposure time, IR filters to use a different span of light

[mikesbike]

The way I remember this matter of CP vs. linear polarizing filter was when AF camera bodies came, the linear type filter could throw off the AF mechanism. So a linear polarizing filter should pose no problem if one truly uses manual focusing, not via the focus indicator. But even so, if parting with money for a filter, why not buy one suited for the camera type so it can be used with AF lenses as well?

If you decide to use a protective filter, be sure to select one of high-quality multi-coated or super multi-coated even though these cost more. This will ensure minimum negative effects of the filter compared to having no filter. Also, for more critical shots one can always remove the filter. The skylight type has a slight warming effect, and wards off blue color shift on overcast days as well as green reflections on skin from nearby foliage in shade. The UV type addresses haze under certain conditions for better clarity and contrast, more likely with telephoto shots.

[StiffLegged]

The choice of CPL versus linear polariser is to suit the camera body and its focussing method, so use a CPL. Doesn’t matter which lens it’s screwed into.

[kypfer]

A reference I can't find for the minute, but written by an apparently knowledgeable person, said that circular polarisers are not needed for Pentax DSLR cameras!
I regularly use readily and cheaply available "old-fashioned" linear polarisers on both manual focus and auto-focus lenses on my Pentax cameras with no apparent problems with either exposure or focus. Indeed, I've found the polarising effect of a linear polarising filter to be often superior to that obtained with a circular polarising filter, on the very odd occasion where I've been in the situation of being able to make a valid side-by-side comparison.
Doubtless there are circumstances where a circular polarising filter is "necessary", but not in my experience!
Inevitably, YMMV

[35mmfilmfan]

My own take on the UV / protection filter is that I keep them on the lens in the camera bag, and when shooting treat them as a transparent lens cap - unscrew them in good weather, leave them on the lens when rain, snow, dust etc is likely to land on the front element (and changing lenses in sheltered conditions, or making do with whatever's on the camera !). Although they may degrade images to a slight extent (and I must say I have never taken comparison images to check for any such degradation), I feel that the image you take is always better than the one you don't.

I too use MF lenses on my K3, but AFAIK (and I think other posts bear me out on this), it is the camera body that mandates the use of CPLs, not the lens. I also have a set of square filters (full ND, hard graduated ND and soft graduated ND) for landscape work, and some 'fun' rotating graduated colour filters for weird effects that I cannot be bothered to try to mimic in post.

[Bob 256]

Linear polarizers can also mess with the switchable overlays in some viewfinders since they are produced with an LCD type polarizer "sandwich in the viewfinder optical path. Key word here is "some".

[UncleVanya]

The choice of CPL versus linear polariser is to suit the camera body and its AF mechanism, so use a CPL. Doesn’t matter which lens it’s screwed into.

I guess if you are using catch in focus that could make sense. Otherwise why would the autofocus system matter on manual focus lenses?

---------- Post added 06-20-21 at 10:22 AM ----------

A reference I can't find for the minute, but written by an apparently knowledgeable person, said that circular polarisers are not needed for Pentax DSLR cameras!
I regularly use readily and cheaply available "old-fashioned" linear polarisers on both manual focus and auto-focus lenses on my Pentax cameras with no apparent problems with either exposure or focus. Indeed, I've found the polarising effect of a linear polarising filter to be often superior to that obtained with a circular polarising filter, on the very odd occasion where I've been in the situation of being able to make a valid side-by-side comparison.
Doubtless there are circumstances where a circular polarising filter is "necessary", but not in my experience!
Inevitably, YMMV

I have tried linear polarizers on my Pentax bodies (k100d super, k-50, k-3, kp) with autofocus lenses and they seemed to work but I wasn’t sure if that was a fully repeatable event. I would love to hear from Pentax if there’s a technical reason for it.