Center Filters - Does software make them unnecessary?

[hdomke]

What are the pros and cons of a center filter for the 32mm Rodenstock lens? I'll be using that on a technical camera with a P65+ back.
From what I can tell a center filter is basically a radial graduated neutral density filter that helps correct vignetting.

Why can't this vignetting be corrected in software?
I know that Lightroom and Photoshop both have very sophisticated tools for correcting vignetting and other lens artifacts. I suspect CaptureOne has similar tools.
Furthermore, I will be creating LCC profiles with each picture. Won't the LCC profile help with vignetting and color artifacts?

$900 is a lot of money to spend on a filter if I can do the same thing with software. Furthermore, won't the filter increase the exposure time? Longer exposure times increase the odds of subject movement or camera movement.

Lastly, adding glass in front of the lens must have some deleterious effect on image clarity.  Light scattering would reduce contrast some (even though it would be minimal). Right?

[Weldon Brewster]

I'd actually like to know the answer to this question too.  I stopped using my center filter and just use LCC files on my 35xl.  Would I get better quality using both?

[Kevin Sink]

Not to take people away from this fine forum, which I use a great deal, but there is a good discussion on this topic on the getDPI forum:
http://forum.getdpi.com/forum/medium-format-systems-digital-backs/29887-centre-filter-lcc-correct-fall-off-tech-cams.html

It sounds like there might be less effect from optical considerations using the center filter vs having the LCC work that hard to even out the tonality.  More artifact noise with LCC vs less image degradation using another piece of glass.  The other big considerations are 1. increased exposure times for using the center filter 2. more diligence required at time of capture to prevent lens flare, which the center filters make the capture more prone to.

[Don Libby]

I've got a CF on my Schneider 35 which I've been using now for over 4 years and never remove it.  While a lot of problems can be fixed using software the less I have to fix after the fact the better it is and much faster. 

You'll still have to shoot a LCC whether you use a CF or not.  I personally feel the use of the CF gives me a better image file to work with.  I use a Cambo WRS1000 with a P65+ on top of a tripod and have never felt the need to remove the filter while shooting landscape.

Just my 2¢ worth...

Don

[JonMo]

Have to agree with Don,
I use CF with my 35xl all the time on both the Cambo wds and rs.
In landscape on a tripod with the early morn or sunset light; I have never had an issue with too little light or flaring.
I even keep it on for "street photography" with the rs hand held durring the day.

I use an Aptus 65s and IQ180

The difference in LCC profiles between having one and not are remarkable.
It's easy to see and the less prossessing to make an image the better IMHO

[Paul2660]

You have a good price on the Center Filter for the 32mm, as most places have it at around 1.5K.
As I recall you go from 86mm to 105mm with the Center filter for the Rodenstock 32m. 

You will be looking at around another 800 to 900 for a ND and Linear Polarizer in those sizes if you
use them.  At the 105mm size you are looking at Heliopan or Tiffen Pro both make excellent glass
and I don't think you will lose image quality. 

As others have pointed out, the center filter is designed to negate the natural vignetting of the wide
angle lenses on the sensor.  What you will get is a much more evenly exposed frame.   Without, you tend
to either get a evenly exposed center, but with a considerably darker edge.  If  you try to compensate for the
edges, you will then overexpose the center.  The underexposed edges will tend to show more noise even
at the lower ISO's 50 to 100.  Your LCC can help balance the exposure of the shot but it will not fix the
noise that was generated when you took the exposure (even if it lightens the corners).  By use of the
centerfilter you will start with a much more evenly exposed frame.  You still need the LCC to correct the
color shifts and if you shift, you need it for the normal amount of light fall off due to shifting.

The Rodenstock 32 at around 8.5 K depending on your mount is very hard to find much written about.
And I have yet to find anything written showing the effect of the Center filter and exposure even on
Rodenstock site. 

I have briefly used the Rodenstock 28mm on a P65+ which is the same sensor as the IQ160 and for sure
it needs a center filter.  The couple of days I was able to use it the owner had left the center filter behind
so we didn't get to use it, however he sent me several comparisons showing the before and after. 

The Rodentock 28mm Center filter is around $900.00 and goes from 72mm to 86mm, however you still need to get to around
105mm with a step up ring if you are going to use any filters or you will catch the vignetting of the filters. 

Paul Caldwell

[Enda Cavanagh]

I use the Centre filter on my Schneider 24mm and 35mm but not on my 28mm where you can only use a digital centre filter plugin in CS due to the huge front lens element. A licenses is supplied with the lens. You can also purchase a license at a later stage. On no account should you use the vignetting too in photoshop or lightroom because it doesn't take the lens movements into account.
Both have pros and cons but I prefer the physical centre filter on the 35 and 47mm lenses without a doubt. There is a huge light falloff on the wider lenses. If you shoot as I do a series of images from underexposed to over exposed images, problems will occur when you have to digitally remove the vignetting. You are basically recovering information which is barely there in the first place because the vignetting is so dark. That results in noise. I don't use capture one but if I use the vignetting tool on the 28mm shots in Phocus I get a lot of colour noise and I mean a lot. The digital centre filter plugin is a big improvement over phocus but it's still not as good as the centre filter on the lens which has pretty much evened out the light at the source (when the shot was taken). The physical filter will still have some vignetting but the vignetting tool in Phocus does a good job of getting rid of that because the vignetting is only slight so it can easily be recovered.
Another downside with the digital centre filter is I have to make a note of the movements and aperture for every single lens movement change. Once I process the RAW file having gotten rid of the colour cast using your remove cast tool I than have to open it in CS and open the digital centre filter plugin. I have to key in the aperture and lens movements. It than removes the vignetting based on these variables. It does a very good job but I'm sure a physical filter would do a better one especially on the underexposed shots. All that messing around adds a lot of time to my workflow. This can be a huge factor, depending on if you are using it professionally and how much you will earn per job. There is the initial investment in the physical centre but you will make that back in time saved.

There is the argument that less glass = better quality and you will have less reflections resulting in less flare and halos. This is probably the case. Halos and flare are less of a problem with the 28mm. It's still more of a problem than with a 35mm digital camera but that's the nature of the beast with view cameras. To be honest it's only a small issue when looking at the sun a while after sunrise or with directional lighting for architectural shots. A few halos are easy to remove with content aware in CS5.

So if the centre filter option is there for the Rodenstock I definitely would go with it.
 

[Guy Mancuso]

I use the CF on the 35XL all the time as well. The images and LCC are just more even in falloff and I feel a easier task for the LCC to make the corrections. If your out shooting with flash and you don't want to make any changes to aperture or bump the ISO to get a well exposed LCC. I will turn a strobe at the camera to get more light on the LCC that way. One way of getting a good exposed LCC shooting with strobes. BTW yes it is a PITA losing 2 stops but there is very little net difference between ISO 50 and 100 on my back so if i really need to get faster shutter speeds i will cheat and bump up the ISO a touch. Nature of the beast but the results smoke the 35D lens so its totally worth it. This is why I went tech cam was wide angles, at least that was the first excuse . I have none for the 90mm lens, except gear slut whore. LOL

Well i do want a tech cam only kit and a DF kit separately at times.

[Wayne Fox]

If you don't use a center filter you lose the equivalent amount of dynamic range in your capture.  Since with most center filters this amounts to 2 or more stops, using one is a great help in keeping shadow noise in the corners acceptable.  As has been mentioned it greatly reduces the data manipulation the file must go through when applying the LCC.

[pixjohn]

If I am shooting with strobe, I use the LCC because of the light loss. If I am shooting available light I use the center filter and LCC. As mentioned before you will get cleaner files with the filter, but I need the f stops from the strobe more then the cleaner file. I will also see noise in the corners sometimes from the LCC and larger camera movements.

[cng]

I'm also using the SK35mm with the CF permanently attached.  I'm not really interested in pushing the edges of my images in software by 2 or more stops without the CF.  Never had a problem with CF-related flare (AFAIK), and the +2 exposure compensation doesn't really bother me for the type of work I do.  In fact, I will buy the long-promised CF for my SK43mm as soon as it gets released.

On the other hand, the Rodenstock 32mm has a much larger front element than the SK35mm, so not sure if the Rodenstock's even larger CF will be an issue with regards to flare.

As others have mentioned, you will have to do a LCC shot (especially with shorter lenses) regardless of whether you are using a CF or not.

[Guy Mancuso]

The 32 is a large lens and the CF is about 1k from what I understand. From when i shot it I am not so sure you really need it. It does falloff but not nearly like the SK 35mm. This one requires more testing to see if it truly does help the cause or not. The 35mm IMHO you just can't shoot without it. I would like more time with the 32mm as i got asked a few questions about it this morning about shifting, rise/fall to 15mm which it certainly was better than my SK 35mm in this regards . I shot a church a couple weeks ago with the 35mm and at 15mm I got mush at the top of the building. From what i can tell without getting in trouble 12mm is my max on the 35mm. I will have access to the 32mm next week and would love to try this test again at 15mm and see if holds better. The 32mm is a wonderful lens but it is big, heavy and expensive. But I believe you can do without the CF on it. Hopefully I can update these observations again and get more time with it. I used it last time on landscape work and not buildings so it was a little hard to tell its limits.

[hdomke]

I hear a general consensus that the results are better if you use the filter instead of software. Does anyone disagree?

To me a software solution seems much more elegant.

Tell me where my reasoning is wrong:
Wide angle lenses have a problem with vignetting, which simply means that the periphery of the image is darker. There are three possible solutions:
1. Use a center filter to darken the center of the image.
2. Use software to lighten the periphery of the image.
3. Use software to darken the center of the image.

Solution 1 (Center Filter)
Problems:
1A Slower shutter speed and hence greater chance of subject or camera movement.
1B Extra glass and darkening material which must degrade the image to some extent.
The extra glass element must scatter some of the light which could reduce contrast.
1C Increased risk of flare.


Solution 2 (brighten the periphery with software).
Problems:
2A Brightening images increases noise.

Solution 3 (darken the center with software).
3A To get a proper exposure with this technique would require over-exposing the initial image. One would have to be careful to avoid clipping.

It would seem to me that the problem of noise could be avoided by solution 3.
However, you would have to use a longer exposure time, but you are already doing that with solution 1.

Thoughts? Comments?

[Don Libby]

While software can provide a solution it nevertheless must have the best possible image file to begin with thus the reason I use a CF on my 35mm. 

Again just my 2¢ worth.  Your mileage may vary....

Don

[Wayne Fox]

Solution 3 (darken the center with software).
3A To get a proper exposure with this technique would require over-exposing the initial image. One would have to be careful to avoid clipping.

There in lies the problem with a software solution ... to avoid clipping highlights while getting enough exposure in the corners.

If scene dynamic range isn't a problem (only 8 stops or so) maybe not an issue.  But most of the time you will get a much better file if you shoot with a center filter and LCC.

I sold my Alpa system ... just didn't fit my shooting style well.  If Live View on MF ever gets much better I will probably revisit it, but I also will probably only use retrofocus lens.  The extreme problems of my Schneider 35mmXL on the Alpa was just too much work and I just never felt the file quality wasn't problematic. Retrofocus designed lenses have much less problems with vignetting and color shifts.

[jsiva]

Solution 3 (darken the center with software).
3A To get a proper exposure with this technique would require over-exposing the initial image. One would have to be careful to avoid clipping.

It would seem to me that the problem of noise could be avoided by solution 3.
However, you would have to use a longer exposure time, but you are already doing that with solution 1.

Thoughts? Comments?

In addition to what Wayne said above, you'd be back to the problems in "Solution 1", i.e. longer exposures, camera/subject movement etc.

I went through this exact thought process...and using LCCs, CFs etc., just did not fit my workflow.  In the end, I got a 28D, and a decent copy of the 35 (from Jack), to go on my DF.  My main need was for stitching, and it seems to work extremely well for me with CS5 (not as fussy as CS4).  Also, which pano stitching, I am always using the centre of the lens, and have all the Phase One lens corrections available to me in C1.

Having said this, in my quest for a proper, large IC WA lens, I recently ran into some samples of the Canon 24TS on the hartblei, with an 80mp back.  It looked extremly good, and still allows about 12mm of shift.  For the price of the Rodie 23 or 32 and CF, I could get  this setup and perhaps even add the 17TS for super wides.  This solution, of course, gives me a good WA solution, and I don't have to tinker around with LCCs or CFs.

Brian Hirschfeld on this forum posted some samples of the Canon TS-e on Hartblei, and I believe he will be doing a comparison against the Rodie lenses.  I am waiting to see his thoughts as well.

In the meantime, I cannot help but think that Phase will release a 35LS and 28LS soon.  If not LS, I'm sure they would still be SK lenses.

Good luck with your quest...

[Kevin Sink]

I would think the most elegant solution to the vignetting would involve the least amount of work, and have the least potential for image degradation.    Software fixes seem to involve the most work and in some circumstances introduce the highest potential for image degradation.  A center filter would probably stay on the lens; just shoot the scene, then you don't have to spend time correcting for the vignetting: the fastest and simplest approach.
 
Single Capture:
I spoke with Rod Klukas, the US ARCA Swiss rep today, and he described the manufacturing of the Rodenstock center filters - extremely time consuming, exacting, using special glass, diamond cutters, etc.  He assured me that these filters ($1,500 for the 32mmHR CF) introduce very little if any image degradation.  (They better not for that price!)  He also stated that correcting for vignetting with software definitely introduces more artifact than using the filter.  So if my logic is accurate, the only disadvantage to using the center filter is the longer exposure time.  So if the wind won't let up, shoot the scene without the CF, and correct with software.  From my experience though, I usually wait for minimum wind even when I've never had a need for a center filter - it's just something we do anyway.
I should also mention that Rod said that several of his customers with the 35mm & 32mm that ordered the CF were very happy with them - he didn't mention a flare issue or reduced contrast.  He also said that the CF creates a "far more even tonality" than with using software.  I have since asked Rod about the contrast question:  in general, the Rodenstock CF's do not reduce contrast.  An exception might be if you had your brightest part of your scene in the very center of your image, in that case the contrast might be affected regionally to a small degree, but the filter does not introduce a global contrast reduction.  As far as flare, he suggested using a lens shade, whether or not you're using a CF.  Using a CF doesn't increase the chance of flare on it's own; the wides are prone to it anyway.

Mutliple capture for stitching:
If you are going to shift a 32mm or other wide angle lens for stitching purposes, then you exaggerate the illumination gradient along the sagittal plane from center to corner, because you're moving towards the darker region of the image circle.  The larger the gradient. the more is required of the LCC and possibly introduce more artifact. With the center filter, you lessen the gradient along that line, making the LCC work less.  C1 is a great program, but as with any processing program, the more you "lean" on it, the better the chances of introducing artifact.

Summary: 
If there is no evidence that CF's damage image quality, then there is little rationale for not using them; provided you can live with the longer exposure times, and expense!

[hdomke]

In addition to what Wayne said above, you'd be back to the problems in "Solution 1", i.e. longer exposures, camera/subject movement etc.

Option 3 (software to darken the center) does give you problem 1A (slower shutter speed) however, the key thing is that it avoids problems 1B (image degradation, however slight), 1C (potential for flare).

If the center filter were really this essential why doesn't the lens designer build it in so it is not optional? 

[jsiva]

Option 3 (software to darken the center) does give you problem 1A (slower shutter speed) however, the key thing is that it avoids problems 1B (image degradation, however slight), 1C (potential for flare).

If the center filter were really this essential why doesn't the lens designer build it in so it is not optional? 

Henry,

I have an Aptus 12 so all my logic is based on using a full-frame 80mp back.  However, I'm sure these lenses perform better re vignetting/colour cast on cropped backs without a CF.

In addition, I doubt we would all be willing to pay 7K+++ (depending on helical mount) for an F8 or F11 lens

[Stefan.Steib]

Using our HCam-B1 makes Center filters obsolete.
We get nearly no Light falloff with 17mm and 24mm TS-E´s, even the 14-24mm Nikon G-ED does pretty good at 14mm !
The retrofocus is not as strong as with MF flange focal distances (44,3mm=Canon EF to 63mm=Mamiya645)
The lenses are higher develloped than their MF counterparts (Aspherics, molded lenses,cheap by mass production and expensive R&D)
NO Distortions (newest computer optimised lens design)
Usable Movements without color casts ! 17mm on 80 MPix about 6mm vertical/5mm horizontal , 24mm on 80 MPix 12mm Vertical/10mm horizontal

The built in correction facilities in Capture one are more than enough to get perfect results from these files.

Greetings from our new office in Lindenberg/Allgäu

Stefan