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Message: <blockquote data-quote="Kevin Purcell" data-source="post: 1355758" data-attributes="member: 68323">To avoid accommodation issues don't use the human eye use a digital camera (like digiscoping).Perhaps using a resolution target (and moving that) rather than moving the focus on the bin is a more accurate way of experimentally measuring the DOF. And avoid the issue of "fast focus".I'd also rather measure at "real" distances. For some reason I have a dislike of close in observations (but it's probably irrational).Combing the two should give an accurate experimental measure of the bin resolution (from the image of the resolution target ... camera folks do this all the time: software is already written) and an accurate curve.You could even extend this to looking in different parts of the field so you could isolate the effect of field curvature.Any property I should control for that I missed?I have my own bin DOF test: focus on a 7m target (with spiders webs for pinpoint focusing) then read a sign 40m away. Then ABCD a group of bins and rank them on how defocused the sign is. The sign is black on white text (with sharp edges) about 0.15 degrees tall so no field curvature effect with the sign in the center of field. I can rank bins this way. With the same magnification. So I conclude they differ. And in fact, in real life, they do. The worst one has a problem keeping a whole wren in focus at close range <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />Oh and for the record my 47 year old eyes have about 2D or so of accommodation (from the close focus for my corrected distance vision). So I don't have a lot of accommodation. But it could still be an issue.So I'm not convinced the simple model that says magnification is the only effect actually applies to real bins. e.g. "Consider a spherical horse ..." (as the joke goes).<a href="http://everything2.com/index.pl?node_id=1674920" target="_blank">http://everything2.com/index.pl?node_id=1674920</a><a href="http://my.opera.com/feldgendler/blog/2005/06/21/let-us-consider-a-spherical-horse-in-a-vacuum" target="_blank">http://my.opera.com/feldgendler/blog/2005/06/21/let-us-consider-a-spherical-horse-in-a-vacuum</a>And yes, I was an experiemental chemist/physcist a while back so I love testing theoretical models.So I have a method for making accurate measurements. Now if the weather would improve. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" /></blockquote>

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