[rollei_list] Re: Tell the tales of Triotars
- From: Eric Goldstein <egoldste@xxxxxxxxx>
- To: "rollei_list@xxxxxxxxxxxxx" <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 6 May 2013 12:33:07 -0400
Sanders, the problem with your question is that these cameras have enormous
individual variation. There was lens variation right out of the factory,
and now do to age there is condition variation. So while we might be able
to test batches of cameras and draw conclusions with
statistical significance, the probability that any individual camera will
conform to these aggregates is not high...
Eric Goldstein
On Mon, May 6, 2013 at 12:23 PM, Sanders McNew <sanders@xxxxxxxxx> wrote:
> So, which of us is correct, do you suppose?
>
> For those just tuning in, here's the question:
>
> You shoot a portrait with two Rolleicords, each at f/4.5.
> One has the f/3.5 Triotar, the other has the f/4.5 Triotar.
> With no other variations, which produces the sharper image?
>
> And why?
>
> Sanders
>
>
> Eric Goldstein wrote:
>
>
> I'm not Richard or Mark but will jump in with this...
>
> I'm remembering that in the 1950s the optimum design speed of an MF Tessar
> was f/6.3. This means that a well-designed f/6.3 Tessar would perform best
> wide open and that it would provide superior corrections compared with an
> f/3.8 or f/4.5 Tessar stopped down to f/6.3. This is because of the
> compromises needed to make these latter two lenses faster than the optimal
> design speed lens.
>
> I do not know what the optimal design speed for a MF Triplet (Triotar)
> would be; my guess it it would not have been f/6.3 in the 50s because with
> only 6 surfaces to work with and 3 glass types, you might need more speed
> to achieve optimal than with a tessar-type
>
> Today with superior glass types available, it is possible that the optimal
> design speed for these lenses could be a bit faster. Using asherical
> surfaces would probably get you another bump faster...
>
>
> Eric Goldstein
>
> --
>
>
>
> On Sun, May 5, 2013 at 5:20 PM, Sanders McNew <sanders@xxxxxxxxx> wrote:
>
> > So, Marc and Richard, help me out a bit here.
> >
> > I have it in my head that when you stop a lens down even one stop from
> > full aperture, its performance improves substantially. I think I read
> > somewhere that it had something to do with not using the extreme periphery
> > of the lens, though that's probably wrong. For this reason, over the years
> > I've always tried to stop down from full aperture when light permitted --
> > to stop a 2.8E down to f/4 (or smaller), for example, whenever possible.
> >
> > Is that correct? And if it is correct, then wouldn't one expect an f/3.5
> > Triotar, stopped down to f/4.5, to provide visibly better results than an
> > f/4.5 Triotar at full aperture? Maybe the advantage of working the Triotar
> > design to a larger aperture was, in part, to improve the visual acuity of
> > the lens at a given working aperture. Or is that a stupid conclusion built
> > on false assumptions?
>
>
>
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