I haven't taken a look at the RAW yet... but there are two or three things to watch out for (ok, maybe 4 in the style of Monty Python ):

1) Down in the shadows, even in RAW, the chance of posterisation increases. The sensors are linear, but photography is logarithmic - consequently the first 1-stop of data takes up the full top half of the available numbers (so, 14-bit RAW with 16384 values will have 8192 for the first one stop). The second stop will take half of the remaining = 4096. Third stop = 2048, Forth = 1024, Fifth = 512 and so on. The K5 is excellent in this regard - but you can see that you can quickly lose colour detail in shadows.

2) Limits of JPG. When outputting to JPG, the colour information is restricted. You only have 8 bits, but the colours are 'mixed', and you will lose of lot of blue detail. You can test for this by exporting from RAW to TIFF instead and comparing.

3) Colour Gamut. You may find that you have an exposure that is correct, but that produces an output colour that cannot be represented within sRGB (and even not in AdobeRGB). Under these circumstances, depending on the colour mapping used, you can experience posterisation. For example, an area that has fine colour gradations but which are all out of gamut will be output as a colour-clipped area and will appear as a block of colour. You can test by exporting to (a) 8-bit sRGB TIFF, and (b) 16-bit ProPhoto TIFF - the ProPhoto colour space is massive and should have no issues with colour clipping.

4) Gamut of the display. Like colour-clipping on output to sRGB/JPG, the display may well be clipping when trying to display rich colours. (Even a Huey calibrated display will have a restricted gamut and will be unable to render all colours accurately.) Some displays are better than others

...much of the above reasons are why the full version of Photoshop has "Soft Proofing" and colour gamut warning ability

Hope that helps!!
Matt

A lot depends on the RAW converter you are using

It looks like the shadow areas are underexposed, and without seeing the original RAW file (or at least a full EXIF) it's difficult to help out...

I have had situations where posterisation occurs in solid colour areas. Noise reduction and other techniques can help - especially when the image has been 'pushed' hard.

EDIT: The image (viewed on my monitor) doesn't look that bad. I can see noise in the shadows and some mild posterisation... but I reckon it would print well. You may also have monitor calibration issues (that make it look worse than it is)

If you have some more technical info that would help!
Matt

Just some update information on this topic...

Wikipedia "Color rendering index" (see the last subheading "Film and video high-CRI LED lighting incompatibility")...

...which references "Solid State Lighting Project"
(Check out the videos with the make-up and props - links are on the bottom right. All the solid state lights looked the same to the human eye, but not to the camera - there are all kinds of weird colour shifts due to metamerism! Yikes!)

(you can find some of this information by Googling the term Metamerism)

Some bed-time reading!
Matt

The e-dials do not have limits. They rotate forever

The effective start and finish point is down to what you are controlling
For example, if you are controlling Av with the e-dial then it will go between the maximum and minimum aperture values of your attached lens - e.g. f/4 to f/22, or f/2.8 to f/32.

If you are controlling Tv, then it's the shutter speed limits of the camera.


The intervals are usually half stops. But you can change that to one-third-stops in the custom menu.

Hope that helps!
Matt

LED lighting has very limited range - but it is continuous lighting which helps with focus and composition

Do be aware that the quality of white LEDs varies greatly and so different makes will give different intensities, white balance, and light quality.

I'd combine the two
Use LED ring lighting to help and a wired flash to give some extra light and 3D quality to the light
Matt

PU is run by Magezine Publishing... who run ePhotozine.

They also run other sites - listed here

As I said before, if you are doing studio style shots where you are controlling all the available light, then I would strongly suggest good 'ol Manual flash (where you set the fractional power amount).

You stick the camera in "M" mode as well (and preferably meter without flash for somewhere between -3 and -1Ev ambient light), and then take a test shot or two to get the flash ratios right. In the end I can set this up by guess work and be ready in a couple of shots easily. Once that's done you just shoot away (as long as the flash-to-subject distance doesn't change much). This is definitely the easiest for taking lots of shots (e.g. at an event).

Reserve P-TTL for situations where you have little control, or where you're moving about a lot (e.g. weddings )

BTW, my e-book on flash usage might prove useful
Matt

Please see this other thread.

Same offer stands

Just a simple thought:

Is the remote flash visible within the viewfinder?

If it is, the camera will see the preflash from the remote, think "Whoaah! That turned out brighter than I thought" and dial back the base exposure to compensate - yielding a very underexposed image.

All remote flash guns should be out of the field of view (even if only slightly) - doesn't matter where, but definitely out of the field.

As it happens, the same thing occurs when you think "I know - I'll use my remote as a white back light". The camera will see the remote as a very bright area and dial everything back. (Hint: you should always use "M" for studio, setup shots where you have complete control over all the lighting. It'll save a ton of time in the end!)

If all that doesn't help...
...just email me a sample image (JPG will be fine) with all EXIF information intact The EXIF contains the complete exposure information - ambient, and preflash - and is helpful in sussing out issues like this

Matt

Look harder
Page 100, section 9.2.2

We are talking about the 50AF-1 Pentax version?

It works like this:
Preflash
* Camera issues flash command
* Flash guns fire
* Camera takes light meter reading and works out final exposure
Main flash
* Camera lifts mirror and opens shutter
* Camera issues final exposure information to flash guns
* Flashguns fire
* Shutter closes and mirror goes down.

Underexposure happens typically when the preflash shows a mass of light so the exposure system dials back the exposure. Also, if the flashgun fires for the preflash but doesn't fire for the main flash you'll get massively underexposed shots.

Finally, if you have any reflective surfaces (hopefully you aren't shooting in front of a mirror!!) then the camera will dial back the exposure to compensate. The 16-segment metering cameras were more 'touchy' in this respect, while the 77-segment K7/K5 are much better controlled for reflective objects with flash.

There will be a simple explanation somewhere as to why you're getting underexposed images...

Matt