Tuesday, 22 September 2009

G1 (or any smaller sensor) and wide angles

I happen to like wide angle lenses, back when I used 35mm film I usually liked 24mm or (used carefully) 21mm. The first thing I found when I picked up digital cameras in the year 2000 was that I didn't like what options existed for wide angles. To this day the options in wide angle for 4/3rds are quite restricted ... I can think of only the Panasonic 7-17mm and the Olympus 9-18mm lenses.

So in this article I'll compare the same angle of view on full frame and the 4/3rds. I say angle of view as focal length is really a meaningless measure unless you clearly understand the relationship between that and format ... not everything in the world is 35mm you know. Thus we are talking about a wide angle of view in this article.

Before I moved over to the Panasonic G1 I was a Canon EOS user for many decades (well since about 1990 actually). I have owned the EOS 10D and 20d but I have not owned a full frame digital, I of course still have 35mm bodies lying around.

One of the things which is true with smaller sensors is that to get the same angle of view you need a shorter focal length lens.

So looking at the diagram to the left to get the same 73 degrees angle of view the smaller sensor (yellow line) needs to be much closer to the lens than the larger sensor (blue line).

This means that for the smaller sensor you need a much shorter focal length to get the same angle of view.

So more or less if you use a 21mm lens on your 35mm camera you need a 10mm lens on the 4/3rds.

If all things were as simple as this then there would be no problems, but they of course are not so simple. For a start the difference between the 35mm frame and the 4/3rds frame means that to get the same angle of view you need about 1/2 the focal length (again since the aspect ratio is different its not exactly that, but lets leave this simple).

As it happens designing a zoom lens of such short focal length that will work on a digital camera is not simple and is as such more complex than a 21mm on a 35mm. This means that your lenses may be more expensive.

I used for this experiment an old Olympus 21mm f3.5 lens on the full frame and an Olympus 9-18mm Zoom for the Panasonic 4/3 camera. As I said I don't have a full frame digital camera, so the full frame images are scanned 35mm film. I used 200ISO negative. Actually this turned out to be an interesting basis for also comparing the latest digital with 10 year old film based digital photography (yes, I call scanned film digital ... no ni).

So firstly lets have a look at the overall image from the 35mm:

Next (not quite the same angle I'm sorry) the image from the G1.

Looking at the overviews I think you'll agree i got the colour quite close ... to get the same look I started with the RAW file and processed that significantly using a few steps which I've learnt. Its interesting to see how the shadow details are similar on both but the digital still managed to have trouble with the white of the birch trunk. That might look ugly in printing if your not careful.

I still find that negative film has much better recording capacity when you need to deal with strong light. I certainly found this in my previous explorations with my 10D and 20D, but its interesting to see that nothing has changed, and even careful use of RAW files does not stop this.

Secondly I am immedately struck by how much nicer the background "bokeh" looks on the 21mm lens ... to me the 10mm looks harsh and distorted. The little Olympus 21mm is a sweet lens for sure.

Now onto the detail. Below is a screen shot of the images at 50% res on the screen. I find this a useful determination of how a print will look at close inspection. Bear in mind we're essentially looking at a print which would be 34.0 x 25.5 cm ...

Its really close isn't it ...

If you think that the top of the mushroom is looking a little fuzzy, thats because the 21mm lens has a shallower depth of field at f5.6 than does the 10mm lens, and the focus was 'just slightly' ahead of the mushroom ... need to be careful in focusing manually!

But depth of field will be effected as the important criteria there is the diameter of the aperture, not the f-stop. Please take a moment to read my article here to confirm that for yourself.

So to have an 10mm lens giving the same DoF as I get with my 21mm @ f3.5 I would need around f1.8 The Olympus 9-18 zoom is simply not that bright, its f4 so to get the same DoF I would need to stop the 21mm down to f8 From this I'm sure you can see that the "look" of images between the lenses focused on something close will not be equal if we get the f-stop the same.

I thought I'd try another angle, one that requires distance this should eliminate DoF and get rid of the significance of any Bokeh.

Full Frame


I think you'll agree that aside from colour matching them (close but no banana) the images look more or less the same (well and aspect ratio).

Differences in colour rendition is significant though as I think that the digital image (lower one) handles the subtle grades in the sky better than negative does ... this is something I've found before, that digital is better suited to capturing subtle shades than Negative is, and that negative works better when you have a wide dynamic to capture.

Looking at the detail there is surprisingly little in it. There is of course no difference between Depth of Field (as infinity is all thats in the focus here) but its also quite significant that the film scanned with the Nikon LS-4000 holds so well against the digital (or is it that the digital does so well against the film? you pick).

So, this cements in my mind that larger format (sensor or film) works best for wide angles. I would very much like to compare a 5D or other full frame sensor camera to the G1 as I think that it would be just fantastic. On the other hand the G1 costs so little that if you pop that onto your 300mm lens then instead of needing to buy a 600mm lens on a full frame camera you'll get better wildlife shots, this for example was a legacy FD series 300mm lens on my G1:

feeding time

Bang for buck that's cheaper than buying anything for the full frame.

My summary is that
  • If you want wide angle and want nice Bokeh then use a full frame camera and a 21mm lens
  • neg has better handling of sunny contrasty conditions,
  • wide angle on the G1 (small sensor) is ugly compared to full frame, but telephoto on the G1 or APS sensor is advantaged
  • unexpectedly the G1 pulls very close to the 35mm in outright resolution (which means that the main advantage of digital is still workflow and materials costs)
  • if desiring of shallow depth of field, when using lenses wide open aperture favors larger formats like full frame (but 6x7 and large format really needs movements to correct for and is harder to manage)


Noons said...

Couldn't agree more.

I'm finding the micro-4/3 concept a better and better alternative to big lumbering dslrs, for all intents and purposes as fun to use as, and on top one can easily mount just about any lens on them, which is even *more* fun!

The G1 is number one in my list at the moment, with perhaps the GF1 a close second. Video is not attractive to me, so the GH1 loses.

obakesan said...


I hear you ... If I'm gonna lumber something along I'd seriously consider a good 6x7 or 6x9 120 film rangefinder. With the G1 tossed in to the bag (at only 600 grams with a lens) you get the best of both worlds (and a nifty light meter for the Medium Format ;-)