Ken Marcus Studios wrote:
As light passes through a pane of Netural Density gelatin, plastic or glass (a filter) there is a slight deterioration of image quality. The more filters you stack together, the less optical precision quality you get.

An example of this would be a screw in optical glass ND filter of three stops can be kept in alignment to the focal plane better than three individual one stop filters that are just stacked together. Each surface that light travels through will deteriorate the quality somewhat.

So you don't make a particular distinction between lens screw ons and plates as much as the quantity of surfaces? If for example I had plates dark enough that I only ever needed 1 at a time that would be equivalent to the screw on variety?

Mad Hatter Imagery wrote:

So you don't make a particular distinction between lens screw ons and plates as much as the quantity of surfaces? If for example I had plates dark enough that I only ever needed 1 at a time that would be equivalent to the screw on variety?

A screw on filter (of any type) would be more likely to be straight in line with the front element of the lens, rather than at a slight angle that could occur from something that is not affixed to the lens.

For most practical uses, there probably isn't much of a noticeable difference between the two types of filters, but if you are concerned with high definition acutance then it might be something to think about.

Given the choice as to which to buy, I'd stick with the screw on filters.

The Other Place wrote:
If you haven't invested much in filters, consider magnetic frames.  There are several brands, and it is much easier to pop on/off magnetic filters, compared to the screw-in type.

What keywords for this magnetic thing? I want to check Amazon.

Mad Hatter Imagery wrote:
Is there a good standard of darkness for a ND filter for midday light and maybe another for overcast?

I usually get sets of three NDs:  0.3, 0.6 and 0.9.  That works for most situations.

You could also get a variable ND.

Mad Hatter Imagery wrote:
What keywords for this magnetic thing? I want to check Amazon.

Before going to Amazon, try a web search for "magnetic camera filters," to see what's available.

Bob Helm Photography wrote:
What is critical with filters is that the filter is parallel to the film plane ( sensor). Most good filters are made from gelatin filters sandwiched between to sheets of glass, so that is six surfaces.

Not sure if the angle of the filter glass is that critical.  Teleprompters employ a large piece of glass at a 45-degree angle with imperceptible image degradation.

Anyway, filters are parallel to the film plane, when they are screw-in or when they use a slotted or magnetic holder/matte-box.

Also, I've shot a lot through gels (mostly flimsy acetate these days), and I haven't any major problems with the image.

The important thing is to position the filter as close as possible to the lens and to flag any extraneous light from hitting the filter, which could cause irregular flare.

Mad Hatter Imagery wrote:
I might be partial to ND filter slides with a holder, but the problem may be that there are 10s of lens thread sizes. Is there a holder that can adjust to different sizes because I have a few different lens sizes.

Get a set of filters to fit your largest lens. Then buy step-up rings for your smaller lenses. They all have the same thread size/pitch.

https://www.bhphotovideo.com/c/product/ … ep_up.html

Mad Hatter Imagery wrote:
Is there a good standard of darkness for a ND filter for midday light and maybe another for overcast?

ND filters are calibrated in f-stops. You need to determine what effect you want: slow the shutter speed, open the aperture, whatever. Then mount the appropriate ND filter.

Mark Salo wrote:

Get a set of filters to fit your largest lens. Then buy step-up rings for your smaller lenses. They all have the same thread size/pitch.

https://www.bhphotovideo.com/c/product/ … ep_up.html

The filters I'm looking at are square slides that slide into a holder. I don't mind big slide filters, but the holder needs to fit multiple lenses.

Mad Hatter Imagery wrote:
The filters I'm looking at are square slides that slide into a holder. I don't mind big slide filters, but the holder needs to fit multiple lenses.

Step-up rings (as @Mark Salo suggested) should work with your filter holder, just like they do with screw-in filters.  Just get a step up ring for each lens diameter that you have.

On the other hand, many filter holders already employ convenient adapter rings for different lens diameters and those rings usually "snap in" faster than screwing on a step-up ring.

The Other Place wrote:

Step-up rings (as @Mark Salo suggested) should work with your filter holder, just like they do with screw-in filters.  Just get a step up ring for each lens diameter that you have.

On the other hand, many filter holders already employ convenient adapter rings for different lens diameters and those rings usually "snap in" faster than screwing on a step-up ring.

These step-up rings are basically size adapters so I only ever need one holder? Just a few rings that match the holder at the outside end?

AG_Boston wrote:
I have had some interesting issues show up with the screw in ND filters. I tried doing a super long daytime exposure once with a screw on ND filter. I think I was gong for a ghost town look here in the middle of Boston, well before covid. In any case, the extended exposure caused the ND filter to reflect the writing around the inside of the lens. So when my super long image was done, it has the f-stop information in the image. If you plan on doing this type of image, I suggest putting super dense, black sharpie, or even paint, on the letters of the lens.

I also use the square slide in ND filters. I tend to do this more with graduated ND filters when I want to dark up the sky, but still get a decent exposure of a subject. Both work well for me, aside from when I try to do extremely long exposures.

The filter should not be that reflective, I would have thought - good multi coating should eliminate the reflection.

Not a problem I had anticipated - thank you for the warning! Maybe I can avoid the problem with some thin strips of gaffer tape (a bit less permanent than paint :-)

AG_Boston wrote:
the extended exposure caused the ND filter to reflect the writing around the inside of the lens. So when my super long image was done, it has the f-stop information in the image.

That perceptible reflection could have been partially caused by extraneous light coming from off-camera that was hitting the lettering.  Definitely flag extraneous light from the lens or use a narrow-as-possible lens hood.

Mad Hatter Imagery wrote:
These step-up rings are basically size adapters so I only ever need one holder? Just a few rings that match the holder at the outside end?

You should be good with one filter holder, as long as your filter holder has an inner diameter large enough to accommodate the diameter of your largest lens.

Again, most filter holders have a variety of adapter rings, which usually attach much faster and more easily than using step-up rings.  This video shows how the adapter rings slide-in and snaps with the Cokin filter holder.  Several filter holder brands are knock-offs of the Cokin system.

One more thing, most of the slide-in type of filter holders made for still photography are open on the sides, so extraneous light can get in.  You might have to flag-off or black-wrap the holder in some situations.  I think that most of the magnetic type of filter holders don't suffer from this problem.

Of course, you could also use a movie matte box, but they (along with the filters that they accept) can be relatively costly and unwieldy for still shooting.

Mad Hatter Imagery wrote:
What is the difference between ring adaptors vs step-up rings? They look similar from internet photos.

Step-up rings have a male thread for the lens and also a larger female thread for the filters.

The Cokin-style adapter rings have a male thread for the lens, but, instead of also having a female thread, there is simply a flat disc, onto which the filter holder snaps.

There aren't many good pictures of adapter rings, but this video shows a pretty good angle of the adapter ring at 03:37, and it shows the filter holder snapping on to the adapter ring at 03:57.

Not all systems utilize this design for the adapter rings, but such rings are usually designed to work faster and more conveniently than using step-up rings.