In an old article, I mentioned that a Canon 18-55mm at high end isn’t that different than the Nikon 17-70mm kit lens in focal length (reach).
My statement was:
After all, you can just shoot the Canon at 55mm @ 1.6x and then crop it down to a 6 megapixel photo and it will look close enough to the Nikon D70 at 70mm at 1.5x.
I’m surprised nobody has called me out on this statement!
Let’s do the math on the 35mm equivalents: a 55mm 1.6x = 88mm and 70mm 1.5x = 105mm. How different is that? A trick I learned from my Physics graduate advisor: All useful numbers in the world are dimensionless parameters. We have to generate a dimensionless parameter to give meaning to this difference: what we need here is a ratio. How about comparing it to the 35mm format?
55mm/35mm = 1.6. Applying my “crop†statement: 1.6*(Sqrt(8M)/Sqrt(6M)) = 1.8. The Nikon example works out to: 105mm/35mm = 3. Hmm that’s not the same at all!
An exception proves the rule
What led to my statement was the general rule of thumb: extra focal length makes a difference on the low end than the high. In this case the 70mm on the Nikon still has 50% more reach than the 50mm on the Canon.
Of course we’re talking about 20mm here. When does 2mm make a big difference?
Going wide
A recent Flickr thread debated between the purchase of the Sigma 10-20mm f/4-5.6 and the Tokina 12-24mm f/4.
Now if you interested in the actual answer to this question, I politely refer you to this venerable Nikonians article which does the best job of comparing them I’ve seen. How? Well after slogging through Ken Rockwell’s treatise1 I can say that he came to basically an identical conclusion.
The part I want to bring up is when the discussion focused on if you can notice the difference of 2mm. Let’s apply our battery of knowledge.
12mm*1.5/35mm = .51 and 10mm*1.5/35mm = .42.
Yep, that difference (20% I could have just as easily did the ration 12mm/10mm and got the same number) is noticeable. In the thread, I claimed it made “a huge difference at wide angles†but that statement is incorrect. It should have been “makes a noticeable, but not huge difference.â€
So when does 2mm make a huge difference?
The answer is when you compare the 10.5mm Fisheye Nikkor to my 12-24mm.
The field of view on it is 180 degrees, while the 12-24mm Nikkor has 99 degrees at wide angle. Wow!
Why? Because it’s a fisheye!
As I mentioned in the thread:
The 10.4mm Nikkor has defishing capabilities if you use Nikon Capture, Peter iNova’s action, LensFix or DxO Optics pro.
I mention this because if you want to go really wide, that’s probably the way to do it. You have a fisheye and a really wide angle. You’ll lose resolution near the edges and composition is going to be a pain, but a 10mm fisheye goes much wider than a 10mm rectilinear so the FoV is phenomenal.
Just sayin’…
How to get even wider
Take a bunch of shots with your 12-24mm and then stitch it together in spherical mode. If you squint a bit, you can pretend you have a fisheye. 🙂
NetService Ventures, Menlo Park, California
Nikon D70, Nikkor 12-24mm f/4G
(15 exposures 1/320sec-1/200sec @ f/8-f/7.1). iso 200, 12mm (18mm)
Of course, you could do the reverse. To know what a de-fished Nikkor might shoot, here is a rectilinear stitch:
Yosemite Falls Overlook, Yosemite National Park, California
Nikon D70, Nikkor 12-24mm f/4G
5 exposures (1/400 – 1/250sec) @ f/9, iso 200, 12mm (18mm)
I wish I could capture the vertigo I felt taking that shot.
I’m curious how Canon was able to do this. Here is and found their optical design in Bob’s review compared to Nikons and they’re not the same at all! I’m curious if this is an example of the uniqueness of the EF-S mount (the mount allows lens elements to be further back in the box. The idea is that you don’t need as powerful “a telephoto in reverse†optics in order to make the light telecentric (important for digital photography).
Does anyone know?