sensor

35mm equivalence for street photography

35mm Equivalence for Street Photography

Transient Eye has posted an excellent piece on how sensor size affects various camera systems. It’s framed for street photographers who generally don’t do much shallow depth of field work and so, the advantages of full frame cameras are lessened.

For better or worse, the 35mm film format has become the standard against which all other file/sensor formats are compared. But understanding how to achieve identical images from cameras with different sensor sizes – i.e. images equivalent to a 35mm “full-frame” camera – is very useful if you use several different formats.

The diagrams are, if nothing else, a great way for those who don’t understand “crop factor” to finally get it.

Cleaning the sensor on a DSLR

As many people with Digital Single Lens Reflex cameras know, the downside of changing lenses is the possibility (more like inevitability) of dust getting on both the mirror and the sensor inside the camera. The sensor is the large piece of silicon, either CCD or CMOS, that is covered with light sensitive transistors that capture the image. The mirror, which is part of the optical/mechanical configuration of any SLR allows the photographer to look through the viewfinder and see exactly through the lens. Dust on the mirror is a visual annoyance but does not get recorded on the image. Dust on the sensor can show up on the image.

To be totally accurate, the sensor itself is not fully exposed; it’s covered by a “low pass filter” that is actually what the dust is getting on. In more serious cases dust can get under the low pass filer and directly on the sensor. This is very bad news but also quite unusual.

One could call this a major design flaw of DSLRs but all brands except one suffer from it. Olympus EVOLT cameras have a filter between the shutter and the sensor that is charged so that dust will fall off of it. I’m not sure how well it works but it sounds like a step in the right direction.

All other DSLRs from Nikon, Canon and every other camera maker that makes cameras with interchangeable lenses suffers from this problem. I suppose one could buy any camera and just the right single lens and never take the lens off and not suffer from the problem, however, few cameras ship new without a bit of dust on their sensors so some dust might not even be from users opening up their cameras in high wind at the beach.

Tips: Before changing lenses turn the camera off and let it sit for a second so the charge on the sensor diminishes so as not to pull in more dust. Leaving the camera turned on and the sensor charged runs the risk of pulling in more dust.

Change lenses inside or in a protected place when possible.

Plan ahead and have the right lens on the camera before you leave for a shoot, the fewer changes the better.

How do you know you have a dirty sensor?
If you shoot Av (aperture priority or preferred) and have fast lenses and shoot with them wide open, you won’t notice a dirty sensor much if at all. However, as you stop down (reduce the size of the aperture) you will start to see the dust, if you have it.

Put any lens on your camera, set the camera to Av mode (aperture preferred) and stop down to f/16 or smaller.

Take a picture of a white wall or a white computer screen.

Look at the picture on your computer. If you see spots, you’ve got dust. Note, it’s useful to try to remember where the spots are so that as you clean you can see if you’re making any progress when you check again.

Here is an extreme example from ©tommycuellar on Flickr:

sensor dusted :(

What to do?
The simplest thing to do is this (and Canon and Nikon recommend it):

1. Buy a Rocket Blower and have it on hand. It’s useful for other camera and lens cleaning chores as well.

2. Find a clean place in your house to work, as dust free as possible. No moving air in the room if possible.

3. Read your manual and learn how to change the mode of your camera so you can clean the sensor. On my Canon 20D there is a menu item called “Clean Sensor” that locks the mirror up automatically and leaves it like that until I turn the camera off. Remember to use a fully charged battery when you lock the mirror up for sensor cleaning.

4. Once the mirror is locked up, take the lens or the body cap off the camera, hold the camera with the opening facing down and use the Rocket Blower to blast some air inside onto the sensor. Do not touch the tip of the blower to any part of the camera. Be careful.

5. Put a lens back on the camera and turn the camera off. This will cause the mirror to fall back into place.

6. Test for dust again by turning the camera on, setting it to Av mode, stopping down, taking picture of white wall and looking at it. If you got rid of all the dust, you’re lucky. If not, did you get any dust off? Did anything change? If nothing changed it may be necessary to try another method.

Warning: do not use compressed air to clean any part of a camera, especially the inside. Generally compressed air has a liquid propellant that can come out with the air and you do not want this propellant on your sensor.

Charged Brushes
Two companies make special brushes for picking dust up off sensors: VisibleDust and Copperhill. I’ve tried the Copperhill brush and it pulled only the very loose dust off of my sensor, anything that was really sticking didn’t move at all with this method. However, this method is pretty safe, it would be hard to scratch the low pass filter covering the sensor with one of these brushes. Both of these methods use a clean brush that is slightly charged, either by blowing compressed air through the bristles or by brushing back and forth on a special piece of material. That charge is what is lifting and holding the dust onto the brush (hopefully). The downside of these brushes is that it’s possible to introduce more dust into the camera or simply move around the dust that’s in there.

Sensor Swabs and wet cleaning
Sensor swabs are plastic spatulas with lintless micro-fiber material attached to the end. You put a few drops of special optical cleaner on the end of the swab and drag it across the sensor to “mop up” dust. I bought both the swabs and cleaner from Filter Connection. The manufacturer is Photographic Solutions and they also sell it. For about four months I kept my sensor relatively clean with this method. The liquid evaporates immediately and leaves no residue behind. However, some dust and dirt may not respond to even this method.

Canon Service Centers
You can take your Canon DSLR camera to any of these service centers and they will clean the sensor at no charge. If there is damage to the sensor they will give you an estimate for a repair if the camera is out of warranty or you caused the problem.

If you don’t live close enough to drive to one, call the nearest one and ask about shipping the camera to them. Generally there is no charge for cleaning the sensor. There may be a small shipping charge to get the camera shipped back.

Canon has three US service centers:

Jamesburg, New Jersey: 732-521-7007
Elk Grove Village, Illinois: 847-364-0900
Irvine, California: 949-753-4200

Locate a Canon Service Center

Canon Service Center, Jamesburg, New Jersey
I’ve had my Canon 20D for about a year. I use only prime lenses (fixed focal length) so I change lenses often. In the early days, I left my camera on and violated all the rules for avoiding dust. I’ve used every method mentioned above and I’ve done a decent job of keeping my sensor reasonably clean but recently I noticed that each time I stopped down smaller than f/5.6 I was looking at a lot of dust on my images. I tried one last cleaning and knew I needed professional help.

I called Canon’s New Jersey Service center and spoke with Jamie, a very nice woman who runs the front desk. I told her my situation and she told me to come down and they’d take good care of me. She was empathetic although she did warn me that if they found problems beyond dirt it might lead to a repair that would cost money and mean leaving the camera with them.

For those of you who live near enough, here’s where Canon’s New Jersey Service Center is.

Get off the New Jersey Turnpike at Exit 8A. Bear right off the ramp. Take a right on Cranbury/South River Rd. Go a few miles, then look for Ridge Rd. / Rhode Hall Rd. Turn left on Ridge and Canon will be on your right. Turn right into the parking lot and then left into a smaller customer service parking lot. The service center is right in front of you.

I drove down, waited an hour while they cleaned about ten cameras including mine. Jamie told me to come back whenever I needed a cleaning done, monthly if I wanted. Some New York pros have it done monthly to multiple bodies, no charge.

I’ll use a blower and be careful from now on but knowing that Canon offers a service like this is reassuring to me.

Note: A number of the people in the waiting area thought I was nuts to have driven down from Connecticut and told me that there were a few closer Canon authorized places to have sensors cleaned. Jamie gave me a list of them and I called one in Connecticut. If the camera is within its one year warranty the cleaning is free and takes ten days. It the camera is outside the warranty the cost is $165. I think I’ll drive to New Jersey and have Canon do it.

More Resources
Cleaning Camera Sensors
Understanding Digital SLR Sensor Cleaning
Cleaning Digital Cameras