Homebrew AF-assist

The AF360FGZ has an red AF-assist lamp, right?

Some modern high-end flashes have a laser AF assist lamp that projects a grid onto the subject, right?

Well, I'd like to make an AF-assist laser for my K100D. Just in a box like this:




I have a laser diode and am prepared to create some electronics (I have a little experience) as well as something that suitably scatters the laser beam.

I'd buy an AF360FGZ to modify (or not), but I can't really afford one and I have my beautiful Vivitar 285 anyway.

So, my question is, how do I find out through the hotshoe when the camera wants an AF-assist lamp? The 360 knows somehow, and if it can work it out, so can my creation.

Thanks!

Alas, the communication between the body and the AF360 is a digital link
There are four connections that deal with legacy flash and the fourth is digital. That digital link provide zoom information, AF-assist, P-TTL negotiation and probably a few other bits.

I've not seen anything anywhere on the 'net about the protocols but personally (as a long time electronics engineer) I would say it's not worth the effort
Matt

OK, thanks I suppose I could find an AF360 that someone's dropped off a cliff and gut it for the circuitry...

pentax flashes and hotshoe mounted l.e.d. and/or hot video lights already fill that need cheaply.

...are there really cheap third-party (or outdated Pentax) flashes available that recognise the AF-assist signal? Even just a tiny box-of-matches flash that sits on the shoe, that has a weedy orange LED on the front? That would be brilliant - I would be quite happy to pull it apart.

FYI, the AF assist in the AF360 is not just an LED. It projects what looks like a bar-code onto the subject - to provide a consistent contrast. Not sure what is done optically inside though
Matt

Then I'm prepared, I suppose, to make a manually-controlled one. Pop it on the shoe and press a button concealed in my palm to illuminate it, perhaps!

Wouldn't a torch be simpler?

It would indeed. But then at parties I'd look even stranger than I usually do walking around with a cocktail and a DSLR

FYI the AF assist lamp on my AF240FT works wonders with my K10D. Since these flashes can't do P-TTL they often go rather cheaply on a certain auction site.

Indeed, as does the 400FTZ

Thanks... I've looked those up and they look exciting, although I'd rather not replace my 285 with something unless it's a really nice flash. I'll buy the AF360FGZ when I win the lottery, but the 285 is the best flash I can get with no (E-)TTL, I reckon.


I suppose my question has changed to:

What is the CHEAPEST way to have some kind of AF-assist that isn't just a bright LED or manic onboard strobe? I suppose I mean a laser grid. What's the cheapest way to get my K100D to project an AF-assist laser on the subject?

As I said earlier, I don't mind home-made, I don't mind ungainly, and I don't even mind having to press a button to make it work as I focus.

This was an experiment around the house.

I've used a small MagLite lke the ones that fit on a key ring strapped to the lens hood with masking tape, I painted the lens red using nail polish, it worked

Severely tempted by the AF400FTZ. I'm aware it uses the wrong kind of metering for the K100D (TTL not P-TTL) so I won't get auto exposure, but I'm fine with that.

But can it talk to the K100D enough so that the AF-assist light works? Otherwise there's no point...

Thanks

Yes, it'll work fine. The AF400FTZ (not AF400T) has a digital interface and hence it has the 4th pin with which it 'talks' to the camera. AF assist is one of its 'conversations'.