Learning the P45

[PoloDigital]

I've now done a second shoot with the P45 and am still trying to master the concept of ISO50 and my light meter. I use the good old L-358 Sekonic which has been very accurate at ISO 100 & ISO 200 with my Nikon DSLRs. I seem to be under exposing by at least 1/2 a stop when using the same techniques that have served me well for the last few years. I've even snapped off a few shots with the D3 at the equivalent exposure (f/8@ISO50 = f/16@ISO200) and been right on. Any ideas here? BTW, ISO100 on the P45 seems to be a bit closer, maybe only a tenth or two under. Of course I can bump the level in C1, but isn't it better to expose correctly in camera?

An example shot at ISO100 that I had to bump the ev by .2 when the meter read f/8 @ ISO 100, 1/125:

Thanks for any suggestions.

 

[gogopix]

underexposed?
She looks pretty exposed to me. At a half stop more exposed we are talking what? fully nude?

 

[thomas]

I seem to be under exposing by at least 1/2 a stop

the file was processed through which software? Camera RAW / Lightroom?

 

[Christopher]

Lightroom underexposes the files by how much ? 1 stop ? I only now that only ISO 200 is correct in Lightroom.

 

[thomas]

Lightroom underexposes the files by how much ? 1 stop ? I only now that only ISO 200 is correct in Lightroom.

I only know that exactly nothing is correct in ACR/LR.
Yes, 1 stop ...

 

[PoloDigital]

The file I posted was processed from the raw in C1 v5, then edited in PS CS4. What I mean is when I meter the key light, it reads dead on f/8, ISO 100 @ 1/125. I expect to see my skin tones with red channel values around 200. This will vary with subjects, but JenAmber is light skinned and I would have expected to be right on or even higher. I adjusted the exposure in C1 to be +0.2 and the values came into the range I expect. It is even worse at ISO50 with the skin tones needing +0.5 bump in exposure to get in range.

I'll do some test shots with a GMB 64 target and see what that reveals at the different ISO settings with the P45 and then use the D3 at ISO 200 for comparison. I would expect to get reading close to the standard, but I'll bet I'm low at every sensitivity. I just was wondering if this was a 'known' issue.

 

[canon5dshooter]

If you shoot at ISO 50 I would imagine you are not loosing much by bumping the exposure a little bit in post. Just my .02 ....

 

[gogopix]

sorry, didn't mean to be flipant in my prior post

I had a P45 (actually, P25, P45, P45+ now P65+)

I am not sure it is raw processing that is the issue. I have a Contax 645, but also use Alpa and True wide with the back

I have noticed that the Phase backs underexpose by about a stop on all (I actually just keep the exposure up on the Contax, and compensate on the ALpa.)

I don't know why - it would mean that when you select ISO 100 the gain is really more like 50.

Backs, being digital have different efficiencies of their photosites. These are supposed to be calibrated, but who knows.

My P65+ was back to P1 and is still under by 1/2 stop. I just learn what it is and compensate

If you believe in "expose to the right" you will need to do that, as pumping up in post will just add noise.

Sometimes I 'force' underexposure just to keep the back gain low (say 100/200) and the do a -2 so that I can get the exposure time down. Again, that is only partially beneficial, since post gain leads to noise leads to noise reduction leads to posterizing.

All that said, it just seems we all live with at least +- 1/2 stop. SO be it.

regards
Victor

 

[dougpeterson]

If someone finds me a piece of TMAX400 that was best exposed at ISO400 or a Velvia 50 which was better exposed at ISO50 then slightly underexposed please let me know.

Until then I will consider all exposure to be best judged based on histogram and intimate working knowledge of your system.

FWIW, it's nearly impossible to see the difference between a half stop under/over exposed ISO50 shot on a P45 and a "properly" exposed shot at that ISO if you compensate in C1. Even a full stop is nearly indistinguishable.

Doug Peterson (e-mail Me)
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[gogopix]

Doug
Couldn't agree more, at 50 ISO.
However, at 100 or 200 I find it is better to overexpose than under, and trying to 'push' (what we called it in film days! ) say 2 to 3 stops can lead to trouble even at 50.
Basically, what Doug says is my experience - with a scene except for the classic "walls", the range in the image is going to mask one stop at least. Lifting shadows is a lot easier if you start 'higher'.

Anyway, my point is and that raw processing is not likely the issue, just normal variations of scenes and gain of the backs. In the end, with 16 bits exposure is rarely an issue for me with the Phase backs except when I try to push too much. Then the noise reduction kicks in, and the detail goes. I'm becoming an "expose to the right' fan

Victor

 

[David K]

Scott,
I've seen the same apparent underexposure with my Sinar back after metering properly. I will pass along the advice I was given (and follow) from a photographer buddy whose opinion I value highly. He told me that if I knew the photo was properly exposed not to mess with the exposure slider. Bring up the brightness, adjust the contrast, tweak to suit but don't fiddle with exposure. I don't understand the inner workings of software (Lightroom and Aperture in my case) to know what difference this makes. Perhaps some of our more knowledgeable members can enlighten us both.

 

[Steve Hendrix]

Scott:

My take is that digital backs are not necessarily dead on the money in terms of the rated or stated ISO. And they are not unique in that respect, there are similar issues with various films, digital cameras, etc.

Our industry attempts to pull actual performance into known and standard traditional quantities. But while some films were frequently ASA 32 instead of the stated 50, the same occurs with digital backs. More so than DSLR's for some reason, in my experience. Even lenses that state the same focal length across different manufacturers, don't always match.

So the best advice I can offer is learn your P45, and if you are using a meter, compensate in-camera accordingly. Know that when your meter reads f8, it may actually need to be f.5.6 and so on.


Steve Hendrix

 

[PoloDigital]

I'm not making any accusations, just wondering if this is a know issue. I've shot thousands of portraits with several Nikon bodies and have adjusted accordingly. I was just curious as if this was specific to my back or this model in general. It just seemed a bit odd, since the higher end I went with Nikon, the closer to dead on exposure I got.

So I'll follow up with a second question; How much quality can I expect to lose (or how much added noise) if I chose to shoot at ISO 100 vs. ISO 50? In the few exposures I've processed, I don't see much.

Thanks for all the input. I appreciate it.

 

[dfarkas]

Scott,

Another option is to use the Sekonic L-758DR. If you shoot the Exposure Profile Target and measure the unmodified (for EV) resulting file from C1 using the Sekonic software, you can calibrate the meter for your camera. This way, when you dial in ISO 50, the meter will automatically compensate for any variation of effective ISO (ie ISO 32).

Hope this helps.

David

 

[Guy Mancuso]

I'm not making any accusations, just wondering if this is a know issue. I've shot thousands of portraits with several Nikon bodies and have adjusted accordingly. I was just curious as if this was specific to my back or this model in general. It just seemed a bit odd, since the higher end I went with Nikon, the closer to dead on exposure I got.

So I'll follow up with a second question; How much quality can I expect to lose (or how much added noise) if I chose to shoot at ISO 100 vs. ISO 50? In the few exposures I've processed, I don't see much.

Thanks for all the input. I appreciate it.

If anything Scott maybe a slight DR difference and I mean very very slight. Like you mentioned you won't see much between 50 and 100 . My back starts at 100 and the only time I wish I had 50 is when shooting water or something like that to slow the shutter down an extra stop . But on this low end range certainly would not worry about it. If higher ISO like 200 and 400 than we would be talking more differences with noise and such. As far as pulling the exposure up on the files again these are very flexible files and you can do quite a bit before really getting into any real trouble. Honestly I don't even use a separate meter any more and go by the histo on the back.

 

[gogopix]

My experience was that the extra stop in speed I could use at same aperture made a sharper image than any loss of detail or increased noise. You are only likely to see the effect in areas like shadows. When you lift the 50 will have SLIGHTLY less noise.

In well lit images I think the speed will get you a better image, esp if you are between the "one to two time FL" speed range.

I stick at 100 90% of the time and now print 24x36 pretty regularly. Detail is all there. I think most people don't realize how much a slight motion in hand held can degrade a shot. For tripod, you need speed if the subject moves (or mirror slap, as many examples here have shown) I shoot a P65+ and these high MP back can really show the slightest
shake when rezed up.

Guy, and many of the pro's here have suggested "stick with the histogram"

I think that is sound advice.

regards
Victor

 

[Jack]

One other thing that often gets overlooked in digital, is that a chosen WB can affect exposure significantly. I find on my P45+ in outdoor daylight shooting, that while using its default daylight WB my histo will consistently show a good exposure in the blue channel, meaning the blue channel is NOT clipped -- but it has a much longer shoulder than the R or G channel at the DL WB setting. So in reality, when I warm up the WB in conversion I am usually ending up about 1/3 UNDER -- meaning that effectively my body is exposing properly for the default WB, but in reality it is about 1/3rd under actual. I don't worry about even a stop under at ISO 50 or 100 for the reasons Doug pointed out; the files are easily corrected in C1 during conversion.

 

[yaya]

One other thing that often gets overlooked in digital, is that a chosen WB can affect exposure significantly. I find on my P45+ in outdoor daylight shooting, that while using its default daylight WB my histo will consistently show a good exposure in the blue channel, meaning the blue channel is NOT clipped -- but it has a much longer shoulder than the R or G channel at the DL WB setting. So in reality, when I warm up the WB in conversion I am usually ending up about 1/3 UNDER -- meaning that effectively my body is exposing properly for the default WB, but in reality it is about 1/3rd under actual. I don't worry about even a stop under at ISO 50 or 100 for the reasons Doug pointed out; the files are easily corrected in C1 during conversion.

Profiles can also affect the visual exposure as they often contain an internal curve.
Also some cameras use in-camera gain push while others shoot at a fixed speed and tag the raw files with an ev value. Hence why with some cameras ACR and LR show the image under exposed.

Yair

 

[Jack]

Profiles can also affect the visual exposure as they often contain an internal curve.
Also some cameras use in-camera gain push while others shoot at a fixed speed and tag the raw files with an ev value. Hence why with some cameras ACR and LR show the image under exposed.

Yair

Excellent point about profiles! C1 however includes several onboard profiles for the P backs -- default for the P45+ is "Flash" and I change that to the "Daylight" profile in my outdoor styles dialog, though the two profiles are very, very similar. Other thing one can do for their P back is create a custom WB for the shooting application they are in, that functionality is built into the back and only requires a gray card.

Re the gain push, this is precisely why ACR/LR cannot generate a decent base image from a Phase back -- as Thomas pointed out, there is never anything that starts out correct in ACR/LR for a P back...

 

[PoloDigital]

One of the first things I learned to do with the P45 (aside from ignoring the image on the LCD) was to set a custom WB. Since I'm primarily a studio shooter, rarely will I change the WB more than a couple hundred degrees one way or the other. The P45 appears to shoot just a tad cooler than my Nikon bodies, but that's easily compensated for.

BTW, why in the world did pro's pay the large amount of $ for these backs with such horrid LCDs? I mean my Nikon D70 display was better, albeit smaller, than the P45 and that was at least a year before the P45 was released. Even today's + series backs have horribly low resolution LCDs for image review. Is there a way to display only the image data and histogram? Does everyone shoot tethered? Focus confirmation is useless with the back's LCD.