test for the IR hotspot
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test for the IR hotspot
by Stan-42
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To the group,
Cameron Shaw and I have swapped a few emails about hotspots. He sent me a few of his IR pictures with a prominent hotspot dead center. I suggested a test he could try, to prove it was the product of IR. Since the test was so simple, I tried a dose of the same medicine. Because my Sony DSC-R1 has an electronic view finder (EVF), I can see the results of an IR scene on the camera monitor. I pointed my camera at blank, white background paper and BOOM, there was the hotspot. I correctly theorized that the hotspot is an IR phenomenon. The smaller the aperture, the smaller and more distinct the heptagon (seven sided object, the shape of my aperture blades). The mark just became visible around f5.6, then got progressively worse going to f16. The deeper filters, 87c and 88 made a heptagon with a distinct but less bright outer ring. No filter, or all IR filters produced a hotspot. With my "full color" filter, a CC1, there was absolutely NO hotspot (it blocks IR light). Now here is why this test was so interesting for me. The Sony has a Carl Zeiss Vario-Sonnar zoom, 14.3-71.5mm (24-120mm in 35mm equiv.). The spot starts to appear at 26mm, gets smaller and tighter at 36mm, then fades out at about 42mm (60mm equiv. was the tightest spot). So, on this lens, when I shoot IR, I will try to avoid the middle focal lengths, especially at small apertures. Focus had no bearing on the spot at all. The blemish was solely due to infrared light, focal length and aperture. The reason I had not seen this mark on my IR pictures is that so many of my scenics are shot at the wide end where the spot is too diffuse to detect. My guess is that every lens will be different; different interior coatings, different lens formulas. But with this simple test, you can map out the bad sectors in your lens/cameras and avoid this blemish. My guess also is that this problem must effect IR film shooters. I just never heard about it before. Stan Patz NYC www.PatzImaging.com * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by Peter-270
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As Stan suggested, this should ALWAYS have been (and still be) a
problem for HIE (or any other IR film) as well. Its neither the fault of the film nor the CCD, it is the lens and aperture causing the hot spot. Fascinating discovery. regards Peter On 13/09/2007, leon aguilera radford <klavaza@...> wrote: > Tahnk to the Gods of technology, I am still using HIE... * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by Stan-42
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To Leon and the group,
Not so fast, no cause to gloat just yet. According to my little test, the hotspot phenomenon should also occur in a film based IR recording system. This would be easy to test; it would just take longer than on a digital system. Aim your film camera, loaded with HIE, at a blank wall. Set your lens to minimum aperture and underexpose the scene using your usual IR filter (make the wall gray so the white spot will show). Do a few exposures with all of your lenses, or use multiple settings on your zoom lens. Focus did not matter on my camera, and any IR filter worked, but the deeper ones showed a slightly better spot. Anyone who tries this test should make some notes and report back to the group. Perhaps we could start a database of which brands or lens formulas work the best for IR shooters. Stan Patz NYC www.PatzImaging.com ----- Original Message ----- From: "leon aguilera radford" <klavaza@...> To: <infrared@...> Sent: Thursday, September 13, 2007 12:11 AM Subject: Re: test for the IR hotspot Tahnk to the Gods of technology, I am still using HIE... * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by WJM
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On 13 Sep 2007 at 17:33, Peter wrote:
> As Stan suggested, this should ALWAYS have been (and still be) a > problem for HIE (or any other IR film) as well. Its neither the fault > of the film nor the CCD, it is the lens and aperture causing the hot > spot. > > Fascinating discovery. My strong guess is the typical angular-sensitive nature of digi- sensors (or better: their light-amplifying micro-lenses on top) is also wavelength variable. Zoom-lenses make very weird movements on their rear lens elements, which directly influences the angle of impact on the sensor....add 'IR-fringe' effects in this angular sensitivity context, and you will see very erratic stuff.... Not sure if lens coatings can also exhibit 'IR-fringe' effects in angular context....because even the angles between the lens elements change while zooming. Best way to confirm this theory is taking a camera with Dalsa-sensor, which doesn't have these micro-prisms sandwiched onto it. (the Mamiya ZD falls into this categorie, forgot which SLR's, probably no compacts or hybrids, not sure) -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand <w.j.markerink@...> [note: 'a-one' & 'en-el'!] * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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RE: test for the IR hotspot - using different lens designs.
by Cameron Shaw
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First thank you to Stan Patz,
for his IR hotspot tests. Also for comments about my Fuji IS-1 which often produces results showing hotspots with 750nm filter. Could this be owing to lens design and the type of glass and coatings used in constructing the elements? I say this because when I used an IR converted Nikon D50 body (hot mirror replaced with IR filter 750nm) the Nikon ED lenses (extra dispersion glass) appeared not to produce IR hotspots. Nikon fit lenses made by Sigma however such as the 30mm f1.4 did not perform well with IR - hard to avoid hotspots. Would be interested to hear from others who have maybe carried out tests with other lenses such as apochromatic. Cameron Shaw This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by Stan-42
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> My strong guess is the typical angular-sensitive nature of digi-
To WJ and the group,
> sensors (or better: their light-amplifying micro-lenses on top) is > also wavelength variable. > Zoom-lenses make very weird movements on their rear lens elements, > which directly influences the angle of impact on the sensor....add > 'IR-fringe' effects in this angular sensitivity context, and you will > see very erratic stuff.... > Not sure if lens coatings can also exhibit 'IR-fringe' effects in > angular context....because even the angles between the lens elements > change while zooming. > > Best way to confirm this theory is taking a camera with Dalsa-sensor, > which doesn't have these micro-prisms sandwiched onto it. > (the Mamiya ZD falls into this categorie, forgot which SLR's, > probably no compacts or hybrids, not sure) > Interesting thoughts. I too suspect something might be going on with the hotspot due to the difference in reflection between film and the sensor cover. A few people testing their film systems could answer that question. FWIW, my converted Sony DSC-R1 lost its AA filter when the IR filter was removed - they were integrated. For sensor protection, for focus(?) and to take up the old AA/IR filter slot, I have something like a cover glass in front of my sensor. No microlenses, Yes hotspot (in one focal length area). Stan Patz NYC www.PatzImaging.com * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by WJM
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On 14 Sep 2007 at 21:55, Stan wrote:
> > My strong guess is the typical angular-sensitive nature of digi- > > sensors (or better: their light-amplifying micro-lenses on top) is > > also wavelength variable. Zoom-lenses make very weird movements on > > their rear lens elements, which directly influences the angle of > > impact on the sensor....add 'IR-fringe' effects in this angular > > sensitivity context, and you will see very erratic stuff.... Not > > sure if lens coatings can also exhibit 'IR-fringe' effects in > > angular context....because even the angles between the lens elements > > change while zooming. > > > > Best way to confirm this theory is taking a camera with > > Dalsa-sensor, which doesn't have these micro-prisms sandwiched onto > > it. (the Mamiya ZD falls into this categorie, forgot which SLR's, > > probably no compacts or hybrids, not sure) > > > To WJ and the group, > > Interesting thoughts. I too suspect something might be going on with > the hotspot due to the difference in reflection between film and the > sensor cover. A few people testing their film systems could answer > that question. > > FWIW, my converted Sony DSC-R1 lost its AA filter when the IR filter > was removed - they were integrated. For sensor protection, for > focus(?) and to take up the old AA/IR filter slot, I have something > like a cover glass in front of my sensor. No microlenses, Yes hotspot > (in one focal length area). Hmm....AFAIK, the AA-filter sits above the microlenses....and the microlenses in some cases might even be integrated with the sensor (I like to think there is one microlens for each pixel....in which case it *must* be sandwiched to the sensor, to get that kind of physics correctly lined up). -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand <w.j.markerink@...> [note: 'a-one' & 'en-el'!] * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by Stan-42
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>> > My strong guess is the typical angular-sensitive nature of digi-
>> > sensors (or better: their light-amplifying micro-lenses on top) is >> > also wavelength variable. Zoom-lenses make very weird movements on >> > their rear lens elements, which directly influences the angle of >> > impact on the sensor....add 'IR-fringe' effects in this angular >> > sensitivity context, and you will see very erratic stuff.... Not >> > sure if lens coatings can also exhibit 'IR-fringe' effects in >> > angular context....because even the angles between the lens elements >> > change while zooming. >> FWIW, my converted Sony DSC-R1 lost its AA filter when the IR filter >> was removed - they were integrated. For sensor protection, for >> focus(?) and to take up the old AA/IR filter slot, I have something >> like a cover glass in front of my sensor. No microlenses, Yes hotspot >> (in one focal length area). > Hmm....AFAIK, the AA-filter sits above the microlenses....and the > microlenses in some cases might even be integrated with the sensor (I > like to think there is one microlens for each pixel....in which case > it *must* be sandwiched to the sensor, to get that kind of physics > correctly lined up). To WJ and the group, Yeah, I lost my concentration there. The Anti-Aliasing filter (it helps break up jagged diagonals in an image) is not the same as the microlens layer which draws light into the sensor photosites. I will try to get more info on the glass used in my Sony next week. Is it just window glass or does it have anti-reflective coating. Stan Patz NYC www.PatzImaging.com * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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Re: test for the IR hotspot
by Henning Wulff
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I've got a Canon 350D converted to IR use, with an 87 filter in front
of the sensor, and used various lenses with that. The 17-85 Canon works well, as do the 10-22 and 100-400. The 100-400 seems to be a bit better (sharper) than the 70-200/2.8 IS. I don't usually use my primes with the IR camera, but have tried some, and use the 35/1.4 regularly. While the zooms all work quite well with few anomalies, the 35/1.4 shows many flare spots, some of which are quite obtrusive. The zooms are 'cleaner' in this regard. No lens hot-spots. I haven't checked to see if the 87 filter is reasonably coated, but would doubt that it is coated to absorb/cancel IR radiation reflections. It could be, though since that is obviously its intended application. I've shot a lot of HIE until lately, both in 35 and 4x5, and have never had a hot spot issue. The 35mm use was pretty exclusively in Leicas, so lens designs were generally not too complex. HIE would not have an issue with high specular reflection of IR wavelengths, which would seem to be necessary for hot spotting to occur. I think that the hot spotting that seems to occur (mostly) in IR cameras in which the IR blocking filter is weak or has been removed and an IR pass filter placed in front of the lens is due to anti-reflection coatings on lens elements and filter packs over the sensor being completely ineffective at IR wavelengths. This is reasonable from Stan's experiments, where the physical arrangements of lens elements seems to have an affect on the amount of hot-spotting. If IR radiation hits the sensor cover, gets reflected back to the lens and then finds that the radiation is reflected almsot straight back, a hot spot can result. If the lens element arrangement is such that the back of the lens reflects the radiation more to the side, less multiple reflection takes place and the hot spot doesn't appear. In any case, the outer edges of the image will never see the effect because multiple reflections into that area are basically not possible. Soo... I think that for hot spotting to occur the cover (glass, filter pack, whatever) over the sensor has be be reflective to IR radiation as a basic condition. HIE doesn't share that characteristic. -- * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@... |[ ]| http://www.archiphoto.com * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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HIE Available
by George L Smyth-2
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When I was at my parents house last weekend my mother mentioned to me that I
had some film in their deep freeze - something I had forgotten all about. One was a partial 400' roll of HIE, and my guess is that about 250' remains on the roll. I am going to eBay the partial roll unless someone would like it. If there is 200' on the roll then that should translate to at least 35 rolls. I would be willing to offer it for $200 which would include shipping within the United States (a little extra outside the US). I've also got about 300' of Techpan on a roll, if anyone is interested. If you would like either roll then please contact me offline at George.Smyth@... (my Yahoo email is mainly spam these days). Cheers - george ------------------------------------- Eclectic Mix: http://EclecticMix.com One Minute How-To: http://OneMinuteHowTo.com DRiP Investing: http://DRiPInvesting.org Handmade Photographic Images: http://www.GLSmyth.com - Blog: GLSmyth.Wordpress.com * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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rent and vancity
by Chris Wulff
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Dad, I forgot to ask if you could check your vnacity account to make
sure 500 has come in for september and october. Chris * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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oops!
by Chris Wulff
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Sorry for the spam (wrong reply-to). Chris * **** ******* ****************************************************** * To remove yourself from this list, send: * * UNSUBSCRIBE INFRARED * * to * * MAJORDOMO@... * *----------------------------------------------------* * For the IR-FAQ, IR-Gallery and heaps of links: * * http://www.a1.nl/phomepag/markerink/mainpage.htm * ****************************************************** |
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