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Author Topic: Why are Phase One backs good for long exposures  (Read 5753 times)

pjtn

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Why are Phase One backs good for long exposures
« on: March 24, 2012, 10:57:49 am »

I'm curious why Phase One P+ backs do long exposures so well compared to Hasselblad cameras which use the exact same sensors. As I understand the H3DII-31 is the same as the P30+ and the H3DII-39 is the same as the P45+.

Is it purely because the Phase One backs do a dark frame subtraction? Or is it something to do with cooling?
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theguywitha645d

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Re: Why are Phase One backs good for long exposures
« Reply #1 on: March 24, 2012, 12:21:57 pm »

Or it could be with simply image/signal processing. The Pentax 645D does even better than the Phase backs with long exposures.
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Graham Welland

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Re: Why are Phase One backs good for long exposures
« Reply #2 on: March 24, 2012, 02:48:35 pm »

It's not just signal processing but also the choice of sensor. The Kodak sensors and xpose+ of the P25+/P45+ etc also are important differentiators vs the P40+/P65+ & IQ backs with their Dalsa sensors.
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pjtn

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Re: Why are Phase One backs good for long exposures
« Reply #3 on: March 24, 2012, 10:07:13 pm »

I take it then that Phase One has never explained why the backs perform well for long exposures?
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Wayne Fox

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Re: Why are Phase One backs good for long exposures
« Reply #4 on: March 24, 2012, 10:30:54 pm »

Not all + series backs good at long exposure.  I do know the p45+ is probably the best, rated at close to an hour, but the p65+ I think is only a minute or so.   I'm not sure about the other p+ backs, but its seems to be a combination of kodak sensor plus Phase firmware.  Since Phase is now pretty much going with dalsa we probably won't see it again.  I also think the Kodak sensors with micro lenses performed better with less issues of CA and Lens Cast, but that may have been simply related to the resolution/sensel size, since the 39mp Kodak was the highest resolution sensor from Kodak phase worked with.
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ondebanks

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Re: Why are Phase One backs good for long exposures
« Reply #5 on: March 25, 2012, 07:13:38 am »

I take it then that Phase One has never explained why the backs perform well for long exposures?

So far as I can ascertain, they have never explained the actual technology behind XPose+. I would love to know too; I've tried asking but got only generic hints (and short shrift) from one of their staff. They subtract a darkframe, but then so does everyone else; that alone does not explain it. My guess is that they operate the chip in a mode which produces less dark current than the Kodak datasheet indicates for a given temperature. Perhaps by turning off subsystems until they are actually needed when the exposure terminates (amplifier etc.). As I said, just guessing.

The dealers seem equally in the dark - Doug Peterson, whom I think we could agree here is the most forthcoming and technically well informed in the dealers camp, could not give me a concrete answer when I put the same question in a thread a year or two back.

Ray
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pjtn

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Re: Why are Phase One backs good for long exposures
« Reply #6 on: March 25, 2012, 07:27:46 am »

What I'm trying to work out is what I should purchase for my long exposure shots. I've been asking lots of questions and it has been going on for a while.

I want to print around 30" x 30", maybe larger, which means to do it well I need a medium format camera. I only have a budget below $10,000 unfortunately. So second hand is a must, Hasselblad is my preferred brand followed by Phase One, I tested the Pentax 645D but did not like the camera.

It would be possible to purchase a camera such as the H3D-39 and stack exposures but I'm not even sure if it will do 15 second to 1 minutes exposures well. The other option is something like a Phase One P30+ on a Hasselblad body, this is more expensive though and has less resolution.

A test someone did for me taking 5 consecutive shots with a H3DII-39 seemed promising, Lightroom removed the hot pixels as far as I could see. However once the files were converted to B&W and edited more hot pixels appeared. They are virtually invisible before editing but are quite strong afterwards.

If anyone has ideas to my problem I'd love to hear. Ideally I would test all the equipment but unfortunately that's not possible.
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Audii-Dudii

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Re: Why are Phase One backs good for long exposures
« Reply #7 on: March 25, 2012, 10:11:30 am »

Not all + series backs good at long exposure.  I do know the p45+ is probably the best, rated at close to an hour, but the p65+ I think is only a minute or so.

In my limited experience, the P45+ is not significantly better than the P30+ when it comes to long-exposure performance.  If you use them apples-to-apples (i.e., both backs set at ISO 100) as I did with my Contax 645 outfit, then it's difficult to identify which file came from which back.  And if you set the P45+ at ISO 50, which usually (but not always) shows a small improvement in IQ over its ISO 100 performance, the exposures are twice as long, which can be problematic, at least for the type of night photography I do.

It seems many people don't realize the P45+'s ability to do longer exposures than, say, the P30+ doesn't mean it's gathering more light during these exposures, but that it's gathering the same amount of light using a lower ISO setting, which may or may nor result in a file with slightly better IQ, depending.

Although there are many valid reasons to choose a p45+ over a P30+ (and I now regret selling the P45+ I owned briefly, although not the small profit I made on it!), long-exposure performance may or may not be among them, depending upon the specific demands of the type of photography you're doing and how you configure the back.
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Paul2660

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Re: Why are Phase One backs good for long exposures
« Reply #8 on: March 25, 2012, 11:03:52 am »

A few more thoughts.

The P45+ is able to get to the 1 hour range with the use a custom firmware and a very special controller card.  I know this much as I owned a very early P45+ which was shipped in March 2008.  At that time Phase was not able to get past 30 minutes (on my back about 15) but promised that with future firmware upgrades the 1 hour range would be met.  About 1 year later, April 2009 I started working with Phase One as I had been told that the latest firmware.  I want to say 2.8.3 was the main release number would now allow this.  However I was also cautioned that certain Phase One backs would not work well with this firmware and lock up, requiring the back to be returned to Phase One.  My back was one of these.  After installing the firmware, my back locked up and was would do nothing.  Phase did fix it and in the process replaced my controller card, reloaded the firmware and the back gained the ability to now shoot up to 1 hours exposures.  It also gained a much cleaner ISO 400 and for the first time useable ISO 800.  My Kudo's to both Phase One, Doug Peterson (who first told me about this issue) and Digital Transitions my dealer at the time who handled the work with Phase One. 

So , be careful when purchasing a used P45+ with a low serial number.  Make sure the back will shoot up to 1 hour without excessive noise.  My serial number was below 400 but I was told during all of this that Phase was using 2 different controller cards and it was a total crap shoot as to which back got which card, the later card worked mine didn't.  I was able to get this all taken care of during my original Value add warranty.  This is typical, you job out for a card and have two vendors or more supply it.  Certain venders versions of the card would not work with the final required firmware.

Just a couple more thoughts.

I worked with the P45+ for over a year on night work, but quickly  soured on it.  Mainly because of the dedicated dark frame required.  Net shoot for 30 minutes, then wait for another 30 min. while the dark frame was written.  Shoot for 1 hour wait for another hour, etc.  Phase One's batteries really are good for maybe 3 30 min frames, or 2 45 min, and really only 1 one hour as you won't have enough battery for another exposure.    Since I prefer to shoot with moonlight illumination, I have found that stacking works better as you get a better working balance between the stars and foreground illumination.  Whereas leaving the camera just open for say 30 minutes tends to wash out most of the stars except for the brightest.  This is for Astro Photography uses.  If you stack with the P45+, the dark frame disrupts the exposures thus you get gaps.  Some of this can be corrected in software but it does add additional work.  However once you start putting together a bunch of P45+ frames you realize you need a good bit of processing power.  Stacking requires a lot more post work, but so far for me the results have been worth it.

Lenses, since I was using the DF body, I only had the 35mm, and 28m to pick from.  Both of these lenses are pretty terrible in the F3.5 to F5.6 (35mm) and F4.5 to F 6.3 (28mm) so I found that really only the center of the image was very good.  You are taking about using Hassy glass, so you may see much better results.
If I took either the Mamiya 35mm or 28mm to F 8 or so, there wasn't enough light unless I pushed the ISO to 400 but then noise became a much bigger issue.  My 28mm Mamiya was especially corner soft in the Lower Apertures from F4.5 to about F8.  My 35 was better but suffered from resolution smearing in the F3.5 to F5.6 range so it's results were not much better.  The 55mm's limited DOF took it out of the running.

I have moved to Canon/Sony for night work, just a whole lot easier and much more forgiving.  I have a few frames from my P45+ that I was proud of, but most nights conditions just didn't pan out for a single long frame and a stack worked better.  With the Nikon D800 now starting to ship, I would consider that also.  At 36mp you should still be able to get where you want for a 30" x 30" print or larger.  (YMMV), but it's a lot cheaper solution.  Nikon will have a great noise reduction program for longer frames and I am sure have the ability to turn off long noise reduction so that you can still shoot in a stack.  The results I get from my 5D MKII many times I feel could get to 30 x 30 and I have printed larger but everyone has their own printing requirements.  For night work, the 35mm Digital  just seems to me a much easier route, has many more options than the P45+ or P30+ and is much less of an investment.

Paul
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Paul Caldwell
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Doug Peterson

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Re: Why are Phase One backs good for long exposures
« Reply #9 on: March 25, 2012, 12:24:31 pm »

The P45+ is able to get to the 1 hour range with the use a custom firmware and a very special controller card.  I know this much as I owned a very early P45+ which was shipped in March 2008.  At that time Phase was not able to get past 30 minutes (on my back about 15) but promised that with future firmware upgrades the 1 hour range would be met.  About 1 year later, April 2009 I started working with Phase One as I had been told that the latest firmware.  I want to say 2.8.3 was the main release number would now allow this.  However I was also cautioned that certain Phase One backs would not work well with this firmware and lock up, requiring the back to be returned to Phase One.  My back was one of these.  After installing the firmware, my back locked up and was would do nothing.  Phase did fix it and in the process replaced my controller card, reloaded the firmware and the back gained the ability to now shoot up to 1 hours exposures.  It also gained a much cleaner ISO 400 and for the first time useable ISO 800.  My Kudo's to both Phase One, Doug Peterson (who first told me about this issue) and Digital Transitions my dealer at the time who handled the work with Phase One.  So , be careful when purchasing a used P45+ with a low serial number.

I'm really glad it all worked out for you! Do note that serial number is not always a direct relationship to age/manufacturing date. Related to the issue you mentioned (but expanding a bit more beyond the firmware version you mentioned), you want a P45+ with at least 3.2.6 firmware and preferably 5.1.2 (current as of the time I'm writing this). If your back has really old firmware (e.g. 2.9.8 or earlier) you want to work with a dealer to step up the firmware one generation at a time (only the most recent is available for public download and you should not skip major versions while upgrading).

   However once you start putting together a bunch of P45+ frames you realize you need a good bit of processing power.  Stacking requires a lot more post work, but so far for me the results have been worth it.[...]

I suspect though part of this statement comes from you being the kind of guy who would cringe at throwing pixels away. If you're stacking P45+ files and process the raws to 20ish megapixel TIFFs rather than full-resolution TIFFs then the time to stack and finalize the composite would be very similar to starting with Canon 20ish megapixel raws.

I have the same cringe. Sometimes I have to actively remind myself that just because I shot an 39 (or 80) megapixel file doesn't mean I need to process it to 100% resolution TIFF, especially if I'm compositing multiple frames and the final use is unlikely to be a large print.

Lenses, since I was using the DF body, I only had the 35mm, and 28m to pick from.  Both of these lenses are pretty terrible in the F3.5 to F5.6 (35mm) and F4.5 to F 6.3 (28mm) so I found that really only the center of the image was very good.  You are taking about using Hassy glass, so you may see much better results.
If I took either the Mamiya 35mm or 28mm to F 8 or so, there wasn't enough light unless I pushed the ISO to 400 but then noise became a much bigger issue.  My 28mm Mamiya was especially corner soft in the Lower Apertures from F4.5 to about F8.  My 35 was better but suffered from resolution smearing in the F3.5 to F5.6 range so it's results were not much better.  The 55mm's limited DOF took it out of the running. [...] I have moved to Canon/Sony for night work, just a whole lot easier and much more forgiving.  I have a few frames from my P45+ that I was proud of, but most nights conditions just didn't pan out for a single long frame and a stack worked better. 

Having used most medium format wide and super-wide lenses I can say pretty safely that none of them are especially sharp in the corners for the first stop or two, regardless of brand.

Keep in mind that one of the most popular applications of long exposure on a P45+ is architecture/landscape where f/8-f/11 is being used with ISO50, often with a center filter or graduated ND, leading to such a low effective ISO that early dusk shots drag into the several minute range. By far (in my experience - amongst customers I've worked with) the least common application of long exposure is the 30-60 minute range; often because, as you explained, the environment has to be perfect for a 30 minute exposure to make sense. In the middle of the night in the desert on a clear night with no moon 30 minutes might work well, but in most environments the "light pollution" from nearby cities (or the moon + slight haze) will make the "background" sky look muddy, at best making post processing a chore (playing with levels, curves, trickery to get the starless sections of sky to return to black) and at worst unusable.

Doug Peterson

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Re: Why are Phase One backs good for long exposures
« Reply #10 on: March 25, 2012, 01:17:25 pm »

So far as I can ascertain, they have never explained the actual technology behind XPose+. I would love to know too; I've tried asking but got only generic hints (and short shrift) from one of their staff. They subtract a darkframe, but then so does everyone else; that alone does not explain it. My guess is that they operate the chip in a mode which produces less dark current than the Kodak datasheet indicates for a given temperature. Perhaps by turning off subsystems until they are actually needed when the exposure terminates (amplifier etc.). As I said, just guessing.

The dealers seem equally in the dark - Doug Peterson, whom I think we could agree here is the most forthcoming and technically well informed in the dealers camp, could not give me a concrete answer when I put the same question in a thread a year or two back.

I can tell you the areas of technology involved.
- Improved Heat Sinking
- Improved Hardware Component Selection
- Improved Firmware (Controlling/Use of the Hardware Components)
- Improved Software Noise Reduction

But you're right that I can't explain far beyond that level of detail.

For instance, Heat Sinking. During long exposures heat builds up near important components, resulting in noise (in electronics heat and noise are closely related). I know the internal design of the P+ series chassis was improved to better transfer heat away from important internal components towards the outside of the chassis where it won't effect the quality of the raw file being produced. But I couldn't tell you the specifics of those improvements; did they change types of metal? Thickness of heat-transmission framework? Did they move components further apart (or closer together)? I do not know, and I do not expect Phase One to tell me.

I think this is perfectly fair - Phase One spent considerable resources learning how to eeke every bit of long exposure performance out of the KAF-9000 (the same sensor found in the H3D-39); there isn't any reasonable expectation for them to provide engineering-level data on how they did it. With a few exceptions (e.g. you) the vast majority of customers just want to know what the end-result is.

The underlying assumption of the question is that two companies using the same sensor should expect nearly identical results. And this is simply not the case. Below is an abbreviated list of technical factors (hardware and software) that affect the final result of the image captured from a given sensor. The sensor is an important part of that chain, but only a part.

Image Quality Chain:
Lens hood (or other method of reducing flare) > Lens coating > Lens elements > Aperture blade design > internal body coating > Anti aliasing filter (or lack thereof) > IR filter spectral cutoff location and sharpness of cutoff > microlens > sensor type > sensor read-out speed and method > heatsinking > cabling to A/D converter > A/D converter > Black Calibration > debayering/detail/color algorithms > noise reduction (based on black calibration file) > color profiling > noise reduction (based on image data) > sharpening.

pjtn

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Re: Why are Phase One backs good for long exposures
« Reply #11 on: March 25, 2012, 06:54:15 pm »

Audii-Dudii that is interesting on your observations between the P30+ and P45+. I'm in the opposite camp where I actually want to use ISO50 to drag the exposure out longer.

Paul2660, I'm glad I don't need exposures as long as yours, mine will be kept below 5 minutes, probably the time of one of your stacked images ;-)

Doug, that pretty much says everything I wanted to know. It was hard for me to understand why two cameras with the same sensor would perform so differently. It makes more sense now.
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pjtn

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Re: Why are Phase One backs good for long exposures
« Reply #12 on: March 26, 2012, 12:56:34 am »

I've found a good price an a P25+ with H1 camera. It does not have the resolution of the P30+ but I'm wondering if the image quality will be similar because of the bigger sensor.
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darylgo

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Re: Why are Phase One backs good for long exposures
« Reply #13 on: March 27, 2012, 12:41:28 am »

I can't say this with absolute (100%) certainty but the p30+ has a bit more sharpness than the p45+ on a pixel level, the only difference I could find are the microlenses on the p30+.   Long exposures with the p30+ are such high quality files that the dark frame price is worth the wait. 
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