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Message: <blockquote data-quote="elkcub" data-source="post: 1703784" data-attributes="member: 14473">Oleaf,  Although Manni can clarify what he really meant, my interpretation of:is that that the combination of a flat field and no distortion necessarily results in a rolling ball effect.  To repeat, I'm not aware that field curvature is involved with the globe illusion at all, but I'm willing to learn.  However, you made a much stronger statement:I don't know of any studies or anecdotal evidence showing such a causal relationship between field curvature and the globe effect.  As an illustration, my 8x32 SEs, which have a flat field, produce no more globe effect that my 8x30 SLCs, which have significant field curvature.  They both have about the same amount of distortion, however.  Kevin,I believe Holger's animations are meant to simulate the effect of a person moving his/her head in a stationary environment (as is usually the case barring earthquakes, and so forth. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />)  Image motion on the retina is the same, so the rolling ball illusion is expected to be the same. That part is fine.  However, real world tasks involving head motion are typically initiated by the observer, not the experimenter, and motivated by target search or tracking objectives.  So it's unclear how much the globe effect (illusion) would be perceived under these real world conditions.  The paradigm simply doesn't address that issue, and it is entirely possible that birders might not be hampered by it.  Swarovski probably made such an assessment and took that design gamble.  IMO, it's much better gamble than Leica took several years ago by way of exaggerating distortion in the BA and BN series.  There you may not have seen much rolling ball, but there sure was a hellova lot of distortion.  :eek!:  Ed</blockquote>

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