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...

A Year On With The Full Spectrum Sony A7

Sony A7 & Voigtlander 35mm f/1.4 lens, with UV/IR blocking filter

It's now been a whole year since I sold my Nikon D3 DSLR, bought a Sony A7 and had it converted to full spectrum by ACS (See the original review here). So am I happy that I made the switch to the A7 and defaced a perfectly good camera? Almost categorically yes. It's not a perfect system, but I do love a lot of what this system has to offer.

   Best & Worst
What I absolutely love about this camera is it's potential for experimentation. The conversion opens up a lot of colour processing potential, but the easily adaptable Sony FE mount has been equally brilliant as well. Pretty much any 35mm format lens works on this camera in full frame and without any corrective optics. This means cheap, reliable adapters that allow huge catalogues of great legacy lenses to be used and for relatively little money. Of course you're stuck mostly with manual focus, but the two focus aids (zoom and peaking) make this a surprisingly friendly experience.

Personally, I can't say enough good things about the A7 system's legacy lens support. However, if you're looking for reasonably priced, compact and fast autofocus lenses then it could be one of the worst choices around. To date I still don't have any native (AF) Sony lenses*. This is partly because they're expensive, but they're also not very fast. For the price of the Zeiss 55mm f/1.8 I've managed to buy most of the lenses you see in the photo above. These are extremely fast by comparison (for their respective focal lengths). That said, I do acknowledged that the Zeiss lens's performance is very impressive. I can see myself buying a Sony lens at some point in the near future, I'm just in no major rush.

* UPDATE: I have now bought my first Sony AF lens, in the form of the 28mm f/2. This small, light and relatively cheap lens is great and will no doubt lead me into the rest of Sony and Zeiss' range later down the line. I hope to do a review on this soon. Spoiler: So far every E mount lens I've tried has had issues with infra-red and caused undesirable hotspots, but more on that soon.

   Alternative AF
If you're interested in using Canon EF lenses in autofocus on the A7 then I can say it works pretty well. Aperture, Exif and focusing all works, but there are a few caveats to that:

Firstly the focusing is slow, like really slow and in low light it will just hunt... slowly. Secondly no AF adapter works with every Canon lens, so check their supported lens list if you're going to get one. Thirdly- and I guess this could be a money saving tip - don't think that the insanely expensive 'Metabones' adapter does anything better than one of the cheap ones, it doesn't. So I wouldn't consider this as a proper alternative to a Sony lens, but it can do in a pinch. All that said, I am still very impressed by this thing. It communicates the lens info well with the body and it even gets all of it's power from the body, not even the Sony adapter does that (although I know why). Combined with the small and cheap Canon pancake 40mm lens it's a pretty nice size and weight. This lens is generally very good and has almost no IR hotspot issues. The focusing is also really quiet because of the STM motor.

   Filters
Native lens and AF adapter issues aside, the remaining troublesome aspects of the the A7 as a full spectrum camera are related to filters. You'll probably want a lot and especially if you have a lot of legacy glass. Step-up rings will get you so far, but you probably won't enjoy using them. I have about 40 filters and still want more. However, with what I know now I could make do with a much smaller number. If I were to start over I would plan for this by keeping the number of different filter sizes I'd need to a minimum. This could be done by carefully selecting a single general purpose zoom or a small collection of primes with the same filter size. For example the following Nikon AI-S lenses all use the 52mm filter size:

24mm f/2
35mm f/2
50mm f/1.2
85mm f/2

Then I would make do with only the following three filters:

• Hot Mirror (this is not the same as a UV/IR cut filter**) - for normal colour photography
• 850nm (B+W 093) - for high contrast b&w infra-red photography
• Red (basic red, or Hoya 25A, this is about 600nm) - for colour infra-red photography

If I'm honest these 3 filters are all I really need. If I had known this a year ago I could have saved a bunch of money. The Red filter can be picked up for very little money, it's even easy to find second hand, often for next to nothing. The other two, although normally much more expensive, will be worth their weight in gold for a full spectrum camera. So if you just spent all your money converting an A7 this basic principle could be just what you need.

** When it comes to shooting normal colour on a full spectrum camera, I didn't do my research. I assumed that a UV/IR cut (or 'blocking') filter would put the colours back to factory default. Many poor purchases and several months later I finally realized this was incorrect. What I needed was a proper 'hot mirror' filter. These work by absorbing invisible light, rather than reflecting it, which makes a huge difference in capturing realistic colours. UV/IR cut filters have a strong red cast which varies across the frame and is impossible to completely correct for in post (there's just not enough play in the white balance of the RAW colour range). Here's a comparison to show you better what I mean:

With the hot mirror filter found and colour issues sorted, full spectrum is a very versatile animal, but there is one more down side to using external filters. Even the best quality filters can't deal with light hitting them in the same way that a lens's front optic can. Any shot you take where the sun or artificial light hits the filter will have an additional flare. If this is likely to bother you (and it does me) then it will make you prey for a simple infra-red conversion, but there's light on the horizon for legacy lens users. DEO Infinity has invented an adapter (called the 'OWL'), that fits 52mm filters behind the lens.

Although the Owl will fix a few image quality issues, it unfortunately bring a few other problems to the table. Firstly it's not as cheap as a normal adapter, although this is only really annoying because you'll need one for each of your legacy lens mounts - again. Secondly, by changing the filter you introduce an extra way to get dust on your camera's sensor. On the flip side - changing lenses (for the same mount) will actually reduce dust exposure. 52mm filters are reasonably priced and you might find you already have a bunch (like me with 14 of the buggers). More impressively you can also use these cheap little filters on super wide-angles or fisheye lenses that can't normally take filters at all. My favourite feature for full spectrum is that if you get a few spare filter holders then changing your spectrum can be a much quicker process. I have ordered an OWL adapter, but I'm not too sure when it will be released. Watch this space though, I will write an in-depth review when it arrives...

   The Benefits Of An EVF 
An electronic viewfinder (EVF) is an absolute marvel for shooting invisible spectrums, like infra-red. Here are some of the features that I like about using it:

• The viewfinder doesn't shrink when using crop lenses
• The possibility of light leaking through the viewfinder is eliminated 
• You can't blind yourself when looking into the sun

And here are the ones that I've grown to absolutelt love (especially for IR):

• Super-imposed horizon level, histogram and focus peaking
• Colours / tones of the spectrum you're shooting in can be seen while shooting
• Correct exposure can be seen, no more horrendous mistakes
• Corrected white balance can be seen
• True focus can be viewed and zoomed in on, no more IR offset worries

Coming from an SLR the EVF was a bit of a shock, but I soon go used to it. There are only a couple of down sides to it realistically and they're not that bad.

• Not being bale to see anything while the camera is off
• The EVF takes more battery power
• Display FPS can slow down in low light, although not a huge issue with fast glass

    Pre Conversion

I kept the A7 for a week before sending it away for conversion. This gave me the chance to see if everything was OK and also take some shots for later comparison. Here are some random samples (pre-conversion):

Kew Gardens, Richmond - Golden Peacock - Nikon 85mm

The flip out screen was amazing for this shot. I simply could not have captured this without it. It's not that I'm against rolling around in the dirt, but if I had it would have frightened the glorified chicken away.

Knightsbridge, London - Ferrari Dealer - Nikon 85mm

    Summary
Overall I am still extremely happy with the Sony A7. It's a great little camera with a lot of scope for experimentation. The lens compatibility would be my favourite aspect if it weren't for the conversion. As a choice for this infra-red project the Sony A7 was perfect, but there are a couple of things that I'd like to see improved. Here are a few negative bullet points about this camera (rated out of 10 for annoyance):

• Body is a bit plasticy and feels fragile (although it's nice and light) - 3
• Battery life is very short (although, again, this helps the cameras be nice and light) - 5
• LCD screen is always exposed leaving it open to damage (but it's quick to use) - 2
• Confusing buttons and uncomfortable layout - 7
• Menu and C2 buttons very hard to press - 5
• Custom button options need work * - 8

* Custom button functionality is a great feature and there are several buttons available to customise here. The down side is a lack of useful finctions available to assign to these buttons and this is rather frustrating. It has some nice options, but most of what I wanted just wasn't there at all. I would really like the following features (rated out of 10 for potential usefulness):

• Switching between LCD, EVF and Auto view would be great. Currently you can only assign a button to turn off the LCD, but it only switches off the feed (the back-light stupidly stays on) - 10
• Auto ISO toggle button (this is even more useful than a hardware ISO dial) - 9
• Focus check as a toggle for quick operation. Currently this is a two button press - 8
• The ability to change the minimum shutter speed before ISO values drop (1/60th only is pretty useless for me because I either shoot with a 35mm or 85mm lens) - 10

OK that's enough bitching, here's the parts that I do like (rated out of 10 for awesomeness):

• 1/8000th shutter * - 10
• Very generous buffer considering it's an entry level model * - 10
• Rotating screen is great for low angle shots - 10
• Nicely placed video button for still photographers. Out of the way, but easy to get to - 7
• Video starts recording with one button press & in any mode - 9
• The ability to output uncompressed video - 9
• Adaptable mount - 10
• Focus Peaking for manual focus - 9
• Rear dial is also a directional switch and works well - 8
• Exposure compensation dial has nice friction - 9
• Exposure compensation works in Manual mode (with ISO) - 10

* The Nikon D600 is more expensive and has neither of these things!

    Post Conversion (IR photos)
Here are a few of my favorite infrared images taken with the converted Sony A7 over the last year

Konica Hexanon 40mm f/1.8 - Hoya R25A (red) - 1/250th, f/8, iso 100

Nikkor 135mm f/2 DC - B+W 093 (850nm) - 1/400th, f/2, iso 100 (P*14)

Nikkor 85mm f/1.4 D - Hoya R25A (red) - 1/320th, f/8, iso 100

Pentax-K 200mm f/2.5 - B+W 093 (850nm) - 1/320th, f/2.5, iso 100 (P*25)

Canon FD 135mm f/2 - B+W 093 (850nm) - 1/200th, f/2, iso 200 (P*40)

Nikkor 85mm f/1.4 D - Hoya R25A (red) - 1/320th, f/8, iso 100

Nikkor 85mm f/1.4 D - B+W 093 (850nm) - 1/160th, f/11, iso 100

Nikkor 50mm f/1.4 D - Heliopan Red - 1/320th, f/8, iso 100

Konica Hexanon 40mm f/1.8 - B+W 093 (850nm) - 1/160th, f/1.8, iso 100

Nikkor 35mm f/2D - Heliopan Red - 1/500th, f5.6, iso 100

Nikkor 85mm f/1.4 D - B+W 093 (850nm) - 1/160th, f/1.4, iso 320

Nikkor 50mm f/1.4 D - Heliopan Red - 1/160th, f/8, iso 100

Nikkor 85mm f/1.4 D - Hoya R25A (red) - 1/3200th, f/1.4, iso 100

Konica Hexanon 40mm f/1.8 - Hoya R25A (red) - 1/160th, f/8, iso 100

Konica Hexanon 40mm f/1.8 - Hoya R25A (red) - 1/80th, f/8, iso 100

Konica Hexanon 40mm f/1.8 - Hoya R25A (red) - 1/1600th, f/1.8, iso 100

Nikkor 85mm f/1.4 D - B+W 093 (850nm) - 1/320th, f/2.8, iso 100

Konica Hexanon 40mm f/1.8 - Hoya R25A (red) - 1/1250th, f/1.8, iso 100

Nikkor 35mm f/2D - Heliopan Red - 1/160th, f8, iso 100

Konica Hexanon 40mm f/1.8 - B+W 093 (850nm) - 1/200th, f/4, iso 100

Konica Hexanon 40mm f/1.8 - Heliopan Red - 1/160th, f/1.8, iso 160

Nikkor 85mm f/1.4 D - B+W 093 (850nm) - 1/1000th, f/1.4, iso 100 (P*38)

Mitakon 50mm f/0.95 - None - 1/50th, f/1.4, iso 2000

Mitakon 50mm f/0.95 - B+W 093 (850nm) - 1/1600th, f/0.95, iso 160

Nikkor 35mm f/2D - Heliopan Red - 1/250th, f8, iso 100

Mitakon 50mm f/0.95 - B+W 093 (850nm) - 1/6400th, f/0.95, iso 160 (P*9)

Mitakon 50mm f/0.95 - B+W 093 (850nm) - 1/320th, f/1.4, iso 100

Nikkor 85mm f/1.4 D - Hoya R25A (red) - 1/2000th, f/1.4, iso 100 (P*53)

Nikkor 35mm f/2D - Schott IR 665 - 1/320th, f8, iso 100

P*14 = A panorama stitched together from 14 individual images.