Just to let you all know that the razer blade trick worked a treat, took half an hour fiddling, but it worked.
Thanks again for the help.
Chris

Thanks for all your help, that certainly seems to be it, can't get the razer blade in at that point, but will perservere.
Many thanks Chris

Has anybody got any info on how to remove a KR mount lens from a Pentax *ist DS?

A friend lent me his macro lens which is a KR mount - fitted OK - won't come off it's solid.

Any suggestions?

Thanks Chris

Hi Matt
Just noticed your reply to this thread, like you I can't believe that Pentax just put them in paralell, but I don't see them using diode coupling either due to the 0.6Voltage drop, unless they use 'switched mode' PSU's which I'm pretty sure they wont. Thinking further on this it could be they use power MOSFET's these can have an internal resistance of only a few micro-ohms across the scource and drain or can be switched to almost infinite resistance (many hundreds of Megohm) But then you would need to know which set of batteries is the 'Master' (i.e. those which are being monitored, I presume those in the camera body) and how would you design the circuit to switch back when the cameras batteries was the higher voltage? I wonder if this is what they've done and your problems are caused by this?

If this is right (and I have no way of knowing this) then the sequence would be;-

1, Camera batteries fall below threshold - switches to hand grip batteries. Everything OK.

2, If hand grip batteries fall below threshold it can't switch back because it's only monitoring the camera batteries. Camera annoyingly turns off.

3, Putting recharged cells back in camera should result in hand grip batteries being turned off. Everything OK again.

4, Putting recharged cells in hand grip with no or low batteries in camera would mean you've reverted to a single battery pack system. Which is probably how it should have been designed in the first place!

Hope this makes sense, and just to reiterate I have no way in knowing if this is true or not, just my meandering mind.

Chris

Hi Matt

If the 2 battery packs are in paralell with each other, which I assume they are, that would be an extreemly bad, if not dangerous, practice!!

As I see it, you have a battery comprised in a set of 4 cells, if one cell is more discharged than the other cells then there would come a point where it will 'see' the opposite polarity and would charge up reversed (i.e. it's +ve pole would be negative and it's -ve pole would be positive). This means that the battery as a whole (4 cells) would be minus the 1.2 Volt of that cell, on top of that the other cells would have to overcome the reversed charge in the 'faulty' cell, so the total battery voltage would be alot less than the nominal 4.8 Volt it should be.

This used to happen in my other incarnation as a fast electric model boater, and is alot more critical with the Amperage we were using, but still applies.

To avoid this problem we used to match cells for internal resistance (using a Wheatstone Bridge) and always kept the cells together as a battery (charge them up together, and discharge them together). With the current required for a camera I don't think we need to match the cells, but never put different A/H rated cells in the same battery pack, because the lower rated one will discharge first and the above phenomana will occur.

Then we come to the point about having 2 battery packs in parallel.

The 'correct' way to do it is to have a voltage sensor circuit which will switch from one set of cells to the other when it detects a lower than required voltage, which is difficult to acomplish due to the 'switching' component having a voltage drop so neither battery pack will produce 4.8 Volt, hence my reason for thinking that they just put the 2 battery packs in parallel.

Why is this so bad?

Most chargers limit the available current in some way, cheaper ones just use timers then limit the current to a 'safe' level, more expensive charger detect the Alpha point (a slight drop in terminal voltage when a cell is 95% charged, but long before it starts to vent) then limit to a safe level.

Imagine a situation where one battery pack is fully charged and the other is discharged, current will flow from the 'good' battery pack to the other due to there being a Voltage difference between the two and there is nothing to limit the current available!!! Further imagine that one of the cells in the discharged pack is totally discharged and begins to charge up 'reversed' this will lower the discharged battery pack voltage still further say to 3 Volts or so, then the Voltage difference is greater so even more current will flow from the charged battery pack to the point where another cell fails exaserbating the problem in a (possibly) dangerous way.

Suggestions,

Always keep cells together as a pack, never mix & match.

Never mix different A/H ratings in a battery pack.

If indeed the 2 packs are wired in paralell then treat both packs as one battery (i.e. charge all 8 cells up together and discharge together) and never have different A/H ratings in any of the 8 cells. In other words use both sets of batteries as if they were one.

Hope this helps Chris

Pentax *ist DS and I presume D & DL too, can set any white balance manually to any colour of light. Page 113, 114 of your manual shows you how.

Chris

Hi All

I think alot of the problems you are talking about in this thread could stem from the fact that you all seem to be using NiMH cells, as most do.
These batteries are great except for the problem of monitoring them. 1.2V per cell, everything OK, 1.1 V per cell everything shuts down when the camera wants to draw current, writing to card etc.

The discharge curve for NiMH cells is virtually vertical from 1.1V per cell, making any metering system difficult. In other words you wont get much warning with NiMH batteries, they either work or they're exhausted.

Leaving a battery for a few minutes allows the cells to partially re-form allowing a bit more discharge.

I think the metering system is tailored around Lithium batteries, these are what is supplied with a new camera after all, and have a much more gradual discharge curve than NiMH.


Chris

Hi

You've already got one!

Just pull up a word processing package on your computer and point your slide copier/camera at the screen.

That's all I do.

You can us Photoshop or similar and just fill a screen with 255 white - your monitor should really be calibrated to be accurate, but how accurate is their tiny screen?

Chris