How to Calibrate Your Zoom Lens To Capture What Your Eyes See
One of my favorite lenses for journalism and street photography is the wide to telephoto zoom. Now we can shoot everything from landscapes to portraits with just one lens. However, there are times when you need a prime “normal” lens to capture exactly what your eyes are seeing. Most of us can adjust our zooms to approximate what were seeing but it usually leads to a less than desirable result.
We know that most modern cameras get the focal length from the electronics within the lens, however, most cameras do not display this information until after the shot. We also know that all lens manufacturers display some type of focal length information marked on the zoom ring. Most of these markings are only approximations of the true focal length and do not take into account the crop-factor of dx type sensors. So how can we be sure our lens is set to a “normal” focal length?
An easy solution is to calibrate your lens to your eye. You are probably thinking, “How is this possible”. We can do so using the same method we use to focus your fathers trusty pair of binoculars.
Calibrating your lens is simple. First, find a suitable static target to focus on. With both eyes open, adjust your camera so that one eye is looking through the viewfinder. Focus your lens at your target as you normally would.
Now, with both eyes open and focused on your target, slowly rotate your zoom ring until your image is sharp and your eyes no longer feel strained. Refocus your lens if necessary and repeat the procedure. You will get to a magic point where your focus and depth perception are “normal”.
At this point, you should be able to remove and replace your camera from your eye with no apparent change in your target. Your lens is now calibrated to your eye. You can optionally create a small mark on your zoom ring that corresponds to the mark on the body. Later on, when you need a “normal” lens, just rotate your zoom ring to that mark, and voila.
Gary C. Millwater has been a freelance photographer since 1976. Originally from New Jersey, he has traveled all around North America, Mexico, and the Bahamas looking for that next great shot. After moving to Florida in 1987, he was forced to trade in his lenses for a “real job”. He now shoots just for the fun of it. His non-published work can be seen at millwater-photography.com
20 Responses to “How to Calibrate Your Zoom Lens To Capture What Your Eyes See” - Add Yours
March 7th, 2009 at 9:40 am
I’ve had this thought too in the past, but I don’t think it works quite as described.
Consider a Canon 1DsIII with a .78x viewfinder magnification, compared to a Canon 5DII with .71 viewfinder magnification. The 5D will need to zoom in closer to get an view in the viewfinder that matches what is seen with the naked eye, so the recorded image will be different. However, if we’re looking for something that matches what we see, given that they are both “full frame” cameras, we’d expect the same recorded image in both cases.
Your process describes how to match the naked eye to the view in the viewfinder, but has nothing to do with matching the naked eye to the resultant image. I suspect, although I am not sure, matching to the resultant image would also involve how large the print is and distance from camera to subject and viewer to print, and several other factors.
Also, your statement “Most of these markings …do not take into account the crop-factor of dx type sensors” is incorrect. Focal lengths are focal lengths and have nothing to do with crop. The focal length of a lens doesn’t change when you put it on a different camera. What does change is the apparent magnification of the image.
March 7th, 2009 at 10:42 am
Thanks for the wrap up, but I’d be interested to hear the author’s response to Silverhalide.
March 7th, 2009 at 1:32 pm
Wait…what? I’m not sure what this post is saying other than how to manually focus a lens…
March 7th, 2009 at 2:10 pm
It’s not how to manually focus a lens — it’s how to adjust your zoom level to “normal”. But honestly, it’s really simple:
1. Look at an object.
2. Look at the same object through the viewfinder.
3. Zoom until the object in the viewfinder looks like the object as you saw it with your own eyes.
Alternative to step 3: Zoom until the object looks like you want it to look in a photo — whether wide, close, or “normal”.
For reference, in 35mm film terms, a 50mm focal length is “normal”, meaning it has the same field of view as human eyes. On Nikon DX cameras, this is about 35mm. On Canon 1.6x crop cameras, this is about 30mm.
March 7th, 2009 at 4:47 pm
This is a great tips and really useful for me :) Thanks~
March 8th, 2009 at 12:05 am
I’m not sure that field of view is correct because even full frame sensor/35mm film is a cropped version of what the human eye sees.
I’ve always taken the “normal- as the human eye sees” to mean perspective. ie at wide angle the distances between objects appear greater than real life while telephoto everything appears stacked together.
I’m probably wrong but I would have thought that 50mm would be “normal” on most dslr’s regardless of the crop factor. The distance between the sensor and the lens is basically the same as the 35mm film days. Someone with a knowledge of the physics of light might be able to either correct me or explain it better.
March 8th, 2009 at 12:06 am
Great tutorial by the way, I just tried it with my 18-55mm kit lens.
March 8th, 2009 at 6:12 am
I have to agree with dcclark above. The 50-55mm range will be “normal” for any lens. What the “sensor” sees brings into play the 1.6x factor (APS-C) as with my Canon 400D and 18-55mm lens. What the sensor sees absolutely must include the x factor and in those terms, normal is around 30mm. The 18-55mm lens is stated (at 55mm) to be moderate telephoto range of about 85mm in standard 35mm jargon. Only with a full-frame sensor can this process be used to approximate “normal”…I hope no one is totally confused now.
March 8th, 2009 at 7:04 am
Before I was having trouble manually focusing the lens, thanks to this essay I know what to do now .
March 9th, 2009 at 1:49 am
I am curious to find out if what is normal is the same for everyone… I did this with DSLR and its APS sensor and my “normal” was 5omm which is about 70 mm when converted to 35mm format.. That seems long for “normal.”
March 9th, 2009 at 3:30 am
I also got 50mm on a 40D as “normal,” which translates to 80mm.
March 10th, 2009 at 6:45 am
I think that perspective and field of view are 2 different things. The sensor size will affect the field of view, with the crop factor. The perspective is left intact, as far as I see it. Therefore, I would suppose that everybody should be getting results around 50mm regardless of sensor size.
I just tried it with my 40D and it came around 55mm.
March 10th, 2009 at 1:06 pm
That doesn’t work at all. I got 70mm as normal on a 18-135mm lens and a DX body. And I know by experience that normal is around 35mm on a DX.
This may work if the viewfinder has no magnification. But that is not the case for most cameras.
March 11th, 2009 at 8:20 am
Actually I’m not surprised that the responses to this article are way too analytical. The premise of the article was to give the user a way to capture an image close to what they are seeing, before they take their shot. Indeed, when we concentrate on something we humans tend to have tunnel vision. If that were to equate to a focal length, I would have to agree on the 70mm range. If we were to relax our vision our fov or aov would be much greater, probably around the “normal” range of around 43.3mm. However, the only way to know for sure would be to take an image after the calibration, enlarge it to life size, then compare that image side-by-side with the subject. But for those it may have helped for whatever reason, your welcome. That’s the whole point of this website…to share anything that may help others in their photographic endeavors. If optical physics is what your after, then there are websites for that too.
March 13th, 2009 at 1:11 am
My zoom lens is a 200-500 you insensitive clod !
Apart from that, that’s one way to set the dioptric setting in the visor.
OTOH, I don’t really see what the point is in geting the camera to see what the eye sees. I might be atypical but I can’t recall ever wanting to use any one of my cameras that way. I use them to capture something specific.
Oh, and it seems to me that with APS sensors, the “magic number” is closer to 35-40mm than to 50.
March 13th, 2009 at 2:00 am
Don’t know if this is the same thing, but this is also how I shoot fast moving sports (volleyball, hockey, soccer). I keep both eyes open, with my field of view calibrated to what I actually see (as described above) and then I can follow the action as its happening and I know before something enters the frame that it is about to. Much less panning around (”follow the ball”) this way. My “outside” eye sees everything happening outside the frame and as it transitions into the frame my “inside” eye (the TTL eye, if you will) picks it up. As the author describes above: “At this point, you should be able to remove and replace your camera from your eye with no apparent change in your target.” I know I have it exaclty right when I no longer feel like I am looking through a camera but that I am just watching the game. It kinda feels like being “in the zone” and I get the best photos in those moments.
March 13th, 2009 at 1:43 pm
Tonya, it seems as though were on the same page. Someone finally got it… Like you, I’ve been using this routine for years shooting motor sports, cycling, and recently, extreme sports. Perhaps others will catch on and find this procedure useful.
March 17th, 2009 at 9:49 pm
Mr. Millwater
I have often thought about this and wasn’t aware of this quick and easy way to find the “normal” view. I have just used the zoom calibration of around 35mm. This works with any zoom in the “normal” range and with any camera. Thanks for the informative post.
March 22nd, 2009 at 2:10 pm
Without getting into whether it’s useful to match what you see in the viewfinder with what you see with the naked eye, I thought I’d mention that dpreview has an interesting blog entry on normal lenses which touches on some of the issues discussed here such as whether normal lenses match viewing angle, and how viewing distance is related.
http://blog.dpreview.com/editorial/2009/03/what-is-a-standard-lens.html
August 12th, 2009 at 10:04 pm
I’m late but this website is huge.
Ok Gary, your article is perfect. To match the two views, we have to do it like you said. There is no other way.
I’m a photographer but also a tv cameraman. Tv Lenses have big zoom ratios, 14x, 16x, 20. When i want to put on screen the same “perspective” relation of size distance, etc, of objects, I use this technic. People have to understand, that there are two different things we are talking about here. One is the relation between objects ( the notion we get of the distance between two trees distant apart 50 meters in our line of view, when we use a 50mm or a 300 mm, is huge – mostly the concept of perspective for photography). The other thing is how wide we can see without moving our eyes. I, have an angle of peripheral view, with detail, of about 120º horizontal. With no detail but still can see you move, 175º. Used to be 190 on my 20’s I’m 50 now). Meaning, I can see more wide than my canon 15mmf2.8 fish eye. But if i take picture with it, the relation of things in distance is diferent from how I see it.( strait line in front, not the optical distortion).
This means, that to have the same notion of reality of my eyes, i use the two eyes method, to try to see as wide as my vision, i use a wide angle.
Just one thing more, for those who didn’t understood it, this is not a technic to manually focus a lens.
For that, you can do two things, first, just do it, manually. Second, also with auto focus of, press halfway, and rotate the focus ring at the same time. When your active focus square sensor( the one that illuminates red) lights, the object is in focus. This is a technic widely used by pros. And it is explaned in some user manuals of some cameras.
BR
Fernando
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