As a long-time user of the Canon EF sysÂtem, I have meanÂwhile a largÂer colÂlecÂtion of high-qualÂiÂty EF lensÂes. To be able to use them on the new Canon EOS R5 with RF bayÂoÂnet, Canon has released difÂferÂent adapters. Right from the beginÂning, I have been using the basic mount adapter on my EOS R5, but I was curiÂous about the posÂsiÂbilÂiÂties of an adapter with extendÂed capaÂbilÂiÂties. Since I use a polarÂizaÂtion filÂter very often, I thereÂfore ordered the Drop-In FilÂter Mount Adapter EF-EOS R* with the C-PL polarÂizaÂtion filÂter about 5 weeks ago.
After a long wait due to the tense delivÂery sitÂuÂaÂtion, I finalÂly received and testÂed it. Here is a short report on the results.
In conÂtrast to the basic modÂel of the mount adapter, the Drop-In FilÂter Mount Adapter EF-EOS R has a filÂter slot, like those of the Canon Supertele lenses.
If someÂbody should think now: Great, then I can use my polarÂizÂing filÂter of my Supertele inside, I have to disÂapÂpoint: I already use a polarÂizÂing filÂter for my EF 400 f/2.8L IS II USM, but it doesÂn’t fit into the mount adapter despite the same inner filÂter diamÂeÂter - great job, Canon!
But before I go into more detail about the filÂter adapter, a few thoughts about the purÂpose of phoÂtoÂgraphÂic filÂters. If all this is already known, the folÂlowÂing secÂtion can be skipped.
Why do you need filters at all?
With anaÂlog camÂeras (these are the ones that used to require the inserÂtion of film 😉 ), the post-proÂcessÂing posÂsiÂbilÂiÂties of the images were very limÂitÂed, so that filÂters were regÂuÂlarÂly used to comÂpenÂsate for colÂor difÂferÂences in artiÂfiÂcial light or strong conÂtrasts in brightÂness between sky and earth in landÂscape shots (with gradÂuÂatÂed filÂters). EspeÂcialÂly when phoÂtographÂing with slide film, the posÂsiÂbilÂiÂty of post-proÂcessÂing was almost comÂpleteÂly eliminated.
In digÂiÂtal phoÂtogÂraÂphy, howÂevÂer, espeÂcialÂly with RAW files, colÂor corÂrecÂtion can also be perÂformed easÂiÂly in post-proÂcessÂing. In the case of high brightÂness conÂtrasts, I often take an brackÂetÂing series of 3 or more shots with difÂferÂent expoÂsure times and comÂbine them on the comÂputÂer to creÂate a shot that reproÂduces the desired dynamÂic range well. To a lessÂer extent, this can also be done directÂly from a RAW file, since today’s camÂera senÂsors have a much greater dynamÂic range than anaÂlog phoÂtoÂgraphÂic film. The extenÂsive posÂsiÂbilÂiÂties of digÂiÂtal post-proÂcessÂing with RAW conÂvertÂers thus make many filÂters disÂpensÂable - but not all.
In short: Since I am phoÂtographÂing digÂiÂtalÂly, I use only two difÂferÂent types of filÂters on my lenses:
Grey filter (ND)
A gray filÂter is what its name says, gray. In fact, someÂtimes it is almost black. Its purÂpose is to reduce the amount of light reachÂing the senÂsor in a uniÂform and colÂor-neuÂtral way (ND stands for NeuÂtral DenÂsiÂty). In conÂtrast to the stopÂping down of the lens, which changes the depth of field, it does not influÂence this. An image of non-movÂing objects takÂen with a corÂreÂspondÂingÂly longer expoÂsure time using a gray filÂter canÂnot be disÂtinÂguished from one withÂout it.
The purÂpose of the gray filÂter is usuÂalÂly to extend the expoÂsure time. When filmÂing, it is indisÂpensÂable to achieve a suitÂable expoÂsure time, which should usuÂalÂly be half the duraÂtion of the sinÂgle frame (e.g. 1/60s at 30 fps), even in dayÂlight and with an open aperÂture. ProÂfesÂsionÂal film camÂeras thereÂfore often have inteÂgratÂed switchÂable ND filÂters of difÂferÂent strengths.
When takÂing phoÂtographs, howÂevÂer, a gray filÂter is often used to achieve motion blur in dayÂlight. This makes it posÂsiÂble to disÂplay water surÂfaces smoothÂly regardÂless of the waves. For this purÂpose, I use an ND 3 filÂter, which only lets 1/1000 of the light through. Instead of 1/30 secÂond expoÂsure time you have to expose the filÂter for 30 secÂonds to get the same amount of light to the senÂsor. In the folÂlowÂing I want to show two examÂples to illusÂtrate the purpose:
In the picÂture above, the long expoÂsure time of 6 secÂonds makes the indiÂvidÂual water drops appear as light tracks, which makes the picÂture look much calmer. AnothÂer examÂple folÂlows here:
The image above was also takÂen with a 1000x grey filÂter (ND-3) and an expoÂsure time of 13 secÂonds. Due to the long expoÂsure time, the surÂface of the water appears smooth, the wave motion is shown like a light fogÂgy coatÂing. The clouds appear more blurred due to the moveÂment, the image thereÂfore has a cerÂtain calmness.
Polarizing Filters
A polarÂizÂing filÂter allows light of only one oscilÂlaÂtion plane to pass. NorÂmal dayÂlight and also artiÂfiÂcial light conÂsists of light rays that oscilÂlate in all planes. On non-metalÂlic surÂfaces, howÂevÂer, the light that oscilÂlates perÂpenÂdicÂuÂlar to them is reflectÂed more strongÂly. If the polarÂizÂing filÂter is adjustÂed to a 90° angle, these light comÂpoÂnents are blocked out. This effect can reduce reflecÂtions on glass, water surÂfaces and othÂer smooth surfaces.
This makes the green of the leaves look more intense and the sky turns to a darkÂer blue colÂor. This effect is most intense when the sun is at a 90° angle to the image detail, directÂly against or with the sun, the polarÂizÂing filÂter has hardÂly any effect. With strong wide-angle lensÂes that covÂer a wide range of angles, the effect can thereÂfore vary in intenÂsiÂty in the difÂferÂent secÂtions of the sky, which can someÂtimes be disturbing.
There are still linÂear and cirÂcuÂlar polarÂizÂing filÂters to be disÂtinÂguished, but to go furÂther into this difÂferÂence would lead too far. In the end, howÂevÂer, in phoÂtogÂraÂphy at present cirÂcuÂlar polarÂizÂing filÂters are used almost excluÂsiveÂly. FurÂther details can be found at interÂest e.g. at Wikipedia.
The above image is takÂen from the same posiÂtion as the one shown above with the ND-3 filÂter. The post-proÂcessÂing in LightÂroom was the same for both images. But this time I used a polarÂizÂing filÂter (B&W KäseÂmann*). The expoÂsure time was now only 1/80 secÂond. In comÂparÂiÂson, you can clearÂly see that the green of the leaves appears much more intense, the sky shows a slightÂly more intense blue, the clouds are more clearÂly strucÂtured and the waves on the water are now perÂfectÂly visible.
I often use the polarÂizÂing filÂter for landÂscape and city shots when the sky is clear.
Back to the Mount Adapter Drop-In
Why did I buy this adapter now? As a long-time Canon phoÂtogÂraÂphÂer I have a large colÂlecÂtion of Canon EF lensÂes, which I would like to use on my new mirÂrorÂless Canon EOS R5 as well. In addiÂtion I want to conÂtinÂue using my proven Canon EOS 5DSR DSLR which can only be used with EF lensÂes. Some of these EF lensÂes are also not yet availÂable for the new RF bayÂoÂnet. Canon was aware of this fact when they introÂduced the EOS-R sysÂtem and thereÂfore offered the posÂsiÂbilÂiÂty to conÂtinÂue using the existÂing EF lensÂes via EF-RF adapters.
In conÂtrast to third-parÂty soluÂtions like those from SigÂma (MC-11) for Sony alpha camÂeras, the EF lensÂes are even nativeÂly supÂportÂed on Canon R camÂeras. ThereÂfore the perÂforÂmance remains at least on the same levÂel as with the Canon DSLR bodÂies. Some lensÂes, like my TS-E 17mm or the 85mm f/1.2L II even work much betÂter on the EOS R5 than before on my DSLR. More details can be found in my iniÂtial expeÂriÂences report about the Canon EOS R5.
Comparison of the filter types
In the picÂture above, I have placed the two filÂter types next to each othÂer. The screw-on filÂter on the right is a high qualÂiÂty mulÂti-layÂer coatÂed modÂel from B&W KäseÂmann* with 77mm thread. If you comÂpare the grey valÂues in the picÂture above, you can already see that the threadÂed filÂter absorbs a bit more light than the drop-in filÂter. Since both filÂters are on a white backÂground and the incomÂing light thereÂfore passÂes the filÂters twice, they appear darkÂer here than in transÂmitÂted light.
Screw-on filters
Since many lensÂes have difÂferÂent filÂter diamÂeÂters, you need sevÂerÂal filÂter sizes or you have to adapt largÂer filÂters with adapter rings, which means a lot of fidÂdling. FurÂtherÂmore, the lens hoods often do not fit anymore.
I have been using a very high qualÂiÂty 77mm filÂter (B&W KäseÂmann) that fits on my Canon EF zoom lensÂes from 16-200mm.
Even if the filÂter diamÂeÂters of the lensÂes are idenÂtiÂcal, the filÂters have to be changed as well or you need sevÂerÂal of them, which is quite expenÂsive. There are also some lensÂes which do not offer the posÂsiÂbilÂiÂty to use screw-on filÂters because of proÂtrudÂing front lensÂes or which have such large filÂter diamÂeÂters that filÂters become disÂproÂporÂtionÂateÂly large and expensive.
CurÂrentÂly I own 3 lensÂes with this probÂlem: the TS-E 17mm, my Samyang 14mm and my SigÂma DG OS HSM 60-600mm (with 105mm filÂter diamÂeÂter!). For the wide angle lensÂes, you might use filÂter holdÂers that are mountÂed in front of the lens, but they are also very bulky, expenÂsive and difÂfiÂcult to mount.
Using the filter mount adapter
The filÂter in the filÂter mount adapter fits for all EF lensÂes and can remain on the camÂera when changÂing lensÂes. By the way, in addiÂtion to the polarÂizÂing filÂter I bought the Drop-in Clear FilÂter A* which can remain in the filÂter mount adapter if I don’t want to use the polarÂizÂing filÂter. This has the welÂcomed side effect of comÂpleteÂly covÂerÂing the shutter/sensor chamÂber when changÂing a lens, so that dust can be effecÂtiveÂly blocked. I think this will prove its worth on dusty safaris (which we hopeÂfulÂly can plan again soon after CoroÂna) in the future.
The quesÂtion that interÂestÂed me now was whether the drop-in filÂter is optiÂcalÂly as good as my proven screw-on filÂter, which alone costs more than $ 100,-. Does it perÂhaps make a difÂferÂence, whether the filÂter is locatÂed in front of or behind the lens?
Comparison test
In order to ensure idenÂtiÂcal conÂdiÂtions of comÂparÂiÂson, I intenÂtionÂalÂly chose a staÂtÂic test setÂup with artiÂfiÂcial light. The motive, that was used, is a small object that is very familÂiar to every Canon user:
I put the lens cap on a white sheet of paper and illuÂmiÂnatÂed it from behind at an angle of about 45°. I aligned the camÂera on a sturÂdy triÂpod at an angle of about 30° to the cap. All picÂtures were takÂen with the Canon EOS R5 and the EF 24-105 f/4L II IS USM lens at 105mm focal length, aperÂture 8, 1/8s expoÂsure time and ISO 100 and editÂed in Adobe LightÂroom ClasÂsic 10 with idenÂtiÂcal paraÂmeÂters. I adjustÂed the white balÂance in LightÂroom with the pipette on the white backÂground of the image withÂout mountÂed filÂters to make any colÂor deviÂaÂtions visible.
The folÂlowÂing picÂtures show the verÂsion with the Canon Drop-In C-PL filÂter on the left and the verÂsion with the B&W KäseÂmann screw-on filÂter on the right.
First a comÂparÂiÂson with both filÂters set to the minÂiÂmum effect:
First of all, you can see here, that the right image is slightÂly darkÂer than the left one. ThereÂfore I have used LR to brightÂen the right image by 1/3 f-stop, in which case the brightÂness is comparable:
All in all, the Canon CP-L shows slightÂly more details only in the 200% view. In direct comÂparÂiÂson, the screw-on filÂter proÂvides a slightÂly warmer image. But both effects are absoluteÂly negligible.
And now the much more interÂestÂing comÂparÂiÂson of both polarÂizÂing filÂters using the maxÂiÂmum amount of visÂiÂble effect:
Again, the image with the screw-on filÂter is slightÂly darkÂer, so here again the comÂparÂiÂson with brightÂenÂing of the right image by 1/3 f-stop:
ForÂtuÂnateÂly, in direct comÂparÂiÂson both images show a comÂpaÂraÂbly good extincÂtion of the reflecÂtions of the light source. This is sureÂly the main thing. Again, the screw-on filÂter shows a slightÂly warmer image and shows slightÂly less detail, which is only visÂiÂble in the 200% view.
By the way, the qualÂiÂty of the resÂoÂluÂtion can be objecÂtiÂfied indiÂrectÂly via the size of the RAW files: Canon stores them interÂnalÂly in a lossÂless comÂpressed forÂmat. More detailed images can be comÂpressed less than images with less detail. Since all othÂer facÂtors (image conÂtent, expoÂsure paraÂmeÂters, lens) are the same for all images, the file size is thereÂfore a suitÂable paraÂmeÂter for meaÂsurÂing the levÂel of detail. The RAW files using the screw-on filÂter are between 1.6% and 1.9% smallÂer than those using the slide-in filÂter. HowÂevÂer, this minÂiÂmal difÂferÂence is cerÂtainÂly absoluteÂly negÂliÂgiÂble in real life.
Comparison under real conditions
In response to a speÂcial request, I comÂpared both types of filÂters under real conÂdiÂtions. This time, durÂing my trip to Africa, I took a phoÂto of Mount KilÂiÂmanÂjaro in Tanzania.
The shots can be found below: on the left the shot with the Canon drop-in filÂter and on the right the one with the B&W KäseÂmann screw-in filÂter. Both shots were takÂen shortÂly one after the othÂer with my Canon EOS R5 and the EF 16-35 f/4L IS with a focal length of 16mm, aperÂture f/6.3. I adjustÂed both filÂters to maxÂiÂmum effect. The image with the screw-in filÂter was brightÂened by +0.23 in Adobe LightÂroom for direct comÂparÂiÂson, all othÂer slidÂers were left in neuÂtral position.
InterÂestÂingÂly, the screw-in filÂter seems to give a slightÂly warmer tone. The WB-autoÂmatÂic of the camÂera deterÂmined a colÂor temÂperÂaÂture of 6250 °K there. With the drop-in filÂter, howÂevÂer, it was 6500 °K. But this minÂiÂmal deviÂaÂtion is sureÂly irrelÂeÂvant in practice.
But enough of the prefÂace, picÂtures say more than 1000 words:
So, what does the comÂparÂiÂson show now?
OverÂall, I see litÂtle difÂferÂence in both shots. At the same time, howÂevÂer, both images show a major probÂlem of all polarÂizÂing filÂters with super wide-angle lensÂes. The effect of a polarÂizÂing filÂter is highÂly depenÂdent on the angle of the light rays to the viewÂing axis. Thus, both images show a maxÂiÂmum effect approxÂiÂmateÂly in the cenÂter of the image, where the light rays come from about 90° from the left. Towards the edges, howÂevÂer, the effect decreasÂes more and more, since the lens covÂers an image angle of 108° in the diagÂoÂnal and thus the angle from the viewÂing axis to the light rays deviÂates strongÂly from the ideÂal 90°. The edges of the image thus appear sigÂnifÂiÂcantÂly brighter and with less contrast.
This effect is thus apparÂentÂly indeÂpenÂdent of whether a drop-in or a screw-in filÂter is used. Whether you like the effect or not is a matÂter of taste. But it canÂnot be avoidÂed when using polarÂizÂing filters.
Résumé
The Canon Mount-Adapter Plug-In EOS EF-R C-PL allows the use of a polarÂizÂing filÂter with all EF lensÂes, even with those which canÂnot be equipped with a front filÂter, like some super wide-angle lenses.
In its effecÂtiveÂness it is absoluteÂly comÂpaÂraÂble to a very high qualÂiÂty screw-on filÂter, the light transÂmisÂsion is even betÂter than with my very good B&W KäseÂmann polarÂizÂing filÂter. In addiÂtion, by using a neuÂtral filÂter, which can be purÂchased sepÂaÂrateÂly, the mount adapter can effecÂtiveÂly preÂvent dust from enterÂing the camÂera, which can be helpÂful in dusty environments.
In the near future I plan to buy an addiÂtionÂal ND-gray filÂter. So far Canon only offers a variÂable ND filÂter*, but it is very expenÂsive and I don’t need the variÂabilÂiÂty. But there are more comÂpatÂiÂble filÂters announced by an exterÂnal comÂpaÂny. I will stay tuned and will report furÂther if necessary…
AddenÂdum: in the meanÂtime I was able to purÂchase the origÂiÂnal variÂable ND filÂter from Canon at a reaÂsonÂable price. I have already used it sevÂerÂal times with good results.
*= AffilÂiÂate Link
