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First Light: Sigma 500mm/F4

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#1 whwang

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Posted 10 July 2018 - 11:43 PM

Hi,

 

I am pleased to share with you my first light image taken with Sigma 500mm/F4:

41525332700_8b4312ddf4_z.jpg

link: https://flic.kr/p/26gsbG5

 

I knew this is an excellent lens from lenstip.com.  (BTW, lenstip.com just released its review on the new Sigma 105mm/F1.4. It's a brilliant lens.)  Recently I was really annoyed by the collimation issue of my TAK Epsilon E180ED.  So I decided to give the Sigma a try.  It has the same focal length, less than 1 stop slower (because of the secondary obstruction of the Epsilon), probably better corner illumination, and probably no need for me to worry about the collimation.  So last week I used my mileage to get a free round-trip ticket to fly to Japan and purchased one.  Japan's tax-free policy for foreigners saves me a lot on this lens.  Even if I include the costs for hotel, food, and local transportation in Japan, I still end up with a huge bargain, comparing with the prices of this lens elsewhere.

 

Taiwan is now under the strike of a hurricane. However, before it arrived, it brought exceptionally good weather.  So I rushed to the mountains to get away from the light pollution and to test this lens.  You can see the result above: sharp stars over the entire full frame.  In addition, here you can see the illumination pattern:

41524357750_57c95fd18a_z.jpg

link: https://flic.kr/p/26gnbSA

It's quite good.  The light loss is only about one stop in the very corner.

 

Overall, I am very happy with this lens. I think it is a nearly perfect astrograph.

 

Cheers,

Wei-Hao


Edited by whwang, 10 July 2018 - 11:48 PM.

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#2 Jim Waters

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Posted 11 July 2018 - 01:07 AM

Exceptional image.Thanks for posting.



#3 whwang

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Posted 11 July 2018 - 01:19 AM

I took a closer look of images taken with Sigma 500mm and TAK Epsilon of the same area of sky.  Epsilon clearly has sharper stars (when well collimated).  The difference could be the optics, or the poor tracking of the mount used for the Sigma 500mm (TAK PM-1).  Next time I will put the lens on a better mount, and see if the sharpness improves.


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#4 calypsob

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Posted 11 July 2018 - 10:10 AM

That looks great Wei Hao, Im sure its alot less of a hassle than the epsilon. I peeped the corners and I think it is probably just tracking error as well.  Im glad to see that new sigma telephoto performing to such a high standard.   They have been churning out some great glass lately.  The only other astrograph I can think of in this price range would be a RASA, and I am sure the Sigma is still way more user friendly.


Edited by calypsob, 11 July 2018 - 10:10 AM.


#5 Ishtim

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Posted 11 July 2018 - 12:30 PM

Nice shot!   What camera did you use?



#6 bnickeson

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Posted 11 July 2018 - 07:08 PM

I took a closer look of images taken with Sigma 500mm and TAK Epsilon of the same area of sky.  Epsilon clearly has sharper stars (when well collimated).  The difference could be the optics, or the poor tracking of the mount used for the Sigma 500mm (TAK PM-1).  Next time I will put the lens on a better mount, and see if the sharpness improves.

It's hard to tell from the small image, but it appears you have the same phenomenon I have with my Canon 400mm f/5.6 where bright stars appear to have two small pie pieces cut out of them on opposite sides.  I don't know if that is typical with dSLR lenses or happens on only a few.  I enjoy that lens's sharpness but bright stars are problematic.



#7 whwang

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Posted 11 July 2018 - 08:46 PM

The funny shape of bright stars is caused by the change of aperture shape at large off-axis angles.  It's a diffraction effect.  Some refractors also show this, including some famous and expansive ones.  So this is not uncommon.  It doesn't make me happy, but at this level it doesn't bother me too much either.  I really care about the sharpness of stars when viewed 100%, and so far this lens hasn't passed the test.


Edited by whwang, 12 July 2018 - 12:45 AM.

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#8 moxican

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Posted 11 July 2018 - 10:19 PM

Nice Job

What software did you use to measure light loss?



#9 Paulimer

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Posted 11 July 2018 - 11:40 PM

Wei Hao, 

 

Any idea if stopping down a bit (like to F/4.5) would help minimise the diffraction pattern or sharpen the stars?

 

Paul



#10 whwang

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Posted 11 July 2018 - 11:40 PM

No measurement is involved.  I just use the bias-subtracted mast flat, make the peak value 1.0, and use ds9 (a FITS viewer) to plot the contours.


Edited by whwang, 12 July 2018 - 12:45 AM.


#11 whwang

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Posted 12 July 2018 - 12:53 AM

BTW, if you are interested in illumination patterns of lenses and telescopes, you can click into the link of the flickr page for the illumination pattern of 500mm/F4.  Then you can find a bunch of illumination patterns of various scopes and lenses under my special account for optical tests.  

 

It's highly unlikely I happened to have tested the same lenses/scopes of yours.  However, by seeing the behavior the some of them tested by me, you may get a rough idea of the behavior of certain classes of lenses and telescopes.

 

I am also thinking about asking people to provide me your master flat and master bias, and include them in my tests and enlarge the database of optical illumination patterns.  Do you guys think this is an interesting to do?



#12 Ishtim

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Posted 12 July 2018 - 07:07 AM

Nice shot!   What camera did you use?

Full frame?  Crop?  DSLR?  CCD?  CMOS?



#13 whwang

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Posted 12 July 2018 - 08:57 AM

Full frame? Crop? DSLR? CCD? CMOS?


Sorry, I missed your question. The camera is a modified Nikon D800. The exposure time is 1.25 hr.
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#14 garret

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Posted 13 July 2018 - 02:50 PM

 

I really care about the sharpness of stars when viewed 100%, and so far this lens hasn't passed the test.

Maybe the Vixen VSD 100 F3.8 will pass the test?



#15 whwang

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Posted 13 July 2018 - 11:52 PM

I used VSD for a few months. It is reasonably sharp. Its faint stars can look as sharp as FSQ106+RD. However, after strong contrast stretch, VSD’s stars “grow big” faster than my Epsilon, making the processing more challenging for faint nebulas in crowded star fields. It can also have collimation issues. The copy I got can show green fringes around stars in one side of the image and purple fringes on the other side, which indicates tilted optical axis relative to the sensor plane. The effect can become apparent and annoying after strong contrast stretch. So I eventually removed VSD from my list.

#16 whwang

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Posted 14 July 2018 - 01:36 AM

Last night I put the 500/F4 lens on a different mount (iOptron CEM60EC) and let it take 30s unguided exposures.  (Previously it was on TAK PM-1, auto-guided.)  The image sharpness substantially improved.  

 

I can't say for sure whether this is because PM-1 is not meant to guide such a big lens, or because of the potentially very different seeing condition.  What I can say is that now its sharpness approaches Epsilon. The difference in star FWHM measured by PixInsight's FWHMEccentricity script is 15% (my best ever Epsilon image vs. 500/F4).  The Epsilon is still slightly better, but the difference is small enough for me to live with.  After all, I am comparing a 500/F4 image taken under thin cirrus without guiding with my best ever Epsilon image hand-picked from thousands of exposures.

 

In addition to its good image sharpness, last night I also realized that its focusing ring is probably the best I have used on camera lenses. It's tight enough that it won't move by itself unless you touch it, but it's also extremely smooth so a very tiny amount of focus adjustment is possible to made by hand.  I really like this.  None of my other lenses (including many other Sigma ones) is like this.


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#17 whwang

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Posted 14 July 2018 - 01:48 AM

Finally, I also compare the star size of the 500/F4 lens with and without the latest Sigma 1.4x tele converter (TC-1401). With the tele converter, the star FWHM increases by 12%. However, since the focal length increases by 40%, that is a 1.4/1.12 = 1.25x net gain in image resolution.  I think this is good, though not perfect.



#18 garret

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Posted 14 July 2018 - 11:54 AM

According to lenstip the Sigma 500 F4 is an outstanding performing lens, there isn't any really weakness, no surprise this lens beats the VSD.

This lens cost in Europe including 21% tax Euro 6500.=

My favorite lens is the Canon 100-400mm its a very good all-rounder for non critical astro-imaging and more demanding terrestrial imaging and.. its only Euro 2100.=, I don't own this lens, still waiting for a decent Canon FF body, the 5Dmk4 is a bit to expensive for me, I was hoping for the 6Dmk2 crazy.gif

 

Garrett


Edited by garret, 14 July 2018 - 11:54 AM.


#19 moxican

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Posted 14 July 2018 - 08:18 PM

Whwang, could you give me some help on how to plot the contours in DS9? Or perhaps point me towards a tutorial?

Thanks



#20 whwang

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Posted 14 July 2018 - 10:23 PM

Garrett,

 

Using the untaxed price of the 500/F4 in Japan and today's exchange rate, I get a price of 3800 Euro.  That's roughly how much I spent on this lens.  Unfortunately it is not a small one.  You will also need to worry about how to carry a huge box through the custom without being taxed when you come back to your country.

 

In general, buying photographic stuff in Japan is the cheapest.  If you buy as a foreign short-term visitor with a non-Japanese passport in a tax-free eligible shop, you can further save 8% of tax.  Some shops further offer a 5% discount if you pay with major credit cards.  Also, some shops have prices lower than others.  If you can figure out which shop to buy, it will be even cheaper.  So if you have constant need of photographic equipments (new or used), and if you know a friend who travel to Tokyo frequently, treat him/her well.  Nearly all my photo gears were purchased in Japan by myself or by my friends.  I also help my friends to buy stuff in Japan.  We help each other.

 

Gusztav,

 

Under the Analysis menu of ds9, there is a function called Contour and Contour Parameters.  You can use the Contour Parameters window and input the exact values of the contours in the right most empty space.  The Contour Parameter window also has its own associated menus.  There you can set the color and width of the contours.  If you want to label the contours like what I did, you need to first enable the "region" function under the Edit menu.  Then under the Region menu you can specify the type of region to be text.  This way, you will be able to add whatever text in the image once you click the image.  

 

ds9 is a powerful FITS viewer and displayer.  It has many useful functions for astronomers, but it's relatively easy to use.

 

Cheers,

Wei-Hao


Edited by whwang, 14 July 2018 - 10:23 PM.


#21 Alone_Ghost

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Posted 16 July 2018 - 03:31 AM

nice shot!



#22 joelin

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Posted 18 July 2018 - 10:49 PM

BTW, if you are interested in illumination patterns of lenses and telescopes, you can click into the link of the flickr page for the illumination pattern of 500mm/F4.  Then you can find a bunch of illumination patterns of various scopes and lenses under my special account for optical tests.  

 

It's highly unlikely I happened to have tested the same lenses/scopes of yours.  However, by seeing the behavior the some of them tested by me, you may get a rough idea of the behavior of certain classes of lenses and telescopes.

 

I am also thinking about asking people to provide me your master flat and master bias, and include them in my tests and enlarge the database of optical illumination patterns.  Do you guys think this is an interesting to do?

I looked at them. Thanks for sharing. I do wish there was a catalog out there of telescopes, lenses, reducers, extenders showing their corner performance and illumination patterns. Such data would be a primary factor in a purchase decision. I'm happy to contribute to that somehow. 



#23 whwang

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Posted 19 July 2018 - 11:29 PM

I looked at them. Thanks for sharing. I do wish there was a catalog out there of telescopes, lenses, reducers, extenders showing their corner performance and illumination patterns. Such data would be a primary factor in a purchase decision. I'm happy to contribute to that somehow. 

 

There are indeed such data, but in Japanese.  The Japanese magazine "Tenmon Guide" published two books dedicated to optical tests oriented toward astrophotography, one for astronomical telescopes and one for camera lenses.  The telescope one was published a few years ago.  It's a bit old, but it's still very useful.  The lens one was just published this year, and it contains many latest lenses.


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