The Phase One, XF camera with Single Focus point is old fashioned – Busted

Recently Phase One released a brand new Phase One Camera, the XF. It replaces the DF-645 and DF-645 + , which were actually Mamiya camera’s.  The XF is engineered and build from the ground up and has many features, but most of all a newly developed focusing system based on a 1Mpixel focus sensor (Honeybee) .

See my video on this here:

Immediate after the release of the new camera critics were received on the Focusing System. Many were expecting multiple focus points, like on standard DSLR’s. Much to their dislikes, the XF has a single central focus point.

I can’t say that I agree with the critics, as I have been using the new XF and before the 645df+ body. Both have a single focus point, located in the center of the lens.   So, allow me to put down some words in defense of Phase One.

There are several reasons why it is engineered the way it is, and like anything else it is a well considered balance between features and quality.

Focus must be fast, accurate and reliable.

All Mirror Reflex camera’s (DSLR’s and Phase One) focus either through phase or contrast method.   It is measured on a special CCD (focus CCD) and mounted inside the camera body along the normal mirror down light path. After all light travels through the lens, hits the mirror, reflects in the prism and hits the eye on the viewfinder.

The Focus CCD provides the needed details on contrast to a compute engine which than drives the servomotor in the lens to increase or decrease the focal length. After each small step, the contrast is checked again. Until full focus is achieved.

Those DSLR’s with multiple selectable focus points (Nikon, Canon etc…) use only a part of the focus sensor.   The focus sensor is partitioned and each partition matches to the selected focus area on the viewfinder. Hence only a sub set of the pixels (focus sensor) are used to track and hunt the focus.

A Phase One camera (single focus point) uses the full 1 Mpixel focus CCD to calculate and acquire focus. It makes it far more precise and accurate then any DSLR.

Furthermore, the Phase One XF uses a central focus point. This delivers the best and sharpest focus, as optical lenses are at best at their midpoint.

There is an usage disadvantage of having only a single center focus point , however that is by far outweighed by the superior focus .

Shooting with a single central focus point results in centric pictures. Not at all pleasing to look at, as we all appreciate the golden cut or 2/3 rules. Of course you could focus on the eyes of a model, and then lock the focus and reframe to a 2/3 kind of arrangement. That works well in most cases, however one can lose the focus especially with 1.4 or 2.8 lenses as they have a very shallow DOF.

With a multipoint focus system like the DSLR, it is easier to selected a single focus point at 2/3 of the picture frame and place it on the eye of the model.   However the focus will not be that accurate as you are off-center and only a fraction of the Focus Sensor is used.

Never the less, the Phase One single focus point performs far better, and if you can’t get the swing of reframing without loosing the focus then shoot center stage. There is plenty of image pixel real-estate to crop in post processing (50,60, 80 and 100 Mpx image sensors).

The bottom line is, the Phase One XF central single focus point uses the full focusing sensor resulting in accurate and very fine adjustments , combined with the best optical performance of the lens ( center).

In the future, we might expect live-view methods. Whereby we will be able to tap on any area on the viewer display to acquire focus. That will be possible without the mirror box and Focus sensor.   The image sensor will be used for both the Image Capture and Focus Sensing. Note that Phase One already has an electronic shutter capability.

 

Thanks for reading.

 

Tilt Shift Magic (photography)

Tilt-Shift magic

I am sure you have seen or even created popular Miniature Effects with one or another creative filter. But there’s more!

A Tilt-Shift (T/S) lens makes it possible to move the optical plane in relation to the sensor plane either with a Shift or Tilt position. Or even both at the same time. The effect created by the T/S adjustment offer a multitude of creative options to the savvy photographer.

The shift function allows you to correct the perspective, a handy method for merging pictures or getting tall buildings onto the sensor without having to step to far backwards.

With the tilt function, you decided exactly where focal plane is and where you want it.

With both together, you get a great deal of control over the image.

The Tilt Shift lenses is nothing new.

The first photographers learned the ins and outs of adjusting a lens relative to the light-sensitive plate. The classic folding camera with frosted glass and bellow remained for decades the ideal tool for the professional photographer. Even today, the monorail camera (also called technical camera), with its very agile lens plate and negative holder are a popular tool in studio’s especially when fitted with a medium format digital back (e.g. phase one).

Technical cameras may indeed provide opportunities for optical corrections, however they are not handy for quick and / or working outdoors.

Optical misfits

Tilt-shift lenses differ in a number of ways from common lenses. Because they are intended for high quality and technically demanding shoots, hence great attention is given to the image quality with low distortion.

At the same time, their image circle – which is the circular projection of the subject on the surface of the sensor – is much larger than necessary in order to completely cover the sensor.

And as with any lens, the central portion of the lens has the best optical parameters. Yet, towards the edge of the circle image the resolution decreases rapidly. A T/S lens has image sharpness down to the edge , but then deteriorates immediately.

Shooting with a Tilt Shift Lens requires careful work. 

Shooting with a Tilt-Shift lens requires some skills and experience. Dealing with the “Shift effect” is rather straight forward and easy. However the Tilt function is more demanding. It certainly takes some time before you can quickly assess the impact of the different settings and adjustments.

Using a T/S lens with a DSLR , will force you to operate in the manual mode for focus, exposure and white balance . Those need to be set while the T/S lens is at 0 Tilt and 0 Shift position also called the neutral position. After all the adjustments of the lens may confuse the various separate measurement systems.

Live View mode can be an option for fine-tuning, especially when combined with focusing aids or a tilting screen.

Always mount the camera with the T/S lens on a solid tripod with a good tripod head.

Check that the camera platform is level. Use a remote control or timer (timer function) to avoid vibrations.

The setting range for tilt-shift lenses on a full-frame DSLRs is usually 10 to 12 mm shift and 6 to 8 ° of tilt. Every movement is controlled separately via a rotary knob with a scale; the setting is locked with a second button. More recent models allow for angles between 0 ° and 90 °. Furthermore the T/S lens can rotate as whole to the camera mount, so you can precisely set the direction of the adjustments.

Which lens for what ?

Tilt-shift lenses can be used in different types of photography. The big two – Canon and Nikon – offer a range of models with different focal lengths. Architectural, interior and landscape photographers usually choose the most popular 24mm version or the more extreme 17mm version.

T/S lenses with focal lengths of 45, 85 or 90 mm are more commonly used in product shoots, still life, food photography, jewelry, close-ups and creative portraits.

However the majority is designed to be mounted on a full frame DSLR. But even then they may not fit every FF camera body. So, always check the compatibility between a T/S lens and your camera body.

Perspective Correction without difficulty

Photos captured by a standard 24mm wide-angle lens and a 24mm tilt-shift lens in the neutral position are identical in image content. However the image circle of the tilt-shift lens is much larger, and covers approximately the same field of view as a normal 16mm lens.

Shift function

The shift function moves the image circle of the lens with respect to the sensor of camera. The effect is similar to a variable cut (crop) of an image created by the use of a lens with a shorter focal length – the big difference here is that with a T/S lens the image falls on the sensor. The most important application of the shift function is the correction of perspective distortion. Parallel lines in the subject are only displayed parallel in the image as the face of the subject and the image plane (sensor) is exactly parallel.

Parallelism of a standard lens

When tilting the camera upwards when photographing a tall building to get everything into the picture, the trapezoid lines will walk towards each other. To display the vertical lines of the building correctly parallel, the sensor shall be perfectly parallel with the building. A tilt-shift lens lets the camera be level so that the vertical lines will remain parallel. Hence, the top of a tall building will be within view while on the other hand some foreground aspects (non-interest) will be missing.

Shifting Up or Down the Shift function of the T/S Lens will bring the building fully into the picture – of course ,as long as the viewing angle of the lens allows.

You can apply the same principle to hold parallel lines running down from a high angle, or to correct horizontal fleeing lines. The latter is done with a horizontal lens shift. (Remember that many of the newer lenses can rotate)

Note, that a perfectly corrected perspective can look unnatural: admit a little bias often gives a more realistic picture.

Can post-processing software do this?

Virtually every software package for post-processing makes it possible to correct the perspective afterwards. Specialized tools can deliver more than decent results.

So why should anyone go and buy those expensive tilt-shift lenses?

An important difference is that during the post processing parts of the original picture will be lost or be outside the frame. Of course one could focus wider during the shoot to compensate… but guess what?   You will lose megapixels, and maybe get a less interesting composition.

Secondly the post processing correction needs to create new intermediate pixel values, whereby resolution and sharpness is lost.

And perhaps most importantly, the correction is not proportional in horizontal and vertical direction. Resulting in deformed proportions within the image. It can usually be adjust manually (for example, by stretching the image vertically) but in the absence of any reference that might be not all that accurate.

Correct proportions are very important when photographing buildings, interiors, furniture or other products that must have a realistic perspective. Working with a tilt-shift lens guarantees predictable result without time-consuming post-processing and guesswork.

Avoiding Obstacles

Sometimes obstacles can hinder a clear view on a subject. Two options are available, move the camera to a better position if possible, or simply use the shift function of the T/S lens to create that clear view and avoiding the obstacle, while maintaining the essence of the composition. Or visa versa by bringing in an object that is just out of the picture.

In other situations, the shift function helps to eliminate reflections on reflective surfaces.

Tilt Function

Creative with sharpness

A tilt-shift lens makes it possible to move the optical plane relative to the image sensor (Tilt). This brings a unique and very powerful feature: it allows the focus plane to be placed as such that it coincides with a well-chosen part of the subject. This “selective focus” opens up many creative possibilities.

Tilt principle

Normally, the focus plane is perpendicular to the axis of the lens, therefore, parallel to the sensor. Depending on aperture, focal length and focus distance, all objects within a certain area just in front of and behind that area are in focus: Depth of Field (DoF). Reducing the aperture (larger F number) enlarges the DoF ,but that ultimately causes loss of sharpness by diffraction effects at high F numbers. Secondly the sharpness area may possibly not coincide with that part of the (three-dimensional) subject that you want to emphasize.

Tilt movements allow for a tilt so far that the sharpness level is no longer parallel to the sensor, but precisely coinciding with a specific area of the subject. All objects in this area will be in focus, even though they are at different distances from the camera.

Tilting causes a depth of field that is no longer a zone which runs parallel to the focus plane, but a wedge-shaped area that ends wider as the distance increases.

The aperture determines how wide the DoF wedge extends. A greater tilt angle and a larger aperture number narrow the selective focus zone.

Miniature Effect

If the tilt function is deliberately applied in the reverse direction, it will cause only a small part of the subject to be within the wedge-shaped edge area (sharpness zone) . The result is the well-known ‘fake miniature effect’ .

The tilt effect applied

For landscape photography the tilt effect can bring both the foreground (e.g. a lake) and the background (e.g. a mountain range) in focus , without having to use a very small aperture (high f number). A small inclination angle is often sufficient for this.

In architecture or urban photography a wall or barrier can be kept in selective focus.

Shift effect of TS Lens

Typical examples can be found in food photography, product images (emphasize one side of the device), close-ups and macro shots (coins or jewelry) …

Remember that after tilting the lens it may be necessary to slightly adjust the framing.

Tilt effects can not be created in post processing software; sure un-sharp area’s can be created from sharp originals, but un-sharp originals can not be made sharp !. The tilt effect of a lens has a 3-D effect on the sharpness zone, post processing is 2-D , hence don’t believe that you can apply tilt effects in Post –processing unless it’s black magic.

The strength of a tilt-shift lens is when both adjustments are combined. It is very important that they can be set independently of each other and in the desired direction. For example, landscapes use both movements most often in the vertical direction. In architectural and product photography, the adjustments are more perpendicular.

Thanks for reading.

The Photoshop “Tilt-Shift “ filter, a meager simulation of the TS Lens

How many times have I come across people claiming that a “Tilt Shift” lens is not needed since it can be done in Photoshop. I don’t know if this is a matter of consumerism, ignorance or plain stupidity.  At best the PS Tilt-Shift filter is an imitation that only works under certain circumstances.

Tilt Shift Lens

So, what is this all about?

Tilt Shift lenses are crucial for architectural work, the reason is very simple.

The capture of a structure must be accurate, proportional and correct, reflecting reality.  I am not talking about creative architectural photography, that is different ball game altogether.

I am sure that we all have been standing one time or another in front of a tall building and tried to capture the complete building into the frame.   Although we fitted a wide-angle lens and stepped back as far as we could, and still we couldn’t get the top of the building in the frame.

What do most people do?

Yes, tilt the camera in a slight upward angel. Eureka! Now we got the complete building in the frame.  Good isn’t it?  Nope. In the final picture the building will appear to fall backwards.  This is caused by the fact that the object  (front of the building) is no longer parallel to the Lens- and Sensor plane. The result is perspective distortion.

No problem, Photoshop will come to the rescue with a perspective correction. Yes, that will work. But have you ever wondered what happens with the pixels that are not there and need to be created through software to execute the correction?  Indeed interpolation, complex algorithms and estimation…. It will never be as good as the real thing.  Given, PS does a fairly good job.

Why not fixing it during the capture?  After all we are photographers and not retouchers.  

Well we could get a sky lift and move upwards to the point were the building fits the frame, a clumsy way but it works perfect.  Or use a Tilt-Shift lens, applying the shift up or down option.  It has a similar effect as standing on the sky lift, and no need for drastic perspective corrections in PS.

The question is “ does this warrant a 2000 Euro Tilt-Shift lens?”   I would say “No” if that was the only feature of the lens.

Parallelism unavoidable with standard lenses

Tilt effect of TS Lens

Now imagine that you need to capture a building, the corner head first with left and right the wings.  The wing of interest is the right wing (see picture) , more specific the spiral stairs, the left wing is of no interest and can be blurred.

In other words we must adjust the Focus plane so that it is no longer parallel to the Lens and Sensor plane….(Scheimpflug principle) . This is not going to work with a normal lens, since the Focus-, Lens- and Sensor plane are “fixed parallel”. Sure the distance can change but  not the parallelism.

Parallelism of a standard lens

We need a lens that can vary the angle between the Lens- and the Sensor plane; the result will be a Focus plane completely different then with a normal lens.  By changing the angle of the Lens plane versus the Sensor plane the Focus plane can be moved to other then normal places.  Hence we are able to create “in camera” a picture with sharpness on the right, and blurred on the left, although the distance between both wings and the camera are as good as identical.

Tilt principle

 PS a meager simulation

Photoshop has a filter called “Tilt-Shift” that simulates this capture method; you can apply the filter to any picture (taken with a normal lens) and make it look like a Tilt-Shift lens effect.  “Make it look like”, that is the key.  It works as long as you will apply blur, it cannot create sharpness!  That is where the Photoshop Tilt Shift filter is “Busted”. Besides the fact that the Photoshop filter can not perform the “shift” function.  That is only possible at the moment of capture with a TS lens.

In practice one would have to make very sharp pictures with a large Depth of Field (DOF). Forcing the capture with a stopped down aperture (high F number). But what if there was not enough light and you need to shoot with a wide open lens (F5.6, F2.8 or less) ?  That is not going to work, the DOF will be limited in the standard parallel plane, and off course not were needed. The PS Tilt Shift filter is not going to help out, as it can only blur. The picture on the left required a sharpness (focusplane) along the fence while shooting with a wide open aperture. The picture is taken with a normal lens, and can not be corrected with the PS TS filter.

Reflections, angle in = angle out

Another very nice feature of the Tilt Shift lens is it ability to avoid unwanted reflections, due to angle of occurrence. If light falls under a 45 degree onto a flat surface it will be reflected at an opposite 45 degreed angle.  Imagine you want to take the picture of bride in a mirror with a normal lens.  Pffff, very difficult framing since the photographer will be partial or fully in the mirror reflection.  A Tilt Shift lens with a horizontal shift, fixes that issue in a heartbeat.

It is not all rosy, the TS lenses are all manual focus and the light metering is not working. It takes some time to get the swing of it, once under control it allows for great shots.

No matter how we twist or turn it, the PS Tilt Shift filter cannot replace the Tilt-Shift lens. It does not even come near.  Try it if in doubt.

Of course if one only takes every so often an architectural picture, Photoshop will be your best ally and the investment in a Tilt Shift lens is out of scope.

Thanks for reading,

Steve

“Shooting with high-speed sync”

A very interesting technique, that can create stunning  “night by day” pictures.

So, why not shooting with high speed sync ?

Imagine that you are asked to do a glamour shoot on the beach, with a shallow Depth of Field (DoF) and focus on the models. The sun is high on the sky casting hard shadows and heavy contrasts. Not at all the most desired light circumstances.  Never the less you have to complete the session.

The lighting crew has put up a large diffusion screen that softens the light and keeps the posing models out of the harsh sunlight. Yet the background (beach-ocean) is so bright that it forces you to use a set of flashlights to light the models.  The art director reiterates that the pictures must have a very shallow Depth of Field and a dark background.So, you set your camera to the base ISO and the aperture to a small F-number  e.g. F2.8 to meet the art directors expectations. The flash units are adjusted and ready to fire. The DSLR flash sync is set to “1/125 second”.   The first shot goes off, disaster strikes.  The background is way to bright and blown out, and yet the flash light metering was OK.

Now what?

We have the control over tree parameters that affect the exposure; aperture, ISO and shutter speed.

The aperture cannot be changed without losing the shallow Depth of Field. The ISO is already at it’s base value.  The only thing that remains is the shutter speed.

DSLR’s have in general a slow Flash Sync speed.  The most common is 1/64 sec and 1/128 sec (sometimes with exceptions for speed lights).  That means that the sensor will be exposed for 1/125 sec (shutter fully open).  Within that time window the flash must go off .   The flash duration is a very short pulse of light and varies depending on the brand.  Most mid-range flash units will have a T.5 pulse duration of 1/900 sec or faster.

Effect of ambient light with a standard Flash Sync

This means that the flash will correctly expose the model for 1/900 of a second (after adjustment of the flash intensity), however the sensor will be exposed to the ambient light for 1/125 seconds.  That is almost seven times the flash duration.  The  ambient is so bright that it creates a very light background.

The solution is to reduce the flash sync time, in such a s way that the influence of the ambient light is minimized.  Hence creating a darker background.

High-end camera’s such as  the Phase One and Hasselblad have the ability to operate with high speed flash sync shutter speeds of up to 1/800 sec. If combined with a leaf shutter lens it can go as fast as 1/1600sec.  Easy, isn’t it.  Just adjust the flash sync time. No need to adjust the flash unit (except if the flash pulse is longer in duration then the flash sync speed of the shutter).

The DSLR Flash Sync is rather limited.

But what if the camera has no high speed flash sync and is limited to 1/125sec or even 1/250sec , like most DSLR’s ?

Note; Flash mono blocks or packs are not the same as speed lights like the Nikon SB900.  ( picture below ;Auto FP relates only to use with speed lights)

DSLR sync speed

Don’t despair; there is an easy way out.

The “Neutral Density filter”.  The ND filter is a gray smoked glass placed in front of the lens, thereby stopping down the light. ND filters come in fixed or variable densities (Stops).  A very useful ND filter is the variable type with a range from 0.5 stops to total darkness.

Neutral Density Filter

Fitting the ND filter on the lens will stop down the ambient light during the 1/125s exposure time, while the flash will still provide a correct exposure of the model.  Stopping down the ND filter requires more power from the flash. So you will have to crank up the flash intensity.

Now you have the ability to shoot with a standard flash sync (1/125sec), low ISO and a wide-open lens even with very bright ambient light.

Thanks for reading,

Steve