[ptx] Extended focus macro work (was "waveblend 0.1.0")

[Rik Littlefield]

Yes, I have gotten good results by adjusting back focus with bellows.  
It is the only method I know to maintain nodal point, at least with the 
lenses that I have.  But the approach has some complications.  Because 
bellows have certain minimum/maximum lengths, they impose strict limits 
on the range of subject focus.  Because the effective f/stop changes a 
lot with bellows length, you cannot just lock the exposure and get 
uniform brightness.  And because magnification changes a lot too, you 
have to rescale and register the images anyway, same as if you moved the 
whole lens/camera assembly. 

One important factor in choosing which approach to use is whether the 
subject has parts that hide other parts, so that what's visible would 
change if you moved the lens.  If it does, then locking the lens in 
place and adjusting back focus solves a lot of problems.  If it doesn't, 
then moving the lens/camera assembly may be equally or more effective as 
well as much simpler.

--Rik

Glenn Barry wrote:

>For close up stuff in the big magnification ranges if you had belllows, you
>could maintain the nodal point by using the rear camera movement to focus, I
>think...
>----- Original Message -----
>From: "Rik Littlefield" <rj.littlefield at computer.org>
>To: "Sebastian Nowozin" <nowozin at cs.tu-berlin.de>
>Cc: <ptx at email-lists.org>
>Sent: Monday, July 12, 2004 5:08 PM
>Subject: Re: [ptx] Release: waveblend 0.1.0 - focus enhancing image fusion
>tool
>
>
>  
>
>>Sebastian,
>>
>>Great job!
>>
>>I ran the same images through the visibility mask algorithm available at
>>http://www.janrik.net/ptools/ExtendedFocusPano12/ .  Results are posted
>>there -- pretty much the same as yours.
>>
>>I am not sure how to compare the two approaches.  Both the beaded deer
>>and the microscope images seem to be fairly simple cases.  I suppose
>>it's time to haul out the macro lenses and try to work a harder
>>problem.  (I play with insects in the 1-10X magnification range.  It's
>>difficult maintaining fixed nodal point in that range, which makes
>>perfect alignment problematic.  I always end up having to edit the
>>masks.  But perhaps there are other ways.)
>>
>>--Rik
>>
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