Hasselblad HC 120mm Macro lens - colour cast - possible?

[Dinarius]

Is it possible for a lens to have a colour cast?

In this case, I mean an extremely subtle red cast in one corner, and an equally subtle green cast in the diagonally opposite corner.

Put it this way, there is no way you would notice it unless you were shooting under even lighting against a white background.

Unfortunately, that's what I'm doing. 

The lens is the type 1 HC 120m. It's a few years old, but it's mint. It's never outside studio conditions.

The exact same setup, shot with the HC 80mm lens (albeit a wider view, obviously) seems perfect.

I've tried a few different situations and the problem is the same.

Any thoughts?

Thanks.

D.

[Christoph B.]

Which camera/back are you using?
Could you maybe show us the picture?
Do you see any color cast when you look though the viewfinder?

[Dinarius]

Thanks for the reply.

I'm using a H3D ll 39MS.

To be honest, I've never checked through the lens.

Here are two files. The X-Rite file is shot with the 80mm lens. The picture file is the 120mm lens.

Note the green cast in the top left hand corner - but spread across the left hand side of the image. Note the magenta cast bottom right hand corner, but also spread on the right hand side of the image.

Note the more neutral band in the middle of the image, pretty much from top to bottom.

Thanks.

D.

[Bart_van_der_Wolf]

Is it possible for a lens to have a colour cast?

In this case, I mean an extremely subtle red cast in one corner, and an equally subtle green cast in the diagonally opposite corner.

Hi,

The way you describe it, it would seem very unlikely that the lens alone is causing that. Only if some lensgroup got partially uncemented might there be some image wide effect in my estimation. It is strange that it seems to be with one (longer focal length) lens in particular as it seems.

Have you eliminated the possibility of lightleaks (covering the rest of the whole camera incl. viewfinder)?

Can you rotate the camera 180 degrees around the optical axis (or minus 90 and plus 90 degrees)? That would at least show if it is in the camera lens combination. When the cast rotates with the camera is would remain the same.

Then there is the possibility of sensor calibration issues, but I know too little of the specific Hasselblad methods that are linked to specific lenses. Does the Hasselblad software offer a Lens Cast correction like Phase One does for their MF cameras/backs, and smaller sensor cameras?

Just some thoughts.

Cheers,
Bart

[Christoph B.]

Could you tell us more about the light source, exposure time, iso setting etc?

I think it might be the back...

Did you make both photos with the same light source and settings?

I may be wrong but I think I can detect a hint of the color cast in the photo you took with the 80mm..

[Dinarius]

Thanks for the replies guys. I will post again with more info.

Meanwhile, this popped up via a Google search.

http://forum.luminous-landscape.com/index.php?topic=54497.0

D.

[Dinarius]

Shot these earlier. A small area of a very large window blind.

To my eye (and eyedropper), the first file (the 120mm) has more colour cast issues than the second (80mm) image.

They were shot within a few minutes of one another.

Thanks.

D.

[Dinarius]

Found this too.........

http://forum.luminous-landscape.com/index.php?topic=79559.0;wap2

D.

[Dinarius]

Finally, here is another shot from the same 120mm setup, but after using the Hasselblad/Phocus Scene Calibration tool. (I had darkened the images in the above post for illustrative purposes. This image is as exposed.)

I'm happy with that. Looks clean.

Only problem I had was I got a "Failed to create correction. Correction error." on a couple of files. Repeated tries with the tool made no difference. Anyone know what the error is referring to? Exposure?

D.

[Christoph B.]

Did you make a neutral calibration shot (through a semi-transparent filter or glass) or did you use photos with content?

[Dinarius]

Did you make a neutral calibration shot (through a semi-transparent filter or glass) or did you use photos with content?

Hi Christoph,

The calibration is from one of the window blind shots I posted earlier. (I'm not in a position to do a proper setup right now.) It's a vast improvement on the very same shot above with the obvious cast, I think you'll agree.

I would expect an even better scene calibration if I was using a semi-transparent filter, or shooting to a white card (which is also possible).

Thanks for your feedback.

D.

[BobDavid]

39-MS/HC 120 macro

The HC 120 is a fine lens. It is perfectly well-suited for a 39-MS setup. Now if you intend to upgrade to MS 200 megapixel back, the 120 II and the 50mm II are far superior.

For fine art repro, I always put a sheet of white foam core over the artwork (covered the entire field) and took a picture of it as a reference shot. I liked putting down the foam core so that I could check illumination across the field with a flash meter. The flash meter made adjusting lights a snap.

I always photographed art in "reproduction" mode to render a flat file. The "reproduction" mode is the way to go for all copy work.

I spent a fair amount of time building custom profiles for art repro. And in the end, I found the native Hasselblad "Natural Color" profile was by far the best.

Another huge consideration is making sure your strobes are putting out consistent color.  I used Elinchrom monoblocks.

[Dinarius]

Bob,

Thanks for the feedback. 

D.

[shaun]

I had this too and it was terrible when shooting kitchen doors on a neutral background with tilt shift combination.

Do a custom white balance. I didn't have a purpose bought disc and used a piece of white perspex infront of the lens. I cranked the iso up to 400 or 800 for the test. Simple. I do it with every studio shot now. As when you know what you are looking for it is obvious.

Shaun

[Dustbak]

The HC vs1 is much more prone to abberations and color cast. In most cases Phocus will be able to get rid of it afterwards. However the HC120 cannot be used with the tilt/shift combination (HTS). You can attach it to the HTS via the extention rings but the calculations for corrections are simply not in Phocus so your results will be awful in that case. You are much better of using the 100 or 150 with extention rings together with the HTS.

The HC vs2 is much better in every way for that matter!

[shaun]

To clarify I was using an 80mm with HTS and not the 120. Same type of result and same solution though.

Shaun