sweet "aperture"

[duncan_twentytwo]

<p>Are there any charts covering Canon lens that give information about the best f stop that delivers the best image with the fewest aberrations ?<br>

I am specifically interested in this information regarding the following 2 lens,</p>

<p>Canon efs 17-55mm 2.8 IS USM<br>

Canon efs 55-250mm 4-5.6 IS</p>

<p>Thanks</p>

[tallplumphotography]

<p>Check: http://www.photozone.de<br>

http://www.slrgear.com/reviews/index.php</p>

 

[g dan mitchell]

<p>There is no "best" aperture since there are a number of factors that change in different ways as you adjust it. There may be a "best" aperture for a particular photo, but that depends on the relative importance of things like center sharpness, corner sharpness, DOF and so forth.</p>

<p>Example: A number of lenses might produce their highest level of resolution at some aperture like - for example, f/5. 6. However, this is measured in the center of the frame. On the other hand, corner sharpness will generally improve a bit as you stop down, so best corner sharpness might be at a different aperture, maybe f/8 or f/11 depending on the lens and the camera. So, which is "sharpest?" - the aperture with the highest resolution in the center of the frame but softer corners or the image with lower center resolution and slightly better across the frame performance?</p>

<p>A good practice is to get to know your own lenses very well and to understand their individual personalities. You can eventually get to this point by making many, many photographs and paying attention to such details. You can sometimes jump start this longer process by making some controlled test photos early on.</p>

<p>Dan</p>

[steve_crist]

<p>I don't know about a chart but a long time rule I've used is 2 or 3 stops closed down from full open seems to work well. If you read enough lens reviews they also seem to confirm this. Just a guideline however.</p>

[PuppyDigs]

<p>The best aperture is usually the one that works best for the intends of your photo. F5.6 may be the sharpest aperture of a certain zoom but isn't such a great choice if it results in a soft image due to camera shake. I mainly shoot at the softest aperture of many of my lenses--wide open--due to low light or a desire to defocus the background.</p>

[vrankin]

<p>I'm with Steve's response. Two to three stops down is generally the classic "sweet spot". The problem comes in though, with tiny sensors and matching optics that might introduce diffraction as soon as two stops down.</p>

[alan_green4]

for the 17-55 it's probably between 4 and 5.6. i think it actually gets worse between 5.6 and 8

[g dan mitchell]

<blockquote>

<p><em>"for the 17-55 it's probably between 4 and 5.6. i think it actually gets worse between 5.6 and 8"</em></p>

</blockquote>

<p>This depends on the focal length.</p>

[jkaufman]

Duncan,

 

This is easy enough to test. Make a series of identical shots at progressively smaller apertures with each lens, and then

compare the results side-by-side on your computer with a bit of pixel peeping. With each lens, you will likely find a sweet

spot between where both chromatic aberrations (from too wide an aperture) and diffraction (from too small an aperture) are minimized.

[roger_smith4]

<p>For the longer lens it hits its stride for vignetting/resolution and aberrations by around 5.6. I'd describe it as a generally soft lens but it's light, cheap and small and can be improved in post-processing. I'm happy with mine.</p>