Internal Kolari ND filter

[Photoworks]

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for the video people...

Here are some filters for the Panasonic and Leica cameras.

https://kolarivision.com/product/kolari-magnetic-clip-in-filters-for-panasonic-lumix-l-mount/?ref=126

 

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[jaapv]

As an emphatic non-expert in video: what is the advantage over in front of the lens filters? 

[frame-it]

1 hour ago, jaapv said:

As an emphatic non-expert in video: what is the advantage over in front of the lens filters? 

you only need one based on the sensor size, not one for every different lens, people who shoot a lot of video and fast dont have time for a bunch of step rings for each lens

[jaapv]

So there is no optical advantage?  I guess it competes with Cokin then.

 

[SrMi]

You do not need to carry filters of various sizes.

A Clear Dust Protective clip-in filter may be easier to clean than the sensor itself.

[jaapv]

But adds thickness to the filter stack. Thanks. 

[SrMi]

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13 minutes ago, jaapv said:

But adds thickness to the filter stack. Thanks. 

Good point. It may make more sense for IR full spectrum converted cameras.

[Stuart Richardson]

12 hours ago, jaapv said:

As an emphatic non-expert in video: what is the advantage over in front of the lens filters? 

Putting a filter behind the lens is generally not done except in cases where it is necessary for some reason and optically factored in. It can cause things like shifting the placement of infinity, vignetting and so on. The focus is shifted by 1/3rd of the thickness of the filter, but perhaps that is fine on mirrorless. I have no idea if Kolari's filter has been designed to address this, but the old advice is to avoid doing it. Any dust or debris will also be much more visible than they would on a filter in front of the lens. The main benefit here is that you don't have to buy multiple filters for your lenses. Otherwise I think it is mostly disadvantages. 

Edited August 7 by Stuart Richardson

[frame-it]

34 minutes ago, Stuart Richardson said:

Otherwise I think it is mostly disadvantages. 

their filters sell like crazy, so obviously they have addressed this in some way.

the main issue will be if using very wide lenses, there will be distortion around the edges

[Stuart Richardson]

I am not sure they can do anything to address it, as it is just physics. Unless of course they are not plane glass and have given the filters a corrective index. I think the fact that mirrorless cameras focus based off the sensor and usually focus past infinity means that any focus shift would be irrelevant in most cases. But if I were using lenses with a hard infinity stop (like Leica M lenses), I would probably want to double check that they could still reach infinity. And as you say, it's probably worth a look into the corners to see if they are significantly affected before you photograph something where they are important. Like many things, it seems like it is probably a trade-off. As for popularity...well, lots of terrible things are popular. I doubt these are, but the old wisdom was to keep filters on the front if possible. I think these make sense if you have lots of different lenses and change frequently, but if you just have a couple different sizes, it's probably better optically to stick with regular filters. 

[Photoworks]

1 hour ago, Stuart Richardson said:

I am not sure they can do anything to address it, as it is just physics. Unless of course they are not plane glass and have given the filters a corrective index. I think the fact that mirrorless cameras focus based off the sensor and usually focus past infinity means that any focus shift would be irrelevant in most cases. But if I were using lenses with a hard infinity stop (like Leica M lenses), I would probably want to double check that they could still reach infinity. And as you say, it's probably worth a look into the corners to see if they are significantly affected before you photograph something where they are important. Like many things, it seems like it is probably a trade-off. As for popularity...well, lots of terrible things are popular. I doubt these are, but the old wisdom was to keep filters on the front if possible. I think these make sense if you have lots of different lenses and change frequently, but if you just have a couple different sizes, it's probably better optically to stick with regular filters. 

If you take professional cameras, they have various ND filters in front of the sensor.

Canon makes lens adapters with drop-in filters. It can not be all that bad.

I think stacking filters in front of the lens is a bigger challenge.

Even back in the film photography days, when shooting with Sinar 4x5 camera, placing one filter in the front and one is the back made a big difference.

Some wide-angle lenses have a build in tray for filters at the mount, 14mm, 14-24mm. The front element is too big to attach a filter in an easy way.

It can all be that bad!?!

"But if I were using lenses with a hard infinity stop (like Leica M lenses),"  do you really put so many filters on your M lenses, ND? 

[BernardC]

6 minutes ago, Photoworks said:

Some wide-angle lenses have a build in tray for filters at the mount, 14mm, 14-24mm. The front element is too big to attach a filter in an easy way.

It can all be that bad!?!

Those lenses are designed that way. Most of them will come with a clear filter, so they always have a filter in the optical path. Many super-telephotos also use rear filters, mainly because they are much smaller and cheaper than 100mm+ front filters.

Video cameras with built-in ND filters usually have a clear filter so that the back focus distance doesn't change. You'll notice that these are offered by brands that have fairly thick sensor filter stacks anyway (Sony, Canon).

There are a few factors that can minimize the impact of rear filters. Most cine lenses are designed for "spinning mirror" cine cameras, so they have a longer back-focus distance. Also, it's very common to shoot video in APS-C (Super 35) mode on full-frame cameras, so the edges of the image circle are cropped-out.

All this is to say that your mileage will vary. Some lenses are barely affected by rear filters, some may be positively affected (in cases where you need to soften-up the image, like portraits), and some might be severely affected. You'll need to run some tests.

[jaapv]

Lenses with a filter at the rear should not be used without. There must always be at least a clear filter in place. It is not really a filter but a double plane lens element. 

[Elliot Harper]

Filters behind the lens and in front of the sensor are mainly for the full spectrum IR modified camera to shoot infrared pictures.

Don't use them for other general purposes.

[MikeZ]

I've used a Kolari filter to protect the sensor on my Canon R5, which was particularly helpful while on safari in Botswana last year, and have not noticed any focus or image issues.  I've been quite happy with the Kolari filter, but this conversation raises some good points.  Is infinity focus the primary (or only) concern?

[BernardC]

1 hour ago, MikeZ said:

I've been quite happy with the Kolari filter, but this conversation raises some good points.  Is infinity focus the primary (or only) concern?

Infinity focus isn't one of the primary concerns with mirrorless cameras, but it would be for a rangefinder or a cinema camera (where the focus scale needs to be accurate).

A bigger concern is that, as Jaapv mentioned, the rear filter is an extra lens element which isn't part of the optical design. This will affect different lenses in different ways. Arguably it is less likely to affect longer focal lengths, but very expensive super telephotos often come with a clear rear filter in a dedicated slot. You don't want your $10,000 lens to perform like a $2,000 lens!

If you didn't notice any effect on your safari, don't worry about it. You were probably using long lenses at medium apertures (large apertures are more likely to be affected), so you were in the sweet spot for rear filters.

[SrMi]

2 hours ago, BernardC said:

Infinity focus isn't one of the primary concerns with mirrorless cameras, but it would be for a rangefinder or a cinema camera (where the focus scale needs to be accurate).

A bigger concern is that, as Jaapv mentioned, the rear filter is an extra lens element which isn't part of the optical design. This will affect different lenses in different ways. Arguably it is less likely to affect longer focal lengths, but very expensive super telephotos often come with a clear rear filter in a dedicated slot. You don't want your $10,000 lens to perform like a $2,000 lens!

If you didn't notice any effect on your safari, don't worry about it. You were probably using long lenses at medium apertures (large apertures are more likely to be affected), so you were in the sweet spot for rear filters.

I see the theoretical obstacle. Has anyone reported issues in practice?

[BernardC]

1 hour ago, SrMi said:

I see the theoretical obstacle. Has anyone reported issues in practice?

I wouldn't know if Kolari or others have done tests for that specific product, but rear filters have been used for over a century in cinema. Often they are specifically designed to degrade the image. The word "degrade" is used ironically: an image can be technically degraded but aesthetically improved. Arri sells a kit if you are interested.

Many Bolex models had gelatin (Wratten) filter slots for colour correction. Those cameras used thick optical blocks and special "RX" lenses, so an extra millimeter probably didn't make huge difference. 

As I wrote earlier, you'll need to run tests on your own lenses and cameras. Different optical designs are affected differently, and your idea of "no material difference" differs from someone else's. Generally speaking, longer focal lengths should show less effect, but $10,000+ super-teles use clear filters to negate the effect even then.

 

Kolari sells their filters in "regular," "slim," and "ultra slim," so that should tell you something. 

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Hallo,

Look here: Leica L-Mount

[SrMi]

10 minutes ago, BernardC said:

Kolari sells their filters in "regular," "slim," and "ultra slim," so that should tell you something. 

I do not see any Kolari options for "regular," "slim," and "ultra slim." 

14 minutes ago, BernardC said:

As I wrote earlier, you'll need to run tests on your own lenses and cameras.

I hoped that someone had done the tests. I do not plan to use clip-in filters for my regular cameras, only for the converted one.

[BernardC]

1 hour ago, SrMi said:

I do not see any Kolari options for "regular," "slim," and "ultra slim." 

They don't offer this product for Leica, but here's the page for Canon RF: https://kolarivision.com/product/kolari-r-clip-in-filter-for-rf-mount/. Not all filters are offered in all thicknesses.