I don't have anywhere near AG's enlarger experience (I haven't used one
for about 30 years) but my thought was something very similar. I didn't
see the light falloff but rather unusual brightness in a semicircular
pattern on each side of the long axis of the film. I had no idea how it
could get there but a reflection as AG suggests is what I thought of.
Chuck Norcutt
Ken Norton wrote:
>> I'm trying a new enlarging lens (Nikkor 50mm f/2.8N) which has amazing
>> resolution, but for
>> some or other reason I'm getting weird light falloff, not in the
>> corners as such, but
>> in parallel to the long edges of my prints. This image shows it clearly:
>
> I've seen this twice before. One was because the enlarger head didn't
> have even lighting--this can get tricky, and the other time was when I
> tried going too low on the enlarger to make a tiny print and a inverse
> vignetting resulted.
>
> I primarily use a diffusion head on my enlarger, but also have
> columinated heads too. The inverse vignetting occured not with the
> diffusion head.
>
> Hmm. Something that MIGHT be happening. Remove the light head of the
> enlarger and look straight down through it with your typical film
> holder in place. Is the film holder bright reflective? If so, there is
> backscatter which ends up causing an uneven lighting as this reflected
> light bounces back up into the head which then comes back down in a
> pattern that could result in wave shaped illumination. Remove the
> holder and look further down. Is there anything bright reflective
> inside the bellows are on the lens-board? If the lens board is
> reflective, the light bounces back to the film and underside of the
> holder. Usually, though, this type of reflectance below the film just
> results in lost contrast. These issues with reflections inside the
> enlarger are more likely when using small-format films inside a
> large-format enlarger.
>
> AG
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