Using a Dslr as a preview for film long exposures

Discussion in 'Medium Format Cameras and Accessories' started by bibowj, Jul 12, 2014.

  1. bibowj

    bibowj Member

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    Hello all- Thanks you very much for taking the time to read my post/question. Ive been getting into long exposure night time photography lately, using a variety of films (so far Acros and Ektar). Im struggling a little with getting a proper exposure, or at least computing for one. So, my question is ... is there anything inherently incorrect in using my DSLR as a 'polaroid' for the scene Im shooting (assuming Ill account for proper reciprocity of the film when I move to the film camera)? I ask because I was doing some long exposure black and white work last night, using a meter and computing by hand (on acros) and now that Ive developed the film, most of my shots came out significantly over exposed.... so I would like a little 'insurance' that my math is correct before I expose the film and I wasn't sure if there are other factors to account for.

    Thoughts?


    Thanks all!
     
  2. Eric Rose

    Eric Rose Subscriber

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    Having done a fair amount of night photography with film and digital I would say you would be better off just learning how your film behaves and leave out the digital stuff. The way each responds to long exposures is just to different. One thing you might want to experiment with depending on the subject matter is ND grad filters to even out the exposures if you have one area that is brighter than others. Night photography at least to me is an organic thing. You just learn to "feel" what the right exposure is once you have enough experience. I have used my darkroom dodging tools in front of the lens during exposures as well. Night photography is one of my favorite things.
     
  3. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Better off just experimenting by bracketing exposures on a night reserved for testing, when you're not photographing anything important, and keeping a record and making a table for reciprocity correction that you can use in the future. As you use it, you may find you can do some refinement, adjusting development time to correct contrast with long exposures as well. Once you have that, you'll be all set, you can concentrate on the aesthetic issues rather than the technical ones, and you don't need to test with another medium that will still require a conversion table anyway.
     
  4. Hatchetman

    Hatchetman Subscriber

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    Please give details of meter, camera, scene, exposure, etc. Let's address why the shots were overexposed prior to resorting to a crutch.
     
  5. bibowj

    bibowj Member

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    In regards to Mr Hatchetman.... I was shooting acros at sunset, over looking the ocean. I was using about 8 stops of ND and using an app on my phone to compute the add exposure time needed to comp for the ND filters, which figured most exposures around 15-30 seconds and some at a minute. Looking back, I realize that that was way too much time.. which is why I was wondering If I could use a dslr to at least get me 'in the ball park' to bracket from that point on.

    Its clear most are going to be against using DSLRs as a starting point, so what if I use a polaroid back with the same rated film as a starting point? Im shooting mostly with a Mamiya TLR but I also have a 645af w/ a Polaroid back that I could use to test where the exposure should aprox be.

    Thoughts?
     
  6. Hatchetman

    Hatchetman Subscriber

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    well my first thought is your ND filter may not actually be 8 stops, which would be pretty unusual as far as I know. A filter labeled "ND8" means 1/8 the light or 3 stops.
     
  7. Neil Grant

    Neil Grant Member

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    A potential problem would be different reciprocity characteristics between the films. You're proposing to use neg film anyway - which has good tolerance of excess exposure. The second camera is just adding complexity to your shoot.
     
  8. bibowj

    bibowj Member

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    ohh, and now that Ive scanned the images..they were actually quite underexposed. Its just that I didn't account for the exposure correctly. I was metering reflective , at a far off area.. no biggie ..just a match mistake on my part. I did one have that turned ok ish.. but the rest were just my screw up.
     
  9. bibowj

    bibowj Member

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    The ok one

    This one worked out.
     

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  10. wiltw

    wiltw Subscriber

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    Film is subject to 'reciprocity failure'...that is, at very long exposure times due to very low levels of light, twice the time does NOT provide twice the response to light...you might see only 20% increase in film response (density) for 100% increase in time, for example...the 'curve' in the response curve of film. In comparison, digital is largely LINEAR in response.

    Your 'underexposure' in post 8 proves the result of reciprocity failure.
     
    Last edited by a moderator: Jul 12, 2014
  11. bibowj

    bibowj Member

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    Even though Acros has no reciprocity failure up to 120 seconds (documented)?


    I was using Acros specifically because of its lack of a reciprocity failure. Like i said, the underexposure was purely my mistake in reading the meter correctly.. I was just wondering if using a DSLR to get me in the ball park would be smart... and THEN add on the reciprocity for the film ( as needed). Bracket from there and so forth.
     
  12. markbarendt

    markbarendt Subscriber

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    It is important to understand what under and over exposure actually mean and there are several ways to define this.

    1 In relation to a standardized process.

    2 By what's available on the negative.

    In the standard processing world the expectation is that if the camera exposure is right then the negative should "print" or "scan" perfectly using a standardized process, no manipulation required. Slides and JPEG shooting are the classic examples of this style. Over and underexposure are anything that falls outside the norm. "In studio" where lighting is completely controlled, it is normal to be able to use a standard process but in non-studio photography, this exactness is the rare exception rather than the rule.

    Negatives don't work like slides and JPEGs. Negatives typically catch a lot more info than is printed, the output mediums available to us simply cannot represent as wide a range of info as a negative can. Acros for example may be able to record detail across a range of 12-14 f-stops or more, paper and monitors can typically only show a 6-8 f-stop range. So half the info from an Acros negative may "straight print", it takes some form of manipulation to get the other half to "print". This is normal for negative films, it is why it is said that negatives have great "latitude".

    A negative is only truly underexposed if the shadow detail you wanted simply isn't there or is too far down on the toe to be usable, if you can dodge and get the detail you want in the shadows the negative isn't underexposed.

    Similarly if you can burn in the highlight details to get what you want, the negative isn't over exposed.

    The disposable cameras that we can get at the grocery store use a negative film's latitude to make shooting simple, no need to adjust camera settings. When the film is scanned or printed the person (or software) doing the work simply chooses which 6-8 stop range to print from the negative.

    With negatives you can very often underexpose by 1 stop. On the over side you may be able to go as much as 3-4 over. You need to experiment to find your personal limits.
     
  13. bibowj

    bibowj Member

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    SO what everyone is saying is that I can't (or shouldn't) use a DSLR and its histogram to get a middle exposure as a 'starting point' to then bracket and ensure that I have all the detail in both highlights and shadows?
     
  14. John Koehrer

    John Koehrer Subscriber

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    I'd use an old Kodak data guide for a starting point.
    There are a number of tables online that've been appropriated but they're all about the same.
    They give a number of lighting examples, sunset, full moon, half tanked and give starting exposures for different ISO
    I keep a copy of one in the bag "just in case". It's much lighter than that other thing you've mentioned.
     
  15. Hatchetman

    Hatchetman Subscriber

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    go ahead. I'm not dropping $300 on a light meter, so I use an old digital camera. works fine. I usually just use the Sunny 16 rule and no meter at all. Sunset on the water is about the most difficult thing to meter IMO.
     
  16. BetterSense

    BetterSense Member

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    I think you are wasting time in this particular scenario trying to use a digital camera , or a meter at all, actually. This type of photography is done with bracketing, good notes, experience, and luck. I'm sorry that there is no easy button.

    You are already halfway there, though. Just use what you have already learned with that film and filter and go from there. You should know what to do next time.

    Digital cameras make good exposure predicting tools in many scenarios within their limits but this is not one where I feel it will be any help getting you results you want on film.
     
  17. elekm

    elekm Member

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    I don't think digital = film when it comes to long exposure. Like the others said, you have to test.

    It's one of those things that requires a bit of testing and for you to get a "feel" for correct exposure.
     
  18. Poisson Du Jour

    Poisson Du Jour Member

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    The sensor in DSLRs is much more sensitive in low light than film and shows nothing about reciprocity for film at an equivalent exposure. Essentially, using a DSLR for proofing in low light is where caution and judgement needs to be exercised, based on experience and known results in particular circumstances. A DSLR is not alien to analog photography: it can be very useful indeed, but it is not a panacea for analog perfection. Sometimes (not on recent busy shoots) I use my Nikon digi for proofing scenes, but never in low light where I am more comfortable and certain with what I am doing (using transparency film) meteringn separately than relying on a sensor with bland and unserviceable exposure feedback. Acros is renowned for having a very wide latitude, even up to 3 minutes and is often favoured among pinhole photographers working at long exposures.
     
  19. markbarendt

    markbarendt Subscriber

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    Use a DSLR if you please. Like any meter though you need to test it to calibrate it to your film systems quirks. Your lenses, your shutters, your personality as a meter operator, your developing technique, your scanner... Dialing the box ISO rating into the DSLR may or may not get you better exposure settings.

    With regard to bracketing, IMO don't bother, just be sure to get enough exposure/avoid under exposure. Negatives are very forgiving of extra exposure.
     
  20. jcc

    jcc Member

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    I third(?) the vote for a DSLR as a lightmeter proxy if you want--there's nothing wrong with that. It's a reflective meter with a better screen! But do calibrate how your film measures relative to your DSLR results (i.e., take notes).
     
  21. MattKing

    MattKing Subscriber

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    If you are trying to experiment with ultra-long exposures, reciprocity failure can be your friend.

    If your film requires three stops more exposure time due to reciprocity failure, you will need three stops less ND filter in order to use that exposure time.
     
  22. markbarendt

    markbarendt Subscriber

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    The other thing I was trying to get across in post 12 was that your current negative may not be underexposed. The problem may be the scan or the post processing.

    It is outside the scope of APUG to get into the details of how, but for a moment forget the rest of the photo, try to scan and print just to get the shadows the way you want.

    If you can get the detail and contrast you want in the shadows (regardless of what the rest of the "print" looks like at this point) the negative is not underexposed.
     
  23. JammyB

    JammyB Member

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    I've had good results so far using a canon g10 to spot meter. It's also useful for previewing the effect of coloured filters on black and white.
    What H/W and S/W are you using to scan. I find if I do a linear scan of a neg I always need to adjust the apparent exposure afterwards in PP.
     
  24. thuggins

    thuggins Member

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    My experience with DLSR exposures is that they are not very reliable in difficult light situations. The software seems to try to guess (wrong) about how to "correct" the image.

    If you really want to gauge the correct exposure in low light get an OM-2 or OM-4/4T. Olympus pioneered the OTF (Off the Film) exposure system and it is still phenomenal. I have made many nighttime exposures from several seconds to several minutes and they always come out beautiful, and that's on slide film!