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Halabriel

Lens Jargon

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I am pretty new at this, and up until now have been happily bumbling along on my own. :)

Then I join this forum and KAPLOW!! a whole new world. :)

 

My current (OK one of my current) problems is lens nomenclature.

 

I have a Canon Ixus in a canon housing, and I have two Inon lenses, one for close up small stuff (Macro) and one for big stuff (Wide Angle). All very simple so far.

My wide angle lense is an Inon UWL-105-AD, where 105 relates to the angle of view

My macro lens is an Inon UCL-165-AD, where 165 relates to the focal distance

 

Now when I read the forums you guys speak in tongues! :(

Your wide angle lenses are rated 10mm focal, but don't mention angle at all

Your macro lenses are either 105mm (OK) or 60mm (Better) - what about my poor 165 (I thought it was good until now)

 

Is this just an Inon quirk? or is it that P&S (jargon for Point and shoot - see I am getting there) also have a macro function that is addative to the macro lens :)

 

Please guys and gals - help out a newbie

 

Cheers

 

Hal

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The naming conventions you are talking about there are quirks of Inon.

 

For DSLRs, we generally talk about the focal length. Back when SLRs were film only, this wasn't confusing. Double the focal length, and you cut the field of view - width and height - roughly in half. So wide angle lenses had short focal lengths (less 50mm) and telephoto lenses had long ones (more than 50mm). 50mm was the "standard" focal length.

 

Unless you're spending $2200 for a Canon 5D, DSLRs have sensors that are smaller than film. Generally, 1/1.6th the height and width of a 24x36mm frame of film. So we talk about 10mm being the "same" as 16mm in film, because the field of view is the same. These cameras, like my Canon 350D, don't change the focal length, they just capture the center of the image to give a smaller field of view.

 

If we talked about lenses in terms of field of view, this would a bit simpler, but we don't. We talk about focal lengths instead.

 

A 60mm lens isn't "better" than a 105mm lens, nor is a 165mm lens "worse." They just have different effective magnification and field of view.

 

For macro photography, a longer lens means you can take a 1:1 image from farther away. Which is nice if you can't get closer, because the subject is skittish, or there's something in the way, like a crab hiding in some coral. But it does mean you have a larger minimum focal distance, so you can't get as close physically, so there's more water between you and the subject, which can sometimes mean backscatter.

 

Personally, I've yet to run into a situation where a few inches is a drawback. In fact, I have a 60mm macro lens, and I just bought a 100mm macro lens for use on my next trip. My experience was that I wanted a longer lens on several occasions.

 

The other main drawback to a long lens is limited field of view. Not for macro photos, but of photos of other fish. The longer the lens, the smaller the field of view, and the more likely it is that you might actually have to back off to capture the entire fish. Now we're talking distances of feet, and backscatter and under-lit subjects are a real possibility.

 

On the other hand, with the 60mm lens the smaller fish were running away before they filled the frame. Which is why I want to try 100mm. But 60mm is really too long to take an effective photo of something big like a turtle. Octopi were about the largest critters I took with 60mm.

 

- Gus

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Setting the Ixus to macro , then clipping on a UCL-165 gives me a working distance of 100-180mm from the subject. How close do you get with a 60 or 100mm lens?

 

Does anyone have experience of stacking these Inon UCL lenses?

 

Cheers

 

Hal

Edited by Halabriel

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The minimum focus distance for the EF-S 60mm f/2.8 at 1:1 is 200mm / 8".

The minimum focus distance for the EF 100mm f/2.8 at 1:1 is 310mm / 12".

 

The Inon-165 has a focal length of 165mm according to my web search. I've not dealt with this sort of attachment lens myself, but I think it's pretty clear that if you're focusing at 100-180mm, you're probably in so-called "super macro" terroritory, larger than life size.

 

I say "so called" because technically, it's not supposed to be "macro" until you get more than 1:1, yet it's conventional to call stuff as small as 1:4 "macro" sometimes.

 

- Gus

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So, let me get this right....

 

A DLSR macro lens with a focal length of 60mm has to be 200mm away from the subject?

My Inon lens focuses at 180mm away from the subject.

 

So they are similar end results, just different ways of doing it?

 

Cheers

 

Hal

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Oh oh oh....just got it

I eventually remembered my high school physics.

 

Lightbeams coming to a lens are considered parallel.

When they strike the lens they are bent to converge at a point.

The distance from the lens to the point of convergence is the focal distance of the lens.

You want your recording media at this point of convergence (in this case the digital sensor)

 

 

post-19209-1208923937_thumb.jpg

 

With a DSLR the lens goes directly onto the camera body and the light is focused on to the sensor

With my Canon, the lens goes onto a mount, which goes onto the housing, so it will be naturally further away from the sensor, thus need a longer focal length ... following along so far.

 

The focusing distance is the point infront of the camera where the light can no longer be considered parallel when it strikes the lens and is independant of the lens' focal length

 

I think...

 

Cheers

 

Hal

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Hi Hal,

 

I'm wondering if your setup has a real 165mm focal length or an apparent 165mm focal length. Focal length is related to the field of view angle but it also depends on the size of the sensor. Because all film cameras, and expensive digital DSLR cameras, use the 35mm format that is what is considered the standard. On my Canon 20D, the sensor is 1.6x smaller which means the field of view is also 1.6x smaller and the focal length appears to be 1.6x larger. So on my Canon 20D the 100mm macro lens behaves like a 160mm lens on a full frame camera. Digital point & shoot cameras have substantially smaller sensors and in adds the focal length that is reported tends to be the apparent focal length. So if your camera has a sensor that is 3x smaller than the 35mm standard format then the 165mm lens would really just be a 55mm lens (3x55=165).

 

To get 1:1 macro the distance from the sensor to the object needs to be 4x the focal length of the lens (I'll spare you the math/physics on that one). For macro lenses with internal focusing, where the lens does not change length as you focus, it actually turns out to be a bit less than 4x because of some trickery where they reduce the focal length of the lens as you get close to macro distance (that way they can keep the lens shorter and lighter). So the 100mm Canon macro achieves 1:1 macro at 31cm instead of 40cm and the 60mm macro has a closest focusing distance of 20cm instead of 24cm. This distance is from the sensor to the object, the distance from the tip of the lens to the object, the working distance, is normally a little less than half that (14.9cm for the 100mm Canon macro lens).

 

If you are more the experimental type, you should assemble your camera, take a ruler and move it closer to your lens until you can only just focus on it. Measure the distance from the lens to the ruler and you have your working distance. Take a shot and see how many millimeters of the ruler fit across the width of your image. If that corresponds to the width of the sensor for your particular camera then you obtained a 1:1 "life-size image". If you get 36mm across then you have the equivalent of life-size on film format (which has 24×36mm dimensions).

 

Hope this has helped more than it added to your confusion

 

Bart

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Let's try something to maybe help clarify things. The simplest camera possible is a pinhole camera: you have a lightproof box, some sort of sensor at one end (it could be 35mm film, a photographic plate, or a digital sensor - doesn't matter), and a tiny pinhole at the opposite end to let the light end. This gives you the definition of "focal length": the distance that the pinhole has to be from the sensor in order to cast the same image as the lens does.

 

You can also figure out the "field of view" through simple trigonometry: it's directly related to the focal length, and the size and shape of the sensor (think of a right angle triangle, with the upright being the focal length, the horizontal being half the sensor, and the hypotenuse giving the limit of what the sensor can see, and then imagine the hypotenuse extending out beyond the end of the box.) This gives rise to the concept of a "crop factor" (also misnamed as the "focal length multiplier"): if the sensor is half the size of a 35mm negative in its linear dimensions, a given lens in front of that sensor will produce the same field of view as a lens with double the focal length in front of a 35mm negative.

 

Pretty much all digital compacts have tiny sensors, much smaller than a 35mm negative. They quote their lens focal lengths as "35mm equivalent". So my PowerShot S50 has a 7-21mm lens (roughly), but it's quoted as a 35-105mm lens, because that's the range that would give the same field of view on a 35mm camera as my PowerShot is capable of capturing.

 

When you get into the digital SLR market, there is no direct mention of the 35mm equivalent. All lenses are sold based upon their true focal length; it's up to the buyer to convert to a 35mm equivalent. For example, I bought a Canon EF 24-70mm lens. On my 20D, that gave me a field of view equivalent to a 38.4-112mm lens on a 35mm body. Now that I have a 5D, it comes back to a 1:1 equivalence, and I'm loving it. But I digress.

 

Focal length has absolutely nothing to do with whether a lens is a macro lens or not. There are macro lenses (that I know of offhand) with focal lengths of 60mm, 65mm, 100mm, 105mm, and 180mm. I'll ignore the 65mm because it's a special case (because of the way it's built), but the others all have one thing in common: at their closest focusing distance, the image that they form on the sensor is the same physical size as the real life object they're focused on. So if I took a photo of a five cent piece using a macro lens on a film camera, and had the film developed, I could put that five cent piece over the top of the film and cover the image exactly.

 

The Inon numbers mean absolutely nothing to me, because I don't know how they came up with them. For all I know, they could be the age of the Inon founder's children in months. But hopefully the above gives you an idea of what we mean when we talk about focal lengths, macro, and such like.

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Borrow or buy a copy of "Basic Photography" by Michael Langford, Focal Press ISBN0 240 51592 7 which explains most photo theory at a reasonable level.

 

It does sound as if Inon have their own descriptive system though! IF your original post is correct, then it sounds as if they are departing from conventions in an attempt to make it easier to understand the functions of the items they supply - and from your post it sounds rather like this hasn't worked.

 

In general terms, angle of view should be easy enough to appreciate and if you think of what was referred to as a 'standard lens' as having a field of view of about 45 degrees, anything between 45 and 90 degrees being wide-angle and anything exceeding 90 degrees being a super or ultra wide (weitwinkel), you will see that your Inon (105 degrees?) lens may converting your lens into super wide territory.

 

The 165 has me stumped as if it relates to focal length, it doesn't mean anything other than a very narrow field of view on your Ixus, however if it gives you macro abilities and works......

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Yeh, my feeling too.

 

If it works, I call it whatever you want me to call it.

This thread was really to help me understand what everyone else was talking about in their posts, which I now do (however imperfectly)

 

Cheers everyone

 

Hal

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Hi all,

I'm using the same lenses with a Canon IXUS 500 at the moment. The UWL-105 is the andle of view- 105 degrees. The UCL-165 is the magnification- 1.6x magnification. I'm also stacking two UCL-165's to do 3.2x magnification. It works really well, but you have to get really close and lighting can be a bit difficult. With a bit of practice, you can get some really good super macro shots.

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