Hasselblad/Imacon red color cast using ND filters

[doogles]

I am currently using a Hasselblad CF 39 back with an H2, using Lee Neutral Density filters.  The filters give the images a red color cast, and the color cast intesifies when more stops of ND are added.  This is causing some color consistincy issues and is really bogging down my workflow.  Has anyone heard of this problem?  Does anyone have any suggestions?

[josayeruk]

I am currently using a Hasselblad CF 39 back with an H2, using Lee Neutral Density filters.  The filters give the images a red color cast, and the color cast intesifies when more stops of ND are added.  This is causing some color consistincy issues and is really bogging down my workflow.  Has anyone heard of this problem?  Does anyone have any suggestions?
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When do you make your grey balance?

Jo S.x

[doogles]

I shoot grey cards everytime the filters change, but it does not fix the problem.  Also, a grey card won't do anything good for me when we are shooting at sunrise or sunset.  I can pretty much match color using custom white balance and curve settings, but that is where the workflow process slows down the most.  And they still don't have the same exact color when comparing to a shot where no filter was used.  Most of the time the client is sitting right there with me, so it gets pretty embarrassing having to deal with that.

[josayeruk]

I guess you are capturing a grey card with the ND filters in place?

What kind of grey card are you using?

I still think you would need to grey card even at sunrise and sunset.  Then tweak it a little with the colour balance sliders to warm up / cool down etc etc.  Otherwise you have no base point to start from.

Jo S. x

[doogles]

Right now we just have a regular grey card from kodak.  we are going to get the grey cards that come with the phase one backs shortly.  basically the grey card has nothing to do with the problem.  It actually does not help at all when the ND filters are in place.  That's why I have to spend time working with curves so much, which is what slows down the workflow the most.  The color cast is there from the very beginning, and what I am trying to understand is why it is there in the first place.  I have a strange feeling that it is the brand of digital back.

[josayeruk]

Right now we just have a regular grey card from kodak.  we are going to get the grey cards that come with the phase one backs shortly.  basically the grey card has nothing to do with the problem.  It actually does not help at all when the ND filters are in place.  That's why I have to spend time working with curves so much, which is what slows down the workflow the most.  The color cast is there from the very beginning, and what I am trying to understand is why it is there in the first place.  I have a strange feeling that it is the brand of digital back.
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I think the grey card is everything to do with the problem.

I am working with similar Hasselblad product and there is no such issue for starters!

If you are not performing a grey balance then the camera has no reference.  To be honest I never use the grey balance presets in camera as I don't find them that accurate.  I either use the H3D to make a custom balance or shoot a grey target and neutralise within FlexColor.

The kodak cards are also dreadful and suffer from metamerism.

Has your dealer not been through the grey balance procedure?  This will apply to any camera shooting a raw file.. Phase, Canon, Leaf etc etc...

Perhaps it would be helpful is you described your workflow to us.  Are you shooting tethered or to a CF card?  Do you use the neutralisation picker in FlexColor at any point?  Do you capture the grey card in camera to make a custom balance?

I would start by making a grey balance before applying the ND filter (how many stops is the ND filter and why are you using one out of interest!), then apply the filter and see if the colour balance holds.

I have no experience of the ND filters from Lee so maybe they are not truly neutral.  Dunno!    

Jo Sx

[pprdigital]

The Kodak grey card could indeed be part of the issue. The Kodak grey card is not a neutral grey card. It is intended for exposure balance, not color balance. A Gretag MacBeth card manufactured specifically for neutral color response would be more effective.

However, Doogles does mention that shooting at sunrise/sunset isn't necessarily the best place to use a neutral grey card. In this case, a color meter would be a valuable tool to have. The Hasselblad digital backs are the only digital backs on the market that allow you to dial in a manual color temperature. So, with a color meter, you could take a reading, and simply dial in that reading. This would accurately preserve the sunrise/sunset color temps if desired, rather than neutralizing the scene.

Steve Hendrix
PPR Digital

[doogles]

Here's the deal.

I use grey cards all the time, so there is always a reference for starters, and I have no color issues whatsoever...until I use the ND filters.  Also, I agree about the presets.  They suck.

I also agree that the Kodak cards are lame as well, but I have had no problem getting correct color using it...until I use the ND filters.  I am currently getting a set of proper grey cards, but I have used them in the past and they did nothing for this current situation.

The other photographer I talked to that has the same problem is using Tiffen filters, and I am using Lee, and the filters are new.  There is a chance it could be the back.

I'm using ND filters because I am on an automotive rig shoot, meaning I need 4-8 second exposures in the middle of the day.  I understand that ND's are not as common now, but they are still very important in the market I work in.

Here is a good example of the problem.

We used an ND Grad on one shot to get more detail in the sky.  Used a grey card, color balanced the shot, and the sky was light red.  It was light red because it was the only part of the shot where the ND filter was applied.  Everything else was neutral.  No grey card can fix that problem!  If I tried to make the sky look proper, the rest of the shot was screwed up.

If anyone has a chance, try getting a hold of an ND or ND Grad filter and see what happens.

[pprdigital]

Here's the deal.

I use grey cards all the time, so there is always a reference for starters, and I have no color issues whatsoever...until I use the ND filters.  Also, I agree about the presets.  They suck.

I also agree that the Kodak cards are lame as well, but I have had no problem getting correct color using it...until I use the ND filters.  I am currently getting a set of proper grey cards, but I have used them in the past and they did nothing for this current situation.

The other photographer I talked to that has the same problem is using Tiffen filters, and I am using Lee, and the filters are new.  There is a chance it could be the back.

I'm using ND filters because I am on an automotive rig shoot, meaning I need 4-8 second exposures in the middle of the day.  I understand that ND's are not as common now, but they are still very important in the market I work in.

Here is a good example of the problem.

We used an ND Grad on one shot to get more detail in the sky.  Used a grey card, color balanced the shot, and the sky was light red.  It was light red because it was the only part of the shot where the ND filter was applied.  Everything else was neutral.  No grey card can fix that problem!  If I tried to make the sky look proper, the rest of the shot was screwed up.

If anyone has a chance, try getting a hold of an ND or ND Grad filter and see what happens.
[a href=\"index.php?act=findpost&pid=103909\"][{POST_SNAPBACK}][/a]

Doogles:

I will certainly do some testing with our backs in the next several days. One way to determine if it's the back - if you use a grey card without the ND filters and there's no cast, there's probably nothing wrong with the back. But this ND filter cast affect may be something that needs unraveling. I'll see if I can reproduce this affect.

Thanks,
Steve Hendrix
PPR Digital

[John_Black]

Assuming the ND is truly neutral, couldn't you create the WB (K value) without the filter and then just apply that WB to the filtered shots?

[pss]

don't want to flame here....but when i tested the Hass backs i deliberately underexposed to see how the  color would react....the reds became unuseable....i think this is a problem with DMF backs in general....my p30 does the same, but to a much lesser degree...the leafs and sinars show it less....i think thsi is a kodak chip problem....i am assuming that using the ND filter makes the problem worse.....
i wonder if phase has a fix fo rthis in their P+ series, they claim much better color AND Cleaner dark shadows......

[pprdigital]

don't want to flame here....but when i tested the Hass backs i deliberately underexposed to see how the  color would react....the reds became unuseable....i think this is a problem with DMF backs in general....my p30 does the same, but to a much lesser degree...the leafs and sinars show it less....i think thsi is a kodak chip problem....i am assuming that using the ND filter makes the problem worse.....
i wonder if phase has a fix fo rthis in their P+ series, they claim much better color AND Cleaner dark shadows......
[a href=\"index.php?act=findpost&pid=103914\"][{POST_SNAPBACK}][/a]

You certainly are not flaming. You're only presenting an experience you had at one point with a Hasselblad product. Was it a CF-39 using Flexcolor 4.65? That's a more relevent issue.

Whatever the problem is, I am extremely confident that it will not require a $6,000 upgrade fee to remedy the situation (not flaming).  

Steve Hendrix
PPR Digital

[doogles]

Thanks for all the feedback.

Before we shoot motion with the ND filters, we shoot static shots without any filters.  These are the files that are truely "neutral".  The files with the ND in use also have the same exact settings, but they are red.

Example: Using the daylight preset without filters, the photo is neutral.  Put a 1 stop ND on, and, with the same daylight setting, the photo will have the reddish cast.  In order to fix it, I have to adjust curves and WB.  This is what slows my workflow down.

[hubell]

Thanks for all the feedback.

Before we shoot motion with the ND filters, we shoot static shots without any filters.  These are the files that are truely "neutral".  The files with the ND in use also have the same exact settings, but they are red.

Example: Using the daylight preset without filters, the photo is neutral.  Put a 1 stop ND on, and, with the same daylight setting, the photo will have the reddish cast.  In order to fix it, I have to adjust curves and WB.  This is what slows my workflow down.
[a href=\"index.php?act=findpost&pid=103921\"][{POST_SNAPBACK}][/a]

It is a kludge that does not solve your question as to why an ND filter is not really neutral, but you could expose a truly neutral grey card under mid-day light, and then expose the same grey card with the various ND filters you use. Open them all in Flexcolor and read the RGB values and come up with a set of CC corrections in FC that adjusts each of the grey cards shot with ND filters to balance with the one shot with no ND filter. Once you have the CC corrections for each ND filter, you can create a separate set-up in FC for each of the ND filters that incorporates those CC corrections.
BTW, it is commonly understood that many ND filters are not really "neutral". You may want to give a call to Singh Ray in Florida, which purports to make truly neutral ND filters and discuss this.
BTW, don't believe those quick to blame Hasselblad backs for this issue as well as for every ailment afflicting mankind as well as photographers. They have no objectivity, just an axe to grind.

[thsinar]

as many have stated here, it is certainly not your back which is the cause of this colour cast. And to rle this absolutely out make a test as suggested by Steve.

The filters are very likely to be the cause f the problem.

Thierry

It is a kludge that does not solve your question as to why an ND filter is not really neutral, but you could expose a truly neutral grey card under mid-day light, and then expose the same grey card with the various ND filters you use. Open them all in Flexcolor and read the RGB values and come up with a set of CC corrections in FC that adjusts each of the grey cards shot with ND filters to balance with the one shot with no ND filter. Once you have the CC corrections for each ND filter, you can create a separate set-up in FC for each of the ND filters that incorporates those CC corrections.
BTW, it is commonly understood that many ND filters are not really "neutral". You may want to give a call to Singh Ray in Florida, which purports to make truly neutral ND filters and discuss this.
BTW, don't believe those quick to blame Hasselblad backs for this issue as well as for every ailment afflicting mankind as well as photographers. They have no objectivity, just an axe to grind.
[a href=\"index.php?act=findpost&pid=103933\"][{POST_SNAPBACK}][/a]

[BernardLanguillier]

I hope you'll excuse the stupid question, but isn't there a way to shoot the scene without using a ND grad filter?

Digitally blending 2 files with different exposures is sometimes a workable by-pass, depending on the type of shooting of course.

It is a great solution when shooting from a tripod, less so when shooting handheld with a slow MFDB back.

Regards,
Bernard

[KAP]

Contact Lee, they are very helpful, if it is a back problem they would make a filter to compensate, if it's the filter they would fix that.

Kevin.

[pss]

You certainly are not flaming. You're only presenting an experience you had at one point with a Hasselblad product. Was it a CF-39 using Flexcolor 4.65? That's a more relevent issue.

Whatever the problem is, I am extremely confident that it will not require a $6,000 upgrade fee to remedy the situation (not flaming).  

Steve Hendrix
PPR Digital
[a href=\"index.php?act=findpost&pid=103917\"][{POST_SNAPBACK}][/a]

no steve it was the 22mpix version....
thanks for reminding me about the fee ...BUT i will try the upgrade before i buy it....if it makes the pretty much perfect P30 even better, i am more then happy to pay that price....

what i meant in general was that it seems like the reds in all digital capture are a little funky...IMO kodak sensor have more problems with it then dalsa chips....skin is the best example, skin in dark shadow is the hardest....canon has the same problem.....i think that phase has a pretty good handle on it, if they can fix it completely, even better.....

[jimgolden]

i have the same issue w/ ND filters from rosco on my strobes. slight pink tinge w/ my 5D and 1DsM2. it's a bugger, but I can usually dial it out in raw conversion and possibly selective color
in PS. I've learned to deal w/ it...

[alexjones]

I have used the Imacon 132c under similar conditions with Lee NDs and not had any problems with it.  The Kodak "gray card" is generally green but not consistently so.  I have never seen one that was red so the red shift seems to be from the card.  Try a 24 patch GretagMacbeth and choose one of the mid grays to see how it reacts.  When I have assisted on jobs not using my back I have seen others have problems from bad gray cards.  I use the Macbeths and have had very good results for a long time.  As was suggested earlier, try a balance through the filters under better illumination an the card.  Get a number from that and apply it to the later scenes.  Like Steve said, I don't think the back has anything to do with it.  The problem is some combination of balance, exposure and filters to my thinking.  There is no reason the chip should be suspected.  I do a fair amount of work with it and even under low light and long exposures it works well.

All the Best,

Alex R Jones, Digital Tech Pittsburgh

http://www.alexrjones.com/alexrjones/assistant.html