SWC and digiback for B&W?

[macmx]

Dear all,

I was just thinking: Does the angle of the light when using SWC, which can cause magenta casts, matter when shooting black and white? Obviously, it matters when converting to black & white and lightening/darkening different colors, but if I use a yellow, red or green filter, will it mess up black and white photographs as well?

Thanks.

Mc

 

[jotloob]

Marc

I believe the magenta cast is not caused by the lens .
Try the following : Use the flash sync cable , set the back to flash sync mode and the exposure time at the back to 2 seconds (or even 3 sec.) , regardless of your shutter exposure time .
Your shots should now not have a magenta cast anymore .

The issue I have in mind is caused by a slightly wrong syncronization between the shutter and the digital back , which is mostly seen with an exposure time of a 1/125 sec. or even shorter . (valid for all SWC cameras)

The reason for this issue is , that HASSELBLAD and other digital backs , are so called "sleeping backs" and they need a kind of wake up .

Please come back with your results .

Jürgen

 

[macmx]

I thought the magenta cast was caused by the light hitting the sensor at an angle, causing certain wavelengths to be removed?

Same thing with the Leica M8, which the M9 now has solved with a new sensor.

 

[alastairbird]

I used to have an SWC/M and I shot with both a 16MP and 39MP backs. Both had fairly substantial magenta/green casts - the cast is caused by the lens - it's inescapable with the SWC because it's a non-retrofocus lens (is that right) - at any rate, you get the colour shifts as you would with movements on a view camera

I would assume that there would be density in those casts and that converting to black and white would minimize them but not eliminate them.

However, there is a solution - you can shoot a custom white correction and then use that to eliminate the colour casts. All you do is shoot with a piece of white plexi over the lens and then set Flexcolor to use that capture as a baseline for correcting the other capture(s). I did that with the SWC shots and it worked like a charm. After that a conversion to BW would be as it would with any normal capture, I believe. However, care has to be taken with the Custom White that you take it when you are shooting the actual capture (you can't shoot one in the morning and use it for all your other captures throughout the day) as different light causes different magenta/green shifts.

 

[jotloob]

I used to have an SWC/M and I shot with both a 16MP and 39MP backs. Both had fairly substantial magenta/green casts - the cast is caused by the lens - it's inescapable with the SWC because it's a non-retrofocus lens (is that right) - at any rate, you get the colour shifts as you would with movements on a view camera

I would assume that there would be density in those casts and that converting to black and white would minimize them but not eliminate them.

However, there is a solution - you can shoot a custom white correction and then use that to eliminate the colour casts. All you do is shoot with a piece of white plexi over the lens and then set Flexcolor to use that capture as a baseline for correcting the other capture(s). I did that with the SWC shots and it worked like a charm. After that a conversion to BW would be as it would with any normal capture, I believe. However, care has to be taken with the Custom White that you take it when you are shooting the actual capture (you can't shoot one in the morning and use it for all your other captures throughout the day) as different light causes different magenta/green shifts.

Alastair

I am aware of what you describe .
The cyan cast is found on the left side of the image and the magenta cast on the right side . This can be corrected by using the custom white balance method you describe . I agree to that , as I have done so a couple of times
when doing stitching .

I did not experience the cyan/magenta cast issue when using the 905SWC and the CFV-16 back . I did not try the CFV-39 yet .

But that still leaves the magenta cast (and only magenta cast) issue , due to the fact that with any SWC the syncronization is slightly wrong .
I can not remember where I read a note (in HASSELBLAD documentation) that the use of the sync flash cable is recommended , due to the fact , that the shutter relase mechnism behaves differnt to the 500/200 series cameras , when using the CFV-16/CFV-39 back .
Also , this issue was once discussed in an earlier thread , about 2-3 years ago , but I can not find that thread any more .

If you reread my previous post , you will see , that I wrote : the issue I have in mind . And that is : magenta cast only .
And that is the "sleeping back issue" .

I can proof that with my 905SWC and also with my ARCA SWISS and a RODENSTOCK digital WA lens , which is not a BIOGON type lens .
And there is a good solution for that kind of issue . Digital back wake up .

Jürgen

 

[alastairbird]

Alastair

I am aware of what you describe .
The cyan cast is found on the left side of the image and the magenta cast on the right side . This can be corrected by using the custom white balance method you describe . I agree to that , as I have done so a couple of times
when doing stitching .

I did not experience the cyan/magenta cast issue when using the 905SWC and the CFV-16 back . I did not try the CFV-39 yet .

But that still leaves the magenta cast (and only magenta cast) issue , due to the fact that with any SWC the syncronization is slightly wrong .
I can not remember where I read a note (in HASSELBLAD documentation) that the use of the sync flash cable is recommended , due to the fact , that the shutter relase mechnism behaves differnt to the 500/200 series cameras , when using the CFV-16/CFV-39 back .
Also , this issue was once discussed in an earlier thread , about 2-3 years ago , but I can not find that thread any more .

If you reread my previous post , you will see , that I wrote : the issue I have in mind . And that is : magenta cast only .
And that is the "sleeping back issue" .

I can proof that with my 905SWC and also with my ARCA SWISS and a RODENSTOCK digital WA lens , which is not a BIOGON type lens .
And there is a good solution for that kind of issue . Digital back wake up .

Jürgen

Hang on. The OP requests information regarding the issues with the light hitting the sensor:

Does the angle of the light when using SWC, which can cause magenta casts

In my response to his question, I assumed he was requesting information on the colour casts you get from the Biogon lens on a digital back, rather than issues with the sync. I wasn't questioning your response, I was stating my own personal experience with colour cast issues from the angle of light from the Biogon lens I owned.

My response was that there are colour casts on a 39MP back from a Biogon (well my Biogon, anyway) and those casts were satisfactorally solved with a custom white adjustment. Sometimes they were magenta, sometimes cyan, sometimes both and sometimes they were almost unnoticeable, sometimes alarmingly strong, depending on the light.

I have only used my CF-39 with the flash sync; I do not own a CFV back. I agree that if there is an overall magenta cast it may be a sync issue that will not be solved with a custom white.

Please note that the original poster does not specify which back he is using or thinking of using nor does he specify whether or not he's using the flash sync or another method of tripping the back. I was under the impression that using the flash sync was the only way to trip the back with an SWC.

 

[jotloob]

Todays test results

I have done a lot of testing today .
Using 905SWC with CFV-16 and CFV-39 as well .
Both backs were set to FLASH SYNC , EXPOSURE TIME 2 sec . ISO100 .
The camera was mounted on a tripod and I used a cable release . FLASH SYNC cable attached .
The weather conditions were grey sky and lots of snow . WB set to cloudy = (6500 k) A WB shot was taken for each test shot , using EXPODISC 95 mm .

Surprisingly for me , the two digital backs behave completely different although all conditions were the same .

The CFV-16 image shows a slight green/cyan cast all over the image .
This can easily be corrected using the the WB correction shot , which shows a similar tonality as the cast in the image , but is of course much darker .
Also slight changes to the WB , EV and other correction functions in PHOCUS or doing some slight corrections in PS will take away the remaining cast .

Surprisingly , in comparison to the CFV-16 image , the image taken with the CFV-39 shows the "typical" magenta cast on the right side and the cyan cast on the left side . I did not expect such a big difference .
The "square portion" in the middle of the image shows a slight magenta cast .

The total cast can not be corrected a 100% using the WB correction shot .
Further slight corrections as described before using PHOCUS and PS help you to get rid of the remaining slight casts .

Jürgen