Re: Latitude and filter-behind-the-lens

[Jaap Los <imagefotografie@xxxxxx>]

Don Roberts wrote:
> 
> So am I correct in assuming that the normal correction for IR focus will be
> adequate?  Or should it be more?  Or less?  Or do I just have to experiment
> based on the thickness of the filter?  I'm thinking Lee polyester here.
> I may have to use gels just to get the mag to lock into place.
> 
> > 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
> >Hi Don, Dave is referring to a situation that doesn't exist with you. So in your case there is no extra correction for filter thickness required. You only need to correct for IR! 


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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