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02-21-2015, 04:40 PM   #1
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Please help, faulty lens or not ?

Hi everyone, I just bought the Bower 14mm f/2.8 mainly to shoot astrophotos and startrails.
I was using my Sigma 10-20mm till now but i needed a faster lens.
I like the lens, it feels great, but looking at the 100% crop of my first test images with it, I have this weird 'halo' around the stars.
Please look at the unretouched crop below, the 3 main stars of Orion's belt clearly shows what I'm talking about..
I shot wide open at f/2.8, 20sec at ISO800 on the K3. I have another shot at f/3.2 and it's a little less obvious but still there.

I obviously don't want this lens if I can't shoot wide open with it.
I have been shooting stars for a long time so I know this is not normal, should I just send it back and ask for another one ? could it be a bad sample ? I bought from B&H so I know it won't be an issue.
Thanks for any feedback!



02-21-2015, 04:49 PM   #2
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That looks like coma to me. I'm not sure whether or not the 14mm is particularly prone to it, but it looks like it might be.
02-21-2015, 05:43 PM   #3
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First. Looks like coma, or not. Coma makes stars to look like comets. And didn't seems to be exactly the case, but can't be ruled out, if you dont make pictures at low aperture, f4, f5 and over.

Second. This is the center of the image? Or the right side? If is the center, or the left side, make another session, with all the aperture, to be clear, and send back the lens. It means that's decentered.
02-21-2015, 05:47 PM   #4
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QuoteOriginally posted by JimmyDranox Quote
First. Looks like coma, or not. Coma makes stars to look like comets. And didn't seems to be exactly the case, but can't be ruled out, if you dont make pictures at low aperture, f4, f5 and over.

Second. This is the center of the image? Or the right side? If is the center, or the left side, make another session, with all the aperture, to be clear, and send back the lens. It means that's decentered.
Hi, yes I meant to mention earlier that this crop is exact center of the image.
I'm going in the back yard right now to shoot a couple more at smaller apertures.
Thank you Adam as well.

02-21-2015, 06:09 PM   #5
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It will be better to compare, eventually to post the left, right, and center side. Even better to post all four corners. That's what I have done when I've discovered that the flange of one of my ex-cameras, wasn't square to the sensor. (many times, until I've corrected). But it was a K-5, so, the sealing allowed me to work with the screws that keep the flange. On a lens, I don't think you can square it.
02-21-2015, 06:10 PM   #6
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Ok, here's the same shot at 3 different apertures, all 100% crop from the center of image...
First one is f/2.8
2nd is f/4
3rd is f/8








So if it is coma, it means it's just the lens ? Pretty useless to me then... Even though it seems to me it is not as bad on tonight's shot compared to yesterday's...
Is it worth trying another sample before getting a refund ?
02-21-2015, 06:45 PM   #7
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I know that is one of the Samyang-Rokinon wide lens, that has much less coma. I will look and send you what. This lens, no, send it back. It could be a bad piece.

Something else is very different. At the first picture, the ''coma'' was at right side of the stars. Now is at left. Is strange.

So, don't hurry. make the same picture, many times, and study every one from one corner to the other. Use Faststone program. It can compare up to 4 pictures at once, and is free.
02-21-2015, 06:45 PM   #8
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I just found several reviews stating this lens has very good coma correction, so I'm just going to send it back and ask for an exchange hoping I will get a better one. Thanks!

---------- Post added 02-21-15 at 20:48 ----------

QuoteOriginally posted by JimmyDranox Quote
I know that is one of the Samyang-Rokinon wide lens, that has much less coma. I will look and send you what. This lens, no, send it back. It could be a bad piece.

Something else is very different. At the first picture, the ''coma'' was at right side of the stars. Now is at left. Is strange.

So, don't hurry. make the same picture, many times, and study every one from one corner to the other. Use Faststone program. It can compare up to 4 pictures at once, and is free.
Thanks Jimmy. I did find on various astronomy forums this lens has a somewhat good reputation regarding shooting stars, so it really looks like I got a bad one this time...

02-21-2015, 07:51 PM   #9
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Good luck next time.
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