High-resolution B&W films and fading

Andrej2 · 2007-05-11T16:17:03+00:00

Hallo zusammen, eine kurze Frage zur Beugungsunschärfe bei hochauflösenden SW-Filmen: dort heißt es immer wieder, dass man nicht zu sehr abblenden sollte,...

Andrej2

Hello everyone, A quick question about diffraction blur with high-resolution black-and-white films: it’s often said that you shouldn’t stop down too much if you want to make full use of the film’s resolving power (e.g. ADOX CMS 20, Technical Pan). Now, I mostly shoot architecture and need/want to avoid vignetting at extreme wide angles, whilst also needing depth of field – in other words, stopping down is the way to go. Is this a trade-off, or am I misunderstanding something? Many thanks for your help, Andrej

Wolf_XL

...well then, take a closer look at the depth of field scales on your ultra-wide-angle lenses – you really don’t need to stop down by more than one or two stops to achieve more than enough depth of field with ultra-wide-angle lenses... And if you make use of the hyperfocal distance, stopping down by one stop is usually sufficient. With my 20mm wide-angle lens, the hyperfocal distance at full aperture (f/4) ranges from 1.3m to infinity. With a high-quality wide-angle lens, vignetting shouldn’t be an issue either after stopping down by one or two stops at the latest.

Andrej2

OK, but that means there is a trade-off. Depth of field was just one aspect. The lens’s maximum optical performance is the second. Shift lenses, for example, achieve this from around f/8. In other words: I’m thinking of buying a PC lens and just want to know whether this is a relevant issue. Best regards, Andrej

Wolf_XL

...with shift lenses, things are a bit different – the lens’s usable image circle is also affected by the aperture... But it also depends on the design of the lens – the larger the image circle at full aperture, the less you need to stop down to achieve maximum image quality. I don’t have any experience with that, though – in such difficult shooting situations, I prefer to use my GF camera.

piu58

A perfectly designed lens would deliver the best sharpness at full aperture. Telescope lenses are designed that way; photographic lenses are not. Compromises are made when competing with other characteristics (e.g. minimal vignetting in the corners). This means that the best sharpness is achieved when stopping down by two stops. After that, the quality deteriorates again because the effective aperture decreases, and this ultimately determines the resolving power. All this applies only to shots of a single plane. Subjects with depth of field also require depth of field. There are studies on the best possible sharpness taking depth of field into account. I don’t have all of this in my head, but I’ve remembered enough to know that for reasonably large objects, an aperture of f/11 to f/16 is optimal. Even an aperture of f/22 or even f/32 (for 35mm and medium format) results in only a slight loss of sharpness within the focal plane. Conclusion: In my opinion, this is overblown. You can stop down quite a bit without really noticing any difference in the image.

CPD

Hello Andrej, "In other words: I'm thinking of buying a PC lens and just want to know if that's a relevant issue." For the price of a shift lens, you can often get a cheap second-hand large-format camera where almost any lens is a potential shift lens and where you can also use a roll film magazine. What’s more, you can then save yourself the hassle of using the highest-resolution films. If you like, have a look here: http://www.grossformatfotografie.de/ Regards, CP