Please help with infinity focus and hyperfocal focus...

[derrickdehaan]

<p>Can you fine folks please help me with my first Canon ultra-wide? I got the lens as lovely gift from my wife a couple days ago. In shear excitment this afternoon, I took it outdoors and set it up with my 5DII, used tripod and timer release. Using the hyperfoacl chart and f/8 and f/16. Came inside and downloaded nothing but mush. So I went back outdoors, same setup and set the lens to infinity focus. Bingo, the foreground and everything beyond is much sharper. Now why would the hyperfocal chart not for me. The chart shows that at f/8 and 16mm focal length, the hyperfocal distance is 3 1/2 ft with a circle of confusion of 0.030 for 5DII. Why was nothing in the image sharp?</p>

[bobatkins]

<p>Focusing at the hyperfocal distance makes the focus at infinity <em>JUST</em> acceptable. Focus one inch closer than hyperfocal and, by definition, infinity falls outside the DOF and is therefore unacceptably blurred.</p>

<p>100% pixel peeping at infinity with the lens set to the HFD will show softening of the image.</p>

<p>I suspect you may have made some other error (I can't guess what), so I'd try it again. The HFD for a 16mm lens at f8 is indeed about 3.5 ft (1.07m).</p>

<p>If you're doing everything right, maybe you're just expecting too much. If so tighten up your allowable COF to 10 microns, which gives you an HFD of around 9.5ft.</p>

[derrickdehaan]

<p>Bob, thanks for the response. I have repeated it many times, and there is nothing in the image in focus at f/8 and 3.5 on the distance scale. And I wasn't pixel peeping. This was all viewed as soon as the image opened in DPP and/or Photoshop. Whatever the default is, regarless its far from100 percent viewing.</p>

[tommyinca]

<p>Try use auto focus to focus at a distant object. Take a look at the scale. Is it at infinity? If not, the alignment for your lens may be off. </p>

[derrickdehaan]

<p>It does focus to infinity with autofocus. I am 99% sure its user error, but I don't know for sure what I am doing wrong. Perhaps I am not guessing correctly where 3.5ft is on the distance scale? The scale has a mark at 3, then the next mark is at infinity.</p>

[lister]

<p>You mentioned that the CoC at 3.5 ft is 0.030mm? But the 5DmkII has a pixel pitch of 6.4um, which is equivalent to 0.0064mm. So the Coc you mentioned is more than 4 times the size of the pixel pitch. I don't see how the image can be sharp on screen.</p>

<p> </p>

[derrickdehaan]

<p>Perhaps that is the issue Kent. THat would change the hyperfocal distance at f/8 to 17.5ft roughly. Is they why everything looks better at infinity than 3.5 ft? I use just using the suggested "35mm" CoC off of the DOF calculator.</p>

[zml]

<p>Yeah, there's a lot of confusion about the appropriate size of the circle of confusion... Try .01 mm for a full frame sensor (pixel pitch notwithstanding) and your calculations will be a bit closer to real life. Also, try this simple setting: f/8 and 16 feet with a 20 or shorter mm lens on a FF body (we don't need no stinkin' calculators...) And of course set your lens to MF :-)<br />Now, as usual there is always an outside chance that the scale index on your lens has absolutely nothing to do with reality...</p>

[david_klaffenbach]

<p>Merklinger dealt with this topic very nicely. I suggest reading "The INs and OUTs of FOCUS".</p>

<p><a href="http://www.trenholm.org/hmmerk/download.html">http://www.trenholm.org/hmmerk/download.html</a></p>

[derrickdehaan]

<p>This may sound like a stupid question, but if one of the distance marks is 3ft, and the next one is infinity.........how do I know where to set it for 16ft? Find something 16ft into the image and focus there I suppose?</p>

[alec_myers]

<blockquote>

<p>o the Coc you mentioned is more than 4 times the size of the pixel pitch. I don't see how the image can be sharp on screen.</p>

</blockquote>

<p>In that case it will be sharp at up to 4:1. Which is still a goodly size.</p>

[david_klaffenbach]

<p>Derrick,</p>

<p>Thin lens equation: 1/o + 1/i = 1/f where o is object distance, i is image distance and f is focal length.</p>

<p>So a 50mm lens at o = infinity has i = 50mm, and at o = 1m (about 3 ft) has i = 52.6mm, in other words the lens is extended by 2.6mm from infinity focus in order to focus at 3 ft.</p>

<p>So to focus at 2m, the extension would be 1.3mm or half the extension. Assuming the focus mechanism is linear, the 6 ft position would be halfway between 3 ft and infinity.</p>

<p>16 ft (4.9m) would require .5mm of extension, so it would about 4/5 of the way from 3 ft to infinity.</p>

<p>I don't know what focal length lens (probably pretty short, as I have a 19mm with markings for 2.5ft, 5ft and infinity) you're asking about, and lenses that do rear or internal focusing (and change focal length with focus distance) mess up this simple model, but similar math will at least get you in the ball park.</p>

[bobatkins]

<p>You're doing something wrong. I don't know what though. When you set the lens to "just over 3", are things which are "just over 3" ft from the camera in focus?</p>

<p>I suppose the "3" could be 3 meters, but that would make infinity sharper than if you were focused at 3ft, not softer.</p>

<p>Indeed, to focus at 16 ft, find something 16ft away and focus on it!</p>

<p>Your CoC value is just fine. That's a red herring. Something else is amiss.</p>

[derrickdehaan]

<p>Bob, I am sure I am doing something wrong, I am not blaming Canon at all. Knock on wood, I've never gotten a single bad piece of kit yet. Perhaps I was expecting too much. I thought that nailing a super deep depth of field with a 16mm lens would be a piece of cake, but some of the answers so far have my head spinning. But to answer your question, no. Things after 3 ft are not in focus. In fact, nothing in the image was in focus.</p>

<p>David, the lens is the Canon 16-35 mkII, sorry I left that out in the original post.</p>

<p>I know a resized sample means very little, but this was the best attempt yesterday. f/16, and I set the distance on the scale to (what I figured) 1.75ft. Sorry about the tripod leg, not used to this much angle of view. It appears that the forground is fairly sharp, but infinity seems very fuzzy, just like alluded to in the previously posted link. Maybe its just wishful thinking on my part to expect to ever get very sharp images from my feet to infinity.</p>

<p>http://i156.photobucket.com/albums/t3/catfishmarbles/websized.jpg%5Bimg%5D" alt="" /></p>

[derrickdehaan]

<p>Sorry, guess I am having trouble uploading photos too....</p><div></div>

[robin_sibson1]

<p>There's a very simple explanation, which is that the distance scale is wrong. Not only are few still-camera zoom lenses truly parfocal, but also there's no compensation link between the zoom and focus mechanisms, so at anything other than the focal length for which the distance scale is calibrated, the distance readings are garbage. For example, on the 24~105 if you use AF to focus on infinity at the 105mm setting, the focus scale is spot on the infinity mark. If you do the same at 24mm, the focus scale reads 4m. So when you think you are setting the focus by scale to 3½ft at the 16mm setting on your new lens, you are probably setting it to a quite different distance. Check what reading you get on the focusing scale if you AF (or indeed focus accurately by any other method) on a point 3½ft away, and then, keeping that focus setting, take a shot including foreground and distance and examine what is in focus.</p>

[derrickdehaan]

<p>I will give that a try Robin. THanks.</p>

[sebastianmoran]

<p>@David, thanks for the reference</p>

 

<blockquote>

<p>I suggest reading "The INs and OUTs of FOCUS"</p>

 

</blockquote>

<p>That's a VERY interesting article. Just to skip to the punch line, he suggests focusing further than would be indicated by hyperfocal and DOF tables. He suggests, if you want the background sharp, then focusing at infinity is often better than many alternatives. Rigorous, with examples, math, and diagrams. He convinced me.</p>

[derrickdehaan]

<p>From my own tests in the last few days of ownership, I have had best luck at infinity when shooting with the 16-35 @ 16mm and f/16.</p>

[jgredline]

<p>Hi folks. I know this is an old thread and perhaps it still has some followers. I see a ton od wisdom here and so I will ask my question. My question is this. The infinity simple that looks like a sideways 8 seems to leave quite a bit of room for error. Is infinity on the leading edge, middle or tail end. Personally, I have found that my lenses seem to perfom better at the leading edge instead of the middle. I should note that I am a Nikon and Pentax user and yes I know that this is a canon forum. LOL..Still great answers here.<br>

Thanks javier</p>

[david_klaffenbach]

<p>Use the middle of the <strong>∞</strong> mark to focus on infinity.</p>

<p>If you want to check it, use a tripod, magnified liveview if you have it and focus manually on stars.</p>