focal length on crop sensor question?

littledrawe · 09-22-2011, 10:11 AM

Would a lens made for the the pentax film SLR with a focal length of 35-135 be the equivalent of the DA 50-200 currently produced if the crop factor is applied to the older lens?

pxpaulx · 09-22-2011, 10:23 AM

If you're asking if they'll be the same, the answer is no. I think you might have it mixed up a little. The 35-135mm will have an approximate field of view of 50-200mm in 35mm terms when used with the APS-C sensors in Pentax DSLRs. The 50-200mm used on APS-C DSLRs has a 35mm film equivalent field of view of 100-300mm.

eddie1960 · 09-22-2011, 10:31 AM

Crop factor is very decptive.
it's about FOV
the 35-135 length when used on apsc provides and approximate field of view of 52.5-202.5 used on 35mm
a 50-200 is still a longer lens on apsc than the 35-135
the focal length of a lens is the same regardless of format, crop factor was a way for old guys who shot 35mm (like me) to estimate how their lenses would look on the crop sensor.
the DA50-200 cannot be used on film bodies do to a smaller image circle since it was designed to cover the smaller sensor, but it's apsc crop factor equivalent would be like a 75-300 on 35mm

That being

eddie1960 · 09-22-2011, 10:31 AM

Originally posted by pxpaulx

If you're asking if they'll be the same, the answer is no. I think you might have it mixed up a little. The 35-135mm will have an approximate field of view of 50-200mm in 35mm terms when used with the APS-C sensors in Pentax DSLRs. The 50-200mm used on APS-C DSLRs has a 35mm film equivalent field of view of 100-300mm.

75-300 (factor 1.5)

RioRico · 09-22-2011, 11:49 AM

Originally posted by littledrawe

Would a lens made for the the pentax film SLR with a focal length of 35-135 be the equivalent of the DA 50-200 currently produced if the crop factor is applied to the older lens?

Moving a lens to a different camera does not change its focal length. Moving a lens to a camera with a smaller frame (film or digital) crops a smaller portion of the projected image, hence the term crop-sensor. Moving a lens to a camera with a larger frame records a larger portion of the projected image. The frame size determines the FOV produced by by any given focal length.

An 18-55mm lens on APS-C has equivalent FOV as a 28-80mm lens on 135/FF.
A 35-135mm lens on APS-C has equivalent FOV as a 50-200mm lens on 135/FF.

Unless you're an experienced 135/FF photographer who is transitioning to APS-C or 135/HF, forget that you ever heard of crap.factor. Just use your lenses and learn what each focal length does on each camera. Back in the day, I sometimes shot 135/HF and 135/FF and 6x6/MF and 9x12/MF on the same day, sometimes with the same lens. My colleagues and I never referred to crap.factor; the term hadn't yet been invented by a marketing wonk. We just learned our lenses. It ain't hard.

**Lowell Goudge** · 09-22-2011, 12:17 PM

back to basics.

Focal length is focal length. it is a physical characteristic of a lens, speccifically measured when the lens is set to infinity. Basically, for s single lens it is the distance from the lens to the focusing plane, such that parallel light striking the lens focuses at a point.

It gets a little more complex when you talk about compound (multiple element lenses) which is where the field of view comes in. Field of view usually measured across the diagonal of a frame, relates to an effective focal length for any one format.

As Rio said forget you ever heard about crop factor. any interchangeable lens is marked with its focal length with no inference to format that it gets put on.

It is only when you look at P&S cameras, that crop factor gets introduced because almost every P&S has a different sized chip, so to make it relitively simple to compare cameras, it seems everyone has adapted an equivelent to 35mm focal length, (based upon the FOV of the lens on the sensor) as if the other formats simply don't exist.

Marc Sabatella · 09-22-2011, 12:44 PM

here's a hopefully simple way of looking at it:

Crop factor is comparing *cameras*, not for comparing *lenses*. It doesn't matter who made the 35-105 or when or what kind of camera they made it for. A 35-105 lens is shorter (wider field of FOV) than a 50-200 lens when both are mounted to the same camer. Period, end of story. However, if you mount that 35-105 to a film / FF camera, it will indeed have a different FOV than it does on a crop camera, and yeah, 35-135 on a FF body is kind of sort of like 50-200 on a crop camera. But it's the camera that does this, not the lens. Again, if both lenses are mounted to the same camera, the 50-200 is longer, every time.

littledrawe · 09-22-2011, 03:42 PM

Originally posted by RioRico

forget that you ever heard of crap.factor.

Thank you sir! I didn't want to get too wrapped up in it, I just wanted to see if my thinking is correct. Thanks for the help everyone!

Parallax · 09-22-2011, 04:15 PM

Originally posted by littledrawe

I didn't want to get too wrapped up in it, ....

You just gave yourself better advice than any of us could give you. If you can't see enough, use a shorter lens. If you want a closer look, use a longer one. Quit worrying about how things compare.

Squier · 09-23-2011, 05:38 AM

Originally posted by littledrawe

Thank you sir! I didn't want to get too wrapped up in it, I just wanted to see if my thinking is correct. Thanks for the help everyone!

Quite right - and due to good advice here, you can now ignore everyone and his brother, and lens retailers too, ( who should know better but have jumped on the ' crop ' bandwagon ) when they tell you / or advertise a 500mm lens having a focal length of 750mm when you pop the lens on a 1.5x crop camera

pxpaulx · 09-23-2011, 08:56 AM

Originally posted by eddie1960

75-300 (factor 1.5)

Thats what happens when you use Pentax along with a couple of micro 4/3 cameras, your brain turns to mush! hahaha.

RioRico · 09-23-2011, 11:08 AM

Wait wait, I have a solution! Yes, there IS magic in the world! Yes, lenses DO change their focal lengths spontaneously! You might ask: How, how can this happen? The answer is simple: FASTER-THAN-LIGHT NEUTRINOS!! Yes, putting a lens on a different camera distorts the local space-time fabric and allows neutrinos (and the photons they drag along with them) to wormhole through the optics at FTL speeds! And *I* discovered this!! Where's my Nobel??

littledrawe · 09-24-2011, 11:44 PM

Originally posted by RioRico

Where's my Nobel??

You've got my vote!!!

bollicina31 · 09-25-2011, 09:29 AM

Originally posted by littledrawe

You've got my vote!!!

I sent many pm, if you answer me do me a favor :ugh:

DaveHolmes · 09-28-2011, 03:06 AM - **1 Like**

Originally posted by Parallax

If you want a closer look, use a longer one. Quit worrying about how things compare.

And if you only have one lens to go at... Walk forwards and/or backwards

09-22-2011, 10:11 AM	#1
littledrawe Veteran Member Join Date: Jan 2010 Location: Red Rock Photos: Gallery \| Albums Posts: 2,514	focal length on crop sensor question? Would a lens made for the the pentax film SLR with a focal length of 35-135 be the equivalent of the DA 50-200 currently produced if the crop factor is applied to the older lens?

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09-22-2011, 10:23 AM	#2
pxpaulx Veteran Member Join Date: May 2009 Location: Twin Cities, MN Posts: 2,867	If you're asking if they'll be the same, the answer is no. I think you might have it mixed up a little. The 35-135mm will have an approximate field of view of 50-200mm in 35mm terms when used with the APS-C sensors in Pentax DSLRs. The 50-200mm used on APS-C DSLRs has a 35mm film equivalent field of view of 100-300mm.

09-22-2011, 10:31 AM	#3
eddie1960 Veteran Member Join Date: Aug 2010 Location: Toronto Photos: Gallery \| Albums Posts: 13,667	Crop factor is very decptive. it's about FOV the 35-135 length when used on apsc provides and approximate field of view of 52.5-202.5 used on 35mm a 50-200 is still a longer lens on apsc than the 35-135 the focal length of a lens is the same regardless of format, crop factor was a way for old guys who shot 35mm (like me) to estimate how their lenses would look on the crop sensor. the DA50-200 cannot be used on film bodies do to a smaller image circle since it was designed to cover the smaller sensor, but it's apsc crop factor equivalent would be like a 75-300 on 35mm That being

09-22-2011, 10:31 AM	#4
eddie1960 Veteran Member Join Date: Aug 2010 Location: Toronto Photos: Gallery \| Albums Posts: 13,667	Originally posted by pxpaulx If you're asking if they'll be the same, the answer is no. I think you might have it mixed up a little. The 35-135mm will have an approximate field of view of 50-200mm in 35mm terms when used with the APS-C sensors in Pentax DSLRs. The 50-200mm used on APS-C DSLRs has a 35mm film equivalent field of view of 100-300mm. 75-300 (factor 1.5)

09-22-2011, 11:49 AM	#5
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Originally posted by littledrawe Would a lens made for the the pentax film SLR with a focal length of 35-135 be the equivalent of the DA 50-200 currently produced if the crop factor is applied to the older lens? Moving a lens to a different camera does not change its focal length. Moving a lens to a camera with a smaller frame (film or digital) crops a smaller portion of the projected image, hence the term crop-sensor. Moving a lens to a camera with a larger frame records a larger portion of the projected image. The frame size determines the FOV produced by by any given focal length. An 18-55mm lens on APS-C has equivalent FOV as a 28-80mm lens on 135/FF. A 35-135mm lens on APS-C has equivalent FOV as a 50-200mm lens on 135/FF. Unless you're an experienced 135/FF photographer who is transitioning to APS-C or 135/HF, forget that you ever heard of crap.factor. Just use your lenses and learn what each focal length does on each camera. Back in the day, I sometimes shot 135/HF and 135/FF and 6x6/MF and 9x12/MF on the same day, sometimes with the same lens. My colleagues and I never referred to crap.factor; the term hadn't yet been invented by a marketing wonk. We just learned our lenses. It ain't hard.

09-22-2011, 12:17 PM	#6
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	back to basics. Focal length is focal length. it is a physical characteristic of a lens, speccifically measured when the lens is set to infinity. Basically, for s single lens it is the distance from the lens to the focusing plane, such that parallel light striking the lens focuses at a point. It gets a little more complex when you talk about compound (multiple element lenses) which is where the field of view comes in. Field of view usually measured across the diagonal of a frame, relates to an effective focal length for any one format. As Rio said forget you ever heard about crop factor. any interchangeable lens is marked with its focal length with no inference to format that it gets put on. It is only when you look at P&S cameras, that crop factor gets introduced because almost every P&S has a different sized chip, so to make it relitively simple to compare cameras, it seems everyone has adapted an equivelent to 35mm focal length, (based upon the FOV of the lens on the sensor) as if the other formats simply don't exist.

09-22-2011, 12:44 PM	#7
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	here's a hopefully simple way of looking at it: Crop factor is comparing cameras, not for comparing lenses. It doesn't matter who made the 35-105 or when or what kind of camera they made it for. A 35-105 lens is shorter (wider field of FOV) than a 50-200 lens when both are mounted to the same camer. Period, end of story. However, if you mount that 35-105 to a film / FF camera, it will indeed have a different FOV than it does on a crop camera, and yeah, 35-135 on a FF body is kind of sort of like 50-200 on a crop camera. But it's the camera that does this, not the lens. Again, if both lenses are mounted to the same camera, the 50-200 is longer, every time.

09-22-2011, 03:42 PM	#8
littledrawe Veteran Member Join Date: Jan 2010 Location: Red Rock Photos: Gallery \| Albums Posts: 2,514 Original Poster	Originally posted by RioRico forget that you ever heard of crap.factor. Thank you sir! I didn't want to get too wrapped up in it, I just wanted to see if my thinking is correct. Thanks for the help everyone!

09-22-2011, 04:15 PM	#9
Parallax Senior Moderator Loyal Site Supporter Join Date: Apr 2008 Location: South Dakota Photos: Gallery Posts: 19,333	Originally posted by littledrawe I didn't want to get too wrapped up in it, .... You just gave yourself better advice than any of us could give you. If you can't see enough, use a shorter lens. If you want a closer look, use a longer one. Quit worrying about how things compare.

09-23-2011, 05:38 AM	#10
Squier Veteran Member Join Date: Apr 2009 Location: Oxfordshire UK Photos: Albums Posts: 706	Originally posted by littledrawe Thank you sir! I didn't want to get too wrapped up in it, I just wanted to see if my thinking is correct. Thanks for the help everyone! Quite right - and due to good advice here, you can now ignore everyone and his brother, and lens retailers too, ( who should know better but have jumped on the ' crop ' bandwagon ) when they tell you / or advertise a 500mm lens having a focal length of 750mm when you pop the lens on a 1.5x crop camera

09-23-2011, 08:56 AM	#11
pxpaulx Veteran Member Join Date: May 2009 Location: Twin Cities, MN Posts: 2,867	Originally posted by eddie1960 75-300 (factor 1.5) Thats what happens when you use Pentax along with a couple of micro 4/3 cameras, your brain turns to mush! hahaha.

09-23-2011, 11:08 AM	#12
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Wait wait, I have a solution! Yes, there IS magic in the world! Yes, lenses DO change their focal lengths spontaneously! You might ask: How, how can this happen? The answer is simple: FASTER-THAN-LIGHT NEUTRINOS!! Yes, putting a lens on a different camera distorts the local space-time fabric and allows neutrinos (and the photons they drag along with them) to wormhole through the optics at FTL speeds! And I discovered this!! Where's my Nobel??

09-24-2011, 11:44 PM	#13
littledrawe Veteran Member Join Date: Jan 2010 Location: Red Rock Photos: Gallery \| Albums Posts: 2,514 Original Poster	Originally posted by RioRico Where's my Nobel?? You've got my vote!!!

09-25-2011, 09:29 AM	#14
bollicina31 Senior Member Join Date: Oct 2009 Location: ita/swiss Posts: 267	Originally posted by littledrawe You've got my vote!!! I sent many pm, if you answer me do me a favor :ugh:

09-28-2011, 03:06 AM - 1 Like	#15
DaveHolmes Veteran Member Join Date: Jul 2010 Location: Yorkshire Posts: 1,501	Originally posted by Parallax If you want a closer look, use a longer one. Quit worrying about how things compare. And if you only have one lens to go at... Walk forwards and/or backwards