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light meter and dxo mark
hi all, I have a Nikon d810 and go to Dxo Mark to look up stuff, i have found some measurements, link down below, http://www.dxomark.com/Cameras/Nikon/D8 … asurements what should i adjust my light meter to for the right calibration? and how do you find out what number to use? thanks Apr 07 16 06:32 pm Link Those are DxO Mark test results only and nothing pertinent on how you setup and use your camera. That setting stuff is what is in your owner's manual on how to use it, or perhaps this site if you want someone to tell you what to set in the camera's menus: http://www.photokaz.com/blog/2015/05/18 … iguration/ It's a complex camera and the many D810 books out there would better explain the overall operation. Apr 07 16 06:51 pm Link Most digital cameras have their meters set to err on the side of caution. If you blow your highlights, they are gone. Shadow detail is much easier to recover. If you adjust the meter to the "correct" settings, expect to spot meter EVERY highlight in the image or risk loss of detail. Just another example of DxO putting statistics above common sense. Or, maybe you are supposed to know these things going in and interpret the data accordingly. If you are looking for information I would consider them one source of many to maintain objectivity. Apr 07 16 06:55 pm Link For what it's worth, let me answer your question strictly in terms of your question / reading the information from DXOMark. Based on this thread, you may well decide not to handle it this way. The key is to look up the specific lens you are using on DXOMark with the D810 body. For example, if you are using a 85mm 1.8G then google "dxomark nikon 85mm 1.8g d810", then click on the most relevant link. After the splash page, on the lens page, make sure the camera body drop down menu is correctly set to "D810". Look on the right side "Lens Metric Scores" under "Transmission". This will give you the tested "T-Stop" value for that particular lens and camera body combination. In this particular example, the T-Stop was tested at "2" for an "f1.8" lens. So your meter adjustment for that particular lens and body is the difference between F1.8 and F2 (the amount of light that is ACTUALLY being transmitted through to the sensor when the lens is set to F1.8 on that particular lens / camera body combination). So you'd need to adjust it so that your corrected exposures allow slightly more light in than the non-adjusted meter reading indicates. Different lenses will have different DXOMark actual tested T-Stop ratings / adjustment values (specific to each tested camera body). Hope that helps! [EDIT] In practical terms, this is actually fairly useful if you're using a separate meter (including flash meter) for incident meter readings. If you're using your camera's built in reflective light meter, then (with all of the other variables that come into play) you might want to consider another approach. [/EDIT] Apr 07 16 07:05 pm Link Wow. That's complicated. I get that f/stops are relative, and that they differ from lens to lens and even copy to copy, and sometimes the differences are pretty big; I own a 1.4 lens that is actually brighter (barely) than another 1.2 lens I own. I also get that not every camera has the same ISO setting, and 'native' ISO is often tweaked based on what the processor can handle. Entry-level Nikon and Olympus cameras are often almost a full stop darker at the same settings and ISO for this reason, while entry-level Sonys and Canons just let that top stop of range clip. But if someone can give me a simple explanation of how the camera's base ISO has any effect at all on how much light the lens itself transmits, I will give them a cookie. And if they can explain why memorizing 'actual' aperture tables for multiple camera and lens combinations is easier than remembering that consumer cameras might be darker and most lenses are not exactly as bright as they say, I will give them several cookies. By continually coming up with new, complicated formulas that require look-up tables, DxO forces the reader to click through several pages, thereby optimizing ad revenue. In some cases, they make the True Believer so reliant on New Math that they need to revisit the site repeatedly, generating even more ad revenue. I'm sure there are other reasons why they might overcomplicate everything, but I can't think of another one that doesn't sound like a conspiracy theory about DxO the Benevolent Website versus The Man And Everybody Else Trying to Steal Our Money. Apr 07 16 07:31 pm Link I'd suggest that used properly, it's not complicated at all. It's important to note that I modified by reply to indicate that, in terms of being useful, we're only talking about incident light meter readings (definitely not for built-in TTL reflective exposure readings!). And many meters will let you dial in / program in a correction factor. While each case is different I've noticed that many of the popular lenses that I've checked, just happen to be extremely close to each other in terms of the correction factor. Often there seems to be between 1/4 and a 1/3 of a stop lost between the theoretical lens f-stop and the actual transmitted light rating for the lens in practice. I.E. Dial in that correction once and forget about it. Although you'd certainly want to check the len's t-stop rating for your camera body once, to be sure. Along with some quick one time tests with and without the correction factor so that you can confirm whether the adjustment value is an improvement or not (I.E. are you confident in the change). As always, it's just a starting reference point exposure value that you can adjust depending on the specific image results you want. At least IMHO! [EDIT] 1/4 to 1/3 of a stop correction seems typical for a large range of PRIME lenses. Zooms appear to suffer from much more of a T-Stop difference (3/4 of a stop or more)... [/EDIT] Apr 07 16 07:40 pm Link The calibration of a light meter is way over thought. Make the light meter match your workflow. A flat lit grey card reading 118 118 118 in Photoshop matches up with where I want to take skin tones and exposure and remains a safe exposure. From a grey card and my 118 setting I am 4.5 stops from white and -4.5 stops from black. Powerful information in the right hands! The default readings are a bit underexposed for my workflow...The last thing I want is to drag the exposure over 2/3 of a stop (or whatever is required to make it look right) in every last image. That is how I do it Apr 08 16 02:36 am Link I agree with Zack, it's a bit too persnickety to make sense in the real world. Add in the factor that zooms are not always consistent in their exposure from one focal length to another and you can pretty much rule out spontaneity as part of your creative tool kit. A poor exposure of a great moment is much more valuable than a "perfect" exposure of what might have happened after that perfect moment is long gone. If you really have to futz about with these sorts of details you could just check your histogram and adjust exposure if needed. Digital is like shooting transparency film in that the highlights are your first concern. Blow them out and they go away. Digital is very different than shooting transparency film in that once you have a reasonable capture of all required luminance in your scene, you can re-purpose your values after the fact. Photography is so often about the moment. Are you ready to shoot NOW or are you fumbling about (in your head or with your gear) trying to make things "perfect"? Apr 08 16 09:20 am Link For those that DO use a flash meter in the studio, wouldn't you prefer that it gave you useful, accurate information? If it's 3/4's of a stop different from your lens / body combination, wouldn't you prefer to have that set in the meter's correction settings (i.e. just read the settings and use as normal)? Or if your meter doesn't have a correction adjustment, then leave it dialed it into your ISO value instead? Lots of cinematographers will tell you that they take their light readings and dial the value into their cine lenses that use T-Stops (instead of F-Stops) for accurate exposure. Don't over complicate it. If you use an incident light meter then leave the correction dialed in. Take a new reading like you normally would, for a scene change or significant lighting change. It's not something that you do "shot by shot", or anything even remotely close to that. Once your lighting is set, shoot away. However, there are many alternatives for those that don't use incident meters or flash meters. And a case can be made for not using them. But if you do, having it reasonably accurate can be somewhat useful...  Apr 08 16 10:49 am Link BlueWolf Photography wrote: much of that depends - on how critical your requirements are, how you like or prefer to correct the the problem, if it exists; and how complicated the calibration gets. Apr 08 16 11:06 am Link I constantly check my meter to MY light set up. It makes total sense with digital to base an exposure not so much on an 18% grey card but to something that is white with detail. Like a terry cloth towel. In PS, that towel should read about 240-245. But to make this easy, I use my overexposure blinkies on my camera's monitor. I set up my lights, meter them for the ratio I want, then take a shot of said towel with all lights on and my meter pointed slightly towards the main light. My meter is usually right but I check anyway. I may even open up 1/3 of a stop just to check for the blinkies. If I just start to see the appearance of overexposure blinkes, I close back down 1/3 of a stop. IF that f/stop is what my meter said, I'm good. If it doesn't, I turn the dial on the back of my Minolta IV (calibrate) so that it does read whatever my aperture is. Rarely is it off but you never know. Apr 08 16 01:01 pm Link Mike Collins wrote: If that's the way you work, I would turn down the contrast on your camera a click or two. It won't affect your RAW file one iota, but the camera uses a jpg to draw the preview and check exposure. Turning the contrast down slightly will give you a reading just a little bit closer to where the actual RAW file clips. Apr 08 16 04:21 pm Link BlueWolf Photography wrote: Ignore what DxO Mark about light. DxO Mark test sensors and lenses and the D800/D810 has awesome sensors. Apr 08 16 05:37 pm Link Zack Zoll wrote: Problem is I shoot AND deliver jpeg most of the time. I know most are in shock reading this but yes, many of us HAVE TO shoot jpeg. I shoot corporate events where the client sometimes want the files right then and there. Like last night after I sent 3 days with Phillips 66. Over 1,000 images. Raw is not even a consideration. Or we are printing them right then and there. No raw files for me. Actually a blessing. Apr 08 16 06:14 pm Link I don't judge. The best system in the world is the one that works for you. And I know you've been around the block to know the difference between what works best and what is easiest or the default. Personally, I tend to shoot digital like I shoot reversal film: I practice lots and lots, to the point where I know my gear well enough to wing it. There are times when I look at my rig, and think, 'shit, I dunno ... open up a stop? I'm sure the camera's DR will catch it.' Anybody watching me would think I'm a moron (as do my students, sometimes), but my process is to learn what math I can avoid. I wouldn't have the right to criticize you if I wanted to  Apr 08 16 07:33 pm Link No disrespect to anybody that does, but I could care less about Tstops. If I have a weird problem lens I deal with it...I have a German lens that is +4/10 hot wide open and zeroed by f3.5...I have a piece of tape on the lens to remind me. K.I.S.S. works for me! If I forget my stupidity shows up on the LCD screen and histogram. Any mental midget can look at his histogram and figure out a base exposure if things are getting weird....That is most people's reason for not wanting a meter...to me the base exposure is less than 1/2 of the story. I want the light meter to deliver skin values that I never need to touch in post. That and the differences in strobes or ambient light power. Where everything is in relation to the camera setting. Apr 09 16 01:52 am Link While the T-Stop / F-Stop difference can be important, in many scenarios (covered above) that difference has already been adjusted for. So here's what I SHOULD have said in regards to compensating for T-Stops: If you're taking a TTL exposure (of a gray card, or chart, etc), then the difference between T-Stops and F-Stops has already been accounted for by your camera. If you're taking a reading with an external light meter and then adjusting your exposure based on your histogram, then the difference has already been accounted for. If you skip the light meter and rely mainly on your camera's histogram then, again, the difference has already been accounted for. If you use any variation of "expose to the right" strategies then, by definition (histogram, white texture and/or clipping points), the difference has already been accounted for. If you use your meter for any form of relative comparative settings, then the difference has been accounted for. If you use your experience to say that well when my meter says "this" for this particular body/lens combo, but I tend to prefer the results when I increase the exposure by this amount, then the difference has already been accounted for. And so on... So when DO you need to pay attention to it? If you're taking an external light meter reading (unadjusted) and relying on that information / dialing it into your camera without further review or adjustments, then you need to understand that you're underexposing it. Typically by about 1/4 stop for many primes and about 3/4 of a stop to a full stop for many zooms (at least as a rough starting point). And yes, there's always Photoshop. Note that the OP specifically asked how to use the DXOMark values for his light meter calibration. Certainly not a bad rough starting point. Apr 09 16 11:28 am Link The other (non cinematography) situation where examining the T-Stop value is useful is when comparing low light lenses for purchase. I.E. The situation mentioned above where a 1.2 lens is darker in practice than a 1.4 lens. Or when you're trying to figure out just how much more light you really are losing with a zoom compared to a prime. I also strongly suspect that the actual exposure difference between a number of these approaches may end up being quite minor (many ways to skin a cat!). If you're increasing your external light meter's exposure value (for the T-Stop / F-Stop difference), you're going to end up with something that's much closer to the "expose to the right" histogram result, than if you don't calibrate it (in one way or another). One of the best examples being Mike's superb "texture in a white towel but 1/3 of a stop up starts the clipping" exposure point. If I get a chance I'm going to try some comparisons to see just how close those exposures end up actually being using different "adjusted" approaches. I suspect that there won't be that much of a difference, but it'll be interesting to see! Apr 09 16 11:36 am Link BlueWolf Photography wrote: sorry, just realized that you did not specify which light meter you are talking about. most of the replies have been talking of handheld, separate light meters - which need to be calibrated. Apr 09 16 11:39 am Link dp Apr 09 16 11:39 am Link The main reason I keep advocating doing things on one's own is because the DxO measurements are for a specific body and lens. That's fine if you own the exact pieces of gear they tested with. Manufacturer changes specifications (every owners manual contains this disclaimer), firmware updates, sample variation, exposure differences at different focal lengths in zoom lenses, using "average" measurements to shoot exceptionally dark or bright scenes, somebody using a lens that is not listed - I adapt vintage lenses to my camera fairly often - these are examples of possible data that may vary from DxO results. None of these variables can be accounted for in the DxO data, it is not possible to do so. No knocks on them for that but that does not make their stats simple or foolproof. Their data is probably perfectly accurate for what it is but how do you know you have gear and circumstances that match their testing methods perfectly? Simple answer, you don't. Google "black white gray exposure test" and all sorts of fun stuff comes up. Apr 09 16 11:51 am Link tp Apr 09 16 12:27 pm Link Unless you lent your personal 810 to DXOMark, there will be enough sample variance to make their measurements not completely valid for you. Its an important test to do--and the fact that there is significant variance at base ISO is interesting. But they weren't testing your camera. The other issue is that there will be variance in the light meter itself--100 ISO may not be true 100 ISO. And your specific use of the meter (dome up or down, pointed at light, etc.) will introduce errors. If you are shooting jpeg and can't chimp, then you can pull your hair out over this issue. If you are shooting RAW, can chimp (either the image or the histogram), and can use exposure compensation, then you don't really have a problem. Apr 09 16 05:22 pm Link SHORT VERSION: Calibrated flash meter for optimal light gray card for Nikon (and Canon's) 12.5% gray (details below). Calibrated based on histogram spike for gray and verified with Photoshop's RAW RGB value from gray card. Repeated with white towel test. Good texture and clipping starts when I upped the exposure 1/3 stop (as per Mike's test). IDENTICAL "optimal" exposure point for gray card, optimal histogram spike, photoshop RAW RGB gray values versus a great "expose to the right" strategy (which I thought would have a higher exposure point). Same routine for other lenses. Significantly different calibration adjustments for each particular lens, but the results comparing the different methods, still came out as being the same. I expected the methods to be fairly close in exposure but not identical! ----------------------------- LONG VERSION (for those that care about the method, etc) So I finally had a chance to do some calibration and comparison tests, including a histogram / gray card / photoshop RGB gray value and Mike's great white towel "expose to the right" example (good texture but 1/3 of a stop down from the start of clipping). I was wondering if I was leaving too much on the table by not pushing it further to the right, so...! First an explanation as different people have different gray cards, different camera sensors, and colorspace gamma values affecting the photoshop values, etc. My Nikon sensor (like Canon) is based on 12.5% gray (although they commonly still refer to it as "18% gray"). My gray card, is actually a light gray card (quite common as it's more useful for white balance readings). So my the actual desired gray card spike on the histogram is 66%, not 50%, and the photoshop gray card theoretical matching RGB reading is 170, 170, 170 (1.5 x 128, 128 128). So I recalibrated the flash meter for each lens looking for the 66% light gray spike. Exposure on color charts,and to the eyeball, all looked dead on. In photoshop the gray scale RGB value (adjusted only the RAW temperature and tint for even colors), all came in within 2 or 3 of the desired 170, 170, 170 values No photoshop RAW exposure adjustment required.. Repeated including the white towel as a starting point for the "shoot to the right" calibration. Looked good as is. Good texture and exposure with no changes required. Opened it up 1/3 stop and yes there was clipping. No changes at all. I wasn't expecting it to be that close! Repeated the entire process for different lenses. There were significantly different baseline flash meter adjustments for each particular lens. But in each case the end results were the same. The 66% histogram (light gray card spike) was extremely close to RGB 170, 170, 170, and the white towel was dead on (with clipping showing at 1/3 stop up). I'm very surprised. I expected a "calibrated" exposure might not vary much from a well handled "expose to the right" strategy. With some older cameras and/or certain types of shoots, shoot to the right would have been my starting point. But the goal of finding your ideal shoot to the right exposure point is quite different from finding your "calibrated" gray card exposure point. ----------------------------- POSSIBLE CONCLUSION: The only thing I can think of is that the camera / sensor makers (when they shifted down to 12% to 14% gray) along with other "optimal" ISO variations, basically already built in a "shoot to the right" exposure strategy. For all of the same reasons that shoot to the right caught on to begin with (lower shadow noise, optimal sensor ranges, etc). Your mileage will likely vary, but it would be interesting to find out how common, or not, this kind of result is. If you decide to test it yourself, don't forget to adjust it for your particular gray card, and your own proven RGB RAW neutral gray value. Basically properly calibrate it using your traditional proven working method versus an well done "expose to the right" approach and see how close they are. Or aren't. it would be interesting to compare! . Apr 11 16 10:33 pm Link P.S. Hopefully before anyone decides to dispute Nikon and Canon's 12% / 12.5% gray value, they'll do some research first. Some interesting history as to how what is referred to as "18% gray" evolved since Ansel Adams original lobbying of Kodak to set it at 18%. Apr 11 16 10:50 pm Link |
