An interesting question today:

Hi,

Great write up on the Leica M8 (8 Reasons why you should buy a Leica M8).  You mention that the Leica M8 is also called the “poor mans Monochrome.”  Is it better to take photos with or without an IR cut filter when shooting with monochrome in mind?  Or does it matter?
 
Thank you!
 
Ed 
I don’t use my M8 with a filter. I know when the IR-thing is going to mess up my shots and for these instances I have a couple of other Leica’s. That sounds snobby, I know, but to be honest, I’m glad I don’t have to shoot commercial shoots with the M8 anymore, even though I COULD if I needed to.
For B&W, you don’t get the annoying purple colors, but there are other things to consider as well. In this interesting LFI thread, my fellow country man Jaap sums it pretty neatly:
“Well, strangely enough it even depends on the lens, as the amount of misfocus with IR light varies with the lens. The basic premisse is that the M8 will record an IR image that is basically about 4-5 stops underexposed compared with the visible light image, but in a different focal plane. It will lighten up foliage and some shadows to a certain extent, reason a number of B&W shooters prefer it.If the lens has an IR hotspot, one will even add vignetting.

However, being out of focus, there will be a slight deterioration of contrast edges, thus of sharpness. Certainly not enough to really spoil a photograph, but still I can see a more crisp image when I use an IR filter.

Add to that that shadow density can be manipulated in Photoshop, I feel there is a case to be made for using IR filters on the M8 even for Black and White..”

So if you need the best possible IQ (and you already have the filters), best use them.