Sony A7 - A Full Spectrum Conversion

By 2014 I had gotten rather tired of big & heavy DSLRs. With full frame mirrorless cameras beginning to emerge I decided to sell all of my existing cameras and switch to the Son yA7. I also sold an infrared converted DSLR, but I didn't want to give up on IR, quite the opposite. I wanted my main camera to be able to shoot IR and colour, so I decided to try a full spectrum conversion.

 

When I look back on this decision it sounds like quite a risky one considering how untested all this was, but it has actually been the most interesting and successful photography choice that I've made so far.

Some of the main options available with Full Spectrum

WHAT IS A "FULL SPECTRUM" CONVERSION?

Off-the-shelf digital cameras are restricted to visible light sensitivity [400 - 650nm (nanometers)] artificially. This is done with a filter that sits in front of the sensor that blocks invisible UV and IR wavelengths. Converting a camera to "Full Spectrum" involves removing this filter (called a 'Hot Mirror'), which opens it up to a much wider range of the electro-magnetic spectrum (300-1200nm).

MIRRORLESS ADVANTAGE

Full spectrum DSLRs have a few key issues with the viewfinder and focusing that mirrorless cameras do not have. Here are the benefits of a mirrorless camera for full spectrum in comparison to the DSLR:

 

  • No focus calibration needed for any lens, or in any wavelength

  • Viewfinder works with visibly opaque external filters (live view not needed)

  • Viewfinder has no colourcast with external hot mirror (visible light)

  • No Live view penalty for speed or focusing

  • Viewfinder shows the correct exposure

  • Viewfinder shows the wavelength you're shooting in / no guessing what you're looking at

  • Viewfinder can show white balance settings (needed for IR)

  • On sensor metering is considerably more accurate*

  • Viewfinder can show live histogram & level

  • Access to almost all vintage 35mm SLR lenses (often much cheaper & better for infrared)

  • No light leaking through the viewfinder

* The meter often looks like it's under exposing with IR, most notably for colour IR like 590nm. This is a good thing however as it's trying to preserve the severely offset red channel. Pushing the WB to get the correct looking colours in IR puts a big strain on the dynamic range. This will bring out noise much more easily than with colour images. Getting the correct exposure is thus much more critical with IR. Relying on auto exposure with mirrorless is a good thing, especially for beginners. DSLR meters cannot see infrared and thus the exposure is whatever it would have been for visible light (not good).

Because external filters largely block the sensors that DSLRs need to function (metering and focusing) this makes an internal IR conversion more sensible for the system, but it still suffers from many of the above issues.

FILTERS

With this conversion you'll need filters to shoot anything accept Full Spectrum itself (which isn't classically very desirable). You'll also want those filters for every lens you have with a different filter size (I will talk about the ways around this later), so I advise planning this carefully. Don't do what I did here if you want to save money, this was just for science...

The image (above) shows most of the options you have when owning a full spectrum camera. If the variety of filter wavelengths and manufacturers aren't overwhelming enough, the post processing techniques are endless, so it can be hard to know how to approach the art. My time with Full Spectrum so far has taught me that you can get away with most effects by using only three filters. If I had known this from the beginning I could have saved myself a lot of money. These are the most versatile filters from my experience:

DSC03090c.jpg
  • 830-850nm - for high contrast b&w infra-red photography

  • 590nm - for colour infra-red photography (red filter)

  • Hot Mirror - for normal colour photography (this is not the same as a UV/IR cut filter, see below*)

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.

 

THE 'HOT MIRROR'

My biggest mistake with Full Spectrum was assuming that a 'UV/IR Cut' filter would return the colours back to factory default. Many poor purchases and several months later I finally realised that what I really needed was a proper 'hot mirror' filter. These work by absorbing invisible light, rather than reflecting it. This makes a huge difference when trying to achieve realistic colours. UV/IR cut filters have a strong magenta cast which varies across the frame and is very difficult to completely correct for in post. There's just not enough play in the white balance of the RAW colour range. Similar to 590nm you could make a custom RAW profile to somewhat correct for this, but it would strain your dynamic range unnecessarily. Here's a comparison between no filter and the other two:

 

This image show the difference between the results of using a UV/IR filter and a Hot Mirror. The latter can be quite hard to track down. I bought all mine from Kolari Vision. They're not cheap and getting them sent from the US to Europe usually gets you a big present from customs as well. I still have some sizes to get (62 & 67mm), which I work around with step-up rings. 

ADAPTING MANUAL LENSES

I intended to use non-Sony lenses with my A7 from the start as a stop-gap, but only until I could afford Sony lenses. I didn't expect that it would become one of the best features of this camera (system) for me. Most people are now aware that the Sony E mount is great for accepting almost any SLR or rangefinder lens without corrective optics, but at the time this was a big surprise to most people. This started with the cropped Sony cameras technically, but since the full frame cameras use the same mount they had a running start with the availability of lens adapters and the larger sensor made lens usability and value even better. This means cheap, reliable adapters that allow huge catalogues of great legacy lenses to be used natively, without corrective optics and for relatively little money.

 

This usually means focusing manually, but the two focus assist systems on the Sony (zooming and peaking) make this a very friendly experience. It's actually much easier and faster to focus old lenses perfectly here (usually with zooming) than it ever was on old an film SLR with a split-D focus screens. Plus these lenses provide far sharper results on this platform than any film was ever capable of. When manually focusing it's a much nicer experience to use an old manual focus lens, although it does still work with most AF lenses too. I'll talk about auto focusing 3rd party lenses in a minute.

 

Combining legacy lenses with the conversion adds another level of brilliance to this package. Older lenses aren't just cheaper, they're generally better for infrared too because they're less likely to cause hot-spots (I will talk more about IR hot-spots in a later chapter). They are also more likely to have indicators on the focus ring for IR offset distances, although this is generally not needed on any mirrorless platform because you'll be focusing on the sensor readout anyway. It's also interesting to see some lack of accuracy with some of these offset markings, perhaps because digital mirrorless is so hyper accurate. I noticed this with a Canon FD 135mm f/2.0 lens.

A small and cheap lens

The Konica AR 40mm f/1.8 (£40 lens, £8 adapter)

A small and fast, Leica M-mount lens

The Voigtlander Nokton 35mm f/1.4 Classic

Some of the worlds fastest glass can be easily used on the Sony

Canon FD 85mm f/1.2 L

ADAPTING AUTO LENSES

The first generation A7 didn't initially support phase detect (PD) AF on 3rd party (non-Sony) lenses. This made it a very slow and frustrating experience. It was almost always faster to focus manually, which made expensive adapters difficult to justify, especially the over-priced and very poorly engineered Metabones (which scratched the mounts on both ends like crazy). Add to this that many Canon lenses had issues or wouldn't focus at all and it wasn't the best way to encourage Canon users to switch over. Compatability did improve a little over time however and the when PD-AF was added in a firmware update it made the original A7 a much better experience when using Canon Lenses. It brought the AF speed up to a fairly similar level as the A7II. AF adapters can now be found for Canon EF, Nikon AF-S/G, Contax G and even Leica lenses (yes, manual lenses). It should be noted that the A7RII and A9 have substantially better focus speed all around and that includes 3rd party lenses.

 

I have auto focused Canon EF lenses on a cheap Pixco adapter, a Metabones mkIV T and a Sigma MC-11 adapter. All have pretty much the same AF performance, with sligtly varying features and support for different lenses. The Sigma MC-11 is a very good choice (cheap-ish and well made) especially if you have any Sigma lenses in Canon EF mount. They also make a Sigma mount version too, but really... I bet they don't make many of those. This adapter also allows the support of Sony's 'Eye Detect' AF on Sigma's lenses, which is a huge advantage, but these lenses aren't exactly fast to focus and that's especially true of the A7 & A7II cameras. Most modern optics do not play nice with infrared photography (this is equally true of Sony, Zeiss and Sigma) - often producing bad hotspots. I plan to test these lenses as much as I can a provide accurate examples of which ones perform well or not. I will start writing this on the IR tab (above) soon.

SONY & ZEISS LENSES

For my first year I lived without any native Sony lenses on the A7. Firstly I adapted all my Nikon glass and then bought other cheap old manual focus lenses. I kept putting off buying a Sony/Zeiss because they're so difficult to justify on paper. A 55/1.8 for nearly £1000? That was just bat-shit crazy... or so I thought! Lenses like this for SLRs were optically good and a fraction of this cost. You can pick up an adapter and an old manual focus version from Ebay for next to nothing. We do have a cheap (ish) 50/1.8 Sony lens now. It's optically a bit below-par for the price and the focus is almost as slow as an adapted lens, but at least we have something. Although the lens catalogue has grown a lot recently the low end is still very much lacking. The 28/2 Sony is probably the best value prime lens we have, it's good, maybe even great, but it stands almost alone. If you have tons of money you're probably fine although most of the best options are very large and heavy which will defeat the purpose for some people. I think there is a lot of potential for the FE mount to have small and big lenses, cheap and expensive. This probably will happen, it will just take a little while to flesh out. 

Keeping the camera as compact as possible was a bit harder on a budget back in the day (3 years ago). If you had tons of money then the Zeiss 35/2.8 was great, but otherwise the best option was a cheap AF Canon EF mount adapter and the Canon 40mm STM lens.

Canon 40mm STM

  • Length: 100mm

  • Weight: 733g

  • Price: £180

Zeiss 35mm

  • Length: 89mm

  • Weight: 575g

  • Price: £650


Including the Metabones adapter in the cost of the Canon lens makes it almost as expensive as the Zeiss, but a Pixco adapter can be bought for a fraction of the price and works better, at least with this lens for me (much better fitting too). The Canon made a nice budget option back in the day, but now we have the Samyang (Rokinon) 35/2.8, which is even smaller and lighter than the Zeiss (wow!) for not too much more money than the Canon option. 
 
Comparing these two lenses and ignoring the price it would be hard to justify the Canon. The Zeiss' extra 5mm of FoV makes it a better travel lens, it comes with a neat lens hood, it's smaller, significantly lighter, has better image quality overall, focuses noticeably faster and with a lot less hunting. Where the Canon pulls ahead is infrared performance. It doesn't suffer with much of a hot spot issue at all, whereas the Zeiss 35/2.8 (and the Samyang) is really quite bad. This is why the image above shoiwing all the different filters was taken on the Canon 40mm STM.

 

I now own a couple native Sony & Zeiss lenses. Even though I now own both of the Zeiss lenses that came out with the original A7 (35/2.8 & 55/1.8) and I love them... well the 55 is amazing, the 35 is still hard to justify, but that's mostly because of the new Samyang (Rokinon) version. Am I just saying that the Zeiss lenses are good to justify me buying them? No, I could easily sell them and make more money than I bought them for, but I won't because they really are that good. I do think it was foolish for Sony to not have cheaper options at the get-go. We have a couple of decent options now. Samyang and soon Sigma are going to pick up the slack and fill the reasonably priced lens void in the Sony catalog. I sure hope so because Sony seem to be concentrating on the super high-end (again) and it's making me wonder how many more great lenses they are going to make for the average mortal.

COLOUR INFRARED PROCESSING

To explain a little about the potential in processing colour infrared images I put this example together.

 

Normal WB

This is how your image will likely look if you don't try to preset the white balance on the camera. This is something like what an 'Auto White Balance' (AWB) will look like. In theory AWB on a mirrorless camera should be more like the 2nd image, but it wasn't for me.

 

Preset WB

You get this by taking a 'Set' (Preset) WB reading from grass or a grey card. On the back of the camera the 'Preset White Balance' (PWB) will look more like the 3rd image, but if you're processing your RAW files through an Adobe program it will look like this because the limit to the WB temperature is 2000k (Photoshop is stupid, what can you do?).

 

PS WB Hack

Well, fortunately there is a hack you can do by forcing the WB to a lower value. I will dig out a link to a tutorial for this soon.

 

R/B Channel Swap

This technique involves swapping the red and blue channels around. In Photoshop you can do this with the channel mixer.

HOT SPOTS

Hot spots are the bane of most infrared photographer's lives, unless they've managed to find a bunch of lenses that don't do it at all. This problem occurs because parts of the lens' internals reflect infrared light rather than absorbs it. This reflected light collects in the middle of the frame as a 'Hot Spot'. The issue is present in most lenses to some degree, is worse (smaller and more intense at) at smaller apertures and can be different at various focal lengths of a zoom lens. 

Colour infrared (mostly lower than 750nm) usually has slightly less intense hot spots, but this could be due to the fact that the colour part of the image is not suffering from the issue. The hot spots will be of different intensities on each colour channel. Blue is usually the worst (not related to blue light). 

 

This is one of many ways that you can process the false colour. This was taken on a 600nm filter. You could use a range from about 550nm to 720nm, but I think that 600nm is a good one because it lets in all of the red and infrared wavelengths. If you're using an orange filter (550nm) I found a good trick was to add a 'Hue Saturation' adjustment layer and push the 'Hue' to 100%. This also gets a blue sky, depending on your white balance value and the camera sensor you're shooting with.

 

This example (above) is a particularly bad example of hot spot. It's from a Mitakon 50mm f/0.95 (taken @ f/16). If you're not familiar with why this happens I should start by saying that it's not the sun, or sun flare (or the moon). It's not fixed, or even helped by using a lens hood. What you're seeing is the brightness of the objects in the frame - reflecting across the lens, like a bright light source and night. It's caused by the lens internals not absorbing light properly in the infrared spectrum. This lens doesn't have great coatings but that's not the issue. It's also not related to it being made in China - super expensive Zeiss lenses can be just as bad. Oh and it's not related to it being a fast lens or a prime either. It happens because manufacturers continue to improve the their lenses internal reflections for colour images, but they do not care about infrared. This is a big shame considering how much more accessible IR photography is these days with digital. Considerably more people shoot infrared these days than ever used to, but because it's still a small percentage the manufacturers would much rather focus on other things. 

Since this issue is really random I have starting making lists of all the lenses that I have tested for IR. There are big lists on Kolari's website, but unfortunately the random users information is so unreliable that it's of little use. The lens used for the above image is rated as 'Good' on Kolari's list... yeah, holy crap! I will be starting my own list soon, which will be much smaller, but it will at least be reliable...

REDUCING THE FILTER NEED

There are three ways to reduce the amount of filters that you need with full spectrum converted Sony:

 

  • Use Step-Up / Down filter rings

  • SLR Lens Adapters with slot-in filter attachments (see below)

  • Internal clip-in Filters - (Astronomik)

Step-up/down rings can be a bit fiddly to use and generally don't allow the use of a lens hood, but they're a very cheap and easy way of reducing the number of filters you need. Another method is something like the internal filters for the Sony A7 by Astronomik. I haven't tried that one, but I did try the SLR lens adapter from DEO Infinity, called the 'OWL'. It allows 52mm filters to be mounted behind lens and it brings a couple of benefits:

  • You'll need less filters and 52mm filters are among the most common / cheapest

  • You can use filters on fisheye lenses (that have no filter thread)

  • Reduces the screwing & unscrewing of filters (if you have enough slot in trays)

  • Can change filters without removing the lens hood

  • Leaves the lens coatings on the front glass, where they belong (reducing ghosting in high contrast lighting)​

 

Unfortunately the OWL adapter comes with a host of down sides as well:

  • This only works on adapted lenses, likely won't fix all your lenses

  • There are only 3 mount types and they're not cheap (not too expensive either).

  • You'll need to buy all your adapters again

  • Canon EF version is a dumb adapter (no aperture control or AF, no focus at all on STM)

  • Changing the filters can be more fiddly because there's nowhere obvious to put them (won't fit in a filter box)

  • No access to circular polarizer rotation

  • Slot in filter holder isn't a very tight fit and has no lock

  • Removing the filter exposes the sensor to dust (this is a bad one!)

Ultimately I would not recommend one, especially not the EF mount. If you have a bunch of Nikkor AI-S lenses then that version would be easier to justify. Yes you can use an EF to Nikon F adapter on top of this (and I do), but it makes the whole thing rather flimsy.

 

The Astronomik internal filters - Ultimately this didn't work out for me because the available wavelengths were not what I wanted and they're very fiddly to change, but I have to admit they are a much more compelling way of switching wavelengths - only needing a few filters and avoiding the image quality issues associated with having glass in front of your lens.

FINAL WORDS

I half expected that converting this camera was going to be an extravagant mistake, but happily it's turned out to be the most practical purchase that I've made, even if it has encouraged me to buy a lot of lenses and filters in the process. It's scope for artistic experimentation is huge and almost impossible to get bored of. The lens compatibility opens up even more potential with the conversion than it normally does due to many cheap old lenses being great for IR. As a choice for this infrared project the Sony A7 was perfect. If if broke today (crossing my fingers that it never does) then I would have to get another one converted. 

CAMERA BODY

I'll keep this brief because you can read a million other reviews on the camera itself, but I do want to say something about this first generation A7 bodies because I do actually prefer them. They lack the 'In Body Image Stabilisation' (IBIS) and full metal chassis of the mkII version and this doesn't bother me much at all. I borrow an A7II quite often and I prefer the original for it's noticeably smaller size and lower weight. I find the button layout to be just OK and it's easy enough to use once you get used to it. I have no major problems when it comes to ergonomics, although Sony could sure take some lessons from Fuji when it comes to design and firmware support. Sony have made great strides with the new A9 and although the most interesting element of that hasn't trickled down to the A7 line it still looks promising. I do hope that they go back to an emphasis on small and light, perhaps just for the low end model, but my guess is that Sony will standardise because it's cheaper. The A7mkII was a step backwards in a few ways for me, but perhaps my thoughts on that are as niche as my obsession with infrared.

IMAGES

Here are some of my infrared images taken on the converted Sony A7. Hopefully you can see the potential of this sensor when it has been unleashed from the grips of a Hot Mirror. If you would like to see the images that I've taken with the camera taken with an external hot mirror (to see how well it does) click here to see my Flickr gallery. 

Edward Noble

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