M 240 bulb long exposure comparison with M9

[tgm]

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Long exposure of the M 240 is limited to 60 s for ISO and even less for ISO 1600 and above the maximum time is only 8 s. This was one of the surprises, especially since the M9 wit CCD sensor allows 240 for all ISO settings.

 

I see two questions, firstly, why did like introduced this limitation (usally CMOS sensors are said to be less prone to heat realated noise). Secondly, are there ways to overcome the limitation, at least in part.

Starting with the second question, as far as I know there is no way to extend the exposure to 60 s. But shooting underexposed images in raw and correcting with a raw converter may allow extending the range of long time expsores under very dark condition.

 

I performed some test, shooting pictures at fixed 60 s and different apertures in a rather dark room.

 

Here is an comparison (100 % crops), standard setting ACR 6.3

 

1) Leica M9 ISO 1600 F/4 60s

 

 

2)Leica M 240 ISO 200 F/4 60 s, corrected by 3 stops in ACR, equivalent ISO 1600

 

3) Leica M 240 ISO 200 F/8 60 s, corrected by 5 stops in ACR, equivalent ISO 6400

 

 

4)Leica M 240 ISO 200 F/5.6 60 s, corrected by 4 stops in ACR, equivalent ISO 3200

 

 

 

All in all, I think the M240 at ISO 1600 and 3200 looks very promising, I see more than 1 stop advantage over the M9. What do you think? I should add that I have to do the WB balance by hand, otherwise the pictures had an awful orange cast.

 

So, that puts the question why Leica limited the exposure time of the M 240 to 8 s for ISO 1600 and above.

 

My summary, the M240 seems to be very useful for long exposure significantly exceeding the M9, as long as you can live 60 s maximum exposure.

 

Thomas

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[jip]

Interesting, I only used long exposures of over 60 seconds once, and that was for light painting fun in Pennsylvania in march this year I guess... (with M9P)

 

Never did long exposures apart from that. At least not longer then 60 seconds.

[tgm]

 

Never did long exposures apart from that. At least not longer then 60 seconds.

 

Yes, I agreee, 60 s is in most cases sufficient. But with the M 240 you can only use ISO 200, for ISO 1600 and above 8 s is the limit. High ISO and up 60 s is in most cases sufficient, for example landscape during night ( 'landscape astrophotography') or polar light.

The tests show that shooting raw at ISO 200 and pushing in the raw converter by up to 5 stops gives results equivalent or better than with the M9.

 

So the question remains why Leica limits the exposure time for high ISO to 8 s.

[jip]

I think it has to do with either processing power for noise reduction, or the actual sensor not being able to do that at high ISO. Like the movie feature of the M goes up to 1600 ISO, with a shutter speed of 1/24 or 1/25th of a second, lots of exposures, of about 25 per second... meaning it can 'cool' down enough probably to keep it stable, higher ISO won't work, and I think that is the case with long exposures the sensor just can't handle, or overheats or something like that.

 

Just my guess.