Finder
Veteran
Why can't you separate reflection and transmission? Reflected light is flare. Transmitted light will form an image. Transmitted light and reflected light are separated at the optical surface. The optical surface, as you pointed out, reflects all wavelengths. So does the coating. It also transmits all wavelengths. So where is the suppression of one wavelength over the other?
The only thing that is happening is that the reflected light from the surface of the coating and the glass are kept 1/2 a wavelength apart (after they are reflected) which is what is needed to eliminate them through destructive interference. This "suppresses" the flare. That has nothing to do with the transmitted light which is still in phase--passing the optical surfaces does not change that.
Coatings also improve transmission. Improved transmission and reduced flare has the ability to improve many things including color rendition. But optics, including Leica optics, should be color neutral. A color shift introduced by the optics would not be ideal.
BTW, I did Google your suggestion. I did not find anything.
RFaddict000
Member
I re-scanned some of the frames. Tweaking with the scanning program helped, especially the "fading correction" options. I used a Canon flatbed. But still I need to tweak the color a little in photoshop to get it right. Anyways, I will shoot some Velvia and see what I get.
As of the topic with lens coating, I am amazed how knowledgeable you guys are!
As of the topic with lens coating, I am amazed how knowledgeable you guys are!
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Roger Hicks
Veteran
Dear Finder,
There's a PDF of a Puts lens book on www.uk.leica-camera.com but I can't figure out a link. He specifically mentions (page 19) the use of coatings to adjust colour balance. Nikon says something similar here: http://imaging.nikon.com/products/imaging/lineup/lens/glossary.htm. It is of course entirely possible that they are referring to some different kind of coating. But nothing I have ever read encourages me to think so.
I've now looked this up in Cox and the Focal Encyclopaedia, and can find nothing in either to support either your view or mine. But I'll keep looking. Can you provide a good reference? Or perhaps Brian could step in.
Cheers,
R.
There's a PDF of a Puts lens book on www.uk.leica-camera.com but I can't figure out a link. He specifically mentions (page 19) the use of coatings to adjust colour balance. Nikon says something similar here: http://imaging.nikon.com/products/imaging/lineup/lens/glossary.htm. It is of course entirely possible that they are referring to some different kind of coating. But nothing I have ever read encourages me to think so.
I've now looked this up in Cox and the Focal Encyclopaedia, and can find nothing in either to support either your view or mine. But I'll keep looking. Can you provide a good reference? Or perhaps Brian could step in.
Cheers,
R.
Sparrow
Veteran
OK I’ve done a new diagram, any closer? I don’t think the reflected red light would progress beyond the coating, however the reflected blue light looks like it would be visible, and because of the phase change would degrade the entering blue light. So to that extent it would alter the colour of the light hitting the film.
PS sorry for yesterday’s rubbish drawing, I’m out of practice
PPS Finder thanks for the detailed reply
PS sorry for yesterday’s rubbish drawing, I’m out of practice
PPS Finder thanks for the detailed reply
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Finder
Veteran
Here is a text version of Puts's Leica lens companion. Start on page 69:
http://www.imx.nl/photo/downloads/files/llcforweb.pdf
All he is saying is that colors are better, which, naturally, less flare and better transmission would produce. As for Nikon, I can believe that is an error with translation or communication. Besides, go look through your multi-coated glass and see if you can see a color induced but the coatings, not the reflections, but the object on the other side.
I can give you numerous links to information about optical coatings, none of which will say anything about color balance. And why would they as the transmitted light is not influenced and any specific wavelength not absorbed would be insignificant. However, here is one link to a Wiki page:
http://en.wikipedia.org/wiki/Anti-reflective_coating
As with all Wiki entries, it is not a final word. But it does have nice illustrations and a clear description--references too. I would give you more, but my technical books are at work and I am home this week.
BTW, this is not my personal "view" of how coatings work...
Roger Hicks
Veteran
We read Puts differently, and blaming Nikon's statement on a 'misunderstanding' does not advance your argument very much.
I shall be grateful for more authoritative references than Wikipedia when you return to work.
Meanwhile a view can be correct or incorrect, but still remains a view. As I have said repeatedly, I'm not sure you're wrong. I'm just not convinced you're right yet.
Cheers,
R.
Finder
Veteran
OK I’ve done a new diagram, any closer? I don’t think the reflected red light would progress beyond the coating, however the reflected blue light looks like it would be visible, and because of the phase change would degrade the entering blue light. So to that extent it would alter the colour of the light hitting the film.
PS sorry for yesterday’s rubbish drawing, I’m out of practice
PPS Finder thanks for the detailed reply
Great for illustrative purposes. If I was going to be picky, the reflection would be going off to the side as the angle of reflection equals the angle of incidence. But basically you are showing the how the coatings shift the phase of the light reflected from the coatings and glass.
I think you are overestimating the influence of the blue. Coatings improve the transmission of a surface up to 99%. So you can have an entire lens with transmission of upward of +90%. The other 10% or so is either reflected, absorbed, or scattered. I don't know the percentages of which is doing to the remaining light. And blue light is only a portion of the total spectrum entering the lens. All in all, coatings only make a lens better. I have never read or experienced any dominant color from an optical coating--you would see the effect in the shadows.
The only other evidence is optics themselves. Compare uncoated, single-coated, and multi-coated lenses to each other. What you see is differences in contrast, not color, although color is nicer with coated lenses.
Sparrow
Veteran
The coatings have always fascinated me, I remember seeing it for the first time when my granddad went down to 35mm around 1960, like a jewel somehow.
I realise the schematic is flawed in many respects, it was just for concept really, I looked the actual wavelength (390-750nm) so yes it’s a bit off from reality, and realise it would be a progressive phase-shift across the spectrum.
I thought a little about multi-coatings and decided to take a Newtonian view on them … so they are clearly magic and therefore the work of the devil and should be rejected by all right-thinking men, which I shall do and think of them no more
Roger; some of the colour correction stuff could easily be “marketing dept physics” wouldn’t be the first time
Finder
Veteran
Roger, why don't you show me a more authoritative reference than Puts or marketing material. You could do some research as I doubt you would accept any reference I would suggest. Coating technology is not exactly cutting-edge.
As for Nikon making an error in their marketing material, I could very well believe that on two accounts. The fist red flag is the term "color balance." Optics should be color neutral, what would you color balance them to?
Second, you will need to differ to my experience here. I do have some insight to this after spending 5+ years in technical documentation for a Japanese optical/camera manufacturer. I can easily see this error could be made.
Finder
Veteran
Light is fascinating stuff. Unfortunately, most photography has very little to do with some of its esoteric nature. When you start imaging in a micro world, you can really take advantage of things like phase. The color and contrast in the two attached images come from a technique called Differential Interference Contrast (DIC) that shows the optical path difference in a specimen. The color is basically a result of phase shift. The two images of the same specimen. BTW, under a microscope, the specimen look white. Viewed at normal less magnification, the bug is green--a color that comes from interference.
Attachments
Sparrow
Veteran
To a 9 year old boy it was that oil-on-water iridescence, it was ascetically so pretty and ephemeral as the light altered ... that and the density, solidity and finish I remember taking pride simply in the fact that man could engineer such a jewel like thing.
I borrowed that particular lens in 1971 and had it until it was stolen in 2000
Finder
Veteran
I am sorry about your loss. I think these minutiae of the interaction of light can only be appreciated by "lightsmiths." And the amazing precision of optical engineering never ceases to amaze me.
But look on the bright side, now you have an excuse to buy a new one...
jbr
Established
Old lenses or old film?
Old lenses or old film?
I've looked quickly through all the posts but haven't seen mentioned the possibility of out-dated film.
Old lenses or old film?
I've looked quickly through all the posts but haven't seen mentioned the possibility of out-dated film.
Tim Gray
Well-known
Or shoddy development. Isn't a blue cast the most likely one resulting from mis-processing C41?
Coatings can affect color balance. I have a box of filters on my desk right now that only transmit light in a 10nm band. That would certainly do a number on color balance. As do the UV-IR filters. I have no idea if this is a technique used commonly on lenses though.
I would imagine that single layer coatings only suppress reflections at one wavelength. With multi layer coatings, you could implement antireflection properties at many wavelengths at once or build up any transmission profile you wanted (within reason).
Coatings can affect color balance. I have a box of filters on my desk right now that only transmit light in a 10nm band. That would certainly do a number on color balance. As do the UV-IR filters. I have no idea if this is a technique used commonly on lenses though.
I would imagine that single layer coatings only suppress reflections at one wavelength. With multi layer coatings, you could implement antireflection properties at many wavelengths at once or build up any transmission profile you wanted (within reason).
Dwig
Well-known
Nope, that is incorrect.
Dear old Isaac Newton figured this one out long ago (some two and a half centuries). Optical coatings display a characteristic colored reflection that is a result of their thickness. It has absolutely no effect on the light that is transmitted by the lens and coating. Check out http://en.wikipedia.org/wiki/Newton's_rings .
When light reflects off of a lens surface with a single layer coating there are actually two reflections, one from the air-to-coating boundary and one from the coating-to-glass boundary. The magic of coatings is that these two reflections together are not as bright as the reflection that would occurs from the single air-to-glass reflection from an uncoated lens. The total reflection from the two surfaces in a single layer coating is the least when the coating's refractive index is roughly halfway between that of air and the particular glass used in the lens element.
The color seen in the reflection is a result of the thickness of the coating being and exact multiple of the wavelength of some color of light. That color is reinforced (brighter) when the waves from the two reflections are in sync. Other colors are dimmed because their waves are out of sync. This property is what produces the "evil Newton's Rings" that so plague users of glass negative carriers and glass slide mounts. These occur when the two reflective surfaces, film and one of the glass surfaces, are about one wavelength of light apart. It is also the property that makes thin oil films on water display those multicolored reflections, colors varying with the film thickness.
Multi-coated lenses have a series of coating where the layer on the glass side is the highest index, near that of the glass itself, and successive layers are in progressively lower refractive indexes. Most of these lenses display a strong green reflection but if you look closely at the reflections from a steeply curved element you'll see the color shift toward the edges. This is because the light path for a reflection traveling at a steep angle through the coating travels a longer path matching longer wavelength and therefore reinforcing a different color.
Back to the OP's post, I've seen many older lenses that displayed slight color differences, even back in the day that they were reasonably new. These differences were always very slight and so easily corrected for when printing a color negative that it could hardly be detected without comparing the filtration needed for the print. If you are seeing a color shift that is so bad you can't correct the scan you are seeing the result of some other problem. Perhaps, as another poster mentioned, you are encountering more flare than you are used to in modern lenses. This veiling flare very often has a dominantly blue cast in daylight resulting from a blue sky being the source of the out of the picture light causing the bulk of the flare.
RFaddict000
Member
OK, guys. I finally shot some Velvia 100 with the Rolleiflex in question. The color turns out great, except when I include the sun only just a little in the frame when I see a lot of flare. So I think the bluish images I got last time with the negative is from lens flare + misty weather, perhaps also sub-optimal developing/scanning. Slide is still the king.
http://www.flickr.com/photos/chanhongsiu/4600047613/
http://www.flickr.com/photos/chanhongsiu/4600664238/
http://www.flickr.com/photos/chanhongsiu/4600047613/
http://www.flickr.com/photos/chanhongsiu/4600664238/
rumbliegeos
Well-known
I have had two Rolleiflex's of early 50s vintage, and neither consistently have made images with a blue cast. When I first saw the image of the flowers I also immediately thought veiling flare, which can do many bad things to color fidelity. The Bar Harbor shot probably should have had strong blue values, especially if shot without a UV filter, because the ambient light around the sea on a sunny day is quite blue (blue sky + blue sea) unless early or late in the day. The dock scene also looks underexposed, and that will also affect color fidelity. The scanning issues can all concatenate any underlying color biases in the original media.
Symeon
Established
cyan bias
cyan bias
Old lenses can occasionally lose their coating (fluorite most usually) and then they let most of the blue light through. Some photographers in the past used to rub the front element of their lenses with the wrong materials (neckties!) thus destroying the coating of the optic. But I could also be wrong with your case.
cyan bias
Old lenses can occasionally lose their coating (fluorite most usually) and then they let most of the blue light through. Some photographers in the past used to rub the front element of their lenses with the wrong materials (neckties!) thus destroying the coating of the optic. But I could also be wrong with your case.