Author Topic: Depth Of Field on telephoto  (Read 1154 times)

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tlaswell

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Depth Of Field on telephoto
« on: November 09, 2018, 11:39:30 AM »
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I was at a show this summer with the NTRAK group.  A guy came by and wanted to use part of our layout as a backdrop for a photo.  He wanted to take a picture of a purchase he had made.  Our modules are 2 feet deep at best and the tracks run along the front of the module.  After placing the locomotive on the track he stepped back and placed his camera on a tripod at module level 2-3 feet away.  Would he of done this to overcome the Depth Of Field problem?  Does it work?

If this is the case then I will have to try that once I get my own module set up.  I guess I would need lots of light since most telephoto's aren't very fast.  I've tried it at the last show with my old Point and Shoot but my hand wasn't steady enough for what light I had to play with.

RBrodzinsky

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Re: Depth Of Field on telephoto
« Reply #1 on: November 09, 2018, 12:12:49 PM »
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Well, there are a lot of other factors that come into play, as well.  What focal length was the lens set to; what was the shutter speed; what was the aperture (f-stop)?  And, each lens has its own unique minimum focal distance.

The key for depth of field is to use a higher aperture (smaller opening) setting. But, the smaller the opening, the less light you are getting, so you need to increase the exposure (slower shutter speed).  Once you get slower than about 1/30th of second, blur caused by hand motion can easily ruin a photo; so use a tripod to steady the camera.

When I do layout photography, and try to make the photo look "realistic", I will tend to shoot from about 1.5-3 feet away, use about 70-90mm (35mm equivalent) focal length, and set  aperture to f9-f13.  This will put most objects in the photo between 2-4 feet from the lens into crisp focus.   Then, just adjust shutter speed for correct exposure.
Rick Brodzinsky
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wcfn100

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Re: Depth Of Field on telephoto
« Reply #2 on: November 09, 2018, 12:20:11 PM »
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  Does it work?

Sort of.

It will help keep the background in focus but at the expense of the perspective creating a very flat image.

Jason

Maletrain

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Re: Depth Of Field on telephoto
« Reply #3 on: November 09, 2018, 10:02:16 PM »
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Given a lens of a particular focal length, the actual distance between the points where it is blurry because it is too close and blurry because it is too far (i.e., the "depth of field") gets bigger as the focus point gets farther from the lens.  But, the image of a specific subject also gets smaller.

Given a specific distance from the lens to the focus point, the depth of field gets bigger as the focal length of the lens gets shorter (wider angle lens).  But, again, the image of the subject also gets smaller.

Changing focal length also changes perspective.  For instance, using  telephoto lens to take a picture looking at a locomotive at an angle will make the locomotive look shorter, and using a wide angle lens will make it look longer. So, it pays to not get too far away from a "standard lens" when taking a picture you don't want to be distorted.  ( A standard lens is approximately 50 mm for a 35 mm film size, and scales from there for other film/sensor sizes.)

The best way to increase depth of field is to make the aperture smaller, which lets in less light.  So, either the exposure needs to be longer or the film needs to be faster (or the sensor set to a higher sensitivity).  The problem with higher film speed is grainy images and pastel colors.  High gain sensors also give washed-out colors and "noise" in the form of spots.  The problem with longer exposure times is blur from camera shake and/or subject motion.

Sooo, what people typically do for increasing depth of field is choose a distance that gives them the subject size they want (with a lens that gives them the perspective they want), set the "film speed" (sensor gain) for the highest they think will give them a decent quality image, and then stop the camera down to the smallest aperture that still allows a fast enough shutter speed to not get blur from camera shake.  Using a camera/lens with "image stabilization" can gain 2-to-3 stops in aperture size without blur.  Using a good, stable tripod can give sharp images with multiple seconds long exposure times. Shining more light on the subject will decrease needed exposure time, allowing for greater depth of field before exposure times get long enough to cause blur.

I guess I should point out that spending a lot of money on a "faster" lens with a bigger piece of glass is not going to help in this situation, because stopping the lens down for max depth of field means you are not using that extra glass to let in more light.

Learning all of this by "doing" in the old "film days" cost substantial money and took a lot of time to see the results after the lab finished developing the film and sent the pictures back to you.  These days, with the instant nature of digital photography, it is easier and best to take some time practicing with your camera to learn what it can do with the adjustments you can make.

The confounding thing about digital cameras is that most of them have automated programs to set the sensor gain, aperture and shutter speed without your input.  Or, maybe you input whether you are shooting "scenery", "portrait", "sport","night time" etc. as a "mode", and the camera uses different criteria for adjusting the combination of sensor gain, aperture and shutter speed to give a properly exposed picture.  If that is what you have, then something like "scenery mode" will try to maximize depth of field, while "portrait" may try to minimize depth of field, and "sport" or "action" may also minimize depth of field while trying to minimize action blur.

« Last Edit: November 10, 2018, 09:23:06 AM by Maletrain »

Cajonpassfan

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Re: Depth Of Field on telephoto
« Reply #4 on: November 10, 2018, 11:18:15 AM »
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@Maletrain, thanks for the concise write up. I guess I already knew all this, but it's nice to have it neatly summarized in the context of layout photography.
And yeah, I've got to stop being lazy and get the tripod out more often....
Otto K.

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Re: Depth Of Field on telephoto
« Reply #5 on: November 10, 2018, 03:03:38 PM »
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Sort of.

It will help keep the background in focus but at the expense of the perspective creating a very flat image.

Jason

This.

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Re: Depth Of Field on telephoto
« Reply #6 on: November 12, 2018, 09:39:33 PM »
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This.

But in that context in a real life situation, is t that the way our eyes would see it as well, flat?

tom mann

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Re: Depth Of Field on telephoto
« Reply #7 on: November 13, 2018, 10:51:17 AM »
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But in that context in a real life situation, is t that the way our eyes would see it as well, flat?

No, the telephoto compresses the depth of field and makes elements in the scene appear to be on the same plane. The angles of perspective appear to be reduced.

Maletrain

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Re: Depth Of Field on telephoto
« Reply #8 on: November 13, 2018, 12:53:54 PM »
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No, the telephoto compresses the depth of field and makes elements in the scene appear to be on the same plane. The angles of perspective appear to be reduced.

That is what I meant about the length of a locomotive looking shortened by a telephoto lens when it is pictured at an angle, rather than flat-on.

tom mann

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Re: Depth Of Field on telephoto
« Reply #9 on: November 13, 2018, 01:54:53 PM »
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That is what I meant about the length of a locomotive looking shortened by a telephoto lens when it is pictured at an angle, rather than flat-on.

When people use a 100mm macro and take a photo of a locomotive at an angle, the far side of the locomotive looks as big as the close side.  Arnold did this with their S1 photos - it just looks weird.

wcfn100

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Re: Depth Of Field on telephoto
« Reply #10 on: November 13, 2018, 02:26:42 PM »
+1
Here's a comparison shot with a Nikon D40X.

35mm


55mm


105mm Macro


Jason

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Re: Depth Of Field on telephoto
« Reply #11 on: November 13, 2018, 04:58:59 PM »
+1
Those five freight cars joined together to become a super train.

chicken45

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Re: Depth Of Field on telephoto
« Reply #12 on: November 13, 2018, 05:09:05 PM »
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Those five freight cars joined together to become a super train.

There's that subtle Mann Brand Humor that only like 2 people will laugh.
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David K. Smith

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Re: Depth Of Field on telephoto
« Reply #13 on: November 13, 2018, 05:31:33 PM »
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Those five freight cars joined together to become a super train.

Somehow that's got to be Voltron-related...
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peteski

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Re: Depth Of Field on telephoto
« Reply #14 on: November 13, 2018, 06:06:41 PM »
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Here's a comparison shot with a Nikon D40X.

35mm


55mm


105mm Macro


Jason

Just for kicks I cropped Jason's wide angle (35mm) photo to look the same as hsi telephoto (105mm macro) photo. Telephoto lens simply has a narrower angle of view.

This is the 35mm photo cropped to what the 105mm macro lens sees.
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