Noisy P65+ Files

[CBarrett]

I've been noticing issues lately from time to time with certain images from my P65+ being much noisier than I would expect them to be, with even the noise suppression being unable to help.

Now, I've been REALLY busy shooting, more than a bit sleep deprived and a little scattered lately so it took me longer than I care to admit to figure the problem out.

I finally noticed that the noise was occurring only on the edges of images, in particularly when I was applying liberal movements to wide lenses.  As it turns out, the noise was introduced when the LCC correction (with Falloff Correction applied) attempted to adjust for vignetting.  Sometimes at full strength, it's trying to compensate for up to a 2 stop loss in light and the information just isn't there in the files.

So yesterday, I just dropped the Light Falloff correction to 25%, pumped more light into the right side of the frame, and all was good again.

It makes me think that (as much as I hate putting anything in front of my lens that I should go back to using center filters on the wide lenses.

I also had one more idea to resolve these instances.... shoot a middle exposure, shoot a +2 exposure and drop that on top of the middle using the LCC exposure (with NO Falloff Correction) as a mask in Photoshop.  I'm gonna have to play with that now.... but first COFFEE.

I'll cross post this to GetDPI, as I think it's pretty pertinent.

C B

[rethmeier]

Chris,
There's a reason why they(Schneider) invented centre-filters.
The Light Falloff correction is just a stop gap.

Are you having the same issues with the HR's from Rodenstock?

Cheers,
Willem.

[ondebanks]

LCC/Falloff correction (what we astronomers call "flatfielding") is merely amplifying the noise along with the signal.
If a 2 stops correction is required to some parts of the frame, you are 4x deficient in signal, so you have 2x the noise [from sqrt(4)=2 being the difference in the Poisson error, aka shot noise].
The LCC corrected pixels will therefore be 2x worse in shot noise, which is the dominant source of noise in most circumstances.

If the shot is taken at ISO 200, say, it will appear post-correction as if the centre is at ISO 200, further out is at ISO 400 and the corners are at ISO800 (as far as noise is concerned).
Does this tally with what you are seeing?

[JonathanBenoit]

Are you experiencing this with the Schneider 35 specifically? I wonder if the Rodenstock 35 HR suffers in the same way. Someone should do a comparison between the two.

[cunim]

It makes me think that (as much as I hate putting anything in front of my lens that I should go back to using center filters on the wide lenses.

I also had one more idea to resolve these instances.... shoot a middle exposure, shoot a +2 exposure and drop that on top of the middle using the LCC exposure (with NO Falloff Correction) as a mask in Photoshop.  I'm gonna have to play with that now.... but first COFFEE.

I'll cross post this to GetDPI, as I think it's pretty pertinent.

C B

If you are working with static subjects such as interiors, why not just average?  It might be easier to take four or nine exposures (0.5 or 0.33 noise) to gain DR.  Then you have more latitude to push the darker areas.  This is not so much a suggestion as a question.  Averaging is commonly used in imaging and I was wondering if it is something commercial photographers do?

[JonathanBenoit]

If you are working with static subjects such as interiors, why not just average?  It might be easier to take four or nine exposures (0.5 or 0.33 noise) to gain DR.  Then you have more latitude to push the darker areas.  This is not so much a suggestion as a question.  Averaging is commonly used in imaging and I was wondering if it is something commercial photographers do?

I'm not sure about how chris feels about this, but Id rather not get into that whole mess of combining exposures unless completely necessary. He probably uses the 35mm more than any other lens and this means that many/most of his shots will need to have substantially more post processing. Center filter would be the best option.

[Harold Clark]

I'm not sure about how chris feels about this, but Id rather not get into that whole mess of combining exposures unless completely necessary. He probably uses the 35mm more than any other lens and this means that many/most of his shots will need to have substantially more post processing. Center filter would be the best option.

If the software could automatically blend two exposures ( one for the center, +2 for the corners ) that would be one thing, but doing this manually would be a real pain I would think. If a center filter would solve the problem I would be tempted to go that route to avoid fiddling with things later in post production.

[BernardLanguillier]

If the software could automatically blend two exposures ( one for the center, +2 for the corners ) that would be one thing, but doing this manually would be a real pain I would think. If a center filter would solve the problem I would be tempted to go that route to avoid fiddling with things later in post production.

I guess that the question is which method degrades image quality most:
- the center filter being a filter is likely to create some amount of flare and some issues with lights directly present in the image,
- the HDR approach will require a very robust tripod/head to limit camera movement between images (it will probably never be pixel exact) as well as a good software to overlay the images percectly and then produce a natural blend. I have found PT Gui to do a great job at overlaying/auto masking images this way.

In the end, why not try both approaches and compare?

Cheers,
Bernard

[ErikKaffehr]

Hi,

Light falloff is mostly related to physics, something called law of "cosine fourth". It's less pronounced on inverted telephoto designs, made for DSLRs but they have other issues and they also have light falloff, but less.

http://photo.net/large-format-photography-forum/003AwE

http://www.largeformatphotography.info/filters.html

http://dougkerr.net/Pumpkin/articles/Cosin...rth_Falloff.pdf

There are some optical tricks which reduce the light falloff, but it's still significant.

Best regards
Erik

Are you experiencing this with the Schneider 35 specifically? I wonder if the Rodenstock 35 HR suffers in the same way. Someone should do a comparison between the two.

[Chris Benes]

P65 Noise issues.

Another option is using a new set of lenses for your images that need camera movements and not have to flood your image with extra light and change the mood of the shot.  Hasrtblei has produced with Carl Zeiss a set of three lenses that are re-purposed V series lenses.   A 40 TS, 80 TS and 120 Macro TS.  They are sharp from edge top edge.    they can be rotated independently and have 8 degrees of tilt and 10mm of shift.

The lenses have Canon mounts that can be controlled electronically though the Hartblei BCam.   The sliding back is motorized so you don't ware out the components and puts the digital back in the correct film plane for ultimate  sharpness.   LL reviewed the product last December.

Chris Benes
Sales and Support Manager
DigitalFusion
Culver City, CA  
714-330-3166
www.phaseonesc.com

[JonathanBenoit]

P65 Noise issues.

Another option is using a new set of lenses for your images that need camera movements and not have to flood your image with extra light and change the mood of the shot.  Hasrtblei has produced with Carl Zeiss a set of three lenses that are re-purposed V series lenses.   A 40 TS, 80 TS and 120 Macro TS.  They are sharp from edge top edge.    they can be rotated independently and have 8 degrees of tilt and 10mm of shift.

The lenses have Canon mounts that can be controlled electronically though the Hartblei BCam.   The sliding back is motorized so you don't ware out the components and puts the digital back in the correct film plane for ultimate  sharpness.   LL reviewed the product last December.

Chris Benes
Sales and Support Manager
DigitalFusion
Culver City, CA  
714-330-3166
www.phaseonesc.com

Please stop. Completely not related to the topic. The is the worst I've seen it. You dealers really need to pick your spots better than this.

[Dick Roadnight]

I've been noticing issues lately from time to time with certain images from my P65+ being much noisier than I would expect them to be, with even the noise suppression being unable to help.
C B

If this is a P65+ issue, not a lens issue, it is what Hasselblad are trying to overcome with the 60Mpx chip... as hotly denied by Doug.

[CBarrett]

If this is a P65+ issue, not a lens issue, it is what Hasselblad are trying to overcome with the 60Mpx chip... as hotly denied by Doug.

Yeah, at first I was like "What's up with my back?!!!" but then fairly quickly realized this was only happening in areas of heavy vignetting that we're being corrected in software.  I'm gonna try a center filter as well as blending exposures (with LCC image as mask).  I already do a fair amount of exposure blending for blown out lighting in interiors.

Got my 55 and 70 back from Arca this week (just waiting on the 43) and the Rm3d will get put to heavy use in the next couple weeks : )  As a side note, the mounting tubes for both the 55 and 70HR add very little length to the overall lens (actually none at all on the 55) so the lenses take about the same room in the case as they did before mounting, something I was a little worried about.

Yada yada ya

CB

[Doug Peterson]

If this is a P65+ issue, not a lens issue, it is what Hasselblad are trying to overcome with the 60Mpx chip... as hotly denied by Doug.

Pushing the exposure of heavily vignetted areas of a frame results in an increase in shadow noise in that area. When you are used to looking at amazingly clean shadow detail it's surprising to see any noise in the shadows.

It's easy to forget/overlook how much the image is being pushed when the LCC simply "corrects" the vignette.

Doug Peterson
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