Lens Terminlogy

[osztertag]

<p>Hello All<br>

I do a lot of shooting at my daughters martial arts tournaments and most of the time I am using either a 28-80 or my 18-200, the convenience factor is high but I am finding these lenses too slow.<br>

So I am looking to buy a non-zoom lens, in the length that I end up shooting most of the pics at. By reviewing the metadata of a typical photo, it might say for example Lens 28-80, Focal Length 34mm. Most of my pics are in the 35+/-5 mm length according to the metadata reviewed. So my goal is to buy a 35mm fast lens. I can use my feet to properly frame the images.<br>

My question is, I shoot on a D90(dx), am I looking to by a 35mm as the metadata suggests or should I be looking for a ~24mm ? (24mm fx kinda = 35mm dx) Does ViewNx report dx or fx ?<br>

I hope this question makes sense. Thanks in advance for the responses.<br>

SteveO</p>

 

[ShunCheung]

<blockquote>

<p>(24mm fx kinda = 35mm dx) Does ViewNx report dx or fx ?</p>

</blockquote>

<p>That part does not make sense. A 24mm lens is always a 24mm lens regardless of whether you use it on FX or DX. That 24mm lens, however, would yield an angle of view on DX similar to that of a 35mm lens on FX.</p>

<p>What you need is a 35mm lens and you'll use it on a DX body, namely the D90. The most affordable way is the 35mm/f1.8 G DX AF-S, which is available below $200. A slightly wider alternative would be the Sigma 30mm/f1.4 at a much higher cost.</p>

[bruce_rubenstein]

<p>Using ViewNX take a look at what focal length you set the zooms to when shooting your daughter. This will give you a feel for what shooting distance you gravitate to, and then pick a prime that's close.</p>

[tommyinca]

<p>Nikon SLR Metadata (aka: EXIF) records the actual lens' focal length not the field of view. So you might want to get the 35/1.8 AF-S as Shun suggested. I also agree 35mm on a DX is perfect for martial art. BTW: It may be a bit short if your kids start winning the big turney :-)</p>

[bruce_brown]

<p>Steven: You are possibly over-thinking it ... if the data shows you use mostly 35=+, then, that's what you are looking for. Good advice above. What are you using the pix for ... how big ... what shutter speed and ISO/aperture? You should already have able equipment for the task of martial arts, it would seem ... I don't think you want flash for this, but is the lighting at these events also very low?</p>

[Peter_in_PA]

<p>You could get a 35mm f1.8DX for a couple hundred bucks, and add a 50mm f1.8D for another hundred or so and have a pair of fast lenses that will ROCK on a D90.</p>

<p>If you want fast at the 24mm length, you will pay very dearly for it.</p>

[CvhKaar]

<p>Peter,<br>

I agree... allmost..<br>

I would not get me a 50mm f1.8D, but the newer AF-s 50mm 1.8 G instead...</p>

[richardsperry]

Shun,

 

"That 24mm lens, however, would yield an angle of view on DX similar to that of a 35mm lens on FX."

 

<That part does not make sense.>

 

The angle of view of a lens does not change with what camera it's on. Just as the focal

length doesn't.

[Peter_in_PA]

<p>Richard.</p>

<p>The angle of view on a lens does indeed change with the camera it's on. It is wider on FX than DX. Which is why it is true to say that a 24mm lens yields an angle of view on DX like a 35mm on FX.</p>

[raczoliver]

<p>A focal length is a focal length, whether you use that on DX or FX or anything else. That's all you need to know if you are not planning to start switching between formats in the foreseeable future. If the metadata says 35mm is what you use most often, get a 35mm, not a 24mm lens. You are making it more complicated than it is. The 35mm f/1.8G is probably a good choice.</p>

<p>In a way you are right that no physical property of the lens will change, but by changing to a larger format, you are recording more of what the lens projects, that's why the field of view is larger.</p>

[Ed_Ingold]

<p>A zoom lens is best used to crop the picture in the camera once you have established the composition you want. Composing "with your feet" is not the same as framing with a zoom lens. Perspective is determined by distance from the subject. Moving closer or further changes the perspective, hence the relative size of near and far objects. You achieve the same effect with a zoom lens as by cropping in the darkroom, without discarding any image area.</p>

<p>Sometimes you can get closer or further away from the subject. You can switch prime lenses or flick a ring on a zoom lens. At a wedding or event, you may not have time to swap lenses, and nobody cares about higher image quality if you miss the shot altogether.</p>

<p>Prime lenses are usually smaller and lighter than zoom lenses of similar quality. They often have fewer elements, which improves contrast and resistance to flare and ghosting. The fastest zoom lenses are typically f/2.8, but it is not hard to find prime lenses two stops faster (f/1.4) or more. When you can select an ISO of 25,000 or more, speed is not as important as DOF control with faster lenses. A good prime may be noticeably sharper than a mediocre zoom lens, but that is not always the case.</p>

<p>In short, choose lenses for what they do or not do as you practice photography, not on some nebulous superiority factor.</p>

[jeff_livacich]

<p>Richard, you are right in absolute terms. But cropping part of the image circle does yield a different angle of view in the final image.</p>

[richardsperry]

Jeff,

 

If there is a difference in the image between the two cameras.

From the same lens, with the same focal length.

Then the lens acts differently on respective DX to FX camera, correct?

 

The angle of view is different on the two different camera, the angle of coverage does not change.

Correct?

[Peter_in_PA]

<blockquote>

<p>The angle of view is different on the two different camera, the angle of coverage does not change. Correct?</p>

</blockquote>

<p>Correct in absolute terms perhaps., but I think that Shun said "angle of view". That's what people normally need to know.</p>

[raczoliver]

<p>I hope Steven is not paying too much attention to this debate, because it will just confuse him even more. I noticed that the majority of times the most heated debates about technical subjects come down to disagreement about phraseology, while everyone knows what the other one means.</p>

<p>Steven, get a 35mm f/1.8, that's what you want:-)</p>

[hapien]

<p>Out of topic kinda,</p>

<p>I'd recommend 50mm f/1.8D AF Nikkor, very fast focusing and nice image quality.</p>

[osztertag]

<p>Thank you all for the advice. <br /><br />Things I learned <br />- choose my words much much more carefully ;-) else that can of worms gets opened.<br />- Metadata reports actual focal length.<br />- Bruce - you are almost correct I am not over thinking it...actually didn't think enough<br />- Oliver - great insight.<br>

Here is a pic from yesterdays games, I was further away from the action and I had to use my zoom in a poorly lit venue, and I didn't bring my 50 prime...need to make that Christmas list for faster glass.<br>

Thanks to all for your insight and shared wisdom.</p>

 

[osztertag]

<p>Thank you all for the advice. <br /><br />Things I learned <br />- choose my words much much more carefully ;-) else that can of worms gets opened.<br />- Metadata reports actual focal length.<br />- Bruce - you are almost correct I am not over thinking it...actually didn't think enough<br />- Oliver - great insight.<br>

Here is a pic from yesterdays games, I was further away from the action and I had to use my zoom in a poorly lit venue, and I didn't bring my 50 prime...need to make that Christmas list for faster glass.<br>

Thanks to all for your insight and shared wisdom.<br>

<img src="http://d6d2h4gfvy8t8.cloudfront.net/14461372-md.jpg" alt="" /></p>

<p> </p>

[ShunCheung]

<p>Steven, your new image indicates that you were shooting @ 52mm, ISO 2000, f5.6, and 1/160 sec. If you get a 50mm/f1.8 AF-S, it should be possible to bring it up to 1/500 sec and maybe the ISO down a bit and without keeping the lens wide open at f1.8.</p>

<p>I think the 50mm/f1.8 AF-S AF a bit faster than the f1.4 version. For sports, you are better off getting the f1.8.</p>

[jeff_livacich]

<p>Richard, the lens does not change. What I said was the angle of view on the <em>final image</em> changes.<br /> On DX, the effective angle of view, i.e., the part of the lens' angle of view that is in the final image, is narrower than the angle of view the lens is capable of accepting and projecting to the image plane. I don't think that's news to you.</p>

[mike_halliwell]

<p>I'd second the sigma 30mm 1.4, but agree that the 50mm version (Sigma or Nikon) would get you a bit closer. </p>

<p>As mentioned above, these questions often devolve down to DX & FX phraseology. How about a new Acronym, <strong>RFOV</strong> for <strong>R</strong>ecorded <strong>F</strong>ield <strong>O</strong>f <strong>Vi</strong>ew?? We all know the Focal Length and Field of View doesn't actually change depending what body it's on, CX, DX or FX, but what's finally recorded does!</p>

[richardsperry]

"I don't think that's news to you."

 

I know how it works. I'm clarifying terminology, which is the topic of this thread.

 

1) Angle of view is determined by the camera/ sensor or film size, but dependant on angle of coverage of the lens.

 

2) Angle of coverage is determined by the lens, and independant of camera/sensor or film size.

 

3) Focal length of lens does not change(of course), but affects angle of coverage of the lens.

 

4) Goto 1.

[mike_halliwell]

<p>I need some additional clarification on 3)...</p>

<p>The area and therefore the <strong>coverage angle</strong> of a 24mm PC-E shift lens is BIGGER than a 24mm AFD......101 Deg v 84 Deg. The PC lens's Output Cone makes a bigger image circle at the focal plane with-in which you can place the film/sensor to produce the effect you want. However, the <strong>recorded angle</strong> is fixed by focal length.and format!</p>

<p>The bottom line is that the recording format ie CX, DX or FX <strong>does not</strong> change the physical/optical attributes of a lens but <strong>does</strong> determine the Recorded Field Of View </p>

<p>You only have to look at the 2 versions of 70-200mm AF-S to find that coverage angle is different for the same focal length......mkI was insufficient to cover the FX format, whilst mkII was. The lens design plays a large part too. Equally <strong>some</strong> DX lenses work on FX, most don't.</p>

<p>Maybe I'm taking this too literally and the word '<strong><em>affects</em></strong>' in 3), is deliberately a bit loose as opposed to the word '<strong>determines</strong>'..... ;-)</p>

<p>As long as the lens's emerging light cone fills (or covers) the recording format size at the focal plane, that's fine. The terms <strong>angle of c</strong><strong>overage </strong>and versions there-of are not helpful in these format discussions other than the obvious 'insufficient coverage' DX lens on FX problem.</p>

[richardsperry]

"As long as the lens's emerging light cone fills (or covers) the recording format size at the focal plane, that's fine. The

terms angle of coverage and versions there-of are not helpful in these format discussions other than the obvious..."

 

 

What's the difference between the light cone and angle of coverage?

 

I think it's important to state that angle of view is determined by the camera format, and angle of coverage is from the

lens. Several posters, including myself, confused to two in previous posts. They are different, and describing or

defining the difference seems important in this discussion; for it makes a difference in how the respective images turn

out.

 

"The bottom line is that the recording format ie CX, DX or FX does not change the physical/optical attributes of a lens but does determine the Recorded Field Of View"

 

No it doesn't. But how the images turn out is definitely different. I don't think that many photographers believe that the physical properties of a lens change dependant upon the camera used. That would defy physics and logic.

[richardsperry]

I have not heard of the term recorded field of view before. Anyway, angle of view appears to be the mire

correct or accepted term for describing that.

 

 

For say that there is no film in the camera, and you are looking at the ground glass or viewfinder, nothing needs to be recorded, and there still exists both the angle of view and the field of view. Recorded field of view would not exist in this case, correct?