Velocity Reviews > Equivalent crop sensor lenses

# Equivalent crop sensor lenses

Peabody
Guest
Posts: n/a

 12-16-2009
Every time I think I understand this, another thought experiment
comes up, and I realize I may not.

So lets say you have a full-frame 35mm DSLR camera (D700, or
whatever) with a fixed 50mm lens, and you take a landscape picture.

Now you move a 1.5X crop-sensor camera (D300) into the same place,
and you want to take a picture with that camera which you want to
have exactly the same field of view as the previous picture - it
shows exactly the same scene.

If the lens on the smaller camera was designed for that size camera
(it's a "DX" lens), what focal length is it?

Does it make any difference that it's a DX lens - would a full-frame
lens produce the same picture in the smaller camera as the DX lens?

My guesses are: To produce the same field of view, the DX lens on
the smaller camera would need to be 33.33mm. And it doesn't make
any difference on the crop-sensor camera whether it's a DX lens or
an "FX" lens, so long as they are both 33.33mm.

Ray Fischer
Guest
Posts: n/a

 12-17-2009
Peabody <(E-Mail Removed)> wrote:
>Every time I think I understand this, another thought experiment
>comes up, and I realize I may not.
>
>So lets say you have a full-frame 35mm DSLR camera (D700, or
>whatever) with a fixed 50mm lens, and you take a landscape picture.
>
>Now you move a 1.5X crop-sensor camera (D300) into the same place,
>and you want to take a picture with that camera which you want to
>have exactly the same field of view as the previous picture - it
>shows exactly the same scene.
>
>If the lens on the smaller camera was designed for that size camera
>(it's a "DX" lens), what focal length is it?

50mm / 1.5x = 33mm

>Does it make any difference that it's a DX lens - would a full-frame
>lens produce the same picture in the smaller camera as the DX lens?

Lenses for dSLRs are almost universally specified in 35mm equivalent
focal length.

>My guesses are: To produce the same field of view, the DX lens on
>the smaller camera would need to be 33.33mm. And it doesn't make
>any difference on the crop-sensor camera whether it's a DX lens or
>an "FX" lens, so long as they are both 33.33mm.

Yep.

--
Ray Fischer
http://www.velocityreviews.com/forums/(E-Mail Removed)

Paul Furman
Guest
Posts: n/a

 12-17-2009
rwalker wrote:
> On Wed, 16 Dec 2009 17:11:36 -0600, Peabody
> <(E-Mail Removed)> wrote:
>
>> Every time I think I understand this, another thought experiment
>> comes up, and I realize I may not.
>>
>> So lets say you have a full-frame 35mm DSLR camera (D700, or
>> whatever) with a fixed 50mm lens, and you take a landscape picture.
>>
>> Now you move a 1.5X crop-sensor camera (D300) into the same place,
>> and you want to take a picture with that camera which you want to
>> have exactly the same field of view as the previous picture - it
>> shows exactly the same scene.
>>
>> If the lens on the smaller camera was designed for that size camera
>> (it's a "DX" lens), what focal length is it?
>>
>> Does it make any difference that it's a DX lens - would a full-frame
>> lens produce the same picture in the smaller camera as the DX lens?
>>
>> My guesses are: To produce the same field of view, the DX lens on
>> the smaller camera would need to be 33.33mm. And it doesn't make
>> any difference on the crop-sensor camera whether it's a DX lens or
>> an "FX" lens, so long as they are both 33.33mm.
>>

>
> Don't know about the DX or FX (My Nikon stuff is very old), but the
> 33.3 is correct.

Yep. It's exactly like cropping (with the pixels jammed in the smaller
space). The DX designation means you'd have dark corners on full frame
because it's only designed to accommodate the smaller cropped view.

The other result is less depth of field, a narrower focus range for the
same lens when it's image finally ends up on a print of the same size.
Cropping obviously doesn't change the absolute DOF but when you print
the same size as the uncropped version it does. That is confusing and
contradictory because you normally would use a wider lens to get the
same view and then the goalposts have moved and you get *more* depth of
field for the same view with a smaller sensor.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

David J Taylor
Guest
Posts: n/a

 12-17-2009
"rwalker" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Wed, 16 Dec 2009 17:11:36 -0600, Peabody
> <(E-Mail Removed)> wrote:
>
>>Every time I think I understand this, another thought experiment
>>comes up, and I realize I may not.
>>
>>So lets say you have a full-frame 35mm DSLR camera (D700, or
>>whatever) with a fixed 50mm lens, and you take a landscape picture.
>>
>>Now you move a 1.5X crop-sensor camera (D300) into the same place,
>>and you want to take a picture with that camera which you want to
>>have exactly the same field of view as the previous picture - it
>>shows exactly the same scene.
>>
>>If the lens on the smaller camera was designed for that size camera
>>(it's a "DX" lens), what focal length is it?
>>
>>Does it make any difference that it's a DX lens - would a full-frame
>>lens produce the same picture in the smaller camera as the DX lens?
>>
>>My guesses are: To produce the same field of view, the DX lens on
>>the smaller camera would need to be 33.33mm. And it doesn't make
>>any difference on the crop-sensor camera whether it's a DX lens or
>>an "FX" lens, so long as they are both 33.33mm.
>>

>
> Don't know about the DX or FX (My Nikon stuff is very old), but the
> 33.3 is correct.

Agreed. However, if the full-frame (FX) camera had an f/4 lens used at
f/4, what aperture lens would be required:

- for the same depth-of-field
- for the same light gathering - i.e. same exposure at same ISO?

David

Martin Brown
Guest
Posts: n/a

 12-17-2009
Ray Fischer wrote:
> Peabody <(E-Mail Removed)> wrote:
>> Every time I think I understand this, another thought experiment
>> comes up, and I realize I may not.
>>
>> So lets say you have a full-frame 35mm DSLR camera (D700, or
>> whatever) with a fixed 50mm lens, and you take a landscape picture.
>>
>> Now you move a 1.5X crop-sensor camera (D300) into the same place,
>> and you want to take a picture with that camera which you want to
>> have exactly the same field of view as the previous picture - it
>> shows exactly the same scene.
>>
>> If the lens on the smaller camera was designed for that size camera
>> (it's a "DX" lens), what focal length is it?

>
> 50mm / 1.5x = 33mm

However, it is quite likely to be marked as 50mm DX
>
>> Does it make any difference that it's a DX lens - would a full-frame
>> lens produce the same picture in the smaller camera as the DX lens?

>
> Lenses for dSLRs are almost universally specified in 35mm equivalent
> focal length.

Which is confusing for anyone who uses other formats than 35mm where the
lens focal lengths are specified correctly in real millimetres. This DX
lens specified in "equivalent 35mm full frame" effective focal length
serves only to confuse people and treats 35mm users like morons.

For every other photographic film format the lens focal length is
specified in real units of length. It was a terrible mistake to scale
DSLR lenses to notional equivalent focal lengths by sensor size when a
convention already existed for other film formats.

Telling people that on the smaller DX format the camera gives a field of
view 1.4x or 1.5x smaller for the same focal length lens makes it a lot
clearer. Just like using a teleconverter on a full frame camera.
>
>> My guesses are: To produce the same field of view, the DX lens on
>> the smaller camera would need to be 33.33mm. And it doesn't make
>> any difference on the crop-sensor camera whether it's a DX lens or
>> an "FX" lens, so long as they are both 33.33mm.

>
> Yep.

Putting the DX lens on the full frame camera will show significant
vignetting but vice versa the FOV will be fine. In fact the FX lens
designed for full 35mm frame illumination and cropped to the smaller DX
sensor size might have appreciably less vignetting at wide apertures
than the physically smaller DX lens. But it may have other internal
reflection problems when facing a CCD though so it is worth experimenting.

The 1.5x factor makes fisheye a lot harder to do on a DSLR a 16mm FX
full frame fish eye lens is barely wider than the wide end of standard
DX zoom lens. I eventually got an 8mm Sigma for this task.

Regards,
Martin Brown

Ofnuts
Guest
Posts: n/a

 12-17-2009
On 17/12/2009 07:46, Ray Fischer wrote:
> Lenses for dSLRs are almost universally specified in 35mm equivalent
> focal length.

Of course not. Lenses for DSLRs are always specified in absolute focal
length. The Canon 300mm f/4 is a real 300mm (that gives the same field
as a 480mm on the APS-C bodies).

On the P&S, however, specs (especially the ones displayed in the store)
are usually 35mm equivalent (because it gives bigger numbers) and the
bridge camera sporting a 28-420mm zoom has actully got a 5-72mm lens.

--
Bertrand

Chris Malcolm
Guest
Posts: n/a

 12-17-2009
Ray Fischer <(E-Mail Removed)> wrote:

> Lenses for dSLRs are almost universally specified in 35mm equivalent
> focal length.

Ah! So you've never actually ever held a DSLR! That explains a lot!

--
Chris Malcolm

Chris H
Guest
Posts: n/a

 12-17-2009
In message <(E-Mail Removed)>, Chris Malcolm
<(E-Mail Removed)> writes
>Ray Fischer <(E-Mail Removed)> wrote:
>
>> Lenses for dSLRs are almost universally specified in 35mm equivalent
>> focal length.

>
>Ah! So you've never actually ever held a DSLR! That explains a lot!

What do you mean?

I am just now buying the Nikon 35mm F1.8 DX and according to Nikon it
gives the same picture on a DX camera as a 52.5 mm lens on a 35mm film
camera or FX DSLR)

So Ray is correct. Even the DX lenses are specified as 35mm/FX lenses.

The point is if ALL lenses use the same system you know where you stand.
The change occurs when you fit it to a camera body. There are AFAIK
various sizes of sensor and 1.2 to 1.6 (?) as well as FX.

As in the future FX is likely to be the standard and the DX will
disappear over the next decade (as new products and the old ones will be
discontented even if people use them for the next 20 years) we will all
forget this temporary DX "blip"

Just as 8 track cartridges, Cassette tapes, Vinyl LP's, flash bulbs,
glass plates, dot matrix printers, 14" CRT computer monitors, all came
and went.

--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

True Info
Guest
Posts: n/a

 12-17-2009
On Thu, 17 Dec 2009 10:42:48 +0100, Ofnuts <(E-Mail Removed)>
wrote:

>On 17/12/2009 07:46, Ray Fischer wrote:
>> Lenses for dSLRs are almost universally specified in 35mm equivalent
>> focal length.

>
>Of course not. Lenses for DSLRs are always specified in absolute focal
>length. The Canon 300mm f/4 is a real 300mm (that gives the same field
>as a 480mm on the APS-C bodies).
>
>On the P&S, however, specs (especially the ones displayed in the store)
>are usually 35mm equivalent (because it gives bigger numbers) and the
>bridge camera sporting a 28-420mm zoom has actully got a 5-72mm lens.

They are not given in 35mm equivalents for P&S cameras as any kind of
marketing ploy. I.e. "because it gives bigger numbers". They are stated
that way in store/advert/review-site specifications to give people an idea
of how that camera's FOV range will perform compared to all cameras and
lenses that have come before. Most people who are buying such cameras are
well aware of this. I know what kind of scenes are best shot in 28mm, and I
know I need 200mm to 300mm and more for much of wildlife photography. I
welcome when they show the 35mm equivalent in the advertised specs. All of
my P&S cameras list the true focal-lengths on the lens barrels. As well as
in the manual's specifications. The 35mm equivalent are listed in
fine-print in parentheses in the manuals, and appear nowhere on the
lens-barrels or cameras themselves. They are not trying to artificially
inflate focal-length numbers or they'd be sure to do so in all aspects of
information presented with the camera. The 35mm equivalents are provided as
a nice courtesy feature for those that already know about cameras and
lenses to make their educated and experienced buying decisions. To someone
who has never held a camera before, a listing of 28-420mm will mean
nothing. An arbitrary range. To someone who has used cameras before and
knows what they are doing, that is important information to present up
front.

With the wide range of sensor sizes available today it makes sense to give
the buyer a common denominator so they don't have to sit there doing the
math trying to figure out if a 1/2.5" sensor has to have the lens' true FL
multiplied by 6.0, or a P&S camera's 2/3" sensor has to have the lens' FL
multiplied by 3.92 to give them an idea of how that camera's lens will
perform compared to all 35mm cameras they've used in the past.

If one day they perfect a 1/8" sensor size to give equivalent or better
images than your APS-C sized sensor, are you going to claim they are
artificially bumping up the 35mm equivalent focal-length FOVs presented
with that sensor so it looks better on paper? Or will you welcome that as
valuable buying-decision information? With so many variables today it makes
perfect sense to provide a common denominator to the educated and

John McWilliams
Guest
Posts: n/a

 12-17-2009
Martin Brown wrote:
> Ray Fischer wrote:
>> Peabody <(E-Mail Removed)> wrote:
>>> Every time I think I understand this, another thought experiment
>>> comes up, and I realize I may not.
>>>
>>> So lets say you have a full-frame 35mm DSLR camera (D700, or
>>> whatever) with a fixed 50mm lens, and you take a landscape picture.
>>>
>>> Now you move a 1.5X crop-sensor camera (D300) into the same place,
>>> and you want to take a picture with that camera which you want to
>>> have exactly the same field of view as the previous picture - it
>>> shows exactly the same scene.
>>>
>>> If the lens on the smaller camera was designed for that size camera
>>> (it's a "DX" lens), what focal length is it?

>>
>> 50mm / 1.5x = 33mm

>
> However, it is quite likely to be marked as 50mm DX
>>
>>> Does it make any difference that it's a DX lens - would a full-frame
>>> lens produce the same picture in the smaller camera as the DX lens?

>>
>> Lenses for dSLRs are almost universally specified in 35mm equivalent
>> focal length.

>
> Which is confusing for anyone who uses other formats than 35mm where the
> lens focal lengths are specified correctly in real millimetres. This DX
> lens specified in "equivalent 35mm full frame" effective focal length
> serves only to confuse people and treats 35mm users like morons.
>
> For every other photographic film format the lens focal length is
> specified in real units of length. It was a terrible mistake to scale
> DSLR lenses to notional equivalent focal lengths by sensor size when a
> convention already existed for other film formats.
>
> Telling people that on the smaller DX format the camera gives a field of
> view 1.4x or 1.5x smaller for the same focal length lens makes it a lot
> clearer. Just like using a teleconverter on a full frame camera.

Er, no. The average photog doesn't use/understand field of view. He
(impersonal pronoun) is likely to think in terms of the 1.5 or 1.6
factor as a mulitplier. Gets to the same place, and it's also simpler to
multiply than divide.

--
john mcwilliams