Homebrew AF-assist

Glad to hear it - thanks!

Is it a good flash in general? Like, will I miss the power/cycle time/70s styling of my V285?

Yes it's a good flash, not lightning fast recycle time but beats 70 seconds on fresh batteries. It's manual zoom though.

More info here.

Again, brilliant, thanks - just what I needed to know. (I'm guessing you meant 7 seconds. )

Another question - the AF-assist beam, what form does it take? Is it just a bright directional LED? A laser grid? A laser pattern? A tiny red man waving a laser pointer in a repeating pattern really fast?

It's strange - everywhere, people talk about what devices have an AF assist, and whether it's dedicated or just a built-in flash in Demented mode, but it's very hard indeed to find qualitative descriptions or even pictures of the beam and its effects.

I'm guessing that, if no-one talks about the qualitative differences between different illuminators, then they must all be effective and I don't need to worry... I mean, I find more discussion about the relative merits of different kinds of lens caps!

That's probably because you'd need two cameras, and probably a good sense of timing - as the AF beam is only flashed up for a second or two.

On the AF360 it's a red and black grid. Bit like a bar-code pattern. Interestingly it seems to retain its contrast across a wide range of distances. Because of the grid pattern the camera can focus on a flat object in the dark (it's not just illuminating the subject)

Maybe I'll try and get a capture of the AF360 focus beam...

Matt

Sorry, I misinterpreted your last post. I thought you meaant the recycle time was 70 seconds. I wasn't paying proper attention. 70 secs would be next to useless I know.

I don't know what form the AF beam takes other than it's red and bright. I've had an AF400FTZ but I've moved on from there. I think my son may still have one with his MZ-6, I'll ask him to check. Others around here may be able to answer that one.

Aha - yes, Seventies styling, rather than a recycle time of over a minute!

hey, here's an idea with some marketing potential....
take the eyecup cover...
drill 4 tiny hloes in it, one in each corner of the viewfinder.
install 4 laser led's. and a push buttton
now with the cap on, you can pust the button and have 4 laser dots hitting you subject at the four corners of your lens's feild of view.
perfect for scuba, macro, and some studio work where framing the shot may be difficult.

Potential! As long as a) it will pass through the focussing screen and b) the effluent ray won't interfere with metering or AF.

If it's possible, why don't new DSLRs have TTL AF-assist?

Time to patent, I think!

ok somebody get a prototype together and we'll all pony up a buck or two for the patents, and split the royalties.
(ps internal light scatter would screw up the metering and af functions....I'm talking about framing without using the viewfinder as in push the laser button to check your framing, release the button, then push the shutter button.).

Hello everybody,

I've also been pondering about this, because I find the AF-assist (AFa) incorporated in my K10 to be at least annoying because of the potenial distraction generated by the strobe flashing and on top of that cumbersome when having to use it when needing AFa, but not wanting to use the flash for the exposure (pop up, AFa, close, shoot picture).
I found out by using the AFa incorporated in my Metz 50 MZ5 flash that it's really beneficial to the built-in AF.

Although not absolutely necessary, a grid placed in front of the AF-a has it's merits. When trying to focus on a surface that's lacking in contrast the grid makes life easier for the AF by introducing the contrast needed for the AF to function properly. The easiest way to make a grid is is to give the grid some depth prividing a tunnel like structure to break up the beam (stacked black drinking straws come to mind after remembering reading about a DIY snoot 'instructable'), filtering out the light not parallel to the aiming direction, reducing diffusion of the AFa light which will diminish the needed contrast for your AF when photographing objects with inherent low contrast.

[job deformation (and geek) mode]

A grid with some depth is a solution also used in my line of work (I'm a X-ray imager (hope this is a correct term, English is not my native language, but I think you catch my drift)). When taking a X-ray we only want to use radiation that comes from the direct X-ray beam. The problem is that X-rays from the primary bundle also excites secondary radiation eminating from the bodypart one is taking the X-ray of. This scattered radiation contributes to the exposure in a negative way, incremental to the thickness of the bodypart. Above 14cm thickness of the body-part, this scattered radiation, being omnidirectional by nature, reduces the contrast of the image to a point that the diagnostic value of the X-ray image is compromised, failing to show small but sometimes oh so important information. A grid constructed from sandwiched lead strips alternated by strips of a radiolucent material, parallel to the primary beam filters out most of the scattered radiation, greatly increasing contrast (and diagnostic value of the X-ray image) as with the grid on an AF-assist in a camera.

Work and hobby combined, as a bridge for getting back on-topic :



(image is much nicer on original analog print, flower exposed with a Siemens mammography device, print (somewhat poorly) digitized using my K10)

[/job deformation (and geek) mode]

I'm not really an expert on laser LED's, but it might be important to consider the light intensity its generating when using such a construction for portrait photography. You wouldn't want to use it when there's the possibility to harm someone's eyesight by shining direct into the eyes of your subject be it man or animal. Maybe it isn't a problem or it's already been taken into consideration, but I thought a word of caution would be prudent, one can't be to carefull regarding one's eyesight.

An elegant solution to switching the DIY-AFa on and off at the right time might be using the 2.5mm remote connector and introducing a third switching step for controlling the external DIY-AFa. Preferably switching on before the AF-switch is triggered, and switching of prior to shooting the pic. The only drawback I can think of is the somewhat decreased hand-holdability of the body due to the open lid at the left side to acommodate the connector and to a lesser degree the mechanics to realise it (maybe 2 swithces for the AFa, one for making and one for breaking connected serially).

My 2 cents, hopefully usefull to someone in the context of this topic, greetings, John.

Wow - we have related careers: I'm an undergraduate biomedical engineering student, and study a lot of optics (and many hours of medical imaging a week next year).

The Metz 50 MZ5... so it's compatible with the Pentax hotshoe and will flash its AF assist at an appropriate time? Does it do P-TTL metering too, or do you set it manually?

I know what you mean with the lead grid - it collimates the beam on a photonic level, so there will be no radiation detectable away from the region where the patient is? I have a feeling that many AF-assist beams do project a grid anyway, which is how they can provide a way of focussing on homogeneous areas which otherwise wouldn't show any contrast regardless of the focus setting.

What confused me a little is that when I had a play with a Metz 58 AF-1 in Calumet in London yesterday, I couldn't see the beam at all. It seemed to have an effect - the camera found focus on things I couldn't see at all, and produced an in-focus flash photo - but I couldn't see the grid.

I'd heard that these use 'near-infrared' beams, and all people seem to say that it's not really infrared, that it's just a visible red projection.

Do some flashes produce infra-red, some red light? Which are lasers, and which are just bright LEDs? I was hoping to be able to see something like this over someone's face.

As far as safety is concerned, I reckon anything ever integrated in a camera flash has been rigorously tested for safety - especially as people are the one thing that everyone takes flash photos of! I think laser diodes in general are mostly eye-safe, so a homemade one would be OK.

The photo is brilliant. I've seen similar scans of light bulbs and laptops. Did the flower appear to have any abnomalities?

Jonathan

Hello Jonathan,

First of all thanks for the compliment regarding my flower.
I think very fortunate to be abled (and allowed by my department head) to use this energy spectrum for my photography hobby, not many are.

Regarding my Metz flash, it isn't PTTL-compatible, but I don't have to use it in full manual setting all of the time. The flash has a nice trick up it's sleeve to surcomvent the non-PTTL-compatibility. It is abled to get information from my K10 (and even more from my Z1, providing full TTL-compatibility when used) regarding used aperture (A-lenses and newer) and focal length if using an F-type or more recent ones. Combined with a built-in light sensor it is abled to produce the right flash power quite succesfull resulting in correct exposed images most of the time (I haven't used it much since buying it recently so this opinion isn't set in stone just yet).

The AF-assist on my Metz uses light in the visible spectrum as can be seen in the following two images:

1: The AF-light and the control part of the flash generating it.




If the image looks a bit strange, it's because I PhotoShopped 3 images into one.

2: AF-assist detail.




You can see the line pattern (not a true grid, but it does the trick very well) which helps with shooting low contrast objects.

No flash uses laser light (monochromatic light is a better term I think, because 'laser-leds' aren't lasers at all afaik). Laser is an abbreviation of Light Amplified by Stimulated Emission of Radiation, which defines the working priciple, not the output it produces. The reason is the inherent risk to someone's eyesight when struck by a energy rich lightsource, such as a laser or 'laser'-led. My caution was directed towards the DIY-plans in one of the replies.
I think infra- (beyond) red is the correct term as it starts directly following red, hence the name. Near or far just places it on one or the other side of the infra-red spectrum itself. An easy way to visualise infra-red light I sometimes use to see if a remote control is functioning properly, is to use a videocamera or webcam as can be seen in the next image featuring my main remote control (poor quality thanks to my crappy webcam):





I was a little comprehensive going off-topic regarding the grid used for reducing scattered radiation in my line of work, but I then realised you're the topic starter, so it won't be a problem. Here it goes:

You're in the right area but you haven't hit the nail 100% with your assumption. I'll elaborate with a figure I cobbled together to visualise the process:




In the figure you can see the primary bundle genarated by the device (blue). Part of it passes through the object, this is the part of the x-rays that exposes the detecting medium, either on film or when using a digital system using detector-arrays or imaging plates.

Ionising radiation has the ability to convert the silver crystals itself, but isn't very good at it. In order to reduce the exposure times, and of course the amount of radiation the patient is exposed to, an image intensifying screen is placed above the film. This sreen consists of rare earth materials, these having fluorescent properties in the energy spectrum used in radiology (by the way this is how Conrad Röntgen discovered x-rays in the first place. Using a vacuum tube which where invented recently he noticed a screen lighting up nearby, even when placing a piece of paper between the two, realising later this could be used in the medical profession, thus giving birth to the line of non-invasive diagnostic internal imaging called radiology).

Digital imaging systems can use other means for imaging, direct or indirect. Direct regards to 2 different principles which might be a little confusing. In one context it is used to explain the difference between detector arrays and image plates.
In the other context to explain the different working priciples used by detector-arrays.

Detector arrays use both ways of information conversion. (1 Reading the amount of ionising radiation directly with a sensor-array (direct, direct), or (2 with a step in between (direct, indirect), converting ioinising radiation into visible light and then reading the light levels with photodiodes for instance (fluorescent principle).

Image plates use another principle, always combined with image intensifying screens (so it's indirect, indirect). In stead of the agitated electrons falling back directly, these excited electrons residing in a higher valency band need to be persuaded to fall back to the original lower band with a little bit of extra energy to nudge it over the edge, so to speak, thereby releasing the stored information, then read out to produce the image. This is mostly done using a laser to provide the energy needed to release the electrons from it's agitated state (phosphorescent principle, also used for glow-in-the-dark paint).

Both have clear advantages and are used both in hospitals. Detector imaging is faster, also less cumbersome, for you don't have to carry around the image plates to and from the reading unit and will be used more and more in the future.
The image plate method requires a much lower initial investment, for one can use the original equipment, you just throw out the film based system and replace the cassetes with image plates and a reader for the plates so you can use the excisting equipment for it's full technical life span, which is almost always very long, 10 years+ in most cases.
This is important, because the radiology department is one of the most expensive departments of a hospital, if not the most expensive. This is caused by the budget needed for equipment, a conventional radiology room costs app. 500.000 euro's, a CAT-scanner depending on its features 1.500.000 up to 2.000.000 euro's, a MRI-scanner even more than that and needs liquid helium for maintaining the temperature of the super-conducting electromagnetic coils (not always used, but by far in the most cases) just a fraction above 0K. Add this to the cost of employing highly qualified employees, all the precautions to be taken regarding the radiation used. Added also are materials used such as contrast enhancing agents, catheters for angiography (allmost all hand-made, the most expensive ones cost 500+ euro's a piece), because all forementioned materials have to meet very strict standards, for they are inserted or injected into a human body) and can be used only once to name a few. And last but definately not least the electricity bill.
Image plates (up till now, I think this will also change in the future) also easier to use with mobile equipment, used for patients who for some reason aren't abled/allowed to leave their room (drains, monitoring and physical condition for instance).

Part of the primary bundle is absorbed by the object it passes through either producing heat, or secundary radiation, mostly through the so called Compton effect. A photon sometimes crashes into an electron in one of the outer shells of an atom, thereby freeing up an electron in the outer shell, or putting one in a higher shell. This energy transfer results in changing the angle and of course the energy level of the original photon and dependent on the binding energy of the stricken electron in secondary radiation when it (or another electron in the same shell replacing it) releases the energy required for the original stricken electron to get it in an higher shell when falling back to the lower shell (btw, these are discrete levels, adhering to the laws of quantum physics). Both secundary radiation and the original deviated photons from the primary bundle are omnidirectional, with some preference to certain directions, something every radiological imager is required to know about for reducing exposure to scattered radiation when being in the room during some procedures, angiographe for instance.


The scattered radiation in the figure is red.

The strips of lead in the grid (green, in detail at bottom) are positioned parallel to the primary beams inherent divergance angle. This is why a grid always has a distancemarked on it where it's apllcable. One can diverge from this distance only so much, thereby increasing the absorbtion level incrementally when not using it at the indicated distance.
There is also always a ratio, specified for instance 1:12. This is the ratio lead strip height : radiolucent material width (taken up in this assumption is that the width of both lead strip and radiolucent material are equal. The higher the ratio the more absorbtion takes place, the forementioned ratio of 1:12 is used most, for children 1:8 max. is preferred. You can imagine the longer the lead lamelles (hope this is proper english) get the more the beam to be abled to pass through has to be parrallel to the angle used in the grid.

I hope this explanes the working of the grid somewhat further. I also hope you din't find it to be too elaborate an explanation, I sometimes get carried away writing about subjects I'm interested in.

Greetings, John.

Hello and sorry for my bad english.

one question: does the flash AF240FT works trouble-free with K10D?
(I know that some functions not available yet - but i need only a simple flash for some situations)

Thank your for your answers.

The AF240-FT works fine on the K10D with the body and flashgun both set to Manual.

G

I heard somehwere else that the hotshoe sends out a voltage no matter if there is a flash on there or not.
I have the 540 flash which works with just the beam when you set it to Standby.
I am not sure if the camera knows if its on SB mode or if the camera just ignores it.
I remember reading that two of the pins produce a voltage for the duration of the focus of the camera when it is in AF-S mode and switch off just before exposure.
Could someone with a volt meter test this accuratley as if its true then it could mean that attaching a small voltage triggered lamp like the ones that you find on keyrings would be great.