[HUG ] Re: AW: Re: Biogons and digital backs

Hi,
some input in the "large sensors vs. SWC" discussion, addressed to no one 
in particular.
As some have mentioned "true" wide-angle lenses (like the Biogon) are not 
ideal for use with large-size digital sensors.
Their exit pupils are quite close to the image plane, making the ray 
angles at the sensor steep. As the sensitivity of a CCD sensor varies with 
angle of incidence, the corners will be a bit dark. (Combine the 
illumination of the Biogon in the Zeiss datasheet with the angular 
sensitivity of a suitable Kodak sensor - the specifications can be found 
with some digging - to get the picture.) There might also be problems with 
colours varying over the image, caused by the shooting conditions being so 
different from the calibration conditions (and a few other things).
However, the main problem might be the presence of sensor cover glass and 
IR cut-off filter, optical components for which the lens was never 
designed. They will introduce some abberrations, field curvature and 
astigmatism being the most prominent. These problems will increase with 
sensor size. For a CFV-type sensor the effects aren't so big, but for 
bigger sensors they might be quite noticeable. (How noticeable will depend 
a lot on the subject.)
Retrofocus type wide-angles (like the HCD 4/28, which has been mentioned 
in this thread) usually have an exit pupil placed far in front of the 
image plane, making them much more suitable for digital use.

Hope this didn't  end up too boring.

Best regards,

Per Nordlund
Optical Design\Hasselblad

hasselblad-bounce@xxxxxxxxxxxxx wrote on 2008-09-30 09:05:19:

> [image removed] 
> 
> [HUG ] Re: AW: Re: Biogons and digital backs
> 
> ronald.arvidsson@xxxxxxxxxxxxxxxx 
> 
> to:
> 
> hasselblad
> 
> 2008-09-30 09:05
> 
> Sent by:
> 
> hasselblad-bounce@xxxxxxxxxxxxx
> 
> Please respond to hasselblad
> 
> Hello,
> 
> Thanks for the most interesting discussions.I'm almost totally a 
> lurker but since digital world is in my sphere I have some points to 
> make.
> 
> The new Kodak 53.6 sensor has a resolution of 8304 pixels. This makes 
> 155 pixels/mm. In order to be useful for resolution ppurposes you need 
> at least  2pixels/line or rather 4 to get a workable resolved line. 
> This does not imply its perfectly resolved. Viewing Zeiss mtf charts 
> shows that the Biogon is a marvelous lens, In fact the MTF center 
> values for 40 lines/mm is about 60% - compare that to many other 
> "digital" APS-C lenses. See the MTF charts from Zeiss at 
> http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/Biogon4.
> 5_38mm_CFi_104942_e/$File/Biogon4.5_38mm_CFi_104942_e.pdf 
> 
> So gentlemen draw your own conclusions how good a lens must be to beat 
> the Biogon. The only drawback - which maybe modern CCDs have overcome 
> - is if the angle of incidence on the sensor as you guys have noted 
> makes for loss of energy on the CCD in the corners of the sensor.
> 
> Cheers,
> 
> Ronald Arvidsson
> 
> 
> Ulrik Neupert wrote:
> > Dear friends,
> > I have no personal experience with digital backs. During Photokina I 
> visited
> > the Phase One booth to have a look at recent developments in digital 
> backs.
> > They now offer the P65+ back with 60,5 MP and sensor size of 53,9 x 
> 40,4
> > mm. I expressed my happyness that now a Hasselblad SWC will still be
> > superwide with this back. They told me that their sensor would not 
> have a
> > problem with vignetting but that the Biogon would not offer the 
> resolution
> > to exploit their sensor fully. If this is true or a marketing 
> strategy to
> > sell their claimed to be superior Phase One camera (Mamiya, i think) 
> i do
> > not know. But I'd welcome comments on this question.
> >
> > Ulrik
> >
> >
> > 
> 
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