Archived posting to the Leica Users Group, 2007/09/30

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Subject: [Leica] Lens reflections from IR cut filter - Mui Wo Ferry Pier
From: hlritter at bex.net (Howard Ritter)
Date: Sun Sep 30 07:39:59 2007
References: <200709300013.l8U0CFOD051278@server1.waverley.reid.org> <A36DDC81-0FF4-47EB-9084-503C0F75B2B0@netvigator.com>

I agree with Leonard that this is a peculiar reflection that probably  
doesn't come from the filter. What is pertinent is that the  
reflection is turned 180 degrees--that is, mirror-imaged in both the  
vertical and the horizontal planes. This is the mark of reflection  
from a concave mirror or transmission through a negative lens. A  
reflection from a planar surface (the filter) wouldn't do this. Is it  
possible that this kind of reflection is happening all the time, but  
is not noticed unless the reflection of a bright feature in a frame  
unless the reflection happens to be superimposed on a dark and fairly  
featureless portion of the image?

I suggest doing this, which I'm going to try with my own M8 and  
filter as soon as I get back in town: in a darkened room, put a  
flashlight on a shelf, pointed out into the room. With the camera set  
on manual to overexpose the flashlight lens but not show the  
surroundings, take an exposure with the flashlight centered in the  
frame. See if a reflection shows up in the dark remainder of the  
frame. Then offset the flashlight image from the center, take a  
photo, and see whether you get a reflection in the diametrically  
opposite location in the frame, just as happened with the photo in  
question. Try it with and without the filter and see whether you see  
a reflection. Report back and so will I.

--howard


On Sep 29, 2007, at 9:55 PM, Howard Cummer wrote:

> Hello Luggers,
> Well my replacement M8 is in Hong Kong with Fedex, according to the  
> tracking, but didn't get delivered on Saturday. Monday is a holiday  
> (China's National Day) so I expect the camera will arrive on my  
> doorstep on Tuesday. In the meantime, Schmidt has given me a loaner  
> M8 and so I have been out on the streets again. Here is a picture  
> of the Mui Wo ferry Pier, where the ferries come in from Hong Kong  
> Island, taken with my newly coded 50mm Summilux Asph, wearing an IR  
> cut filter. I know that conventional wisdom is that lenses longer  
> than 35mm don't need to be coded, nor are IR cut filters really  
> required, but I have decided to code and filter equip all my lenses  
> - so that I don't have to think about switching lens detection on  
> and off for Coding and IR filters. Besides I like to know the focal  
> length in the EXIF data. One problem, however, with using IR Cut  
> filters unnecessarily is unwanted reflections. Please see the  
> attached photo of the Mui Wo ferry pier.
>
> http://gallery.leica-users.org/v/Howard+Cummer/Hong+Kong+Pix/ 
> MuiWoFerryTerminalBWw.jpg.html
>
> http://tinyurl.com/29vhzk
>
> Cheers
> Howard
> (Hot but Happy in Honkers and waiting for Santa to come on Tuesday)
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information


In reply to: Message from cummer at netvigator.com (Howard Cummer) ([Leica] Lens reflections from IR cut filter - Mui Wo Ferry Pier)