[Leica] Lens reflections from IR cut filter - verified and modified.

[cummer at netvigator.com (Howard Cummer)]

Hello Luggers,
Cementing my reputation as a gear head I have been following Len?s  
lead and using Howard Ritter?s procedures for checking out  
reflections possibly caused
by IR cut filters. I shot a series of pictures ? placing a flashlight  
in the upper right
corner and looking for reflections in the lower left. I did this with  
both my 50 Summilux Asph and my 35 Summilux Asph. Findings: with IR  
filters on at f1.4
both lenses exhibited the reflection from the upper right flash light  
in the lower left of the photo.
With filter off there was no reflection with the 50 Lux Asph and a  
slight ghosting with the 35 Lux Asph ? so at least for the 50mm lens  
the filter is the sole contributing factor.
Here are some snaps at ISO 640, camera tripod mounted, to support my  
conclusions:

1. The 35 Lux with IR cut filter on at f1.4 showing the ghosting on  
the books on the lower left shelf.

http://gallery.leica-users.org/v/Howard+Cummer/UV+IR+Code+Pix/ 
Lux35IRonw.jpg.html

http://tinyurl.com/3b9vrg

2. The 35 Lux at f1.4 with no filter ? there is a slight blue smudge  
of ghosting still visible just above the books in the lower left  
shelf so lens design also contributes to the reflection

http://gallery.leica-users.org/v/Howard+Cummer/UV+IR+Code+Pix/ 
Lux35noIRcutw.jpg.html

http://tinyurl.com/2tyl57

3. Here is the 50 Lux Asph at f1.4 with IR cut filter on and
the refection is present

http://gallery.leica-users.org/v/Howard+Cummer/UV+IR+Code+Pix/ 
Lux50IRcutfilterw.jpg.html

http://tinyurl.com/2tg8ax

4. The 50 lux at f1.4 with no filter and no reflection

http://gallery.leica-users.org/v/Howard+Cummer/UV+IR+Code+Pix/ 
Lux50nofilterw.jpg.html

http://tinyurl.com/2jan65

I closed down the 50 Lux with the filter on to see when the  
reflection would disappear. At f4.0 there was still a slight  
reflection but by f5.6 it was gone.
The 35 Lux asph exhibited similar characteristics so I didn?t bother  
to post thiosde pictures.


5. The 50 lux at f4.0 with filter and a slight reflection

http://gallery.leica-users.org/v/Howard+Cummer/UV+IR+Code+Pix/ 
Lux50withIRatf4_0w.jpg.html

http://tinyurl.com/3x88ht

6. The 50 lux at f5.6 with filter and no reflection

http://gallery.leica-users.org/v/Howard+Cummer/UV+IR+Code+Pix/ 
Lux50wIRfilteratf5_6w.jpg.html

http://tinyurl.com/37ne4e

What does this prove? What we all knew for a long time ? that filters  
tend to cause unwanted reflections ? and should be avoided for that  
reason, if possible.
But, because of the magenta issue with the M8 that is not possible so  
we will have to live with it and in 99.9% of my pictures it isn?t an  
issue.

Cheers
Howard (in Hot Hong Kong still waiting for his new M8)

On 1 Oct 2007, at 3:36 AM, lug-request@leica-users.org wrote:

> Message: 1
> Date: Sun, 30 Sep 2007 12:28:09 -0400
> From: Leonard Taupier <len-1@comcast.net>
> Subject: Re: [Leica] Lens reflections from IR cut filter - Verified
> To: Leica Users Group <lug@leica-users.org>
> Message-ID: <18E1602D-E3AD-476A-8940-B6F95C3C84B9@comcast.net>
> Content-Type: text/plain;     charset=US-ASCII;       delsp=yes;      
> format=flowed
>
>
> I was able to duplicate Howard's lens reflection problem using Howard
> Ritter's procedure.
>
> <http://gallery.leica-users.org/v/LeonardT/M8+Filter/
> Reflection.jpg.html>
>
> or
>
> http://tinyurl.com/3blq22
>
> I was not able to duplicate the problem using a 50mm Summicron with
> filter but was able to duplicate it using a Noctilux at f1.0 with a
> UV/IR filter. I could not duplicate the problem with the filter
> removed. The smaller light is very bright. Also note the coma with
> the Noctilux. Unfortunately my Summilux is still with Leica getting 6-
> bit coded so I couldn't try it.
>
> Len