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Thoughts on Askar FMA135 vs Samyang/Rokinon 135mm?

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#1 JanSpace

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Posted 23 October 2021 - 11:13 AM

They are both at a similar price bracket and I've been trying to compare them both.

On one hand the Rokinon at f2.8 gathers 2.5x the amount of light the Askar does at f4.5, which a lot of folks have mentioned makes for quite the difference.


On the other end, the Askar is an APO triplet and it weighs almost 4 times less, so big plus on portability and (probably?) CA, Coma (?).

The RokSam does have a huge following (and a lot of pictures to look at) though I'm curious to hear what more folks who have an Askar FMA135 think of it.

This is mainly for DSO imaging with a crop sensor APS-C, though I'll probably also use a mono planetary cam through it for fun at some point.

#2 woldsstargazer

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Posted 23 October 2021 - 01:29 PM

Picked up the Samy (Canon fit) for under £300 and use it with a Star Adventurer. Very easy setup for Astro and great results for a range of targets. Does it really weigh x4 the Askar?! Seems unlikely but may be true. Otherwise,  f2 is a huge plus over f4.5 and the Samy really is sharp at f2. The interesting Askar is the ACL 200m which is the William Optics Redcat competitor. 



#3 Andy Lucy

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Posted 23 October 2021 - 02:51 PM

The original review by Charles Bracken that brought attention to the Samyang 135mm lens for astrophotography may be found here:

https://digitalstars...-f2-astrograph/

 

From this review it is noticeable that he recommends stopping down the lens to f/2.8 to improve sharpness.  It is also very clear from his images that corner distortion is low but the lens exhibits red fringing in the centre, transitioning to blue fringing in the corners. This fringing behaviour indicates that both focal plane curvature and spherochromatism are present.

 

I have used both the Samyang 135mm lens and the Askar FMA135 telescope and much prefer the Askar - primarily because colour fringing is much lower on the Askar.  For me this outweighs the greater light gathering power of the Samyang and that it illuminates a full frame sensor whereas the Askar only illuminates an APS-C sensor.

 

Andy



#4 JanSpace

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Posted 23 October 2021 - 03:22 PM

Picked up the Samy (Canon fit) for under £300 and use it with a Star Adventurer. Very easy setup for Astro and great results for a range of targets. Does it really weigh x4 the Askar?! Seems unlikely but may be true. Otherwise,  f2 is a huge plus over f4.5 and the Samy really is sharp at f2. The interesting Askar is the ACL 200m which is the William Optics Redcat competitor. 

815g on the Samyang vs 280g on the Askar :) Ok its more like 3 times the weight, apologies



#5 JanSpace

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Posted 23 October 2021 - 03:23 PM

The original review by Charles Bracken that brought attention to the Samyang 135mm lens for astrophotography may be found here:

https://digitalstars...-f2-astrograph/

 

From this review it is noticeable that he recommends stopping down the lens to f/2.8 to improve sharpness.  It is also very clear from his images that corner distortion is low but the lens exhibits red fringing in the centre, transitioning to blue fringing in the corners. This fringing behaviour indicates that both focal plane curvature and spherochromatism are present.

 

I have used both the Samyang 135mm lens and the Askar FMA135 telescope and much prefer the Askar - primarily because colour fringing is much lower on the Askar.  For me this outweighs the greater light gathering power of the Samyang and that it illuminates a full frame sensor whereas the Askar only illuminates an APS-C sensor.

 

Andy

Ahh that's an interesting read, thank you again Andy. This is the thread I started before I saw your excellent message from earlier, it honestly highlighted most of the things I was curious about when opening this thread.




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