[rollei_list] Re: Rolleiflex 35mm Cameras
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Tue, 10 Nov 2009 22:42:35 -0300
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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