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Hi guys,

unfortunately I haven't been able to shoot anything for a while but I have a friend who has the same 24mm Samyang as me and is having issues with it.

These are his sample images:

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he is on the K1 mk II, so exactly the same wide setup as me...

His concern is that the lens is no good, this is his second one after the first one was returned.


What do you guys think?


From what I'm told, it is hard to focus the lens and there is considerable off center trailing.


As I have the same lens and body, I find mine really easy to focus and really nice to work with so I'm not sure what the issue is here??


Side note - I pointed his attention to Mossy's Astro Lens Test post


In the lens review section it seems that many people actually do have issues with wide lenses from Samyang, so it could just be that he got another bad sample but I don't know what to make of it. From what I see the focus is out and there is trailing all over like AT wasn't dialed in well, but that's just my best guess....

Hi!

Are these with astrotracer on? If so, with wide-angle lenses you expect to see weird things happening near the corner. Most wide-angle lenses have some distortion, and when astrotracer moves the sensor behind the lens, due to that distortion the stars further from the center will not look like points. This is not unexpected. With a tracker or mount that does not happen as the map of the star field to the sensor stays constant because the lens and sensor move at the same time (sorry for this less than clear explanation).

If a single shot, without astrotracer, with a shorter exposure time shows good star behaviour, the lens should be fine. That should be relatively easy to test.


Regarding focus: this is only a problem with the lens if focus cannot be achieved at all. Even then, if the focus stop is set to less than infinity, in most samyang lenses changing the focus stop is relatively straightforward. Typically samyang lenses do not come with the infinity stop dialed in correctly from the factory, so making sure focus is as good as possible is up to the user.

I'd recommend testing the lens for things like decentering (a common samyang problem) and ability to focus near and far in daylight conditions. I'm not an expert on these things, so I'd recommend your friend to google the common procedures for this.

That's kind of what I see too... mostly coma in the corners. I don't have the Samyang, but I get this same sort of stuff with my Irix 15mm f/2.4, so I have to plan on cropping that out. I have heard about the quality-control issues with Samyang/Rokinon lenses, and although I don't know anyone who's had to do this, I have heard of individuals having to try 3 copies to get one that works properly. (I'm sure that with some retailers, when a "bad" lens is returned to the retailer, they just send it back out with the next order...).

Hi Xandos and batscanner2 ,

sorry for the delay in response. I was consulting with my friend in the meantime. As English isn't his primary language he is a little nervous in posting here plus he's been given a hard time it seems over the Samyang lens by other people that he's asked assistance from. <- I keep telling him how cool this group but still.... sigh

Xandos/batscanner2 - how have you guys been?? Hope everything is going well in the meantime

Here's an example of his 15mm Irix: received_373989401261721.jpeg - Google Drive

as an astro-landscape guy he really is doing great things and lives in an ideal location too.


For the Samyang, I think part of the problem for him maybe focus related. Comparing my Irix 150mm to my Samyang 24mm, the Irix has a much stiffer focus ring and a focus lock which is true for all Irix lenses. The Samyang has a stiff focus ring but not as stiff as Irix. It seems that is the primary cause of the issue, that he just can't get used to it.

It's kind of strange because the Pentax lenses I have, the DFA 28-105mm and FA*300mm both have much looser focus rings.


This maybe something either he needs to work on or use a focuser like DeepSkyDad with computer assistance.


I think DSD already have developed a version for the 135mm Samyang??



Again thanks for the responses guys, especially as I'm kinda acting like a proxy here

Hi back-- I agree that the Irix lenses have a stiffer focus, which I actually like since it is easier to sort of creep up on the focus (if you know what I mean). I have also found that both of my Irix 15mm (I have one for my Canon system, and one for my Pentax) are just about the ONLY lenses I've ever had where there is a click-stop for infinity that seems to actually be infinity--or pretty darn close to it. My Samyang 135mm is much looser than either of my Iris lenses, and I wish that it were a bit tighter.

That is a super shot, and really, the only issue I'd complain about (if it were my shot, which I wish it was!) is the coma in the corners. But that's a known thing with wide-angle lenses, as discussed above. Maybe he could try using a Bahtinov mask to aid in focus? I bet that would help immensely. I had one run on a 3D printer at a local place, but I know that other places do this too. Or he can buy a ready-made Bahtinov mask that is sized for a small telescope... the vanes are farther apart but these seem to work just about as well as ones with tighter vanes (in my limited experience).

That is a cool image indeed! As to the Bahtinov: that will become increasingly difficult at shorter focal lengths, so I'm unsure whether a homemade one or 3d printed one is feasible. I think that lonely speck sell one specifically for wider lenses.

I have always coveted the Sharpstar! I moved to telescopic stuff before I managed to nerve myself up to buy one. The compatibility chart on lonelyspeck's site says that a 24mm should work fine down to f/5 and is "OK" at f/5.6. But they would be focusing wide-open anyway, so that's fine. You'll note that it's simply a flat piece of plastic, so they'll need some sort of holder to keep it on the lens (unless you just do your focusing pointing straight up, which would certainly work!).

Thank you so much again for your feedback and input

batscanner2, HoutHans, fewayne....

Yep, I suggested the Bahtinov and he is now waiting on this: TS Optics Bahtinov mask, 65-100mm

to be delivered.


batscanner - yep totally agree with your diferentiation between the Samyang and Irix designs. My 150mm Irix is pretty close to Infinity too, though for me I rely usually less on what is printed on the lens but more on what my eyes are seeing.


One of the primary things with any piece of technology or equipment is learning how to use it. Unless it's really faulty and way off many things have quirks which one needs to get used to.


To show my friend that he wasn't alone in this department I made a stack of 30 frames the other night.

Result was this: field_stack_24mm.jpg - Google Drive

Trailing everywhere at 24mm. There's also a bit of banding of the sky. Perhaps stacking or focus related - will need to check the individual frames to see. But virtually 2.5 hours and a whole session that will be deleted. The thing is, and I think that many people don't realize is that, this is astro. It's not a simple form of click and shoot style photography, it takes time to setup then get right.
- or in fewayne's case, around 1 or 2 hours before his new RC becomes stable temperature wise.


fewayne, the BM has adjustable lugs on it so it will work directly on the lens and even on the hood if it can grab the petals.

Could be worse. Could be an SCT. At least the RC design is open to the air (no corrector plate).

True, but the RC design is one of the most highly sought after ones in the more scientific levels of astro. The open carbon truss design for example is extremely stable.

I was reading a great article on them the other day: https://www.amateurastrophotography.com/top-5-wish-list-scopes

just left me drooling. - and crying at the prices too!!


Also this one:
the 10micron mount is already $10k but definitely worth every dime from the build quality and usability perspective.



Again some more images from my winging friend

received_398146588340192.jpeg - Google Drive

This one was taken using the Irix 15mm, the location was a wind farm

received_1376423042803829.jpeg - Google Drive

This was the Samyang 24mm that my friend is convinced is a bad copy


One thing that Mossy once told me and I quote: "astro is a subject where you can throw lots of money at, but the point is to be able to learn and work with you've got"

Indeed if you have the budget of NASA you can throw $6 million or Euros if in Europe on something like this: AZ2500 f6 - Astrosysteme

but if you don't know how to get what you need or want out of it, it's just a waste!!


Though in the hands of some of you lot, no doubt you will prove that aliens actually do exist and that there are Vorlons or Earth currently (old Babylon5 joke) :P

Holy expensive glass Batman.... 1st I'd need a 5 or so acre ranch to put these on in bortle 2 or better skies. Well I guess I've got to play the lottery this week. <SIGH>

You and I both!!

With my 4 lens setup I should be able to acheive way more then I am. My complaints are really two things: 1. My location sucks, 2. I need a tracking mount

Though it would be a nice dream to have a fully robotic observatory...

If you check out the images from the Planewave and Baader Planeterium websites, they will really get your tail wagging. Mine won't stop haha


https://planewave.com/


Baader Planetarium GmbH ? Aiders in Astronomy

Hi Kaya,


For the purposes of this discussion, I think its important to distinguish different effects. The vertical trailing you see here is most likely due to the astrotracer not having a good calibration, or perhaps an unstable tripod.

The other effect that you see in both your picture and your friends are the diagonal blurring towards the center near the corners. That is due to distortion of the lens, that is only a problem when using astrotracer, this should not show up in a short single shot. (which you can easily test either in daytime or a single shot without astrotracer at night).

Again, I'd really recommend your friend to test for focus and decentering either in daylight conditions or at least without astrotracer on with short shots at night. The stuff you see near the corners is not a problem with the lens, but something that inevitably happens when using astrotracer with a lens with some distortion (ie, nearly all or perhaps fully all wide-angle lenses)

Thanks Xandox,

I'll get him to do that ;-)

As for my image, AT was callibrated properly and the tripod was very stable

It might have been conditions?? Will try again when I get a clear night.

It's the first time I've had that happen to me actually. I usually run the precise callibration around 3 times but this time I ran it more because I took the camera inside as I was having trouble mounting it on the head - I couldn't see and need to buy a head torch <sigh>

First up my friend says "Thanks!" to everyone's help and suggestions

These are what he provided me with:

f1.4:

single-shot-f1.4.jpg - Google Drive

f2.8:

single-f2.8.jpg - Google Drive


No AT, exposures were at 8 - 10 secs.


To me they look perfectly fine and normal behavior for 24mm, but if anyone else can spot anything....??