Star Adventurer Mount and Nikon Z8 with Tamron 35mm f/1.4 Di USD
Introduction
Sometimes a lens comes a long that is a game changer optically. As much as I strongly dislike that phrase, there is simply no other way to describe the level of perfection this lens achieves, in particular with starlight, however it also excels across other genres too. This lens came about in 2019, when Tamron instructed it’s team of optical engineers to design the best 35mm lens they could. And they achieved just that. Some might say, ‘oddly’ for the usual DSLR mounts. Why not mirrorless? I don’t know, or care, because for me it’s actually an advantage; I shoot across mounts. I use lenses on DSLRs and on mirrorless, so I simply use the Nikon FTZII adapter to use it on my Z8 body. It is important to note that Tamron have been around a long time and have vast experience to draw on; they were founded in 1950. Many lenses for the big camera companies have been Tamron designs. (One that comes to mind is the Nikon 14mm 2.8D lens which was outsourced by Nikon to Tamron for it’s design).
Why A 35mm Lens For Astrophotography?
I hear this from so many people. I think the confusion comes from the thinking that wider is better. Well that really depends…35mm lenses have huge advantages when making panoramas (or better termed, mosaics) of the night sky. Due to general low distortion that these lenses have, coupled with their fast apertures, makes them sensible lenses to collect the strongest signal from each area of the night sky in order to build a proficient picture. They are also excellent for isolating a deepsky object or constellation, or even aurora that is low on the horizon. Read here for more information. While a 35mm prime lens will include less angular view of the night sky than a wider lens, it has the huge advantage that it collects vastly more light due to it’s large clear aperture size compared to wider focal lengths and apertures:
Planetary Alignment on the 26th February 2025 showing Mars (top left) and Jupiter (lower right). This image is a mosaic of 5 individual sky pictures using the Tamron 35mm f/1.4 Di USD lens on a star tracker.
Fast Aperture Lenses
To capture faint starlight, we want the fastest lenses we have. In terms of light collection, some of the most efficient lenses at gathering light are between 24-50mm and with an f/1.4 aperture. This is due to clear aperture size (the amount of light a lens collects is based on it’s aperture and focal length. We have to remember that aperture is a ratio, thus it is affected by the focal length of the lens. A 14mm 2.8 lens does not gather anywhere near the same amount of light as a 50mm 2.8 lens does). To work out a clear aperture size for a lens, we take the focal length and divide it by it’s aperture. Thus:
For a 24mm f/1.4 lens we get:
24 / 1.4 = 17mm diameter of clear aperture
For a 35mm f/1.4 lens we get:
35 / 1.4 = 25mm diameter of clear aperture
Now let’s look at something that everyone jumps onto when shooting the night sky, or aurora. Ultra Wide Angle lenses. Now they can have some advantages, however, with regards to light collection, let’s look at the numbers:
For a 14mm 2.8 lens we get:
14 / 2.8 = 5mm diameter of clear aperture
Since clear aperture is a direct correlation of the light collection abilities of a lens, we can deduce that ultra wide angle lenses are not necessarily the best as everyone thinks they are, and 35mm 1.4 lenses are actually one of the best we can get, with 25mm diameter of clear aperture up for grabs. In contrast, ultra wide angle lenses collect ridiculously poor amounts of light compared to longer focal lengths, even when they have fast apertures (remember, it’s a ratio). However, I hear you say, ‘they let me shoot for longer because the Earth is rotating,’ etc. Yes of course. They can partly compensate for apparent star motion. However, test out how much brighter faint aurora comes out with a 24/1.4 or 35/1.4 lens and you will see what I mean here. Ignore star motion for a moment and take a 35/1.4 shot for 10 seconds, then take a shot with a 14/2.8 for 10 seconds. Notice how much darker than 14mm lens is? For further reading on this subject, please see here.
Lens Characteristics
The Nikon version of this lens comes in at 805g. It comes with a lens hood that is lockable and well made compared to the Sigma 35/1.4 version I shot with for years. One reason I sought another 35mm was I had two separate Sigma 35mm f/1.4 lenses go bad on me, and my equipment is babied. Two went decentered and even despite sending to Sigma, they never seemed to get it right again. So I bought another, as I generally liked the lens, and low and behold about a year later it occurred again. Something was definitely up here; I was done with that lens by then. It should be noted, I treat this a strange unexplainable occurrence. I shoot with the 14mm f/1.8 Art and have never had issue. I can only assume there is something poor about the lens element glue within the lens; something is moving over time to cause these problems I encountered. The Tamron has a 72mm filter thread and is just over 100mm in length. and 80mm in diameter. In short, combined with it’s weight it’s neither huge nor small. I would go as far to say that for what it does optically, it is fairly compact. It is much smaller and lighter than the Sigma 40mm f/1.4 Art (1260g!). It has a special fluorine coating on the front element to repel dust and moisture and make it easily cleanable. It comes with a manual - autofocus switch on the body of the lens. Autofocus on my D810 (and Z8) is very good. There is much less variability that plagued the Sigma 35mm f/1.4 I came from; consistency is back and it is very welcomed. Autofocus is also quick (for a 35/1.4) and not too noisy. It has nine aperture blades with a circular diaphragm which actually produces nice sunstars with 18 points around light sources. It stops down to f/16, and has a minimum focal distance of 30mm. It feels solid in the hands and well built, even better than the seemingly already good Sigma 35mm f/1.4 that I came from. However, compared to the Sigma, optically it is in a different class:
Optical Excellence
Tamron released the 35/1.4 in 2019 as the 40th Anniversary of their ‘SP’ (Superior Performance) range of lenses, and stated it was the best Tamron lens ever made. It’s easy to see why once you get your hands on it. This lens also represents to me the best balance of painterly, artsy, rendering while meeting demands for critical applications such as astrophotography where we need things like astigmatism, chromatic aberration, coma, and other aberrations under tight control. Let’s look at how good the Tamron is by examining the MTF chart for the lens:
MTF (Modulation Transfer Function) curves describe to what extent the tested lens can faithfully reproduce contrast of the subject in images it captures. The closer the 10 lp/mm (line pairs per millimeter) curve (the thick line for low frequency) in an MTF chart to "1" of the vertical axis (the higher up), the higher the contrast reproduction performance of the tested lens will be. The closer the 30 lp/mm curve (the thin line for high frequency) to "1" (the higher up), the higher the resolving power and thus the subjective sharpness of the lens will be. The closer both the solid and dotted lines are to each other indicate a better control of astigmatism.
Lens performance differs depending upon directions. Solid lines show performance in the sagittal (radial) direction while dotted lines indicate performance in the meridional (circumferential) direction. When sharp lenses capable of delivering uniform optical performance over the entire image field are tested, MTF charts show curves plotted in good balance.
Performance characteristics of photographic lenses cannot be expressed with only MTF charts. There are other factors that are expressed in different methods, such as taste of softness and degrees of compensation of various aberrations. But you can use MTF charts as a general scale to measure lens performance.
Controlling the Aberrations
The major aberrations that degrade images in astrophotography are well known to us. Astigmatism causes point light sources at the edge of the frame to appear to stretch in a line, and it is something that nearly all fast wides have. Some are almost unusable wide open for this reason. Coma (or Comatic Aberration) causes point sources of light at the periphery of the image frame to elongate into comet like shapes. Chromatic aberration causes colour shifts around points of light at the focal plane, causing white light to split into it’s respective colors of the rainbow. Most fast lenses will have this to some degree, and it will often be more prevalent in the corners of the frame. Spherical Aberration will cause point sources of light to show soft, symmetric halos. SA will usually be noticeable throughout the entire image, and not just the corners as some other aberrations. Distortion will bend straight lines and cause imperfections more noticeable on man made structures. Vignetting will cause the edges and corners to appear darker than the central portion of the image. Field Curvature tends to be more often seen in older optical designs but can still exist, to some degree in modern designs. This shows up as softer areas of the frame, sometimes about one third out from the central portion. Flare is something that is going to affect daylight shooting more than astrophotography, however I am pleased to note this is under very good control also.
The Tamron 35mm f/1.4 controls all of these aberrations exceptionally well in a vast balancing act. This image below shot on a starfield accurately depicts how good it really is - if you are on mobile, pinch zoom into the far corners of this and prepare to be amazed:
Star Quality - Tamron 35/1.4 wide open, singular 6s exposure at ISO 400
Notice how, there is no real enlargement of the stars at the far corners or periphery, even on very close examination. This shot was a singular test shot from my backyard recently. I have not done any corrections; this shows the natural, easily-correctible lens vignette, and tiny touch of chromatic aberration which is easily removed in post processing. Notice further that the stars are sharp, there is no spherical aberration noted and no coma either. Star colour is picked up well with this lens when proper exposures are used to record them (more noticeable on non-moon evenings). This was a f/1.4, six second exposure at ISO 400. The truly beautiful thing about this lens is that it can be used wide open at f/1.4. Stopping down mainly reduces the vignetting in the corners, and ever so slightly improves the corner stars even more than their already exceptional performance wide open. Focus is critical with a fast 35mm prime lens such as this. Especially one that is so highly tuned right into the corners. This means, a hair back or forward on the focal ring can dramatically fine tune star shapes. You do not want to mis-focus with this lens.
Orion under Moonlight in my Parents Backyard - ISO 64, f/1.4, 6s
Closing Thoughts
I have only recently acquired this lens and have only had moments between moonlight and cloud to test it to the full. Despite this, I can already see it is going to be a huge improvement over my previous lens of choice for this focal length. As I shoot more with this lens, I will come back and further add to this article in due course, hopefully updating it with some more pictorial examples.