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I have been enjoying many images in the Leica Q Macro section. This has inspired me to begin experimentation with this aspect of my cherished Q. Several images posted were made with two attached Marumi 200 (+5) Achromat Macro close-up filters attached to the Q with lens set to Macro. Having just received my close-up filters, I have done a simple experiment that I thought to share with the forum. I know very little about the science of optics but wished to learn how these filters affect magnification, distortion, and vignetting of the images. (They also affect contrast and resolution but measuring that is beyond my abilities). The technical definition of a Macro lens is when the image on the sensor is (at least) as large as the actual object being photographed (ie. magnification of 1.0 (or 1:1). The Leica Q in Macro is not a true Macro lens by this definition – it is more technically described as a close-up lens. For me this does not matter as I find the close up images pleasing. I seek to explore what can be done with my Q and acknowledge there are other more refined tools in the Macro field for those who seek that level of magnification. My experiment is simple. Using a camera copy stand, I photographed 1mm ruled paper (actually EKG paper) at a distance of exactly 170mm from the sensor plane. This was done using native lens alone, a single +5 diopter filter, and then two +5 diopter filters (which I will refer to as +5x2 ). With the native lens in Macro mode, at 170 mm from sensor, the magnification is 0.235 (or 4.25:1). The image area captured is approximately 150mm X 100mm (or 6X4 inches). There is no visible distortion or vignetting ( ie. it appears to be very well corrected in camera). Attaching a single +5 filter, the magnification at 170mm from sensor is 0.3 (or 3.33:1). There is visible pin cushion distortion and vignetting in the corners. The distortion is fairly well corrected in Lightroom using a manual distortion correction setting of -17. I achieved only partial vignette correction. (This may be a function of my inadequate lighting.) The best I could correct was with a vignette correction of +19. These corrections were done by eye – others might have done better. Attaching two +5 diopters (+5x2), the magnification at 170mm from sensor is 0.387 (or 2.58:1). The pin cushion distortion and vignette were more prominent. Distortion correction required -28 and partial vignette correction was +30. In the two filter scenario, I was able to focus as close as 135mm from the sensor. At this distance, magnification was 0.493 (or 2:1). Partial vignette correction was +60. Distortion seemed to adequately correct at -22. In close-up and macro, the theoretic depth of field is determined by the factors of magnification, f-stop, and the size of the circle of confusion on the sensor. Lens focal length is not a major factor. From some references I have seen on the net, theoretic DOF in these magnification ranges are 2-3mm (f8), 3-4mm (f11), and 4-5mm(f16). My impression is that the higher the magnification, the softer the image but I do not know how to measure this. The narrow DOF may also contribute to this perception. Making photos has everything to do with making pleasing images and much less to do with knowing the precise magnification factor or extent of distortion. Much of the edge distortion will be masked by the prominent (and pleasing ) bokeh. However for the occasional image where the entire subject plane is within the DOF, knowing parameters for distortion correction may come in handy. Focus stacking will help enhance DOF but not correct for distortion. These measurements are predicated on a subject to sensor distance of 170mm. I do not see much sense to using the filters at longer distances as the native lens will provide a better image (at 170mm). As a beginner in close-up photography, using the Leica Q, I can see a need to train myself to ‘know’ the distance 170mm in front of the sensor plane. (BTW, there is a short white line on top of the Q that demarcates the sensor plane). I apologize for the length of this posting. I hope it is of some small value to at least a few. I encourage members to enjoy the images in the Leica Q Macro posting. Shown below are the measurement images at 170mm from sensor using two +5 diopters (+5x2); uncorrected and then corrected (using the settings noted above). Out of camera - graph photo (+5 x 2) filters, 170 cm from sensor Above photo corrected in Lightroom (distortion -28, vignette +30 )