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Forum: Troubleshooting and Beginner Help
05-23-2018, 07:47 PM
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Thanks for suggestion! I'll try to spot when the condensation occurs and give it a try.
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Forum: Troubleshooting and Beginner Help
05-23-2018, 02:30 PM
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Agreed, but I don't think the condensation is so persistent. It's probably just a matter of waiting longer in circumstances where the temperature and humidity suddenly change, but it's made difficult because the condensation isn't on the front of the lens.
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Forum: Troubleshooting and Beginner Help
05-23-2018, 05:47 AM
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Sorry the sample images are missing. Flickr has been bought by Smugmug and I'm not yet comfortable with the TOS.
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Forum: Troubleshooting and Beginner Help
05-23-2018, 05:47 AM
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Sorry the sample images are missing. Flickr has been bought by Smugmug and I'm not yet comfortable with the TOS.
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Forum: Troubleshooting and Beginner Help
05-18-2018, 04:42 AM
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I agree - although I was thinking more along the lines of there being a little bit of condensation on those two occasions. However, the light coloured blob appeared in the centre of an image again today, so I'm going to experiment a bit more to see if I can reproduce both the light and dark blobs predictably.
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Forum: Troubleshooting and Beginner Help
05-17-2018, 09:53 PM
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No. The Tamron was the first lens where I went with suggestions of other people now to use a protective filter - mostly because the lens was much cheaper than the Pentax equivalent.
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Forum: Troubleshooting and Beginner Help
05-17-2018, 04:40 PM
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Does anyone have any thoughts on the possibility that condensation is the cause of the blobs?
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Forum: Troubleshooting and Beginner Help
05-17-2018, 05:46 AM
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Thanks Ken! I assume you mean dust on the sensor. As I mentioned, I have checked this by photographing the sky at the highest f-stop. I agree that it does seem to show up dust on the sensor if any is there.
---------- Post added 17-05-18 at 11:02 PM ----------
I've only seen the blob in images at 17mm. It always seems to be the same size and always in the exact centre of the frame. Yes, I can see that the green blob is lens flare from the backlit subject, but it also appears in several frames, and always in the exact centre of the image. I can't help feeling that there is a link between the two. I have never had lens flare with any other lens that always appears at the exact centre of the image as a fuzzy blob. Flare is usually one or more shapes leading from the light source (usually the sun). Flare is most often quite sharp edged, not fuzzy. There's two other lens flare spots in the image of the gate, up and to the left. Neither is nearly as indistinct as the blob in the centre.
I have a thought for a possible cause - the day in Kyoto was very cold and I think quite humid. The day in Townsville was hot and very humid - and I had not long before got out of an air-conditioned car. I'm wondering if it could be a circle of condensation somewhere in the lens. That could explain what is seen in both images. When I first arrived in Townsville, I tried to photograph a bird in the car park and had to wait for a long time for the condensation on the lens to go away (although in that case it was the HD 55-300). It was the front element which had fogged on the weather sealed lens, but the Tamron isn't weather sealed. In the case of the Tamron, the condensation could be on an interior element.
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Forum: Troubleshooting and Beginner Help
05-17-2018, 04:09 AM
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Yes, the blob is always in the exact centre of the image. I've never noticed the blob at the time when I have taken a photo where it has appeared, so it's a bit difficult to try an equivalent Pentax lens in exactly the same circumstances. Of the lenses I have, the only one which is close to equivalent is the old DA 16-45 f4. All the situations where I've noticed the blob have happened when I have been travelling so it's not practical to carry two similar lenses.
Bizarrely, the blob isn't always dark. One of the first times I spotted it, the blob is actually pale green in a dark image. Like this:
Higashi Hongan-ji Gate by RobGeraghty, on Flickr
In this case, it does seem to be lens flare. This photo was taken with my previous camera, the K5iis.
---------- Post added 17-05-18 at 09:11 PM ----------
Yes, I did exactly that this afternoon, deliberately overexposing the sky and trying both the highest and lowest f-stops. No blob. I checked one of the images of the panorama where the blob is most obvious and the photo was f11. The panorama has lost most of the image information because of the stitching software.
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Forum: Troubleshooting and Beginner Help
05-16-2018, 10:21 PM
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Sure. Logically though, if it was on the sensor it would appear on photos with other lenses, but it never has.
I just took a couple of images of the sky, deliberately overexposed by about 3EV, at maximum and minimum f-stop and minimum focal length with the Tamron lens and my Pentax HD DA 55-300 PLM. No sign of the dark spot. If it was dust on the sensor, I'd expect it to be visible clearly at the highest f-stop. I've seen this when there has been dust on the sensor.
 Quote: By definition: Flare is non-image forming light, a dark spot indicates an absence of light. So calling it flare is a bit of a misnomer. I agree to an extent, although logically a lens behaviour could equally cause bright and dark spots relative to the image of the scene - for example if the lens system brightened everything except a certain spot, you could end up with a dark spot. I was simply looking for a word to describe a variation which is apparently cause by the lens rather than the camera.
Thanks for the suggestions. It's odd, because 99% of the time the lens captures great images (hende why I posted a couple of other examples of good images), and is certainly better than the Pentax DA 16-45 which it replaced. The Tamron does have a fault, which is that sometimes it ceases to function when zoomed to 50mm but readjusting the zoom causes this to go away. There must be a faulty contact inside the lens affected by the zoom. However, the electronic misbehaviour doesn't explain an odd optical behaviour.
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Forum: Troubleshooting and Beginner Help
05-16-2018, 08:58 PM
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A dark circle appears in some photos from the Tamron 17-50 f2.8. Viz:
Mount Stuart Panorama by RobGeraghty, on Flickr
This crop is out of a stitch. The full image is linked below, and the dark circle appears in at least two of the images that make up the panorama. It's quite visible on the left side and right side.
Mount Stuart Panorama by RobGeraghty, on Flickr
The dark spot appears very seldom. I have a lot of photos from this lens where there's no sign of it. It doesn't appear in other photos taken with different lenses on the same K3, so I don't think it's the camera, and it doesn't appear in many photos at all. Being a dark spot it's annoying and difficult to remove. Has anyone seen the same thing with other copies of this lens? Does anyone have any idea what it could be? If it was a spot on a lens element, I'd expect to see it in every photo of far more often. I've never heard of lens flare which causes a dark spot.
Here's another image where I'd expect to see the spot and there's no sign.
The light of Fuji by RobGeraghty, on Flickr
Or this one:
A Broad View of Politics by RobGeraghty, on Flickr
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