View Full Version : IR filtration in lenses?
A bit of blue sky thinking here.
Assuming that the severe IR sensitity issues are going to remain structural to the M8 and Leica is commited to digital imaging long term, are there any technical reasons why a IR blocking layer could not be coated onto an internal lens element in new lenses? I'm not an optical scientist, but from what I have read about the science of IR coatings, it appears that a coating would have absolutely no adverse effect on lens speed or optical quality, and if anything would actually improve sharpness by cutting out IR which comes to focus at a slightly different focus point to visible image forming radiation. Also, because there is no new glass interface, the addition of flare/ghosting would not be an issue. Am i missing something obvious here?
Mark
Well, nothing more obvious than the fact that it would prevent people from shooting IR photography with Leica lenses... Beyond that, existing lenses would have to be disassembled and recoated, which I think would be cost prohibitive, not to mention extremely labor intensive for Leica. Think how long it has taken them to just recode lenses...all that is taking a mount off and switching it out. To add the IR coating they would need to disassemble the whole lens, remove the element, coat it, replace it, put it back together and then test to make sure everything is still performing perfectly.
But anyway, if you are only talking about new lenses, I figure it is probably possible, but probably not optimal. I think the cyan vignetting would be a liability on film bodies where it would not be able to be fixed. If you are shooting slides with a 24mm lens with IR blocking, you would have slides that had permanent cyan fringing in the corners. I don't think Leica would like that to be a hallmark of their lenses.
I was only thinking of new lenses. If the coating was somewhere near the centre of the the optical axis, would the light path not be fairly straight thus minimizing or eliminating the cyan cast due to image forming light coming from overtly oblique angles which is where I assume the problem comes from? Again, I emphasize that I am not an optical scientist. Regarding those that wanted to do IR photography, perhaps integral IR filtering could be an option rather than an imposition.
visiondr
04-09-2007, 16:50
It seems to me that Pinphot is correct here wrt the angle of incidence of the light rays on the coating. If they are at or near parallel to the optical axis, there should be no cyan drift.
I look forward to Gore Vidal's opinion on this issue, and if Chomsky wished to express an opinion, I would be interested in hearing that too:D
I was out at a local restaurant last night and took a few photos of my friend sitting across the table with my M8, v. 1.092, 35 Cron with the just recieved IR filter. She had on a very dark blue sweater. I was shooting at f2 under a large tung. light and got the terrible mangents. I guess that the problems are not solved as of yet.
Hope that something is done with the next firmware version.
Gary B
I was out at a local restaurant last night and took a few photos of my friend sitting across the table with my M8, v. 1.092, 35 Cron with the just recieved IR filter. She had on a very dark blue sweater. I was shooting at f2 under a large tung. light and got the terrible mangents. I guess that the problems are not solved as of yet.
Hope that something is done with the next firmware version.
Gary B
If it is extreme, a bit of IR will leak through any filter, however, in that case it is not that hard to correct using appropriate profiles.What you describe is a situation where a DSLR with full IR filter on the sensor would have shifted towards magenta as well.
Can you post the picture? Because I think people have been pretty much unanimous about the filters solving the IR problem. I know that I have not had problem with magenta blacks since I started using the filters...I have thousands of images since then. This is not to say that it did not happen, I am just suspicious that something else might be at play here.
But anyway, if you are only talking about new lenses, I figure it is probably possible, but probably not optimal. I think the cyan vignetting would be a liability on film bodies where it would not be able to be fixed. If you are shooting slides with a 24mm lens with IR blocking, you would have slides that had permanent cyan fringing in the corners. I don't think Leica would like that to be a hallmark of their lenses.
This is incorrect, Stuart. I used a Tegea 9.8 mm lens with the IR filter between the lens elementsl and it exhibited no cyan vignetting at all. So it seems to me that this solution is indeed optimal.
I am very glad to be wrong Jaap! But I do not want to spend millions to replace all my Leica lenses...hmmm.
I am very glad to be wrong Jaap! But I do not want to spend millions to replace all my Leica lenses...hmmm.
I thought you were going to spend those millions on extending your lens collection, Stuart ;) :p
Right you are...how silly of me to forget.
I wonder putting an IR coating somewhere on one of the internal surfaces is a simple matter, or if they would need to recompute the optical formulae as a result. If the former, then it could be possible to have it done to existing lenses, if the latter then that'd be a lot of R&D and perhaps some retooling and only applicable to new lenses.
I wonder putting an IR coating somewhere on one of the internal surfaces is a simple matter, or if they would need to recompute the optical formulae as a result. If the former, then it could be possible to have it done to existing lenses, if the latter then that'd be a lot of R&D and perhaps some retooling and only applicable to new lenses.
I doubt that to be the case Ben, the lens I mentioned had a slot taking the filter and having it in or out only makes a difference in the filtration. Otoh for instance the R 280/4.0 APO may not be used without a filter being present.
My 400/6.8 has a filter drawer in the rear tube also. A Series 7 (or a 49mm with the threads ground off) fits, which is probably how I would place an IR filter. But I recall reading how the optical designers at Leica figure the thickness and number of anti-reflective coatings into the optical computations of the lenses, so just wondered about the effect of adding an IR coating to one of the elements. Perhaps since it doesn't affect visible light it wouldn't be an issue. Way out of my knowledge base!
If you use a dimmer on a tungsten filement light bulb then the relative intensity (%) of the near IR will increase dramatically... You need to over run bulbs to minimise the IR %, shots in dim singles bars may be at risk.
An internal IR filter should work ok.
Leicia could develop a inter element material like 'adsorban' but for IR, adsorban absorbs uV, but dont expect it to be popular with the IR photo crowd.
Noel
visiondr
04-12-2007, 10:19
Screw the IR photo crowd, I say!:D :rolleyes:
Trying to post attached picture for StuartR.
I did just download the new firmware v. 1.102 so I'll try it later today.
Gary B
Some people like the M8's IR response... for B&W IR shots, stick a red filter on it...
Noel
grduprey
04-12-2007, 12:24
What happens to the photo if you correct the WB? Does it also correct the Magenta cast? I would guess it would effect it some and possibly reduce the effect. I have seen no magenta since using the filters, even under similar conditions as you show here.
Trying to post attached picture for StuartR.
I did just download the new firmware v. 1.102 so I'll try it later today.
Gary B
Gary, sorry to mess with your picture, I couldnt help myself.
Working from a web jpg is far from ideal, if you want this shot perfect one must use the right profile when converting DNG in C1LE,that would have gotten rid of the rest of the magenta and the residual yellow cast but still I feel this version may be closer to the original:
http://i36.photobucket.com/albums/e32/jaapv/corr_bewerkt-1.jpg
Gary,
I messed with the jpeg also. Just a couple of quick curve layers in Photoshop. I think the camera just got fooled on what white was in the photo.
Michael
Photo was shot as JPG as i don't have Photoshop. Mostly use iPhoto and Graphic Converter. No problem with working over a test shot. That is what I shoot them for.
GaryB
Photo was shot as JPG as i don't have Photoshop. Mostly use iPhoto and Graphic Converter. No problem with working over a test shot. That is what I shoot them for.
GaryB
Why don't you use C1LE as provided with the camera.:confused: It offers enough options to get very good results out of the M8 with very little effort.For most applications photoshop is not needed at all. I have not used my full version since I have the M8. Any supplemental things I wanted to do, PSElements with a few plugins was overkill already. Jpgs are a whole lot inferior to DNG's on this camera in my experience.
Screw the IR photo crowd, I say!:D :rolleyes:
In the interests of maintaining Vidal's philosophy of liberal pluralism, this should only be an option. Admittedly, IR photography has has always been something I've never really taken an interest in and have no desire to do, (a bit like foxhunting), but i'll defend to the death one's right to do it.
How come it took you guys and gals so long before deluging us with opinions?
I'm actually an r-d1 user, but that does not mean that I am not taking an active interest in the development of the M8, as having been a Leica M film user in the distant past, I appreciate the engineering and haptics and would very much like to return to the fold. However I feel that the IR issues and lack of flash pc socket are deal breakers for me on the M8. In that I will defend the rights of IR photographers to have an appropriate tool for their purposes. I am not going to fetishise the Leica name by asserting that camera is purely a tool wielded by the spiritual heirs of Cartier Bresson. As someone who shoots everything from street photojournalism to lit portraits on whatever tool i feel suits the moment and is available to me, I feel that Leica has forgotten the bedrock of their customer base and those that their reputation is based on, the multitude of working photographers who have used their products for generations but have been forced into using the digital SLR at the demands of their markets. Leica have got to differentiate between the consumers of their products that buy limited edition snakeskin covered fetish objects and those that need reliable usable tools. The r-d1 is not the ideal tool, in that there are still some, (easily fixed), IR isues and vignetting on ultrawides but as a predictable tool, it works. It is half the price of the M8 and has been cobbled together as some frankenstein hybrid of Cosina, Epson and Nikon from already proven technology, (albeit in slightly different technological arenas), but at the end of the day it works and probably cost a tiny fraction of what it cost Leica to develop the M8. I would dearly love to go back to the handling experience of leica bodies, and may ultimately have to when the Epson ultimately wears out. However, I bet Zeiss are sitting back and taking very careful notes for if and when they should deign to release something onto the market, and unless Leica fix the M8 and make a predictable tool then most working photographers , (who are on the whole quite pragmatic), are going to pass Leica by and go in search of alternatives. The same goes for their lenses, perhaps if Leica didn't spend so much on r+d exercises which eliminate one set of quality issues whilst opening up an entire pondoras box of others, they could bring their lens pricing to a position where they could be bought by those who's imperatives are dictated by their wallets. I think a 28mm Summicron is very nice, but not 5 times as very nice as the Voigtlander alternative.
I have not posted this in attempt to promote a flame war, and ask others to respect this sentiment and see this as a rally to spirited discussion. However, I feel that if Leica is to survive then they have really got to start respecting the opinions of those who really appreciate the potential of the M8 as a working tool because I don' think they will survive solely on the sale of limited edition gold plated, snakeskin kitch. Although I'll defend to the death you're right to buy such things.;) Well, maybe not quite to the death!!:D
http://www.thebppa.com/Mark-Pinder
http://www.unp.co.uk/photographers/photographer.php?title=mark_pinder
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