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...

IR Hot Spots - Part 1

For those who don't know what an infra-red Hot Spot is, here's an example (above). This is not a normal lens flare (the sun is directly behind the camera here). It's not something that can be fixed by using a lens hood, nor is it something that changes with a different brand of filter.

     The Cause
The culprit is the lens itself and unfortunately it cannot be fixed. It's caused by bright parts of the exposure reflecting off the coating inside the lens (and/or the elements) and back to the sensor. These coating are designed to absorb light and stop it from reflecting, but how well this works for infra-red light is quite random.

It's worth noting that even when a lens is highly susceptible to this internal reflection it may only be obvious in 10% of your images or less. It's not only dependent on scene contrast & angle of light, but it shows up more clearly on dark flat tones and is deminished by wider apertures.

     The Consensus & The Problem
There are a few websites that talk about hot spots and what lenses it affects. Both Life Pixel & Kolari Vision have a list (the latter being the most extensive). These, and many other websites that mention the hot spot issue, generally categorize lenses as simply either good or bad. However, due to subjectivity and various reporters, I don't feel that this black and white evaluation is the best approach.

After shooting primarily infra-red on a mirrorless camera for more than a year, with various types of lenses (old and new) I'd like to re-evaluate how IR hot spots are reviewed. I see this issue as something that affects every lens to varying degrees (like sharpness or CA). I've used several lenses described by several sources as not suffering from hot spots and still found the issue (although they do usually suffer from it less than others) and not just when stress testing.

My aim is to make a new review-category for each lens that I use. Something that will better show infra-red photographers how well each lens copes with the hot spot issue and better aid them in future acquisitions.

     The Plan
The above example (from the Mitakon 50mm f/0.95 @ max aperture of f/16) is the worst I've seen from this lens, it's also one of the worst hot spot I've ever seen. There are a few reasons why this scene shows the issue so clearly and this gave me an idea. I plan to use a similar set up to measure the IR performance for each lens that I test. Let me first explain the technical details of this test...

For this test I will use an 850nm infra-red filter (B+W 093 or Kolari K850), which lets through mostly IR light and this produces better contrast than say the common Hoya R72. This helps show up the hot spot issue more clearly. Since hot spots are essentially a white blob in the middle of the frame it helps to locate them with a clean dark centre to the image. I achieve this using a clear blue sky and face away from the sun (as directly as possible). To best contrast this I fill as much of the outer frame with well lit foliage and due to facing away from the sun this should be as bright as possible.

Camera Settings - Firstly, I set the camera to auto exposure, with +1 stop compensation. Aperture is set manually. Shutter speed and iso are left to the camera as I go through the entire aperture range. For each shot the focus & exposure is set on the foliage, before moving some clear sky into middle of the frame to release the shutter. Once back on the computer I process all the images in RAW. Other than the saturation being set to 0, the only other adjustment is done in the curves to maximize the histogram and balance out any small differences in exposure.

Problem - The first complication here is that all lenses suffer from vignetting when at their widest apertures. This confuses the results a bit because a dark vignetted border looks rather like a large hot spot. I don't believe that these two issues are intrinsically linked, rather that when a lens is wide open, infra-red images are showing both vignette and a hot spot at the same time. The hot spot is just so big that the effects are amplifying each other and are difficult to separately identify. If you look at the effect (below) at f/22 and work your way back up the images (as the aperture opens), what you see is an effect that essentially blurs out. It gets bigger and less intense, but it never fully goes away. The more infrared images I analyse from different lenses the more I feel that this might be a rule.

The Results - I recently purchased two of Sony's auto focus primes for the A7. Here's how they performed in IR, using this new hot spot test scene:

      Sony 28mm f/2

This Sony 28mm lens is not the best or worst for IR, but I can still see the effect at f/2. It might be subjectively acceptable here somewhere in the middle, but if this issue really bothers you it might only seem reasonable at f/2.8, which could make it a terrible lens for you. This is where all the subjective assessments get tricky to read with Kolari's list. It's worth noting here that this is the worst case scenario. In general shooting it's mostly fine at f/11 and I've even shot images at f/22 where I've seen no hint of hot spot. It all depends on what's in the middle of the frame, what angle you shoot into the bright areas and its relative intensity to the rest of the scene.

So you've seen one bad example and one slightly annoying one, but now for an example of a good infra-red lens...

     Zeiss 55mm f/1.8

I recently bought the Carl Zeiss Sonnar 55mm f/1.8 lens for the Sony A7, but before I did I had no idea how it would perform in IR. In most circles this lens is considered to be extremely good for visible light photography, and I'd have to agree (DxO give it the highest score of any autofocus lens). In infra-red there's just no guarantee it will work well. I was well and truly crossing my fingers when I first took this lens out with the IR filter. The Zeiss 35mm f/2.8 was the only other prime lens around when the Sony A7 was launched. I borrowed that from a friend a few months back and found out that it produced quite an obvious hot spot from about f/5.6, so this made me nervous. Fortunately though, this Zeiss turned out to be not only the best performing Sony AF lens so far, but it's the best lens I've ever tested, period!

That said, although this is the cleanest looking infra-red samples I've seen, @f/22 it's not quite 100% void of issue. If you look closely you'll see that there is a large, but faint disc starting to appear at the top of the image (monitors with high gama show this more clearly). This is a mirror image of the bright foliage at the bottom, but in an even more odd pattern than the 28mm and extremely subtle. So, as close as this Zeiss lens gets to perfection, thus far I've not found a lens that produces zero hot spot effect at all. Right now I'm wondering whether any exists when subjected to this kind of intense test.

Here is the last image from the Zeiss 55mm @f/22, brightened up by several stops, to show the effect:

Don't let this pushed result fool you though, this lens' IR performance is right up there with the best of them. Well that's my current experience anyway, but I haven't tested every lens, so...

     Feedback
If you have a lens that you think performs better than the 55mm Zeiss here please let me know which they are, or better yet try to replicate this test and share the results. I appreciate any feedback you may have on my thoughts here, Especially if I have gotten anything badly wrong.

     Reviews
These two images go a long way to forming the basis of the next two reviews that I want to write (Sony 28mm / Zeiss 55mm). I will be rewriting the existing reviews in new format before I tackle those, but they will be coming soon.

     Weather
Due to the rather 'changeable' weather here it may take me some time to test all my current lenses. Clear skies are not all that common, but I will do my best to update all the old reviews and will continue to work on new ones as well.