INFRARED-Image-Thread

[zampelis]

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I think you are right GP concerning the hot spot. There is definitely one and I am not sure what affects its intensity. I have highlighted it in this screenshot. I needed to manipulate it in photoshop in order to not have it visible. In real life is not as bad a the screenshot, I have intentionally highlighted the area red, but it is still there... Maybe it is affected by the ISO settings? Hmm.. Interesting...

 

[zampelis]

A different shot, but it too had the same spot

 

Edited May 20, 2018 by zampelis

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[david strachan]

Hi Zampelis. I've been enjoying your nice IR's. It's not an easy genre.

 

I have some lenses with hot spots. The easiest way to determine them is take a full frame image of high evenly lit IR subject like a lawn, on a bright warm day. Also shooting at different f-stops will define the edges of the hot spot, as it is stopped down. You'll need a tripod for this test.

 

Good luck and hope you don't find it too much of a problem.

 

...

[bags27]

Hi Dimitrios,

 

Is it because of the channel swapping? I've looked back on your first IR photos on the image thread and I don't see hot spots.

[gbealnz]

I too wondered that Bags, the B&W shots that started this were not like that as I recall. Mind you a slight difference in colour can draw the eye.

 

Dave has a valid point too, the working aperture might be accentuating this.

 

Gary

[zampelis]

To be honest I am too wondering about that!! The only difference between the first colour shot I posted on this thread was that I used a polarising filter. But I am pretty sure that polarising filters have no effect in the infrared spectrum.

 

The thing is, how the sensor react to changes like these.. does polarising the light hitting the sensor affects its response to IR light? Also the spot is not very prominent. it is as if there is a tad bit of sensitivity in some specific photos.

 

When the photos are turned to B/W it is not visible at all. It seems that I can see it when I swap red and blue channels and adjust the green one. I will follow David's advice and one bright day I will take some shots of a uniform lawn with various settings and will post here my findings..

 

Will do it some time next weekend as it sounds like quite a project to do and also there is no sun when I come back from work!

[zampelis]

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Hi Zampelis. I've been enjoying your nice IR's. It's not an easy genre.

 

I have some lenses with hot spots. The easiest way to determine them is take a full frame image of high evenly lit IR subject like a lawn, on a bright warm day. Also shooting at different f-stops will define the edges of the hot spot, as it is stopped down. You'll need a tripod for this test.

 

Good luck and hope you don't find it too much of a problem.

 

...

 

How rude of me David, I didn't say thanks on first place!!

 

Thank you for the kind words, the great advices and will definitely investigate the matter further!!

Edited May 20, 2018 by zampelis

[farnz]

.

Here's one I took handheld today as an example of no hotspot.  Channel swapping isn't the cause of IR hotspots as far as I'm aware.  Some lenses just have them and others just don't.  I've heard tht the 35/3.5 Summaron is quite good for IR although I've never used one.

 

Old Royal Naval College, London.

 

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M8 and 21/2.8 Kobalux wide open with SinghRay I-Ray IR filter (850+ nm).

[farnz]

.

Actually I would expect a polarising filter to affect infrared.  

 

Apologies if this sounds a little like a lecture: light (in its wave form, not its photonic form) is made up of two waves that travel at 90 degrees to each other and have been named HE1 and HE2.  (Put your hands side on in an X formation and that pretty much describes it.)  Polarising filters simply don't transmit one or other of the HE1 or HE2 waves of radiant energy (light) which is why polarisers add a stop or two of exposure.  This will be no different in the infrared spectrum so a polarising filter will attenuate (decrease) infrared light that tries to pass through it.

 

Pete.

[bags27]

well, I did some IR today, the first picture I took I used the polarizer also, just as a snap shot. The first picture was only processed in LR to convert it to B&W. The second is the same DNG but with one of the B&W presets, just to give it a bit more punch to see if that hot spot would show. I don't think I see any.

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Edited May 21, 2018 by bags27

[bags27]

same picture without polarizer but with the same "punch" preset (bigger file because it was only one file and didn't need to be shrunk to fit)

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Edited May 21, 2018 by bags27

[bags27]

bridge is about a mile from my home

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[farnz]

bags27, 

 

If you look at the at the centre of the picture, particularly the whites, appear brighter than those away from the centre.  It's less visible in the first picture but still there and quite evident in the others so I regret that it looks like a hot spot to me.  I'm not suggesting that it ruins the pictures but it's certainly visible to me. 

 

Pete.

[bags27]

Thanks Pete. I do see what you mean: I was literally out in the sun so long yesterday that I had it in my mind that every picture I took was into the sun (and some were ruined by so much flare), but the axis of these shots are 180 different, so it's not the sun in both cases. 

[farnz]

I notice that in your last picture of the bridge there seems to be an angled criss-cross pattern all over it.  I'm not sure what's caused that unless it's a form of Pattern Noise.  I can't see it on your other pictures fortunately.  Did you use a polarising filter on that one?

 

Pete.

[pico]

Bags, is that the restored Warren Bridge?

[jip]

How are the exposure times? 

 

As in let's say normal without filter shot would be 1/1000 what would the IR shot need?

 

How is focussing? Manually or automatic TTL with filter mounted? 

[Martin B]

Thanks Pete. I do see what you mean: I was literally out in the sun so long yesterday that I had it in my mind that every picture I took was into the sun (and some were ruined by so much flare), but the axis of these shots are 180 different, so it's not the sun in both cases. 

 

Clearly both photos have a hot spot in the middle - it has nothing to do with external conditions, this is a property of the lens you used. Hot spots might also appear at smaller apertures - again, depending on the lens. I wouldn't use this lens for IR photos if I were you. 

[Martin B]

Polarizing filters have from my experience only very little or no effect in IR. They can be more of a debit than benefit here since they might lead to additional reflection of IR light on the filter glass. Let's not forget that the polarizing filters are all optimized for visible light, too. 

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[pico]

Clearly both photos have a hot spot in the middle - it has nothing to do with external conditions, this is a property of the lens you used. Hot spots might also appear at smaller apertures - again, depending on the lens. I wouldn't use this lens for IR photos if I were you. 

 

Martin, how about center filters and IR? Any peculiarities?