How well does a digital camera`s TTL metering translate to a 4x5 camera?

Discussion in 'Large Format Cameras and Accessories' started by Treymac, Oct 11, 2010.

  1. Treymac

    Treymac Member

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    Hey guys. I`m having a lot of trouble coming up with exposure times. One of the problems is that I`m certain that the light meter I`m using isn`t giving me accurate enough times. This is because I`m trying to use it to meter through ND filters (edit: not real ND filters but a welders glass), which I can`t put flush up to it, resulting in a 3/4 inch gap between filters and meter, allowing extraneous light to come between them, throwing off the metering. So what I`ve thought about doing is just putting the filtering setup I`ll be using onto my digital SLR camera and using it to get the metering, then just use that. But I want to know how close the metering will translate onto the 4x5 camera. I`ve done this with my medium format camera and it worked quite well, but this is really my first time with a large format.

    What do you guys think?



    Oh ya, do shutter speeds just start doing the exact opposite once it hits 1 second? like 1s, 2s, 4s, 8s, 15s, 30s, 60s, 125s, 250s, 500s

    Thanks.
     
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  2. dehk

    dehk Member

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    Why don't you just do the math? The filter tells you how many stops it cuts down.

    Shutter speed, yes it does, but you have to worry about reciprocity failure for long exposures. Most manufactures will have this data in their data sheet for the specific film online.

    Cheers
     
  3. Treymac

    Treymac Member

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    Hey. Sorry, I was going to try to update my post but the forums were having problems for a second.

    I`m not actually using real ND filters but a welders glass, which is somewhere around 10 stops, but who really knows. So I`m only left with trying to meter for it, and this is the problem.
     
  4. Sirius Glass

    Sirius Glass Subscriber

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    Welder's glasses are not ND filters. That is your first problem.

    Steve
     
  5. Treymac

    Treymac Member

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    Thanks for the tip, I thought welders glass really was an ND filter /s. They have the same effect, but are much stronger with a little less clarity. And a lot cheaper.
     
  6. JBrunner

    JBrunner Moderator Staff Member Moderator

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    Honestly interested why anyone would need to cut ten or so stops with a large format camera? The problem is usually the entire opposite. In any case you can use another cameras TTL to determine the density of the camera, digital or otherwise, as long as you meter a uniform subject, like a grey card or similarly neutral field. In addition to not being optically correct, I'm pretty sure a welders glass isn't anything close to neutral. Density aside, most likely the result on B&W will emulate using a #11 or thereabouts. Might work for a few things, really ugly for most. Hideous for color unless you're photographing algae. Probably not worth the bother, but you seem determined. I'll be curious of the results.
     
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  7. dehk

    dehk Member

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    As the other poster said, welder's glass are not ND glass. But, i take it you do not have a spot meter to stick it right at the glass. Well, in that case, yeah try to meter with your SLR. Even with multi zone / matrix metering as long as its the same scene. Good luck. Or alternatively, spot meter to something with and without the glass to like a grey card, so you know how many stops its cutting off and you can just do the math the next time.

    If anything it will be interesting.
     
  8. Treymac

    Treymac Member

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    Ok, thanks a lot. I`v been curious about that for a long time. I`m trying to get a long exposure to still the ocean and capture the movement of the clouds.

    One thing I`ve been thinking about also is that since I do have 2 ND 0.6 and 1 0.9, stacking them together will give me 7 stops. The reason I didn`t think about going this route is that the welders glass is just one piece of plastic, while the filters are 3, kind of a toss up of which is worse doing optically. But I figured that using the actual filters with a metering of f5.6 @ 1/60, applying them will give me 2 seconds. And that`s not long enough. But I never considered adjustments. Tell me if I`m correct. With a reading of f5.6 @ 1/60 the filters give me f5.6 @ 2s. Going f8 @ 4s because of less light through the aperture, I have to keep the shutter open. Continuing, f11 @ 8s. Finally, f16 @ 15s. And 15 seconds is around the time that I want.

    Is that correct, my brain hurts now. I always get flustered and make stupid mistakes when I`m starting with something completely new.
     
  9. JBrunner

    JBrunner Moderator Staff Member Moderator

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    You get to 15s and you'll need more exposure than you are calculating. For instance with FP4 if a 15s exposure is indicated, I expose for around a minute. You have plenty of ND on hand for what you want to do. Forget about the welders glass and look up reciprocity.
     
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  10. Treymac

    Treymac Member

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    Ok, cool. I`m using Delta 100 so it`s fairly close.
     
  11. JBrunner

    JBrunner Moderator Staff Member Moderator

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  12. Treymac

    Treymac Member

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    Crazy, so when exposures get up to a considerable length, time doesn`t make as big of a difference as when it`s in fractions of a second for a normal shot.

    I`m also using D76 for developing.
     
  13. dehk

    dehk Member

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    Reciprocity failure(borrowed from wikipedia)

    At very low light levels, film is less responsive. Light can be considered to be a stream of discrete photons, and a light-sensitive emulsion is composed of discrete light-sensitive grains, usually silver halide crystals. Each grain must absorb a certain number of photons in order for the light-driven reaction to occur and the latent image to form. In particular, if the surface of the silver halide crystal has a cluster of approximately four or more reduced silver atoms, resulting from absorption of a sufficient number of photons (usually a few dozen photons are required), it is rendered developable. At low light levels, i.e. few photons per unit time, photons impinge upon each grain relatively infrequently; if the four photons required arrive over a long enough interval, the partial change due to the first one or two is not stable enough to survive before enough photons arrive to make a permanent latent image center.
     
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  15. JBrunner

    JBrunner Moderator Staff Member Moderator

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    Yeah, that's pretty much it, two minutes is only about a stop more exposure, or maybe less, depending on subject contrast and developing. You may also experience an expansion effect because when reciprocity kicks in different tones don't receive the same exposure as they would if the film was acting normally because density builds on the negative at different rates according to the local reciprocity effect, and this happens even if the emulsion isn't one that likes to expand when one is trying to achieve expansion using conventional methods. Charts are basically serving suggestions, and can be right on or wildly inaccurate depending on who what when where and how. In other words results may vary. It's important to be consistent in methodology and keep good records of what you did, so you can adjust or duplicate.
     
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  16. Treymac

    Treymac Member

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    I didn`t have enough time to do a lot of research into my project, so I`m glad my tripod broke today before I really got into taking many photo`s. I did take one with the welders glass though, so I`m looking forward to how it turns out.

    Thanks guys, sounds like I won`t have to be bracketing too much now.
     
  17. dehk

    dehk Member

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    Make sure you show me the photo taken with the welder's glass, I do have 2 masks sitting out in my shed also!!
     
  18. Q.G.

    Q.G. Inactive

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    Just a niggle: when the aim is to teach about film's behaviour at long exposures (and quote Wikipedia), let's call it by its proper name, i.e. "reciprocity failure".
    "Reciprocity" of time and intensity is what we enjoy at 'normal' shutterspeeds.
     
  19. JBrunner

    JBrunner Moderator Staff Member Moderator

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    Very true and correct, and a good catch. I think maybe many just say "reciprocity" when speaking of reciprocity failure because reciprocity doesn't actually concern us very much when it's working correctly.
     
  20. Dan Henderson

    Dan Henderson Member

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    Treymac: Meaning no disrespect, from reading your posts I think you need to learn the basics of photography, including exposure. I recommend you buy a good, beginning photography book. "Photography" by London and Upton comes to mind, but there are others. If you study one of these texts, things like reciprocity (and reciprocity failure) will make sense to you and at some point will become second nature. If you are short of funds I am quite sure that you can buy a used one from Amazon or some such place for a reasonable price.
     
  21. Treymac

    Treymac Member

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    Hey guys. Ok, so I took my photo's yesterday, and developed today. The welders glass didn't turn out because I didn't give it enough exposure time. But the rest that I just used ND filters on did come out nicely. I figured reciprocity into my timing, which actually is pretty sweet because it gives me a lot more time to keep the shutter open. Unfortunately I ran into some problems with the negs though. One was from developing them, I had streaks from the carriers that look pretty awful. It's pretty disappointing. There was also another problem, and this I think came from one of the filters. There are some squiggly artifacts that show up, mostly in constant light areas like sky and water, and since that's the majority of my photo's, it's kind of really disappointing. But I did get 3 out of 10 that I think I can work with. It's going to require major cropping and the actual photo that I took is going to be lost, but at least I will have something. Good thing it's large format.

    So I'm also planning on going out again, probably next Tuesday to get some more photos. But I'm going to be using medium format 645 just because it's so much quicker to get around. And using iso 25 speed film, either Rollei Ortho 25 or Rollei Pan. At least with 25 speed film, I won't need to use as many filters, which will improve image quality as well. I love using large format but it wasn't a lot of fun packing the camera, tripod, and the rest of the equipment all over the city. I feel a little defeated, but at least my pictures did work. So my project is going to be a mix of large and medium formats.
     
  22. bdial

    bdial Subscriber

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    This is most likely caused by processing or dust on the film and not your filters. Your agitation technique in the developer may need some work.
     
  23. 2F/2F

    2F/2F Member

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    As I mentioned in another thread that you (or someone else using welder's glass) started on this issue, you can use the digital camera to test the effect of the glass (to find the required exposure compensation when using the glass), but I would not use it to decide exposure itself, for reasons that have been discussed ad nauseam in other threads.
     
  24. Thingy

    Thingy Member

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    I see you haven't encountered Lee's 100mm Big Stopper ND filter which gives approximately 10 stops...
    :tongue: :laugh:
    http://www.robertwhite.co.uk/product.asp?P_ID=3086&PT_ID=713

    Whilst it is not an ND filter that you need to normally use with MOST 5x4 lenses, it is VERY useful for one lens in particular: Cooke's PS945*, which being mounted in a Copal 3 shutter has a minimum shutter speed of 1/128. Whilst this is not a speed I ever use with the rest of my LF lenses, with the PS945 I typically use an aperture of f5.6-8, and very occasionally f4.5. F5.6-8 seems to produce the nicest results for close-up (typically 1:2) flower photographs. Unfortunately the shutter speed I would need to use with an aperture of f5.6 in sunlight (for optimum effect) is siginificantly greater than even my 1.2 ND filter offers, so I find the Big Stopper useful in these limited circumstances.


    *Can also be used on a 5x7 camera! :smile:
     
  25. Treymac

    Treymac Member

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    Hey 2F/2F. I didn't actually use the digital camera for metering, I used my light meter and applied the ND stops + the reciprocity failure.



    I don't know what could have been a problem with the agitation. Every 2nd minute I would do a slight agitation by bringing the holders up to the top of the box and letting them sit back down. Pretty much as we've been instructed to do.
     
  26. Treymac

    Treymac Member

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    Hey guys. So I finally did my prints today of the 4x5 shots. For some reason they look much better on full size prints than they do on the contact sheets. There is still what looks blotchy in the sky, although it's not terrible. The scan is pretty bad, just quick and full of dust, but here's is a shot of Vancouver from Granville Island:

    [​IMG]

    What do you guys think?