Re: Horizon 202 - banding problems

[Alan & Shari Kafton <shmooze@xxxxxxxxx>]

Keith Davison wrote:
> 
> I have just obtained an Horizon 202 and am experiencing
> problems with horizontal banding.
> 
> Firstly, let me emphasize that these horizontal bands run
> parallel the to the long axis of the frame, they are NOT the vertical
> flare bands that appear across the short axis of the the frame
> when bright light sources such as the sun are in the field.
> 
> I mainly use Royal Gold 25 neg film, but had occasion to put two
> rolls of 200ASA colour neg through the Horizon, both on bright,
> sunny days.  Both of these films showed banding in smooth toned
> areas such as sky, on some frames.  More importantly, the pattern
> of the banding striations was identical on the two films, despite
> their being different brands and being processed at different labs.
> Banding seemed to be virtually absent on my RG25 negs.
> 
> I decided to investigate, and ran a series of tests with 200ASA
> colour neg film, I shot light overcast sky in the evening from a
> shadowed location, allowing the gradual dimming of nightfall to
> allow me to shoot a range of f-stops on the 1/250, 1/125 and 1/60
> speeds.  I then contact printed the negs on b&w paper and scored
> them for banding before checking the frame numbers against my
> taking-notes (to eliminate observer bias), the results were very
> consistent.
> 
> Banding is most severe with the 1/250 speed, but for any given
> speed it increases with f-number. The worst case in the test was
> 1/250 at f11, but banding is still faintly visible with 1/250 at f2.8.
> Banding is almost invisible below f8 at 1/60, (which explains
> why I had not noticed it with my RG25 negs!).
> I then examined the bands using colour scans of the worst frames.
> There is no chromatic shift associated with the banding, only a
> change in density.
> Converting the scans to greyscale, I used the Optimas image
> analysis package to extract an averaged luminance profile across
> the bands.
> The bands show both density increase and decrease relative to
> local unbanded areas, and are of non-regular widths and
> separations, but these are constant within the pattern from film to
> film.
> 
> Examining the taking slit at the back of the drum, I notice that the
> non-adjustable side of the slit seems to effectively be the edge of
> the outer drum, in my case, anodised brown.  The edge of this drum
> is very poorly machined, being quite rough.  My guess is that the
> striations are caused by this rough edge, this would explain why the
> banding is worse at 1/250.  With a narrower slit, the variation in
> width caused by the "hills and valleys" of the rough edge will be
> proportionately greater, and hence cause more pronounced
> banding.  Also as the lens is stopped down, the image forming light
> cones become narrower and will project a sharper impression of
> the edge back to the film, also intensifying the banding.
> 
> Has anyone else experienced this problem?  Bear in mind it will
> only be really obtrusive at f8 and above with 1/250 or 1/125, and
> that the banding (although still present), is masked to the human
> eye by image content, being very apparent only on large smooth
> toned areas, such as sky.
> 
> I will be returning my 202, and will test the replacement when I
> receive it, but I am worried that this may be a common problem.
> Given that the only control over close focus with the 202 is
> depth of field, I do not wish to have this further restricted
> when hand holding with fast film.
> 
> Does anyone know if it is feasible to strip the drum out of the
> camera?  If this were possible, the rough edge could then be ground
> perfectly flat to eliminate this problem, I would rather live with
> the resulting slight overall exposure increase, than with the f-stop
> limitations imposed by the banding.
> 
> As a last thought, there have been several reports of 202s with an
> extra 1\500 speed, this is presumably achieved by an even narrower
> slit than usual, it would follow that these cameras would be even
> more susceptible to the banding problem at the 1\500 speed.
> Perhaps these 202s have improved machining on the slit edge to
> allow the extra speed?  Anyone willing to check?
> 
> Cheers,
> Keith Davison

Keith,

Bingo!

I've gone through 5 Horizons now looking for a defect-free one.  Three
of them exhibit the horizontal banding you describe.  The worst was one
of the 1/500 sec versions, and as you describe, the worst striping was
at the narrowest slit width.

I too looked carefully at the slit, saw the irregularities and
speculated that exposure variation was the cause.  When I posted my
findings on this list, Willem-Jan Markerink replied he thought I was
wrong, that it may have been due to refections off the slit edge --
which of course would vary if the edge were irregular.  So I'm not
really sure of the "real" cause.

I do believe, however, that many (if not most) Horizons have this
problem to some degree.  How to best find out if your's is one? 
Easy....

Use slide film (which is much more sensitive to exposure variations) and
take a picture of the sky on a nice clear day.  With ASA 100, take a
range of shots F16, F11 & F8 at 1/250 of a second, and try a few at
1/125 and 1/60.  I'll bet if you look carefully, you will see the lines
on the fastest speed, diminishing or non-existent at slower speeds.

OK all you Horizon owners, give it a try & report in!!

Happy shooting,

--Alan Kafton