MF lens on digital body

On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an 80mm
lens on 35mm film. You should understand, though, that the focal length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like you
would use a 50mm lens on a manual body. They would give roughly the same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

...or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.

--
Owamanga!

On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an 80mm
lens on 35mm film. You should understand, though, that the focal length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like you
would use a 50mm lens on a manual body. They would give roughly the same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

...or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.

--
Owamanga!

On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an 80mm
lens on 35mm film. You should understand, though, that the focal length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like you
would use a 50mm lens on a manual body. They would give roughly the same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

...or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.

--
Owamanga!

"Owamanga" wrote in message
...
On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm
frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if
you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an
80mm
lens on 35mm film. You should understand, though, that the focal
length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like
you
would use a 50mm lens on a manual body. They would give roughly the
same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

..or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.


Well, as I understand it, DOF will be different. The effect of OOF areas
will be different. I would say that distortion is worth taking into account
as well, seeing as different FL lenses are made to different tolerances,
designs and for different purposes.
So, no, it's not going to look the same. Of course, this might only seem
like a small difference in real-world scenarios, but I think it's well worth
taking into consideration.

Chris.

"Owamanga" wrote in message
...
On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm
frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if
you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an
80mm
lens on 35mm film. You should understand, though, that the focal
length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like
you
would use a 50mm lens on a manual body. They would give roughly the
same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

..or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.


Well, as I understand it, DOF will be different. The effect of OOF areas
will be different. I would say that distortion is worth taking into account
as well, seeing as different FL lenses are made to different tolerances,
designs and for different purposes.
So, no, it's not going to look the same. Of course, this might only seem
like a small difference in real-world scenarios, but I think it's well worth
taking into consideration.

Chris.

"Owamanga" wrote in message
...
On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm
frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if
you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an
80mm
lens on 35mm film. You should understand, though, that the focal
length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like
you
would use a 50mm lens on a manual body. They would give roughly the
same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

..or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.


Well, as I understand it, DOF will be different. The effect of OOF areas
will be different. I would say that distortion is worth taking into account
as well, seeing as different FL lenses are made to different tolerances,
designs and for different purposes.
So, no, it's not going to look the same. Of course, this might only seem
like a small difference in real-world scenarios, but I think it's well worth
taking into consideration.

Chris.

So you can't just put a 28mm lens on a digital body, and use it like you
would use a 50mm lens on a manual body. They would give roughly the same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

Er... I can understand why the depth of field would be different, but not
the perspective. Same vantage point, same angle of view. What's different?

So you can't just put a 28mm lens on a digital body, and use it like you
would use a 50mm lens on a manual body. They would give roughly the same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

Er... I can understand why the depth of field would be different, but not
the perspective. Same vantage point, same angle of view. What's different?

On Tue, 19 Oct 2004 17:28:51 +0000 (UTC), "Chris B"
wrote:


"Owamanga" wrote in message
.. .
On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm
frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if
you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an
80mm
lens on 35mm film. You should understand, though, that the focal
length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like
you
would use a 50mm lens on a manual body. They would give roughly the
same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

..or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.


Well, as I understand it, DOF will be different. The effect of OOF areas
will be different. I would say that distortion is worth taking into account
as well, seeing as different FL lenses are made to different tolerances,
designs and for different purposes.
So, no, it's not going to look the same. Of course, this might only seem
like a small difference in real-world scenarios, but I think it's well worth
taking into consideration.

Chris.

So, a 70mm at f8 on a 1.5x DSLR is going to have a different DOF than
a 105mm at f8 on an SLR for a subject that is the same distance from
the camera in both cases. I hadn't realized that, and I don't see why
it should. Does anyone know how to calculate the effective f-stop
conversion required to keep a similar DOF between both setups?

Of course a 70mm and 105mm have different DOFs at the same f-stop, but
that 70mm (which would have a wider DOF than the 105mm) on the DSLR
isn't behaving like a 70mm, it's behaving like a 105mm so I would
expect the DOF to be the same as the 105mm on the SLR.

At any rate, I've taken about 300 shots on a DSLR, with about 50
different subjects and haven't noticed any widening of the DOF
compared to my SLR. (Haven't done side-by-side tests though)

I still don't think lens distortion is that relevant - it is primarily
present in the areas of the wider angle shot that are being cropped
away, the DSLR concentrates instead on the less distorted central lens
area. All lenses distort somewhat from tele to wide, it's just much
more apparent at wider angles.


--
Owamanga!

On Tue, 19 Oct 2004 17:28:51 +0000 (UTC), "Chris B"
wrote:


"Owamanga" wrote in message
.. .
On Tue, 19 Oct 2004 15:38:48 +0000 (UTC), "Chris B"
wrote:


"John Honan" wrote in message
...
Chris B wrote:
It still has the same focal length, but the field of view changes -
generally digital camera CCDs have a smaller sensors than a 35mm
frame,
so
less of the rendered image is recorded by the CCD than by 35mm film.

You can talk about '35mm equivalent' focal lengths though - IIRC if
you
put
a 50mm lens on a DSLR it would probably be roughly equivalent to an
80mm
lens on 35mm film. You should understand, though, that the focal
length
hasn't really changed, it's just less is recorded by the sensor.

Hope that made sense.

That makes sense, thanks Chris.

I can understand the piece about the digital sensor area being smaller
than the film area (and therefore only 'seeing' a smaller part of the
image), which is why I asked the question.

So in moving from film to digital body, your existing wide-angle lenses
would become medium-ish. i.e. put your old 28mm on the digital body and
you'll get a field of view equivalent to a 50mm. However, it will still
act like a 28mm in the way it treats perspective in foreground objects
(for example)

So you can't just put a 28mm lens on a digital body, and use it like
you
would use a 50mm lens on a manual body. They would give roughly the
same
field of view, but they would treat perspective in different ways.

Yep, you've got it!

:-)

Chris.

Well, you lost me. Got the 1.5x multiplication thing due to smaller
sensor size, but what does 'treat perspective in different ways mean?'
- are we talking about barrel/pincusion distortion of the lens?

Ignoring distortion issues, a zoomed/cropped portion of a wide-angle
shot would overlay exactly a tele shot of the same scene.

..or are you suggesting that a 70mm lens on a DSLR is not going to
look the same as a 105mm lens on an SLR - if so, I don't agree.


Well, as I understand it, DOF will be different. The effect of OOF areas
will be different. I would say that distortion is worth taking into account
as well, seeing as different FL lenses are made to different tolerances,
designs and for different purposes.
So, no, it's not going to look the same. Of course, this might only seem
like a small difference in real-world scenarios, but I think it's well worth
taking into consideration.

Chris.

So, a 70mm at f8 on a 1.5x DSLR is going to have a different DOF than
a 105mm at f8 on an SLR for a subject that is the same distance from
the camera in both cases. I hadn't realized that, and I don't see why
it should. Does anyone know how to calculate the effective f-stop
conversion required to keep a similar DOF between both setups?

Of course a 70mm and 105mm have different DOFs at the same f-stop, but
that 70mm (which would have a wider DOF than the 105mm) on the DSLR
isn't behaving like a 70mm, it's behaving like a 105mm so I would
expect the DOF to be the same as the 105mm on the SLR.

At any rate, I've taken about 300 shots on a DSLR, with about 50
different subjects and haven't noticed any widening of the DOF
compared to my SLR. (Haven't done side-by-side tests though)

I still don't think lens distortion is that relevant - it is primarily
present in the areas of the wider angle shot that are being cropped
away, the DSLR concentrates instead on the less distorted central lens
area. All lenses distort somewhat from tele to wide, it's just much
more apparent at wider angles.


--
Owamanga!