The real Bigma - or How High The Moon?

On Thu, 30 Nov 2006 09:02:48 -0600, Eric Miller wrote:

That is: the focal length is 1700mm. If you mount it on a camera with a
36mmx24mm sensor, it will behave exactly like a 1700mm lens designed for
that sensor (except for financial purposes). If I then mount it on a
camera with an APS-sized sensor, it's exactly the same as if a 1700mm lens
designed for 36mm by 24mm sensor size had been mounted; thus, multiply by
the crop factor (1.5 or whatever).

What he probably doesn't understand is that, in comparison to FF 35mm, there
is a "reverse crop factor" for medium format. I.e., on the Hassy, a 1700mm
lens would have the same field of view of a much shorter lens on a 35mm
camera.

No. That's exactly the point I tried to make. And the same focal
length lens on an FF camera would have the same field of view as a
shorter lens on the APS camera. So these individual differences, or
let's say, crop factors, would each be less than the crop factor of
an APS sensor that was based on a comparison with a sensor the size
of the Hasselblad's sensor, instead of the more commonly compared FF
(35mm film size) sensor.


Because the 1.6 - 1.5 of APS sensors is a ration derived from
comparison to FF 35mm, you can't use the 1700 focal length as part of the
equation used to determine the effective focal length comparison of APS to
Medium Format.

True, unless it's just a part of a more complex equation.


In order to to compare APS to Medium Format, under the
"comparison to FF 35mm" nomenclature, you would first need to start with the
shorter apparent focal length of Medium Format in comparison to 35mm. So the
medium format film would have a .6, more or less (couldn't find the exact
number), reverse crop factor. So in comparison to the fov on a 35mm camera,
the 1700mm lens would have the same field of view of a 1020mm lens. So if
you want to use the crop factors of both 35mm and APS, then you must start
with 1020mm (more or less) to get the right result. Of course, you should
come up with the same apparent focal length by simply multiplying 1.6 x
1700, but that is apparently just too easy.

Too easy is correct. If the reverse crop factor used for FF and
Hassy comparisons is 0.6, then wouldn't the crop factor of APS
sensors (when compared to Hassy sized sensors) be on the order of
1.6 * (1/0.6)? This would indicate that a 1,700mm lens on the Hassy
would be comparable to 2833mm (1,700 / 0.6) on a FF camera and
4,533mm (1,700 * 1.6 / 0.6) on an APS camera. But a 1,700mm lens on
a FF camera would be comparable to 2,720mm (1,700 * 1.6) on the APS
camera. Based on the last of your sentences quoted above, it would
appear that there's little to no difference between a Hassy sensor
and a FF sensor, since the 1,700mm lens on either would be
comparable to 2,720mm when used with a camera with an APS sensor.
Is that what you really meant or did I misread it?

ASAAR wrote:
Too easy is correct. If the reverse crop factor used for FF and
Hassy comparisons is 0.6, then wouldn't the crop factor of APS
sensors (when compared to Hassy sized sensors) be on the order of
1.6 * (1/0.6)? This would indicate that a 1,700mm lens on the Hassy
would be comparable to 2833mm (1,700 / 0.6) on a FF camera and
4,533mm (1,700 * 1.6 / 0.6) on an APS camera. But a 1,700mm lens on
a FF camera would be comparable to 2,720mm (1,700 * 1.6) on the APS
camera. Based on the last of your sentences quoted above, it would
appear that there's little to no difference between a Hassy sensor
and a FF sensor, since the 1,700mm lens on either would be
comparable to 2,720mm when used with a camera with an APS sensor.
Is that what you really meant or did I misread it?

That 1700mm on an aps camera would behave exactly like a 1700mm lens
designed for a 35mm camera if used in the aps camera. How hard is this
to understand?

On Thu, 30 Nov 2006 15:08:39 -0500, ASAAR wrote:
In order to to compare APS to Medium Format, under the
"comparison to FF 35mm" nomenclature, you would first need to start with the
shorter apparent focal length of Medium Format in comparison to 35mm. So the
medium format film would have a .6, more or less (couldn't find the exact
number), reverse crop factor. So in comparison to the fov on a 35mm camera,
the 1700mm lens would have the same field of view of a 1020mm lens. So if
you want to use the crop factors of both 35mm and APS, then you must start
with 1020mm (more or less) to get the right result. Of course, you should
come up with the same apparent focal length by simply multiplying 1.6 x
1700, but that is apparently just too easy.

Too easy is correct. If the reverse crop factor used for FF and
Hassy comparisons is 0.6, then wouldn't the crop factor of APS
sensors (when compared to Hassy sized sensors) be on the order of
1.6 * (1/0.6)? This would indicate that a 1,700mm lens on the Hassy
would be comparable to 2833mm (1,700 / 0.6) on a FF camera and
4,533mm (1,700 * 1.6 / 0.6) on an APS camera. But a 1,700mm lens on
a FF camera would be comparable to 2,720mm (1,700 * 1.6) on the APS
camera. Based on the last of your sentences quoted above, it would
appear that there's little to no difference between a Hassy sensor
and a FF sensor, since the 1,700mm lens on either would be
comparable to 2,720mm when used with a camera with an APS sensor.
Is that what you really meant or did I misread it?

You're over-complexifying things.

The lens has a focal length of 1700mm. On a 35mm full-frame camera, that
corresponds to a certain field of view. On a camera, like the
Hasselblad, that has a bigger active area, the field of view is bigger.
Hence, the 'blad sees a FOV that is the same as a 35mm camera with a
shorter lens, so the lens has a "Hasselblad-effective" focal length of
maybe 1000mm.

On a camera with a smaller active area (ie an APS-C sensor
camera), the field of view is smaller, corresponding to what a 35mm
camera would see if it had a 2800mm lens.

-dms

"acl" wrote in message
...
SimonLW wrote:
"ASAAR" wrote in message
...
From the Dec. PP&I comes a brief mention of a new Zeiss lens,
custom manufactured for a private client. Intended for use on a
Hasselblad 203 FE to "photograph wildlife at a great distance", its
focal length is 1700mm and weighs in at 564 pounds. Aperture and
cost not given, but a small photo of this BWL is on the bottom
corner of page 18. Anybody know what the effective focal length
would be if it could be adapted for use with an APS sensor DSLR?

If my calcs are any good, it gives the angle of view of something like a
5200mm.
-S

Am I missing something here? If it is 1700mm, then it's 1700mm,
irrespective of which part of the image you crop. Or do you all mean
something else that I am missing?

The key term is "angle of view". Many compact digital cameras have zoom
lenses of, say, only 5 to 23mm. This means little to the typical user
because there are numerous sensor sizes. Manufacturers often list the
equivalent focal length for the same angle of view the lens provides if it
were designed for a 35mm film camera. 35mm is often used as a standard due
to it's former popularity. In this example it could be a 38 to 140mm lens.

Most people are familiar that a 50mm on a 35 mm camera is about "normal",
not wide nor long. If it were possible to mount that 50mm lens on a digital
compact camera, the FOV becomes equivalent to about 400mm lens on 35mm.

If that hassy is 6x6 film, the diagonal measurement across the film plain is
about 3 times that of a APS sensored dSLR, thus the angle of view shrinks
down as if it were a 5200mm equiv. lens on the hassy.
-S

nospam wrote:
In article , David J. Littleboy
wrote:


"Never before has the world of photography seen such a lens. The ZEISS
Apo Sonnar T* 4/1700 was developed by Carl Zeiss for a customer with
very high demands and a special interest in long distance wildlife
photography." dpreview

Actually this Zeiss statement is hype: Canon made 5000mm lenses for the
.....


this one?

http://www.canonfd.com/mirrorlenses/pages/page10.html
Talking about hype:
"...this is the only lens in the world capable of thaking photographs
of objects 18 to 32 miles away..."
What is that supposed to mean ?
I guess that I am missing something, I would have said that all lenses
are capable of taking picture of objects at any distance (greater than
the minimum focus distance). Or is there something special about the
18-32 miles range ?

On 30 Nov 2006 12:24:12 -0800, acl wrote:

That 1700mm on an aps camera would behave exactly like a 1700mm lens
designed for a 35mm camera if used in the aps camera. How hard is this
to understand?

I understand that perfectly well. I've already acknowledged that.
How hard it is for YOU to understand this?

On Thu, 30 Nov 2006 20:25:08 GMT, Daniel Silevitch wrote:

Too easy is correct. If the reverse crop factor used for FF and
Hassy comparisons is 0.6, then wouldn't the crop factor of APS
sensors (when compared to Hassy sized sensors) be on the order of
1.6 * (1/0.6)? This would indicate that a 1,700mm lens on the Hassy
would be comparable to 2833mm (1,700 / 0.6) on a FF camera and
4,533mm (1,700 * 1.6 / 0.6) on an APS camera. But a 1,700mm lens on
a FF camera would be comparable to 2,720mm (1,700 * 1.6) on the APS
camera. Based on the last of your sentences quoted above, it would
appear that there's little to no difference between a Hassy sensor
and a FF sensor, since the 1,700mm lens on either would be
comparable to 2,720mm when used with a camera with an APS sensor.
Is that what you really meant or did I misread it?

You're over-complexifying things.

The lens has a focal length of 1700mm. On a 35mm full-frame camera, that
corresponds to a certain field of view. On a camera, like the
Hasselblad, that has a bigger active area, the field of view is bigger.
Hence, the 'blad sees a FOV that is the same as a 35mm camera with a
shorter lens, so the lens has a "Hasselblad-effective" focal length of
maybe 1000mm.

On a camera with a smaller active area (ie an APS-C sensor
camera), the field of view is smaller, corresponding to what a 35mm
camera would see if it had a 2800mm lens.

You're missing the point.

With the 1,700mm lens as used on an APS camera, what focal length
would be needed to get the same FOV on an FF camera? I get 1,700 *
1.6, or 2,720mm.

With the 1,700mm lens as used on an APS camera, what focal length
would be needed to get the same FOV on the Hasselblad? I get 1,700
* 1.6 * (1/0.6), or 4,533mm. The 1/0.6 factor was based on Eric's
reverse crop factor of 0.6, used for comparing the Hasselblad with
an FF camera. Would you get a focal length substantially different
than 4,533mm?

SimonLW wrote:
"acl" wrote in message
...
SimonLW wrote:
"ASAAR" wrote in message
...
From the Dec. PP&I comes a brief mention of a new Zeiss lens,
custom manufactured for a private client. Intended for use on a
Hasselblad 203 FE to "photograph wildlife at a great distance", its
focal length is 1700mm and weighs in at 564 pounds. Aperture and
cost not given, but a small photo of this BWL is on the bottom
corner of page 18. Anybody know what the effective focal length
would be if it could be adapted for use with an APS sensor DSLR?

If my calcs are any good, it gives the angle of view of something like a
5200mm.
-S

Am I missing something here? If it is 1700mm, then it's 1700mm,
irrespective of which part of the image you crop. Or do you all mean
something else that I am missing?

The key term is "angle of view". Many compact digital cameras have zoom
lenses of, say, only 5 to 23mm. This means little to the typical user
because there are numerous sensor sizes. Manufacturers often list the
equivalent focal length for the same angle of view the lens provides if it
were designed for a 35mm film camera. 35mm is often used as a standard due
to it's former popularity. In this example it could be a 38 to 140mm lens.

Most people are familiar that a 50mm on a 35 mm camera is about "normal",
not wide nor long. If it were possible to mount that 50mm lens on a digital
compact camera, the FOV becomes equivalent to about 400mm lens on 35mm.

If that hassy is 6x6 film, the diagonal measurement across the film plain is
about 3 times that of a APS sensored dSLR, thus the angle of view shrinks
down as if it were a 5200mm equiv. lens on the hassy.

I understand this. The question was (I quote): "Anybody know what the
effective focal length would be if it could be adapted for use with an
APS sensor DSLR?". Your answer was that it gives an angle of view "of
something like 5200mm", which I interpret to mean "equivalent to a
5200mm lens on a 35mm camera". Well, this is not true. Used on a Nikon
(say) APS camera, it would give an angle of view equivalent to 2550mm
for 135mm film. This is for the reasons I already mentioned.

The question you are actually answering is: "If I use a 1700mm lens on
an APS SLR, it would give a FOV equivalent to what focal length on
6x6?". To which your answer is indeed correct! Somewhere there was bad
communication...

ASAAR wrote:
On Thu, 30 Nov 2006 20:25:08 GMT, Daniel Silevitch wrote:

Too easy is correct. If the reverse crop factor used for FF and
Hassy comparisons is 0.6, then wouldn't the crop factor of APS
sensors (when compared to Hassy sized sensors) be on the order of
1.6 * (1/0.6)? This would indicate that a 1,700mm lens on the Hassy
would be comparable to 2833mm (1,700 / 0.6) on a FF camera and
4,533mm (1,700 * 1.6 / 0.6) on an APS camera. But a 1,700mm lens on
a FF camera would be comparable to 2,720mm (1,700 * 1.6) on the APS
camera. Based on the last of your sentences quoted above, it would
appear that there's little to no difference between a Hassy sensor
and a FF sensor, since the 1,700mm lens on either would be
comparable to 2,720mm when used with a camera with an APS sensor.
Is that what you really meant or did I misread it?

You're over-complexifying things.

The lens has a focal length of 1700mm. On a 35mm full-frame camera, that
corresponds to a certain field of view. On a camera, like the
Hasselblad, that has a bigger active area, the field of view is bigger.
Hence, the 'blad sees a FOV that is the same as a 35mm camera with a
shorter lens, so the lens has a "Hasselblad-effective" focal length of
maybe 1000mm.

On a camera with a smaller active area (ie an APS-C sensor
camera), the field of view is smaller, corresponding to what a 35mm
camera would see if it had a 2800mm lens.

You're missing the point.

With the 1,700mm lens as used on an APS camera, what focal length
would be needed to get the same FOV on an FF camera? I get 1,700 *
1.6, or 2,720mm.

With the 1,700mm lens as used on an APS camera, what focal length
would be needed to get the same FOV on the Hasselblad? I get 1,700
* 1.6 * (1/0.6), or 4,533mm. The 1/0.6 factor was based on Eric's
reverse crop factor of 0.6, used for comparing the Hasselblad with
an FF camera. Would you get a focal length substantially different
than 4,533mm?

Well, you actually asked:
Anybody know what the effective focal length
would be if it could be adapted for use with an APS sensor DSLR?
And now you're saying that this actually means "what FL on the Hassy
would correspond to 1700mm on an APS SLR"?

Last time I waste time with your posts.

"acl" wrote in message
oups.com...

SimonLW wrote:
"acl" wrote in message
...
SimonLW wrote:
"ASAAR" wrote in message
...
From the Dec. PP&I comes a brief mention of a new Zeiss lens,
custom manufactured for a private client. Intended for use on a
Hasselblad 203 FE to "photograph wildlife at a great distance", its
focal length is 1700mm and weighs in at 564 pounds. Aperture and
cost not given, but a small photo of this BWL is on the bottom
corner of page 18. Anybody know what the effective focal length
would be if it could be adapted for use with an APS sensor DSLR?

If my calcs are any good, it gives the angle of view of something like
a
5200mm.
-S

Am I missing something here? If it is 1700mm, then it's 1700mm,
irrespective of which part of the image you crop. Or do you all mean
something else that I am missing?

The key term is "angle of view". Many compact digital cameras have zoom
lenses of, say, only 5 to 23mm. This means little to the typical user
because there are numerous sensor sizes. Manufacturers often list the
equivalent focal length for the same angle of view the lens provides if
it
were designed for a 35mm film camera. 35mm is often used as a standard
due
to it's former popularity. In this example it could be a 38 to 140mm
lens.

Most people are familiar that a 50mm on a 35 mm camera is about "normal",
not wide nor long. If it were possible to mount that 50mm lens on a
digital
compact camera, the FOV becomes equivalent to about 400mm lens on 35mm.

If that hassy is 6x6 film, the diagonal measurement across the film plain
is
about 3 times that of a APS sensored dSLR, thus the angle of view shrinks
down as if it were a 5200mm equiv. lens on the hassy.

I understand this. The question was (I quote): "Anybody know what the
effective focal length would be if it could be adapted for use with an
APS sensor DSLR?". Your answer was that it gives an angle of view "of
something like 5200mm", which I interpret to mean "equivalent to a
5200mm lens on a 35mm camera". Well, this is not true. Used on a Nikon
(say) APS camera, it would give an angle of view equivalent to 2550mm
for 135mm film. This is for the reasons I already mentioned.

I don't assume eveyone knows about the "effective FL issue" clearly. The
last line in my previous post answered the question.
Your 2550mm "effective FL on 35mm is not correct. 6x6 has a diagonal measure
(~85mm) of about twice that of the 35mm film frame (43mm). This gives is
about 2x crop so the lens is effective 3400mm. On a APS sensor, the diagonal
of the 6x6 frame is 3 times so the efective FL is around 5000mm.

The question you are actually answering is: "If I use a 1700mm lens on
an APS SLR, it would give a FOV equivalent to what focal length on
6x6?". To which your answer is indeed correct! Somewhere there was bad
communication...