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<blockquote data-quote="WayneF" data-source="post: 533787" data-attributes="member: 12496">I'm curious how you are able to accomplish focusing while at f/22 ?&nbsp; With which lens and procedure?&nbsp; I assume you are aware that SLR lens are&nbsp; always held at wide open aperture&nbsp; for benefit of the brighter viewfinder and focus when wide open, so we can see it and AF can work.&nbsp; Lenses only stop down to the selected setting when the shutter button activates the actual mirror rise and shutter activation.&nbsp; It is not focusing then, the focus system is in the viewfinder (and the mirror is up).This wide open maximum aperture is the issue.&nbsp;&nbsp; A few of the Nikon cameras (including the D800 family) can&nbsp; auto focus at f/8, meaning maximum aperture.&nbsp; Or rather, 11 of the 51 sensors can claim f/8. The other DSLR models say they can focus at f/5.6.&nbsp; &nbsp; This means the maximum wide open aperture, which is used for viewfinder and focusing.The 1.4x TC increases fstop number by 1 stop.&nbsp; The 1.7x by 1.5x stop, and the 2x by 2 stops.&nbsp; The 200-500 is a f/5.6 lens, and so adding 1.5 or 2 stops exceeds f/8 in the wide open position. This is the meaning of Nikons warning.&nbsp;&nbsp; I don't think their &quot;AF not possible&quot; means&nbsp; AF is absolutely 100% totally impossible past f/8, but they are saying don't call them when there is any issue.&nbsp; I think they consider that you have been warned.&nbsp; &nbsp; But f/5.6 with TC 1.7 is only half a stop past f/8, it probably might work sometimes, on a D810.I have a TC-17, but my lenses that accept it are f/2.8 lenses.&nbsp; I have a Tamron 150-600 f/5-6.3, but I'm not going to put the TC on it. Not sure it would even mount.</blockquote>

[QUOTE="WayneF, post: 533787, member: 12496"] I'm curious how you are able to accomplish focusing while at f/22 ? With which lens and procedure? I assume you are aware that SLR lens are always held at wide open aperture for benefit of the brighter viewfinder and focus when wide open, so we can see it and AF can work. Lenses only stop down to the selected setting when the shutter button activates the actual mirror rise and shutter activation. It is not focusing then, the focus system is in the viewfinder (and the mirror is up). This wide open maximum aperture is the issue. A few of the Nikon cameras (including the D800 family) can auto focus at f/8, meaning maximum aperture. Or rather, 11 of the 51 sensors can claim f/8. The other DSLR models say they can focus at f/5.6. This means the maximum wide open aperture, which is used for viewfinder and focusing. The 1.4x TC increases fstop number by 1 stop. The 1.7x by 1.5x stop, and the 2x by 2 stops. The 200-500 is a f/5.6 lens, and so adding 1.5 or 2 stops exceeds f/8 in the wide open position. This is the meaning of Nikons warning. I don't think their "AF not possible" means AF is absolutely 100% totally impossible past f/8, but they are saying don't call them when there is any issue. I think they consider that you have been warned. But f/5.6 with TC 1.7 is only half a stop past f/8, it probably might work sometimes, on a D810. I have a TC-17, but my lenses that accept it are f/2.8 lenses. I have a Tamron 150-600 f/5-6.3, but I'm not going to put the TC on it. Not sure it would even mount. [/QUOTE]

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