Disassembled my camera to convert to IR...

This morning I decided to convert my old Samsung GX1L to be a proper IR-capable camera. This involves taking it to bits of course, so it was with some trepidation that I commenced unscrewing parts of it.

There are about 26 screws (all different sizes) and many ribbon cables (three types of connection) to undo, plus about 10 wires that need to be unsoldered in order to get into the guts of it. I thought the GX1L was supposed to be a rebadged Pentax *ist DS, but the main board is definitely that of a *ist DL (which explains the 'L' I suppose).

Here's what it looked like after a couple of hours of butchery - I used my wife's discarded contact lens holders for the little pots to keep everything separate:



The IR-blocking filter is visible in the picture. I then cut a 28x22mm filter out of a Hoya R72 filter and put it all back together.

On turning the camera on the top LCD, autofocus, rear LCD, all modes, menus and functions including flash all work fine.

Except that the pictures captured are just coloured noise

The problem seems to be that the ribbon cable connector for the sensor block is one of those where there is a little brown sliding bar that sits under the cable, and the bar doesn't click back into position properly. I've reseated the ribbon a few times, but it just doesn't get locked in by the broken bar. Since everything else works that seems the most likely reason for the junk images.

That camera cost nearly £10, and was used for my Mono Landscapes entries last week. I don't think I'll be able to fix it

Anybody familiar with rectifying bad slide-action ribbon cable connectors?

The Hoya filter is also the wrong thickness, so it will be optically out as well.

Have you got a close up of the broken connector?

Ah, that is compensated for by moving the sensor module - it is on three posts that can take thin washers. The autofocus can be adjusted via the debug menu, and the focussing screen can be shimmed too.

If I could get a picture...

Not very close, but here it is the one below the eyepiece (unbroken):



Once the platen is removed you can see the ribbon coming out of the top of the sensor module. It is quite a tight loop of ribbon:



The little sliding 'wedge' that locks under the ribbon has lost one of its ends, so doesn't lock into the holder. Whether that's the only problem I can't say...

They look like the 'standard' Samco or similar connectors. You can get replacements (Farnell etc) and although they are surface mount you can replace them with a standard soldering iron if you are careful The trick is to put more solder on and flood the tracks to get it all the pins hot at the same time. After you get it off you clean the excess solder off with braid. Then place new one down and rub the hot iron across the pins to reflow the joints. Or you might be able find a local electronics company that can do it for you, all the better if they have a proper SMD rework station.

Thanks - having come this far it seems silly to give up.

Looking at the above pics from the service manual I'm not convinced I've assembled it right anyway. In the pic above, for the one below the eyepiece, it looks like the clip is above the cable. The one on the left has the clip below the cable, so that just the ends are accessible to be pushed out.

I'll strip it down and see if the remains of the clip can be persuaded into position above the cable. So many screws to get there though...

Success!

The offending cable is now secure, and the camera takes pictures.

After some calibration I've adjusted the autofocus to +320 via the debug menu and that gives sharp focus using the centre AF point. Interestingly the Samsung GX1L has 5 AF points instead of 3 on the Pentax *ist DL, so still not exactly the same...

Interesting findings with lenses:

The Tamron 17-50 is fairly sharp at 17mm and f/2.8 but gets a central hot spot as it is stopped down, so f/4 is about the limit of usefulness. That's disappointing.

The Sigma 10-20 at 10mm gives a sharp central area but the sharpness falls off dramatically off-centre, it looks like a Lens Baby image. Stopping down to f/11 sharpens it up a bit, but it is still very poor near the corners. No hot spot here, although this lens does hot spot on Canons and Nikons in IR. I haven't tried other focal lengths yet.

The Mark I kit 18-55 is fully sharp at 18mm and f/3.5 and stays like that when stopped down, with no hot spot. It works better in IR than it does in normal light!

The problem may be that this is a 720nm filter so there is some visible light getting through, and the Sigma in particular is unable to focus both anywhere near each other. I've got a Tiffen 87 filter that lets much less visible light through so I can put that on the front and see if it makes a difference.

All told this is looking good...

WEll done so far, extreme bravery award follows!

Have you remembered to compensate for the focus point of IR light? Unfortunately this will also vary with lens and with the focal length set on some zoom lenses as none of them are corrected for IR light.

However, perhaps if you use a prime lens you could set things up quite accurately?

The piece of Hoya R72 is 2.45mm thick, the original appears to be 2.0mm, so that difference moves the focus plane of an infinity white-light image by 0.45 * (n-1)/n (approx - assuming the refractive index 'n' is 1.5) so 0.15mm. However, as you say the IR is focussed differently so I took the approach of leaving the sensor where it is and simply adjusting the AF compensation in the menu. The AF sensors see the normal light now, so they obtain focus for that and then the compensation provides the IR focus. More or less, and will need final tweaks for the lens I use the most.

I'm still experimenting. The viewfinder image shows a slightly different focus point to the actual (AF-derived) one since the optical paths are now different, but it isn't too bad. I might shim the screen if it needs it, depending on how the screen in this body is arranged.

Now to take some real pictures...

Well done, very interesting project.
Your infra-red film pictures look good so look forward to seeing some digital ones.

Just more testing so far...

Using the Samyang 85mm at f/1.4 the final AF adjustment is 540 um (so 0.54 mm) to allow for the IR and the thicker filter.

For the Sigma 10-20 the AF is generally useless. The Sigma shots have some very strange characteristics, if I focus on the conservatory door from the garden (using AF) I get a sharp door, but everything else is out of focus, particularly away from the centre. If I focus at a greater distance manually the door is no longer sharp, while the wicker furniture inside the conservatory is sharp (as you'd expect) but the brick paving in front of the door is also sharp (cue Twilight Zone music). There are two planes of sharp focus in the same picture and neither of them include the door. Perhaps this is to do with different wavelengths and the lack of correction for one of them.

Simply setting the Sigma manually to the 1.5 feet mark and f/8 seems to give good results and the kit lens seems happy with AF so I'm covered for the ultrawide and wide range that I'm interested in.

Tomorrow I really will try to use it for taking pictures...