Back for the Future? IQ180 arrives...

[Wayne Fox]

Btw, do you think that the central magenta cast is related to the subject? It seems to be a close match to the white vehicles/foliage in the middle ground of your image.

I thought of that as well, and may test it a little more today. If an LCC takes on a cast because of subject matter then neutralizes that cast, wouldn't the concept be flawed? After all, all it is supposed to do is eliminate the faults of the sensor/lens combination. If this were the case the only good way to do LCC's would be shooting on completely neutral backgrounds so the only color cast and falloff caused by the sensor and not subject matter is removed.

Wayne, what WB setting did you apply to your image and LCC prior to rendering the LCC? And did you by any chance adjust WB for the image and not the LCC before you applied it? Finally, was the LCC frame shot immediately after the image under similar lighting conditions?

Yes, shot seconds after the first image. White balance was default. Do most force the back to a set WB when using a TC? Of course, the problem seems extreme no matter what, in fact it seems my image circle isn't large enough.

I shot this with and without the center filter, and end result is very similar either way.

Going to do some more testing today with the 35 as well as the 47. My results certainly seem much worse than I'm seeing from Tashley's images so maybe I'm still missing something in the process.

 

[Guy Mancuso]

Wayne I only use daylight on the back or tungsten. AWB can be thrown all over the place so I never use it.

 

[dougpeterson]

The "Analyze Technical Wide" right now can throw off the global white balance, requiring you to hand-correct the image back to neutral. It's something I expect they'll improve in the next version. I'd file this under very annoying but ultimately not a major issue.

 

[Jack]

Wayne I only use daylight on the back or tungsten. AWB can be thrown all over the place so I never use it.

The "Analyze Technical Wide" right now can throw off the global white balance, requiring you to hand-correct the image back to neutral.

White balance was default. Do most force the back to a set WB when using a TC?

As Guy indicated, AWB on the back throws WB all over the place, so if you then use "As Shot" when you convert in C1 your LCC will be unreliable. I use "Daylight" on the back, then the first thing I do in C1 is highlight the entire session of images and apply my base "Style" which includes WB, Sat, Sharpening and NR defaults. THEN I go and do LCCs and apply them to the relevant images, THEN I start editing that corrected file, including any WB tweaks. Note that it is crucial that your LCC frame and take frame both have identical WB, so if on my final the WB tweak is significant, I will sometimes delete the existing LCC, rerun the LCC frame with the new WB and reapply it, s per Doug's comment. That second application may be a little over the top, but it's really the only way to ensure accurate LCCs and then color across the frame...

Hope that makes sense.

 

[Wayne Fox]

Makes sense, but still doesn't explain my issues entirely. Worked with it some more today, making sure of WB issues etc. The 35xl still has some slight magenta cast at edges and is lighter at edges after carefully following everyone's recommendations. The LCC file still shows very strange discoloration in the middle of the image, and this also shows up to a lesser degree when shooting the the 47xl. The 47xl does seem to correct out to an acceptable file, still maybe a little light at the edges. The Rodenstock 70 also shows some magenta discoloration in a similar region although larger and softer and not as obvious. This is the part that isn't making sense ... the color cast and falloff should be somewhat uniform and move from the center to the edge. I'm going to shoot some LCC's by shining a light directly on the the white plate to see if I still get the odd color casts in the middle. I think I'll also rotate the back to see how the odd color moves in relation ... am I correct in that the IQ180 is actually several "stitched" sensors acting as one?

 

[yaya]

Wayne I'm not sure if this was raised before but what sort of diffuser filter do you use? It needs to be quite thick and sit flush to the lens to prevent any internal reflections that may lead to uneven corrections and difference in luminosity across the frame

my ¢2

Yair

 

[gazwas]

Having colour casts with the 70HR doesn't sound right IMO and possibly could point to your back having the issue, not the lens.

 

[Wayne Fox]

Wayne I'm not sure if this was raised before but what sort of diffuser filter do you use? It needs to be quite thick and sit flush to the lens to prevent any internal reflections that may lead to uneven corrections and difference in luminosity across the frame

my ¢2

Yair

I believe the one I have is from Phase. It is very thick, one side glossy one side matt. I've tried shooting it both ways, (no instructions on which side should face the lens that I could find) and it doesn't seem to make much difference.

I'm going to run tests tomorrow with the plate lit with direct light, and rotate the lens and back to see if the middle color casts are affected.

 

[cunim]

As Guy indicated, AWB on the back throws WB all over the place, so if you then use "As Shot" when you convert in C1 your LCC will be unreliable. I use "Daylight" on the back, then the first thing I do in C1 is highlight the entire session of images and apply my base "Style" which includes WB, Sat, Sharpening and NR defaults. THEN I go and do LCCs and apply them to the relevant images, THEN I start editing that corrected file, including any WB tweaks. Note that it is crucial that your LCC frame and take frame both have identical WB, so if on my final the WB tweak is significant, I will sometimes delete the existing LCC, rerun the LCC frame with the new WB and reapply it, s per Doug's comment. That second application may be a little over the top, but it's really the only way to ensure accurate LCCs and then color across the frame...

Hope that makes sense.

Nice clear explanation Jack. I will try it this way.

 

[tashley]

With Mamiya extension tubes on Phase 80mm at F10 ISO35 and studio lights (a softbox and a Mola dish). Shot tethered, which worked well but not flawlessly. Full sized file available for download at the link provided.

http://tashley1.zenfolio.com/p512009864/h185980ca#h160bc217

 

[Wayne Fox]

Again, sorry for hijacking this thread, but now I've done so this seems the best place for follow up. I've just sent samples to my dealer, but what I'm seeing from my IQ180 has me puzzled and suspecting my back might have an issue. I look forward to downloading the tests from Doug when I get somewhere with a faster connection so I can compare their 35mmXL vs. mine.

Anyway, here are 3 LCC files, all shot with the PhaseOne plate, shooting directly into a 6 foot softbox. Illumination was very even.

35mmXL

Here I rotated the back 180 degrees, which eliminates all other variables except the way the back is recording the data.

Last, here is one with the Rodenstock, and while it is far more even than the other two, you can still see some density and very subtle color shifting. I've never seen this with this lens, and in fact quit shooting LCC's with my p65 because they always came out almost perfectly even.

I didn't shoot the 47mmXL, but it shows similar problems, not as bad as the 35, but bad enough to be a problem. I've gotten away without shooting an LCC with the 47 before, but now I can't because of the discoloration in the middle.

I assume this is still lens cast issues because of the proximity of the sensor to the lens, but somehow because of they way the sensor is made it seems to be more of a problem than with the p65. I can understand issues at the edges but such shifts in the middle are problematic. I'm just trying to find out if this is the way it is with the new back, or if my back might have a problem - any opinions? My dealer should be calling me shortly.

 

[gazwas]

Wayne, I was shooting with my P65+ and 43XL today and the zero position LCC looked very similar to yours above. The cast was not quite as strong but still very noticable and the same unusual pattern/stripes of magenta across the LCC and strange patchy brightness. The wierd thing is once shifted these casts appear as expected, a subtle graduation from light to dark as does the magenta casting. I just think this is how the Schneider glass works with these sensors. The LCC in C1, for me at least removes these casts 100%.

I keep thinking of switching to the wide Rodenstocks but unless I'm reading the charts wrong the MTF curves of the 32 and 40 HR-W seem to suggest that while they are super sharp in the middle, the sharpness falls off quite a lot further from the centre, especially when shifted. The Schneiders MTF puts the centre not as good as the Rodies but stays sharper further to the edges so you can't win and there is no simple solution.

Rodies less colour cast when shifted but not as sharp at the edges. SK more colour cast stopping large shifts but sharper at the edge when shifted. :banghead:

 

[PeterL]

Wayne, it seems to me - if you turn the back upside down and the magenta center area shifts, - it's the back that is problematic and not the lenses at all.

Cheers, -Peter

 

[Wayne Fox]

Wayne, it seems to me - if you turn the back upside down and the magenta center area shifts, - it's the back that is problematic and not the lenses at all.

Cheers, -Peter

Yes that was why I did it ... flipping the back and the problem remains the same in relation to the back eliminates everything in front of the sensor, including lens, LCC plate, light source, etc.

 

[Wayne Fox]

Well since I already took over this thread, I thought it would be best to update my situation here to keep things together.

After some additional testing and working with my dealer (thanks Optechs), I found my back required an LCC for pretty much every shot to correct a density and magenta color shift, even with my 55 and my 75-150 on my DF. Some files were sent to Denmark and after receiving them Phase is shipping me a replacement IQ180 as soon as they can.

 

[Christopher]

Thanks for the update it sounds like a similar problem I had with my first back even though it wasn't that bad. I'm just a little surprised what phase is shipping. If every back is hand tested before shipping I'm surprised that such things can be overlooked.

 

[vjbelle]

Well since I already took over this thread, I thought it would be best to update my situation here to keep things together.

After some additional testing and working with my dealer (thanks Optechs), I found my back required an LCC for pretty much every shot to correct a density and magenta color shift, even with my 55 and my 75-150 on my DF.

My god...... I was so alarmed reading this that I shot my 80mm LS to see if I got any discoloration. I'm even from edge to edge. I don't have a Phase mount yet for my Alpa..... The only lens I own is the 35XL and with all of the problems everyone seems to be having I decided to wait for the dust to settle for maybe a fix from Phase.

Victor

 

[Christopher]

I have one question I would like to get some clarification:

"The "Analyze Technical Wide" right now can throw off the global white balance, requiring you to hand-correct the image back to neutral. It's something I expect they'll improve in the next version. I'd file this under very annoying but ultimately not a major issue."

What does it mean?

A: If the shot was 5500 it could go to 5350 or 5600 after the LCC is applied or something like that ?

OR

B: The WB stays at 5500 after the LCC correction, but there is still a general color shift (WB shift) going on, but the WB setting stays the same ?


Can anybody explain it in more detail, if it would be B, I would call it a major issue. I don't feel like hand correcting files for panoramic images. This would take forever and be very annoying.

 

[Wayne Fox]

My god...... I was so alarmed reading this that I shot my 80mm LS to see if I got any discoloration. I'm even from edge to edge.
Victor

my replacement back has been shipped, hoping it arrives tomorrow. I appreciate you testing this ... I was worried it was more widespread, just nobody has checked it out. It certainly isn't very apparent on normal images with the DF, so most wouldn't bother shooting an LCC. I would recommend to everyone with an IQ180 that doesn't have a technical camera to go ahead and make sure they aren't seeing this problem by shooting an LCC, I've heard of one other back with very similar symptoms.

 

[vjbelle]

Wayne,

I have also received a 60XL which is just a sweet heart of a lens (at least this copy!). I haven't even bothered to shot an lcc with this lens as I haven't been able to detect color casting (although I haven't tried shifting yet).....been testing side to side focus accuracy. I am VERY pleasantly surprised.... Can't recommend this lens enough for anyone who needs this focal length. Good luck with the new back.

Victor