Re: What, no ideas?

[Colin McKie <colinmckie@xxxxxxxxxx>]

Don Roberts wrote:
> 
> Last week I posted the following and got no responses.  I can't believe
> that no one even has any speculation so I'll try again.  Any ideas
> please.  I don't want to waste any more IR film if I can help it.
> 
> > I am very new to the IR area so I hope this isn't an old question.  I
> > just processed a roll of HIE and a roll of Konica IR750 and discovered
> > that most of the images are unusable because of what appears to be lens
> > flare.  The puzzling thing to me is that both were shot with reflex
> > cameras and I was not seeing flare through the viewfinders.  The HIE was
> > shot in a Nikon 8008s with a 28-70 zoom and between-the-rails #25
> > filter.  The Konica was shot in a Rollei TLR with a #25 filter in a
> > bayonet ring over the taking lens.  I have enough problems trying to
> > figure out the way to get sharper images without having flare too!
> > Anybody got any ideas about why this occurred?
> >
> > To be more specific, I have a line of images of the iris opening coming
> > across the neg.  I have used these cameras before in similar situations
> > but without the filters and haven't run across this problem.  Does
> > internal reflection become more of a problem with this setup?
> > --
> 
> --
> Don Roberts
> Bittersweet Productions
> Iowa City, IA

Don,

If no-one else has much to say, here are my thoughts.

First, the flare spots are not visible when you focus the Nikon because
the diaphragm is wide open at that point, and the flare image is caused
by internal reflections of the closed down aperture. This is very common
when a light source or bright specular reflection appears in the field
of view. A preview button can show this if you have one.

You don't see it on the Rollei because you are looking through a
different lens.

Secondly, you see a line of flare spots because the reflection bounces
between the front surface of the lens and the flat back of the filter.
It may be worse at infra-red because the multiple coatings on the lens
which reduce these reflections for visible light are working out of
their design spectrum and the filter is probably uncoated.

In general, be very careful with bright points of light in frame with IR
film. The effects can be very good or they can wreck the shot!

Good luck and stick with the IR!

Colin McKie


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