What aperature delivers peak performance on Hasselblad 100mm f3.5 and 180mm f4

[art_arkin]

After shooting and processing lot of film but having no access to

quality scanning or darkroom facilities I've finally got my darkroom

up and running. I've bought a fine enlarger with equivalent optics.

(Devere 504 with Ilford B&W multigrade head. Rodagon 80mm and an

absolutely mint and unused Nikkor 105mm N series lens.

 

I dug out a negative of a studio portrait shot on Agfa APX 100 (deved

in Rodinal 1+50) using my CF 180mm with a fully extended pro hood to

kill any strobe flare, no filters. Lighting was with powerful strobes

at f16, the camera was studio tripod mounted.

 

On examining the models eyes through the grain magnifier I expected to

find every lash looking crystal clear but instead I see less than

ideal sharpness, they are positively soft and I'd go as far as saying

out of focus. When printed to 8x10 paper it looks great so I may be

splitting hairs but I don't think it'll hold quite so strong at 16x20.

 

Given the 180mm is considered one of Hasselblad's sharpest optics I

was surprised to find this lack of sharpness. The camera was in my

opinion set up for optimal performance, perhaps not. My guess is that

diffraction softness has kicked in at f16, could someone please

confirm that the 180mm (and my other lens, the 100mm 3.5) perform best

at f8 or 11 and should one expect significant degradation of

sharpness by f16.

 

I don't think it's a film back issue, it looks like diffraction

softness but I could be wrong. My focus is definitely centered on the

models eyes.

 

Any thoughts or suggestions, most appreciated.

 

Thanks in advance.

[bob_the_builder1]

Arthur, the only way to find out is to test it yourself as no two lenses are the same. Try using

slide film as that way you eliminate the developer effect...

[steve_levine]

Most 'Blad glass is sharp edge to edge, wide open. But any optical system's "corners" always benefit from a stop or two down.

 

 

FWIW, check PHOTODO.com. They have resolution comparisions for Hasselblad(and others) lenses, at various apertures.

[dan_fromm2]

Um, 16x20 is right at the edge of what can be done well with 6x6. It needs at least 9x magnification. The best resolution you can get at f/16 is 100 lp/mm, a good print wants >= 8 lp/mm. You'll have to work very hard to get as much as 90 lp/mm with APX 100.

 

You may have had problems focusing the camera or the enlarger. But on the whole you'd do well to shoot at f/11 or wider. And if you want super 16x20 prints, perhaps its time to move to 4x5 or to be a little less hard on yourself. And try TMX, it is a bit sharper than APX 100.

[gary_ferguson1]

I'm familiar with the 100mm and 180mm Hasselblad optics, they're both outstanding MF lenses which also fully deliver the goods in the 2 metres to 10 metres portrait range. If there's a problem with sharpness it's unlikely to be this glass.

 

As has already been pointed out, 16x20 is approaching the critical limit from 6x6, and by that I mean the enlargement size where the benefit of a larger camera format starts to become readily noticeable. But from experience I can say that with good technique and these two lenses 16"x20" is fully achievable at f16.

 

There's three areas I'd immediately explore for an explanation.

 

First is mirror lock up. Unlikely to be an issue with a tripod and/or strobes but not impossible if you're shooting at say 1/60s with bright ambient light or if you're hand holding. The Pentax 6x7 comes in for a lot of criticism for mirror slap, but IMO the Hasselblad's no feather footed fairy either, the reason Hasselblad made MLU so easy to use is because it's meant to be used.

 

Second is your enlarger set-up. Are you absolutely sure the enlarger is square on to the baseboard with the grain sharp in all four corners? I used to reset my enlarger every month or two with a laser pointer, if you're aiming for critical sharpness you'll have to fuss like a mother hen over your enlarger.

 

Thirdly, and most likely, is focus error. If you're working from the lens scale then be aware that the Zeiss standard for an acceptable circle of confusion is something like 60 microns for medium format. With a x7 or x8 enlargement that means a "blur circle" of nearly half a millimetre in the print. And that's plain soft. The rule of thumb I use with a Hassie is that the lens scale's fine for 10"x8", 11"x14" requires working to one stop tighter, and 16"x20" requires two stops tighter.

 

Furthermore this assumes you even got the focus within the lens scale in the first place. In my experience it's very difficult to achieve consistent focus accuracy with portrait photography, and the tighter the shot or the more dynamic the session then the harder it gets. One thing I've found that significantly increases my own success rate is to use a split rangefinder Acu Matte D with the rangefinder set vertically rather than the more normal horizontal positioning. This then aligns clearly across the model's eye and makes critical accuracy easier.

[simonpg]

Arthur, while I can't give you a detailed "scientific" answer; I can give you a very experienced and fussy user's answer.

 

Yes the Sonnar 180mm f4 (mine is the CF type; the CFi benefits from impoved/enhanced interior paint which benefit few users will ever truly experience) is superbly sharp. I often wonder: could anything be sharper - if it were, who could tell? Mine is so sharp in every image taken I have to use a softar for portraits as many say they do too.

 

I find it's peak performance is at f5.6 - it's quite possible that technically the peak is at f8. BUT, definitely (and the same would logically apply to any lens for that matter) at f16 you will detect the effect of diffraction - if you have amazing eyes or special equipment!

 

Interestingly Zeiss has published results of a close "scientific" examination of the new Leica M-mount Biogon 25mm f3.5. Peak performance is at f4 and diffraction is detectable at f5.6 - wow!

 

You don't full describe "softness" or how that is visualised when looking at a print rather than under close examination.

 

But for sure my understanding is that as a "general rule" many of the Hassy/Zeiss lenses' peak perform at f8 and my personal "visual" experience supports that (looking at slides on a light box under about 5x magnification.

 

The reality is that these lenses are as good as their users say - but, no lens is as good as the "legendary" status they sometimes earn no matter how well earned. I supopose the trick is to read between the lines of overly superlative comments.

 

Like you say there a a number of links in the chain - your lens may need adjustment; your film back may not have perfect flatness; your focusing may have been a micron out - or just maybe f16 has that much diffraction.

 

I've never used the 100mm or 110mm.

 

Finally a suggestion - why not email Zeiss - they can be very responsive.