[rollei_list] Re: Rolleiflex 35mm Cameras
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 11 Nov 2009 15:45:59 -0300
Hi Austin
I’m a practical photographer and this is an example: if
you have a normal lens (f.e.) and you like a fountain in the square
(f.e.) and you also like the size it appears in the viewfinder from
the distance you are focusing it, but for some reason you also would
like a bigger size for the church in the background keeping the image
size for the fountain in the foreground as you saw it with the normal
lens, the solution could be to use a telephoto focusing the fountain
from a longer distance than with the normal lens, being the distance
enough to reproduce a similar relative size for the fountain according
you saw it with the normal lens; due to the telephoto magnification
and design, you also will get your bigger church in the background;
but, what is happening with your exposure and your DOF?: if your
exposure was f11 with the normal lens, it will be f11 probably with
the tele since you are exposing for the fountain in the foreground and
the DOF will be similar because you cancelled the factor different
Focal Length for the DOF walking the right distance with your tele
lens, it was necessary this real action to cancel the FL factor. Using
the same DOF calculator I mentioned yesterday, I have that with a 50mm
lens, the fountain focused at 5 metres and f11, the DOF area is 12.3m;
now I want my bigger church in the background and the same size for my
fountain, I use a 135mm lens, the fountain focused at 17.3m, F11,the
DOF area is identical, 12.3m. I did it several times and I always knew
it as a practical knowledge, in fact a basic knowledge that you can
learn taking photos without to read any book or web page, but note
that my main interest was to increase the background size and not to
equal the DOF for both lenses.
The initial poster wrote: " It can be argued that DOF is purely a
function of aperture and not FL.". It was my error to cross this so
brief statement without to ask a major explanation, I was really doing
a parallel work and had no time to read the quoted web pages in
detail, I open one of them, saw a lot of equations and closed it
again, the initial poster did not explain his opinion or position. It
was by night that I had more time and read again your post saying I
was not considering the subject relative size and then suddenly I
realized what you were talking about, it's something so obvious to me
that perhaps it was one of the reasons I did not get the point
initially.
I insist that in practice you only need a DOF calculator or indicator
to take the photograph.
Carlos
2009/11/11, Austin Franklin <austin.franklin@xxxxxxxxxxx>:
> Hi Carlos,
>
> Well, then why on earth did you say Eric was wrong (and continued arguing
> with both Eric and me about it, though you now acknowledge that we weren't
> wrong) if you supposedly already understood all this? Puzzling ;-)
>
> Regards,
>
> Austin
>
> > -----Original Message-----
> > From: rollei_list-bounce@xxxxxxxxxxxxx
> > [mailto:rollei_list-bounce@xxxxxxxxxxxxx]On Behalf Of CarlosMFreaza
> > Sent: Tuesday, November 10, 2009 8:43 PM
> > To: rollei_list@xxxxxxxxxxxxx
> > Subject: [rollei_list] Re: Rolleiflex 35mm Cameras
> >
> >
> > 1) I understand very well that if you want to keep the same relative
> > image size using a wide angle lens (f.e.35mm) and a telephoto
> > (f.e.135mm), you need to move further away the necessary distance to
> > compensate the telephoto longer focal length; from certain point of
> > view could be useful to keep in mind that even if the main subject in
> > the foreground has a similar size, the background will appear bigger
> > and closer for the telephoto image and then this "compensation" by
> > distance is relative and not absolute. This change for the background
> > perspective and relative size could be desirable or not desirable for
> > the image composition, but this is other issue.
> >
> > 2) I understand very well that given the similar image relative size
> > and keeping the same f stop for both lenses, the DOF will be similar
> > because the aperture is the same, f8 is always f8 for the WA lens and
> > the Tele lens, if the distance from the subject "compensated" the
> > difference for the focal length, DOF must be similar due to the
> > identical f stop.
> >
> > 3)For practical photography, things work different in general, if you
> > put a WA lens on your camera, it's because you want the WA lens angle
> > of view and the DOF provided by its short focal length, you have no
> > reason to think about the relative image size issue regarding the DOF,
> > and similar reasoning for any other focal length, in general you
> > choose the lenses for their different angle of view and the different
> > DOF.
> > Anyway, I accept that for certain marginal situations (like the lack
> > of the right lens for your wishes or necessities) could be useful to
> > know the focusing distance to the subject for two different focal
> > length to obtain a similar DOF for the same given f/stop.
> >
> > 4) As a regular and intensive user of a camera provided with a built
> > in taking lens, I know very well the issues about focusing distance
> > and image relative size.-
> >
> > Carlos
> >
> >
> >
> >
> > 2009/11/10 Mark Rabiner <mark@xxxxxxxxxxxxxxxx>:
> > >> Hi Carlos,
> > >>
> > >> What you're not doing when you use your DOF calculators, is
> > adjusting the
> > >> distance to maintain the same relative image size. That's the
> > point you
> > >> seem to be missing..."same relative image size".
> > >>
> > >> I suggest you read the references Eric so kindly provided.
> > Start by looking
> > >> at the chart titled "DOF for f/8, M ~= 1/20, 35mm format" at
> > the bottom of
> > >> this section:
> > >>
> > >> http://www.normankoren.com/Tutorials/MTF6.html#DOF_focal_length
> > >>
> > >> It shows total DOF for same aperture, different focal lengths,
> > with distance
> > >> adjusted to provide the same relative image size. Note the
> > total DOFs are
> > >> nearly identical for all lenses at the same aperture. Then,
> > ask your self
> > >> why... If you need help understanding that, perhaps someone
> > here would be
> > >> willing to help. But, please read the references first.
> > >>
> > >> Regards,
> > >>
> > >> Austin
> > >
> > >
> > > Another view of what Austin is saying might be:
> > > You put on a wide angle lens and you are getting more in focus
> > front to back
> > > But you also are shooting the whole house not just the front door.
> > > Should you back up with your longer lens to also get the whole
> > house you'd
> > > get just as much front to back as the wide did.
> > >
> > > So every time you change lenses you'd have to move back or
> > forward to get
> > > the same non zoomed in or zoomed out or cropped picture.
> > >
> > > My part is:
> > > At that point your depth of field would be about the same.
> > > Not exactly the same.
> > > But close
> > >
> > >
> > > Mark William Rabiner
> > >
> > >
> > >
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