Sony made the internet go wild the last week over their new flagship model, the Sony A7RIV. Boosting a massive 61 megapixel CMOS sensor they shocked the crowds. Wow 61 megapixels, say bye to medium format and 61 megapixels why would I need them are the 2 strong voices you hear everywhere on the internet.
I won’t argue with both camps as every photographer has different needs and there are enough camera models out there to suit your needs.
But if you want to use the new Sony A7RIV and want to use it’s full potential there are some things to think about and one of the main things is your lens choice.
What lenses to use on the Sony A7RIV?
As much as I want this to be a simple subject and as much as I want to tell you which lenses to use there is some background to the story that gets more and more important with higher resolution cameras.
As we see all camera manufacturers move into the very high megapixel models on full frame sensors (mostly all made by Sony) the lens choice has become more and more important.
Why? Because of things like the sweet spot of the lens (f-stop), diffraction, fine detail contrast and sharpness all depict your final image quality. And the higher the megapixel count of the sensor the more important these things get.
Ok but which lenses should I get for my Sony A7RIV?
Generally speaking I would strongly suggest to use only very high quality lenses on the new Sony A7RIV because you need lenses that are able to produce high quality images that contain a lot of fine detail and contrast to really use the 61 megapixels.
– Sony GM series
– Zeiss Batis series (see my full review here)
Those are the only 2 type of lenses that I would put on the new A7RIV.
Why? I’ll try to explain why below.
What lens qualities do we need for high resolution sensors?
The new sensor in the Sony A7RIV is really making a leap from the one in the A7RIII. 61 Megapixels on a full frame sensor is something unique and at the same time we can ask ourselves do we need it, or better said can we use the full potential of the sensor? Well not all photography genres will come to the full potential of this sensor and I’ll try to explain why.
Basically there are a few things we need to have a look at:
- Problems with high pixel density on full frame
- fine detail (contrast)
- sweet spot of the lens
- MTF charts
High megapixel full frame sensors and the problems
While it is fantastic to have 61 megapixels at your disposal for various reasons it also brings some problems.
The advantages of such a high megapixel sensor is that you can crop your images without ever compromising on quality (as most people only use their images online). Printing big sized prints will be even easier with the files coming out of this 61 megapixel beast. I can really see the advantages for fine art prints. As Sony states the amount of detail captured is very high, so your images will be crisp and of great contrast because of this sensor. But only if you use the right lens.
The disadvantages of the very high full frame megapixel sensors is precisely that, you need a very good lens to really get that image quality they promised you.
And no, it will not be the same as medium format but that will be clear later in this article.
Difraction and fine detail
Diffraction makes the image softer because we loose sharpness on pixel level. This becomes more visible if we stop the lens down (higher f-stop).
Diffraction is caused because the light hits the aperture blades and diffracts (it shatters). The different wave lengths of light travel different distances and thus when they should meet up at a single point this point becomes fuzzy. When we open up the aperture the diffraction is nearly 0.
A low resolution image sensor will have less problems when diffraction takes place as a higher resolution image sensor. To make this more digestible think of a light source as an airy disk that gets projected onto our sensor. (see also the very good explanation in the video below) When we project these airy disks on a sensor grid you can see that the same light point affects more pixels on a higher resolution sensor than it does on a lower resolution sensor. Thus the image quality on the higher resolution sensor degrades faster.
Steve Perry explains it way better as I can and by watching this video you will understand what lens diffraction is and how it affects your images, especially on high resolution cameras.
So to get the most out of our new 61 Megapixel Sony A7RIV we need to make sure we use lenses with as low as possible diffraction, thus we need to use a lower f-stop (wider aperture).
Good so we now know that we should use a lower f-stop on higher megapixel sensors (I’ve talked about this earlier in other posts regarding the Zeiss Lenses). With lower f-stops we loose some depth of field, so it won’t be ideal for Landscape and Architecture photographers who mostly use higher f-stops (narrower apertures) to get everything in focus while still staying around the sweet spot of the lenses. (more on this in a bit)
With the higher megapixel sensors we can record more fine details, that is if the lens gives us just that. We need to make use of lenses which have a good micro contrast.
As you can read in my review of the Zeiss Batis (well all Zeiss lenses actually but we are talking about Sony here) these lenses deliver just that. Images with high micro contrast and sharpness throughout the image even wide open. And as we can conclude that is exactly what the Sony A7RIV needs.
The Sony GM serie lenses are also very good at this point and to me especially the 100-400 GM. I find the others good but not exceptional and to me the Zeiss Batis prime lenses are just better as the zooms in the lower range from Sony (24-70 for instance).
Sweet spot of the lens
When considering the above about diffraction and high resolution sensors you could probably conclude that the sweet spot of the lenses moves further and further towards a full open aperture.
We define the sweet spot of a lens as the aperture at which the image sharpness and contrast (image quality) is the highest. Nowadays with image sensors of 42 megapixel (Sony A7RII and A7RIII) that sweet spot can mostly be found around f/5.6 to f/8. But as diffraction becomes more noticeable on higher resolution cameras, the sweet spot moves more towards f/4.0.
Now this has some serious effects on the depth of field that we get at the settings of maximum image quality!
Ok but now I want to buy a lens and want to know before I buy this if it will give me my maximum available quality on the Sony A7RIV. I can read the MTF charts and it’s done right?!
Many people hop over to the famous testing websites who tell you all about the qualities of a lens with a MTF chart. But these charts aren’t always using the same metrics. Canon uses formulas and Nikon uses metrics to come to the results for instance. So it isn’t always comparing apples to apples.
I have found a very clear and good article about this subject over on Cambridge in Color. There you can find a complete tutorial about how to read MTF charts and how to use the data.
I won’t copy and paste it here, but I encourage you to read it.
So we shouldn't buy the A7RIV?
I’m not saying that, as a matter of fact when you are able to get the most out of the camera you really should buy one!
But be aware of the things that I’ve outlined above. When you really want to get the maximum image quality of the A7RIV you really should invest into high quality glass. It’s more important than ever.
I strongly suggest only to use the Sony GM series and/or the Zeiss Batis serie lenses as these will give you the quality you need.
Sony A7RIV for who?
Based on all this information I think it’s safe to say that the Sony A7RIV is very useful but not to all photography genres.
- Portrait photographers
- Studio photographers
- Astro photographers
- Wildlife photographers
- Fashion photographers
- Sports photographers
Less useful for:
- Architecture photographers
- Landscape photographers
If you need to maximise your depth of field (and thus have to use narrower apertures) this might not be the camera for you if you go for maximum image quality. When you are mostly shooting wide open this beast will help you even more by capturing the beautiful details of your subject, if you use the right lenses.
And the death of medium format?
This is a rather funny subject to me. Because it is comparing appels to oranges. Comparing the Fuji GFX or Hasselblad their sensors to the full frame Sony A7RIV is just nonsense.
The problems we just talked about in this article are way less apparent at medium format cameras. Why? Just look at it like the comparison between high resolution full frame sensors and low resolution sensors and the single Airy disk.
A Medium format sensor is bigger and thus the single pixels are bigger. Since the diffraction is less apparent on the ‘lower resolution’ sensor it is the same when we blow up the grid in size. The singe fuzzy Airy disk is still on one single pixel at medium format sizes. So it will be less apparent.
Thus the medium format cameras are able to register even more fine detail at narrower apertures and thus the usage (area of photography) of those cameras is much wider and versatile as the Sony A7RIV will be.
Oh and one more thing
All of this really only applies to the photographers who need high resolution imagery. Who print large prints or who produce fine art prints. For those who’s image are being used by high end clients.
As 90% of the buyers will only share their massive 61 megapixels images at 1080 px by 1080 px on instagram, you won’t even see any difference but you can say in your captions and hashtags that you have taken the images with the latest camera and awe by the amount of megapixels the sensor has.