Welcome to the second part of this review, outlining the first-light of the utterly stunning Samyang 135mm F/2 ED UMC Apochromatic prime lens. First off, I must apologise that this part is also much longer than the last, so sit back with a cup of coffee as you’ll probably need it to get through it all!
Just a note in regard to this part of the review: when the following images were taken, I had yet to undertake the infinity focus fix outlined in the previous post, so please bare that in mind when viewing the individual sub-exposure and final result.
For the first few weeks of 2022 the weather has seemingly been coordinating itself with us astrophographers; we’ve had a string of clear nights recently that has been a much welcomed change. The only downside though is that they have been absolutely freezing, even in my sheltered back garden the temperature has had a noticeable drop.
So, on the 12th of January, I joined a couple of members from the Wolverhampton Astronomical Society at our observatory to truly put this lens through its paces in rural skies. To start with, I don’t have a star tracker…yet! So I was faced with a static tripod and extremely short exposures. And I mean REALLY short. However, what I did have on my side though was the F/2 wide-open aperture of the Samyang…and I’m glad of it!
Fitting Orion’s Belt along with Messier 42 into the frame was relatively painless. Straight away I could see the bright core of the nebula, along with the stars of Alnitak, Alnilam and Mintaka. I could therefore accurately judge where everything was going to be in the frame throughout the night as the stars moved across the image. Of course, if I was using a tracker I could get a fixed framing position and it would stay there as the tracker did its work. Unfortunately though with a static tripod, every minute or so I had to re-centre the image which was a bit of a hinderance, but the ball-head on my tripod certainly made it easier!
With the framing sorted, I moved onto the next hurdle, determining an exposure length…
As Orion doesn’t rise 35º above the horizon at this time of year, I knew the exposures were going to be seriously short. So for a rough starting point, I used the 300 rule to calculate the very maximum exposure length that I could use:
300 ÷ 135 = 2.2 Seconds
Initially I took a 2-second test exposure, just to check that the calculations were correct, and lo and behold…I got star trails. That calculation though is for up at the zenith directly overhead, so trailing was to be expected in all honesty. The next step down on the intervalometer was 1-second exposures, which produced much rounder stars; anything less than that wouldn’t capture anything at all, and I was already set at ISO1600 to make sure I didn’t underexpose!
So with everything finally set, I started a series of 300 shots, along with a 1-second gap between each exposure to allow for the sensor to cool slightly. Whether it did any good, I don’t really know for sure, but it’s better than nothing!
As mentioned previously, after a minute or so I had to recenter the image, but that gave me enough time to look through a DIY binocular parallelogram mount, designed and made by one of the WolvAS members. The views of the moon, M42 and M45 were truly stunning under these cold rural skies!
The night sky was almost completely washed out with the moon at 75% illumination. It was so bright, that I didn’t really need a head torch to set up everything! The included lens hood really helped in reducing any glare that might of occurred.
Along with the lens, I also bought a USB dew strap that perfectly fits all of my lenses, and it was certainly needed that evening. The temperature was easily below freezing by around 7:30PM as well as the humidity being quite high, so perfect for dew forming on camera lenses, binoculars and telescopes alike. This combination lead to some thick low mist forming around us, but fortunately where we were situated up on a slight hill, the mist was below us for the most part. I set the dew heater to ‘High’ all night long just incase, and it kept the dew at bay. Shame it couldn’t do the same for my DSLR screen, which kept having to be wiped continuously!
Over the period of a couple of hours, I managed to capture 659 exposures, with 650 of those being stacked to give a total exposure of 10 minutes 50 seconds. I left the camera taking for slightly longer than I should have on one of the runs, and the target went out of frame unfortunately. The rest of the exposures were crystal clear though, with perfectly round stars, as show below:
So as you can see, Messier 42 is clearly visible in the lower right third, with the three belt stars stretching up towards the top left corner. If you look carefully around the bottom star of the belt, Alnitak, you can also see the orange glow of the flame nebula. It’s quite difficult to see in the unprocessed image, but it is definitely there.
At the end of the night, I remembered to capture 100 darks and 100 bias frames to aid in the subtraction of thermal noise and any hot pixels – which I know my camera has a few. The following evening, I captured 30 flat frames by simply placing the same setup on top of my iPad set to a white screen. Flat frames are easy with this lens, as the hood is not attached to the focusing part of the lens. Instead, it is attached to the outer frame of the lens itself – another advantage of this internally focusing lens!
Everything was stacked within Deep Sky Stacker as per my usual method, and then post edited within Photoshop CC 2022. The hardest part was trying to reduce the amount of stars to truly highlight the nebulae. Due to the slight bloating caused by the lens not being focused at true infinity, the stars were simply overwhelming everything else in the image. Multiple iterations of star minimisation were applied to try and calm everything down, leaving only the three brighter stars to really highlight the belt.
Overall, I’m really happy with the amount of detail that I was able to capture in such a short time! To say that this was made of 650 x 1-second exposures, this lens is truly outstanding to be able to produce an image this detailed as the end result! The Flame Nebula has also been highlighted after barely being there in the single sub-exposures; even a slight reddening of the stars beneath it can be seen- the Horsehead Nebula. It’s a shame that it’s not also visible as this would be a truly incredible shot, but it simply just needs greater integration time to be brought through I reckon.
To round up then, the Samyang 135mm F/2 ED UMC is a truly outstanding lens, and I 100% understand the hype that it gets within in the astro-community. Its accurate reproduction of any image, even taken wide open, with no coma or chromatic aberrations is to be highly commended. It is honestly the sharpest lens that I have ever used, and certainly puts many of the more expensive Canon L-Series or Sigma Art lenses to shame. If it wasn’t going to be used for astrophotography, the infinity focus issues most likely wouldn’t cause any issues, and many would call it perfect. However, I would have to give it 99% due to that slight issue, but as mentioned in the previous post it can be very easily fixed to great effect.
Part 2B – Post-Infinity Fix Comparison
As mentioned in the previous post, I did some minor lens surgery to move the infinity hard stop ever so slightly, thus allowing the lens to come to true infinity focus. I just wanted to show here the improvement in the star bloat that can be expected when this is done correctly.
Just a quick note; I have colour corrected both images to allow the nebulae to be easily viewable, along with the true star colour. The first image is from the session at the observatory under Bortle 5 skies, whereas the fixed image is from my driveway under Bortle 7 skies with a full moon shining from the other side the house. Therefore, there are stars viewable on the pre-fix image that aren’t that clearly defined on the post-fix image, but that is purely down to sky quality and nothing to do with the lens itself.
The image on the left is the pre-infinity fix, and the image on the right is the post-infinity fix.
As can be seen, it’s not a true comparison, but it clearly shows the reduction in the star bloating by being perfectly focus. It’s most notable on the stars just above M42 and in-between the three stars in the belt.
For a 5-minute task, it perfects an already perfect lens, and makes this a truly outstanding wide field astrograph.
Part 2C – Mounting Hardware
Following on from the imaging sessions, I felt the need to attach this lens to my AZ-EQ6-GT in the future to get some tracked shots of other targets, such as the Heart & Soul Nebula, that fit perfectly together with this lens, as shown below:
I didn’t want to just use the camera thread to attach the setup to a dovetail. Therefore, I looked for other options that would allow me to achieve rotation of the lens, similar to how I have rotated my telescope within its own rings – which is exactly what I ended up purchasing.
These rings, Losmandy-size dovetail and finderscope rail were bought from 3d.ashtronomy on eBay as a kit; he can also be found on Facebook. Everything is properly 3D printed with the correct thermally-stable plastics, and completed by fitting metal screw threads to all attachment points. They fit the Samyang 135mm perfectly while also allowing 360º rotation of the camera – perfect for any framing requirements. There’s also space to fit an attachment for a ZWO EAF to allow it to be a fully autonomous rig.
This kit allows me to safely attach the rig onto my mount as I intended, and with a little addition of a camera thread adapter in the bottom of the dovetail, it would also be mountable to a star tracker too.
This would then be a nice little portable astrophotography rig that doesn’t need any external 12V power or laptop control, and would happily run on my USB power bank with a 128GB SD card inserted into the camera. However, that’s for a future purchase!
In the meantime, the clouds have now rolled back in and look here to stay for the foreseeable future unfortunately, so I’ll probably have another quiet period until I can get back outside again. Orion is still calling me and my 130PDS!
Once again, I do apologise for the ridiculously long post this time around, and I hope that you stuck with it all the way through!
Till next time, whenever that may be, I wish you clear skies!