Background
Since I began shooting Deep Sky Objects (DSO), I have been reading lots of reviews about refractors. Since I could'nt decide what to buy I went and bought a used Canon EF 300/4L USM and not long after that I stumbled upon a very cheap and in mint condition Canon EF 400/5.6L USM. They are both excellent tools for DSO imaging and the latter is stellar in my opinion.
Why buy lenses designed for daily shooting? For me it was both about economics and useability. I don't have a dedicaed cooled astro camera and I shoot a lot other things like sports, wild life, portraits and weddings. At that time I didn't know either whether this exepensive nisched genre what something I would go deeper into it. Selling lenses is quite more easy to do than selling astro gear and buying/selling used lenses is about zero loss of money. Another thing was that back in those days (less than a year) I only had a portable iOptron Skyguider Pro as my strongest and most reliable tracker with a maximum payload of 5 kg and the more you load it the less reliable tracking you get. A lens weights much less than a refractor!
I did fell in love with DSO imaging so it didn't take long before I bought a Skywatcher EQR-6 Pro along with a TS-Optics 115/800 for a deeper dive into space!
During this summer I started again to look into refractors, selling my both lenses, 300/4 and 400/5.6 and getting a fast triplett refactor with aboou the same Field of View FoV) at the same cost I sold my lenses. Only problem was that any refractor good enough for me would cost more than that and weight much more than I wanted them to do. Even if I had the EQR-6 Pro to handle the payload, I still wanted to be portable from time to time when doing Astroscape at the same time or using both trackers simultaneously.
A friend of mine recently got hands of an old Tokina 300/2.8 which suppose to do quite well for DSO imaging and after a few weeks of scouting the web, I got hold of an old Sigma 300/2.8 EX HSM. I tried to look for reviews of this lens, but there are very few of them. Since the shop had a deal of 30 days of right withdrawal and 60 days of insurrance I couln’t resist to press the BUY button. I figure that I can do the testing myself and decide afterwards.
The questions that had to be answered were:
Why buy lenses designed for daily shooting? For me it was both about economics and useability. I don't have a dedicaed cooled astro camera and I shoot a lot other things like sports, wild life, portraits and weddings. At that time I didn't know either whether this exepensive nisched genre what something I would go deeper into it. Selling lenses is quite more easy to do than selling astro gear and buying/selling used lenses is about zero loss of money. Another thing was that back in those days (less than a year) I only had a portable iOptron Skyguider Pro as my strongest and most reliable tracker with a maximum payload of 5 kg and the more you load it the less reliable tracking you get. A lens weights much less than a refractor!
I did fell in love with DSO imaging so it didn't take long before I bought a Skywatcher EQR-6 Pro along with a TS-Optics 115/800 for a deeper dive into space!
During this summer I started again to look into refractors, selling my both lenses, 300/4 and 400/5.6 and getting a fast triplett refactor with aboou the same Field of View FoV) at the same cost I sold my lenses. Only problem was that any refractor good enough for me would cost more than that and weight much more than I wanted them to do. Even if I had the EQR-6 Pro to handle the payload, I still wanted to be portable from time to time when doing Astroscape at the same time or using both trackers simultaneously.
A friend of mine recently got hands of an old Tokina 300/2.8 which suppose to do quite well for DSO imaging and after a few weeks of scouting the web, I got hold of an old Sigma 300/2.8 EX HSM. I tried to look for reviews of this lens, but there are very few of them. Since the shop had a deal of 30 days of right withdrawal and 60 days of insurrance I couln’t resist to press the BUY button. I figure that I can do the testing myself and decide afterwards.
The questions that had to be answered were:
* Is the extra cost of this lens worth it?
* Canon EF 300/4L vs Sigma 300/2.8 EX HSM?
* Is the weight too heavy for reliable unguided tracking on the iOptron Skyguider Pro?
* How is the star shape?
* Chromatic Aberation (CA)?
* Sharpness and contrast?
* Ease of focusing?
* Canon EF 300/4L vs Sigma 300/2.8 EX HSM?
* Is the weight too heavy for reliable unguided tracking on the iOptron Skyguider Pro?
* How is the star shape?
* Chromatic Aberation (CA)?
* Sharpness and contrast?
* Ease of focusing?
Sigma 300/2.8 EX HSM vs Canon EF 300/4L USM
f/2.8 vs f/4
2400 grams vs 1200 grams
$1000 vs $500
f/2.8 vs f/4
2400 grams vs 1200 grams
$1000 vs $500
Coma and star shapes in controlled environment
Here are the four cornes displayed with 1:1 crop. The distance is 6 meters to the test image and the focus was set at the center of the image. The test was done 3 times with refocusing with the same outcome. As you notice, There is visible CA and the stars are not completely round.
As for comparison the image below is the uppe left corner going head to head with Canon EF 300/4L.
As for comparison the image below is the uppe left corner going head to head with Canon EF 300/4L.
Less CA is apparent with Canon as expected and none of them has round stars Both are shot wide open of course, Sigma at f/2.8 and Canon at f/4.
Stacking
Just for fun since no clear skies was due for days, I did a contrast/reslution test combined with the difference that one lens is slower than the other. Both sets was shot with a tripod at lower light with 1/15 sec wide open at ISO100 ar 6 meters distance. The Sigma did 30 images and since Canon was a stop slower, it did 60 images. I stacked them and got this results.
The Sigma had a total of exposure time of 2s while Canon had 4s. The Canon shows more resolution and contrast but also suffers more of banding since I also had to crank the exposure value of +1 eV. This is also what I would have hve to do if I shoot DSO for real.
Canon wins win round too even if the banding is present!
The Sigma had a total of exposure time of 2s while Canon had 4s. The Canon shows more resolution and contrast but also suffers more of banding since I also had to crank the exposure value of +1 eV. This is also what I would have hve to do if I shoot DSO for real.
Canon wins win round too even if the banding is present!
But those tests are done at finite distance, stars are at infinite.. What about an infinity test?!?
This silo is about 800 meters away so we can say that for focusing a lens, it is almost at infinity. The problem doing these tests are that we are shooting through alof of atmosphere which can and will affect the test results. To overcome this, I shot 20 frames (with a tripod of course) and stacked them. I shot the Sigma at 1/8000s while the Canon was at 1/4000s so the noise levels would be the same. I have then devonvoluted the stacked images using Moffat Beta=4.765 (Trujillo) to counteract the atmospheric disturbances. Same settins for both stacks. The image above is a 200% view. For me, Sigma wins this test. But after seeing this in the computer, I was a bit confused of the results so I redid the test with the same outcome.
The CA was still a problem for Sigma at longer distances though.
Canon lacks any sign sign of CA.
Canon lacks any sign sign of CA.
Portrait at 10 meters away 1:1 crop handheld sharpness test. Sigma on the left f/2.8 and Canon f/4 on the right. Same editing. The Sigma has a more yellowish tint.
Clear skies!!!!
Finally clear skies! f/2.8 at ISO400 and 30s
The four corners. There are coma and CA, just like the inital test.
Center crop. This is how an oversaturated big star looks like. Even in the center, the stars a malformed and with CA
Upper left crop Sigma vs Canon. The thinn clouds in the sky makes the CA worse. Canon has better control of both aberrations than Sigma. All stars from the Sigma image are funky, even the smaller ones.
Stacked image, 1:1 view of the stars, f/2.8
3:1 view of the stars after correcting the star shapes in post. A plus is this operation also takes care of some of the uniform noise in the background.
Handling and tracking performance
Focusing can be a challenge, but I don't find it harder to do than on any lens I have and I don't see any problems with tracking unguided o ´n my smaller tracker, iOptron Skyguider Pro. I haven't yet have had the chance to use and test the guiding, but I have shot with 3min long subs with no trails and almost 100% keepers. 3min at 400mm on a FF camera (and 60MPx) is my upper limit to have tracking with most of the subs useable so I don't have tried longer subs yet. Still f/2.8 is four times as much light to the sensor than if I would have used the Canon EF 400/5.6 which would be equivalent of 12min subs.
For focusing I will invest in microadjuster and that said, I think I have also told you that I will keep the Sigma and sell the Canon, even if that one is a good DSO lens. (Must say again, it's good, but not as good as the EF 400/5.6)
Microadjuster from Astrokraken.fr
Example images
