[stoppingdown]

Ok, just a couple of days ago we were discussing about UWA and coma. I said that the Samyang 12mm Æ’/2 has excellent reviews in this respect, I own it but I hadn't find the time to test it yet.

 

So, yesterday I thought it was high time for that. No, I wasn't able to shoot at the Perseids: I actually prepared everything in the garden, but then I waited for the moon to set and... in the meantime I fell asleep.   I'm really not an astrophotography man, apart from some rare exceptions. 

 

In any case, during the preparation I did shoot a couple of tests... and I was surprised. The crops below are at mid height, from the extreme left and right borders. At the left border there's no sign of coma. At the right one, it's quite evident. It starts to be visible at the rightmost 1/4 of the image, and annoying at 1/10. No big deal: knowing it, it's just a matter of properly composing so that I later crop a bit.

 

But now I'm curious: is this a sign of decentering?

 

PS Full aperture, of course, and - for what matters - 30sec, ISO 200, Sony a6000.

[Klaus]

Looks like a centering issue to me.

The "right" image looks smeared rather than showing coma.

[stoppingdown]

I think you're right. I did just very few tests of this lens so far, and just a couple at full aperture. But this crop from the right border seems to show the defect, that appears only at the extreme right border. In another photo it's not so evident, though.

[JJ_SO]

I don't know much about astrophotography. I tried this morning between 2 and 4 a.m. and found times between 6 and 10 secs wide open and between 400 and 1600 ISO sufficient. But I guess, the "wow" milky way shots are done by exposure stacking and at shorter times. To me, the "smear" looks more a result of earth rotation than of optical flaw.

 

And in the corners of the 20/1.4 Sigma it's coma, but in each corner equally and always pointing rectangular to the center, so I don't think it's because of decenterring. It's just because these lenses are usually not made to be best at infinity wide open, from center to corner. Some do have the butterfly appearance, but then, when I see our light pollution, I don't think it's worth to see how bad my  other f/1.4 lenses are.

 

But no matter how bad those lenses are for astrophotography: Getting up at this time in the night is not my cup of tea anyway and still I enjoyed a lot the comets. I think I saw a dozen.

[stoppingdown]

 

But no matter how bad those lenses are for astrophotography: Getting up at this time in the night is not my cup of tea anyway and still I enjoyed a lot the comets. I think I saw a dozen.

 

I too fell asleep for the second time, so no Perseids at all.    Later in the month, when the moon is almost completely vanished, perhaps I'll try something again - just for the stars - at a feasible hour.

[JJ_SO]

Comets can one become sleepy...

 

I don't want to invest (sleeping) time and cost for really great milky way shots. It's nice and decorative, this much of stars, but beside of it...  :wacko:

 

^_^

[chrismiller]

You should be able to do exposures up to around 30 seconds before star trailing becomes apparent when using a ultra wide lens.

[davidmanze]

, 

Ok, just a couple of days ago we were discussing about UWA and coma. I said that the Samyang 12mm Æ’/2 has excellent reviews in this respect, I own it but I hadn't find the time to test it yet.

 

So, yesterday I thought it was high time for that. No, I wasn't able to shoot at the Perseids: I actually prepared everything in the garden, but then I waited for the moon to set and... in the meantime I fell asleep.   I'm really not an astrophotography man, apart from some rare exceptions. 

 

In any case, during the preparation I did shoot a couple of tests... and I was surprised. The crops below are at mid height, from the extreme left and right borders. At the left border there's no sign of coma. At the right one, it's quite evident. It starts to be visible at the rightmost 1/4 of the image, and annoying at 1/10. No big deal: knowing it, it's just a matter of properly composing so that I later crop a bit.

 

But now I'm curious: is this a sign of decentering?

 

PS Full aperture, of course, and - for what matters - 30sec, ISO 200, Sony a6000.

The crop of the yacht marina shows softness at the right edge which "if" it is not there on the left side shows de-centerering. The two star shots the left shot  shows coma, the right looks like star trail! 

 If the lens "is" de-centered return it for another. Futher checks on distant views of tree/foliage the toughest test!

[davidmanze]

You should be able to do exposures up to around 30 seconds before star trailing becomes apparent when using a ultra wide lens.

With the Samyang 14mm star trails are just visible at 15 seconds on the D750, 20 secs clearly so. I limit it to 15 seconds!

 

**********************************************************************************************************************************

 

 "But I guess, the "wow" milky way shots are done by exposure stacking and at shorter times."

 

Personally I can't be bothered with shot stacking, I take a single shot and boost areas with the adjustment brush and full on "clarity", if you keep on adding with the adjustment brush after about 3-4 passes the milky ways stands out nicely!

[chrismiller]

well its a balance between noise and star trails.