celasun

<p>Thank you very much to you all.<br> The comments and the provided links were most informative.<br> For my particular case (macro shooting under continuous and relaively low light), this means I should be better off using the lens with the widest maxumum aperture (to allow for easier working conditions); without much regard to focal length. </p>

<p>Ellis and Joseph, thank you for your contributions. This correspondence did help my understanding of the issue better.</p> <p>I thought, in the meantime, perhaps it may be better to rephrase my query like below (I admit a picture might have been better):</p> <p>The first hypothetical positioning (from left to right):<br /> Fuji GX680 (stationary)... 80 mm rail and bellows... 100mm lens... object magnified 1:1.<br /> The second hypothetical positioning :<br /> Fuji GX680 (stationary)... 80 mm rail and bellows... 180mm lens... object magnified 1:1.</p> <p>I guess, in the second example the object will be farther away from the camera. That may place it towards the wider part of the now (tilted) cone-shaped DOF. Hence, a longer lens may help achiving more DOF for this particular object which sits entirely within the cone.<br /> However, I can also imagine that the longer lens will have a narrover cone shaped DOF and perhaps this nullifies the above optimistic hypothesis. That is, even if I can put the object farther away than that of the first position, the DOF will not change for the better (as long as the magnification is the same).<br /> Boring? Sorry :(</p>

<p>John, <br> Thank you for your response.<br> The link you provided deserves a detailed reading tonight!<br> Actually, my confusion stems from an illustration at the middle of this page:<br> http://www.cambridgeincolour.com/tutorials/tilt-shift-lenses2.htm</p> <p>As you can see, the DOF (using the Scheimpflug principle) appers to increase dramatically when the subject to lens distance increases. I just wonder if this applies for the increased distance due to the focal length. It may well be independent of it. I just don't know / understand. </p>

<p>I may be a bit confused about selection of a focal length for macro work using Fuji GX680 (II). <br> I know one can employ practically any lens for macro and I have the 80mm rail to allow for this. <br> My project my necessitate using the lens movements at limits (of the GX680 system). <br> We know that for the usual cameras without bellows extensions, longer focal length lenses allow a longer working distance for a given magnification. <br> I wonder if this is true for the GX680 system. <br> I ask this because a longer subject distance can help me use the Scheimpflug principle better allowing for more DOF for the same magnification (that is using the 180mm lens vs the 100 mm).</p> <p>Do I miss something?</p>

<p>Thank you very much. Much appreciated :)</p>

<p>Sigma 70 mm EX Macro f/2.8 is also the lens I love and use most for macros. I also have Pentax SMC F 50mm Macro and Vivitar Series 1 105 mm f/2.5 Macro. For whatever reason, my hand always picks the Sigma!</p>

<p>Les,<br> Beautiful colors and, somehow, a sense of smile!</p>