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Irix 15mm lens review

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Lens review: Irix 15mm f/2.4

The Irix Firefly 15mm wide angle lens

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The Irix 15mm f/2.4 lens is an interesting wide lens from the Swiss company Irix.

It’s a fully manual focus lens, with auto aperture, available in Nikon/Canon EF/Pentax mounts.

The lens comes in two different body designs, Blackstone and Firefly, with identical optics.

Keith’s test lens was supplied by Pixedo and is tested on his Canon 5Ds

irix 15mm f/2.4 lens

About the Irix 15mm f/2.4 lens

I’m looking at the Firefly model of the lens. It turned up in a nice tin, with a soft carry bag.

First up, why are there two versions, and what differences will I see?

From my POV, the optics are the same, so I guess your choice would depend on how roughly you treat your lenses and the depth of your pockets.

Here are the differences from Irix. [Irix 15mm web page]

15mm versions

I treat my kit with care so it likely comes down to the roughly $700/500 price difference. Have a read through my comments about how well the lens works and then decide which features matter to you?

Lens specifications

The basic specifications of the lens (from Irix)

15mm specifications

The internal optical arrangement.

internal optics

The levels of distortion (very slight barrel) are low and my tests support the Irix data.


Any distortion is at a level that you won’t notice for most shots and very easily corrected in software. I have some more examples of the versatility you can get from a lens like this with software adjustment later in the review.

The supplied MTF data is in a distinctly different format to many other manufacturers, so immediate comparisons are tricky.

15mm MTF

I’d guess from the widest angle (frame edge) set of data (orange)  that I’ll maybe see some some splitting of fine lines towards the corners.  That said, comparing MTF charts is probably more useful for seeing how a new version of a lens is different from the old one.

Using the lens on my Canon 5Ds

I’m testing the lens on my 50MP Canon 5Ds.

Many photos are taken on a tripod (the TC2534 I was also testing) where I’ve used liveview to ensure good focus.

live view

Many of the other hand-held shots are either manually set at a guessed distance, or have the lens set at infinity.

The lens comes with a firmly fitting lens hood.

irix 15mm f2.4

Note the section at the far side.  This is a small window that opens up to allow access to filters.


Pixedo also sent me one of the Irix ‘Edge’ 95mm circular polariser filters that Irix can supply. This is a low profile one that gave no vignetting.

filter opening

Here’s the filter with no lens hood.

As an aside, note how small the front element is in comparison to the width of the lens front.

edge filter

The little window in the hood is a nice idea, but I find that circular polarisers often need quite a bit of movement and found myself reaching in through the front.

There are filter holding clips at the other end of the lens that will take gel filters (Irix recently announced some)

rear filter

Lens focus

The lens focus is smooth, with a near half turn (~150 degrees) from near to infinity.

There is a click stop at infinity and a friction ring just in front of the focus ring that with a quarter turn locks the focus. A nice touch if you are swapping lenses and forget that it’s a manual focus lens. I have inadvertently changed focus just by removing/attaching a manual focus lens – it’s annoying to do …

Unusually for a modern lens there is a hyperfocal distance scale on the lens.

hyperfocal settings

It so happens I have a particular dislike of the hyperfocal focus technique for wide lenses. I won’t go into it here, other than say that I’ve written an article explaining my approach to focusing wide lenses with out hyperfocal settings.

One feature that may appeal to some people wanting to check infinity focus (for stars for example) is an adjustment feature that lets you move the position of the infinity stop.

focus calibration

A godsend to the tinkerers. Just remember that modern complex lenses like this can be quite temperature dependent in their focus, if you are going out at night for some time.

Performance at different apertures

Whilst I’m afraid I just don’t have the patience to go through exhaustive lab tests, I’ve a few specific sample images. This is the usual view across the street from my house, that I use with any new lens.

The images are in two galleries that you can click on to see at a larger size. One shows the whole frame and the other a corner sample.

The images show how vignetting (strong at f/2.4) drops of significantly by f/4 and at the sort of aperture I’d use for general use (f/6.3-f/8) it’s quite low.

I’d note that Canon/Nikon cameras will show the f/2.4 aperture as f/2.5 due to working in 1/3 stop increments. This is not a fault, you are getting f/2.4.

There is very little chromatic aberration and it’s easily fixable in RAW file processing.

The image softness you get from diffraction only really shows much at f/22.

However, I feel some people worry about diffraction far too much. I’m of the opinion that stopping right down for massive depth of field can easily outweigh any slight softness for some shots.

If you want the best sharpness with any lens/camera, then go out and take some test shots at different settings.

Your own testing trumps ‘forum perceived wisdom’ every time.

The lens handles flare quite well.

Take this shot (f/6.3), it’s  under exposed so as not to burn out the colour of the sky.

into sun

The shadow tone is easily boosted in processing, but shows up a bit of flare.


After applying a few adjustments in Photoshop, I’ve an image that has the right feel for its tonality.

I’m removed the slight flare and have an image that looks great as an A2 sized print.

swithland trees

The tonal balance here is for printing, where even with a good printer, a boost in vibrance will give extra life to such an image as a print. Remember that prints are not the screen, so the best looking screen version of an image does not always make the best looking print (and vice versa).

The 9 blade aperture will give modest 18 point star flares to bright light sources, most visible on apertures f/11 and above.

Those leaves and twigs make for a testing subject for wide lenses.

Looking low down, with focus set at about 1 metre, the leaves are nice and sharp.

leaves on ground

The top of the image gives a feel for out of focus areas and in the top left shows how off axis vignetting affects this. (click to enlarge)

background blur

A 100% crop showing detail in the leaves.

leaf detail

I’m afraid that the weather (and living in a city) means I’ve not had much chance to photograph stars (a traditional test for lenses).

As such, I decided to experiment with artificial stars. I’ve written up details of the test star technique elsewhere, but it confirms that wide open, there is some distinct ‘batwing’ coma in peripheral star images. This does drop off considerably once you start to stop the lens down.

This first shot is taken indoors. You can just see the tiny green spot of my test start in the top left. I’ve left the room lights on just to give a feel for the technique.

coma test photo

The three shots below are 100% crops from 50MP images at three aperture settings.

coma left top f/2.4

The drop to f/4 makes quite a difference. The ‘star’ subtends less than 10 seconds of arc, so is a pretty good test. It’s also much more repeatable, and a lot warmer.

coma left top f/4

The performance at f/6.3 mirrors what I’ve seen in image detail for TV aerials and twigs on trees.

coma left top f/6.3

I’m taking those tree shots in Swithland Woods, not far from Leicester. It’s late November, but not all trees have given up their leaves.

autumn leaves

Many of the remaining shots I’ll show were taken to get a feel for what sort of images you get at 15mm.

There are quite a few images that I’ll show with specific post processing.

Some might say that they are not a test of the lens itself.

So? I’m rather more interested in what this lens lets me do photographically.  I don’t buy lenses for lens testing.

Making use of the Irix 15mm

This view of the trees in a clearing shows the typical ‘lean’ you get when you tilt your camera upwards.

leaning trees

With buildings, you need to be a lot more careful to make sure the leaning effect doesn’t ‘overpower’ the rest of the image.

This is around the docks in Ipswich, not far from where I grew up. It was a busy working dock then though.

ipswich docks jh1

If you run the horizon through the middle of the frame, you don’t get the convergence.


You do need to think a lot more about the foreground, unless you are going to crop it out.

I’d note that even a square crop of the image above gives a ~30MP image from my Canon 5Ds.

As ever, you can just make use of the geometry that such a wide lens provides.

Ipswich docks wine rack

This unfinished building is known locally at the ‘Wine Rack’.

A view from the other side shows the effect of having the horizon across the middle of the frame.

unfinished building, Ipswich Docks

It also shows how slight the geometric distortion is with this lens. This is quite simple to fix, if I want to.

Two very different views of part of the Grade 1 listed Willis building (Foster, 1975) in Ipswich. Listed in 1991 – it was the youngest building to be so protected.

reflections - Willis building, Ipswich

One I remember being built when I was at school.

Willis building, Ipswich

The 15 mm focal length is a good one for general ‘street’ photos.

This also in Ipswich has the focus set at just over 2m. At f/7.1 I’ve quite a bit of depth of field, but notice the slight softness of more distant parts.

hot sausage stall

15mm is wide enough though that this view of Ipswich Town Hall and the market stalls  feels odd, and I’ve walked past it hundreds of times on my way home from school.

ipswich town hall

A focal length that makes you think about what you’re seeing through the viewfinder in a more subtle way than the extremes of 11-12mm.

Fixing lens issues

After loading an image in DxO ViewPoint 3, I’m offered the chance to download a correction module for my lens/camera combination.

DxO lens module

It’s not guessed correctly, but the Irix module is there.

One of the most useful features of ViewPoint for my architectural work is the ability to rectify images to varying degrees.

Straightening the verticals of the building at the docks gives me this view.

james hehir building

If you are correcting images like this, be aware that you will lose a lot of the sides.

This is the correction needed for my hand held shot.

viewpoint adjustment

It will come as no surprise that my preferred solution is to use a shift lens for such photos.

This photo was taken in a cafe, whilst I was having a break from doing some commercial photography training.  The camera is just resting on my camera bag on a table (1/3 second at f/6.3)


A quick correction with ViewPoint for horizontals and verticals tidies it up nicely.

cafe vp3 correction

One other ‘distortion’ some people notice with wide lenses is a tendency to stretch things at the sides.

In the example above it’s quite noticeable with the person at the left.

It’s important to note though, that this is a natural consequence of having a wide lens that keeps lines straight.

I’ve discussed this in some of my reviews of even wider angle lenses and will return to it when I get a look at the Irix 11mm f/4 lens.

Lens geometry correction

To ‘fix’ it, you need to move to a slightly different image geometry, where straight lines start to bend.

The full version of this would be the fisheye lens, but we’re not going that far.

Compare these two versions of a photo, taken at a meeting I was at.

The first is as-shot and shows all the distortion of people you expect as your lens gets wider.

wide uncorrected

The second show an application of Photoshop’s adaptive wide angle filter.
DxO ViewPoint also offers several solutions to this problem.

wide AWA fixed

Better views of the people, but I’d suggest that a crop is necessary…

Sometimes you just want to show a space, such as this small bathroom in a new house


Part of my work involves providing training for companies looking to improve their in-house photography.

I was with a group of property professionals, showing how to improve their photography, and used this shot as an example of the difference between the standard ‘kit lens’ on a DSLR and a ‘real’ wide angle shot.

I’ve found that going as wide as 15mm is something that many people can get to grips with. Going wider still needs a lot more care in set-up and composition.  When I say 15mm I’m referring to the field of view on a full frame/FX camera – you’d need a 10-11mm lens for this width on a crop/APS-C sensor.

Multiple shots and stitching

Stopping the lens down to f/6.3 reduces corner softness and vignetting significantly. These improvements make it easier to stitch multiple images together for high quality images that will print well at a large size (several metres wide).

My preferred software solution for large prints is still Autopano Giga. I’m using V4 now, but it’s essentially an improved version of V3.5 in my review.

Just to see how it would go, I took 12 shots hand held, from a clearing in the trees

leaning tree

As you’d expect, trees lean all over the place.

AutoPano Giga handles such tilted images with ease. Here’s a screen shot after I’ve started to stitch a few of the images.

stitching images

With a bit of tweaking I have a quite nice image for a 2m wide print (click to enlarge)

swithland woods panoramic

Once again, colours are at a level for printing on a lustre finish paper.

A simple stitch of two shots, one above the other, gives me this image. Once again a good print at 30″ square.

woods square print

An 8 shot stitch of the view at Ipswich docks (click to enlarge). The full size image is 29k pixels wide.

Ipswich docks panoramic

[Autopano Giga V4.4 Panini projection]

Conclusions: Irix 15mm f/2.4

The build quality of the Firefly model of the lens is solid and robust. I don’t work that often in bad weather, so the extra weather sealing of the front element of the Blackstone is not quite so important.

The Blackstone model is an all metal construction, so if you mistreat your kit, a bit more forgiving.

The 95mm filter size is a large and relatively uncommon one, so not cheap.

Looking at the Irix lenses on the Pixedo site I noticed that the ~£400 15mm was being supplied with a free Edge 95mm UV filter – this was a limited offer, but is worth looking out for.

If I’m working in places with sparks and corrosive dust, such as a foundry, I prefer to keep such a filter in place.

The lens also takes a gel filter set. This wasn’t available at the time of testing, so I’ll be looking at the filters when I get an 11mm to try out.

Optical performance is crisp and with good detail once you stop down a bit. My rough and ready testing suggests that on my 5Ds, f/6.3 or 7.1 give the best overall performance. That said if it’s a central subject the f/2.4 setting restricts DOF enough to soften the background for closer subjects. The amount of coma and vignetting at the widest aperture may be an annoyance for astro photography, but it’s on a par with many other wide lenses I’ve looked at.

If you’re not used to it, then manual focus definitely will take some getting used to, but after a while you rarely need to give it too much thought.  Modern DSLR viewfinder focus screens are pretty poor for manual focus, so even with a focus confirm indication, your distance estimating skills will improve too.

Before you worry about manual focus too much, remember that the shorter the focal length, the broader the depth of field, so manual focus wide lenses are a lot easier to use than telephoto ones.

My personal dislike for hyperfocal focus settings [more info] means that unless I need to specifically focus on something close, I spent much of my time with the lens locked at infinity.  The infinity adjustment setting is something that you should not touch, unless you are sure you need to.

With an 11″ minimum focus distance, it isn’t a macro lens (mag 0.11x) but close enough for some unusual shots. Just beware that manual focus of moving objects (cats/children) is tricky when close.

For the performance you are getting, the Irix 15mm Firefly lens looks to be good value, particularly if you add in the free 95mm and gel filters that I’ve seen from some.

Buying the Irix lenses

If you buy a lens though one of our links it helps support the running of the site – thanks

Pixedo, (EU/UK supplier) who kindly lent me the lens to try
Amazon US | Amazon UK | B&H

Gallery of images

Large versions of many of my test images created with the Irix 15mm f/2.4

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  • Keith Cooper | Dec 14, 2017 at 8:54 am

    Thanks – it was easier with my 1Ds3 which had interchangeable focus screens. It’s probably the biggest annoyance for my own use of the 5Ds.

  • entoman | Dec 14, 2017 at 4:02 am

    Well written article and the images are great for demonstrating the versatility of the lens – much more useful than MTF graphs or test charts. Love those forest scenes! Such a pity that modern viewfinders are so useless for manual focusing or assessing depth of field – it was so much easier with film SLRs! Also a great pity that Canon pro cameras don’t have tilting screens – it can be very awkward to use the rear monitor to check focus when the camera is low down.

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