I can confirm your results. That’s why I use the Benro Master filters made of glass. In combination with a well thought filter holder (polarizer in a special ring in the holder itself) a perfect for combination me.

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As you can see, there is no difference between using a lens with or without a glass filter. And we have shown before in our clear filter tests, if one uses high quality glass in front of a filter, there is no impact on the lens’ resolving power. So it looks like if one uses glass filters similar to the ones from NiSi, one can get maximum sharpness from the camera + lens setup.

In the context of lasers, fluorescence in the laser crystal (or other gain medium) by spontaneous emission is lost for the laser operation because only a tiny fraction of it goes into the laser resonator mode. The fluorescence lifetime for fluorescence from the upper laser level is usually called the upper-state lifetime. Fluorescence is the most fundamental reason why a certain laser threshold has to be overcome to achieve lasing (exception: thresholdless lasers). Note also that when the pump source of a laser is turned on, laser action normally starts from a tiny amount of fluorescence in the laser resonator mode, amplified to high levels in many resonator round trips.

There are also light-emitting diodes (LEDs) which generate white light in a process that involves the excitation of a phosphor. In that case, however, the actual LED produces blue rather than ultraviolet light, and this blue light is partly converted to red and green fluorescence light in the phosphor, and partly emitted by the device.

For the sharpness test, we used the Nikon 105mm f/1.4E ED, which we are in the process of evaluating for an upcoming review. The lens was mounted on the Nikon D810 and shot in Mirror Lock Up mode, with EFCS (Electronic Front Curtain Shutter) enabled, as detailed in our how to reduce camera shake on a tripod article. While the numbers are not yet final (only one sample was tested with a high-resolution chart at a very close distance, which can skew mid-frame and corner numbers), you can see that the lens looks absolutely amazing, almost Zeiss Otus-like in terms of center sharpness – definitely one of the sharpest Nikon prime lenses we have ever tested.

Keep in mind that these tests were performed with a 36 MP camera. If I were to show you difference with 42 or 50 MP cameras, the differences would be even more apparent. Please don’t try to view these images on a small mobile device / tablet, or a large super high-resolution screen, since pixels would be packed too closely together and you would never see any differences. 15% does not look like a big number for sure, but if you look closely at edge detail, the differences are definitely there. Now if those differences are too small for you to care about, then by all means, forget about the existence of this article! However, if you do want the best edge detail your camera can provide for landscape or architectural photography needs, you might want to re-evaluate your setup and potentially look into getting resin filters replaced with glass filters.

In comparison, glass filters are obviously superior in sharpness and they are less prone to scratching. However, they do require better handling in the field, so you must be able to provide good protection for them not only while transporting, but also while using. If you drop a glass filter, unless it lands on grass, you will have to look for a replacement.

Dear Nasim I am not a professional photographer from St.Petersburg, Russia, I would call myself an amateur I have used Lee Filters 100 mm system on my Nikon D800+77 mm lenses since 2012. Last Saturday I decided to buy a 150 mm system for my Nikon 14-24 mm 2.8 lens, and what made me choose the Lee SW150 system was your comment to avoid using a polarizer on wide -angel lenses, as well. So I came to think that rotating CPL feature wouldn’t tip the balance to the NiSi system, moreover, given the fact that the Nisi site is very inferior to the site of Lee Filters in terms of marketing and selling. I would say the NiSi website is underdeveloped. The point of comment was that the NiSi system’s rotating polarizing filter feature does not necessarily mean its superiority for wide-angel systems. But I have to admit that I have started to regret my choice of the Lee Filters system for Nikon 14-24- mm after your NiSi systems review. I should have read it before I made my choice.

For very long decay times, usually involving triplet states with forbidden transitions, such luminescence is called phosphorescence. Is also the phenomenon of delayed fluorescence, which can involve a weak intersystem crossing to a triplet state and later back to the original singlet state.

Now you might be wondering, can these differences be seen in images? Let’s take a look at two crops taken from the above-mentioned tests:

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In many cases, there are non-radiative processes which compete with fluorescence and reduce or even fully suppress it (→ quenching). In particular, multi-phonon transitions are very strong for level pairs with an energy distance which is at most a few times the maximum phonon energy of the host material. In other cases, energy transfer processes can deplete the population in a metastable level.

Various processes can lead to pronounced non-exponential fluorescence decay, with a faster decay shortly after excitation and a slower decay later. For example, this can be caused by contributing atoms with different lifetimes, or by upconversion processes which are stronger for high level populations.

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Fluorescence light can be useful, e.g. for direct use for optical measurements, such as for measuring the transmission spectra of optical devices. It is also the basis of fluorescence spectroscopy, fluorescence microscopy and of optical refrigeration. By combining multiple types of emitting rare earth ions in an optical fiber, very broadband radiation can be generated [1].

Landscape photographers often deal with the dilemma of choosing between different types and brands of neutral density and graduated neutral density filters for use in high-contrast situations such as sunrise and sunset, where their cameras might not have enough dynamic range to be able to capture the entire scene. While we are not going to go over each and every brand to see which one performs better, we do want to show the difference in sharpness between glass and resin filters. For this particular test, we used three 0.6 (2 stop) filters from three different manufacturers – NiSi (glass filter), Lee (resin) and HiTech (resin). The latter two are probably the two brands that are used the most among photographers in the field.

At the same time, take a look at what happens when a resin filter is mounted on the camera. I have been using Lee and HiTech filters for years and previously, I never really noticed much loss of sharpness in my images when using lower resolution cameras. After I started using high-resolution cameras such as the Nikon D810, Sony A7R II and Canon 5DS R, I did start noticing differences in sharpness in my images. Not to the point that would make me not want to use filters, but definitely to the point where I started wondering if perhaps my filters needed to be replaced.

The optical spectrum of fluorescence light (see e.g. Figure 1) generally differs from that of the light which initially caused the excitation of the medium. A significant Stokes shift (difference in photon energies of absorbed and emitted light) can occur because a part of the excitation energy is converted to heat in the medium. For example, the excited atoms or ions may first undergo an optical or a non-radiative transition to some intermediate level, before emitting fluorescence light in a transition to the ground state, or to some higher-lying energy level. It is also possible that a cascade of emission processes occurs, i.e., a cascade of transitions to lower-lying energy levels; in that case, more than one fluorescence photon can be emitted for one absorbed photon.

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In solid-state laser gain media, phonons lead to very fast thermalization within Stark level manifolds. As the emission occurs on a much longer time scale, the spectral shape of the emission spectrum does not depend on the exact wavelength of the exciting light. It depends only on the spectral dependence of the emission cross-sections, combined with some other factors. The frequency-dependent fluorescence intensity (actually a power spectral density) related to spontaneous emission from some level <$j$> to level <$i$> is given by [3]:

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As you can see, the NiSi 10 stop ND filter performed really well compared to the HiTech resin filter, which actually caused quite a bit of damage – practically a 30% drop in sharpness! So keep this in mind if you want to do long exposure photography. Looks like glass is the way to go not only if you want to preserve original colors (no color cast), but also if you want to keep the resolving power of your lens.

Nasim Mansurov is the author and founder of Photography Life, based out of Denver, Colorado. He is recognized as one of the leading educators in the photography industry, conducting workshops, producing educational videos and frequently writing content for Photography Life. You can follow him on Instagram and Facebook. Read more about Nasim here.

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Personally, I am planning to start using glass filters from now on. However, in case I do lose a filter in the field, I am planning to bring my Lee filters along, just in case :)

A special kind of fluorescence, which is not related to the excitation of atoms or ions in a substance, is parametric fluorescence in nonlinear crystal materials. This effect does not involve the excitation of electrons in the media, but rather a nonlinear interaction. Such fluorescence occurs only as long as some pump light propagates in the medium.

I use Olympus EM5 mark II micro 4/3 sensor with 12-40 f 2.8 lens. I want to buy hitech filter. But I still confused to chose resin or glass?

Fluorescence is a short-lived photoluminescence, excited by irradiation of a substance with light. The light hitting a sample puts atoms, ions or molecules in the sample into excited states (by absorption of photons), from where they decay into lower-lying states (e.g. their ground states) through spontaneous emission of fluorescence photons. This phenomenon is exploited for illumination, particularly in fluorescent lamps. It also occurs at a side effect in various kinds of optically pumped lasers and amplifiers, e.g. in solid-state doped-insulator lasers and amplifiers (including fiber lasers and fiber amplifiers), in optically pumped semiconductor lasers, and in dye lasers. The resulting radiation is called fluorescent light.

Resin filters definitely have their own advantages – they handle great in the field and if you drop them on a hard surface, they do not break like glass does. They don’t shatter under pressure, since they have the flexibility to bend. However, they are quite prone to scratches and even moderate use of resin filters can introduce small scratches all over the filter. While scratches don’t do additional damage to your images in terms of sharpness, they certainly can reduce contrast and potentially introduce more artifacts to your images when shooting against bright sources of light (in the form of ghosting and flare).

I do not enjoy traveling with rectangular filters because of their size and bulk, including the filter holders and since landscape photography is not my primary intent when traveling. Instead, I carry a few round glass filters protected by stack caps. I carry a set of 77mm filters: B+W 10-stop, 2-Heliopan GND (one hard and one soft) along with a B+W full grad and a pair of B+W polarizing filters (77mm and 67mm). I use the 77mm grads with a 67mm adapter for my 70-200mm f/4L IS lens and I have 67mm and 77mm polarizers since I often shoot with two cameras, one using a lens that takes 67mm filters and one that takes 77mm filters. This is not the ideal kit but, I have found that on trips, when I took my Lee filter setup, I seldom went to the trouble of setting up that system since my primary intent is not landscape photography. Using round filters is quicker and easier… I simply crop when I want the horizon at other than mid-way in the frame. I WISH HOWEVER: that some filter company would offer a set of two GND round filters in which the dark portion covered 1/3 of one of the filters and 2/3 of the other. Carrying an extra two filters would not add any appreciable weight or bulk to my travel kit, yet would allow me to come a lot closer to ideal framing of the horizon (rule of thirds) when using a round filter – without as much cropping involved…

In optical amplifiers, fluorescence can be even more important. In the form of amplified spontaneous emission (ASE), it may extract significant power and thus limit the achievable gain. It also determines much of the quantum noise contributions to laser noise and amplifier noise.

What types of filters do you personally use? Resin or glass? Have you tried both to see what is practical in the field? Would love to hear your thoughts in the comments section below!

Nasim, I just found your comparison more or less randomly. Your findings matches my obersvation perfectly by 100%. With the 5DsR, I encountered a noticable loss of sharpness using resin filters (Lee, Singhray) especially when using a longer focal length. I switched to NiSi in late 2015 and the results were good again. Regards, Michael

After excitation with a short pulse, the fluorescence decay is often of exponential nature with a decay constant which is called the fluorescence lifetime or upper-state lifetime ( because the fluorescence lifetime is identical to the lifetime of the population in the upper level of an electronic transition). For so-called allowed transitions, the fluorescence lifetime is typically of the order of a few nanoseconds. In solid-state laser gain media other than semiconductors, one is often dealing with weakly allowed transitions, where the fluorescence lifetime can be much longer, e.g. microseconds or even milliseconds. In any case, the upper-state lifetime can at most be the radiative lifetime (limited by fluorescence only), and possibly be shorter if there are additional non-radiative decay processes.

Fluorescence in transparent polymer sheets, which are doped with some luminescent species, can be used for luminescent (or fluorescent) solar concentrators [2]. Sunlight hitting the polymer sheets from any direction can be absorbed and efficiently transformed into fluorescent light, which is partly trapped in the sheets and thus sent to the edges, where solar cells receive the concentrated radiation. Potentially suitable luminescent agents can be certain organic dyes and quantum dots. Further research is required to optimize the still limited lifetime of dyes under irradiation with sunlight and the quantum efficiency of quantum dots.

We also decided to run another test to compare two 10 Stop ND filters from NiSi (glass) and HiTech (resin). Aside from serious color cast issues pointed out in our NiSi Filter System review, we saw a pretty dramatic drop in sharpness when comparing NiSi to HiTech filters. Take a look at the MTF numbers below:

Thanks for in-depth articles. I do have Lee big stopper and looking for GND filter (Hard edge), however I am not able to find anything with glass and most of the brand out there are offering only Resin and not glass (I am only looking at Rectangular GND). Can you provide your input on this.

We stopped down the lens to f/5.6 to yield maximum sharpness (although MTF numbers at f/4 look even more impressive in some cases) and we used a few different focusing techniques to yield the best possible performance without any filters, while a NiSi filter holder was already attached to the lens. Once maximum resolution numbers were achieved, we mounted one filter at a time, without touching the focusing ring.

Fluorescence of the single atoms, ions or molecules of a sample usually occurs in an uncoordinated manner, i.e., uniformly in all spatial directions and without temporal correlations between the emitted photons. However, certain conditions lead to amplified spontaneous emission (superluminescence) or superfluorescence, where this is no longer the case.

Fluorescent solar concentrators might be the basis for cheaper electricity from photovoltaic panels (solar modules), as they allow to collect radiation from a large area while requiring only relatively small photovoltaic cells.

The quantum efficiency (or quantum yield) of fluorescence from some level is the average number of fluorescence photons obtained per ion which is put into the upper level. Solid-state gain media (e.g. laser crystals or rare-earth-doped fibers) often have laser transitions with a quantum efficiency very close to unity, whereas some levels (e.g. the lower laser level) exhibit virtually no fluorescence due to strong multi-phonon transitions.

Hi. A little detail caught my attention when I bought a complete Cokin filter set. All made with c39 resin optics. Then I started thinking why not glass, I came across the article on your site. The article was very revealing to me. I realized that the square filters must be glass. LEE filters were also very expensive for me. Thank you I saved my money from wasting.

Fluorescence is widely used in fluorescent tubes for illumination purposes. The most common fluorescent lamps contain mercury vapor inside a glass tube, where an electric discharge excites the mercury atoms to emit mostly ultraviolet light. A fluorescent material (called the phosphor) on the inner surface of the tube absorbs the ultraviolet light and converts it into fluorescence light, mostly in the visible spectral region. The phosphor contains several substances mixed in such a way that the overall emission spectrum corresponds to white light (with the color tone adjusted according to the envisaged application). Although part of the energy of the ultraviolet light is lost in the phosphor, fluorescence lights are still several times more energy-efficient than incandescent lamps.

The graphs above show a very typical situation when using resin filters – there is a definite and visible drop in sharpness on high-resolution cameras, even at 36 MP. As you can see, Lee’s two stop 0.6 GND (Graduated Neutral Density) filter had a pretty dramatic drop of sharpness, almost 17.5% lower in center sharpness compared to not using a filter and around 15.8% lower in center sharpness compared to NiSi’s glass filter.

Actually, the numbers were even lower when I initially mounted resin filters. Due to changes in optical path when using resin filters, I actually had to refocus my setup and see if I can get better numbers. I was able to get higher numbers in the center of the frame and due to the change of plane of focus, the change did affect mid-frame numbers as well, which is why they show up a little higher in comparison to not using a filter at all.

After testing out my Lee filter, I decided to mount HiTech’s 0.6 GND as well and see what it would yield. As you can see, although its performance looks a tad better, overall, it is really not much different compared to Lee. Center performance drops by roughly 15%, which is certainly not a small number – that’s practically worse than using a cheap circular filter in front of your lens.

Once upon a time when I had my first 35 mm Camera, a Kodak Retinette 1A, wow that was something in those days of 120 and 620 film format and 5×4 press cameras. I obtained glass Wratten filters, both CT and CC in a glass mounted “clip on” stainless ring which clipped on to the end of the lens they were made for the Graflex 5×4 as well. They seemed to disappear very quickly with the advent of Hoya and other brands coming on the market as screw in filters. All mine were in a leather case each filter separated by leather lined with felt. At that time they cost me 37 Pound which was quite a lot of money as my pay packet was 10.12.6 (Ten pound twelve and six pence) a week. It was easy in the field, and there were many fields, seldom dropped one easy to “push on” and a gentle twist and pull would remove it then put it back into the case. Screwing a filter in takes a lot longer, maybe the “new” 100mm ester filters could be made of glass if the holders were made so they would not slip out. A rethink on this I think, or maybe I’m just an old codger bordering on dynasaur.

Fluorescence effects can be quite disturbing under certain circumstances. For example, certain spectroscopic measurements can be disturbed by unwanted laser-induced fluorescence in glass windows or tubes. Such fluorescence often originates from certain impurities.

Cases with resonance fluorescence – most often with atoms or molecules – are those not involving additional transitions, where the interacting atoms or molecules can be considered as simple oscillators with a certain resonance frequency. The emission wavelengths are then close to the excitation wavelength.

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Upconversion processes lead to the population in relatively high-lying energy levels, from where blue and even ultraviolet light is emitted. Such fibers are suitable for lasing in the blue spectral region near 480 nm. (The weak peaks around 700 nm are artifacts, caused by second-order diffraction of ultraviolet light in the spectrograph. Data taken by R. Paschotta.)

Substances emitting fluorescence, or sometimes just parts of larger molecules, are called fluorophores. Some artificial fluorophores may be added to samples in fluorescence spectroscopy.

I travel with large glass filters all the time, and have never had any problems with them. A little bubble wrap, and a small plastic box from an art supply store is all one needs. Not quite sure what the all the fuss is about, concerning traveling with glass filters.

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where <$\sigma_{ji}$> is the emission cross-section and <$N_j$> the density of ions in the starting level <$j$>. The given quantity <$I_{ji}(\nu)$> has units of J/m3, and multiplied with a small frequency interval <$\rm{d}\nu$> one arrives at W/m3 – consistent with the radiated optical power per unit volume.