Re: Latitude and filter-behind-the-lens

[Jaap Los <imagefotografie@xxxxxx>]

David N. Horn wrote:
> 
> Latitude means tolerance to errors in exposure.
> A Latitude of three stops means that one can vary exposure within a
> three stop range and still get a usable negative.
> Latitude should be expressed in plus X stops, minus Y stops.
> Most negative film is more tolerant to overexposure than underexposure.
> For example, you could say such and such film has a -1/+2 stop latitude.
> In my limited experience, HIE has little latitude.
> Most consumer color negative films, and Ilford XP1, have a lot of
> latitude. Three stops is a lot.
> 
> >
> > Just in the process of getting my head round some of the info in Laurie
> > White's 'Handbook'.
> >
> > It says that HIE has a latitude of 3 stops - is that to say that if you
> > expose HIE on the straight line portion of its curve, a change in
> > exposure of 1/3 stop will be equivalent to a change of 1 zone in density
> > on the negative. That is are the ten zones spread over the 3 stops of
> > latitude ?
> >
> > Or does it work differently ?
> ===============================================================
> 
> Placing a filter of significant thickness behind the lens WILL alter
> the focus.
> If you put a filter, other than a wratten type, behind the lens, you
> will have to increase the film/lens distance to compensate.
> Some polaroid film backs that cannot bring the polaroid film to the
> original film plane, use a glass or plastic plate to move the plane
> of focus back to where the polaroid back places the film.
> 
> > > As owner of same equipment I'm very interested in the subject you
> > forward to the List. IMHO a good quality filter placed in front of the
> > lens doesn't alter the focus. When placed behind the lens there will be
> > no alteration either. Also in your case where the filter is placed in
> > the filmback. So you still have to correct your focus for IR as usual. I
> > don't have that special 70 mm back, but I think that this also applies
> > for your back. What do others think about this?
> >
> Hope this helps!
> 
> Dave Horn
> *
>Dave, we are talking about filters of 0.4 mm and 0.1 mm thickness. We have to be practical and that means, that list members (IR photographers), who work with these type of filters do not have to adjust their focus settings because of the filters they use. That was the question of Don Roberts and he isn't using a Polaroid back! 
Sincere greetings
Jaap Los
Alkmaar, The Netherlands

See also my Infrared Photography Homepage specially made for you with
lots of information and links to other sites.
at:   http://home.wxs.nl/~losjb/

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End of Infrared-Digest V0 #586
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