Tuesday, March 13, 2018

Filters in Photography

Brief discussion about the most basic optical filters in conventional (film) and digital photography. There's a lot of misconceptions about their effects and finality of use by beginners and even more advanced users.


Let's start by the simplest filter ever, the UV. It looks like a flat glass disk without any obvious feature, but as it name suggests it blocks, or at least attenuates, the amount of ultra violet light that reaches the film or sensor.

Film is sensitive to UV light and the excess of it can cause a bluish cast and haze on the photo. But why this ?

Let's talk about ultraviolet light. It's the light spectrum with wavelengths between 400nm and 100nm, being 400nm the very edge of the visible spectrum and 100nm a very penetrating and dangerous form of electromagnetic radiation. The Earth's blocks the shorter wavelengths more than the longer ones. 

To keep it simple, accept that the 100-300nm part will be totally blocked from space to the altitude of about 7km. Some of the 315nm may reach the lower altitudes (1500-2500m) and in some places even the surface, Longer ones will reach it, depending on the latitude, season, solar activity, pollution and other factors.

But what causes the bluish cast ? One of the causes are the very small dust particles in suspension. Small particles are able to reflect small wavelengths very efficiently, and thus, why they reflect more blue-violet than red light. That reflection makes the particles itself visible. Blocking the shorter light wavelengths will make the particles less visible, resulting in a clearer image.

Note that the particles also absorbs light from what's behind them, and this absorption will not be reduced or influenced by the UV filter.  

Films are sensitive in some degree to UV light and this is also an important issue.

Digital cameras are less prone to the problem but in a minor degree, they still are.

Camera sensors usually have a filter to block UV and IR (infrared) light and let pass the visible spectrum without being attenuated. This filter is technically a combination of a high pass and a low pass filters, resulting in a bandpass one.

But the filter cut-off limits aren't like a wall. It's a curve with a certain inclination.

Schneider B+W 010 UV Haze transmission curve
(C) Schneider Kreuznach 
The graphic above is the transmission curve of a typical good quality UV filter. The darker curve is for a multicoated filter. Note the higher transmission because of less loss of light due reflections.

The visible light window is, for practical information, between 400 and 700 nanometers. At about 800nm note that the filter also start to block infrared light.

This particular filter blocks 100% of the UV shorter than 350 nm but just 60% at 375 nm. This means that some UV will pass, depending on the wavelength. It's a more sophisticated filter, if compared with the standard UV filter.

There are other types of UV filters with slightly different curves:

UV filter family curves
(C) Hoya

But there are lots of makers and filters belonging to the UV family and quality varies a LOT depending on this. Some filters are flawless and other will degrade the image quality.

Keep in mind, for any filter type:

- Good filters aren't cheap but they don't degrade the image sharpness.

- A good anti reflection coating is a must. Ignoring this may result in undesired reflections and flare.

- Good UV filters have almost no light absorption.

- There are lots of counterfeit filters on the market., specially fake Hoyas. Be careful with eBay, Amazon and similar sources. If possible always buy from a trustable seller or store.


First of all, a Skylight and UV filters are NOT the same thing. The main difference is the pinkish tint on the Skylight.

The Skylight filter blocks UV light but also attenuate a little the purple-blue part of the spectrum, resulting in a slight warmer image.

Skylight 1B filter curve
(C) Hoya

Both filters are extremely useful for film photography, specially for mountain/snow/beach areas.

There are different types of filters belonging to this family:

- SKY 1A
- SKY 1B
- Haze 

The difference between them is basically the intensity of the warming they add. Those filters are maybe the most widely used on film photography and have less impact on digital due the possibility of post processing.

On digital cameras with auto white balance set, the warm effect may be not present on the final image.


Those are supposed to be neutral filters, with no attenuation of the light spectrum and no color cast, at least on theory.

Again, a good coating is always a good idea and of course good filters come for a price.

They are excellent for lens protection against impacts and they saved me more than once. I remember some years ago, I was taking pictures at a mountain place and a small pebble came from somewhere and hit exactly the center of my Leica Apo Telyt and cracked a Hoya HMC Skylight filter. I was using a metal lens hood and it didn't make any difference. If the lens was hit, I'm pretty sure that it would be damaged.

It's also easier to clean a filter than a lens and if by some bad luck you scratched it, just buy another one.

In my view, good quality protection (or UV) filters are a must have. 


Black and White FILM photography can be tricky if we're talking about contrast and tones.

It's easy to imagine a scene in plain colors, but not so easy to have a precise idea about the final look on black and white film.

B&W photography is all about contrast and tones and to make things worse, there are color tones that will be rendered exactly the same way on film, even being quite different colors.

There are four main filter types for B&W photography:

- Yellow
- Orange
- Red
- Green

There are other ones, like blue, lime, but let's talk about the four main ones for now.

Light Spectrum
Take a look at the spectrum image above and let's talk about the work horse of the b&w filters, the yellow one.

Transmission curves for filters (C) Hoya
Y2 = Yellow
YA3 = Orange
R1 = Red
X1 = Green
X0 = Lime

Filters like the yellow, orange and red are lowpass filters. They attenuates higher frequencies and let pass the lower ones with sight or no attenuation.

Take a look at the figure and let's talk about the transmission curve of a yellow (Y2) filter. The cut-off frequency of this filter is about 475nm. It will block all wavelengths below, let's say, 425nm. But the blue is at something like 470nm and will be just partially blocked. Looking at the graph I would guess that the blue light will be reduced by something like 10-15%.

This slight reduction on blue light can result in a slight contrast enhancement between a cloud and the blue sky. The sky will look a bit darker than the clouds.

The orange filter transmission curve "knee" is shifted to a longer wavelength, and will reduce dramatically violet, blue and some green.

And the red filter will cut from green to violet. 

A yellow filter makes colors with shorter wavelengths than yellow to appear darker than the longer wavelengths and all the longer wavelengths will have the same look as without the filter. The orange and the red ones follow the same rule .

Green filters have a different transmission curves. The Green (X1) is a band-pass filter, with the central point at something like 540 nanometers and it will attenuate any wavelengths in both directions but in a not so steep way.

Green filters makes green objects lighter (or brighter if you prefer) than objects of other colors. They're also nice for portraits of people with white skin, giving a more natural tone.

The lime filter is something like a combination of a band pass and a low pass filter, and can be used as a general purpose filter for b&w photography, if you plan to photograph people and vegetation.

The BLUE filter does the opposite of what the Red does. It will lighten the colors at the blue side of the spectrum and darken the ones at the red side. Blue filters are high-pass or band-pass filters, depending on the manufacturing process.

Important to mention is the fact all the above mentioned filters blocks 100% of the UV light.


All filters blocks some light and this quantity is called FILTER FACTOR. It's expressed in how many times the light will be attenuated. It's simple, if you're using a red filter it will reduce de light to 1/8 or -3 stops. Remember to compensate the exposure if you're not using TTL metering or if the filter is not covering the light sensor of your camera.

B&W Filter effect table

The skylight filter is like the Y1 filter, but for color photography.

Do NOT use physical Y/R/O/G filters on digital cameras with Bayer or X-Trans sensors, even if the camera is set to monochrome. This WILL cause interpolation errors during the demosaic process and may give very strange results. In this case you need to use software based filters.

But if you have a Sigma camera with the Foveon sensor or a Leica Monochrom and plan to shoot in b&w, you need the filters, like you were using b&w film. By the way, Foveon's pictures shot this way are amazing. 

Original image in color
Yellow filter, slight blue attenuation
Orange filter
Red filter
Green filter
Blue filter, severe yellow to red attenuation

Another set with more green.

Color, no filter
B&N no filter


As a motto, you really want a Skylight filter attached to your lens for normal photography. But sometimes we need to use a color correction filter.

Color Warming filters

The #81 family cuts off the UV light and attenuates the bluish part of the spectrum in a way that contrary to the Y/O/R filters used in BV, would not totally mess up with the colors. The result will be a "warmer" light in the whole image, looking like the spectrum was shifted to the longest wavelenghts. But since it's a subtrative process, this not actually happens.

(C) Hoya

There are three 81 filters in different intensities:

  • 81A (1.2x factor, 3400K to 3200k, minus 200K)
  • 81B (1.3x factor, 3500k to 3200K, minus 300K)
  • 81C (1.4x factor, 3600K to 3200K, minus 400K)

A stronger effect can be obtained using a #85 filter.

(C) Hoya

  • 85A (2.0x factor, 5500K to 3400K)
  • 85B (1.6x factor, 5500K to 3200K)
  • 85C (1.8x factor, 5500K to 3800K)

The #85 series can be used to balance tungsten light film to be used on daylight conditions.

Opposite to the warming filters are the cooling ones. There are two main groups:

The #82 family is the opposite analog of the #81 family (sort off). They cool down the color temperature by absorbing the longer wavelenghts.
Like the previous mentioned warming filters, they come in three strengths 82A, 82B and 82C

They looks like pale blue filters. Below, the transmission curves of the #82 family. Note the opposition to the warming filters.

(C) Hoya

The #80 family is mostly used when someone need to use a daylight balanced film under tungsten light. They also come like 80A, 80B and 80C. They are deep blue filters.

(C) Hoya

  • 82A (1.3x factor, 3000K to 3200K)
  • 82B (1.5x factor, 2900K to 3200K)
  • 82C (1.6x factor, 2800K to 3200K)
  • 80A (4.0x factor, 3200K to 5500K)
  • 80B (3.0x factor, 3400K to 5500K)
  • 80C (2.0x factor, 3800K to 5500K)

There are many other special purpose filters, like neutral density, gradient, color enhancers and a myriad of special effect ones, like stars, diffusers, soft focus, diffraction, vignetting and more.

In a near future, I'll be discussing about ND, polarizers and gradients, but not the other ones.


Also known as ND filters, they are made to reduce the light by a known factor. Usually they are marked in a very easy way, just a ND followed by the factor, like ND-2, ND-4, ND-8, and so on.

A ND-2 will cut the light to a half (or 1 point), a ND-4 to a quarter (or 2 points), etc.

So, why would someone need less light ? There are so many reasons like the following:

  • A camera having a "slow" maximum shutter speed and using high ISO film, like a Konica Hexar Silver with an 800 ISO film in daylight because the maximum shutter speed for this camera is 1/250s
  • To allow the use of large apertures in high light conditions
  • To allow the use of slow shutter speeds in high light conditions, like to create the "water blur" effect.

ND factors can be very high. There are also variable ND filters, made by the combination of two polarizers. Personally I don't like the variable ones because some times you don't want any polarizing effect at all.

ND filters are useful in both film and digital photography. 

To be continued...  

Sunday, March 11, 2018

Fuji GA 645 Pro

Fuji GA645 Pro

This is one of the most underrated cameras ever. This is ridiculous because it's a real monster and the image quality is nothing less than superb.

It's an electronic, autofocus, takes medium format film (6x4.5 format) with Program, Aperture Priority and Manual exposure modes.

The exposure system is extremely accurate, like the autofocus system.

It's a very reliable, precision crafted professional grade equipment. It's also very compact for a medium format camera.

The viewfinder is a very large Galilean type with framing, AF and parallax marks very visible. There's also a red LED display in the bottom that shows the shutter speed, aperture and focus distance.

It also has a built in electronic flash, very useful for daylight fill in.

The EBC Fujinon 60mm F4 is one of the sharpest medium format lenses ever made, with extremely high resolution and no visible chromatic aberration of softness even wide open at the corners.

It has a very nice and unique feature. It's capable to print the exposure data, date and time outside the image frame area.   

Other features are exposure compensation and program shift. In a few words, everything you need, without whistlers and bells. 

The only drawback I found in this camera was the Robocop-like noise it makes !

Compared to my other 645 camera I have, the Mamiya 645, it's much lighter, has more modes, it's autofocus and way easier to carry in a trip. The electronic leaf shutter is virtually vibrationless helping the use of low speeds.

Tuesday, March 6, 2018

Mamiya 645 1000S

Oh, the Mamiya 645 ! This is a very special camera, the best 6x4.5 medium format SLR considering the cost and the quality you receive back.

It's wonderfully crafted in a black painted metal chassis, covered with leatherette. It's not a mechanical camera, but commanded by an extremely reliable electronic circuit that controls the cloth curtain shutter, offering exposures from low as 8 seconds to 1/1000s.

There's no light meter on the body and the film advance is done by an old fashion crank. Perfect.

It has a fair X-Sync flash speed of 1/60s, which is not bad for a medium format camera.

Besides the obvious shutter button on top it also has a second one at the camera's front. Other controls are a depth of field view and a mirror lock up levers and a mechanical self timer.

Being electronic, it needs a battery. Thanks it's just a very common 4LR44 alkaline that lasts for ages, but do the right thing, take it out when not using the camera.

At the body's top there's a HUGE focusing screen. The basic one will depend on the camera batch. Mine came with a diagonal split plus a microprism collar. This screen is very bright and easy to use.

The basic model comes with a waist level finder, nothing more than a foldable light hood and a viewing magnifier with focus adjustment. There's also a wire frame "sports finder" for rough framing.

There are four more view finders for the 645:

  • Prism Finder - A plain pentaprism finder
  • CDS Finder - Same but with a CDS light meter (matching needle on the right side) 
  • AE Finder - With an aperture priority shutter command. It shows the shutter speed by a scale/needle at the top of the view finder frame. It uses the camera's battery.
  • PD Finder - It's like the CDS finder but uses 7 leds instead of the match needle.

The standard objective is a stunning Mamiya-Sekor 80mm F2.8, the "normal" for the 120 film format. It's superb.

It's usually complemented by a standard wide angle Mamiya-Sekor 55mm F2.8 (roughly equivalent of a 35mm lens on 35mm film size) and a standard tele, the Mamiya-Sekor 150mm F4. Both lenses are very sharp. I have the 3 lenses plus a 80mm F4 Macro.

There are plenty of other lenses, from fisheyes to long telephotos, macros, zooms and more.

Tuesday, February 6, 2018

Sigma 18-35 F1.8 "ART" focus issues

Some years ago, I bought a Sigma 18-35 F1.8 "Art" lens for my Pentax K-5II and, besides its huge size and weight, I liked it very much.

It's a very high optical quality lens for an unbeatable price. Image is tack sharp from edge to edge even at maximum aperture. At least on the K5-II.

Things started to be strange when I got my K3-II and I noticed that the lens was not sharp in any aperture larger than F4 independently of the focal length. Wow. Something was smelling bad.

I put the lens back on the K5-II and it worked without any problem. Was my K3-II faulty ? I checked it with three Pentax DA lenses (40, 50 and 70 mm) and besides a very slight front focus in the 70mm that I corrected by the in camera AF micro adjustment, everything was tack sharp and the focus dead on. So the problem was, at first, not the camera itself.

Then I decided to use the Sigma USB dock to fix the focus issues. Camera on a sturdy tripod, a measuring tape, a focus target and everything else needed.

I used the live view and the central AF point for the adjustments and for my surprise, all pictures came in perfect focus ! Strange. I took the camera and shot some random pictures at maximum aperture and... Some of them were out of focus.

To keep things short, the camera was missing the focus when the optical viewfinder was in use and making it dead on when using the live view.

This of course has to be something to do with the contrast and phase focus detection system.

After some DAYS wrestling with this lens and the USB dock I managed to get it working in a decent way.

There are lots of reports about this lens causing issues on Canon and Nikon bodies with the lateral focus points.

There are no real information from Sigma about what's the cause or if is it fixable by a lens or camera firmware update.

My advise is to TEST this lens in your camera before buying it. If it works well, you'll get by far the best lens on its class. If not you'll get a very frustrating and expensive paper weight.

I found a good article here about this.

Sunday, February 4, 2018

Konica Hexar Silver

Konica Hexar Silver

Konica Hexar Silver

Top controls

This is one of greatest film cameras of all time. It's wonderfully made and maybe the most silent 35mm camera.

It's a multi mode autofocus camera with Program, aperture priority and manual exposure modes. The viewfinder is very large, clear and distortion free, with three exposure and a focus confirm leds.

The Hexanon 35mm F2.0 lens is superb in all aspects, razor sharp even at full aperture. The only drawback is the maximum shutter speed of 1/250s at maximum aperture.

Sometimes you can find one at e-bay, but expect to pay a high price for it.

The optical performance is comparable with a Leica Summicron 35 but for a fraction of the price.

I said before it's silent ? It's very silent. Seriously. It's a perfect camera for street photography and also my personal pick for travel light.

It has all the possible modes you need, exposure compensation, sport metering and a very sophisticated autofocus system. I don't remember about having a single out of focus or bad metered photo with this camera ?

I think it's a much better deal than any Leica with a 35/2.8 Summaron. It simply does better and cheaper.

Wednesday, November 29, 2017

The Nikon "universal" mount. Not so fast !

Before some people start to go crazy about what I wrote, be advised that I have used Nikon for years. From Nikkormats to D800. So just relax and read before raging against someone who dared to say something against your god. =) 

Nikon and a huge legion of its users and fans always keep saying that Nikon has the most backward compatible lenses and mount system on earth. Wrong. Very Wrong.

The Nikon mount system is a total mess:

- Pre Ai lenses (prior to 1976)
- Ai and Ai-S manual focus lenses with aperture ring
- AF lenses with and without built in motor
- AF lenses with and without aperture ring
- Full frame and APS size sensor sizes
- Cameras with and without aperture ring
- Cameras with and without built in AF motor

- Coupling "horns" of two types

The real fact is that Nikon has no total backward compatibility and even worse, even lenses and camera bodies from the same year may not be compatible. The nikon mount is a mess by definition. Some lenses can even damage some bodies if you try to fit them together. What was supposed to be good can turn into a real nightmare and waste of time and money.

Lenses from 1959 to 1976 are the original A mount type. They can't be mounted in ANY Nikon body except pre-Ai bodies and the ones that have a foldable aperture index tab on aperture coupling ring, like the flagship Nikon DS. 

If you try, for example, to fit an old Nippon Kogakku 50mm F1.4 from 1970 (excellent lens by the way) , and if was not not modified to Ai, on ANY camera without the folding tab you may break the body's aperture coupling ring and stuck the lens on the camera mount.

There are two types of autofocus lenses, with the AF motor built in the lens itself and without it. Lenses without motor won't AF on camera bodies without AF motors. 

For example:

The D5XXX has no AF motor on the body neither the aperture coupling ring. You can use AF lenses with motor and Ai/Ais manual focus lenses that have electronic contacts. No contacts = no light metering.

The D7XXX has AF motor and the aperture coupling ring. You can use all lenses on it , but *NOT* old "Pre Ai" lenses.

There are even lenses with and without aperture ring. You can't use any lens without aperture ring in any non AF nikon, for example, the FM2. The FM2 will accept just Ai/Ai-S lenses or AF fullframe lenses with aperture ring.


- If you have an OLD Nikon like a Nikkormat you need a pre Ai lens with the famous "horns" to couple the lens aperture ring with the camera aperture ring. 

Be advised that there are TWO "horn" types and they're not compatible and mounted in opposite ways.  Pre Ai lenses have the aperture coupling "horns" facing to the lens front. Ai and later lenses have it facing backwards, to the lens rear. If you plan to use an Ai lens on a pre-Ai body you need to reverse the horn orientation to have the proper coupling.

Nikon Pre-Ai coupling "horn"
Nikon Ai coupling "horn"

- If you have a camera like the FM, FE, FM2, N2000 you need an Ai / Ai-S or pre-Ai converted to Ai lens, with aperture ring for proper metering.

- For autofocus cameras like the D40 to D70 and D5xxx you can use AF lenses with or without aperture ring but you need the AF motor on the lens to have autofocus. You need lenses with CPU for proper light metering.

- If we're talking about high end autofocus cameras like the D600 and D7xxx you are allowed to use all nikon lenses but NOT pre-Ai ones, unless they were converted to Ai. Those cameras should work with all AF lenses, with or without autofocus motor and aperture ring.

- Finally if your camera has a foldable tab on the aperture ring, like the Nikon DS, you'll be able to use any kind of Nikon mount lenses on your camera. This tab purpose is to allow the use of pre-Ai lenses.

If you want a really universal SLR system, go for Pentax. All K lenses work on all K bodies and you have an extra bonus, can also use all M42 screw mount lenses on a Pentax K body with a small and cheap adapter.

Funny fact: Any Canon EOS and any Mirrorless system with the proper adapter can properly exposure meter with any Nikon lens with aperture control ring. Just set the camera to aperture priority. Sorry but the Nikon F mount sucks.

Saturday, October 14, 2017

Pentax Espio Mini

The Pentax Espio Mini is probably my favorite compact camera.

It's a very tiny 35mm autofocus camera fitted with a very high performance 32mm F3.5 lens. It's beautifully coated and capable of jaw dropping images. It can easily fit in a pocket.

The autofocus is fast an precise and the exposure is fully automatic from 2s to 1/400s, and there's even a B setting (but no external cable release!). It also has a slow sync mode for night shots.

There's a panorama 16:9 crop mask that can be used to create pseudo panoramic images.