IR and vignetting clarification needed

[nickmeertens]

All,

I'm new to the M8 and need some clarification. I understand I need an IR filter the prevent issues with black clothing turning purple in color photography. Clear so far.

Then I need coded lenses to correct an issue with magenta casting in the corners. Here is my first need for clarification. Is this magenta casting the result of the IR-cut filter or something that always happens, with or without the IR filter?

When the firmware fixes the magenta cast after reading the coded lens, is that done on jpeg files only or the RAW files as well?

Thank you for your help!

Nick

 

[jaapv]

The lens recognition is only needed for lenses of 35 and shorter. The magenta cast is fixed by the filter, the resulting cyan drift is fixed by the firmware and lens recognition.

 

[Ben Z]

I understand I need an IR filter the prevent issues with black clothing turning purple in color photography. Clear so far.

Many of us long-time M8 users also recognize that there are other situations in which IR sensitivity can negatively alter the color of certain objects, for example, lush green foliage that reflects a lot of IR can come out looking anywhere from very pale green to yellowish to even pink. Basically, anything that reflects IR will come out color-shifted, more or less, depending on what color it is really, and how strongly it reflects IR. Even when shooting or planning to convert to b/w, the IR issue can alter the gray tone of certain subjects just like a filter does in traditional b/w. That is why many (I think probably, most) of us M8 users consider the IR filter mandatory, and keep one on every lens all the time.

 

[nickmeertens]

The lens recognition is only needed for lenses of 35 and shorter. The magenta cast is fixed by the filter, the resulting cyan drift is fixed by the firmware and lens recognition.

Ok, thank you Jaap!
Cyan drift is caused by the filter, that is good to know. And the correction the firmware applies, is that done on raw files as well as jpeg's in camera?

Thanks again, Nick

 

[jaapv]

The correction is done before the camera starts writing the files, so it applies to RAW and JPG equally. The effect is caused by the fact that the IR filter is an interference (dichroitic) filter, which is sensitive to the angle of incidence of the IR light. Basically the same thing that makes an IR filter on the sensor impossible. The camera also makes corrections for the optical vignetting of WA lenses. On lenses of 35 mm and longer the effects are too small to be of practical significance, so coding is not needed in that case.
Another consideration is that IR light focusses in a different plane than visible light, so the sharp image is overlaid by an out of focus IR image of about four stops less, causing loss of microcontrast. Another reason to use filters at all times.

 

[nickmeertens]

Thank you Jaap and Ben, that clarifies it for me.

 

[cam]

i just got my first IR filter and can already tell what a HUGE difference it makes -- not just in the colours, but also in the clarity of the glass. it removes a sort of fog i was seeing in all sorts of shots, if that makes any sense....

a question to those in the know:
my lens is an older one (35mm Lux pre-asph) that can not be coded. in the menu, the only way to choose IR filter is to use Lens Detection. do i need to turn that on even though it can't be done? or do i just use the filter with the Lens Detection off?

thank you in advance.

 

[POINT OF VIEW]

IR benefits

IR benefits

Some of us like the absence of a IR filter in the camera. The M8 is a perfect camera to shoot inferred photos. Add a filter to any lens and your shooting in the world of inferred light. Bill

 

[sandymc]

my lens is an older one (35mm Lux pre-asph) that can not be coded. in the menu, the only way to choose IR filter is to use Lens Detection. do i need to turn that on even though it can't be done? or do i just use the filter with the Lens Detection off?

If the lens is uncoded, best practice is to leave lens detection off. Although it's unlikely to happen is practice, with lens detection on, there is the possibility that the sensor may pick up marks/screws/whatever on the lens mount, and give you corrections that don't apply to your lens at all.

Sandy

 

[cam]

If the lens is uncoded, best practice is to leave lens detection off. Although it's unlikely to happen is practice, with lens detection on, there is the possibility that the sensor may pick up marks/screws/whatever on the lens mount, and give you corrections that don't apply to your lens at all.

thank you for the warning, Sandy!

and i know if i have problems with vignetting, i can always use the wonderful CornerFix.