Posts Tagged ‘lens’

Camera / Lens Test

November 6, 2009

I’m always looking out of my apartment window at the grand view I have of Bangkok. The window faces west and I have a fine view all the way from Rachadapisek Road all the around to the tall office buildings in the Chatuchak District.

Today I noted someone had erected a new billboard on a building about three miles away to the north. I thought I’d see if I could read it from a photograph.

I have two Canon DSLR bodies: a 2004 vintage EOS-300D (the original silver Digital Rebel) and a 2006 EOS-30D.

My longest lens is the Canon EF 75-300mm F4-5.6 zoom (non-IS). It is good for a US$200 lens but of course not up to “L” standards.

I decided to do a test using the same lens on both bodies with the same shooting conditions. Fortunately today was clear in the morning so I had a good view.

I set the cameras up on a tripod with a cable release with these settings:

  • Aperture priority – F8. (I read this is the len’s optimum aperture)
  • ISO 100.
  • RAW
    • 3072 x 2048 for the EOS-300D‘s 6.3MP sensor.
    • 3504 x 2336 for the EOS-30D‘s 8.2MP sensor.
  • Pattern metering mode.
  • Zero exposure compensation.

I took photos at 75mm, 100mm, 135mm, 200mm and 300mm with the same lens on both cameras.

I imported all the pictures into Lightroom 2.4, converting them to DNG and the Pro Photo RGB colour space in the process. I used the Lightroom “Camera Landscape” camera calibration profile (which matches Canon’s Landscape Picture Style). I set the white balance to Daylight (5500K).

Here are the views taken at 75mm:

Bangkok Chatuchak District from the Apartment (EOS-300D)

EOS-300D

Bangkok Chatuchak District from the Apartment (EOS-30D)

EOS-30D

You can examine larger pictures on Flickr by clicking on each picture.

I was interested in the pink billboard at the centre of the pictures.

I used Lightroom to make two crops of the 300 mm pictures’ DNG files to show only the billboard. Here they are:

Billboard (EOS-300D)

EOS-300D

 

Billboard (EOS-30D)

EOS-30D

 

Yes! I could read them.

They are advertising new “Paradise” condominiums on Chaeng Watthana Soi 14. They have an offer of free furniture.

But I was surprised that the picture from the old EOS-300D seemed clearer. I think I applied the same processing parameters in Lightroom. I would have thought that the newer EOS-30D would have delivered a better result.

Maybe the EOS-30D’s sensor is dirty. I don’t have the courage to try to clean it myself.

I have not yet found anywhere in Thailand where I can rent Canon camera equipment. It would be great to rent a L telephoto lens for a few days to compare the results in real use.

Is there anything wrong with my methodology?

Camera Lens Depth of Field

October 31, 2009

I recently learned from Michael Willems that lens Depth of Field (DoF) is a law of physics. It depends on the aperture of the lens only. He taught me that it does not depend on the manufacturer, lens design or quality of the lens components or coatings.

A Canon 50mm F 1.8 will have the same DoF character as its Nikon sibling. A 50mm F 1.8 manufactured 50 years ago will have the same character as one today.

Other aspects of lens quality have advanced, for example aberrations, but DoF cannot.

I would like a choice – a fast lens that gathers lots of light so I can photograph the proverbial “black cat in a coal hole” but also one with good DoF so that its tail is in focus as well as its nose when the lens is fully open. But it can’t be done!

Unfortunately I do not have matched pairs of lenses to check this out for myself. I did have some fun taking some photos with my Canon EF 50mm F  2.5 “Compact Macro” at different apertures.

The F 2.5 is my fastest lens. I set up the Canon EOS-30D on a tripod, locked the mirror up and used a cable release. You can definitely see the increase in DoF as the aperture decreases. Beyond F 8 it does not get much better in practice as “diffraction effects” start to apply. I’m not sure if the diffraction effects are laws of physics too. It seems like we should be able to make improvements in that area using different formulae for optical glass that alter its diffraction capabilities.

By the way, there are some good tutorials on photography concepts at http://www.cambridgeincolour.com/tutorials.htm including one on DoF at http://www.cambridgeincolour.com/tutorials/depth-of-field.htm.

From the DoF tutorial the student can infer that the DoF is indeed a law of physics and not lens design because design is never mentioned.  There’s a theoretical DoF calculator where the brand or design of the lens isn’t a factor.

I ran a calculation using this tool with the following parameters:

  • Camera type: DSLR with a crop factor of 1.6X.
  • Actual lens focal length: 50mm.
  • Focus distance to subject: 0.5 metres.

Then I varied the aperture and got the following results.

Aperture Closest distance of acceptable sharpness (m) Furthest distance of acceptable sharpness (m) Total Depth of Field (m)
F 1.2 0.498 0.502 0.004
F 1.4 0.497 0.503 0.005
F 1.8 0.497 0.503 0.006
F 2 0.496 0.504 0.007
F 2.8 0.495 0.505 0.010
F 4 0.493 0.507 0.014
F 5.6 0.490 0.510 0.020
F 8 0.486 0.515 0.029
F 11 0.481 0.521 0.040
F 16 0.473 0.531 0.058
F 22 0.463 0.543 0.080

Note that if you use a full-frame 35mm sensor camera then the DoF is much greater. It varies from 0.007m at F 1.2 to 0.129m at F 22. Thus accurate focusing is more important on a crop camera.