Category Archives: Digital

Digital Photography (general topics)

Digital SLR sensor size, crop factor and magnification

There are lots of discussions on this topic all over the Internet, so I figured I may as well add my own. Obviously, I enjoy photography, but I’m not a professional. I’m a software architect and developer, though, and that provides for a different angle of view, so to speak, on the concept.

Let’s get some things out of the way first…

  1. A 300mm lens is a 300mm lens, always.
  2. There are other factors that go into the overall quality of an image beyond the number of pixels and how large it is. This is not a quality discussion.

For the purposes of this article, I’m going to use the Pentax K10d, K20d, and the Canon 5d Mark II. The first two are APS-C (1.5 crop) and the Canon is full frame (equivalent to 35mm film size). The specifications of interest are:

  • Pentax K10d – 2.7 million pixels per cm2 on APS-C.
  • Pentax K20d – 4.0 million pixels per cm2 on APS-C.
  • Canon 5d Mark II – 2.4 million pixels per cm2 on FF

Doing some ratios here, the K10d has 1.125 more pixels per area than the Canon. That means, over the same physical region of sensor, the K10d captures at a higher resolution and thus gets more detail in that space. So, that ratio makes a 300mm lens resolve comparable to a 337.5mm lens with a field of view equivalent to a 450mm lens in comparison to the Canon. The Canon will capture a larger field of view, but will contain less detail in the same space as the K10d. Of course, there’s an advantage the Canon has: if you put a lens around the 337.5mm mark on it, it will capture the same detail, but it will have a much larger field of view because it’s FOV will also be for 337.5mm. More picture for the same detail.

The game changes with the K20d though… The pixel ratio between it and the Canon is 1.666 (repeated) and so the K20d will capture comparable to a 500mm lens with a 450mm field of view. So, to match the detail, the Canon would need a 500mm lens, but then it gets less of the picture because the field of view is for 500mm, not 450mm.

Understand, however, that these numbers are not absolute numbers, they are comparison numbers between two cameras. If the Canon has a density to match the K20d, then there is no way for the K20d to outresolve it and the comparative magnification would change. The numbers can only work when you make a relative comparison between two cameras or, more specifically, two sensors.

So, what does that mean? Well, the crop factor of the sensor is a crop, you’re definitely getting less of the image circle of the lens. However, the resolving power of the sensor may, potentially, give magnification beyond the focal length, if the lens can provide the detail to the sensor to capture it, but the magnification is relative to another camera. If the “native” capability of 35mm film is, for the sake of this discussion, 4.0 megapixels per cm2, then relative to traditional film, the Pentax K20d simply crops. If it is less, then the K20d magnifies, if it is larger, the K20d shrinks it.

So, hence the answer to the question… Yes, maybe. Of course, when you get down to the brass tacks about your camera, be it digital or film, the real question to ask is: do you enjoy using it? Nothing else really matters.

The world of the “fanboy”

Have you ever seen a message board thread about Apple versus Microsoft? You’ll know what I’m talking about if you have…

I’m not going to specifically talk about them, though, this is more about another arena that kind of surprised me: photography. Specifically, I was reading a forum thread on a Nikon oriented site about the price reduction Pentax made on their dSLR cameras. I gather, based on some comments, that Nikon has recently increased their prices, but that wasn’t really the nature of the thread. There were some interesting comments though…

“desperation and publicity. pentax is as good as dead. noone cares. stick a fork in em”

Based on the superior writing skills of the poster, we can only take his word as gospel. Pentax isn’t dead, this prediction comes up year after year.

“who cares? the pentax brotherhood is as rabid as they come. defending products that are irrelevant to the world today. pentax… we dont care, go away inbreds. even sony is more relevant in todays market than you are.”

Another awesome writer with a bad accusation. As a point worth noting, the products in question are basically something that takes in light in a controlled manner to shine it on a capturing surface such as a sensor or film. In that context, Nikon, Canon, Sony, Pentax, and a host of others are making very relevant products.

“pentax sells crappy cameras today. it’d rather buy a sony now than a pentax.”

Notice a trend in the writing? It’s a bad assertion anyways since every professional photography review utterly disagrees with him.

I could go on, but it’s not really worth it. It’s more to illustrate something: as soon as you see a message like this, you can freely judge the opinion of the poster as worthless. They are not capable of providing any form of useful information and you will only be steered wrong if you listen to them.

Now, in regards to the best camera, I’d suggest you try them out and find what works best for you. For me, that was Pentax, but your mileage may vary. Understand that all of the traditional makers are producing very good equipment, be it Pentax, Nikon, or Canon amongst others. The gear is there, it’s really a question of the photographer and no camera in the world is going to make a bad photographer great, but a great photographer can make a bad camera great. It’s not the tool, it’s who is using it.

Testing my Vivitar 2x multiplier

First off, let me start by noting that this multiplier is ancient. There are no contacts for any automation so when you use it it’s old school photography and you have to control the aperature, shutter speed, and focus. Yes, you can do stopped down metering, but it’s not necessary. Of course, the multiplier causes a loss of two stops, so f/16 had to become f/8 when I added the multiplier into the mix in order to get the same amount of light at the same shutter speed. In this case, I used the Sunny f/16 rule and shot all the pictures at f/16 (or equivalent) and 1/180s.

The baseline shot, at 50mm (approximating the field of view of a human eye) is:

Now, here is the series of a Sigma 70-300m lens (70, 100, 200, and 300):

Now, the series of a Sigma 70-300m lens (70, 100, 200, and 300) using the multiplier:

As you can see, quite the impact! The series with the multiplier is slightly darker, a result of there being slightly less light hitting the CCD for capture, but given I snapped these quickly and didn’t do any clean up other than resizing, I’m pretty impressed at the optics in the Vivitar device as I didn’t readily detect any quality degradation. Of course, my eyes may not be as keen or critical in that regards as a professional might be.

As a side note, I never realized how weather beaten that silo was until I got a lens that close to it…

Some essential tools for the amateur dSLR photographer in the wild

If you have a digital SLR, there are some great tools, software or hardware, out there that are either free or won’t totally break the bank. Of course, photography can be an expensive hobby, so your mileage may vary here.

In the Field

I bought an iPod Touch as a handy field computer when taking pictures in the great outdoors and this, alone, is pretty handy because you can store all sorts of reference material on it. I don’t use it for music (I have another iPod for that), I use it for photography. That brings me to a very handy application for it if you like nature photography: DoF calculator. This little app for the iPhone/iTouch allows you to select your camera model (or enter the baseline information directly), specify distance, focal length, and aperture to get not only the depth of field but also the hyperfocal distance. There are two or three other DoF calculators, but I found this one to the best. It’s also a massive $1.99 to buy.

I like doing nature photography and spent a fair amount of last summer wandering conservation areas taking a variety of pictures. At one point, during a camping trip, I got an opportunity to take some pictures of a great blue heron catching dinner. The pictures came out okay, but the problem was my telephoto is only 300mm maximum and I really needed a bit more than that. Needless to say, once bitten, twice shy, I don’t want to be caught with some awesome opportunity and no suitable lens to capture it, but the price of telephoto lenses above 300mm gets pretty expensive… There is a solution, though, and it’s significantly cheaper: a 2x teleconverter. Okay, at $370 it’s not cheap, but an 800mm lens is $7800! The doubler takes my 300mm telephoto to a 600mm telephoto, which isn’t quite 800mm, but it also didn’t cost me close to $8000. You can also get a 1.4x teleconverter for a little less money and little less range.

Bear in mind that a teleconverter will have some effect on the overall quality of the result, but it’s generally minimal and there are ways to deal with it after the fact. Also, a lot of lens faults are more to the edges and the average dSLR has a smaller sensor than standard 35mm film, thus dropping off the outer edges of the circle.

Get a good carrying case! I got a Lowepro Slingshot 300 that allows me access to a variety of compartments without removing the backpack from my back. A very handy thing when it’s not always feasible to take it off.

Get a tripod! Now, getting a good one can be expensive, so you’ll have to balance your needs with the price you can pay, but a tripod is essential to outdoor photography. Remember, a lot of outdoor shots will be taken with a telephoto and that makes camera shake much more likely and that includes cameras with shake reduction. A good rule of thumb is that your shutter speed should be no slower than the reciprocal of your lens length. So, for example, with a 200mm focal length, go no slower than 1/200th of a second. Better yet, just put the camera on a tripod. So, which tripod? Well, in the wild, you want to get something that is both light and sturdy. Mine is a 4 segment carbon fibre from Manfrotto, but there are very good cheaper options out there, so shop around. Just make sure that you can carry it for extended periods of time and that it has a hook for weighing it down in windy conditions.

That’s the tripod, but what about the head? Most consumer tripods come with the tripod head already, but most of these aren’t really the best option for nature photography. It’s okay when you have plenty of time to line up the shot, but most wildlife aren’t anywhere near that patient. So, a good tripod head can make a world of difference and so some features to consider are:

  • Quick release – allows you to remove the camera from the tripod without fuss.
  • Easily adjusted – I have a “joystick” style head that allows me to freely and quickly move the head by just gripping it.
  • Levelling bubble – useful if you want to make sure you’re square.

That’s the basics, but you’ll probably accumulate more stuff as you go. I’ve been adding to my field collection with plamps, translucent filters, small reflectors, etc. The hardware is the expensive part, you get hooked and then you start adding to your collection so that you can do more.

On more thought, don’t discount the use of a flash in the field. Mine, sadly, is a little under-powered, but it is still handy for filling in where the shadows are quite deep. The little flash on the camera itself is often useless in this role, so it’s worth looking for something a bit more powerful.

Back at the Computer

Lets face it, the best piece of software for post-processing your digital images is Adobe Photoshop (I have CS3), but it comes with a hefty price tag. There are, however, some alternatives that will let you get the job done and done nicely. Before I get into those, you are shooting in RAW format right? If you aren’t, then get a bigger storage card and find out how to do it for your camera model. If you shoot in JPEG, you’re giving up enormous control of your image for absolutely no gain, so switch your camera to RAW and forget it ever had a JPEG setting. Now onto the tools…

Raw Therapee is, by far, the best piece of software you can get for RAW image processing outside of Adobe Photoshop. It supports a huge variety of formats, can create JPEG files from your source (which is why you don’t need your camera to do it for you), and gives you a lot of fine-tuned control over white balance, exposure, colour balance, and more. The best part? It’s absolutely free and runs on Linux and Windows.

The GIMP (aka Gnu Image Manipulation Program) is the closest you’ll get to Photoshop without having Photoshop. It does a ton of stuff, is constantly being worked on, has a huge array of plugins and enhancements, and can be used for much more than image processing. Best of all, it’s free and runs on absolutely everything.

In terms of printing the final result, inkjet printers have come a long way. Yes, you can take your SD or compact flash card off to the nearest department store or photography place to get them printed, but if you’re like me and bought a dSLR because you were unlikely to take your film in for development, then a printer is a must. As with most things, price often determines quality and that’s basically true for inkjet printers as well, but it also very true for the paper you use. Avoid printing on regular paper, it’s just a waste of your ink because the final result will look like crap regardless of how good your inkjet is. Get proper paper.

For the printer, what you get will determine a lot of what you can print. Your basic point and shoot can, usually, print a nicely bordered image on 8.5 x 11 stock, anything larger will require software scaling and that can be iffy at best because the software has to “guess” (interpolate) the each new pixel being added. It’s easy to artifact as a result. On the dSLR front, the resolution of the camera will somewhat determine the approximate native size of an unscaled print. Mine, which is 10.1 megapixels, is about an 11 x 17 print unscaled.

So, based on what you want to print, pick your printer. Personally, I highly recommend the Canon Pixma Pro 9000, which is what I have. It has 8 ink tanks and will print upto 13 x 19 inch output. The tanks have a reasonable life and are individually replaceable and not too badly priced. The output quality is superb, Canon claims photolab quality and I believe it. Mind you, this the higher end of the pro-sumer market, and there are excellent alternatives for the less avid for a lot less money. Shop around.

By the way, don’t buy a printer under the assumption you’ll save money. You probably won’t. The advantage of your own printer is time and instant gratification, along with a lot more paper options, it’s not money.

Conclusion

Okay, dSLR photography isn’t cheap, especially if you want to get out there and take great shots of our wilderness. However, if you have reasonable financial means, you can do some really great stuff and not break the bank doing it. Build up your collection slowly and have fun.