Hasselblad 24mm (or 25mm) f2.5V and 135mm f2.5V

[MGrayson]

But those electronic steps steal resolution! This seems to be the approach to smaller pixel dimensions in the future that will require wider apertures to eliminate the effects of diffraction but all at the cost of resolution. I, for one, would rather have slower lenses with less distortion at a possible cost of being slightly heavier.

Victor B.

Since de-mosaicing screws up resolution anyway, I'd love to see tests done on a monochrome sensor. Then we could really see the tradeoff between trying to eliminate distortion optically and digitally.

I was going to claim that the Leica S 24/3.5 was big and heavy and distortion free, but I just played with a file and it has a fair bit of mustache distortion if uncorrected. This side of tech camera lenses, I don't know of a large aperture very wide lens that doesn't have it, including the XCD 21/4. (I find the Voigtländer terminology - Super Wide, Ultra Wide, Hyper Wide, Ridiculously Wide, Insanely Wide - pretty amusing. OTOH, what else do you call a 10mm FF rectilinear lens?)

Matt

 

[TechTalk]

...From the published MTF charts the XCD 25-V looks to be quite sharp across the field when stopped down to f/5.6, already showing signs of diffraction on center. Comparing these data with the XCD 21 and XCD 30 - both outstanding optics - takes a bit of imagination, given the different focal lengths and apertures at which the tests were performed (assuming, of course, that these represent actual measurements, which Hasselblad was known to publish for the previous legacy Zeiss lenses). I'm guessing that one will need to split hairs to discern any appreciable difference in sharpness when stopped down to f/8-f/11. Looking forward to seeing some real world images with the new lens...

John

Thanks for providing links to the data sheets and MTF charts. Zeiss may still use a prototype or production lens for their published MTF measurements. Unless otherwise stated, I would assume published MTF data from other lens makers use lens design data to calculate MTF values as that has been the convention for some decades.

Hasselblad, Leica, and Rodenstock MTF charts are at least realistic in that diffraction is incorporated into their published MTF calculations and so they can be reasonably compared. They, along with Zeiss, also provide more complete lens data than you will generally find these days.

For the convenience of anyone interested, below are side by side MTF charts for the XCD 21, 25, and 28 mm focal length lenses.

 

[MGrayson]

And for a sense of ho much distortion correction is being applied, Hasselblad publishes the uncorrected distortion

Here's the XCD 21/4


The XCD 25/2.5


And the XCD 28/4


The 21 and 25 look quite similar (and complex). The 28P's is smaller and simpler.

The XCD 120 Macro, focused at 0.8m, has a maximum uncorrected distortion of about 0.1

 

[TechTalk]

...Note that many if not most of the modern designs rely on pretty aggressive software corrections, which have become quite advanced and (I'm speculating) have freed up lens designers to make different compromises in terms of correcting optical aberrations that can be easily handled after the fact by software.

Right. The ability to better control specific lens aberrations which require optical correction by including some degree of under-correction of other aberrations which can be well corrected thru digital post processing (such as vignetting or distortion for example) allows for more freedom in lens design and improvements which would not be possible without incorporating software correction into the design.

This article from Richard Butler, Technical Editor at DP Review, may be of interest to some... A distortion of the truth? Here’s why we’re not against software lens corrections

 

[TechTalk]

Yes, as does LR. The whole imaging pipeline has optical and electronic steps. They've just moved geometric distortion control from the glass to the silicon. Lenses with flat fields and no distortion are wonderful, but have other compromises, e.g., the SK 35XL issues with the latest Hasselblad back. I think the "fix geometry in software" is one of the best design tradeoffs in years. Lenses get smaller and have fewer other aberrations.

Well said. Lens design revolves around tradeoffs and compromises to arrive at a balance which satisfies the overarching goals of the design.

Modern lens design now includes the entire imaging process and can produce smaller, lighter, faster, and sharper lenses as a result. The ability to improve image quality by some degree of specific under correction in the lens has been well understood for a very long time. Now optical designers are finally able to incorporate post processing software tools into their designs to make even better lenses and a wider variety of designs which were not previously practical.

As one example, intentional under-correction of vignetting to gain resolution is a lens design principle which has been understood and used for a very long time.

Handbook of Optics Volume 1 – 3rd Edition The Optical Society of America:

General Principles of Geometrical Optics - Chapter 1.81

"When vignetting occurs, the image irradiance is changed, and its diminution with field height is faster than it otherwise would be. Aberration properties are also changed, so vignetting is sometimes used to eliminate light that would unacceptably blur the image."

Components - Chapter 17.15

"It should be noted that vignetting is often used in these and other lens types to control the higher-order aberrations that are often observed at large field angles. Although a loss in illumination occurs, the gain in resolution is often worthwhile."

This article from optical design software maker Zemax which discusses "Designing optical systems with intentional vignetting" may be of interest to some.

 

[MGrayson]

That's really interesting. I never thought about how vignetting could act to effectively reduce the aperture far from the center.

Actually, even with a pinhole, it's pretty clear. The edges are further from the aperture, so its angular size is smaller. There's also the aperture appearing elliptical. There's some power of cosine that gets tossed around - cubed? - that is natural for vignetting. I should go read the book...

 

[TechTalk]

Preordered from Capture Integration. B&H has it in stock...

B&H is already showing the lens out of stock, but Capture Integration at this moment still shows one available from their allocation. No need to wait when you still have an opportunity to get it from a great dealer.

 

[Ai_Print]

I'm not really in the market for this lens as I don't need something that wide, but it is nice to see they made less of a compromise in the design in order for those light rays to hit the corners and form a sharp image.

 

[buildbot]

Well said. Lens design revolves around tradeoffs and compromises to arrive at a balance which satisfies the overarching goals of the design.

Modern lens design now includes the entire imaging process and can produce smaller, lighter, faster, and sharper lenses as a result. The ability to improve image quality by some degree of specific under correction in the lens has been well understood for a very long time. Now optical designers are finally able to incorporate post processing software tools into their designs to make even better lenses and a wider variety of designs which were not previously practical.

As one example, intentional under-correction of vignetting to gain resolution is a lens design principle which has been understood and used for a very long time.

Handbook of Optics Volume 1 – 3rd Edition The Optical Society of America:

General Principles of Geometrical Optics - Chapter 1.81

"When vignetting occurs, the image irradiance is changed, and its diminution with field height is faster than it otherwise would be. Aberration properties are also changed, so vignetting is sometimes used to eliminate light that would unacceptably blur the image."

Components - Chapter 17.15

"It should be noted that vignetting is often used in these and other lens types to control the higher-order aberrations that are often observed at large field angles. Although a loss in illumination occurs, the gain in resolution is often worthwhile."

This article from optical design software maker Zemax which discusses "Designing optical systems with intentional vignetting" may be of interest to some.

This is really interesting, thanks for educating us!

 

[Steve Hendrix]

Well said. Lens design revolves around tradeoffs and compromises to arrive at a balance which satisfies the overarching goals of the design.

Modern lens design now includes the entire imaging process and can produce smaller, lighter, faster, and sharper lenses as a result. The ability to improve image quality by some degree of specific under correction in the lens has been well understood for a very long time. Now optical designers are finally able to incorporate post processing software tools into their designs to make even better lenses and a wider variety of designs which were not previously practical.

As one example, intentional under-correction of vignetting to gain resolution is a lens design principle which has been understood and used for a very long time.

Handbook of Optics Volume 1 – 3rd Edition The Optical Society of America:

General Principles of Geometrical Optics - Chapter 1.81

"When vignetting occurs, the image irradiance is changed, and its diminution with field height is faster than it otherwise would be. Aberration properties are also changed, so vignetting is sometimes used to eliminate light that would unacceptably blur the image."

Components - Chapter 17.15

"It should be noted that vignetting is often used in these and other lens types to control the higher-order aberrations that are often observed at large field angles. Although a loss in illumination occurs, the gain in resolution is often worthwhile."

This article from optical design software maker Zemax which discusses "Designing optical systems with intentional vignetting" may be of interest to some.

You didn't pay $937 for your copy, did you?


Steve Hendrix/CI

 

[TechTalk]

The Handbook of Optics was a gift from a generous friend. Proof that it pays to be nice to people!

 

[TechTalk]

That's really interesting. I never thought about how vignetting could act to effectively reduce the aperture far from the center.

Actually, even with a pinhole, it's pretty clear. The edges are further from the aperture, so its angular size is smaller. There's also the aperture appearing elliptical. There's some power of cosine that gets tossed around - cubed? - that is natural for vignetting. I should go read the book...

Thanks! For anyone looking for a place to begin exploring the topic, a concise and informative article on the subject of vignetting can be found here. It concludes with: "It should be mentioned that vignetting is not always a bad thing. A lens designer can deliberately introduce vignetting in favor of a better control of aberrations, sacrificing field coverage for overall contrast and sharpness."

Links to other useful and concise articles about optical characteristics from the same author can be found here.

 

[MGrayson]

Thanks! For anyone looking for a place to begin exploring the topic, a concise and informative article on the subject of vignetting can be found here. It concludes with: "It should be mentioned that vignetting is not always a bad thing. A lens designer can deliberately introduce vignetting in favor of a better control of aberrations, sacrificing field coverage for overall contrast and sharpness."

Links to other useful and concise articles about optical characteristics from the same author can be found here.

Ah. Cosine to the fourth, and very clearly explained. I was aware of mechanical vignetting and cat's eye bokeh - it's hard to miss, but natural vignetting is less obvious. Thanks!

 

[rdeloe]

Thanks @TechTalk for those Wayback Machine links to Paul van Walree's old Toothwalker site. I'd encountered Paul's writing years ago, but wasn't ready for it. I'm somewhat less not ready for it now and am finding his text and illustrations extremely useful. I'll probably have to read them all multiple times, but so many things that I didn't quite understand before, or at all, make a lot more sense. Losing this work would have been a small tragedy because his pages are the most accessible lens optics primers I've ever encountered. I had no idea that natural and optical vignetting were different, and now I finally understand why the rangefinder and symmetrical technical camera lenses I use the most are the way they are.

 

[jng]

Thanks @TechTalk for those Wayback Machine links to Paul van Walree's old Toothwalker site. I'd encountered Paul's writing years ago, but wasn't ready for it. I'm somewhat less not ready for it now and am finding his text and illustrations extremely useful. I'll probably have to read them all multiple times, but so many things that I didn't quite understand before, or at all, make a lot more sense. Losing this work would have been a small tragedy because his pages are the most accessible lens optics primers I've ever encountered. I had no idea that natural and optical vignetting were different, and now I finally understand why the rangefinder and symmetrical technical camera lenses I use the most are the way they are.

I thought the content and style looked familiar. I just checked and found the old toothwalker.org URL sitting in one of my bookmark folders - what a great resource this was! Thanks to @TechTalk for pointing us to this page.

John

 

[FloatingLens]

Any sample pictures produced with the 25V from forum members yet? I am curious.

 

[mrcmrc]

I have the 38V, I think it fits better than the 55V for the way I see and take pictures. To add a wide angle I might have preferred the 21‘s focal length than this 25’s. But I guess since this one came out we won't see a wider one soon, right?

- m.

 

[SrMphoto]

You have a good point on this.
Still, it seems to me just like giving up on addressing the core issue, which is real optical optimization. It always sounds like taking a shortcut.
Anyway, the key of all engineering work is finding the best compromise, at the target price.

Allowing for slight software distortion correction may allow for the optimization of other more relevant optical quality improvements.

 

[Geoff]

Just for comparison - the Leica M 21 SEM f3.4 - while the info shows some distortion, its a really good architectural performer.

 

[MGrayson]

Been awfully quiet here. Anyone receive an XCD 25/2.5? Are shipments happening?