Calculating bellows factor with large tilts and/or swings?

[Matt Blaze]

Matt, I am really happy if my explanations are meaningful to your experiments.

Yes -- extremely helpful and exactly what I was looking for. Thanks again.

Additional notes:
- I should not have used "rear tilt" ; in fact the relevant tilt angles for light fall-off effects is the total tilt angle between the lens board and the film plane, equal to the sum of the front tilt + rear tilt on the camera, in the usual sense for view camera movements.

Right, I understood that (which is the only thing that makes sense, given that the camera doesn't know which standards are tilted, only their relationship to each other and the subject).

- on the previous slide #2 the formula for close-up should read : d^2 / f^2 = (1+M)^2

And so log_2 {(M+1)^2} (or log_2 {(d/f)^2}) gives the correction in f stops.

- For those inclined to really esoteric things I have made an additional slide (see below) explaining how the luminance of the aerial image, equal to the luminance of the source, explains the above mentioned formulae. The notion of luminance is something totally non intuitive and perfectly lambertian sources hardly found in our photographic subjects (an approximation of such an ideal source could be a perfect matte screen covered with fine powder of magnesium oxide, illuminated by a perfect large-size diffusor)

Terrific; thanks. These slides deserve to be archived somewhere; perhaps someone can link to them in the tutorial section on largformatphotography.info.

Best

-matt

[Matt Blaze]

While you have formulae that explain the losses up close, a fast and acceptably accurate working plan is what one needs to get work done. Most folks won't want to consult a spreadsheet to shoot a closeup.

Well, yes and no. While few photographs demand or benefit from an exact lighting or exposure calculation, these equations are not particularly onerous, and understanding them (even without making accurate measurements of the lighting, bellows length or reproduction ratios for any given exposure) provides the basis for developing an intuition about how a setup can be expected to behave and what kinds of corrections will be required. At least that's how I work.

Best

-matt

[David A. Goldfarb]

I don't see myself making these calculations in the settings were they might be relevant (pretty much exclusively tabletop work), but I think it is an interesting explanation of a phenomenon that is worth being aware of. In practice, I could see myself looking at a Polaroid and adjusting the lighting to compensate for falloff of this type, and knowing in principle why this type of falloff would be happening would provide some insight into what might happen if, say, I were to recompose and use less extreme tilt/shift. Knowing about this possibility, I might be more likely to make meter readings at the groundglass using a booster probe, and that could save a Polaroid ($15 for 8x10") or two.

[Emmanuel BIGLER]

I agree with David G. and C.G. ; and as an amateur using the view camera with film and mechanical shutters, I accept of course the electronic hand-held meter but I would definitely be reluctant to carry anything else but a paper chart or the Rodenstock specialized slide rule in the field ! ( I belong to one of the last generations where we had to learn how to use the slide rule at school !!)

This yields a question about the use of boosters in the image plane or similar devices ; I have in mind a device marketed in the seventies-eighties by Sinar, based on a Gossen meter analyzing the ground glass. Arca Swiss had a device with silicon light-metering sensors embedded in the ground glass.
I have spoken of such devices with French professionals who had worked with a view camera on a daily basis, none of them were really enthusiastic about them and recommend the spotmeter aiming at the subject to analyze the scene + corrections, the classical close-up corrections for example.

Well, one could argue that often professionals in the past were reluctant to new tools when they had elaborated good lighting & metering methods that worked for them, but my feeling was that metering on the ground glass brought also some specific problems and never convinced professionals...
And there was the instant polaroid image for preview ! This seemed, on the conrtrary, to be a favourite method in studios in the past... at a nominal cost as explained by David.

[Drew Bedo]

Hello All;

I know that there is a practical need to "get it right " in one shot when working in LF, yet with a complex set-up i.e. extream macro and large tilt/swing, has any one tried bracketing to see what actually happens and by how much?

[CG]

Well, yes and no. While few photographs demand or benefit from an exact lighting or exposure calculation, these equations are not particularly onerous, and understanding them (even without making accurate measurements of the lighting, bellows length or reproduction ratios for any given exposure) provides the basis for developing an intuition about how a setup can be expected to behave and what kinds of corrections will be required. At least that's how I work.

Best

-matt

I don't see what gets accomplished beyond a theoretic knowledge by going to some set of equations that give you a perfect explanation almost no one will actually use.

Isn't it enough to know that the extension and repro ratio at each area of the gg determines the correct light loss? There are several methods for working it out, that are, in the real world, exact. I sort out my losses from that. You, I'm sure do also.

It's implicit in your example of the "coins". Measure the coins. Measure the images. You now have the repro ratio. The calculations are the basic ones. No more specialized calculations are needed.

I get concerned that photography tends to devolve into an exercise of expertese-itis and esoteric technical legerdemain. I'm enough of a geek to get that and to appreciate it, but to do a photograph I'm a believer in finding the approach of greatest and simplest practical utility. Bellows extension and repro ratio calcs or behind the lens metering - take your pick - are necessary and sufficient.

...a device marketed in the seventies-eighties by Sinar, based on a Gossen meter analyzing the ground glass. Arca Swiss had a device with silicon light-metering sensors embedded in the ground glass.
I have spoken of such devices with French professionals who had worked with a view camera on a daily basis, none of them were really enthusiastic about them and recommend the spotmeter aiming at the subject to analyze the scene + corrections, the classical close-up corrections for example

The probe meter is not for everyone, but it was a very practical answer to these sorts of annoying exposure issues - and the probe takes care of bellows extension and tilt etc all at once.

Best,

C