MX300 has a three bladed diaphragm
 

I was having a look at my aperture blades yesterday and I was interested to see that what looks like a five bladed diaphragm in the Lica Dicomar lens is in fact a three bladed one. In reality it's a two bladed diaphragm that has a third blade that carries the ND filter.

The top and botton blades are V shaped and simply come together to make a smaller and smaller aperture. The third blade comes up horizontally from the bottom and carries with it the in-built ND filter. If you look at your diaphragm blades in action you can see that at the widest aperture in telephoto (f2.8) the ND filter always partially obscures the opening.

This explains the MX300's poor performance in low light and also goes some way to saying that the MX350 and 500 suffer the same failing. It's not until you reach maximum aperture that the ND is completely removed from the light path - and of course maximum aperture is only available to you at the wideangle end of the zoom.

Just thought you'd like to know.

tom.

Thanks, Tom. A year or so back I asked Pana, why the 2-blade iris? The reply was along the lines that it's needed for the frame mode.

Did you ever get to clean those heads with a swab?

Well there is one advantage to this in that the ND filter is 'automatic', eliminating the frustrating blinking 'ND' message (one manual ND filter on the tRV900 and two on the VX2000!) and the need to stop filming and engage the ND filter and then start filming again, which does no end of damage to the continuity...

Personally I prefer the way the MX300 compensates 'automatically' and copes with a much broader range of light variation under normal filming conditions at the expense of a stop or two at the low end of the light range...

Why the two balded iris? Cost Frank, cost. Sony use a 6 bladed in the TRV900 and VX2000 and seeing Panasonic's profits, reverted to a two bladed diaphragm in the TRV950/PDX10.

I had another look at the tape path in bright sunlight yesterday. There really is no substitute for real bright sunlight, and my appraisal of the situation is this: If it ain't broke, don't fix it. So no, I haven't taken off the little side door for a full tape path clean but will be doing so when I start to see the gunk buildup on the capstan and pinch roller.

tom.

Tom, I know, I know, it's about cost. I was just repeating what Pana said.

Ahh, so you chickened out..., good man! You had me worried there.

I have looked into the MX350 and sure enough the 2 bladed iris has the ND popping up automatically.

Thanks for letting me in on this fact (the MX500 has the ND independently moved, should be better in tele mode).

I guess that shooting in low lights means that I should keep to wide angle mostly.

Most certainly YCH. Take another look down that lens and see that at anything other than maximum wideangle you've always got some of the ND in place, whether you like it or not. This has serious consequences for the camera's low light performance and is the price you pay for not having to manually switch in an ND filter.

For folk who don't have the time or photographic inclination to switch NDs in and out of the light path the in-built auto ND is a "good thing". For all others it most certainly isn't.

Another thing. Because the aperture scale in my MX300 goes down to f16 I'm wary of believing these figures. I suspect that all the aperture readouts are in fact theoretical rather than actual, in that f16 is actually a diaphragm opening of f8 with an ND4 (two stops absorbtion) in the light path. The reason I believe this is that the diffraction losses at f16 are nowhere near as bad as they are on other 1/5" chipped cams at the same aperture.

tom.