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02-23-2009, 02:27 AM   #1
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Mirror image problem

Hi,

I have just bought K200D and I have Tamron 18-200mm with Kenko UV- filter.
Problem is that I get mirror + flip ghost image on long exposure.
What could cause the problem? (see the image from the link below)

http://img23.imageshack.us/img23/7361/ongelma.jpg

02-23-2009, 03:38 AM   #2
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Nice effect in the image... Nevertheless the ghosting is either caused by the filter or by the many lenses in the zoom. Remove the filter for night time shooting - this is my basic rule for filter use. If that does not remedy the problem, you need another lens. These zooms are simply very complicated with many lenses inside and the probability of reflections, ghosting and flare is massively increased, compared to simpler lens designs.

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02-23-2009, 04:30 AM   #3
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QuoteOriginally posted by Valojuova Quote
Problem is that I get mirror + flip ghost image on long exposure.
That most certainly looks like a reflection from the filter (ghost image mirrored using the centre as the "mirror point"). Maybe a better filter will produce less of a ghost image, but as Ben_Edict said, it is best to not use any filter at all for such shots.
02-23-2009, 08:48 AM   #4
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I eagerly await an optics based explanation of why the ghost image is inverted and in-focus.

I'm guessing it must involve reflection from the sensor .. but then what?

Dave

02-23-2009, 09:27 AM   #5
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QuoteOriginally posted by newarts Quote
I eagerly await an optics based explanation of why the ghost image is inverted and in-focus.

I'm guessing it must involve reflection from the sensor .. but then what?

Dave
I don't think it is a reflection off the sensor. The reflected image is very weak, compared to the completely overexposed light source - exactly what you would expect from the reflection of a coated glass surface (the filter backside). The reflection probably stems from the front lens' surface of the zoom, which is convex and would project the image into infinity. The only thing I cannot answer immediately is, why it is inverted. So maybe , it originates from the second lens or whatever, which would make inverting the image by the first lens, easier to understand? I can only say from experience, that this is consistent with reflections I had with filters even during film days. Which is the reason I always remove filters for night shots.

Ben
02-23-2009, 01:50 PM   #6
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Thanks for everybody... problem solved. It was the UV filter causing the reflections.
Would any other filter perform better, Hoya etc.? I think it will have some effect to daytime pictures also but not so remarkable. My current filter is Kenko UV (0) SL-39 Double Face Coated. I think it's low end model because it was in bundle with the camera and lens.

http://img24.imageshack.us/img24/7610/solved.jpg
02-23-2009, 01:58 PM   #7
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QuoteOriginally posted by newarts Quote

I'm guessing it must involve reflection from the sensor .. but then what?
According to this article on lens flare you are correct in assuming that sensor reflection is part of the phenomenon. The rest is reflection from the filter.

The better the filter coating, the less the ghosting will be. Under normal circumstances and with a high quality filter, the negative effects of the filter are negligible.
02-23-2009, 02:52 PM   #8
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It seems there are still some reflections. Those 2 pictures where taken with 200mm and this one 18mm. The filter can cause the reflections and also the lens on right position if taking long exposures and over exposuring.
It seems that only the lights positioned on the center cause problems.
But the major problem is solved =)
I think these kind of phenomenons are more common in cheap lenses. My Tamron cost only 200 € :P

http://img141.imageshack.us/img141/8350/testf.jpg

02-23-2009, 03:00 PM   #9
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QuoteOriginally posted by Valojuova Quote
It seems there are still some reflections. Those 2 pictures where taken with 200mm and this one 18mm. The filter can cause the reflections and also the lens on right position if taking long exposures and over exposuring.
It seems that only the lights positioned on the center cause problems.
But the major problem is solved =)
I think these kind of phenomenons are more common in cheap lenses. My Tamron cost only 200 :P
These reflections are quite different from the very prominent ones, caused by the filter. First and formost they are not sharply defined, but very blurred, but still the general shape is recognizable. So I would think, that's more or less typical lens flare, but that now could indeed be a sensor induced reflection - though I must admit in real life I have never seen that myself.

Ben
02-23-2009, 03:05 PM   #10
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oops... The aperture settings are not the same in the pictures.
With high aperture rate F22 there is not any reflections and with F6.3 there is.
02-23-2009, 03:07 PM   #11
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I see this even with good filters

I usually keep my Kenko Pro 1 Digital protective filters on my DA70 and DA16-45 all the time, but I've often regretted not to take them off before doing night photography.

Here the strong lights of the pier in the foreground are faintly reflected to the left of the smoke from the chimney of the cruise ship:
02-23-2009, 03:25 PM   #12
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QuoteOriginally posted by Valojuova Quote
oops... The aperture settings are not the same in the pictures.
With high aperture rate F22 there is not any reflections and with F6.3 there is.
As I cannot see, how the aperture would influence the reflection by the sensor, it boils down to internal lens flare in the zoom, for me. Nothing you can cure, except perhaps by trying to avoid centered light sources in your images.

Ben

EDIT: Well, I can imaging, that aperture influences sensor reflections, but this is really something very obscure and a remote possibility...
02-23-2009, 08:23 PM   #13
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The thing that made me think reflection from the sensor is involved in the original posting is the ghost image is up-side down with respect to the primary image & is in pretty good focus.


The article referred to by Class A explains clearly what might be going on.

http://toothwalker.org/optics/flare.html#filter

Dave

PS it even predicts a decreased ghost image with smaller aperture reported later by OP.

Last edited by newarts; 02-23-2009 at 08:45 PM.
02-24-2009, 03:25 AM   #14
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QuoteOriginally posted by newarts Quote
The thing that made me think reflection from the sensor is involved in the original posting is the ghost image is up-side down with respect to the primary image & is in pretty good focus.


The article referred to by Class A explains clearly what might be going on.

Flare

Dave

PS it even predicts a decreased ghost image with smaller aperture reported later by OP.
This article very clearly states, that the culprit is the filter, though it makes reference to the film as a mirror for the incident light.
Whether film or the sensor contribute much to the image formation is open to question, but sure possble. But the detrimental ghost image is clearly - and the referenced article states that expressedly - formed by the filter.

There is one big caveat about the efficiency of the film/sensor as a strong reflective light source and that is (especially with the lens here in question), that the accompanying graphics only references a thin lens construction. A zoom or super-zoom is much more complicated, especially when made for digital, as these tend to be designed as a telecentric lens system, which has a different ray trace, than the simple example on the the web page.

Anyway: if the sensor would be a major contributor to this kind of ghosting and flare, there wouldn't be much, we could do about it. Luckily, at least my personal experience with Pentax DSLRs is otherise, as I never have seen any sensor induced flare in my images. All the flring I have had could easily be traced to the lens in question, for example the old K 15/3.5, which is a wonderfully sharp and contrasty lens, but very prone to flaring.


I think, the conclusion in the referenced article is something, that is still underappreciated, especially by beginners: use a good lens hood all the time! Considering, that for instance, the K-m comes with a kit lens, which lacks the hood, this can be a real quality killer and the aspiring photographer will not even have a clue, why his images turn out insufficient.

Ben
02-24-2009, 03:32 AM   #15
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QuoteOriginally posted by Ben_Edict Quote
Considering, that for instance, the K-m comes with a kit lens, which lacks the hood, this can be a real quality killer and the aspiring photographer will not even have a clue, why his images turn out insufficient.
I can't understand why they did that. Just another "me too"? (I guess at least Canon doesn't provide hoods with their cheaper lenses)
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