[Leica] Re:Tale of Two Telyts Part Deaux - the Evil Twin (Hoppy's Observation)

[rpalmier at depaul.edu (bob palmieri)]

(Joe, you might wanna read this one backwards, if you know what I 
mean...)

On Jul 8, 2006, at 12:03 AM,Hoppy wrote:

> Bob, I looked again at this effect for my own education.
>
> I am more than ever convinced that this is a digital artifact we are 
> seeing.
>
>
>
> When you enlarge the image so that the individual pixels are very 
> blocky,
> (say 500%)you can see that the purple is a discrete and very even line 
> at
> the edge of the blown highlight.
>
> Yet it is not present at all on the (very fine) highlight on the 
> vertical
> edge of the leg. If this was an aberration in the analog info, I would 
> have
> thought that there would be some other traces of it in the other areas.
>
> Along the edge of the log where the highlight is completely white the 
> fringe
> is just about a perfect diagonal 4 pixel wide line. (1/1000th inch 
> line in
> the scanned slide?????)
>
>
>
> I'd really be interested to hear the definitive outcome of this
>
>
>
> Cheers,
>
> Hoppy
>
> Happy to be proven wrong, but love to learn
>
>
>
> Bob, pardon me if this is a silly question.
>
> Is this aberration definitely visible on the film?
>
> (I assume its transparency film)
>
> After your image is captured on film, obviously it must then be 
> scanned to
> produce your digital image for posting. I wondered if the aberration 
> was
> being introduced at that (weak link) point by the scanner?
>
>
>
> Cheers,
>
>  Hoppy
>
> (who'd like a focomat in his coolscan)
>
>
>
> -----Original Message-----
>
>
>
> ------------------------------
>
>
>
> Message: 20
>
> Date: Thu, 6 Jul 2006 10:41:31 -0500
>
> From: bob palmieri <rpalmier@depaul.edu>
>
> Subject: [Leica] Tale of Two Telyts Part Deax - The Evil Twin
>
> To: lug@leica-users.org, leicareflex@freelists.org
>
> Message-ID: <0c6a689957fb15b7e15c496265b09547@depaul.edu>
>
> Content-Type: text/plain; charset=US-ASCII; format=flowed
>
>
>
> Folks -
>
>
>
> As promised, here's an example of a disturbing symptom I encounter
> occasionally with the 400 Telyt.
>
>
>
> Here's a snap of a blue heron impersonating a stick:
>
>
>
> http://gallery.leica-users.org/album409/Camoflage_Heron_Crop
>
>
>
>
>
> And here's a 100% pixel crop showing heavy purple fringing around the 
> feet
> and along the top edge of the log (in areas of serious
>
> overexposure):
>
>
>
> http://gallery.leica-users.org/album409/Camoflage_Heron_PurpleCrop
>
>
>
>
>
> I've seen the same effect on Kodachrome, so I don't think it's one of 
> those
> artifacts of digital sensor architecture (despite all the talk you hear
> about purple fringing in digicams.)  My questions are as
>
> follows:
>
>
>
> 1. Is this just a classic case of chromatic aberration in a simple 
> achromat?
> (I hear tell that the Anomalous Dispersion glass (whatever that is) in 
> this
> design is supposed to control this kindof thing to a pretty acceptable
> level.)
>
>
>
> 2. If so, is it really possible that the results in the normally 
> exposed
> areas can look as good as they do (not that this snap is the best 
> example;
> things were getting pretty dim at the time and the shutter speed was
> probably quite low) with a level of CA this high?
>
>
>
> 3. Does someone who uses both this lens and the probably staggeringly
> CA-free 280 APO (Doug??) ever see this effect in their 400 shots and 
> not in
> those shot with the APO ?
>
>
>
> Inquiring minds want to know...
>
>
>
> Bob Palmieri
>

Hoppy -

This is indeed a very interesting observation in your part.  Although I 
can sorta visualize a way in which the digital representation of an 
analog phenomenon could take on this characteristic I also thing you 
may be onto something here.  Plus, I'm impressed with your persistence.

So, I'm gonna forward this thread to an imaging scientist friend and 
see what he has to say.

Bob Palmieri