In Photoshop, there are several ways to convert an image into black & white. For example:
Image > Adjustments > Desaturate;Image > Adjustments > Hue/Saturation and set the Saturation to 0;Saturation blend mode.For 1. and 2. the outcome is identical, but 3. yields something different. Which method is the 'right' one to use, if there is any?
Actually, there are even more ways to make an image gray scale, e.g. via the channel mixer or several other methods, explained in this post:
How do I change a single layer to grayscale in Photoshop CS4?
Some of them offer different opportunities of fine tuning, yielding in very different outcomes. So there isn't really a 'right' method.
See those articles for some interesting results:
Digital photography school: seven ways to create sepia images
Spoongraphics: the best way to make your photos black and white
I had a teacher in college tell us the best way to convert a file to grayscale was to first convert the RGB document to LAB, then delete the A/B Channels. It provides a pretty could starting point, though I've yet to use it very often in my workflow 12 years after the fact…
I think there are a bunch of different ways to do this, and you may or may not see different results with any of them, but it might be good to try a couple and see which one gives you the bed result for the image you are working with.
The "black and white" adjustment layer offers the most fine tuning options.
Photoshop tips for the best way to convert to grayscale
If you're shooting in RAW, the h/s/l adjustments are the second best option.
Other ways of executing are fine; they just offer less control over the details.
if you really really convert an image to grayscale, the best way is: Edit > Convert profile > Output profile > Gray Gramma 2.2 If you click in Channel panel, you look one channel (Gray), but with the other method you still look 3(RGB/LAB) o 4(CMYK) channels.
Good Luck.
Image > Adjustments > Black & White