The new Sigma 2.8/14-24mm DG DN is a fantastic ultra wide-angle lens. Sadly it has no filter thread for front filters (like most ultra wides). But at least it has an integrated rear filter holder and several rear filter options exist now for this lens.

This is likely an evolving review that will be updated in the next months whenever I get new filters or new information.

If you are just interested in just a summary of the test results and would like to skip all the details please go directly to the end of this blog post.

The lens

The Sigma 2.8/14-24mm DG DN defines a new performance level for ultra wide-angle lenses.

It is at least as good as the best ultra-wide prime lenses like the Sigma 1.8/14mm stopped down to f/2.8 and at the same time much smaller and lighter than the 1.8/14. It has wide open at f/2.8 nearly perfect corner sharpness und very low coma. Contrast and colors are also comparable to the best Zeiss prime lenses. It is therefore perfectly suited for both nightscapes and classical landscape photography. I’ve sold my Sigma 1.8/14mm and will use now the 14-24mm DG DN instead. This lens is currently available for Sony e-mount and Sigma/Leica/Panasonic L-mount only. Don’t mix up this lens with the Sigma 2.8/14-24 DG HSM for DSLR systems. This is a completely different design.

Several technical reviews already exist on the internet. Therefore I won’t publish my test results here and instead point you to an interesting thread on fredmiranda.com with many test images and comparisons to other lenses.

As already mentioned the Sigma 14-24 DG DN lens has no front filter thread but instead an integrated rear filter holder.

Why filters are still needed

Some people say, that with current sensors and digital post-processing options there is no need for filters anymore. In addition, many hesitate to use pol-filters on ultra wide-angle lenses due to the often uneven darkening of the sky. I very rarely use graduated neutral density (GND) filters anymore due to the high dynamic range of modern sensors (and the much better results by using the digital GND filters in LR instead). I think pol-filters on wide-angle lenses are still useful to reduce glare and reflections on water surfaces or wet leaves. But the most important filters for me are neutral density (ND) filters. They are absolutely necessary for timelapse photography and/or filming to get into the range of the 180° shutter angle. In addition, I use them often in combination with moving water to achieve this smooth look of the water (which not everybody likes).

Front filter options

Despite having the rear filter option on the 14-24mm DG DN some people prefer using front filters instead. Although the lens has no filter thread, several front filter holders, especially for this lens, exist. They are all designed for 150mm square filters. Such a front filter system is also the only option for the Sigma if you want to use pol-filters or GND filters. The best front filter systems for this lens are currently NISI and Haida. The advantage of the NISI system is, that if you just need a combined ND-pol-filter (or just a pol-filter) they offer a slightly more compact round filter option especially for their holder. The advantage of the Haida system is the quick release concept which makes mounting and unmounting of the holder very fast. Both systems can be used with 150mm square filters of different brands. I’ve used for example 150mm Rollei square filters in a NISI holder in the past without any problems.

The biggest disadvantage of any 150mm front filter system is its size. They are all huge and very difficult to store in any bag. Since I travel a lot they are no real option for me (unless I travel by car and don’t plan to do any long hikes).

Rear filter options

The integrated rear filter holder was originally designed for gel filter sheets that have to be cut by yourself in a certain shape. A template for cutting the gel filter sheets is included with the lens.

In addition to the classic gelt filters, several pre-cut options, especially for this lens, exist. Below is an overview of the rear filter options I currently know. Besides the Aurora prototype I’ve bought all the filters myself and have no connection to any of these brands. The Aurora prototype filter was provided for free by Aurora for evaluation.

Lee Filter Sheet

The Lee ND filter sheets are by far the cheapest option, especially if you share them with other photographers. You can cut more than 100 rear filters out of a single filter sheet. The very thin material has certain advantages and disadvantages as shown below. The available ND range is rather limited (maximum is ND 1.2).

The sheet is often sold as a roll. Several people on the internet have complained, that the delivered new sheets were already full of scratches and dirt. But mine arrived in perfect condition.

Links: http://www.leefilters.com/lighting/colour-details.html#299 and Lee ND filter sheets

Thickness: ~0.1mm

Material: plastic, uncoated

Available ND strength: ND 0.15 (0.5-stop) ND 0.3 (1-stop), ND 0.6 (2-stop), ND 0.9 (3-stop), ND 1.2 (4-stop)

Price: 9$ / 6€ (for a 25 x 123 cm sheet which is enough for cutting >100 filters)

Kodak Wratten Filter

The Kodak Wratten Filter (type no. 96) is similar to the Lee but consists of a different material (gelatine vs. plastic). This leads to some advantages and disadvantages compared to the Lee filter (see below).

Since they are very expensive even compared to the specialized glass filters I haven’t bought a Wratten ND filter. But to evaluate just the material I ordered a cheap (4€ instead of 150€) Skylight Wratten filter.

Link: https://www.kodak.com/BD/en/motion/products/lab_and_post_production/kodak_filters/wratten_2_filters/default.htm

Thickness: 0.1mm

Material: organic dyes dissolved in a gelatine material, uncoated

Available ND strength: ND 0.1, ND 0.2, ND 0.3, ND 0.4, ND 0.5, ND 0.6, ND 0.7, ND 0.8, ND 0.9, ND 1.0, ND 2.0, ND 3.0, ND 4.0

Price: 90$ / 150€

Haida Rear Lens ND Filter Kit

The Haida Rear Lens ND Filter Kit is specially made for the Sigma 14-24 DG DN lens. It consists of rather thick glass (which has some advantages and some disadvantages, see below). Contrary to the other filters (and the Sigma template) it has no lower nose.

Links: https://www.haidaphoto.com/en/product-show-411.html and https://www.haidaphoto.com/en/story001-1091.html

Thickness: 0.5mm

Material: glass, multi-coated

Available ND strength: ND 0.9 (3-stop, 8x), ND 1.2 (4-stop, 16x), ND 1.8 (6-stop, 64x), ND 3.0 (10-stop, 1000x)

Price: 149$ / 140€ (for a set of four filters)

Kase Rear Filters

The Kase Rear Filters are also specially made for the Sigma 14-24mm DG DN lens. At first, they looked like a really good choice because of the very thin glass which has advantages regarding the optical performance. Sadly I had problems mounting the filter on my lens (see below at the section Handling). Therefore I wasn’t able to include the Kase filter in the first test round.

Links: https://www.kasecn.com/en/newsshow.aspx?ID=1643 and installation video on FB

Thickness: 0.3mm

Material: glass (coating unknown)

Available ND strength: ND 0.9 (3-stop, 8x), ND 1.8 (6-stop, 64x), ND 3.0 (10-stop, 1000x)

Price: 69$ / 66€ for a single filter, 189$ / 188€ for a set of three filters

Aurora Rear Filters (Prototype)

The Aurora Rear Filters are also specially made for the Sigma 14-24mm DG DN lens. Currently, they are in a prototype stage and will be released end of Q1/2020. They differentiate from the competition, that they use a frame around a very thin glass. This much improves the handling and avoids the negative consequences of using a thicker glass. The final product will have a different frame design. Aurora is planning to use a magnetic connection in the final product to further improve the handling. The glass of my prototype filter should be identical to the final product. Therefore the evaluation of all optical performance aspects based on this prototype should also be valid for the final product.

Links: https://aurora-aperture.com/ and https://youtu.be/nEuK6gzF0UE

Thickness: 0.33mm

Material: glass, multi-coated (frame of final product: metal, prototype-frame: plastic)

Available strength: ND 0.6 (2-stop, 4x), ND 1.2 (4-stop, 16x), ND 1.8 (6-stop, 64x), ND 2.4  (8-stop, 256x), ND 3.6 (12-stop, 4096x)

Price: currently unknown

Release date: end of Q1/2020 (after mechanical re-design of the frame)

Handling

How easy is it to mount and unmount the filter? How useful is the supplied filter box and how easy is it to store the filter?

Lee Filter Sheet

• difficult to mount and unmount due to its flimsiness and flexibility
• has to be cut in the right shape before usage
• storage of the cut filters is difficult, no box supplied with the sheet (I use a small B+W filter box for these filters instead)
• rating: –

Kodak Wratten Filter

• similar to the Lee filter
• rating: –

Haida Rear Lens ND Filter Kit

• slightly easier to mount due to no lower nose and thicker glass
• the supplied filter box makes it very easy to grip the filters but is unnecessarily big which impedes the storage in the photo bag
• rating: +

Kase Rear Filters

• mounting was very difficult on my lens, the lower nose of the filter is slightly too thick for the lower slot on my lens
• after countless failed attempts I was able to mount the filter by sliding it from the side into the lens slot
• other photographers have reported, that on their filter-lens-combinations, the mounting is possible but very sensitive to the mounting angle
• the supplied filter box is also slightly too big and doesn’t support the gripping of the filters
• rating: –
  

Aurora Rear Filters (Prototype)

• much easier to mount and unmount compared to the other filters due to the external frame around the filter glass
• the filter box for the final product will look different, therefore an evaluation of the box is currently not possible
• rating: + +

•  

Robustness and cleaning

How easy is it to scratch, break, or damage the filter? Is the filter susceptible to fingerprints and how easy is it to clean the filter?

Lee Filter Sheet

• very easy to scratch and crinkle
• handling of the filter will always leave fingerprints on it
• very difficult to clean without inducing additional scratches
• rating: –
  

Kodak Wratten Filter

• very easy to scratch and crinkle
• handling of the filter will always leave fingerprints on it (which can damage the gelatine surface)
• sensitive to moisture and temperatures above 50°C
• rating: – –

Haida Rear Lens ND Filter Kit

• handling of the filter will always leave fingerprints on it
• fingerprints can very easily be cleaned with a microfibre cloth
• very robust, in an unplanned test my Haida filter has fallen from 1.5m height on a stone floor => no signs of any damage, but please don’t repeat this test 🙂
• rating: + +
  

Kase Rear Filters

• handling of the filter will always leave fingerprints on it
• fingerprints can very easily be cleaned with a microfibre cloth
• very thin glass without a frame has a high risk of breakage
• rating: +
  

Aurora Rear Filters (Prototype)

• the frame allows handling of the filters without any fingerprints on it
• the surface of the filter can very easily be cleaned with a microfibre cloth
• rating: + +

Resolution (center sharpness)

Has the filter any influence on the center resolution of the lens?

The test was done on a very stable tripod, using an A7RII with self-timer, ISO 100, uncompressed RAW, IBIS off, and manual focus on the center at max magnification. Every shot was repeated three times with a new manual focus. Later the sharpest image out of the three was chosen for the comparison. The lens was set to 14mm and f/2.8. The focus was close to infinity. In Lightroom the following sharpening parameters were used: 50 / 0.7 / 100 / 0

These are two 100% center crops with no filter as a reference to compare with the filter image crops below:

Lee Filter Sheet

• slightly reduced contrast compared to no filter
• rating: +

Kodak Wratten Filter

• not tested

Haida Rear Lens ND Filter Kit

• • very slightly reduced resolution/contrast compared to no filter
  • rating: +

Kase Rear Filters

• not tested (due to mounting problems during the first test round)

Aurora Rear Filters (Prototype)

• resolution and contrast similar to no filter
• rating: + +

Resolution (corner sharpness)

Has the filter any influence on the corner sharpness of the lens?

The testing procedure was identical to the center sharpness test with the only difference that manual focus was directly at the corner. This excludes intentionally any effects on field curvate which will be evaluated separately.

These are two 100% corner crops with no filter as a reference to compare with the filter image crops below:

Lee Filter Sheet

• slightly reduced contrast and resolution compared to no filter
• rating: +

Kodak Wratten Filter

• not tested

Haida Rear Lens ND Filter Kit

• clearly reduced resolution and contrast compared to no filter
• rating: –

Kase Rear Filters

• not tested (due to mounting problems during the first test round)

Aurora Rear Filters (Prototype)

• slightly reduced contrast and resolution compared to no filter
• rating: +

Field curvature

Has the filter any effect on the field curvature of the lens?

For a definition of field curvature FC see here and here.

Especially with wide-angle lenses, an additional optical element between lens and sensor influences the field curvature characteristic of the lens. This is a well-known effect if you use a lens designed for a certain cover glass thickness in front of the sensor on a camera with a significant different sensor cover glass thickness (like a Leica M lens on a Sony E-mount camera). How strong the effect is, depends on the design of the lens and the thickness of the filter glass. The thicker the filter the more impact on FC.

Field curvature can change over the focus distance, especially with ultra-wide-angle lenses. But since it is very difficult to evaluate field curvature at close distances (the sensor plane and the plane of the subject have to be completely parallel for this test) I will evaluate the FC effect only at infinity.

To test for the impact of filters on FC I will compare the corner sharpness with and without rear filter while focusing on the center instead of the corner. Otherwise, the testing procedure is the same as above.

These are two 100% corner crops with no filter as a reference to compare with the filter image crops below:

Lee Filter Sheet

• very slightly reduced contrast and resolution compared to no filter
• rating: + +
  

Kodak Wratten Filter

• not tested

Haida Rear Lens ND Filter Kit

• very clearly reduced resolution and contrast compared to no filter
• rating: – –
  

Kase Rear Filters

• not tested (due to mounting problems during the first test round)

Aurora Rear Filters (Prototype)

• reduced contrast and resolution compared to no filter
• rating: +

Flare resistance

How good is the coating of the filter? Do you see reduced contrast, artifacts, ghosts, or flare if you shoot against point light sources?

To test for impact on flare I’ve shot from the exact same position and angle against a LED flashlight. The lens was set to 14mm and f/11.

Without any filter, the image shows neither flare nor any ghosts.

Lee Filter Sheet

• lots of induced flare, ghosts, and artifacts
• reduced contrast
• rating: – –
  

Kodak Wratten Filter

• not tested

Haida Rear Lens ND Filter Kit

• nearly no induced flare
• some small ghost/artifacts visible
• rating: +
  

Kase Rear Filters

• not tested (due to mounting problems during the first test round)

Aurora Rear Filters (Prototype)

• some flare visible as well as some small artifacts
• it is possible that the flare is the result of the white plastic frame of the prototype which will be changed on the final product (I will retest the Aurora for flare when I get the filters with the final design)
• rating: –

Color transmission

Does the ND filter induce any color casts?

To test for color casts I’ve shot a white surface with controlled artificial light with and without rear filters (focal length 24mm, f/2.8). The white balance of all images is first adjusted to a neutral gray in the center of the image without a rear filter. The resulting images and histograms can be visually compared. Then all images are corrected to a neutral gray WB in the center of the images. The number of corrected WB values can be compared.

The following image and histogram show the neutral gray without a filter as a reference:

Lee Filter Sheet

• color difference ND 0.9 vs no filter: Temp -150 K, Tint +2 red
• color difference ND 1.2 vs no filter: Temp -150 K, Tint +21 red
• ND 0.9 rather neutral, while ND 1.2 induces a strong color cast
• rating: –
  

Kodak Wratten Filter

• not tested

Haida Rear Lens ND Filter Kit

• color difference ND 0.9 vs no filter: Temp +150 K, Tint +9 red
• color difference ND 1.2 vs no filter: Temp +50 K, Tint +12 red
• color difference ND 1.8 vs no filter: Temp +250 K, Tint +9 red
• color difference ND 3.0 vs no filter: Temp +50 K, Tint +1 red
• ND 0.9 and ND 1.2 induce slight color casts, ND 1.8 has a rather strong color cast and ND 3.0 is astonishing neutral
• rating: +
  

Kase Rear Filters

• not tested (due to mounting problems during the first test round)

Aurora Rear Filters (Prototype)

• color difference ND 1.2 vs no filter: Temp -50 K, Tint -1 red
• color difference ND 1.8 vs no filter: Temp +200 K, Tint -6 red
• ND 1.2 is extremely neutral while ND 1.8 shows a medium-strong color cast
• rating: +

Summary

Below is a quick summary of the test results followed by a recommendation.

Lee Filter Sheet

Handling: –

Robustness and cleaning: –

Resolution (center sharpness): +

Resolution (corner sharpness): +

Field curvature: + +

Flare resistance: – –

Color transmission: –

Kodak Wratten Filter

Handling: –

Robustness and cleaning: – –

Resolution (center sharpness): not tested

Resolution (corner sharpness): not tested

Field curvature: not tested

Flare resistance: not tested

Color transmission: not tested

Haida Rear Lens ND Filter Kit

Handling: +

Robustness and cleaning: + +

Resolution (center sharpness): +

Resolution (corner sharpness): –

Field curvature: – –

Flare resistance: +

Color transmission:+

Kase Rear Filters

Handling: –

Robustness and cleaning: +

Resolution (center sharpness): not tested

Resolution (corner sharpness): not tested

Field curvature: not tested

Flare resistance: not tested

Color transmission: not tested

Aurora Rear Filters (Prototype)

Handling: + +

Robustness and cleaning: + +

Resolution (center sharpness): + +

Resolution (corner sharpness): +

Field curvature: +

Flare resistance: –

Color transmission:  +

My recommendation would be to wait for the Aurora filters (available end of Q1/2020). It is very likely that they will offer the best compromise between handling and optical performance. (see update below)

Update January 11, 2020:

As written above I wasn’t able to really test the Kase filter, since it doesn’t fit in my lens. But if you are interested in the performance of the Kase filter take a look at the review of Paul Monoghan, he managed to fit the filter in his (L-mount) Sigma lens and did some tests using the 24MP Sigma FP camera:

https://www.diyphotography.net/keeping-it-small-using-rear-filters-for-the-sigma-14-24-f2-8-art-dg-dn/

He has evaluated most of the important topics like sharpness, color transmission, and handling. Just an evaluation of the impact on FC is missing.

I’m more and more convinced that the fit of the filter is a matter of tolerances. Right now I have the feedback of four different people: two of them were able to fit the filter in their Sigma lenses and two of them not (even after dozens of attempts at different angles).

And here is a nice video from Steve Woodall where he explains very detailed how he mounts the Kase filter in his lens (Steve is one of the two people mentioned above who are able to mount the filter):

https://youtu.be/xUayAXSfdWc

Update January 21, 2020:

I was in contact with Kase Filters Germany during the last two weeks to solve the mounting problem with their filter. After several suggestions that didn’t work, they finally came up with the idea to slide the filter from the side into the lens slot. I tried this a couple of times and with the right amount of force, I was finally able to mount the filter. Thanks to Kase Germany for their support. To compare the optical performance of the Kase filters to the other filters I will have to repeat most of the tests. Since this takes a lot of time I will do this when the redesigned production samples of the Aurora filters arrive. Due to the new information about the Kase filters, some of the text in the review above was also updated today. Here is a video by Kase Filters Germany which shows how to slide in the filters from the side:

Update February 2, 2020:

Duston Abbott has published a YT video about rear filter options for the Sigma 14-24mm DG DN. He hasn’t tested for FC but otherwise got similar results:

Update May 15, 2020:

Some news from Aurora. They will start a Kickstarter crowdfunding process next week for their new rear filters. The current plan is to ship the filters to customers in September. Their mounting concept looks really promising.

Update Mar 17, 2021:

Since Aurora still hasn’t sent their (pre-payed) filters from their Kickstarter campaign nor reacts to any emails I can’t recommend their products anymore. I currently use and recommend the Haida rear filters for the Sigma lens.