stopping down on rotational cameras

[Bill Glickman <bglick@xxxxxxxx>]

George

         Comparing the 220 VR with Nikon lenses and Roundshot 65 with a LF
lens optimized for that camera is not a good comparison at all....

          You raise some good points about the film travel distance matching
the lens fl... I totally agree with that...and with the Roundshot 65, Werner
explained this is calibrated at the factory.  While the 220 VR's are left up
to the user to provide perfect calibration for each lens.  And as I stated
in my earlier posts, this is no easy task for several lenses!   Putting this
issues aside, I can offer the following which relates to lens sharpness and
rotational cameras....

           A 35mm lens has very small image circle compared to a LF lens.
(the type used on the 65)  Check the specs and you shall see.  As the you
move away from the center of the image circle towards the edges, the image
resolution degrades, this is true for all lenses.  A look at the MTF curves
produced by the maker will show exactly how much the image degrades from the
center at each f stop.  (well, at least 3 or 4 f stops)  So a 35mm lens
whose image circle struggles to reach the large 220 roll film edges, is
definitely delivering part of its inferior image circle to film.  This is
amplified of course if rise and fall movements are used.  Each 35mm lens has
its own characteristics, so try to check each one out.... typically the
longer the lens, the lager the image circle.   What compounds this problem
is wider f stops produce smaller image circles.  Therefore, you are torn
between shooting at very slow speeds, (high f stops) to stretch the image
circle, possibly to cover for movements.   I know there is some who
disagreed with this, but the information is all readily available for
review... I did run this entire scenario by Werner before buying my 220 VR
with MF adapter, and he agreed with every part of it.   Several optical
engineers also fully agreed with this.   This is why, when I purchased mine,
I would only consider MF lenses vs. 35mm.   I actually prefer them over LF
lenses due to the fact they are optimized to be shot at faster f stops.  But
as I mention below, this may not be too much of an issue...but the ability
to change fl was mandatory for my shooting.  So this eliminated the cameras
with fixed LF lenses.

    Just to give an example, in lens test where the center and edges are
checked for resolutions, it not uncommon for a lens to register 70 lpmm at
the very center and 20 lpmm towards the image circles edge.   So if you are
getting some of the 20 lpmm in your image, and you want to maintain 5 lpmm
in your final print (what the human eye can detect as sharp) then the 20
lpmm can only produce a 4x enlargement.  If you have no standards on the
lpmm on the final print, then you can enlarge as big as you want.  Beauty is
in the eye of the beholder!  That is why so much of this is subjective.

     As you can see, larger image circles always win out.

George you wrote:

>I have heard that stopping way down with these cameras
> really doesn't do much for sharpness. Is that a fact?

         That depends on 4 things.  The first obvious one is depth of field.
If stopping down is required to achieve the depth of field, then yes it will
make or break a shot.   The second is image circle.... if the image circle
is large enough to maintain the sweet spot on the film...then no benefits to
stopping down.  The third issue is movements...if you do extreme movements
then you might move the film into the inferior part of the image circle...in
which case stopping down will increase the size of the image circle and
possibly bail you out.   The 4th issue is the MTF curve of the lens...... if
wide open produces a small image circle with fast degradation towards the
edges, then stopping down would help.  Not the case with 35mm lenses which
almost always optimized at faster f stops.  (but produce their smallest
image circles)    So as you can see, there is no one simple answer for all
lenses / cameras, so much to consider, image circle, MTF curve, camera
movements, Depth of field, etc.....

        Another issue with moving far from the center of image circle is
darkening.  All lenses experience Cosine Theta 4 fall off.   Simply put, the
further you move out from the center, the darker the image gets..... up to 2
stops on some lenses!   On standard box cameras this is often not a problem
since the image circle exceeds the film area so its never noticed, however
once you start moving the image circle in relationship to the film, you can
approach this dark area.  I notice with my shorter Mamiya lenses, using full
rise for fall, at wide open f stops, I get into the darkened area just a
bit.  But easily workable.  However, this may not be the case had they be
35mm lenses.

       On the other hand, a LF lens on your 65, which has a massive image
circle compared to 35mm and even very much larger than MF lenses..... will
always have the sweetest part of its image circle going to film...even if
extreme movements are used.   So LF lenses like the 65 should produce the
best images compared to any other method for rotational cameras. (specially
if stopped down)   However, LF lenses, evidenced by there MTF curves, only
produce very sharp images throughout their full image circle at higher f
stops, usually for 65mm at f11 or higher.   Shooting at lower f stops, such
as 4.5 degrades the image very quickly moving from the center on out.
However, considering the film is seeing such a small amount of the image
circle, there is a good chance even with movements, you will still capture
the sweetest spot of the image circle and avoid the very inferior outer
part.  You would need to look up the MTF for the LF lens to know for sure
where these break points are.  Schneider shows them on their web site, while
Rodenstock will send them to you.  From what you mentioned in your post, I
would guess that my above statement is correct... which is fabulous,
because, shooting LF (4x5) images at those f stops produce poor
results...but remember the film area of 4x5 is huge compared to your roll
film.  (specially with movements)  So once again, there is a lot to be said
for large image circles!

        The only potential drawback of very large image circle is loss of
contrast in the film.  I notice this sometimes in my LF work.  This happens
because the excess image circle that does not touch the film has to go
somewhere.  It is believed this extra light can bounce around and get onto
the film, which reduces contrast, making the chrome look less snappy.   This
is an excellent reason to always use the compendium provided with the
camera.  It drastically reduces unwanted light from hitting the film.

Hope this helps some....

Regards
Bill G



----- Original Message -----
From: "George Pearl" <alps007@xxxxxxxxxxxxxx>
To: <panorama-l@xxxxxxxxxxxxxxxxx>
Sent: Monday, August 07, 2000 9:32 AM
Subject: Re: One hour sunset picture exposures?


> Hi Bill and others...
> I have both kinds of cameras. I have shot the 65 Roundshot using 70mm film
> at wide open f/4.5 for stadium shots at night with superior results in
> sharpness. I don't have enough experience with the 220VR to make any
> worthwhile comment on the use of the Nikor lenses on that camera, except
> that all jobs shot with the camera have produced great shots so far. I
have
> had one soft focus problem using the 300mm lens set at 100 meters though.
I
> am not sure why that happened yet, and will need to test it. The lens is
> tack sharp. I have been using the 220VR to shoot some sunsets with the
135mm
> and the 85mm lenses (Nikon), and the shots were in the 3 or 5 minute range
> using 400 Portra film. I usually stop down 2 or 3 stops and let her rip.
The
> pictures are sharp with no grain printed 48" long. I really don't think
the
> lens has that much to do with the sharpness of these rotational cameras as
> does the proper film speed through the camera in relation to the rotating
> speed of the camera. I have heard that stopping way down with these
cameras
> really doesn't do much for sharpness. Is that a fact? Who really knows the
> answer of sharpness here? Looks like this will take a bunch of testing to
> come up with a true answer.
> My best,
> George S. Pearl, BCQDE, BCEP, FEPIC, QPP
> ALPS - Evidence & Photo
> 2139 Liddell Drive, NE
> Atlanta, GA 30324-4132
>
> Tel: 404/872-2577
> National: 1-800-USE-ALPS
> Fax: 404/872-0548
> Home: 404/634-1139
> Cell: 404/771-9121
> ALPS Website: "http://www.ALPSLABS.com"
> Atlanta Panorama is a division of ALPS...
> "http://www.AtlantaPanorama.com"
>
>
> ----- Original Message -----
> From: "Bill Glickman" <bglick@xxxxxxxx>
> To: <panorama-l@xxxxxxxxxxxxxxxxx>
> Sent: Sunday, August 06, 2000 3:18 AM
> Subject: Re: One hour sunset picture exposures?
>
>
> > George,
> >
> >     I guess I should have explained further... I do not shoot the shot
if
> it
> > needs 30 minutes at sunset... I was just stating that if one shoots a
180
> > deg. sunset, even with 200 speed film, its not uncommon at f 16 to see
30
> > minute exposures.... hence the benefit of MF lenses over LF lenses,
> whereas
> > at least we have the option to shoot at 5.6 to reduce the 30 minutes
down
> to
> > say 4 minutes, which is a bit more feasible.  The fixed fl roundshot
70's
> > use LF lenses which the MTF curves make it mandatory they shoot at 16 or
> > above.  That was my point... make more sense now?
> >
> > Regards
> > Bill G
> >
> >
> >
> > ----- Original Message -----
> > From: "George Pearl" <alps007@xxxxxxxxxxxxxx>
> > To: <panorama-l@xxxxxxxxxxxxxxxxx>
> > Sent: Saturday, August 05, 2000 4:05 PM
> > Subject: One hour sunset picture exposures?
> >
> >
> > > Bill, will you please tell me just how you can take a one hour sunset
> > > picture? By the time you get through taking so long of a sunset,  one
> half
> > > of the panorama would be in sun while the other half would be in total
> > > darkness wouldn't it? Or do you start the exposure say...55 minutes
> before
> > > official sunset? What do you do?
> > > Just wondering.
> > > My best,
> > > George Pearl,
> > > Atlanta, GA
> > >
> > > ----- Original Message -----
> > > From: "Bill Glickman" <bglick@xxxxxxxx>
> > > To: <panorama-l@xxxxxxxxxxxxxxxxx>
> > > Sent: Friday, August 04, 2000 2:18 PM
> > > Subject: Re: interchangeable lenses vs. fixed focal length
> > >
> > >
> > > > From my experience, yes and no.  Yes if you do not tweak the
> > > interchangeable
> > > > camera so its near perfect.  No, if you masterfully tweak your
lenses.
> > > One
> > > > major benefit often overlooked with interchangeable lens cameras
like
> > the
> > > > 220 VR is that MF lenses are designed to be shot at wide apt., while
> the
> > > LF
> > > > lenses used on the fixed fl cameras produce their sharpest images at
> > small
> > > > apt. like f16 and higher.  This can make for some very long
> > exposures....
> > > > not uncommon for me to see 30  minutes to an hour during sunset
shots
> at
> > > 180
> > > > Deg. with 200 ISO film...
> > > >
> > > > Bill G
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Katherine Enos" <enos@xxxxxxxxxxx>
> > > > To: <panorama-l@xxxxxxxxxxxxxxxxx>
> > > > Sent: Saturday, July 01, 2000 11:34 AM
> > > > Subject: interchangeable lenses vs. fixed focal length
> > > >
> > > >
> > > > > Do rotational cameras that use one fixed focal length lens tend to
> > > achieve
> > > > > higher quality (sharpness over the entire film plane?) than those
> that
> > > are
> > > > > made to take lenses of numerous focal lengths?
> > > > >
> > > >
> > >
> >
>