Full-Frame & Keeping The Compactness

For nearly three years now, Sony's A7 series have been the uncontested champion of compact, full-frame ILC's (Interchangeable Lenses Cameras). Keeping them small can be tricky however. In a push for ultimate image quality most of Sony's newer lenses are large and heavy.

Although I've since sold the Voigtlander 35mm f/1.4 (above) because it was bad for infrared, I have tried a few other small lenses during my time with the A7. Here are my thoughts on what makes a good choice when trying to keep the size and weight of your camera bag to a minimum.

Before I go any further though, let me iterate why this camera/system is so interesting for infrared... 

• EVF means you get to see in the wavelength you're shooting in
• Ability to adapt to any SLR/RF lens helps choose lenses that don't suffer from hot spot
• Cleaner Full-Frame IQ helps with heavy manipulation often needed for IR processing

Adapting to SLR lenses (especially older ones) often helps with the IR hot spot issue, but it also adds to the size & weight (due to the larger, usually metal, adaptors), thus compromising on size & weight.

Shown off the camera you can see the difference in size a little more easily. This also illustrates how a moderately sized SLR lens can become quite front heavy when added to an adaptor for the A7. Although the Nikon 35mm f/2 lens is a great IR performer I will not be featuring it here due to it's lack of compactness. Here are the lenses I will be talking about...

35mm and 40mm lenses are a great for general / travel photography in my opinion. Just the right balance between wide and tele. Plus they're usually the smallest option, as long as you don't want them too fast. Over the last two years I have used the three lenses above and I wanted to compare them all here because I like each of them for different reasons. Here are some technical details before I start to get into more opinions.

NOTES: The dimensions, below (length & weight) are including the camera. The weight is with no strap or lugs (not to reduce weight, but because I hate camera straps). The weight also doesn't include a lens cap or hood, but it does include the battery and memory card, so this is what you'll notice when actually using them (in most cases). I haven't included the price of the adaptor (where needed) here, but I will mention it in the text below.

Weight

In this regard the Zeiss is king by a mile. Even with it's meager f/2.8 max aperture it's hard to believable how light it is. The official weight of the camera is listed as 474g (including battery and media), but mine comes to 455g, for some reason. The breakdown for the full Zeiss 35mm package is as follows:

• Camera: 411g
• Lens: 119g
• Battery: 42g
• Hood: 12g
• Cap: 5g
• SD: 3g

So, the total (including the hood and lens cap this time) is 592g. It makes a rather interesting comparison to my previous camera - the Nikon D3. Now I know these cameras are very different, but what do I really miss from the transition? The main thing is AF speed, especially in low light, because the D3 was a miracle by comparison. Apart from that I really don't miss much about the pro DSLR. My camera is now with me most of the time and much of this is down to the weight.

Let me put this change into perspective - The Sony A7 body, Zeiss 35mm lens, memory card and 5 (yes five) batteries weighs less than half that of the Nikon D3 body alone (with no lens)! OK, how about this... All of this next list weighs less than the Nikon without anything (no memory cards, battery or lens):

• Sony A7
• Zeiss Batis 25mm f/2
• Zeiss 35mm f/2.8
• Zeiss 55mm f/1.8
• 2x batteries + SD card

To be fair 5 Sony batteries probably don't last as long as 1 in the Nikon D3, but that's not totally fair because of the EVF and live-view being on constantly. Before roasting me about dual memory cards and other features; I do admit that it's not exactly fair to compare the cameras on this level. This is purely about how amazing it is to have a functioning camera that weighs so little, whilst still being able to produce amazing quality images. It has made a huge difference to me and where I take it.

Size

The other two lenses are much heavier. If we concentrate on AF options the Canon + Metabones is quite a bit heavier. It weighs almost as much as the Zeiss 55mm f/1.8, which is not only a phenomenal lens for colour, but for IR as well. That said it is quite a bit longer, so apart from it being the wrong focal length I didn't include it here for that reason. The newer Sony 50mm f/1.8 lens is different story and I am tempted to add that one to the comparison because I do own that one as well.

If you're OK with spending good money on manual focus lenses there are some other choices that I will mention now, but can't talk about extensively here because I haven't tried them. If you're curious I advise looking in to rangefinder lenses from Leica and Voigtlander. It's not just because they're small, but the adaptor is much thinner too (see the top image for reference). 

There is an AF adaptor for rangefinder lenses now, in the form of the Techart Pro. This is about the same price as the Metabones (£350), which isn't too bad in of itself, but the price of the lenses and the fact that it only focuses "well" on the A7RII has stopped me from being able to try one. If you have the high-end Sony however then that's not your only other option for mini AF lenses though. Techart also make an AF adaptor for Contax G mount lenses. This would enable you to use the fabulous looking Contax 35mm f/2 lens (which is actually Zeiss made). The lens is not too expensive for what it is either, but be warned this AF adaptor is no longer listed (or supported?) on the Techart website and the lens doesn't have a 'normal' manual focus ring.

Cost

Including the Metabones adaptor in the cost of the Canon lens makes it almost as expensive as the Zeiss, but with the latest firmware (June 2016) it allows pretty decent phase detect AF, even on these first generation A7 models. This makes it a really nice option if you want to use other Canon lenses. If you're only buying it for this pancake lens however then you might want to think twice, unless you're more interested in IR performance and have to have AF.

The Konica 40mm lens is a great option if you're on a tight budget and can live with manual focusing. It's possibly the best lens here for IR image quality too. The fact that it's over a stop faster than either of the two AF options and weighs less than the Canon, despite being all metal and glass and needing a big SLR adaptor is really impressive. The wide open performance is fine on close up portraits, but for distance shots it's awful. You'd need to stop it down to f/4 to get real sharpness, but is that really different from many other lenses? and here the sharpness does impress. For something so cheap it's stunning. 

Autofocus Only Options

Since the latest update for the Metabones adaptor (June 2016) the Canon 40mm STM lens focuses so much faster on the first generation Sony A7 bodies! Getting proper access to phase detect AF. This is a huge benefit  to owners of the older Sony cameras (like me), but this update wasn't really hyped so some may have missed it. Before this it was painfully slow to focus on anything, even with good light. With low light it would generally fail to focus at all. This would really put you off using Canon lenses on the original A7/r/s. Now that it's got PDAF however it seems faster to focus than the new Sony 50mm f/1.8 lens (although I haven't done a direct comparison for that yet, or been able to try the firmware upgrade for the 50mm).

I could have included Sony's new nifty 50 here (purely based on size), although it would have been the biggest, but I decided to stick to slightly wider lenses that are better suited for travel. If you're really curious to see this comparison let me know because I could add it later...

Comparing the two AF lenses together directly doesn't come out particularly well in favour of the Canon. The 35mm Zeiss lenses extra 5mm of FoV makes it a bit better as a travel lens, but it's also smaller, significantly lighter, has better image quality overall, focuses noticeably faster and hunts less as well. 

Where the Canon pulls ahead is with infrared performance and this is why I keep it around. That and I managed to save £300 on the Metabones adaptor by getting it with the camera. That saving made it less than half the cost of the Zeiss, so if you can find a deal like that I highly recommend it. 

Filters For IR

Ultimately I couldn't resist the charm of the little blue badge. It's IR performance can be annoying, but I'm soon going to be trying it out on an AR (Anti Reflective) coated internal filter conversion, so I'm hoping it does a lot better there. Time will tell on that one, but one other thing I wanted to mention about IR is when using filters. The Zeiss lens' hood is quite clever, but when using thicker (49mm) filters the hood may not attach any more. If that happens then you also can't get the lens cap on and this is a really stupid design flaw. If only they included a 49mm lens cap in the box as well as the weird 40.5mm version then this wouldn't be a problem. If you're buying this lens for use with a full spectrum conversion then do yourself a favour, buy a spare 49mm lens cap as well. The official ones can be picked up for as little as £6, so why on earth they didn't include one in the box is beyond me.

The Canon lens' filter size is the most common 52mm, thus making it cheap and easy to find anything you want for a full spectrum or IR conversion. The Konica is more annoying, with a 55mm filter thread. It may not sound like much, but this is a pretty rare size to find second hand options, so this will push the price up if you want some specialised filters. What's most annoying about this is that stepping down to 52mm works fine, with no vignetting, If this was just because they wanted the weird text on the front that's super annoying.

Here's one more shot of the two main AF options on the original Sony A7...

Kolari's Answer To The Hot Spot Issue

Kolari Vision are a popular choice for IR conversions on many camera types. Their prices are reasonable and they have many wavelengths on offer. Recently they've added an option to have any of these internal filters coated with a special anti-reflective (AR) coating to reduce hot spots. When I heard about this I had to give one a try because a lot of native lenses for the Sony FE cameras (A7 series) suffer from hot spots and many of them quite badly. Normally there is no fix for the hot spot issue because it's due to the lens, but let's put it to the test to see if it's as good as they advertise...

Anti-Reflective coated external filters are nothing new, so it's been possible to use them on a full spectrum conversion for a while. Filters like the 093 MRC, from B+W (an 830nm IR filter) have this coating. You can spot these because instead of being an opaque (black) colour they reflect a blue/purple. The same is true of the Kolari internal filter (see below).

Full spectrum conversion (left) vs the AR coated 720nm conversion from Kolari (right)

The problem with these external filters is that they don't do anything for hot spots. I have tested this on several different types and there is no discernible difference at all. Because of this I was a little dubious as to the effectiveness using a similar trick on the internal filter replacement. Fortunately that concern was very short lived because this internal coating does indeed work. It doesn't completely remove the effect, but it does take it down by 1-2 stops in intensity. What I mean here is that; Let's say a hot spot normally starts to show up on a lens (using a normal internal conversion) at f/8, it will start closer to f/16 on the coated conversion, and that can make all the difference.

Results

Here are some samples, comparing a few different AF lens options for the Sony FE platform. All of these options are known to produce a hot spot to varying degrees. These will be compared between a standard (uncoated) 720nm filter and the Kolari Anti-Reflective Coating conversion. From left to right, these lenses are:

• Sony FE 50mm f/1.8
• Zeiss Batis 25mm f/2
• Sigma 35mm f/1.4 Art (with MC-11 adapter)

Note: In all the below samples Kolari's coated version will be on the right.

Sony FE 50mm f/1.8

▲Uncoated Filter▲ -  f/1.8 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/4 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/8- ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/22 - ▲Kolari AR Coating▲

The IR hot spot on the FE 50mm is not bad at all. It's not as clean as theSony/Zeiss 55mm f/1.8, but then not many lenses are. What little hot spot there is here on the smaller apertures is almost non-existent on Kolari's coated filter. Let's see how it does with a worse performer...

Simga 35mm f/1.4 Art

▲Uncoated Filter▲ -  f/1.4 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/2 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/4 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/8 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/16 - ▲Kolari AR Coating▲

The difference here, between the standard and coated filter is much more noticeable. The difference at f/8 being the stand-out one for me. This lens really starts to get annoying at f/8 on a normal filter, whereas the coated version is considerably better.

Zeiss Batis 25mm f/2

▲Uncoated Filter▲ -  f/2 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/4 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/8 - ▲Kolari AR Coating▲

▲Uncoated Filter▲ -  f/22 - ▲Kolari AR Coating▲

Some lenses provide terrible results when stopped down and this is frustrating true of native wide Sony Lenses. Although the coatings clearly help, it won't be enough to save the day in these extreme cases. It'a worth noting that 720nm is also pretty forgiving. The hot spot will be intensified with the stronger wavelengths like 830nm or higher.

At 720nm the Batis lens is generally acceptable at f/4, when using Kolari's coated conversion. With a standard 720nm filter the chances of getting usable results on the same lens and settings are heavily against you, producing a large amount of failures. This is where the coated option shows it's true value in my opinion. Common middle apertures see improvements that often make the difference between a good image and a bad one.

Vignetting

You may have noticed that there is significantly more vignetting on the normal filter. In some small part this may be due to the improved hot spot, but there is another big reason why this is happening. As well as the AR coating this conversion is also using a special 'thin' filter. This has the effect of greatly reducing vignetting on the Sony A7 due to the normal filter cluster having very thick glass on the filter. You can read more about that here. This service can be applied to normal Sony A7 series cameras as well as full spectrum or IR conversions. I'm so impressed by this that I want to have it done to all of my A7 cameras and I will if I can.

Summary

I don't really need to write much here as the pictures speak for themselves. Kolari's 'anti reflective' coating is doing a great job in my opinion. It's not going to fix any lenses hot spots entierly, but it will help and can make the difference of certain apertures being acceptable or not. I wouldn't necessarily suggest upgrading your current conversion for this, but that's totally up to you how much you're affected by this problem and that will depend on what lenses you're using. However, if you're thinking about getting a camera converted then I highly recommend going for this.

Future Tests

I will continue to post results comparing lenses on these two cameras. next up will be the Sony/Zeiss 35/2.8, this was another bad performer and could become not too bad with the Kolari camera. I want to do more testing on the Sony/Zeiss 55/1.8 because although that lens doesn't suffer from hot spot it did suffer from some issues with external filter, which I assume would be gone here. I'm also curious whether the thin filter on the Kolari conversion would adversely affect corner sharpness, so all those tests will be coming soon...

Lens Review - Carl Zeiss Sonnar T* FE 35mm f/2.8

This was one of the first lenses to come out for the FE mount & A7 series cameras. It typifies the dream of having a really small full frame camera that's also able to pull off some impressive image quality.

For a relatively normal fov prime with a lacklustre aperture it actually isn't that small. What's worse is that it costs a lot considering those specifications. For colour use it mostly justifies the badge price with some generally stellar sharpness and decently fast auto focus. Can it pull a similar rabbit out of its hat for infra-red though? Let's see...

      Stats
● Mount: Sony FE
● Adapts to DSLR: No
● Adapts to (other) ILC: No
● Focal Length (FF): 35mm 
● Field of view (FF): 63.4°
● Lens Elements: 7
● Lens Groups: 5
● Aspherical Elements: 3
● Aperture range (f stop): 2.8 - 22
● F-stop increments: 1/3
● Aperture Blades: 7 (curved)
● Aperture Ring: No
● Autofocus: Yes (silent)
● Manual Focus Ring: By Wire
● Min. Focus Distance (cm): 35
● Max Reproduction Ratio: 1:8.33
● Internal Focus: Yes
● DoF Scale: No
● IR offset markings: No
● Body Material: Metal
● Filter Thread Material: Plastic
● Filter thread: 49mm
● Static Filter Rotation: Yes
● Dimensions (mm): 61.5 x 36.5
● Weight (g): 120
● Dust / Moisture Sealed: Yes
● Mount Seal: No
● Manufacture Country: Japan
● Manufacturing Span: 2013 >
● Price New: £550 - 700
● Price Second Hand: £350 - 400
● Accessories (Included): Hood (ALC-SH129)

     Quick IR Performance Scores

● Pure IR HotSpot (Lack of): 2/10

● Colour IR HotSpot (Lack of): 2/10

● IR Sharpness (Middle): 8/10

● IR Sharpness (Edges @ f/8): 5/10

● IR Sharpness (Edges @ f/2): 5/10

IR Quality / Hot Spot

Here's a new set of images, a test for IR hot spot that I'm trying out (see more about it here). Basically what you're looking for here is a clean dark sky, with no bright spots.

Like most lenses, this one vignettes noticeably when wide open and that can look like a large hotspot. Here there actually is a large hot spot at f/2.8, but usually its vignetting that's largely responcible for this confusion. With this lens the opposite illusion occurs. It almost looks like a perpetual vignetting, all the way up to f/22. You'll still notice the hot spot is more obvious closer to the bottom right of the set. There is so much stray reflection here that it's difficult to see where the true value of the clear sky actually is, even with access to the same scene in every aperture. The hotspot will always be present, even if its hidden in detail.

Another sign that the hot spot is bad is being able to tell how many aperture blades the lens has from the reflected light. In a traditional lens flare that's quite normal, but with hot spot it's on the disturbing side.

This video helps illustrate the hot spot performance at f/22. As well as the strong central circular hot spot, the reflection issues can continue outwards to the very edge depending on where the bright areas are in the scene. Although the main spot is concentrated when fully stopped down (f/22) it's often noticeable and annoying at f/8. These issues never fully go away, even wide open (f/2.8) and that can make it very difficult to use in general.

This colour IR set was shot using a Hoya R25A filter (which is roughly 590nm). Usually when using this colour infrared filter most of the hot spot issues improve or go away entirely, but here it's so extreme I didnt even need to shoot a clear sky to show how bad it is. This example also helps to illustrate how the hot spot effects the colour of the overal scene, because the reflection is concentrated to the blue channel. This makes colour very difficult or impossible to process.

Lens Flare

Here are some samples at different wavelengths to show how it copes with unavoidable lens flare in each. These are all shot at f/8. As you can see the more infra-red light that comes through the filter the more obvious the flare becomes. It's actually very good in colour and even when external filters are used like this. In IR however it looks downright horrible. I wouldn't advise shooting into the sun when taking infra-red photography on this lens.

Kolari Vision Hot Mirror (Colour)

Hoya R25A (Red / 590nm)

B+W 093 (850nm)

Sharpness

The sharpness of the Zeiss 35/2.8 is pretty good in the middle. I'll give it its due credit and say it almost lives up to the badge & price here, but on the outer edges of its full frame I'd label it as wholy average. There's nothing to write home about here and it left me rather disappointed.

Competition

There are now two Zeiss 35mm lenses for the FE mount. The newer f/1.4 version is the size and weight of the moon however, so is in no way (shape or form) comparable to this, almost pancake-like, lens. If you want something like this on a tighter budget there are other options. Not much can rival the small size of the Zeiss (and certainly not the weight), but there are some interesting alternatives.

On the left here we have a Canon 40mm f/2.8 STM lens with an auto focus adapter. Unfortunately this isn't a fast focusing system on the first generation A7 bodies, but it's performance is uncomfortably close to the Zeiss for colour photography. For infrared photography however things change completely. The Canon is a superb performer in IR, producing very little hot spot, even at f/22. Considering this costs less than a 1/3 of what the Zeiss does (including the adapter) it's extremely good value for money. I will be reviewing this lens in more detail soon.

On the right we have a Nikon 35mm f/2 AF-D lens. As yet there is no way to focus this automatically with the A7 cameras. Although it looks like an AF adapter won't be too far off. The adapter you see here allows filters to be mounted behind the lens, which has huge image quality implications for full spectrum users like myself. I also feel the need to point out here that without the adapter this lens is roughly the same size as the Zeiss, while being a whole stop faster. Clearly Sony & Zeiss have issues making truly compact lenses with the short flange distance of the A7 cameras. When it comes to infrared image quality and lack of hot spot this Nikon lens also hits it out of the park. At under half the cost of the Zeiss (again, including an adapter) this also puts the Zeiss to shame, even if it's more for infra-red and subject isolation than sharpness.

Overall Score (Colour IR): 3/10

Overall Score (pure IR): 2/10
Very Poor IR Performance

Conclusions 

As good as this lens is for colour photography it doesn't often relate to infrared. Anything shot with apertures smaller than f/5.6 are a gamble, which isn't necessarily obvious when looking through an EVF either. Although contrast is still good it's wholy dependant on hot spot, which one of the worst I've seen. Infra-red image sharpness isn't as good as it is with colour either, although it's not the extreme difference that I saw with the Sony 28mm f/2 lens.

The included lens hood is both good and bad. On the the good side; it keeps the lens really small while protecting the filter really well. On the bad side; if your filter doesn't fit inside the hood then you can't use the hood or the lens cap at all. Circular polarisers would be a pain (although they always are with lens hoods), but you'd still have no lens cap. If you're going to be brave with a hood design like this then include a second 'normal 'hood and provide a 49mm lens cap as well. This solution seems rather short sighted.

35mm is my favourite focal length for a general walk around lens and I like that it shares the same filter size as the Zeiss 55mm and Sony 28mm FE primes. Despite not being particularly fast this could have been my favourite lens for IR on the Sony A7 and that's what makes this lens such a disappointment. Unlike the Sony 28mm its mostly hot spot that kills this lens for IR use. Bright sunlight can give some decent results, just make sure you have enough central detail to cover up the hot spot and be very aware how big/bold that hot spot will be on your chosen aperture. I gave colour IR a slightly higher score for a couple of reasons. Firstly, despite some bad results, some images can look great and secondly - you can avoid the blue channel to get clean B&W IR images.

General Pros and Cons

    Pros (rated out of 10 for how awesome they are)
(9) - Fast, accurate and silent auto focus
(7) - Good construction (metal... mostly)
(6) - Extremely small & light, although not for it's specification
(4) - Included lens hood is interesting (some caveats to that though)

    Cons (rated out of 10 for how annoying they are)
(9) - Infra-red Hot Spot is extremely bad, almost makes it unusable for IR
(9) - IR colours are tricky because the hot spot is in the blue channel
(7) - Nasty looking lens flare in IR
(7) - Image quality should be better for the price (mostly corners)
(5) - Focus by wire speed is inconsistent, lack of feedback make it difficult to use
(5) - No Aperture ring
(3) - Plastic filter thread (unforgivable at this price)

   IR Samples

Here are some b&w infra-red images, taken with the B+W 093 filter (on the full spectrum Sony A7). This filter has a 50% transmission at 850nm (the amount of visible light that passes through this filter is nominal).

f/22

f/2.8

These two B&W samples (above) are opposite apertures. This is to show how a hot spot can be hidden inside the detail of an object. This can be acceptable if you keep it away from flat tones (like this sky), as long as your expectations are fairly low. If you're looking for a very clean result here it's likely that you'll never be happy with this lens. Even wide open (f/2.8) it produces a noticeable glow from the middle of the frame.

 

f/8

This last B&W shot illustrates how a medium sized hot spot at f/8 might not be very noticeable on it's own, but if you look at the bright grass in the middle it looks overexposed. It's actually not clipping here at all, it's just washed out by the addition of the hot spot.

Here is a colour infra-red video that I took with the 35mm lens. This has had it's motion stabilised via YouTube, so it's a bit rough, but it is better than it was.

f/5.6

These next few colour infra-red samples taken with the Hoya R25A (Red) filter (on the full spectrum Sony A7). This is roughly 590nm. All images are processed using the 'false colour' technique, unless the foliage is blue or it's been turned B&W like this next one:

f/5.6

f/5.6

f/5.6

f/5.6

f/4

f/4

Lens Review - Sony FE 28mm f/2.0

For over a year I have been using the full spectrum A7 with only manual lenses (Nikon and various other legacy glass). I recently bought and tested the Carl Zeiss Sonnar FE 55mm f/1.8 and found it to be the best infra-red performer I've ever seen! If you're thinking "of course it's good, it's an expensive Zeiss lens" think again, as I've heard reports of bad hot spot performance in almost every other Zeiss lens for the Sony FE system.

This 28mm is the cheapest prime lens for the FE system by quite a bit. It has a surprisingly fast f/2 aperture for its price too and although it's not that small (what fast FE lens is?) it is quite light. In the handfull of tests that I've seen for this lens it comes out pretty well for visible colour, but let's see what kind of skillz it has with infra-red...

      Stats
● Mount: Sony FE
● Adapts to DSLR: No
● Adapts to (other) ILC: No
● Focal Length (FF): 28mm 
● Field of view (FF): 75°
● Lens Elements: 9
● Lens Groups: 8
● Aspherical Elements: 3 (1 Advanced + 2 ED)
● Aperture range (f stop): 2.0 - 22
● F-stop increments: 1/3
● Aperture Blades: 9 (curved)
● Aperture Ring: No
● Autofocus: Yes (silent)
● Manual Focus Ring: By Wire
● Min. Focus Distance (cm): 29
● Max Reproduction Ratio: 1:7.7
● Internal Focus: Yes
● DoF Scale: No
● IR offset markings: No
● Body Material: Metal
● Filter Thread Material: Plastic
● Filter thread: 49mm
● Static Filter Rotation: Yes
● Dimensions (mm): 64 x 60
● Weight (g): 200
● Dust / Moisture Sealed: Yes
● Mount Seal: No
● Manufacture Country: China
● Manufacturing Span: 2014 >
● Price New: £240 - 400
● Price Second Hand: £220-300
● Accessories (Included): Hood

     Quick IR Performance Scores

● Pure IR HotSpot (Lack of): 5/10

● Colour IR HotSpot (Lack of): 5/10

● IR Sharpness (Middle): 6/10

● IR Sharpness (Edges @ f/8): 4/10

● IR Sharpness (Edges @ f/2): 2/10

IR Quality / Hot Spot

Here's a new set of images, a test for IR hot spot that I'm trying out (see more about it here). Basically what you're looking for here is a clean dark sky, with no bright spots.

This lens does vignette fairly heavily wide open and that can look like a large hotspot, but most of this is not. You'll find the hot spot more obvious here closer to the bottom of the set. This 850nm IR filter shows a patternef spot starting to get anmoying at f/8 here, but if a clean sky is important to you then even f/4 is still an issue. To some extent the hot spot is always there, it just gets larger, more blurred and subtle as the aperture opens up. Since this is the worst case scenario here f/8 is almost always fine under normal shooting conditions and mostly so is f/11. Thus I would say this lens is generally acceptable in relation to the hot spot issue. If you're someone who shoots pure infra-red at f/16 - f/22 often then I'd recommend you think carefully before buying this lens.

Here is a video to show the hot spot performance at f/22. This helps show how related to the bright areas of the scene they are. Unlike a standard circular spot these are not very easy to remove and compensate for.

This next set was shot using a Hoya R25A filter. On a full spectrum camera this is very similar to a 590nm conversion.

Although the sky wasn't quite so clear when I took this set with the R25A filter you can still see how much cleaner the colour infra-red is compared to the pure 850nm B&W samples. This could be partially because of less IR light coming through the filter, but also because of the reduced contrast in the scene. All the noticeable hotspot here is contained in the blue channel, not that it's much comfort if you're trying to process a colour IR image.

Check out these next couple of samples to see how some particularly high contrast scenes can be problematic, even at wider apertures. These are both shot at f/8, which is much more distressing. The bright spot here shows up very clearly on the tree trunk. I'm showing two samples here to show how the spot moves and confirm that it's not a fluke light on the tree itself.

Lens Flare

Here are some samples at different wavelengths to show how it copes with unavoidable lens flare in each. These are all shot at f/8. As you can see the more infra-red light that comes through the filter the more obvious the flare becomes. It's actually very good in colour and even when external filters are used like this. In IR however it looks downright horrible. I wouldn't advise shooting into the sun when taking infra-red photography on this lens.

 Kolari Vision Hot Mirror (Colour)

 Hoya R25A (Red / 590nm)

B+W 093 (850nm IR)

Sharpness

When I did a test between colour, UV and IR filters recently I got a lot of good comparison samples for this lens at different wavelengths. The difference in sharpness between the colour shots and all infra-red ones was quite noticeable. It was obvious overall, but in the corners it was especially apparent. All the shots were taken on a tripod and with accurate autofocus so I knew it was a fair test. I was unhappy with this lenses IR shots before this test and after looking closely at these samples I could now see exactly why. Click the image below to see the comparisons for yourself. It even shows up on these compressed samples at less than 2 mega-pixels, thus they certainly don't stand up scrutiny at 24mp (nearly fourteen times the size).

Competition

Like most Sony lenses there isn't much in the way of competition for autofocus lenses (yet), but there is more here than with the 50mm FOV. There is now a 25mm f/2 in the form of the new Zeiss Batis, which is a high performance lens and has the added size, weight and cost associated with the brand. You could also get a Canon EF 28mm f/1.8 with an AF adapter. It might be a little faster than the Sony lens, but focusing will be sluggish on the first four A7 bodies. A potentially larger issue is the size and price by comparison (not including the cost of the adapter). I actually paid £100 less for the Sony 28mm lens (with a cashback deal) than the Canon usually costs.

If you're willing to forgo autofocus and buy second hand primes there are many options, but it will be hard to save money while keeping decent image quality and the relatively fast f/2 aperture. Although some old 28mm f/2 lenses can be picked up from companies like Vivitar or Sigma for a little less money, they tend to be rather lacking in corner quality. Models from Pentax, Canon and Nikon are interesting for their image quality, but they cost as much or more than the autofocus Sony. Although the adapters for them can be cheap they make the lenses quite a bit bigger and heavier too. Mostly front heavy & oddly balanced compared to the Sony 28mm.

The Leica M mount Voigtlander Ultron (with adapter) will be a better match for the size and performance of the Sony lens (albeit it a bit heavier), however it will cost more, have an odd filter size and still be without autofocus. On the flip side it does look cool on the A7 bodies (or retro, or hipster, depending on your opinion).

Conclusions 

I wish there were more lenses like this for the Sony A7 series FE mount - Primes with faster apertures, at a more reasonable price (and quality). If there were I'm sure that the Sony A7 series would be even more popular than it is already. Perhaps Sony are hoping that 3rd party lens makers will fill these gaps later, but that was a risky strategy when they started out. Now that they've done so well there's a much bigger chance of that happening. Thus I feel much better recommending the system to people on a modest budget these days, but it certainly wasn't like that, even a year ago. As it stand right now, this Sony 28mm f/2 feels like the odd one out in an exclusive, high-end catalog. The FE lens collection is growing fast though, so this could change with the next announcement. I'm certainly crossing my fingers for more lenses like this soon.

In visible colour this lenses is a brilliant addition to the FE system and a game-changer for value primes, but... for infra-red I'm not at all convinced. Its IR quality just doesn't match that of its colour performance. It's like a totally different lens in infra-red and that's a real shame because this could have been a very nice walk-around landscape lens indeed. The hotspot that it produces isn't even the main problem. It's not the most extreme hot spot I've seen, nor does it show up often during normal shooting, it can just be problematic at times. The main issue here is sharpness (and to a lesser extent contrast). Infra-red photography can be passable, but it just never seems to shine. Clarity is generally low. Corners start to get better when stopping down heavily, but not long before diffraction becomes a problem. Now I'm making it sound plain horrible here and that's quite not fair.

Perhaps I've been spoiled by the insane performance of the Zeiss FE 55mm, but I do feel that if you're someone who zooms in on your photos to revel in their beauty in any way you won't be happy with this lens for infra-red.

General Pros and Cons

    Pros (rated out of 10 for how awesome they are)
(9) - Accurate and silent auto focus
(7) - Good construction (metal... mostly) and great balance with the camera
(6) - A great value prime lens for Sony FE at last (although not really for IR)
(4) - Included lens hood is nice

    Cons (rated out of 10 for how annoying they are)
(9) - Infra-red is noticeably less sharp and especially in the corners
(8) - Nasty looking lens flare in IR
(6) - Hot Spot can be problematic
(5) - Focus by wire speed is inconsistent, lack of feedback make it difficult to use
(5) - No Aperture ring
(3) - Plastic filter thread (forgivable at this price though)
(1) - Vignette could be better

Overall Score (Colour IR): 4/10

Overall Score (pure IR): 4/10
Below Average IR Performance

   IR Samples

Here are some b&w infra-red images, taken with the B+W 093 filter (on the full spectrum Sony A7). This filter has a 50% transmission at 850nm (the amount of visible light that passes through this filter is nominal).

 f/4

 f/11

  f/8

  f/11

 f/11

Here are some colour infra-red photos taken with the Hoya R25A (Red) filter (on the full spectrum Sony A7). This is equivalent to about a 590nm conversion. All images are processed using the 'false colour' technique:

 f/8

f/11

f/22

This last example shows the real-world colours (before WB / channel manipulation), exposure and tones of the hot mirror, 850nm and Hoya R25A filters together. The overlapping of the first two show a near black image. This illustrates what happens when an IR filter in front of a normal (non-converted) camera. The latter two show that a low wavelength conversion can be switched to a higher one by using external filters.

f/5.6

Bonus - Multi-Spectrum Sample

This lens seemed to like UV a bit better than it did IR. It was more sensitive than the Zeiss 55mm f/1.8 even though it wasn't quite as fast. Here is a test shot of it using the Baader-U UV filter showing some sunscreen. The shoulder stripe had just been applied here, but the sunscreen on the face was applied 3 hours before and been washed just before taking this image. Showing that it does stand up to water somewhat, like it is supposed to.