exposure issues using a DSLR as a lightmeter

[Simon Liddiard]

screenshots are from the digital files, Greg. What I am missing here is how could my former point&shoot digi nail very similar exposures, but mostly how could the correspondent film shots be literally almost black...

If you were using your 5D in raw format, and your cheap P&S only shoots jpeg then that would almost certainly explain the discrepancy. Opening raw files in Lightroom 5 illustrates this perfectly - the first image to appear is the jpeg preview, then the raw data is rendered, often giving very different results

[Simon Liddiard]

Well a couple of things come to mind.

First of you are shooting expired film. This alone could cause various issues in exposure.

Second many film photographers don't actually shoot shoot film at the speed listed on the box. Form example I like to shoot most ISO 100 films at ISO 50. But because every film type is different testing is required to find out what ISO a certain film pro forms best at for you.

Andrea is clear in her post that she re-did the test with fresh and expired film, but I'm struggling to understand how down-rating the films ISO is relevant to this issue - please can you elaborate further?

[Andrea Gazzoni]

so the camera is displaying a much darker raw file in the lcd? this should lead to overexpose, isn't it?

p.s. Simon, I am a male with obvious beard :-)

[Greg Miller]

screenshots are from the digital files, Greg. What I am missing here is how could my former point&shoot digi nail very similar exposures, but mostly how could the correspondent film shots be literally almost black...

I think it could be a lot of things, which none of us can tell for sure without knowing more. 2 of the 3 screen shots are not exposed properly (in my opinion; others may disagree) so maybe we all have a different idea of proper exposure. And your idea of 1 or 2 stops underexposed might be different than my idea. 2 stops underexposure on Velvia is very significant and would yield an extremely dense transparency. The screen shots all show using most of the dynamic range of the DSLR, which is way more dynamic range than Velvia can handle. It is entirely possible that the Velvia exposure was proper for holding highlight detail, but the contrastiness of Velvia pushed the mid-tones into deep shadow. That's just a matter of knowing your film and how it's dynamic range will cause a scene to render. Based on the screen shot histograms (which appear to show about 8 stops of dynamic range), I don't think Velvia is the right choice for any of them. On a different note, If you were using a Nikon camera as a meter I would say underexpose intentionally based on the Nikon's meter reading because Nikons tend to "expose to the right" which is fine for digital but not necessarily for film. Especially Velvia, with its limited dynamic range. Also, when I used Velvia, I always rated it at a lower ISO because I found I always was slightly underexposed when using at its rated ISO.

But I have to wonder about how accurate your LF lens is. How old is it, has been CLA'd, have you ever tested for shutter speed accuracy. Its quite possible that the lens is off by 1 or 2 stops, and it was juts a coincidence that the P&S gave you good meter readings.

Bottom line is you should be able to use the DSLR anyway for metering. Just set it on spot metering mode and do some calibration testing. Shoot several LF sheets at exposures around the Canon's meter reading, and see which sheet looks to be exposed the best. Compare that exposure with the DSLR's reading and you know how to compensate going forward.

[Simon Liddiard]

so the camera is displaying a much darker raw file in the lcd? this should lead to overexpose, isn't it?

p.s. Simon, I am a male with obvious beard :-)

Dude I'm so sorry, I did wonder! I have a couple of male friends called Lyndsey and Loren, which everyone misspells Lauren

[Greg Miller]

Agreed! The histogram is the only way to go if you're going to use a digital camera as a device to measure your exposure.

Firstly, if you shoot raw then the image on the back of the digital camera is only a jpeg rendering of the actual data captured by the sensor, and is subject to the interpretive processing designed by the camera manufacturer. Secondly the backlit LCD screen - possibly even with adjustable brightness - might well throw your guestimation even wider of the mark.

If you shoot jpeg the the preview will be more accurate, perhaps bringing you closer to a true WYSIWYG scenario... even so I think the histogram is more accurate than using the image preview.

The histogram is based on the jpg that is rendered, not the RAW file. I set my DSLr's so that they use the picture mode with the least contrast. This helps render a jpg whose histogram will most closely match the content of the RAW file.

[Andrea Gazzoni]

Its quite possible that the lens is off by 1 or 2 stops, and it was juts a coincidence that the P&S gave you good meterings

shouldn't a slow shutter lead to overexposed sheets?

anyway, this is not a lens issue.
I have the same results with both a 90mm and a 210mm..

[Greg Miller]

shouldn't a slow shutter lead to overexposed sheets?

anyway, this is not a lens issue.
I have the same results with both a 90mm and a 210mm..

The lens could be slow or fast.

You can pick up two light meters of the same brand/model and get different readings. If it were me, I would just run a calibration test and get on with life. That's what I do with any meter of any type.

[Simon Liddiard]

so the camera is displaying a much darker raw file in the lcd? this should lead to overexpose, isn't it?

The other way round - the camera LCD is displaying a jpeg interpretation of the raw file. Generally I find my LCD displyas a brighter more contrasty image, which when opened in a raw converter turns into a flatter, slightly darker image

I keep referring back to this article: http://www.luminous-landscape.com/tu...aw-files.shtml

This is also helpful - http://forums.adobe.com/message/4698680 (a lot of the posts are chit-chat, but the linked pages are good)

Getting a little off-topic now, but if you want to modify the camera settings to give a more accurate preview then search for UniWB

http://www.malch.com/nikon/UniWB.html

http://www.luminous-landscape.com/fo...?topic=63997.0

and finally, for your camera - http://www.luminous-landscape.com/fo...?topic=59776.0

[Simon Liddiard]

The histogram is based on the jpg that is rendered, not the RAW file. I set my DSLr's so that they use the picture mode with the least contrast. This helps render a jpg whose histogram will most closely match the content of the RAW file.

Yeah I'm just doing this now! (D700 - owned for 3 years, don't know why I haven't done it yet!)