# Power Factors,,,Hmmmmm

Discussion in 'Digital Photography' started by Nick Beard, Jan 10, 2005.

1. ### Nick BeardGuest

Ok Smithers,, Now for some real math.

I have two bodies, a D70 and a F100. I want to use a 200mm zoom with a 1.7
converter. What I am trying to work out is the multiplication factor or X
factor (dont ask!!..I like challenges ) from the standard view which would
be 50mm for the film body and 35mm for the digital. Ok so far?

I have no probs with the film calc but the digital X factor seem way to
high. Here is what I have:

Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!

Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This seem
way too much. If it is correct as it seems then this could explain why some
digital products show a mad X factor a la digital camcorders and certain P&S
jobs

Ok let take your flack....ouch not too hard!!!!

Nick Beard, Jan 10, 2005

2. ### Siddhartha JainGuest

Nick Beard wrote:
> Ok Smithers,, Now for some real math.
>
> I have two bodies, a D70 and a F100. I want to use a 200mm zoom with

a 1.7
> converter. What I am trying to work out is the multiplication factor

or X
> factor (dont ask!!..I like challenges ) from the standard view which

would
> be 50mm for the film body and 35mm for the digital. Ok so far?
>
> I have no probs with the film calc but the digital X factor seem way

to
> high. Here is what I have:
>
> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>
> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This

seem
> way too much. If it is correct as it seems then this could explain

why some
> digital products show a mad X factor a la digital camcorders and

certain P&S
> jobs
>

Perspective yes, magnification no.

Siddhartha Jain, Jan 10, 2005

3. ### scottGuest

"Nick Beard" <> wrote in message
news:crujrk\$ksg\$1\$
> Ok Smithers,, Now for some real math.
>
> I have two bodies, a D70 and a F100. I want to use a 200mm zoom
> with a 1.7 converter. What I am trying to work out is the
> multiplication factor or X factor (dont ask!!..I like challenges )
> from the standard view which would be 50mm for the film body and
> 35mm for the digital. Ok so far?
> I have no probs with the film calc but the digital X factor seem
> way to high. Here is what I have:
>
> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>
> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This seem
> way too much. If it is correct as it seems then this
> could explain why some digital products show a mad X factor a la
> digital camcorders and certain P&S jobs
>
> Ok let take your flack....ouch not too hard!!!!

Your lens is 200 mm times 1.7 for the converter, that is 340 mm.

That is 6.8X bigger than 50 mm or 9.7X bigger than 35 mm.

scott, Jan 10, 2005
4. ### Nick BeardGuest

>
> Your lens is 200 mm times 1.7 for the converter, that is 340 mm.
>
> That is 6.8X bigger than 50 mm or 9.7X bigger than 35 mm.

You follow me for the top 'Film' calc o.k but the in the digital calc it
would be the equiv of 510 not 340 mm in respects to 35 Film
therefore it seems that 510 mm is 14.57X bigger than 35 mm (which provides a
'standard view on digital D70)
Remember I am taking the 'standard lens' as a datum point i.e film 50 mm /
dig 35 mm.

Next!!

Nick Beard, Jan 10, 2005
5. ### Nick BeardGuest

> Your lens is 200 mm times 1.7 for the converter, that is 340 mm.
>
> That is 6.8X bigger than 50 mm or 9.7X bigger than 35 mm.

Ah yes, but for the digital you are working with a 510 mm equiv in 35mm film
due to the 1.5 x crop factor.
I know were talking perceived focal length but this is what we have on the
D70 with this setup. And the standard view on the D70 is still found using a
35 mm lens which times 14.57X

Nick Beard, Jan 10, 2005
6. ### Jim TownsendGuest

Nick Beard wrote:

> Ok Smithers,, Now for some real math.
>
> I have two bodies, a D70 and a F100. I want to use a 200mm zoom with a 1.7
> converter. What I am trying to work out is the multiplication factor or X
> factor (dont ask!!..I like challenges ) from the standard view which would
> be 50mm for the film body and 35mm for the digital. Ok so far?
>
> I have no probs with the film calc but the digital X factor seem way to
> high. Here is what I have:
>
> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>
> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This seem
> way too much. If it is correct as it seems then this could explain why some
> digital products show a mad X factor a la digital camcorders and certain P&S
> jobs
>
> Ok let take your flack....ouch not too hard!!!!

First off, you're calculating field of view..

200mm x 1.7 = 340mm 340mm x 1.5 = 510mm 510mm/50mm = 10.2x

But.. *You aren't gaining any magnification from the lens*. You're
reducing the field of view due to the fact a portion of the image is
falling outside boundaries of the sensor.

You'll have an actual focal length of 350mm with the field of view of
a 510mm lens.

The 'magnification' doesn't take place until you *print* the image. This
is hard to comprehend with digital cameras because the images produced
have no physical size to make comparisons.

Consider using a 35mm film camera, taking two identical shots, then
cropping an APS sized chunk out of the middle of one of the negatives.

Now, using an enlarger, make two 6"x 4" prints, one using the full negative
and the other using the APS sized crop.

To make a 4x6 print out of the piece you cut out, you'd have to enlarge
the APS sized section 1.5x *more* than you have to enlarge the complete
35mm negative.

This extra enlarging at the time the image is printed is what causes the
apparent magnification. The only difference is that with digital,
the crop takes place at the time the image is shot. The crop occurs
because s portion of the focused image falls outside of the sensor.

The fact that part of the image didn't land on the sensor can't alter
the focal length or the magnification of the lens in any way.

Jim Townsend, Jan 10, 2005
7. ### Nick BeardGuest

Ooookay!!

"scott" <> wrote in message
news:geBEd.779\$...
> "Nick Beard" <> wrote in message
> news:crujrk\$ksg\$1\$
>> Ok Smithers,, Now for some real math.
>>
>> I have two bodies, a D70 and a F100. I want to use a 200mm zoom
>> with a 1.7 converter. What I am trying to work out is the
>> multiplication factor or X factor (dont ask!!..I like challenges )
>> from the standard view which would be 50mm for the film body and
>> 35mm for the digital. Ok so far?
>> I have no probs with the film calc but the digital X factor seem
>> way to high. Here is what I have:
>>
>> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>>
>> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This seem
>> way too much. If it is correct as it seems then this
>> could explain why some digital products show a mad X factor a la
>> digital camcorders and certain P&S jobs
>>
>> Ok let take your flack....ouch not too hard!!!!

>
> Your lens is 200 mm times 1.7 for the converter, that is 340 mm.
>
> That is 6.8X bigger than 50 mm or 9.7X bigger than 35 mm.
>
>

Nick Beard, Jan 10, 2005
8. ### scottGuest

"Nick Beard" <> wrote in message
news:cruoo8\$3d9\$1\$
>> Your lens is 200 mm times 1.7 for the converter, that is 340 mm.
>>
>> That is 6.8X bigger than 50 mm or 9.7X bigger than 35 mm.

>
> You follow me for the top 'Film' calc o.k but the in the digital
> calc it would be the equiv of 510 not 340 mm in respects to 35 Film
> therefore it seems that 510 mm is 14.57X bigger than 35 mm (which
> provides a 'standard view on digital D70)

No. If a 35 mm lens provides your "standard view" on a camera, then a 340
mm lens will provide an image zoomed in by 9.7 times on this standard view,
irrespective of whatever camera you are using.

If on another camera you think 50 mm provides the "standard view", then a
340 mm lens will provide an image zoomed in by 6.8 times on this standard
view.

If on another camera, you think 5 mm provides the "standard view" (ie P&S
camera) then a 340 mm lens will provide an image zoomed in by 68 times
compared to this standard view.

scott, Jan 10, 2005
9. ### Nick BeardGuest

Thanks Jim, I understand your analogy well.
It is just if you take the end perceived result of the 1.5X cropped 340 mm
(i.e 510) and the 'standard perspective' of 35 mm lens on a Nikon digital
slr, you come up with some whacky figures as opposed to the film body
calculation

"Jim Townsend" <> wrote in message
news:...
> Nick Beard wrote:
>
>> Ok Smithers,, Now for some real math.
>>
>> I have two bodies, a D70 and a F100. I want to use a 200mm zoom with a
>> 1.7
>> converter. What I am trying to work out is the multiplication factor or X
>> factor (dont ask!!..I like challenges ) from the standard view which
>> would
>> be 50mm for the film body and 35mm for the digital. Ok so far?
>>
>> I have no probs with the film calc but the digital X factor seem way to
>> high. Here is what I have:
>>
>> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>>
>> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This
>> seem
>> way too much. If it is correct as it seems then this could explain why
>> some
>> digital products show a mad X factor a la digital camcorders and certain
>> P&S
>> jobs
>>
>> Ok let take your flack....ouch not too hard!!!!

>
> First off, you're calculating field of view..
>
>
> 200mm x 1.7 = 340mm 340mm x 1.5 = 510mm 510mm/50mm = 10.2x
>
> But.. *You aren't gaining any magnification from the lens*. You're
> reducing the field of view due to the fact a portion of the image is
> falling outside boundaries of the sensor.
>
> You'll have an actual focal length of 350mm with the field of view of
> a 510mm lens.
>
> The 'magnification' doesn't take place until you *print* the image. This
> is hard to comprehend with digital cameras because the images produced
> have no physical size to make comparisons.
>
> Consider using a 35mm film camera, taking two identical shots, then
> cropping an APS sized chunk out of the middle of one of the negatives.
>
> Now, using an enlarger, make two 6"x 4" prints, one using the full
> negative
> and the other using the APS sized crop.
>
> To make a 4x6 print out of the piece you cut out, you'd have to enlarge
> the APS sized section 1.5x *more* than you have to enlarge the complete
> 35mm negative.
>
> This extra enlarging at the time the image is printed is what causes the
> apparent magnification. The only difference is that with digital,
> the crop takes place at the time the image is shot. The crop occurs
> because s portion of the focused image falls outside of the sensor.
>
> The fact that part of the image didn't land on the sensor can't alter
> the focal length or the magnification of the lens in any way.
>
>

Nick Beard, Jan 10, 2005
10. ### Colin DGuest

Nick Beard wrote:
>
> Ok Smithers,, Now for some real math.
>
> I have two bodies, a D70 and a F100. I want to use a 200mm zoom with a 1.7
> converter. What I am trying to work out is the multiplication factor or X
> factor (dont ask!!..I like challenges ) from the standard view which would
> be 50mm for the film body and 35mm for the digital. Ok so far?
>
> I have no probs with the film calc but the digital X factor seem way to
> high. Here is what I have:
>
> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>
> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This seem
> way too much. If it is correct as it seems then this could explain why some
> digital products show a mad X factor a la digital camcorders and certain P&S
> jobs
>
> Ok let take your flack....ouch not too hard!!!!

Your first equation should be 200 x 1.7 = 340: 340/50 = 6.8x (note the

Your second equation is wrong, since you have applied the crop factor
twice - once when you set the standard lens at 35, and again when you
included the 1.5x crop factor. If you include the 1.5x crop factor then
you must use the 50mm lens in the equation.

Colin

Colin D, Jan 11, 2005
11. ### Nick BeardGuest

Now this makes a little more sense, thanks. I thought I was applying it
twice but I could'nt see where. And thanks for pointing out my typo + istead
of =. I hit the 'shift' key to much, I knew what I meant though.

So the 'manipulated' X factor is 10.2X as stated by Jim. In any event it is
greater than 6.8X on the Film body.

Cool!

"Colin D" <ColinD@killspam.127.0.0.1> wrote in message
news:41E32013.3CD88390@killspam.127.0.0.1...
>
>
> Nick Beard wrote:
>>
>> Ok Smithers,, Now for some real math.
>>
>> I have two bodies, a D70 and a F100. I want to use a 200mm zoom with a
>> 1.7
>> converter. What I am trying to work out is the multiplication factor or X
>> factor (dont ask!!..I like challenges ) from the standard view which
>> would
>> be 50mm for the film body and 35mm for the digital. Ok so far?
>>
>> I have no probs with the film calc but the digital X factor seem way to
>> high. Here is what I have:
>>
>> Film - 200 X 1.7 + 340 / 50 = 6.8X. Ok this is perfect!
>>
>> Digital - 200 X 1.5 crop factor = 300 X 1.7 = 510 / 35 = 14.57X This
>> seem
>> way too much. If it is correct as it seems then this could explain why
>> some
>> digital products show a mad X factor a la digital camcorders and certain
>> P&S
>> jobs
>>
>> Ok let take your flack....ouch not too hard!!!!

>
> Your first equation should be 200 x 1.7 = 340: 340/50 = 6.8x (note the
>
> Your second equation is wrong, since you have applied the crop factor
> twice - once when you set the standard lens at 35, and again when you
> included the 1.5x crop factor. If you include the 1.5x crop factor then
> you must use the 50mm lens in the equation.
>
> Colin

Nick Beard, Jan 11, 2005