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-   -   m4/3 lenses for IR (http://e-group.uk.net/forum/showthread.php?t=48242)

drmarkf 2nd July 2018 11:01 AM

m4/3 lenses for IR
 
Dear all,

I've had my E-M10ii converted to full spectrum by Protech (speedy and nice to deal with, BTW) and I'm having great fun playing around, initially with a Hoya 720nm filter.

I've been using the Panasonic 12-35 f2.8, which is widely said to be quite good for IR - it is, but there is a just-noticeable hotspot towards the centre of the frame especially at smaller apertures and with IR-bright elements in the frame. This isn't a major issue and is fairly simple to correct in PP, but I was wondering what other lenses people had tried with success?

My Pan-Leica 15 is better, but I'd like a standard zoom, really, and ideally something wide to super-wide. I haven't yet tried the Laowa 7.5 or Oly 7-14, while the 12-100 is hopeless, BTW.

I've seen recommendations for various iterations of the Oly 14-42 and the 12-50, but does anyone have any experience either way?

Many thanks.

angelpaaul 2nd July 2018 11:16 AM

Re: m4/3 lenses for IR
 
I’ve used both the 14-42 and the 12-50 with no problems. Currently using a Panny 12-32. It suits my needs, small, light, right focal length and give acceptable results. Only other I’ve tried is the Olympus 12-40 pro, excellent results but a bit out of place on my Panny GX1.
Hope this helps you.

drmarkf 2nd July 2018 10:49 PM

Re: m4/3 lenses for IR
 
Many thanks.

I've done some more playing around this evening, and doing a B&W conversion in Capture One and playing around with the colour conversion sensitivity sliders removes the hot spot for all practical purposes. I'm not quite sure what's going on (it is quite variable anyway, and certainly isn't down to flare on the lens or external filter) so I'll persist with the 12-35 for now. I like some of the images I got on a club outing to Greenwich yesterday.

I've ordered an 850nm filter for monochrome and I'll see what effect that has on the issue.

I guess it might cause more of a problem when I want to try false colour, but that's a whole different processing ballgame and a bridge I'll cross when I want to meet it.

Petrochemist 3rd July 2018 01:29 PM

Re: m4/3 lenses for IR
 
I've used the Panny 14-42, 50-200 Olympus 9mm BCL & 17mm/2.8 for IR without any hot spot issues on my converted camera.
But I have seen hot spots with the 14-42 when shooting IR on a non-converted camera, So far at least the 50-200 has been free of hot spots with the standard camera.
I've also seen hotspots with c-mount lenses but possibly this was down to the extension tubes I was using.


I think hot spots are less of a problem with false colour IR (it's a problem with the IR part of the image) but chromatic aberration can be an issue with wider wavelength images.

drmarkf 3rd July 2018 03:14 PM

Re: m4/3 lenses for IR
 
Quote:

Originally Posted by Petrochemist (Post 450318)
I've used the Panny 14-42, 50-200 Olympus 9mm BCL & 17mm/2.8 for IR without any hot spot issues on my converted camera.
But I have seen hot spots with the 14-42 when shooting IR on a non-converted camera, So far at least the 50-200 has been free of hot spots with the standard camera.
I've also seen hotspots with c-mount lenses but possibly this was down to the extension tubes I was using.

I think hot spots are less of a problem with false colour IR (it's a problem with the IR part of the image) but chromatic aberration can be an issue with wider wavelength images.

Interesting, thanks.

Dave in Wales 8th July 2018 07:39 AM

Re: m4/3 lenses for IR
 
Well, where are the example shots then ?

I've always been of the opinion that it's a good camera ruined to produce gimmicky shots that are very quickly forgotten.

But I stand to be corrected.

*chr

Graham_of_Rainham 8th July 2018 01:59 PM

Re: m4/3 lenses for IR
 
I think the "hot spot" is coming from diffraction.

Some time back, I pressed to service my ever co-operative muse for this crude set of tests ;)

http://dpnow.com/galleries/data/814/WP3310040.jpg

With the camera set to f/22 and manual focus, I took 3 pictures.
The one above, with the bare flash, one with a Red gel over the flash and another with a Blue gel

http://dpnow.com/galleries/data/814/WP3310039.jpg

http://dpnow.com/galleries/data/814/WP3310041.jpg

I then removed the colour from the RAW files, examined them and cropped an area which I think best shows the effect.

RED Light
http://dpnow.com/galleries/data/814/P3310039_cr.jpg

Blue Light
http://dpnow.com/galleries/data/814/P3310041_cr.jpg

The filters used are very saturated "effects" filters and beyond any colours that you would get from natural light, but serve to show how the longer wavelength of the red light is diffracted more than the short wavelength blue light.

IR being even longer than the red I used will diffract even more through small holes...

Ricoh 8th July 2018 02:31 PM

Re: m4/3 lenses for IR
 
Quote:

Originally Posted by Graham_of_Rainham (Post 450593)
I think the "hot spot" is coming from diffraction.

Some time back, I pressed to service my ever co-operative muse for this crude set of tests ;)

http://dpnow.com/galleries/data/814/WP3310040.jpg

With the camera set to f/22 and manual focus, I took 3 pictures.
The one above, with the bare flash, one with a Red gel over the flash and another with a Blue gel

http://dpnow.com/galleries/data/814/WP3310039.jpg

http://dpnow.com/galleries/data/814/WP3310041.jpg

I then removed the colour from the RAW files, examined them and cropped an area which I think best shows the effect.

RED Light
http://dpnow.com/galleries/data/814/P3310039_cr.jpg

Blue Light
http://dpnow.com/galleries/data/814/P3310041_cr.jpg

The filters used are very saturated "effects" filters and beyond any colours that you would get from natural light, but serve to show how the longer wavelength of the red light is diffracted more than the short wavelength blue light.

IR being even longer than the red I used will diffract even more through small holes...

Whatever a man gets up to in the privacy of his own home, ah! 😉

angelpaaul 8th July 2018 03:06 PM

Re: m4/3 lenses for IR
 
Quote:

Originally Posted by Dave in Wales (Post 450583)
Well, where are the example shots then?

Here's a few of mine. As for "a good camera ruined", not in my case, this particular camera was headed for the scapheap. The conversion gave it a new lease of life. I've been taking IR images for years, even back in the 'old days' of film, never get bored of it. Might even get one of my old cameras converted to colour.

http://www.e-group.uk.net/gallery/data/508/park-01.jpg

http://www.e-group.uk.net/gallery/data/508/Park-03.jpg

http://www.e-group.uk.net/gallery/data/508/Park-02.jpg

drmarkf 8th July 2018 06:36 PM

Re: m4/3 lenses for IR
 
Nice.

Yes, I'll post a few when I feel I've got my processing sorted. I have liked the monochrome IR effects for many years, and it's particularly good when you want to shoot in the countryside in the middle of a sunny day (i.e. every day at the moment). Conventional photography then gets reduced to macro or shady waterfalls if you want anything worth keeping.

BTW one of the advantages of a full spectrum camera is that you can return it to what passes for normality by screwing the appropriate filter on the front, so ruination isn't an option *chr

angelpaaul 8th July 2018 06:54 PM

Re: m4/3 lenses for IR
 
Quote:

Originally Posted by drmarkf (Post 450609)
BTW one of the advantages of a full spectrum camera is that you can return it to what passes for normality by screwing the appropriate filter on the front, so ruination isn't an option *chr

I weighed up the pros and cons of a full sprctrum but for what I wanted it was too much of a compromise. If I do convert a spare camera, I'll get a 720nm filter for the false colour. The above where taken with an 830nm filter.

Ricoh 8th July 2018 06:58 PM

Re: m4/3 lenses for IR
 
What’s the going rate for conversion? I have a GX7 gathering dust.

angelpaaul 8th July 2018 07:01 PM

Re: m4/3 lenses for IR
 
Quote:

Originally Posted by Ricoh (Post 450615)
What’s the going rate for conversion? I have a GX7 gathering dust.

These Guys are excellent - http://www.protechrepairs.co.uk/

MikeOxon 9th July 2018 03:17 PM

Re: m4/3 lenses for IR
 
An unconverted camera can also provide the infra-red effect, albeit at the expense of long exposures. I have a set of Schott long-pass filters and experimented with these on my E-M1-ii camera with 17mm f/2.8 lens (chosen because my 25mm diameter filters cover the small-diameter lens)

The results are shown below - note that the exposure increases from 1/400s@f/8 for the unfiltered shot to 1/10s@f/2.8 when the red (RG645) filter is applied. The exposure increases further as the cut-off wavelength moves into the infra-red.


http://www.e-group.uk.net/gallery/da...RedFilters.jpg

Also notice how the sky becomes black and the green foliage becomes bright, once the cut-off wavelength reaches 780nm. By this point, the Bayer filter array no longer works and all three filter components (red, green, blue) start to transmit, so distorting the 'colour' that is recorded by the sensor.


I believe that this is why bright red subjects, such as roses in strong sunlight, acquire a magenta tinge, since these flowers reflect a large amount of infra-red radiation. I usually darken the magenta component of images of such subjects, to restore the red colour that we actually see directly.

Petrochemist 9th July 2018 04:09 PM

Re: m4/3 lenses for IR
 
I also find the 17mm/2.8 ideal for those 25mm filters. Have you come up with a good way of holding the filters?
I have one ancient (?series) filter holder that they fit into which is fitted to a 37mm stepping ring but I've not found any others. Since I have half a dozen of these little glass discs a few more mounts for them would be nice!


While roses reflect quite a bit of NIR not all bright red subjects will. I've photographed a red Ferrari & found a few panels looked different in IR probably the difference between metal panels & plastic ones :)


The degree of NIR contamination varies considerably with camera model & of course it gets MUCH worse with a converted camera, often noticeable in artificial blacks. I've had some come out in brown or lilac while others stay black (the color shown is mainly dependent on the fabric & the NIR it reflects).


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