Another great question Tony (and one that has come up here in the studio quite often.)
So let’s address the concept of “ideal” viewing distances. I have been privy to a number of heuristics over the years regrading this. Some have stated an outright distance (e.g., 6-7 feet), while others have put forward an interesting rule based on some formula (e.g., ideal distance should be three times the width of the piece.) While obviously both of these may work in some scenarios—as with many other aspects of the art experience—I believe that context will determine what is ideal (including but not limited to content, resolution, medium, environment, and as Yarbus stated regarding eye movement—whatever problem faces the viewer at the moment of perception.)
As with most issues regarding the art experience, I think that the best way to tackle the issue is to start by looking at ourselves to determine how we might find an “ideal distance” in a visual art viewing scenario.
The standard visual field (the portion of space in which objects are visible at the same moment during steady fixation of gaze in one direction.) The normal eye can detect stimuli over a 120º range vertically and a nearly 160 degree range horizontally. From the point of fixation, stimuli can typically be detected 60º superiorly, 70º inferiorly, 60º nasally, and 100 degrees temporally. Your greatest acuity in this field (foveal vision) which accounts for about 2º of visual angle (this is about the size of your fingernail at arm’s length.) A few other references to better picture this are the avg. sun/moon is about .5º, or fist at arm’s length, about 8-10º. We trend to orient visual targets in such a way so as to maximize information yield. I find most exhibition spaces (at least in most of the museums and galleries that I have visited) tend to appeal to a range of “Goldilocks zones” that allows for high acuity (including a reasonable amount of saccade/fixation) without losing the opportunity to experience the “gestalt” or whole of the image. If I had to guess where the mean Goldilocks zone would be for most scenarios (again, not saying that this would hold independent of context) would be about 20-30 degrees of visual angle (roughly a piece of US Letter paper (8.5x11") held at arms length.)
Interestingly enough, there was a study published in 2017 titled Art Perception in the Museum: How We Spend Time and Space in Art Exhibitions by psychologist Claus-Christian Carbon that touches on this:
"…we observed a mean viewing distance of 1.75 m at initial viewings of the pictures, ranging from 1.49 to 2.12 m. Locher et al. (2001) also observed viewing distances from artworks in a museum being mostly larger than in typical lab settings (with a range of between 60 and 120 cm). Interestingly, the lower limit of viewing distance was observed when visitors viewed a quite small-sized painting (i.e., “Portrait of a Carthusian” by Early Dutch painter Petrus Christus in 1446, sized W × H = 21.6 × 29.2 cm [indicated as W = 20.3 cm in the original publication by Locher et al. (2001)]). This is very similar in size to an A4 sheet of paper, yielding visual angles of 20.4° × 27.3°—which is quite compatible with the viewing conditions of typical computer testing scenarios in the lab. So at least with such smaller sized pictures, the viewing conditions in terms of the visual angle seem to be quite compatible between a lab and museum context. This could even be the reason why many people feel immersed in a lab context (known as the facsimile accommodation effect, see Locher, Smith, & Smith, 1999); at least, when such smaller sized pictures are depicted on the display. Locher et al. (2001) also revealed that the largest painting in the tested museum setting (“Aristotle with a Bust of Homer” by Rembrandt, sized W × H = 136.5 × 143.5 cm) yielded the biggest viewing distance of 1.2 m, resulting in visual angles of W × H = 59.0° × 61.4°. Although the latter visual angles are much larger than the ones revealed by the present study, they probably point in the same direction of conclusion: If people are allowed to adjust their viewing distance on their own, they tend to use larger distances for bigger pictures.
…Regarding the different viewing distances at which visitors choose to inspect the paintings, we again observed that conditions were very different to the typical ones employed in lab research. On average, the visitors in the present study distanced themselves from a painting M = 1.72 m across all viewings, which was not substantially different from the distance they used when only initial viewings were analysed (M = 1.75 m). First of all, the essential difference between a museum and a lab context is mainly that a museum offers enough space for visitors to choose their personal distance from an artwork. On what basis visitors choose their distance remains unclear, but it is seemingly done by intuition without any deeper rationale behind it. This intuition seems to have a basis in the extension of the artwork, here the canvas size: The larger the artwork the more viewing space is chosen. It is important to note that the revealed linear relationship with a very close fit between data and model was achieved at a very specific art exhibition devoted to one painter only; it should, however, also be noted that Gerhard Richter’s oeuvre is definitely a very wide, rich, and diverse one, and even the selection of six paintings here showed some obvious diversity in style and age. Although an exhibition displaying much more heterogeneous styles of various artists from different cultures would probably also have caused adapted parameters for the model equation, the uncovered psychophysical model—which I would like to term “art viewing distance accommodation”—needs further investigation as it potentially points to an implicit aesthetic viewing behaviour of trying to optimize the immersion and perceptual understanding of a painting."
Here’s a few of the figures from that study:
Histograms of viewing distances (in metre) for all used pictures plus mean (thicker, solid line) and median values (thinner, dotted line) for initial viewings only (red bars; top 2 rows) and for all viewings aggregated (blue bars; bottom 2 rows). The plots are grouped based on the raw area sizes of the pictures (small, medium, and large).
Relationship between area size of paintings (in square metre) and the self-chosen viewing distance (in m). Black solid circles indicate empirical data for the mean distance of all viewings; red solid circles only show the empirical data for the initial viewings of a picture. Regressions lines are based on N-weighted simple linear regressions, dotted lines indicate 95% confidence interval limits.
Now I tend to think that resolution indeed invites more intimate proximity viewing but at the price of long-distance communication. As most of you know, as viewing distance increases we will experience value lifts, diminished contrast, diminished apparent size, detail-loss, and chroma-loss (including possible hue shift over great distances). As such, more “punchy” boldness in painting tends to communicate more successfully over greater distances, but may lose their ability to communicate as effectively in more intimate proximities.
So just as Yarbus stated in regards to eye movements and fixations in his 1967 publication “Eye Movements and Vision”, …In conclusion, I must stress once again that the distribution of the points of fixation on an object, the order in which the observer’s attention moves from one point of fixation to another, the duration of fixations, the distinctive cyclic pattern of examination, and so on are determined by the nature of the object and the problem facing the observer at the moment of perception.”, I feel that the ideal viewing distance will be that which allows a viewer to elicit the desired level of information with respect to all of the environmental factors that influence said task.
To the latter part of your question (fine lines on the instrument), I would ask you—if people approach the work to see those lines—will the surrounding context/content survive (from a visual communication standpoint) inspection at that proximity? If not, and your goal is a coherent image at a given distance for a standard observer, then I would probably not add the lines that would pull a viewer beyond a point that may adversely affect communication from surrounding content/context. Does that make sense?
Hope this helps in your decision!