Why did Hasselblad's 80mm Planar change from 6 to 7 elements

[j._mose]

Hello,

 

I would like a technical explanation on why the 80mm Planar, supplied

to Hasselblad, changed from 6 elements to 7 elements in the early

1960's. I have asked around and no one seems to know why? Thanks for

your help!

 

Best regards,

 

J. P. Mose

[godfrey]

It's a simplistic answer, but Zeiss likely wanted to improve

flatness of field, corner/edge sharpness, evenness of

illumination, etc and found a 7 element solution gave the right

results for the Hasselblad mount.

 

Godfrey

[patric_dahl_n]

The 2,8 Rolleiflex has a 5-element Planar. But this version couldn't be used in the Hasselblad/Rollei SLR because of mechanical reasons. The rear element would come too deep in the camera body, and you know, in there is a moving mirror. So they had to modify the Planar to fit in the camera. Just wanted to mention this. The seven element planar is not superior to the five element version, but better than the early six element in the 'blad. ;-)

[Rob F.]

So, then, Patric is saying that the Hassie version has a longer back focus than the Rollei version. That would apparently make the Hassie version a retrofocus lens. I wonder if that's the case. You wouldn't think they would offer a retrofocus as their standard lens, given that they do introduce some distortion. Then again, maybe the 100mm (a favorite of mine) was meant to address that issue.

[david_goldfarb]

It wouldn't surprise me if better coatings had something to do with it. The 6-element Planar is actually quite an old design that was relatively unsuccessful before the advent of lens coatings (i.e.--a good design for a fast lens from the calculations, but too many glass-air surfaces to produce good contrast without lens coatings). With better coatings, which would have come along about that time, you could add an element for finer corrections without compromising contrast.

[joseph_albert]

David got it right. Before the advent of multicoating technology, there has been a tension between how well corrected a lens is, and contrast. The Planar is actually an older design than the Tessar,

but before the technology of optical coatings was in use, the 4-element Tessar was a tradeoff of some of the correction to get good contrast. Wide open, a moderate amount of spherical aberration is left uncorrected.

<p>

As coating technology came in, and gradually was improved, lenses began to have more elements. Multicoating has enabled such lenses as floating element retrofocus wide angles and zooms which can have anywhere from 8 or 9 elements for the floating element wide angle to as many as 17 elements in a zoom. Without modern multicoating, such lenses likely would suffer from mediocre contrast.

<p>

With the Planar for 6x6, Zeiss has sought to improve its performance during different re-designs, and, using the full technology available, has chosen to increase the number of elements. With modern multicoating, this can be done while still having a lens that delivers snappy contrast and vibrant colors.

[j._mose]

Thanks for the responses so far. Very interesting indeed. So between the time that Hasselblad introduced the 6 element Planar (1957) and the 7 element Planar (1961/1962) coatings had improved. I didn't realize this. I assumed nothing had changed until the T* coating started in the early 1970's. Thanks again.

 

JP Mose

[q.g._de_bakker]

While the difference between an uncoated lens and a single coated lens may be huge, especially when transmission is concerned, i don't think that the differences between the various single layer coatings were that great that they warranted adding another lens element. So i really doubt that this would indeed be the reason.

[patric_dahl_n]

The Planar on the Rolleiflex GX and FX is still a 5-element design.

The first Planar lens was indeed a 6-element design, but it was compleatly different than the modern Planar. Symmetric.

[kornelius_j._fleischer]

A brief comment from inside Zeiss: Rob F. is on the right track: The current Zeiss Planar 2,8/80 for Hasselblad (and Rolleiflex 6000 series) has to be a little bit of a retrofocus design. This avoids collision with the SLR mirror (the mirror in a TLR does not move, so the Rollei TLR can utilize a more compact lens design). A "standard" Planar lens for Hasselblad without any retrofocus aspects is the Planar 100. Many of those who have the Planar 100 say it´s their favourite lens. It is a great documentation tool with excellent corner-to-corner sharpness and extremely low distortion.

[uk]

Very interesting. Thanks.