Please explain "focus peaking"

[Docderm]

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I would appreciate a clear explanation of when one can expect focus peaking to be present or absent. When I see it it really helps but other times it doesn't seem to be present at all. Sometimes I cannot see it in the magnified view but I can see it in the non-magnified view.

 

Are there any tricks to help make it more visible in circumstances in which it is barely visible or not visible at all?

 

Thanks

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[thighslapper]

It will only work well where there is a high contrast edge in items in, or close to the plane of focus ....... ie what would normally be accepted as the 'in focus' bit of the subsequent image on screen or in print. 

 

In many ways it mirrors what AF cameras do that use contrast detection to focus .... with manual lenses and peaking on you are seeing a rough representation of what the camera does when it uses AF ..

 

Just as with AF it varies in accuracy depending on whether items in the focal plane have enough contrasty edges to enable the camera firmware to detect the difference ........ which depends on  a host of factors:

 

 - The sensitivity that the software is set to ....... too high and everything flags up and too low and nothing does.....

- The nature of the subject ....... clearly a featureless blank grey wall is going to be useless ..... but a black chain-link fence will show up nicely

- The sharpness of the lens in showing up the necessary detail to reveal the differences in contrast ...... so crappy old lenses work poorly

- Similarly fast lenses wide open can struggle as they tend to be a bit softer 

- The size of the DOF region ...... on a 50/0.95 wide open it is wafer thin and only a few points may show and illuminate ..... whereas a 21/3.4 will illuminate throughout the DOF region 

- This is why a magnified view often helps ...... the points are often very small and infrequent and show up poorly on the normal full image view. 

- This in turn limits the usefulness for wide angle lenses ...... judging the optimal focus point is difficult when a large deep area is illuminated

- Poor illumination, high ISO's and narrow apertures all conspire against focus peaking as the camera is amplifying a crappy signal and detecting contrasty edges is again problematic

- As far as I am aware the firmware sensitivity doesn't compensate for lens type, ISO/aperture etc so sometimes it works fine, and sometimes not as per the above factors.... hence the 2 settings in the menu options (some cameras have more)

 

No doubt someone out their has a better grasp of this than me and my offer a different view .....

[steppenw0lf]

Focus peaking is there, if you turn it on.

If it results in what you expect is another question.

 

Consider 10x enlargement and focus peaking as two tools to consider and choose when they are useful.

For me most often focus peaking is less useful than the 10x enlargement.

For example with wideangles when often too much is in focus. Or in the opposite case when a lens has a very narrow depth of field. And in "bad weather" (haze, fog), bad light,  etc. etc.   Or with bad objects like clouds, steam, etc.

 

Short: 10x enlargement is the main tool - focus peaking is a nice add-on.

 

The only way to influence it is to change the color (red, green, blue, etc.)

 

Enlargement works always - focus peaking only if there is a useful contrasty edge. (useful meaning being in the right place)

[Docderm]

Thanks to everyone who has contributed their knowledge. 

 

Question: I think I sometimes find that maximum focus peaking on the subject is actually not quite in focus. If I use the 10X magnification, then I find I need to slightly nudge focus to get it spot on. 

 

Anyone else had this experience? Suggestions when to doubt focus peaking's accuracy and instead solely use 10x magnified view? 

 

Thanks

[steppenw0lf]

Yes, that is also my impression, so I usually prefer the enlargement. This is simply because often the edge to focus on is not where I need it.

(No need to doubt it (FP), simply use it less often).