Zoom lenses

[boBQuincy]

From Wikipedia:
For a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF; decreasing magnification increases DOF. For a given subject magnification, increasing the f-number (decreasing the aperture diameter) increases the DOF; decreasing f-number decreases DOF.

So, DOF is a factor of focal length, f/stop, and magnification (if the sensor size stays constant). DOF is further determined by the Circle of Confusion, which is open to interpretation and so is not a well defined number.

As for "better", the bokeh is really more a characteristic of a particular lens than of a focal length. Canon's 50mm f/1.8 and 50mm f/1.4 have very different bokeh.

 

[WDWFigment]

Although Bob is right about the bokeh being a characteristic of the lens rather than focal length, this does overlook a very important role that focal length plays: perspective compression. If you frame an object the same size in your shot at 18mm as you do at 200mm (obviously, you'd have to move away from it for the framing to be the same at 200 as it was at 18), you will have totally different backgrounds thanks to perspective.

My point is that with the same subject at 18mm and 200mm, the bokeh will definitely look different.

 

[seashoreCM]

As for "better", the bokeh is really more a characteristic of a particular lens than of a focal length. Canon's 50mm f/1.8 and 50mm f/1.4 have very different bokeh.

Hmmm. If the 1.4 lens is stopped down to f/1.8, is the bokeh still different after the finished pictures (as prints) for both are enlarged to the same size?

(Again, everything else -- camera body, subject and framing, post processing, etc. -- being the same.)

 

[boBQuincy]

Hmmm. If the 1.4 lens is stopped down to f/1.8, is the bokeh still different after the finished pictures (as prints) for both are enlarged to the same size?

(Again, everything else -- camera body, subject and framing, post processing, etc. -- being the same.)

Yep! The nifty fifty has a none too pleasing bokeh at all apertures, maybe that's Canon's way to get us to buy the f/1.4.

To clear up a confusing point about focal length and compression, focal length has no affect on perspective, only the distance from the subject does. Where much of the confusion comes from is that many photos taken with a wide angle are close up and many photos taken with a long lens are from far away. Still, if we take photos with wide and long lenses from the same position the perspective will be identical!

 

[GrillMouster]

Bob is exactly right. I was going to type a similar respose last night, but a sudden urge to play with my toddler preempted that plan. I just did a quick Google search to see if there was already a good explanation on depth of field, specifically how it's affected by focal length. The first result (link below) proved so satisfactory that I didn't bother looking at any of the other results.

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

In response to the OP's question regarding whether you'll get better bokeh with a smaller or larger aperture (larger f#), the answer is a larger aperture (smaller f#) will give you better bokeh. Bokeh refers to the quality of how the the out of focus areas are rendered, and is afffected by the roundness of the lens diaphram. So, two images with identical depth of field can have different bokeh. Generally, the wider the aperture, the more circular the diaphram becomes, and thus, the nicer bokeh effect. As you stop down the aperture, the diaphram's shape becomes more polygonal, producing what is generally considered less nice bokeh, as it's distracting.

 

[Groucho]

One way to see the difference is to look at the DoF markings on an older push-pull zoom lens (since newer ones are unlikely to have DoF markings!) The lines are far apart at the wide end of the zoom and come closer at the narrow end.

If you want specific numbers, you can check out the online depth of field calculator, which should give you some hard data.

For bokeh... roundness of aperture is very important (hence higher-end lenses having more blades) but if you're shooting wide open, the number of blades doesn't matter since they will be fully retracted and you should have a fully round pathway for the light at that point. The optical construction will determine most of the rest of the bokeh question, I think (but I haven't done much research into that side of things.) In the Canon 50mm F1.4 vs F1.8, I think you're talking about fewer optical elements (in the F1.8), fewer aperture blades, and a generally icky construction (as I think even the biggest fans of the lens would admit) that may make it more likely to have internal misalignments (just a guess.)

 

[PaulD]

It sounds like this question has been answered pretty thoroughly so I won't rehash it other than to say that bokeh assumes the shape of the aperture. A more angular aperture (i.e. less blades) will produce bokeh that is less smooth. In fact, at smaller apertures (say f/11 and above) this becomes very apparent. For kicks, take a look at this page:

http://www.diyphotography.net/diy_create_your_own_bokeh

By adding a filter in front of your lens you can create out of focus highlights that take on any shape you want. The example shows hearts but it can be anything. Has anyone tried this with a Mickey Mouse silhouette? That could be pretty cool...

 

[WDWFigment]

Okay, so that may not be the correct term (Code? anyone?) but this is a technique I've seen grow in popularity among Disney photo folks. Let's see some of your zoom exposures.

I'll correct the title if/when the correct term is "revealed" to me.

Here are my zoom exposures:



Clicking either image takes you to its Flickr page (where there is EXIF, explanation, etc.).

 

[WillowBelle]

How'd you do those? The second one I can make work out in my mind. The first though, with the train tracks almost in the center, almost looks like a double exposure picture.

Going to Gatlinburg for the first time ever this weekend. Excited because a friend of mine said they are still decked out in Christmas lights. Hoping to break in the fisheye and play with the Lensbaby a bit while I'm there.

 

[Todd_H]

Not sure of the photography term for it... "zoom during long exposure" or "zoom + long exposure" is what I have heard it called.

 

[Golf4food]

I took this one using my favorite prime lens...

I keep meaning to try the zoom technique and always forget. Gotta write it down or something.

 

[Evad]

Not sure of the photography term for it... "zoom during long exposure" or "zoom + long exposure" is what I have heard it called.

Love this shot Todd I like the way the words jump out you.

You and Tom have had much better luck then I when doing this. Mine look like crap.

Does it matter if you start zoomed in or out first.

 

[TheGoofster]

I'm not sure if this is the same thing, but after seeing this thread, I thought I would give it a try.
This is a hand held shot (I think the shutter speed was at 1/10).

I want to try this technique again, but with a tripod next time.

 

[JoeDif]

Taken during the fall with a 1 sec. exposure. I stood under a tree and pointed the lens up into the leaves and zoomed from 14mm to 42mm

 

[Icemann]

Taken during the fall with a 1 sec. exposure. I stood under a tree and pointed the lens up into the leaves and zoomed from 14mm to 42mm

thats cool can't even tell it's a leaf

 

[bob100]

those kind of "zoom" shots are nice but it's a lot easier to just use photoshop !

 

[sdshutterbug]

I love them all! I had it on my to-do list to take one of these during my most recent WDW trip, and never seemed to get around to it. :-(

 

[PhotographyDR]

Here is my version of SSE.

 

[WDWFigment]

Yep! The nifty fifty has a none too pleasing bokeh at all apertures, maybe that's Canon's way to get us to buy the f/1.4.

To clear up a confusing point about focal length and compression, focal length has no affect on perspective, only the distance from the subject does. Where much of the confusion comes from is that many photos taken with a wide angle are close up and many photos taken with a long lens are from far away. Still, if we take photos with wide and long lenses from the same position the perspective will be identical!

Maybe I'm not understanding what you're saying, but I didn't think this was the case. Focal length affects perspective, as does where you stand (and a combination of the two). If I were to stand 10 feet from the castle and take the same shot at 11mm and 200mm, the perspectives (as well as the subjects) will be different. If you stand in different locations to get your subject looking the same (see below), your perspective will be different, but that is by virtue of the focal length causing perspective compression. http://en.wikipedia.org/wiki/Perspective_distortion_(photography)

I'm not trying to contradict any of you guys (I know you both have more knowledge about photography than I)...am I misinterpreting what you're saying, or what?

Rough example of perspective compression:

 

[WDWFigment]

Creating the effect in Photoshop is fine if that's what you're after, but it looks too perfect for my liking (sort of like when you "create" smoother bokeh in post). The slight imperfections, among other things, are what makes it look cool when done in camera.

Plus I don't think it's possible to replicate perfectly with PS.