Wednesday, May 31, 2017

Photographing night skies with medium format

Phase One XF, IQ1-100 Schneider LS45mm
f/2.8 10-seconds ISO 3200 10:24pm

This this not meant to be a discussion on which is better, Phase One or Fujifilm 50s.  What I hope to accomplish is showing just how well either system is in capturing nightscape photography using high ISO and long shutter speeds.  If you think you’re about to read how I favor one over the other then give it up and stop reading.
Let's begin our discussion with the following observations.  Up until a very short while ago you couldn’t think of capturing the Milky Way or any nightscape images using digital medium format.  That is unless you had a Phase One P45+ which is capable of 60-minute exposures.  I’ll only address Phase One and the new Fujifilm 50s as those are the two systems I’m familiar with so if I miss a product from Leica or Hasselblad please forgive me.
2-shot panorama
Fuji GFX 50s GF63mm
f/2.8 5-seconds ISO 800 2:34am
Phase One introduced their first CMOS sensor with the 50 megapixel IQ150 crop sensor offering ISO range between 100-6400 and a 60-minute exposure.  Phase One now offers a 100-megapixel IQ1 and IQ3-100 full frame sensor with an ISO range of 50-12,800 and a 60-minute exposure.  The Fujifilm GFX 50s is a crop 51.4 megapixels sensor offering ISO range of 100-12,800 (extended range of 50-102,400) and a 60-minute exposure.
When you research night photography all the information is centered on using a 35mm system which makes sense when you think about it.  The sensor used in 35mm is a CMOS while the typical medium format is CCD. (CMOS is complementary metal oxide semiconductor and CCD is charged couple device). CMOS sensors will typically offer a better battery life as well as higher ISO. The other difference is a slightly different color and dynamic range offered between the two-sensors.

Phase One XF, IQ1-100 Schneider LS 35mm
f/3.5 5-seconds ISO 800 11:42pm
Since 35mm has been the king of the hill the vast majority of images produced are from them as well as historic testing.  What I’ve been doing is reading the 35mm testing and attempting to use it in using medium format.
The 500 Rule.  This rule is simple on the surface; divide 500 by the lenses being used. If you’re using a 21mm lens, 500 divided by 21 equals 23.80 (rounding down to 23).  23 becomes the longest shutter speed I’d use using this lens before introducing star smear.  This is fine if I’m using a standard full frame 35mm camera such as a Sony A7rII.  What about medium format…
Fujifilm GFX 50s GF32-64 at 32mm
f/4 8 seconds ISO 3200 2:44am

Take a look at any medium format lens and it will offer the equivalent range in conventional 35mm terms thus the Phase One 45mm f/2.8 when used on my IQ1-100 is 28mm and my Schneider LS 35mm is equivalent to 22mm.  Take a look here on Capture Integration's web store for information on the Schneider 35mm.  Keeping these equations in mind, when using my Phase One XF, IQ1-100 I factor in the 35mm equivalency dividing 500 by 28 for the 45mm (17-seconds) and 500 by 22 (22-seconds) the 35mm.  I also err on the safe side by rounding downwards for the maximum shutter speed.  This works since I’m using a full frame digital medium format sensor with the 100-megapixel IQ1-100.  What about crop sensors..
Fujifilm GFX 50s GF63
f/2.8 5 seconds ISO 1000 2:54am
The Fujifilm 50s medium format camera uses a crop sensor of approximately 0.79 rounding up to .80 for ease.  I currently have 3-lenses with a 4th-on order.  The crop factors of the current lenses are as follows.

GF 32-64mm f/4 is equivalent to 25-51mm in 35mm and has an equivalent 35mm f/stop of f/3.2
GF 63mm f/2.8 is equivalent to 50 in 35mm and has an equivalent 35mm f/stop of f/2.2
GF 120mm f/4  is equivalent to 95 in 35mm and has an equivalent 35mm f/stop of f/3.2
GF 23mm f/4 is equivalent to 18mm in 35mm and has an equivalent 35mm f/stop of f/3.2
Based on the above information I divide 500 by 25 (20) for the 32-64 if shooting at 32, 500 by 50 (10) for the 63mm and 500 by 18 (27) for the new 63mm.
All research so far show the wider the lens the better it is for nightscape and Milky Way images since the wider the lens the longer the shutter can be opened before star smear.
Fujifilm GFX 50s GF63
f/2.8 10 seconds ISO 3200 11:50pm
I’ve covered shutter speeds and will address ISO next.  Your ISO setting will depend on the environment you are shooting in as well as how fast your lens is.  A lens at f/2.8 can capture at a lower ISO than one which is f/4.  You’ll also need to experiment as you shoot.  I normally will begin at ISO 1600 and go to 3200 if needed or lower to 1000 or 800.  The final figure depends on what I see on the histogram.
Another factor is noise.  The higher the ISO the more noise you’ll introduce thus the need for “dark frames”.  The easiest way to describe this is that when using a dark frame the amount of time you shoot a single capture is double; a 20-second exposure takes 40-seconds.  Phase One does this automatically while Fujifilm GFX 50s must be set up.
Phase One XF, IQ1-100 Schneider LS 35mm
f/3.5 8 seconds ISO 1000
I like both systems and enjoy using them both.  Stay tuned for more. And as always, thank you for your comments and suggestions.



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