[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*Subject*: Re: [Rollei] OT: pupil distorsion and MTF effects*From*: bigler@ens2m.fr*Date*: Sat, 10 Jan 2004 10:43:24 +0100 (CET)*References*:

From Richard Knoppow, about subtel effets of pupillar distorsion in wide-angle lenses : >...I've also not seen any explanation of the effect of the tilting >entrance pupil on MTF variation with image angle. Presumably it could >increase resolution away from the axis beause the stop is not >vignetted in the same way as usual. However there may be other >effects. Richard, thank you very much for your additional comments on Roosinov principles. It is always better to proper credit the original inventor. I have seen one thing related to pupillar effects on MTF in the edges, namely in Rodenstock MTF charts posted by Paul Butzi in his web site. http://www.butzi.net/rodenstock/rodenstock.htm Rodenstock large format and enlarging lens literature Rodenstock's view camera lens MTF charts are simulated and not measured like in Zeiss datasheet, but they are quite informative. You will notice on those charts that the ultimate MTF limit due to diffraction is plotted as a reference and is smaller in the edges than at the centre of the image field for wide-angle grandagon lenses. My understanding is that there is also no absolute compensation of light fall-off by pupillar distorsion in the edges, since Rodenstock like Schneider sells centre-filters to compensate for this. The elementary theory of diffraction tells you that the angle under which you see the exit pupil from a given image point actually yields the cut-off spatial frequency due to diffraction f_c = 1/(N_eff*lambda) where N_eff = distance/pupil diameter. In the edges of the fiels, the distance increases, and the pupil diameter changes both by the effect of a naturela cosine factor counter-balanced by some Roosinov effects. In fact, this N_eff factor is the same as in photometric formulae used for close-up (actually : (N_eff)^2 is proportionnal to the bellows factor), so in a sense if lightfall-off occurs in the edges, the elementary diffraction theory predicts that diffraction effects are worse also, in the same proportion as N_eff. I'm really dubious about the actual validity of the elementary (paraxial) Fraunhofer diffraction theory for wide-angle optical systems, but there appears to be at least a certain consistency with what is simulated by Rodenstock experts. - -- Emmanuel BIGLER <bigler ------------------------------

- Prev by Date:
**Re: [Rollei] Optimist of the week award** - Next by Date:
**Re: [Rollei] Magazine 150 exposures by FlashPhot, Paris** - Previous by thread:
**[Rollei] Re: Rollei Users list digest V13 #174** - Next by thread:
**Re: [Rollei] Magazine 150 exposures by FlashPhot, Paris** - Index(es):