Is a ir cut filter required on 90mm lenses?

[defektive]

I read somewhere that there was no benefit in using an ir cut filter on the summicron 90mm asph. Is this also the case with the E55 pre-asph summicron 90?
And is the E55 thread just the standard 55mm filter thread or do I need special filters?

Cheers,
Sam

 

[LCT]

You mean on M8 or M8.2 i guess. If so you will need IR-cut filters on every lens no matter their focal length can be.

 

[Shade]

Yea if you're on the m8 or m8.2 you'll need the ir cut filter no matter the focal length..

 

[jbr]

The sensor in the M8 has no (or not sufficient) IR-Filtering in front of it, so the IR-problem is independent of the focal length of the lens.

You may be referring to the 'magenta corners' which appear when using uncoded wide angle lenses; with coded lenses, this aberration is compensated by the firmware. With longer lenses there is no need for that so you can use them uncoded.

 

[Roger Hicks]

It's possible to overstate the problem. Foliage, and black synthetic fabrics, will look better with a filter. Many other subjects won't show any problems at all. This is not theory: I have used my pre-aspheric 90/2 on all the digital Ms since they came out.

And yes, it is a standard thread.

Cheers,

R.

 

[former member]

The M8 has a 0.5mm thick IR absorbing glass filter in front of the CCD. It gets rid of ~95%? When an object is dark in visible, but very bright in IR- the problem arises.

This case is all-black in visible.
This picture is with a modified Nikon Coolpix that is "full-spectrum", clear glass in place of the IR filter.

You get two artifacts introduced into the image: 1) the color shift, 2) a secondary image that is somewhat out of focus. Most lenses are not corrected for IR, and you get a blurred image as a result.

APO and Mirror lenses are corrected well enough for IR that this second problem does not show up. SO- on the 90 APO, color shift but no secondary image that blurs the picture.

Canon 85/2 on the Leica M8 without IR cut filter:

WITH IR Cut Filter.

Chloropyll in plants is a reflector of IR, so what is "green" in visible is white in IR.

 

[defektive]

Thanks for the info everyone.

Brian, it must be the APO function of the newer 90 that reduces the necessity of using a filter on it which means I will look at getting one for my version of the lens.