[LargeFormat] Focus Shift on Stopping Down

[Les Newcomer]

Somebody with a better background than I do in glass properties and
optics could answer this. It all has to do with the lens design.

Most of the early minuscus "landscape" lenses in both single and casket
sets had a focus shift, but Protars, with their multi element design do not.

the most commonly used modern lens that exhibits this to a noticeable
degree is the dagor.

Les

Clive Warren wrote:
> 
> We have heavy rain here in Bristol this weekend - at least it's not too cold
> - the British obsession with weather is really only due to the large number
> of wet weekends in Winter and sunshine during the week - for me that is when
> you can't take the time out to do personal photography.....
> 
> Anyway, on this rather damp Saturday morning I was wondering about focus
> shift on stopping down. Some lenses are more affected by this than others -
> can be a bit of a pain if you are using compact field lenses that have small
> apertures. Checking the ground glass is difficult enough when wide open, let
> alone checking for focus at smaller apertures.
> 
> So, which lense types are most affected by focus shift?  For example the
> very bright Wollensak Velostigmat Series II 12" is affected....
> 
> Anyone have rules of thumb?
> 
> Cheers,
>        From the rain soaked leave strewn streets of Bath today,
> Clive
> 
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