Fisheye focus

[Marvin]

<p>How much of an issue would a non-autofocusing fisheye lens (Rokinon) pose on a 50D or 7D?<br>

Is such a lens sharp even when you don't focus on a specific spot in the wide firld of view?</p>

[JosvanEekelen]

<p>Use hyperfocal focussing. If properly set everything will be in focus from (for instance) 40 cm to infinity at f/5.6. The lens probably has distance and DOF scales, use to learn these and you'll have no problems focussing.</p>

[Robin Smith]

<p>Personally, I would want to focus it: you could use Live View. I find that, just because it is a fisheye, it does not mean that focusing is not desirable. As its field of view is so great many objects at widely different distances are included in the field of view, so it remains important to make the main object as sharp as possible otherwise you tend to end up with a shot that is OK but your pic will appear less than optimum - I speak from experience. Just because something is within the depth of field does not mean it is sharp: the only objects that are truly sharp are the objects you actually focused on. Rather to my surprise, I found that the depth of field of a fisheye is not a panacea that allows you to not worry at all about focusing. Obviously if you are shooting at f16 you don't need to be as precise as when you are shooting at f2.8 or f4.</p>

[JDMvW]

<p>When the lens is supplied without a focusing mechanism, you can bet that the manufacturer of the lens does not think it needs one.</p>

<p>On some fisheyes, the zone "said to be in focus" extends from a few inches in front of the lens to infinity. Even where there is a focus mechanism, it's of doubtful utility in so wide angle a lens. Again, you can't focus it without a mechanism to do so.</p>

<p>BTW, autofocus often 'fails' with ultrawides, precisely because the user does not pay attention to which focus points are active in so wide a field of view.</p>

[Robin Smith]

<p>Agree about AF: the AF zones/points are more likely to cover objects at disparate distances with fisheyes so may have difficulty focusing on what you actually want.</p>

<p>I think in the case of the Rokinon the lack of AF is an economy measure not because they think focusing is unimportant, as they have functioning manual focusing rings. For the 14mm non-fisheye I understand the marked distances are pretty inaccurate.</p>

[james_elwing]

<p>The Rokinon lens does have manual focus, just doesn't autofocus. As long as the focus is roughly accurate by guess or measurement, it should be OK.<br>

I can't believe anyone could focus such a lens accurately using focus confirmation blips, or that this would be useful.</p>

[dcstep]

<p>I'm not sure how large the aperture is, but if it's f/2.8 or so, you'll only need to worry about things relatively close in the foreground. OTOH, at f/16, it'll focus close and out to infinity.</p>

[ali_baba2]

<p>Its not an issue, you wont be able to focus in the viewfinder but at f11 DoF is quite a bit to not have to worry and you wont fiddle much with it in most shots. Dont close it too much or sharpness will suffer, f5.6 to f11 seems to work best.<br>

If a store near you carries it go try one and you will see what i mean<br>

On a lens of that kind the markings dont need to be that accurate... might not be calibrated perfectly, you will find out with your first shots if you need to account for a bit of correction</p>

[ali_baba2]

<blockquote>

<p>Robin Smith wrote:<br>

I found that the depth of field of a fisheye is not a panacea that allows you to not worry at all about focusing</p>

</blockquote>

<p>I dont see the big DoF of a fisheye as the cure for bad focus, its the kind of things the lens is mostly used for... its so wide that, save for particular cases, its not exactly like focusing for a portrait. Rather than "not worry at all" id put it as "worry less" and how much less depends on what you're using it for... i guess thats why some think of it as set&forget and others dont</p>