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-   -   Re: Interesting article on dla (http://www.velocityreviews.com/forums/t915494-re-interesting-article-on-dla.html)

RichA 03-23-2012 03:56 AM

Re: Interesting article on dla
 
On Mar 22, 10:24*pm, "Dudley Hanks" <dha...@blind-apertures.ca> wrote:
> I was surfing around the web, looking for info on how diffraction limits pix
> quality at various apertures, and I came across this:http://photo.stackexchange.com/quest...-diffraction-l...
>
> I found it interesting that even the worst blurring at F/22 in some of the
> tests resulted in a sharper image than could be achieved with the lens wide
> open, or even slightly stopped down.
>
> Enjoy,
> Dudley
>
> --
> "The balance between staying positive and being realistic lies somewhere in
> the area of remaining hopeful." *Irwin Barker


Just means some lenses have a long way to go before they are anywhere
near perfect. A perfect lens, that provides 1/10th wave accuracy (1/4
isn't perfect) should have as sharp an image wide open as stopped down
to f5.6. If the lens's actual resolution was measured, it would
resolve more when wide open. It's hard to prove visually as sensors
are not pixel-dense enough to exploit it. No wide angle and normal
lenses meet this criteria, at all. Some macro lenses are pretty
good. Some telephoto lenses are close, principally high-end
telephotos with reasonable apertures. 300mm f4.0's that kind of
thing.
Diffraction-limited lenses are capable of being mated with equally
good teleconverters, which of course wide and normal lenses can't be.

Bruce 03-23-2012 01:01 PM

Re: Interesting article on dla
 
RichA <rander3127@gmail.com> wrote:
>Just means some lenses have a long way to go before they are anywhere
>near perfect. A perfect lens, that provides 1/10th wave accuracy (1/4
>isn't perfect) should have as sharp an image wide open as stopped down
>to f5.6. If the lens's actual resolution was measured, it would
>resolve more when wide open. It's hard to prove visually as sensors
>are not pixel-dense enough to exploit it. No wide angle and normal
>lenses meet this criteria, at all.



Not true. The Leica Elmarit-M 24mm f/2.8 ASPH is at its sharpest in
the centre when wide open at f/2.8 and at the edges at f/4. Stopping
down from f/4 gives no further gain in resolution, so the lens is
diffraction limited at f/4 across the frame and at f/4 in the centre.
The resolution of this lens is so high that no currently available
digital sensor can exploit it. However, ultra high resolution film
can, and the results are outstanding.

There are several other Leica M lenses that are almost as close to
perfect as the 24mm Elmarit. Once again, they will only produce to
their full potential on film such as ADOX CMS-20, which is one of two
black and white films I use with my rangefinder gear.

<http://www.adox.de/english/ADOX_Films/ADOX_Films/ADOX_CMS_Films.html>

The other black and white film I use is Kodak BW400CN. You would
expect an ISO 400 chromogenic film to be way behind a highly
specialised ISO 20 emulsion when it comes to resolution, but I am
constantly surprised by what BW400CN can achieve. If and when it is
discontinued by Kodak I will buy a freezer that is large enough to
store enough BW400CN for the rest of my life. It really is that good.


Bruce 03-23-2012 01:08 PM

Re: Interesting article on dla
 
Bruce <docnews2011@gmail.com> wrote:

> Stopping
>down from f/4 gives no further gain in resolution, so the lens is
>diffraction limited at f/4 across the frame and at f/4 in the centre.



Sorry, should obviously be f/2.8 in the centre.


RichA 03-23-2012 05:37 PM

Re: Interesting article on dla
 
On Mar 23, 9:01*am, Bruce <docnews2...@gmail.com> wrote:
> RichA <rander3...@gmail.com> wrote:
> >Just means some lenses have a long way to go before they are anywhere
> >near perfect. *A perfect lens, that provides 1/10th wave accuracy (1/4
> >isn't perfect) should have as sharp an image wide open as stopped down
> >to f5.6. *If the lens's actual resolution was measured, it would
> >resolve more when wide open. *It's hard to prove visually as sensors
> >are not pixel-dense enough to exploit it. *No wide angle and normal
> >lenses meet this criteria, at all.

>
> Not true. *The Leica Elmarit-M 24mm f/2.8 ASPH is at its sharpest in
> the centre when wide open at f/2.8 and at the edges at f/4. *Stopping
> down from f/4 gives no further gain in resolution, so the lens is
> diffraction limited at f/4 across the frame and at f/4 in the centre.
> The resolution of this lens is so high that no currently available
> digital sensor can exploit it. *However, ultra high resolution film
> can, and the results are outstanding.
>
> There are several other Leica M lenses that are almost as close to
> perfect as the 24mm Elmarit. *Once again, they will only produce to
> their full potential on film such as ADOX CMS-20, which is one of two
> black and white films I use with my rangefinder gear.
>
> <http://www.adox.de/english/ADOX_Films/ADOX_Films/ADOX_CMS_Films.html>
>
> The other black and white film I use is Kodak BW400CN. *You would
> expect an ISO 400 chromogenic film to be way behind a highly
> specialised ISO 20 emulsion when it comes to resolution, but I am
> constantly surprised by what BW400CN can achieve. *If and when it is
> discontinued by Kodak I will buy a freezer that is large enough to
> store enough BW400CN for the rest of my life. *It really is that good.


Good info. I almost bought the Leica 24mm f2.8 R lens. I wonder if
it's as good as the M?
Any idea of the ADOX film is the same as this Rollei?

http://www.freestylephoto.biz/422201...oll?cat_id=402

Very roughly, it's = 70 megapixels on a 4/3rds size piece of film at
normal contrast. However, I really wonder how much of that resolution
is preserved until the print stage?
This is definitely something I'd like to test out.

Bruce 03-23-2012 06:48 PM

Re: Interesting article on dla
 
RichA <rander3127@gmail.com> wrote:
>On Mar 23, 9:01*am, Bruce <docnews2...@gmail.com> wrote:
>> RichA <rander3...@gmail.com> wrote:
>> >Just means some lenses have a long way to go before they are anywhere
>> >near perfect. *A perfect lens, that provides 1/10th wave accuracy (1/4
>> >isn't perfect) should have as sharp an image wide open as stopped down
>> >to f5.6. *If the lens's actual resolution was measured, it would
>> >resolve more when wide open. *It's hard to prove visually as sensors
>> >are not pixel-dense enough to exploit it. *No wide angle and normal
>> >lenses meet this criteria, at all.

>>
>> Not true. *The Leica Elmarit-M 24mm f/2.8 ASPH is at its sharpest in
>> the centre when wide open at f/2.8 and at the edges at f/4. *Stopping
>> down from f/4 gives no further gain in resolution, so the lens is
>> diffraction limited at f/4 across the frame and at f/4 in the centre.
>> The resolution of this lens is so high that no currently available
>> digital sensor can exploit it. *However, ultra high resolution film
>> can, and the results are outstanding.
>>
>> There are several other Leica M lenses that are almost as close to
>> perfect as the 24mm Elmarit. *Once again, they will only produce to
>> their full potential on film such as ADOX CMS-20, which is one of two
>> black and white films I use with my rangefinder gear.
>>
>> <http://www.adox.de/english/ADOX_Films/ADOX_Films/ADOX_CMS_Films.html>
>>
>> The other black and white film I use is Kodak BW400CN. *You would
>> expect an ISO 400 chromogenic film to be way behind a highly
>> specialised ISO 20 emulsion when it comes to resolution, but I am
>> constantly surprised by what BW400CN can achieve. *If and when it is
>> discontinued by Kodak I will buy a freezer that is large enough to
>> store enough BW400CN for the rest of my life. *It really is that good.

>
>Good info. I almost bought the Leica 24mm f2.8 R lens. I wonder if
>it's as good as the M?



Best avoided. Like quite a lot of the early Leica R range, it was
based on an old Minolta design that wasn't particularly good to start
with. The focal length is not one with a long tradition in the Leica
range where 21mm and 28mm are firm favourites, so there wasn't enough
demand to justify replacing it with a 100% Leica design.

Even in the M range, the 24mm f/2.8 ASPH was not a top seller until
recently in spite of its superlative optics. The 21mm f/2.8 ASPH sold
much more strongly despite being optically inferior.

The 24mm finally became a popular lens for the M8 and M8.2
rangefinders because the widest set of frame lines in their viewfinder
was for the 24mm focal length.

It has now been replaced in the range by two lenses, an f/1.4 and an
f/3.8, both of which are optimised for digital capture. The
superseded (though still available) f/2.8 performs very well indeed on
my M9P but the vignetting is significant.

The new f/1.4 costs almost double the price of the last f/2.8 and the
new f/3.8 about a third less. I am so happy with my f/2.8 that I
haven't even tried the new ones.


>Any idea of the ADOX film is the same as this Rollei?
>http://www.freestylephoto.biz/422201...oll?cat_id=402



No idea, sorry. As with my 24mm lens, I have grown very fond of the
ADOX emulsion and would prefer exploring its sublime abilities to
learning how to use yet another emulsion that seems not to offer any
advantages at all. However, the Rollei film is worth a try for anyone
who isn't quite as wedded to another film in the way that I am. ;-)


>Very roughly, it's = 70 megapixels on a 4/3rds size piece of film at
>normal contrast. However, I really wonder how much of that resolution
>is preserved until the print stage?
>This is definitely something I'd like to test out.



It is very hard work getting every last bit of resolution out of these
films. I use a sturdy tripod for all my shots and take meticulous
care with focusing. That can include making small manual corrections
to the rangefinder focusing to compensate for focus shift. That
doesn't affect my 24mm lens but it does affect the 35mm.

Processing has to be done with the greatest of care. The developer
needs accuracy in mixing and the nature and amount of agitation during
developing can make a significant difference to the results.

Finally, printing needs to be done with the very best equipment. I
use a Leica V35 enlarger but with a rather exotic Schneider lens. In
fact I have two V35 enlargers, one with a Schneider 40mm lens that
allows "autofocus", and the other with a Schneider 45mm lens that
doesn't because the V35 linkage that preserves focus at different
print sizes only works with the 40mm focal length. The Leica 40mm
Focotar was supposed to be a stellar lens but it is seriously
outclassed by the more recent Schneiders.

There is something very satisfying about using the world's best lenses
for capture, the world's highest resolution film for recording and the
world's best enlarger lenses for printing. But it does mean that
every other aspect of the workflow has to be absolutely right, and the
slightest imperfections stick out like a sore thumb.

It makes Kodak BW400CN and one hour developing at a minilab look very
attractive as an alternative. Compared with CMS 20, BW400CN is easy
and very forgiving. ;-)



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