Sony RX1 - Full Spectrum Conversion

I love the fixed 35mm focal length for travel, so this small and light gem was always on my radar. Last year I decided to it would be a great idea to finally get one and convert it to full spectrum. The problem was I couldn't find anyone else who had tried it. The risk was that the lens was no good for infrared, making the conversion rather pointless... What could possibly go wrong?...

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The Sony RX1, with wrist strap, wooden shutter button, filter pouch and lens hood

THE 35mm IR DREAM

Having a small & light travel camera with a fixed 35mm lens that's great for colour and IR is a dream of mine. Previously I have used a non-converted Fuji X100, but although it will allow hand-held IR shooting (just) it's a little restrictive and does suffer from IR hotspot issues.

 

Ever since I started using the Sony A7 for infrared photography I have wanted a compact autofocus 35mm lens that was good for IR. Unfortunately I could not find one (check my hotspot lens test here) from Sony, Sigma, Samyang, Zeiss or Tamron. It seems like almost all modern lens coating are built for visible light at the expense of infrared and this is especially annoying for anything wider than 50mm. The RX1 offers the same full frame image quality as the original A7, with a sharp 35mm f/2 lens. The big question: Is it any good for infrared (or full spectrum)?

THE RISK

Considering how expensive the RX1 was originally I couldn't justify the risk of converting it for another £300 in case its fixed lens was not good for IR. Recently I saw one come up for a reasonable second hand, so I decided to go for it. It was still a big risk, but now under £1000 all in. If it all went wrong I was fairly certain it would work ok for visible light and IR Chrome in a pinch.

 

As soon as I received the RX1 I sent it off to Alan Burch (of IRCC UK) who did a fantastic job! He discovered that it needed a glass layer to replace the hot mirror to focus correctly (unlike most of the cameras he converts). He bought a batch of the glass so now offers the conversion on his website here (although currently for UK only orders due to Brexit shenanigans).

 

So, how did it go? On to the results...

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Kolari Vision IR Chrome filter - Interlaken, Switzerland

INFRARED PERFORMANCE

The short answer is; The RX1's does really well for infrared hotspot, at least for a 35mm. Only at f/22 does a very faint hotspot start to show in some situations, but this is a non-issue as diffraction means most photographers will avoid that setting anyway. A score of 8.8/10 @f/8 is very respectable and it doesn't get much worse when stopping down to f/16. Blooming and ghosting of bright objects are a bigger issue however (keep reading for more about that).

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If you're not familiar with my IR testing, a perfect score is a straight line along the top. This would be a consistent score of 10/10 at every aperture, which is what you would see in visible light / colour.

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BLOOM

The red line ("worst") is a bloom / glow effect from the objects in the scene that reflect infrared light. This can be seen in the below image as a large yellow tint to the sky in the middle of the frame. Ideally the sky (clear or clouds) should not be yellow in a false colour 590nm scenario. This is disappointing as it's impossible to fix and doesn't really change at any aperture. This is likely amplified by the overcast conditions and highly reflective surfaces on the building. I did not experience this during landscape photography even when shooting high contrast lighting (see samples below). 

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GHOSTING

The RX1 also occasionally suffers from ghosting, at least that's what I'm going to call it. This is where bright objects get repeated in the frame as if you overlayed another frame slightly zoomed in. Although boosted to better show the effect (below) it's unfortunately still noticeable with normal processing on occasion, so it can be annoying. This is caused by very high contrast lighting and unfortunately doesn't differ much throughout the aperture range. 

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LONG EXPOSURES / HIGH ISO

The previous issues are rather rare and subtle, but this one is bigger problem. It seems that the RX1 has an internal IR diagnostics LED for long exposures. This will start to fog images when pushing the shutter and/or ISO values with the internal hot mirror removed (IR or full spectrum conversion). Here are some use cases where the issue starts to become a problem...

 

  • At ISO 100 this issue starts to become visible at shutter speeds longer than 10 seconds

  • At ISO 3200 this issue starts to become visible at shutter speeds longer than 1/15th of a second

Low light, hand-held shooting should not be a problem, but 10 stop ND filter use might be and night sky images will almost certainly be off the table. If you push your exposure in post this will become an issue sooner than suggested above.

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30 seconds @ f/2, ISO 3200 with lens covered - This should be black, ouch!

All of the above issues might seem disappointing, but I have rarely run into them in normal shooting. I wanted to highlight them so you can carefully consider whether they might affect your photography. On my two week trip to Switzerland I didn't see any of these issues at all (see samples below).

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Various filters from the Sony RX1 - Schwende Disctict, Switzerland

SENSOR

Being a precursor to the original Sony A7, the RX1 uses the same 24mp full frame sensor. This is still pretty competitive on sharpness, dynamic range and ISO noise today. Unlike the RX1R mkII (See below) it doesn't have anything image quality issues in infrared.

LENS

This Zeiss Sonnar lens is very good in optical quality and corner performance. In my experience; for the price of a second hand RX1 you cannot buy a 35mm f/2 AF lens in this class. The filter size is a nice, common and usually pretty cheap 49mm. As a nice bonus the screw thread is metal, which makes switching filters a much nicer experience and is increasingly rare these days.

FOCUSING

Although auto focus is slow and not very advanced, it is pretty reliable when it does lock. Being mirrorless this is a sensor-plane system, so thankfully (unlike a DSLR) doesn't require re-calibration when switching filters. It just works in every wavelength.

SCREEN

The screen not tilting and being difficult to see in bright conditions can be rather frustrating experience without a viewfinder, so I highly recommend getting an additional one (see below)...

 

VIEWFINDER

There is a an optical viewfinder for the RX1 from Sony (FDA-V1K) although since it just sits in the hot shoe without contacts you could technically buy any 35mm viewfinder for it. I highly recommend the electronic viewfinder (FDA-EV1MK). It's not cheap and will add a bit of size and bulk to the camera, but it's often extremely useful and it's great to be able to see each wavelength with white balance adjustments in a higher resolution and shaded OLED screen. As a bonus it also tilts, so can help with lower angle shots.

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Kolari Hot Mirror (Colour) vs Kolari IR Chrome filters - Sandweidli, Switzerland

RX1R

This version of the RX1 is identical accept for not having an anti-aliasing filter on the sensor. Since this is connected to the cameras hot mirror it will be removed during conversion (to infrared or full spectrum) and thus there will be no difference at all between a converted RX1 and RX1R.

RX1R mkII

This version of the RX1 fixes many of the issues from the original. You get a flippy LCD screen, a built in EVF, much improved auto focus and a higher resolution screen. This could be the perfect travel camera for full spectrum, but I am concerned that it might have the same striping issue from the PDAF sensors that cause horrific banding in infrared. I have not heard of anyone trying this yet, so it would be a very risky conversion considering it most likely suffers like the A7RII, A7III etc. 

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Hoya R25A Red filter (channel swapped) - Lauterbrunen, Switzerland

CONCLUSION

Despite being almost a decade old this is still the smallest and lightest full frame camera and lens available today. Battery life, grip ergonomics, AF speed, LCD visibility, buttons & menus are rather lacklustre due to its age and size, but I don't find these things too annoying and the image quality is still extremely competitive today. Most infrared aberrations are extremely rare in real-world use, so as long as you don't shoot very high ISO or very long exposures you will likely not have any image quality issues in any spectrum.

 

Anyone looking to travel light with a high quality, full frame, full spectrum camera on a moderate budget I would highly recommend the RX1. On my last trip (shown in the samples below) I took this RX1 as a backup camera to test it, but in the future I will be taking only this and a light tripod (Manfrotto Befree Carbon) - the entire kit weighing only 1.7Kg (3.75Ibs)!

 

All the above images are taken with various filters. You can generally spot which image is taken with which filter like this:

  • Black & White = B+W 093 - (830nm) infrared filter

  • Red foliage = Kolari Vision IR Chrome filter

  • Yellow / orange foliage = Hoya R25A - (590nm) Red filter

COLOUR / VISIBLE LIGHT

Here are some images from the full spectrum RX1 using the Kolari Vision Hot Mirror, to illustrate how visible light photography can look from the camera after conversion. I have been really impressed by the colour from this camera. It seems more vibrant and more reliable on auto and preset white balance modes than the full spectrum Sony A7 was. The A7 was usable, but the WB settings often needed tweaking in post and the colours usually felt rather dull and lifeless. I don't feel that issue with the full spectrum RX1, which hopefully the below samples show.