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Thread: Help with multiple strobe hit calculations

  1. #1

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    Help with multiple strobe hit calculations

    I guess this has probably been discussed, but sometimes things don’t make perfect sense until you play them out in your own situation… I have discovered that, against natural lighting work in the field, studio work with a 4x5 is a whole new animal.

    I own four low-ish powered strobes at 200w/s each. At first I was very intimidated by using multiple pops to fulfill the smaller working apertures on my 4x5 lenses, especially on slow films such as RVP 50. However, I spent the day figuring out a system and I was hoping some of you could help me verify or tune what I’ve come up with.

    I use an L-358 light meter and I have decided to work with 1/10 stops. Here is my workflow:

    Say I am using a 210mm lens with an aperture range of 64 to 5.6. I setup my scene and perform a focus analysis using my camera’s DOF calculator (on the fine focus knob). I determine that the largest applicable aperture for the DOF range that I want is f/32. I back focus from the nearest point by half and lock the focus down.

    I then use my QuickDisc, or I do an extension calculation, and determine that my bellows factor is 6/10 of a stop.

    I then take a meter reading (incident) and my meter returns an aperture of f/16 and 8/10 for an ISO 50 film. Because this is too large of an aperture for my intended DOF, I need to scale this figure and use multiple hits of my strobes. Here is what I am doing:

    First I subtract my bellows factor from my initial meter reading to get an adjusted value of f/16 and 2/10, this is my target exposure. My working aperture is, again, f/32, so I adjust this to f/32 and 2/10 with the error on the side of greater DOF, which is safe. My target exposure of f/16 and 2/10 is, then, exactly two stops brighter than my adjusted working aperture of f/32 and 2/10.

    The reason I am adjusting the working aperture to be a multiple of the target exposure is because I don’t want to change my strobe powers, I want to figure whole hits of my strobes as they stand.

    So, given the adjustment, I will need (2 stops = 4) four hits of my strobes to meet my target exposure with my aperture set to approx f/32 and 2/10 (physically, slightly below the f/32 and 1/3 mark on my lens scale).

    I have now verified my math by doing a multi-reading with my flash meter and setting the exposure compensation to -0.6. The result of four hits on my meter is f/32 and 3/10. Just 1/10 of a stop off from my calculations, which is finer in resolution than I can probably set my lens aperture, heh. That is hugely satisfying, I am so proud of myself right now, lol. I know that I could just rely on my meter, but I’d rather get used to doing the calculations myself because this will make me universally more prepared to handle any situation in any studio.

    Is this a sound method? It seems that it would be adaptable to just about any situation and any factor can be adjusted to fit the scene, which is just great. I have just exposed two sheets of 4x5 Velvia 50 using this method, one on my 210mm and one on my 180mm (both Nikkor-W’s) so I guess I will see some hard proof as soon as I get them processed. But if anyone would care to chime in and suggest any adjustment to this method, from math knowhow or experience, I am all ears!

  2. #2

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    Re: Help with multiple strobe hit calculations

    yeah good

  3. #3

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    Re: Help with multiple strobe hit calculations

    Just set the shutter to 1/60 and make the multiple exposures.
    Apeture controls the light from the flash unit. Shutter has more effect on the contribution of any ambient light.

  4. #4
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    Re: Help with multiple strobe hit calculations

    Just count your pops and add an extra one in for good measure!

  5. #5
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    Re: Help with multiple strobe hit calculations

    Quote Originally Posted by aphexafx View Post
    ... I have decided to work with 1/10 stops....
    Relax somewhat. Even on Ektachrome a third of a stop difference is barely noticeable.
    While you're at multiple flashes, you might a well do plenty of them and stop down a bit more (but do it in the dark without shutter vibrations). You can't go wrong over 16 'pops' but you can go wrong in the 4 'pops' area.

  6. #6

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    Re: Help with multiple strobe hit calculations

    Thanks for all the replies, thanks Frank, thanks Christopher. Regarding ambient light, I have factored this out - my meter is set to 1/60th and is reading 100% strobe contribution in my workspace, whereas I am making my strobe exposures in the dark with the shutter open.

    "Relax somewhat. Even on Ektachrome a third of a stop difference is barely noticeable.
    While you're at multiple flashes, you might a well do plenty of them and stop down a bit more (but do it in the dark without shutter vibrations). You can't go wrong over 16 'pops' but you can go wrong in the 4 'pops' area."

    I agree that 1/10 stop is extremely fine, but that is how my meter reads so why not? I could set my meter to 1/3 or 1/2 stops, but then it reads direct f/stops (18, 20, etc.) which, for me, is much harder to deal with than wholes stops and tenths. The final adjusted aperture value can be rounded to the nearest 1/3 stop at the end if desired. I just wanted to make sure that I was doing the calculations correctly.

    Otherwise, I think what you are saying is that I should tend towards smaller apertures and tend to use more hits of the strobes because that will result in less average error overall? Interesting point and it makes sense.

  7. #7

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    Re: Help with multiple strobe hit calculations

    If a client is paying for the film, shoot in 1/3 stop brackets. Otherwise you can loosen up, erring on the underexposed side for chromes and over for neg.

  8. #8
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    Re: Help with multiple strobe hit calculations

    Quote Originally Posted by aphexafx View Post
    ...I think what you are saying is that I should tend towards smaller apertures and tend to use more hits of the strobes because that will result in less average error overall? ...
    Absolutely. Since you take the trouble to do multiple flashes, you might as well sit there and even things out. Same goes for Tungsten film and long exposures. Shots at 10, 30, 60 minutes for the same stop are all good - just different.

    While we are at it, here's a prickly argument:
    Stopping far down represents things as the are. So you put 'things', people and situations right there on the page and you, the photographer, and your photograph become invisible.
    Shooting wide open adds a strong level of abstraction. So that you are now putting the actual photograph on the page; and you, the photographer, are incumbent.
    I suppose it depends who is paying for the shot. If it's your money, be an artist!

  9. #9

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    Re: Help with multiple strobe hit calculations

    "If a client is paying for the film, shoot in 1/3 stop brackets. Otherwise you can loosen up, erring on the underexposed side for chromes and over for neg."

    "I suppose it depends who is paying for the shot. If it's your money, be an artist!"

    Right now I am definitely paying for everything.

    I've completed five exposures (tabletop) designed to test my calculations and my camera - I will hopefully get these processed tomorrow and examine how things have turned out.

    Thanks for all of your input, I appreciate it to no end! I can see now that my strobes will be getting quite a workout when shooting ISO 50 film with my 4x5! But that is what they are for.

    I am a bit concerned about the limited DOF I am getting with my 210mm and 180mm lenses, even at f/64, when shooting at ~3 feet from lens to subject. My big book of commercial photography ("Still Life and Special Effects Photography" from RotoVision) is filled with examples of 4x5 studio shots using similar focal lengths and they seem to exhibit more DOF than I am getting on planes which are perpendicular to the lens axis (so, without movements to compensate) - I am searching for a thread about this right now: Even though longer lenses have shallower DOF in general, I am wondering if by standing my camera back from the scenes I will get deeper working DOF at the scene level??? Do I need a longer lens for deeper perpendicular DOF at tabletop/still-life/product scale???

    Here is a prototype digital shot (Nikon DX format) that I made which I am currently unable to replicate using my 4x5 due to depth of field:



    I cannot get the background and glasses in focus even at f/64, even when I back off...

    I would REALLY like to get this scene (or equivalent) onto a 4x5 chrome, there has to be a way to do it!

  10. #10
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    Re: Help with multiple strobe hit calculations

    Quote Originally Posted by aphexafx View Post
    ... I am wondering if by standing my camera back from the scenes I will get deeper working DOF at the scene level??? Do I need a longer lens for deeper perpendicular DOF at tabletop/still-life/product scale??? ...
    I80mm is about the limit on 4x5. Any longer and the subject become remote from (loses contact with) the viewer. This has to do with the viewer's natural feeling for perspective. Maybe stand back, leave some room or maybe do without background focus.

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