enl lens: tessar or double gauss

Manufacturers (eg Rodenstock) typically state that their 6-element Double Gauss designs are their top quality lenses and that their 4-element Tessar types are slightly less good. I can believe this, but at optimum apertures - which we would usually be free to choose - I would expect the differences to be very small. The claim that 6-element types display a more consistent performance with respect to changes in magnification is also frequently made - though the reason for this is not given. I can only assume that this is because a Double Gauss lens is more symmetrical than a Tessar. Can anyone comment on this?

If you're talking about large format lenses, then the advantage of the 6 element lenses (actually Plasmats, not D.G.) is that they cover a larger area, making movements on the camera easier. If you mean 35mm or medium format, where Double Gauss designs are commonly used for the standard lens (50mm lens for 35mm film, for example), then the advantage is speed. Tessars are limited to f2.8 max aperture, D.G designs are typically offered in f1.8, f1.4, and sometimes even f1.2 speeds.

Hello Neil,
IMHO, the 6 lenses Gauss Designs are able to produce a flatter field and have less chromatic aberration. They can be highly corrected for a precise range of magnification (which Rodenstock state in their adv.).
I agree with you that the Tessar design is very good when at optimum (and when well made. some of them are real dogs...)
The 6 lenses designs become mandatory when the color processing spread out. I owned a couple of Tessar designs which where good for B&W enlarging and terrible for color work. Unfortunately, now, even B&W enlarging use "colored light"... (for multi contrast paper).

While the differences might be small at optimum aperture for the 4 element enlarger lenses they aren't as good when not stopped down and edge sharpness drops off rapidly as they are opened up.

For small prints the differences may not be significant, but over 10x8 sized enlargements lens performance becomes far more critical.

Ian