Focus illumination lamp not functioning

Yep, just checked the D800 and it also disables the focus-assist lamp for focus points other than dead central. How stupid!

Nikon's only excuse is that the light focusses fairly tightly at about 15 to 20 foot from the camera, where it just doesn't have enough coverage to be very useful to AF points other than the central one.

So lesson learned. Forget the dozy built-in AF assist and carry a torch!

Still working on that diagram Mike. I haven't forgotten. Just pondering if I can re-arrange more readily available logic gates than an EXOR package and still keep the chip count at one.

I've always been surprised no-one has made a small cube-like hot-shoe mounted AF assist lamp, bit like the cubic part of the SC-29.

Just had a thought, don't suppose the SC-29 'cube' would work if the cable to the flash was 'cut' and suitable 6v (?) power applied??

Bit left-field but who knows??

Bit like this...

YONGNUO YN12AF AF-assistant – Focus Assist Light for Canon | FLASH HAVOC

EDIT. Looks like it didn't work so well and disappeared from the market.

My brain must be dulled; either from festive drinking, old age or both!

The AF light CCT that Mike wanted only needed two NAND gates, and one of them is used as a logic inverter.

Here's the functional diagram. Excuse the awful phone-camera copy.

Open numbers are 74HC00 pin numbers. Circled numbers are those of the Nikon 10 pin plug.

I believe that a 74HC gate will drive an LED to a reasonable brightness, but maybe not. In which case a spare nand gate can be use as an inverting buffer and connected to the base of an NPN transistor, via a suitable resistor, and the LED driven by the collector of the transistor.

I found some time to put a revised version into a cct design programme.

The additional gate - still part of the quad nand package - and transistor should make it more robust against variations in gate drive capability. In fact, 4000 series CMOS logic could be used.

R1 limits the LED current and should be selected to give the desired brightness.

Connections to the 10 pin socket have been omitted for clarity.

I found some time to put a revised version into a cct design programme.

Thanks for this RJ!

I even found the right bits in my random components box. Result!

Now, quite where my soldering iron is?

....or maybe a bit of breadboard first...;)

Breadboard?!

I reckon you could just solder a few bits of wire and the 2 or 3 other components directly onto the pins of a DIL logic package, and stuff the entire thing into the casing of a cheap wired remote - apart from the LED and its dropper resistor, which would need to sit on or alongside the camera of course.

BTW, if anyone wants to adapt the above CCT to another camera or use: The Nikon 10 pin connector has built-in pull-up resistors on its AF and Shutter inputs. For other applications you may need to add a couple of pullups to the logic package inputs.

I've always been surprised no-one has made a small cube-like hot-shoe mounted AF assist lamp, bit like the cubic part of the SC-29.

 

Just had a thought, don't suppose the SC-29 'cube' would work if the cable to the flash was 'cut' and suitable 6v (?) power applied??

 

Bit left-field but who knows??

Someone did make a small cube led light tat also can work as a flashlight ... : LumeCube | Portable, Durable, Powerful Lights for Photo and Video

a small cube led light that also can work as a flashlight

I couldn't find the bit about it being for AF assist only, ie it goes OFF just as the shutter is tripped?

I always assumed (dangerous!) the whole idea of a AF assist light, is that they don't contribute to the actual exposure?

Breadboard?!

I reckon you could just solder a few bits of wire and the 2 or 3 other components directly onto the pins of a DIL logic package, and stuff the entire thing into the casing of a cheap wired remote - apart from the LED and its dropper resistor, which would need to sit on or alongside the camera of course.

 

BTW, if anyone wants to adapt the above CCT to another camera or use: The Nikon 10 pin connector has built-in pull-up resistors on its AF and Shutter inputs. For other applications you may need to add a couple of pullups to the logic package inputs.

Probably too late if Mike has all the bits, but you could use a dual CMOS NAND buffer in an 8 pin DIP. These can sink 100mA so no transistor needed.

http://www.ti.com/product/CD40107B

Probably too late if Mike has all the bits

Looks like I can get 6 for a fiver, so no worries if it's a 'simpler' circuit, esp. with the much higher LED current available.

Anyone up to redrawing the circuit for me...:)

I'm OK at making kits and following plans for stuff but circuit design is a little bit beyond me esp. when it involves a £££ camera!

Looks like I can get 6 for a fiver, so no worries if it's a 'simpler' circuit, esp. with the much higher LED current available.

 

Anyone up to redrawing the circuit for me...:)

 

I'm OK at making kits and following plans for stuff but circuit design is a little bit beyond me esp. when it involves a £££ camera!

I'm going down with a virus and feeling rough (so info. should be checked!) but you should be able to use Joe's original diag.

Pins 1,2 and 3 become pins 1,2 and 3 (same)

Pins 4,5 and 6 become pins 6,7 and 5 (the gate on the other side of the DIP.

Pin 7 becomes pin 4

pin 14 becomes pin 8

The layout is the same except that there's only one device each side of the DIP package - you want the plastic E version.

You will need a pull-up resistor on the output of the first gate (pin 3) going to Vcc (around 5.6k to 12k should do), so the saving in components is small though there is less wiring and a space saving.

If you have any tantalum bead capacitors in the box it's good practice to put one across the supply, perhaps 10-50 microfarad.

I do have a few concerns:-

1. Just how much current do you need to drive a white light LED sufficiently and what is the voltage across it at that current?

2. How much current can the 10 pin connector safely supply?

3. If the circuit develops a short is the camera protected internally from damage?

i knew i had seen a similar idea somewhre else ...

founfd it : Adapting Camera: The need for an external auto focus assist light

2. How much current can the 10 pin connector safely supply?

3. If the circuit develops a short is the camera protected internally from damage?

Good questions.

The 'permanently on' 10 pin supply is stated as 6v, so obviously not directly connected to the Lithium battery. Nikon seem to remain silent about the current capability and, like everyone else, I'm reluctant to test one of my cameras to destruction!

It might therefore be better to sacrifice some weight, bulk and complexity to incorporate a battery in the design. A rechargeable 9v PP3 would supply a fair amount of current and should have sufficient voltage headroom to overcome the voltage drop of any LED. (White LEDs drop between 3 and 5 volts IME.)

Milliampere capacity shouldn't be an issue either, since the LED only need be lit for the short time it takes the camera to acquire AF lock.

You could even get really clever and use a small boost converter module to charge the PP3 from the camera.

i knew i had seen a similar idea somewhre else ...

founfd it : Adapting Camera: The need for an external auto focus assist light

Hmmm. That gizmo needs an existing IR or light-source to trigger its own LED. So it won't work with Nikon's daft centre-only AF light.

And if you've got a speedlight in the hotshoe with its own red AF illuminator; why bother?