24mm 1.4L II on 7D (depth of field)

[tim_klimowicz]

<p>I *love* the look of the 35mm 1.4L on the full frame bodies, but I own the 7D and have no plans to go full-frame any time soon.</p>

<p>Part of the look I like of the 35mm 1.4 (in addition to the sharpness and contrast, as well as the happy-medium not-too-wide-not-too-tight FOV) is, of course, the tight depth of field wide open, and how a fairly wide-ish lens can still achieve pretty amazing separation from a distant background even when the subject is a pretty good distance away.</p>

<p>So, my question is: Could I expect a relatively similar narrow depth of field with the 24mm 1.4 on the 7D's cropped sensor? The focal length winds up being about 38mm, which is close enough to 35mm for me, but are the depth of field characteristics altered in some way, or would the 35mm 1.4 on a 5D look very close to the the 24mm 1.4 on a 7D?</p>

<p>Relatively minor issue, I know....but it's not every day I even think about spending $1700 on a lens. :)</p>

<p>Thanks!</p>

[anov]

<p>Plug your numbers here:<br /><a href="http://www.dofmaster.com/dofjs.html">http://www.dofmaster.com/dofjs.html</a></p>

<p>in short no, the 35mm @ f/1.4 on FF still has narrower DOF, but might be close enough for your use. The 24 will be closer to 35mm FF @ f/2.</p>

[peter_langfelder]

<p>Roughly speaking, 24/1.4 on the 7D will behave like a 38mm f/2.2 lens on full frame. In this light you may want to think twice whether you want to invest into a 24/1.4, or get a 5D with 35mm f/2 for about the same money.</p>

[bobatkins]

<P>And the explanation is here - <A href="http://www.bobatkins.com/photography/technical/digitaldof.html" mce_href="http://www.bobatkins.com/photography/technical/digitaldof.html">http://www.bobatkins.com/photography/technical/digitaldof.html</A></P>

<P> </P>

<P>Basically you get about 1.6x more DOF. However DOF and distant background blur are not the same thing and they are often confused. See <A href="http://www.bobatkins.com/photography/technical/bokeh.html" mce_href="http://www.bobatkins.com/photography/technical/bokeh.html">http://www.bobatkins.com/photography/technical/bokeh.html</A></P>

<P> </P>

<P>Your infinity blur will be quite a bit less. The only calculator I know of for this is mine! See <A href="http://www.bobatkins.com/photography/technical/bokeh_background_blur.html" mce_href="http://www.bobatkins.com/photography/technical/bokeh_background_blur.html">http://www.bobatkins.com/photography/technical/bokeh_background_blur.html</A></P>

<P> </P>

<P>Sorry to be "plugging" my website, but it's just about the only place I know that deals with this stuff. Basically, the larger the format the more background blur you're going to get and the smaller the DOF, given a set aperture and angle of view.</P>

<P> </P>

<P>If you want to isolate a subject get a full frame DSLR and use the 35/1.4 (or better still the 85/1.2)</P>

[zml]

<p>If you are unsure rent one before purchase: many places will apply the rental fee toward the purchase price should you decide to buy. See for yourself how the lens you want performs on the body you use.</p>

[tim_klimowicz]

<p>Wow, excellent responses so fast. Thanks, everyone. I was afraid of that, but it's good to know for sure. I know the cropped cameras come with some limitations (though they also have their strengths), and it's a bummer to know that this is another one that just can't be made up for in some other way.</p>

<p>Thanks!</p>

[hal_b]

<p>It's a shame, but there's no way around physics on this one. Large sensors (large format film) have the ability to focus better at long distances with better separation. Using a crop sensor, you could get the same "effect" if you also scaled down the entire world by 1.6x. i.e. instead of shooting a 6' subject from 10' away, shoot a 3.8' subject from 6.3' away and you'll get the same DOF effect with a 22mm lens.</p>

[jeff_conrad]

<p>As several others have mentioned, you'd get about the same DoF as you would with a 35 mm f/2.2 on full-frame 35 mm.</p>

<p>The background blur is trickier than it may seem. Although the background blur spot is indeed larger (it's roughly proportional to focal length), the magnification of the background object is increased by the same factor as the blur spot, so it may not appear more “blurred.” This is demonstrated pretty well by the two photos in Bob's article. The image on the left has greater blur, but the background is arguably as recognizable as in the image on the right. The longer lens still has an advantage, though: the angle of view is narrower, so it's easier to crop out distractions such as the white blob in the photo on the right.</p>

<p>The situation changes a bit when format is changed. Assuming everything is the same except for format (i.e., the focal length is scaled to maintain the same angle of view), the blur spot is smaller with the smaller format. But the smaller format needs greater enlargement, so the background blur in the final image is the same for both formats.</p>

<p>Though given scant coverage in most treatments of DoF, this issue actually has been discussed. Merklinger touches on it in <em>The INs and OUTs of Focus,</em> showing that separately controlling DoF and recognizability of background objects isn't possible without changing the subject-to-background distance. The topic is also covered in the Wikpedia article on <a href="http://en.wikipedia.org/wiki/Depth_of_field">Depth of Field</a> , and illustrated in Paul van Walree's page on <a href="http://toothwalker.org/optics/dof.html">Depth of Field</a> . Nonetheless, DoF and background blur remain among the most misunderstood areas of photography, especially when comparing different formats.</p>

<p>So, to repeat, you'd get 1.6x the DoF, but about the same distant background blur. If the blur is the main objective, this should be fine.</p>

[tim_klimowicz]

<p>Jeff, you've got that right about the lack of understanding with DoF and background blur. I'd like to think I'm pretty technically sound with a lot of areas of photography and light (though that can't be said about the application of these things -- much to learn after so many years!), mostly because I try to really gain an understanding beyond the abstract; that is, I almost *need* to know not only that something works because of X, but *why* it works because of X. That said, I've still never been able to wrap my head fully around DoF as it relates to different formats and multipliers. On the surface I get it, but without understanding the physics on even a basic level, I'm lost. :)</p>

<p>Anyway, I took Michael's advice and ran out to Adorama after work tonight to rent the 24mm 1.4L II for a week. I'm almost hoping to be underwhelmed so I don't binge on a very much not-needed purchase I really shouldn't be making in the first place....</p>

<p>Thanks again everyone. I'm going to re-read this thread and Bob's links a few times to maybe finally understand it fully.</p>

[jeff_conrad]

<p>Tim, you're not the only one confused. Background blur is definitely trickier than it seems ... I misspoke on getting the same background blur with both the APS-C/24 mm lens and the FF/35 mm lens. When the subject <em>distance</em> (rather than the subject <em>magnification</em> ) remains constant, the final-image background blur is proportional to format size. So with the 24 mm lens on APS-C, you'd get 0.625 the background blur that you'd get for the “same picture” (i.e., same angle of view) with the 35 mm lens on full-frame 35 mm.</p>

[markonestudios]

Wow, Bob, great insight. Thanks :)

[mendel_leisk]

<blockquote>

<p>I *love* the look of the 35mm 1.4L on the full frame bodies, but I own the 7D and have no plans to go full-frame any time soon.</p>

</blockquote>

<p>I just threw in the towel and went to full frame, problem solved.</p>