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Tamron 15-30mm -odd star trailing/coma?

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Sandino Pusta

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Hi Guys,

I'm a new member in this forum and found this while searching for issue of Tamron 15-30mm. I'm fairly new to astrophotography and one thing I've noticed in Tamron 15-30mm that aat 15mm the upper right side corner of my astrophoto having some ?star trailing/coma while the rest of the star on the center and left side are look more pin point.

Does anyone have encountered this problem? Would like to ask some advice how to eliminate this issue. I've attached one of my shoot with an issue. Thanks.

5e6868cdea4b4927a0aea48d6366b08e.jpg
 
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Try a couple things:

1. Shorter exposure time. While the 500 rule would imply an exposure of 33 secs (500/15), the more exact formula using the Tamron and the D750 is more like 18 secs. This would point to you whehter it is a streaking problem.

2. Smaller aperture to rule-out if it is really a coma issue with your lens.

Good luck.
 
mbo27 said:
Try a couple things:

1. Shorter exposure time. While the 500 rule would imply an exposure of 33 secs (500/15), the more exact formula using the Tamron and the D750 is more like 18 secs. This would point to you whehter it is a streaking problem.

2. Smaller aperture to rule-out if it is really a coma issue with your lens.

Good luck.
Click to expand...
I don't think it's either of those two things. If you look at the image, you'll notice on the right the points of light are elongated. On the left, they are, for the most part, points of light with no elongation. I'd say this is a decentered element in the lens causing one side to distort. My Tamron 15-30mm exhibits the exact same traits when I'm doing astrophotography. If it were a matter of to long and exposure time, then the points of light on both sides would be equally elongated. I'm considering sending my lens in to Tamron to have a look at it.
 
I dunno, I see coma in your upper left corner. Classic wings.

Little you can do about it aside from using a better lens in that attribute.

You are also exposing too long. I get pixel-peepable (but not so much at regular viewing sizes) streaking at 20 seconds on a 14mm Samyang.
 
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KennyXL said:
mbo27 said:
Try a couple things:

1. Shorter exposure time. While the 500 rule would imply an exposure of 33 secs (500/15), the more exact formula using the Tamron and the D750 is more like 18 secs. This would point to you whehter it is a streaking problem.

2. Smaller aperture to rule-out if it is really a coma issue with your lens.

Good luck.
Click to expand...
I don't think it's either of those two things. If you look at the image, you'll notice on the right the points of light are elongated. On the left, they are, for the most part, points of light with no elongation. I'd say this is a decentered element in the lens causing one side to distort. My Tamron 15-30mm exhibits the exact same traits when I'm doing astrophotography. If it were a matter of to long and exposure time, then the points of light on both sides would be equally elongated. I'm considering sending my lens in to Tamron to have a look at it.
Click to expand...
Thanks guys, I havent know about decentered until KennyXL pointed out the issue. I've searched about decentered, it very similar to what KennyXL explained and it looks like that is the issue with my lens. Yes I've tried using shorter exposure and it still the same, the right corner is very different on the left. Thanks to all your response.
 
hence, less distance traveled during exposure (relative to camera sensor). You can't fool a rotating Earth. Coma is actually more obvious on the left hand very bright stars, though I don't think it detracts. Coma looks like "wings" extending out from the star. It's a good image.

Loading…

en.wikipedia.org
 
Sandino Pusta said:
Sandino Pusta said:
mbo27 said:
Try a couple things:

1. Shorter exposure time. While the 500 rule would imply an exposure of 33 secs (500/15), the more exact formula using the Tamron and the D750 is more like 18 secs. This would point to you whehter it is a streaking problem.

2. Smaller aperture to rule-out if it is really a coma issue with your lens.

Good luck.
Click to expand...
I don't think it's either of those two things. If you look at the image, you'll notice on the right the points of light are elongated. On the left, they are, for the most part, points of light with no elongation. I'd say this is a decentered element in the lens causing one side to distort. My Tamron 15-30mm exhibits the exact same traits when I'm doing astrophotography. If it were a matter of to long and exposure time, then the points of light on both sides would be equally elongated. I'm considering sending my lens in to Tamron to have a look at it.
Click to expand...
Thanks guys, I havent know about decentered until KennyXL pointed out the issue. I've searched about decentered, it very similar to what KennyXL explained and it looks like that is the issue with my lens. Yes I've tried using shorter exposure and it still the same, the right corner is very different on the left. Thanks to all your response.
Click to expand...
There is a way to tell if this is due to streaking (earth's rotation) or decentering. Make three long exposures. Point one more-or-less at the pole (it does not need to be exact, but the closer the better), one at about 45 degrees to the right of the pole, and one about 45 degrees to the left of the pole.

If the lens is good, the streaking in the first image (pointing at the poles) should be constent in the corners (both lower corners should be the same amount but in different directions, both upper corners should be the same amount but in different directions).

Again, if the lens is good, the other two images should have more streaking on one edge than the other, but it should be on opposite edges (the image to the left should have streaking mostly on the left, the image to the right should have streaking mostly on the right).
 
Sandino, You may well have a degree of decentering in your Tamron, most zooms have at least a bit at some focal length or other and you may also be seeing a bit of tilt. You're going to get a lot of conjecture on this forum that ultimately may confuse you and lead you to conclude that swapping lenses, switching brands or paying uber bucks is going to guarantee optical happiness. I can guarantee that having discovered this issue you will look for it, and possibly find it to some degree, in your next lens. My suggestion is to read some of Roger Cicalas' blogs on tilt and decentering in lenses or better still, email him at LensRentals.com with you questions. He is a wealth of information and well respected on these forums. Aloha.
 
AustinMN said:
Sandino Pusta said:
AustinMN said:
mbo27 said:
Try a couple things:

1. Shorter exposure time. While the 500 rule would imply an exposure of 33 secs (500/15), the more exact formula using the Tamron and the D750 is more like 18 secs. This would point to you whehter it is a streaking problem.

2. Smaller aperture to rule-out if it is really a coma issue with your lens.

Good luck.
Click to expand...
I don't think it's either of those two things. If you look at the image, you'll notice on the right the points of light are elongated. On the left, they are, for the most part, points of light with no elongation. I'd say this is a decentered element in the lens causing one side to distort. My Tamron 15-30mm exhibits the exact same traits when I'm doing astrophotography. If it were a matter of to long and exposure time, then the points of light on both sides would be equally elongated. I'm considering sending my lens in to Tamron to have a look at it.
Click to expand...
Thanks guys, I havent know about decentered until KennyXL pointed out the issue. I've searched about decentered, it very similar to what KennyXL explained and it looks like that is the issue with my lens. Yes I've tried using shorter exposure and it still the same, the right corner is very different on the left. Thanks to all your response.
Click to expand...
There is a way to tell if this is due to streaking (earth's rotation) or decentering. Make three long exposures. Point one more-or-less at the pole (it does not need to be exact, but the closer the better), one at about 45 degrees to the right of the pole, and one about 45 degrees to the left of the pole.

If the lens is good, the streaking in the first image (pointing at the poles) should be constent in the corners (both lower corners should be the same amount but in different directions, both upper corners should be the same amount but in different directions).

Again, if the lens is good, the other two images should have more streaking on one edge than the other, but it should be on opposite edges (the image to the left should have streaking mostly on the left, the image to the right should have streaking mostly on the right).
Click to expand...
Hi AustinMn,

Thanks for that advice, I'll try to test that method, good thing you mentioned this earlier before I will go to Tamron service center.
 
NikonHaoleboy said:
Sandino, You may well have a degree of decentering in your Tamron, most zooms have at least a bit at some focal length or other and you may also be seeing a bit of tilt. You're going to get a lot of conjecture on this forum that ultimately may confuse you and lead you to conclude that swapping lenses, switching brands or paying uber bucks is going to guarantee optical happiness. I can guarantee that having discovered this issue you will look for it, and possibly find it to some degree, in your next lens. My suggestion is to read some of Roger Cicalas' blogs on tilt and decentering in lenses or better still, email him at LensRentals.com with you questions. He is a wealth of information and well respected on these forums. Aloha.
Click to expand...
HI NikonHaoleboy,

Thanks for your suggestion, I'll check that blog for sure. I'll need to know more about decentering issue.
 
Sandino Pusta said:
NikonHaoleboy said:
Sandino, You may well have a degree of decentering in your Tamron, most zooms have at least a bit at some focal length or other and you may also be seeing a bit of tilt. You're going to get a lot of conjecture on this forum that ultimately may confuse you and lead you to conclude that swapping lenses, switching brands or paying uber bucks is going to guarantee optical happiness. I can guarantee that having discovered this issue you will look for it, and possibly find it to some degree, in your next lens. My suggestion is to read some of Roger Cicalas' blogs on tilt and decentering in lenses or better still, email him at LensRentals.com with you questions. He is a wealth of information and well respected on these forums. Aloha.
Click to expand...
HI NikonHaoleboy,

Thanks for your suggestion, I'll check that blog for sure. I'll need to know more about decentering issue.
Click to expand...
Hi,

Your lens suffers from strong astigmatism on the right side and not so much on the left side. It is decentered, but having not measured the 15-30 in volume I cannot tell you if this is normal for that model or not. You may wish to try exchanging it, since it certainly isn't properly aligned.

Regards,

Brandon
 
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