FA 50 1.4 and the DA 50 1.8. Is there any focal length difference?

ziscwg · 09-12-2014, 06:51 PM

Since one is for 35mm film (the FA), would I have a 75 mm aps-c equivalent using the FA 50?

Last edited by ziscwg; 09-14-2014 at 11:07 PM.

dave sz · 09-12-2014, 06:55 PM

Focal length is a physical attribute of the lens, isn't it? Therefore 50mm=50mm.

ziscwg · 09-12-2014, 06:58 PM

Originally posted by dave sz

Focal length is a physical attribute of the lens, isn't it? Therefore 50mm=50mm.

I meant in practical terms of what gets put on the sensor. Since the sensor is smaller area than film, does it have a "telephoto" type effect?

jimr-pdx · 09-12-2014, 06:58 PM

50 is 50, the difference is that the fa50 is projecting light further past the edges of your smaller sensor while the da50 is designed to illuminate the smaller sensor area. Both look like a 75mm lens on your camera .. but only if you make a print & compare it to a same size print from 35mm film!

ziscwg · 09-12-2014, 07:03 PM

Originally posted by jimr-pdx

50 is 50, the difference is that the fa50 is projecting light further past the edges of your smaller sensor while the da50 is designed to illuminate the smaller sensor area. Both look like a 75mm lens on your camera .. but only if you make a print & compare it to a same size print from 35mm film!

I think that makes sense then. The DA makes the image smaller to fit on the sensor.

I guess I will have to read up on this a bit more.

dave sz · 09-12-2014, 07:11 PM

Originally posted by ziscwg

I think that makes sense then. The DA makes the image smaller to fit on the sensor.

I guess I will have to read up on this a bit more.

Both will work the same on a crop sensor camera but taking a lens made for APSC and using it on FF will give you a round image with black borders.

Andi Lo · 09-12-2014, 07:27 PM

Originally posted by dave sz

Both will work the same on a crop sensor camera but taking a lens made for APSC and using it on FF will give you a round image with black borders.

To complicate things a bit, some lenses that are "made for APSC" can actually work fine in full frame

with a few caveats

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/31629-da-le...thread-10.html

MadMathMind · 09-12-2014, 08:29 PM

In theory, no.* 50mm is 50mm. The confusion arises because when a 50mm lens is put on a film camera, you will see a larger field of view than when you put that same lens on an APS-C camera. That's a property of the camera, not the lens itself. A film era lens won't show any more or less than a lens designed for digital, all other things being equal.

*In practice, not all lenses are actually the focal length they claim. But that's really a different issue.

Venturi · 09-12-2014, 09:25 PM

Theoretically, there should be no difference. But, marketing texts and manufacturing specs are not synonymous. You'd have to test them side-by-side but I would not be shocked to learn that there was as much as a 2 degree difference in angle of view between them.

johnmflores · 09-12-2014, 09:41 PM - **1 Like**

Originally posted by ziscwg

I think that makes sense then. The DA makes the image smaller to fit on the sensor.

Not exactly. Look at it this way….if Pentax had a full-frame camera, and you took the same exact photo twice, once with the DA50 and once with the FA50, here's what you'd see:

FA50: the entire frame would be filled with the image
DA50: the center of the image would be identical to the FA50 but it would fade to black towards the edges. You'd basically have a round image in a field of black

Now conduct the same experiment on an APS-C camera

FA50: the entire frame would be filled with the image
DA50: the entire frame would be filled with the image

What you wouldn't see is that the FA50 actually had extra image outside of the frame that spilled outside of the sensor area of APS-C.

Instead of thinking of DA making "the image smaller to fit on the sensor", think of the FA spilling extra, unused image outside of the sensor on APS-C. That way, it's easier to that on APS-C, both the DA50 and FA50 take the same picture.

ziscwg · 09-12-2014, 10:54 PM

Originally posted by johnmflores

Not exactly. Look at it this way….if Pentax had a full-frame camera, and you took the same exact photo twice, once with the DA50 and once with the FA50, here's what you'd see:

FA50: the entire frame would be filled with the image
DA50: the center of the image would be identical to the FA50 but it would fade to black towards the edges. You'd basically have a round image in a field of black

Now conduct the same experiment on an APS-C camera

FA50: the entire frame would be filled with the image
DA50: the entire frame would be filled with the image

What you wouldn't see is that the FA50 actually had extra image outside of the frame that spilled outside of the sensor area of APS-C.

Instead of thinking of DA making "the image smaller to fit on the sensor", think of the FA spilling extra, unused image outside of the sensor on APS-C. That way, it's easier to that on APS-C, both the DA50 and FA50 take the same picture.

So, to expand this, these two lenses would also take nearly the same picture on a K-50? (ignoring the 70 to 77 difference)

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Name: 2lens.JPG
Views: 417
Size: 28.3 KB

Sandy Hancock · 09-12-2014, 11:06 PM

Originally posted by ziscwg

So, to expand this, these two lenses would also take nearly the same picture on a K-50? (ignoring the 70 to 77 difference)

Attachment 237041

Yes, they would be very similar. Except that the FA77 is faster and contains much more pixie dust

The same applies to the DA40 and FA43.

MadMathMind · 09-12-2014, 11:07 PM

Originally posted by ziscwg

So, to expand this, these two lenses would also take nearly the same picture on a K-50? (ignoring the 70 to 77 difference)

Yes.

Take a step or two back with the 77 and you'd see exactly what you see with the 70.

Andi Lo · 09-13-2014, 06:51 AM

Originally posted by MadMathMind

Yes.

Take a step or two back with the 77 and you'd see exactly what you see with the 70.

For practical purposes, yes but they're not exactly the same. Distance from subject affect perspective.

09-12-2014, 06:51 PM	#1
ziscwg Senior Member Join Date: Mar 2010 Posts: 110	FA 50 1.4 and the DA 50 1.8. Is there any focal length difference? Since one is for 35mm film (the FA), would I have a 75 mm aps-c equivalent using the FA 50? Last edited by ziscwg; 09-14-2014 at 11:07 PM.

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09-12-2014, 06:55 PM	#2
dave sz Veteran Member Join Date: Dec 2006 Location: carpentersville, IL Posts: 693	Focal length is a physical attribute of the lens, isn't it? Therefore 50mm=50mm.

09-12-2014, 06:58 PM	#3
ziscwg Senior Member Join Date: Mar 2010 Posts: 110 Original Poster	Originally posted by dave sz Focal length is a physical attribute of the lens, isn't it? Therefore 50mm=50mm. I meant in practical terms of what gets put on the sensor. Since the sensor is smaller area than film, does it have a "telephoto" type effect?

09-12-2014, 06:58 PM	#4
jimr-pdx Pentaxian Join Date: May 2010 Location: now 1 hour north of PDX Photos: Gallery \| Albums Posts: 3,897	50 is 50, the difference is that the fa50 is projecting light further past the edges of your smaller sensor while the da50 is designed to illuminate the smaller sensor area. Both look like a 75mm lens on your camera .. but only if you make a print & compare it to a same size print from 35mm film!

09-12-2014, 07:03 PM	#5
ziscwg Senior Member Join Date: Mar 2010 Posts: 110 Original Poster	Originally posted by jimr-pdx 50 is 50, the difference is that the fa50 is projecting light further past the edges of your smaller sensor while the da50 is designed to illuminate the smaller sensor area. Both look like a 75mm lens on your camera .. but only if you make a print & compare it to a same size print from 35mm film! I think that makes sense then. The DA makes the image smaller to fit on the sensor. I guess I will have to read up on this a bit more.

09-12-2014, 07:11 PM	#6
dave sz Veteran Member Join Date: Dec 2006 Location: carpentersville, IL Posts: 693	Originally posted by ziscwg I think that makes sense then. The DA makes the image smaller to fit on the sensor. I guess I will have to read up on this a bit more. Both will work the same on a crop sensor camera but taking a lens made for APSC and using it on FF will give you a round image with black borders.

09-12-2014, 07:27 PM	#7
Andi Lo Veteran Member Join Date: Jul 2008 Location: Halifax, Nova Scotia Posts: 2,924	Originally posted by dave sz Both will work the same on a crop sensor camera but taking a lens made for APSC and using it on FF will give you a round image with black borders. To complicate things a bit, some lenses that are "made for APSC" can actually work fine in full frame with a few caveats https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/31629-da-le...thread-10.html

09-12-2014, 08:29 PM	#8
MadMathMind Veteran Member Join Date: Dec 2013 Location: Houston, TX Photos: Gallery Posts: 1,717	In theory, no.* 50mm is 50mm. The confusion arises because when a 50mm lens is put on a film camera, you will see a larger field of view than when you put that same lens on an APS-C camera. That's a property of the camera, not the lens itself. A film era lens won't show any more or less than a lens designed for digital, all other things being equal. *In practice, not all lenses are actually the focal length they claim. But that's really a different issue.

09-12-2014, 09:25 PM	#9
Venturi Veteran Member Join Date: Mar 2008 Location: Tulsa, OK Photos: Gallery Posts: 2,636	Theoretically, there should be no difference. But, marketing texts and manufacturing specs are not synonymous. You'd have to test them side-by-side but I would not be shocked to learn that there was as much as a 2 degree difference in angle of view between them.

09-12-2014, 09:41 PM - 1 Like	#10
johnmflores Veteran Member Join Date: Apr 2009 Location: Somerville, NJ Photos: Gallery \| Albums Posts: 5,361	Originally posted by ziscwg I think that makes sense then. The DA makes the image smaller to fit on the sensor. Not exactly. Look at it this way….if Pentax had a full-frame camera, and you took the same exact photo twice, once with the DA50 and once with the FA50, here's what you'd see: FA50: the entire frame would be filled with the image DA50: the center of the image would be identical to the FA50 but it would fade to black towards the edges. You'd basically have a round image in a field of black Now conduct the same experiment on an APS-C camera FA50: the entire frame would be filled with the image DA50: the entire frame would be filled with the image What you wouldn't see is that the FA50 actually had extra image outside of the frame that spilled outside of the sensor area of APS-C. Instead of thinking of DA making "the image smaller to fit on the sensor", think of the FA spilling extra, unused image outside of the sensor on APS-C. That way, it's easier to that on APS-C, both the DA50 and FA50 take the same picture.

09-12-2014, 10:54 PM	#11
ziscwg Senior Member Join Date: Mar 2010 Posts: 110 Original Poster	Originally posted by johnmflores Not exactly. Look at it this way….if Pentax had a full-frame camera, and you took the same exact photo twice, once with the DA50 and once with the FA50, here's what you'd see: FA50: the entire frame would be filled with the image DA50: the center of the image would be identical to the FA50 but it would fade to black towards the edges. You'd basically have a round image in a field of black Now conduct the same experiment on an APS-C camera FA50: the entire frame would be filled with the image DA50: the entire frame would be filled with the image What you wouldn't see is that the FA50 actually had extra image outside of the frame that spilled outside of the sensor area of APS-C. Instead of thinking of DA making "the image smaller to fit on the sensor", think of the FA spilling extra, unused image outside of the sensor on APS-C. That way, it's easier to that on APS-C, both the DA50 and FA50 take the same picture. So, to expand this, these two lenses would also take nearly the same picture on a K-50? (ignoring the 70 to 77 difference)

09-12-2014, 11:06 PM	#12
Sandy Hancock Moderator Site Supporter Join Date: Feb 2012 Location: Adelaide Hills, South Australia Photos: Gallery \| Albums Posts: 11,275	Originally posted by ziscwg So, to expand this, these two lenses would also take nearly the same picture on a K-50? (ignoring the 70 to 77 difference) Attachment 237041 Yes, they would be very similar. Except that the FA77 is faster and contains much more pixie dust The same applies to the DA40 and FA43.

09-12-2014, 11:07 PM	#13
MadMathMind Veteran Member Join Date: Dec 2013 Location: Houston, TX Photos: Gallery Posts: 1,717	Originally posted by ziscwg So, to expand this, these two lenses would also take nearly the same picture on a K-50? (ignoring the 70 to 77 difference) Yes. Take a step or two back with the 77 and you'd see exactly what you see with the 70.

09-13-2014, 06:51 AM	#14
Andi Lo Veteran Member Join Date: Jul 2008 Location: Halifax, Nova Scotia Posts: 2,924	Originally posted by MadMathMind Yes. Take a step or two back with the 77 and you'd see exactly what you see with the 70. For practical purposes, yes but they're not exactly the same. Distance from subject affect perspective.