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Minolta AF 20mm f/2.8
World's First AF Ultrawide (1986-)
Full-frame MAXXUM and Sony Alpha
© 2013 KenRockwell.com. All rights reserved.

Intro   Specifications   Performance   Compared   Recommendations

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Minolta Maxxum AF 20mm f/2.8

Minolta Maxxum 20mm f/2.8 (Covers full-frame, for Minolta MAXXUM and Sony Alpha cameras, metal 72mm filter thread, 10.0 oz./284 g, about $375 used if you know How to Win at eBay; I paid only $305 for this one for instance). enlarge. My biggest source of support is when you use this link directly to them at eBay, or use any of these links when you get anything, regardless of the country in which you live. Please always use these links when getting any of your gear so I can continue to share what I know for free — but I receive nothing for my efforts if you buy elsewhere. Thank you for your support! Ken.

Sample Image File

Tower 29, 23 May 2013

Tower 29. (Sony A99, Minolta MAXXUM AF 20mm f/2.8, f/11 at 1/200 at Auto ISO 100.) Full-Resolution.

 

May 2013   Minolta   Sony   Pentax   Nikon   Canon   All Reviews   Better Pictures

How to Use Ultrawide Lenses.

Why Fixed Lenses Take Better Pictures.

 

Introduction         top

Intro   Specifications   Performance   Compared   Recommendations

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This Minolta Maxxum AF 20mm f/2.8 is a very well made ultrawide lens for all Minolta MAXXUM and Sony Alpha cameras. Used on today's Sony A99 it has image stabilization and ultra-fast autofocus — and it's better-made and half the price of today's similar Sony 20mm f/2.8! These classic MAXXUM 20s sell every day on eBay.

It works perfectly on the Sony A99, except that the AF-D Depth Map AF (whatever that is) and the automatic lens corrections don't work. So what, the images look great and everything else works, like face recognition and all the focus modes including Direct Manual Focus (DMF) override, so all is well.

Unlike the mostly plastic Sony and Nikon 20mm lenses today, this Minolta has a metal filter thread, metal hood mount and metal focus ring. Ha!

This MAXXUM 20mm AF has rear-group focusing, which means that nothing moves externally (except the focus ring) when focused. The front of this lens is solid metal, not plastic wiggling around on a loose helicoid as in Nikon's 20/2.8 AF.

This is a full-frame lens for 35mm film and full-frame digital, and will be reviewed thusly. Do not use this on cropped-frame cameras since you'll get the same or better performance for less money with any 18-55mm zoom instead. This 20mm is an ultrawide lens and shall be used as an ultrawide lens only.

This is the world's first autofocus ultrawide lens, introduced a year after the Minolta MAXXUM 7000, and it is still the best compact ultrawide lens available for the Sony A99 today.

 

Minolta Maxxum AF 20mm f/2.8

Minolta Maxxum AF 20mm f/2.8. enlarge.

 

Specifications         top

Intro   Specifications   Performance   Compared   Recommendations

 

Name        top

Minolta calls this the MAXXUM AF 20mm f/2.8 (22).

MAXXUM is Minolta's autofocus brand, called Dynax outside the US.

The (22) is the smallest f/stop.

 

Optics        top

10 elements in 9 groups.

Rear focus; the front and exterior of the lens never moves as focused.

Multicoated.

 

Diaphragm        top

Front, Minolta MAXXUM AF 20mm f/2.8

Minolta 20mm f/2.8 at f/22. bigger.

7 straight blades.

Stops down to f/22.

 

Coverage        top

35mm film, full-frame and smaller format digital.

 

Focal Length        top

20mm.

When used on an APS-C style camera, sees an angle of view similar to what a 30mm lens sees when used on a full-frame or 35mm camera.

 

Angle of View         top

94.4º on full-frame.

 

Close Focus        top

0.8 feet (0.25 meters or 10 inches) from the image plane.

That's about 5 inches (130mm) from the front of the lens!

 

Maximum Reproduction Ratio        top

1:7.7 (0.13x).

 

Hard Infinity Focus Stop?        top

Yes.

This is great for astronomy; just turn to the stop and you have fixed laboratory-perfect focus all night.

 

Focus Scale        top

Yes.

 

Depth-of-Field Scale        top

Yes.

 

Infra-Red Focus Index        top

Yes.

 

Aperture Ring        top

No.

 

Filter Thread        top

55mm, solid alloy.

Does not move.

 

Size        top

3.0" (76mm) diameter by 2.1 " (53 mm) extension from flange, measured.

 

Weight        top

10.020 oz. (284.1g), actual measured.

Minolta specifies 10.1 oz. (285g).

 

Hood        top

Minolta 20/2.8 AF Hood

Hood.

Plastic bayonet hood, included.

 

Caps        top

Minolta 20 2.8 with caps and hood

Minolta 20 2.8 with caps and hood. bigger.

72mm snap-in front cap and standard MAXXUM rear cap.

 

Case        top

Often seen with a tubular case.

 

Quality         top

Made in Japan.

 

Minolta Product Number        top

25791.

 

Price, USA        top

About $375 used if you know How to Win at eBay.

I paid only $305 for this one, for instance, while stupider people might pay up to $400.

 

Performance         top

Intro   Specifications   Performance   Compared   Recommendations

Overall    Autofocus    Coma    Distortion  Ergonomics

Falloff    Filters   Flash Exposure   Focus Breathing   Ghosts

Hood    Lateral Color Fringes    Macro    Mechanics

Sharpness   Spherochromatism  Sunstars   Survivability

 

Overall       performance     top

The Minolta 20mm f/2.8 is a classic 1980s 20mm f/2.8, performing the same optically as Nikon's plastic 20mm AF-D, but much better made mostly out of solid alloy.

This is the same lens as the cheesier Sony 20/2.8 sold today for twice the price.

 

Autofocus       performance     top

 

AF Speed

AF speed is ultra fast, with one full turn (two half-turns) of the AF screw bringing it from infinity down to 1.1 feet.

 

AF Accuracy

On the Sony A99, focus is dead-on every time at f/2.8, presuming you're letting the A99 lock-on to the right thing.

 

Manual Focus

Manual focus is the usual ring.

The metal ring is a bit narrow, and partially shadowed by a ridge on the barrel behind it, and so what: you can flick it with just a fingertip.

 

Coma       performance     top

Coma (saggital coma flare) often causes weird smeared blobs to appear around bright points of light in the corners of fast or wide lenses at large apertures.

Yes, the Minolta 20mm f/2.8, like other conventional 20mm f/2.8 lenses, has some coma at f/2.8.

It's completely gone by f/5.6.

 

Distortion       performance     top

The Minolta 20mm f/2.8 has the usual barrel distortion seen in similar lenses, which is a complex "moustache" distortion where the center bulges-out while the sides stay relatively straight.

The best you can do in Photoshop's lens distortion filter is to try a coefficient of +2.0 regardless of distance.

The Sony A99 doesn't recognize this lens for any automatic correction.

 

Ergonomics (handling and ease-of-use)       performance     top

Minolta 20mm f/2.8

Minolta 20mm f/2.8. bigger.

This lens is mostly metal, so it feels much better than the plastic garbage from Sony.

The plastic barrel is mostly rubber grip.

The solid metal focus ring has to be touched from the side, not up from the rear of the barrel because the barrel has a flare which hides the rear of the focus ring.

 

Falloff (darkened corners)       performance     top

Falloff on FX and 35mm is visible at f/2.8, and gone otherwise.

The Shading Correction in the Sony A99 makes no difference.

I've exaggerated the falloff by shooting a gray field and placing these on a gray background.

 

Minolta AF 20mm f/2.8 falloff on full frame and 35mm at infinity, no correction:

f/2.8
f/4
Minolta 20mm f/2.8 falloff Minolta 20mm f/2.8 falloff
Minolta 20mm f/2.8 falloff Minolta 20mm f/2.8 falloff
f/5.6
f/8

© 2013 KenRockwell.com. All rights reserved.

 

 

Filters, use with       performance     top

Thank goodness this Minolta AF 20 has a solid alloy front end, not crappy plastic. Filters easily spin right on and off, without cross-threading.

There is no problem with vignetting on full-frame with any normal filter. With two stacked filters, you'll get a little vignetting.

It's close with a thick rotating filter like a grad.

Don't use any ultrawide with a polarizer, nature looks funny when shot that way.

The filter ring doesn't move, even with focus.

 

Flash Exposure        performance     top

This original Minolta AF 20 has no distance encoding, but that doesn't stop it from making great images with flash.

Yay Ryan! 23 May 2013

Yay Ryan! (Sony A99, Minolta MAXXUM AF 20mm f/2.8, f/8 at 1/125 at Auto ISO 100, Sony HVL-F20AM flash.) bigger.

 

Focus Breathing       performance     top

Of interest mostly to cinematographers focusing back and forth between two subjects, the image from the Minolta 20mm f/2.8 gets larger as focused more closely.

 

Ghosts       performance     top

Ghosts are no problem with this multicoated lens, even on the complex Sony A99 which has all sorts of internal mirrors in the optical shooting shooting path.

Here's looking directly into the disk of the noonday sun, which was blinding in person:

Minolta 20mm f/2.8 ghosts

Minolta 20mm f/2.8 at f/8. enlarge.

Enough glare to blind a dead man, and this is the worst I could show for it after several tries.

 

Hood       performance     top

Minolta MAXXUM AF 20mm f/2.8 with hood

Minolta 20mm f/2.8 with hood. bigger.

The plastic hood is included.

It easily bayonets on the metal bayonet.

It has a red line which stands out as you see, making it a zillion times easier to mount quickly in the field than other lenses that use the same silver-white paint for everything.

 

Lateral Color Fringes       performance     top

Lateral color fringes are this lens' biggest fault. If you look for such things, you'll see some magenta-green fringes on the 24 MP full-frame Sony A99, with lateral color correction turned OFF.

Oddly, the lateral color gets stronger if you turn correction ON in the A99! Leave the corrections OFF in the A99, since the A99 doesn't recognize this lens.

Your camera will differ.

 

Macro       performance     top

It gets exactly as close as every other 20mm f/2.8 SLR lens has for the past 30 years:

Minolta 20mm f/2.8 macro performance

Complete image at close-focus distance at f/2.8 on full-frame.

 

Minolta 20mm f/2.8 macro performance

Crop from above image at f/2.8 as shot on the 24MP Sony A99. If this is 6" wide on your screen, the complete image printed at this same magnification would be 40 x 60!" (1 x 1.5 meters!)

Thus the MAXXUM 20mm f/2.8 gets close (just 5" from the front of the lens), but since it's so wide it doesn't look that close. The great news is that it's super-sharp, even wide-open, at any distance due to the rear-focusing design.

 

Mechanics and Construction       performance     top

Minolta 20mm f/2.8

Minolta 20mm f/2.8. enlarge.

The Minolta 20mm f/2.8 is much better made than Sony's and Nikon's 20mm f/2.8 AF lenses. Unlike the others, this MAXXUM lens has an all-metal front end.

 

Filter Threads

Metal.

 

Hood

Plastic bayonet.

 

Hood Mount

Metal.

 

Identity Ring

Engraved metal front ring, filled with two colors of paint.

 

Front Barrel Exterior

Metal.

 

Main Barrel Exterior

Plastic.

 

Focus Ring

Solid metal.

 

Depth-of-Field Scale

Yes.

 

Aperture Ring

None.

 

Mount

Chromed metal.

 

Barrel Markings

Paint.

 

Mounting Index Dot

Red plastic ball.

 

Serial Number

Engraved into bottom of barrel and filled with paint.

 

Moisture seal at mount

No.

 

Noises When Shaken

Some clicking and clunking.

 

Made in

Japan.

 

Sharpness       performance     top

Yes, it's very sharp if you know what you're doing. Image sharpness depends more on you than your lens, and lens sharpness doesn't mean much to good photographers.

The MAXXUM 20mm's biggest limitation is lateral color. It's sharp and has a flat field otherwise.

As shot on the full-frame 24MP Sony A99:

 

At f/2.8

The center is sharp.

The corners are dark and somewhat blurrier. They get so much darker that I doubt anyone would notice this; the corners on full-frame aren't that bad even at f/2.8.

 

At f/4:

The center is perfect, and the corners are much lighter.

Now that you can see them, the corners are softer, but not that much.

 

At f/5.6:

The corners are even a little bit better and brighter than at f/4.

At f/5.6, this Minolta 20/2.8 is just about optimum, which is a lot more than I can say for Canon's 16-35mm f/2.8 L II and 17-40mm f/4 L which usually need to be stopped down to f/11 for best results!

 

At f/8

f/8 is the optimum aperture.

 

At f/11

It's about the same as at f/8, with the center just slightly dulled from diffraction. (Diffraction isn't as obvious in the corners since they tend to be softer.)

 

At f/16

It's softer all over; diffraction is limiting performance.

 

At f/22

It's softer all over; diffraction is limiting performance.

 

Spherochromatism       performance     top

Spherochromatism, sometimes mistakenly called "color bokeh" by laymen, is a minor aberration which can add slight color fringes to out-of focus highlights in fast, long lenses.

This lens is neither fast nor long, and I see no spherochromatism.

 

Sunstars       performance     top

Minolta 20mm f/2.8

Sunstar at f/22. enlarge.

With its conventional 7-bladed diaphragm, the AF 20 /2.8 can make great 14-pointed sunstars on brilliant points of light. Bravo!

 

Survivability       performance     top

This Minolta 20mm f/2.8 is from 1986 and is still working perfectly today in 2013 after having been bought from a random stranger on eBay.

It has no motors and no encoders. There is nothing to go wrong that a good repairman can't fix. The only electronics are a ROM chip that should not wear out unless you go doing something stupid, like trying to take it apart.

It is perfectly normal for the rubber on the barrel to turn white. The whiteness rubs off with use; a white looking barrel means a lens that hasn't been used much.

Therefore unlike many AF lenses today, this 20 AF ought to last last for plenty of more decades of great pictures.

 

Compared         top

Intro   Specifications   Performance   Compared   Recommendations

Minolta downgraded this 20mm AF to much more plastic and rounded the diaphragm, destroying sunstars some years after this model. Otherwise, it's the same thing in an obviously crappier package.

Nikon's 20mm f/2.8 AF (1989-) has always been all plastic. Its optics are about the same, and uses the same mechanical screw AF technology.

Sony's 20mm f/2.8 (2006-) is the same lens. It uses the same optics with crappier plastic mechanics, but adds a distance encoder to help flash exposure. As you've seen, flash exposure on a Sony A99 is marvelous with this lens, so you won't see me buying a new Sony version of this for twice the price!

Canon's 20mm f/2.8 USM (1992-) is a much newer kind of lens and also made with plenty of metal. Its optics are about as good, but it uses an internal ultrasonic motor and offers instant manual-focus override on all Canon EOS cameras — something none of these other lenses can do with their mechanical couplings for autofocus on their brands of cameras.

 

Recommendations       top

Intro   Specifications   Performance   Compared   Recommendations

I bought this Minolta 20mm f/2.8 for my Sony A99. I see no reason to pay twice as much to get a plastic version with the Sony brand on it. This classic MAXXUM lens makes great images, focuses super-fast, gives great flash exposures and feels so much better than the all-plastic copies.

On the Sony A99, turn off the lens corrections in the sixth gear menu for less lateral chromatic aberrations; the A99 adds them back in of you turn its corrections ON!

If you've found the time, effort and expense I incur researching and sharing all this information for free, this free website's biggest source of support is when you use this link to get yours at eBay as I did, or use or any of these links when you get anything, regardless of the country in which you live. Please always use these links when getting any of your gear so I can continue to share what I know for free — because I receive nothing for my efforts if you buy elsewhere. I'm not NPR; I don't get any government grants or have annoying fund drives.

Thanks for your support!

Ken.

 

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