There is another great timelapse 5D2 video from timescapes.org:
[vimeo]http://vimeo.com/moogaloop.swf?clip_id=6686768[/vimeo]
Additionally, the vimeo source contains very interesting Making Of videos to learn from
So, I wondered what it would take to do this with a K-7.
First of all, note that the video feature is not required or used. It is timelapse. Nothing K-7 specific here.
But a capture of a moving Milky Way is great and needs very good light capturing capability. timescapes.org used a full frame 5DII with EF 16-35/2.8 II lens (ISO1600).
There are two factors to consider when computing light gathering capability:
1. The amount of light thru the lens onto the sensor, ~ (d/f f/N)^2 where d is the sensor diameter, f the focal length and N the f-stop number.
2. The possible shutter opened time before blur (here, due to the earth's rotation), ~ d/f
Note that I do not consider the FoV to be predefined. Moreover, I do not take into account that the Milky Way is a finite surface light source which appears brighter at a wider angle.
This gives an overall formula for night timelapse light gathering power
I:
I = 0.15 d^3 / (f N^2)
and
I (timescapes.org) = 97
(the factor 0.15mm^-2 in front was choosen arbitrarily to make the reference about 100)
Note the factor d^3: this is the most significant FF advantage I have seen in any application so far.
The following values for I are achievable with a K-7:
Lens(low zoom end) f/N: I
Sigma 12/4.5: 14
DA 15/4: 14
DA* 16/2.8: 27
FA 50/1.4: 35
FA 31/1.8: 34
DA 14/2.8: 31
Sigma 10/2.8: 43 (closest match to timescapes.org movie)
Sigma 30/1.4: 58
So, a lens with comparable FoV can only deliver about nearly 1/2 of the gathering power and the best possible gathering power is about good 1/2 as well (both not from Pentax). On the other hand, the 20mm/1.8 lens on FF would yield even twice the gathering power, and the 24/1.4 maxes it out at I=260.
While in most applications, the FF advantage is nil (like if DoF must be kept finite), here it is huge, a factor of three to four.
And last but not least, the new timescapes movie is just amazing. Great stuff!
Last edited by falconeye; 09-29-2009 at 06:22 AM.