Why no "real" normal lens for apsc

RioRico · 02-11-2012, 05:27 PM

Originally posted by civiletti

There is nothing normal about a normal lens.

That's optics-speak. Others disdain calling a plastic-body fixed-focal length lens a 'prime'. I won't label a bribe-taking pol as "the honorable". Every jargon has its jinks.

Tonto · 02-11-2012, 05:54 PM

Well there are 3 normalish lenses- the DA 35 2.4, the DA 35 Macro Ltd and the FA31 1.8 with 35mm having a 52mm equivilency.

However if one wanted to strictly adhere to a 43mm equivilent lens then you only options are to go for Sigmas 28mm or some of Pentaxs older lenses on the 2nd hand market.

The reason Pentax doesnt have a current 28mm is it is too close to 31-35mm see above.
This is why many are encouraging Pentax to re-release the FA24 or create a new lens at this FL as it is a good spacer between 14-15mm and the 31-35mm primes in the Pentax lineup.
This would most likely be a faster lens as there is already the DA 21 ltd available so it could be bigger and more expensive probably similar to a FA43 in size and cost.

I for one would welcome this lens although a DA 21 fits in better with my current FA 31.

As a side note wouldn't it just be amazing if they did an update to the FA31 along the lines of the DFA 100 Macro, next 5 years perhaps?
(slightly smaller, WR, different lens hood, quick focus

)

Bruce · 02-11-2012, 06:21 PM

Originally posted by RioRico

What we're used to. What we're comfortable with. How we limit our vision.

Normal is such a subjective term! When I am shooting sports at an oval, my 'normal' lens is a long telephoto. When I am in a stadium my 'normal' lens is a medium telephoto. When I am shooting macro, you guessed it, I use a macro lens (normally a 105mm), when I am doing anything else I normally pick a lens that has the FOV that I think I need (sometimes I even get that right), but I normally have a 31mm attached to my camera, just for convenience. Am I normal? Hey I don't know, but I am normal in my house (it helps when normality is dictated by a community of one DSLR user)!

OutOfFocus · 02-11-2012, 06:22 PM

The K30/2.8 would also qualify as a "normal" lens on APSC, especially if its focal length really is on the short side of 30.

stevebrot · 02-11-2012, 06:42 PM

Originally posted by OutOfFocus

The K30/2.8 would also qualify as a "normal" lens on APSC, especially if its focal length really is on the short side of 30.

Very true, except that it has been out of production for over 30 years. The OP is complaining that the current Pentax lineup is a smidge long for him unless you spring for the 31mm LTD.

Steve

Marc Sabatella · 02-11-2012, 06:55 PM

Originally posted by westmill

Our eyes dont even come close to that even taking into account perphirel vision, which is genrally used for detecting movement.

Apparently you've never done the experiment. Try it some time; you'll be surprised. Or, just read the Wikipedia article on Visual field. You might be referring to macular vision only.

Quote:

certainly has not
got anything to do with prints.

Yes it does. Look up the term "perspective distortion" some time - again, the Wikipedia article works fine.

Quote:

My comment was that most people consider that 50mm in 35mm terms is considered as a standard lense.

Yes. I was just pointing out that the reason for this has nothing to do with FOV; that's a common myth. It's all about perspective distortion, and that is something you can't measure until you print the image.

isaacc7 · 02-11-2012, 10:36 PM

Originally posted by stevebrot

Huh? The Sigma 1.8 may well be crap, but it has nothing to do with the size of its image circle.

As for retrofocus design for APS-C vs. 35mm vs. 645 vs. you name it...if the camera has a mirror box, there will be a focal length threshold below which you need retrofocus to allow the rear element to clear the mirror. This is one of the big arguments in favor of mirrorless cameras.

Steve

BTW...who said that retrofocus = bad performance?

Plus, for digital cameras, retrofocus lenses have some real advantages. Keeping the rear element away from the sensor helps minimize vingetting and color fringing. A design like the biogon would be a worst case scenario for a digital camera. It was one of the big things that Olympus touted about its original 4/3 standard. They kept the lenses far enough away to ensure "tele centricity" in order to minimize digital specific problems. The "feature" of thinner requires some tricky optical/sensor combinations to get around the inherent limitations. With all of the people complaining about how big the k-01 is, I wonder if it will be easier to hold steady than the really thin Sony cameras.

stevebrot · 02-11-2012, 11:58 PM

Originally posted by isaacc7

A design like the biogon would be a worst case scenario for a digital camera.

I was thinking specifically about the Biogon and its semi-legitimate relative, the Jupiter-12. That rear element is pretty impressive until one considers the havoc it can cause with most digital sensors when only a few millimeters from the sensor surface!

Dealing with the "close element" issue was one factor influencing the sensor design in the new Fuji X-Pro 1 as well as the optical design of the lenses for that camera.

Steve

Class A · 02-12-2012, 03:13 AM

Originally posted by zapp

The 1.8 Sigmas are crap and not designed for APS-C.

The Sigma 28/1.8 EX lens I own is anything but crap. It is very sharp and has amazing close focusing abilities. It is an FF lens but performs great on APS-C. It has an average rating of 9 in the lens database.

BTW, the concept of a "normal" lens is well-defined but is unrelated to human anatomy. A normal lens only functions as such, when you view the final image (need not be a print, the screen is fine) from a distance that corresponds to the final image diagonal.

If you view the final image from a distance that is twice the size of the final image size diagonal, the respective lens that keeps angles natural has a focal length that is twice the diagonal of the film/sensor.

This should make it clear that a "normal lens" just puts the eye of the beholder of the final image exactly in the place where the film/sensor was when it saw the scene. You can make a wide-angle image look "normal" when you look at it from close enough and make a telephoto image look normal by looking at it from far away.

The special character of a standard normal (28mm on APC-C, 43mm on FF (the 50mm was just a bad approximation)) comes from the convention of looking at images from a distance that roughly corresponds to the diagonal of the image.

westmill · 02-12-2012, 10:33 AM

Originally posted by Marc Sabatella

Apparently you've never done the experiment. Try it some time; you'll be surprised. Or, just read the Wikipedia article on Visual field. You might be referring to macular vision only.

Yes it does. Look up the term "perspective distortion" some time - again, the Wikipedia article works fine.

Yes. I was just pointing out that the reason for this has nothing to do with FOV; that's a common myth. It's all about perspective distortion, and that is something you can't measure until you print the image.

Im well aware of the meaning of perspective distortion thank you very much ! You stick to your wikipedia !

Anvh · 02-12-2012, 11:59 AM

Originally posted by RKKS08

I miss such a lens for APS-C badly: a SMALL full metal manual focus 2.0/30 with acceptable IQ at 2.0 and very good IQ from 4-5.6 on FOR NOT MORE THAN €100 ($125) new. THIS would be the real equivalent to what Pentax offered during the film era. If not possible, I may accept a plasticy lens body, if the bajonet is made of metal.

The reason 50mm are so cheap is because they are easy to make for this register distance, because Pentax didn't shorten the register distance to match APS-C format better it means they need to use a different design for wider lenses.
So we will never see cheap 28/30mm f/2 or faster lens for the k-mount, compared to 50mm that is.

Anvh · 02-12-2012, 12:01 PM

Just remembered that there was a DA*30 on the old lens roadmap which would have roughly the same design features as the DA*55 .
I wonder if Ricoh wll bring it back... sadly there is nothing on the roadmap at the moment.

lytrytyr · 02-12-2012, 12:06 PM

Originally posted by Anvh

The reason 50mm are so cheap is because they are easy to make for this register distance, because Pentax didn't shorten the register distance to match APS-C format better it means they need to use a different design for wider lenses.

Keeping the longer register distance enables the light rays to hit the sensor wells at a better angle
(avoiding the issues the GXR Leica mountor has to deal with),
as well as eliminating the need for an adapter to use older lenses.

Anvh · 02-12-2012, 03:20 PM

You are right but that isn't what is being discussed.

If you want to have cheap and fast 28mm lenses like the 50mm are then you need to shorten the register, there is no other way around it.
I'm not saying they can't make fast 28mm but they wont be cheap.

lytrytyr · 02-12-2012, 03:30 PM

The problem with wide angle lenses is as much a question of the coverage angle as the register distance.
If you shorten the register distance for a given sensor format, you increase the coverage angle from the back of the lens.
It's a tradeoff, and doesn't lead to cheaper lenses.
As an example, a Zeiss ZM Biogon 28/2.8 on a NEX
costs pretty much the same as the ZK Distagon 25/2.8 in K-mount.

02-12-2012, 03:13 AM	#54
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 11,251	Originally posted by zapp The 1.8 Sigmas are crap and not designed for APS-C. The Sigma 28/1.8 EX lens I own is anything but crap. It is very sharp and has amazing close focusing abilities. It is an FF lens but performs great on APS-C. It has an average rating of 9 in the lens database. BTW, the concept of a "normal" lens is well-defined but is unrelated to human anatomy. A normal lens only functions as such, when you view the final image (need not be a print, the screen is fine) from a distance that corresponds to the final image diagonal. If you view the final image from a distance that is twice the size of the final image size diagonal, the respective lens that keeps angles natural has a focal length that is twice the diagonal of the film/sensor. This should make it clear that a "normal lens" just puts the eye of the beholder of the final image exactly in the place where the film/sensor was when it saw the scene. You can make a wide-angle image look "normal" when you look at it from close enough and make a telephoto image look normal by looking at it from far away. The special character of a standard normal (28mm on APC-C, 43mm on FF (the 50mm was just a bad approximation)) comes from the convention of looking at images from a distance that roughly corresponds to the diagonal of the image. Last edited by Class A; 02-12-2012 at 03:25 AM.

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02-11-2012, 05:27 PM	#46
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Originally posted by civiletti There is nothing normal about a normal lens. That's optics-speak. Others disdain calling a plastic-body fixed-focal length lens a 'prime'. I won't label a bribe-taking pol as "the honorable". Every jargon has its jinks.

02-11-2012, 05:54 PM	#47
Tonto Inactive Account Join Date: Apr 2010 Location: Wellington Posts: 969	Well there are 3 normalish lenses- the DA 35 2.4, the DA 35 Macro Ltd and the FA31 1.8 with 35mm having a 52mm equivilency. However if one wanted to strictly adhere to a 43mm equivilent lens then you only options are to go for Sigmas 28mm or some of Pentaxs older lenses on the 2nd hand market. The reason Pentax doesnt have a current 28mm is it is too close to 31-35mm see above. This is why many are encouraging Pentax to re-release the FA24 or create a new lens at this FL as it is a good spacer between 14-15mm and the 31-35mm primes in the Pentax lineup. This would most likely be a faster lens as there is already the DA 21 ltd available so it could be bigger and more expensive probably similar to a FA43 in size and cost. I for one would welcome this lens although a DA 21 fits in better with my current FA 31. As a side note wouldn't it just be amazing if they did an update to the FA31 along the lines of the DFA 100 Macro, next 5 years perhaps? (slightly smaller, WR, different lens hood, quick focus )

02-11-2012, 06:21 PM	#48
Bruce Veteran Member Join Date: Oct 2009 Location: Sydney Photos: Gallery \| Albums Posts: 448	Originally posted by RioRico What we're used to. What we're comfortable with. How we limit our vision. Normal is such a subjective term! When I am shooting sports at an oval, my 'normal' lens is a long telephoto. When I am in a stadium my 'normal' lens is a medium telephoto. When I am shooting macro, you guessed it, I use a macro lens (normally a 105mm), when I am doing anything else I normally pick a lens that has the FOV that I think I need (sometimes I even get that right), but I normally have a 31mm attached to my camera, just for convenience. Am I normal? Hey I don't know, but I am normal in my house (it helps when normality is dictated by a community of one DSLR user)!

02-11-2012, 06:22 PM	#49
OutOfFocus Senior Member Join Date: Aug 2009 Location: Houston, TX Photos: Gallery Posts: 140	The K30/2.8 would also qualify as a "normal" lens on APSC, especially if its focal length really is on the short side of 30.

02-11-2012, 06:42 PM	#50
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by OutOfFocus The K30/2.8 would also qualify as a "normal" lens on APSC, especially if its focal length really is on the short side of 30. Very true, except that it has been out of production for over 30 years. The OP is complaining that the current Pentax lineup is a smidge long for him unless you spring for the 31mm LTD. Steve

02-11-2012, 06:55 PM	#51
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Originally posted by westmill Our eyes dont even come close to that even taking into account perphirel vision, which is genrally used for detecting movement. Apparently you've never done the experiment. Try it some time; you'll be surprised. Or, just read the Wikipedia article on Visual field. You might be referring to macular vision only. Quote: certainly has not got anything to do with prints. Yes it does. Look up the term "perspective distortion" some time - again, the Wikipedia article works fine. Quote: My comment was that most people consider that 50mm in 35mm terms is considered as a standard lense. Yes. I was just pointing out that the reason for this has nothing to do with FOV; that's a common myth. It's all about perspective distortion, and that is something you can't measure until you print the image.

02-11-2012, 10:36 PM	#52
isaacc7 Forum Member Join Date: Feb 2012 Posts: 87	Originally posted by stevebrot Huh? The Sigma 1.8 may well be crap, but it has nothing to do with the size of its image circle. As for retrofocus design for APS-C vs. 35mm vs. 645 vs. you name it...if the camera has a mirror box, there will be a focal length threshold below which you need retrofocus to allow the rear element to clear the mirror. This is one of the big arguments in favor of mirrorless cameras. Steve BTW...who said that retrofocus = bad performance? Plus, for digital cameras, retrofocus lenses have some real advantages. Keeping the rear element away from the sensor helps minimize vingetting and color fringing. A design like the biogon would be a worst case scenario for a digital camera. It was one of the big things that Olympus touted about its original 4/3 standard. They kept the lenses far enough away to ensure "tele centricity" in order to minimize digital specific problems. The "feature" of thinner requires some tricky optical/sensor combinations to get around the inherent limitations. With all of the people complaining about how big the k-01 is, I wonder if it will be easier to hold steady than the really thin Sony cameras.

02-11-2012, 11:58 PM	#53
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by isaacc7 A design like the biogon would be a worst case scenario for a digital camera. I was thinking specifically about the Biogon and its semi-legitimate relative, the Jupiter-12. That rear element is pretty impressive until one considers the havoc it can cause with most digital sensors when only a few millimeters from the sensor surface! Dealing with the "close element" issue was one factor influencing the sensor design in the new Fuji X-Pro 1 as well as the optical design of the lenses for that camera. Steve

02-12-2012, 10:33 AM	#55
westmill Veteran Member Join Date: Jan 2012 Location: Stoke on Trent Photos: Gallery \| Albums Posts: 1,146	Originally posted by Marc Sabatella Apparently you've never done the experiment. Try it some time; you'll be surprised. Or, just read the Wikipedia article on Visual field. You might be referring to macular vision only. Yes it does. Look up the term "perspective distortion" some time - again, the Wikipedia article works fine. Yes. I was just pointing out that the reason for this has nothing to do with FOV; that's a common myth. It's all about perspective distortion, and that is something you can't measure until you print the image. Im well aware of the meaning of perspective distortion thank you very much ! You stick to your wikipedia !

02-12-2012, 11:59 AM	#56
Anvh Veteran Member Join Date: Sep 2011 Posts: 4,616	Originally posted by RKKS08 I miss such a lens for APS-C badly: a SMALL full metal manual focus 2.0/30 with acceptable IQ at 2.0 and very good IQ from 4-5.6 on FOR NOT MORE THAN €100 ($125) new. THIS would be the real equivalent to what Pentax offered during the film era. If not possible, I may accept a plasticy lens body, if the bajonet is made of metal. The reason 50mm are so cheap is because they are easy to make for this register distance, because Pentax didn't shorten the register distance to match APS-C format better it means they need to use a different design for wider lenses. So we will never see cheap 28/30mm f/2 or faster lens for the k-mount, compared to 50mm that is.

02-12-2012, 12:01 PM	#57
Anvh Veteran Member Join Date: Sep 2011 Posts: 4,616	Just remembered that there was a DA30 on the old lens roadmap which would have roughly the same design features as the DA55 . I wonder if Ricoh wll bring it back... sadly there is nothing on the roadmap at the moment.

02-12-2012, 12:06 PM	#58
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	Originally posted by Anvh The reason 50mm are so cheap is because they are easy to make for this register distance, because Pentax didn't shorten the register distance to match APS-C format better it means they need to use a different design for wider lenses. Keeping the longer register distance enables the light rays to hit the sensor wells at a better angle (avoiding the issues the GXR Leica mountor has to deal with), as well as eliminating the need for an adapter to use older lenses.

02-12-2012, 03:20 PM	#59
Anvh Veteran Member Join Date: Sep 2011 Posts: 4,616	You are right but that isn't what is being discussed. If you want to have cheap and fast 28mm lenses like the 50mm are then you need to shorten the register, there is no other way around it. I'm not saying they can't make fast 28mm but they wont be cheap.

02-12-2012, 03:30 PM	#60
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	The problem with wide angle lenses is as much a question of the coverage angle as the register distance. If you shorten the register distance for a given sensor format, you increase the coverage angle from the back of the lens. It's a tradeoff, and doesn't lead to cheaper lenses. As an example, a Zeiss ZM Biogon 28/2.8 on a NEX costs pretty much the same as the ZK Distagon 25/2.8 in K-mount.