Archived posting to the Leica Users Group, 2009/05/31
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]In general digital signal capture the AA filter is there to prevent data with a higher frequency than half the sampling frequency getting to the digital to analogue convertor, since this would generate non- correctable spurious data. The AA filter in a digital camera has this function and effectively limits the maximum resolution of the lens to match the resolution of the sensor (or it should). If one is using a relatively low resolution lens the AA filter should have no effect. In fact to re-convert the digital signal back to analogue a matching filter must be applied to remove spurious data which would be generated at the limit of resolution (if data exists there). The correct settings for the filter will depend on the AA filter and sensor characteristics which generated the original data. That is why raw convertors have camera dependant sharpening algorithms. That is also why people who believe they can properly compare two cameras by converting raw data "with no sharpening or other corrections" are completely mistaken, and are therefore deceiving themselves. There are lots of subjective reasons for not using the camera makers recommended corrections, and each raw convertor software supplier has their own algorithm for each camera to give the look they want. Others work out their own personal preference for each camera profile. cheers, Frank On 31 May, 2009, at 00:11, David Rodgers wrote: > Thein, > > The whole concept of AA filters has me a bit baffled. If they > improve acuity so much, why do camera companies like Nikon and Canon > use them in their top end cameras. I mean, they have smart > engineers. So AA they must be there for a reason. And Leica, by not > using them, must gain something; but they also must be giving up > something, too. I have my own opinions of what those somethings are, > based on using a D200 that had the hi pass filter removed. > > A lot probably depends on what type of photography a person does. > What may be an issue with some subject matter may not be with > another. Acutance is important in some types of photography. But not > so much in others. If the ability to resolve fine detail dwarfed all > other factors, Tech Pan would have outsold TriX, instead of visa > versa. > > I've always put a lot of stock in low light performance. But that's > just me. Probably because I learned long ago that if I have to shoot > at too low a shutter speed any potential acutance in the tools I'm > using disappears in a hurry. > > DaveR > > > > > -----Original Message----- > From: Ming Thein [mailto:mingthein at gmail.com] > Sent: Friday, May 29, 2009 7:27 PM > To: Leica Users Group > Subject: Re: [Leica] OT: D3x vs 'Blad CFV 16MP full sized samples > > > You still have to use sharpening all the time to get optimal acuity. > You don't with the M8. > > Thein Onn Ming > Sent from my iPhone > > On May 30, 2009, at 0:39, "David Rodgers" <drodgers at casefarms.com> > wrote: > >> Thein, >> >>>> The D3x still has an AA filter, and while it has the best per- >>>> pixel detail I've seen, it doesn't come close to the M8/DMR/CFV. >>>> Those cameras have no AA filter.<< >> >> Could you please be moir? specific regarding "doesn't come close"? >> >> DaveR >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information