Depth Of Field on telephoto

[tom mann]

But look at the vanishing lines in the telephoto photo: they are almost parallel.

[peteski]

I wonder if each photo was taking from the exactly same vantage point, but I do see what you mean.

[wcfn100]

I wonder if each photo was taking from the exactly same vantage point, but I do see what you mean.

Should be, since that was the point. 

Jason

[tom mann]

This is why those photos looking down railroad tracks look like roller coasters. Depth and perspective are reduced, making gradual grade changes look drastic.

[RBrodzinsky]

Should be, since that was the point. 

Jason

Unfortunately, they aren’t. The cars are not even at the same spot on the tracks

[peteski]

Unfortunately, they aren’t. The cars are not even at the same spot on the tracks

I was thinking the same thing.  The 105mm shot has the cars sitting in a different location on the track than the other 2 photos.

[wazzou]

This is why those photos looking down railroad tracks look like roller coasters. Depth and perspective are reduced, making gradual grade changes look drastic.

Yeah, but that is the awesome part of 1:1 telephoto photography!

[wazzou]

Unfortunately, they aren’t. The cars are not even at the same spot on the tracks

I would surmise the gon is a full car length further down the track based on its relation to the unballasted track.

[RBrodzinsky]

I was thinking the same thing.  The 105mm shot has the cars sitting in a different location on the track than the other 2 photos.

and the tracks are at a very different angle.

Doesn’t change Tom’s point, of course.

[wcfn100]

Unfortunately, they aren’t. The cars are not even at the same spot on the tracks

The first two are the same.   If I had shot the thrid exactly the same, I would have only gotten the right half the gondola and left half of the reefer into frame so I panned the camera to the left a little and rolled the cars into frame IIRC.  I think the tripod is the same.  By having a broader angle, the perspective should have gotten greater, but the 105mm focal length still flattens out the shot tremendously.

Jason

[peteski]

That explains why the angle is different.  It would have been interesting to see how the cropped image from the 35mm shot compares to the 105mm photo.  I think that this could have been done if you composed the shot using 105mm setting, then zoomed out and took the 55 and 35mm photos from the same exact location.

[DKS]

Telephoto lens simply has a narrower angle of view.

No, it's not "simply" a narrower angle of view. Here's an illustration showing what's going on, with a wide angle lens on top, and a telephoto lens on the bottom:



The green and blue boxcars have yellow circles superimposed showing the size of the boxcar ends relative to the field of view. Notice that, to the wide angle lens, the green boxcar appears smaller as compared to what the telephoto lens sees. Even when the wide angle image is cropped (dashed lines) so that the blue boxcar is the same size in both images, the green boxcar still appears smaller.

This is why telephoto images of layouts look "odd." Even though the depth of field (apparently) increases, the perspective is increasingly distorted. Same thing happens in 1:1 images.

 

[tom mann]

It took me a while to understand your drawing but it shows exactly what's happening here.

[Maletrain]

It is confusing me that some posters keep writing that use of a telephoto increases depth-of-field.  The way I use telephotos, they decrease depth-of-field, at least for a given image size of a particular subject.  And, that is what I remember from reading old Model Railroader layout photography articles and photography articles about portrait photography for people.  Portrait photographers typically choose a lens that is about double the "standard" focal length (say 105 mm for 35 mm camera) just so they can get a soft background.  They focus on the part of the face they want to draw attention to.  That is typically the eyes for an actual portrait, but can be lips or nose or eyebrows for commercial photographs trying to sell products for enhancing those parts.  The portrait lenses are chosen for good "bokeh", which is the aesthetic quality of the blurriness in the out-of-focus background.

I think that it is the wide angle lenses that increase depth of field for a given subject image size.  The problem with that is that it makes things look less flat than they really are.  Think about the pictures of a person's nose that make it look much larger when taken with a wide angle lens.

[RBrodzinsky]

David's diagram also helps to explain all those beautiful pictures of, for example, the sun (or moon) setting behind the Golden Gate Bridge - photographed with a large telephoto from Berkeley.  The Sun/Moon looks huge in comparison to the bridge (and possibly Alcatraz).   With a wider angle lens (say <50mm) the orb's size is more normal to what the eye sees.

The actual field of depth has little to do with focal length, being driven primarily by aperture.  A given lens' minimal focal distance does come into play more for model photography, since in most cases we try not to get too far from the models (or can't). And, of course, all depends on the composition one is looking for.