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Photography Question 
Ken Pang
 

Is this DoF right??!!


This can't be right... I went to a DoF calculator, (BTW Jim, you should put one on Better Photo! I've found a javascript one that's in the public domain!)

I'm trying to get an upper body portrait. I found to compose a shot like that at 200mm, (Wanted the flattening effects of a telephoto), I had to be about 3m away. I got the photos back that appeared to have no sharp points in the photo - so I went to a DoF calculator, to figure out how much DoF I had at the f/4 I shot at. About 5cm.

I recalculated as if I had shot at f/8, and it's still only 10cm.

I intend to redo these portraits, but I want to shoot with Velvia (ISO 50). There is no way I can shoot at f/16 or slower and get a steady shutter speed. Especially since I don't want to lug a tripod around. (Outdoor portraits)

Does anyone have any suggestions? How is this normally done? I want at least 50cm depth of field so that head chest and arms is sharp, but the background is not. (Background can be from 30m to 500m away, so that should not be a problem)

Thanks!


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1/8/2002 8:21:57 PM

 
Ken Pang   Oh, by the way, I was shooting 2 hours before sunset (6:30pm) while the sun was low on the horizon. on a ISO 400 speed film, I was getting 1/200th shutter speed at f/4. Obviously, at ISO 50 and f/8, I can't take a good picture.


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1/8/2002 8:42:55 PM

 
Jeff S. Kennedy   For starters let me warn you about using Velvia to shoot people. Velvia gives awful reddish skin tones. If you need to use slide film (and slide film is not ideal for portraits due to it's contrast) I would strongly recommend Provia. It gives much better skin tones and it is available in ISO100 and 400 which will help you with your perceived DOF problem.

To your problem. I'm not sure why you are so interested in getting the head, chest, and arms sharp (unless this is a nude). The main thing to worry about in a portrait is that the eyes are sharp. If you must handhold, use the slowest shutter speed you are comfortable with on that lens, shoot at the corresponding aperture, and focus on the eyes. If this isn't giving you the DOF you desire then use your tripod. It's pretty simple. BTW Provia is very pushable so if you find that even the ISO 400 isn't allowing you to do what you want you can always push it a stop.


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1/8/2002 11:50:19 PM

 
Ken Pang   Thanks Jeff,

I've used Velvia before and it's turned out really well. The person I took a photo of themselves was a very big contrast though: White skin, black hair and very bright clothing.

However, one thing I didn't quite like is the eyes sharp, and the ears already fuzzy look. It's good for romantic shots, but I just wanted more of a modelling look to it.

It's all experimental at the moment anyway. It's not paid work or anything I really particularly want to keep. I'll use your suggetions and keep trying!

Thanks,

Ken.


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1/9/2002 4:27:33 AM

 
Hermann  Graf   200 mm is not the optimal focal length for portraits. Even if DOF is ok., the pics appear "flat". Better try 80, 105, or 135 mm.


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1/10/2002 3:34:21 AM

 
Jeff S. Kennedy   I'm going to disagree with Hermann here. I've shot portraits with focal lengths up to 300mm (and some of those were head shots) with great results. Those shorter focal lengths are more versatile in that it's easier to take full length shots without having to stand across the street from your subject but the longer focal lengths can deliver excellent results.


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1/12/2002 1:19:25 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Ken,
Yes, that's about right! Shoot at f/22 if you can; it will get you 20-25cm DoF. With a magnification of about 1:14, even at f/32 it's a little over 30cm. At this magnification, changing focal length won't help, it will only change the perspective and how out of focus the very distant background appears.

I'll second Jeff K.'s remarks about critical focus point for portraiture: "The eyes have it!" Especially true if the subject is engaging the camera (and therefore the viewer). There should be a very compelling reason to deviate from that. It depends on what you have envisioned for the photograph.

Depending on level of enlargement desired, Provia 400 may also work in lieu of pushing Provia 100F and paying for "push 2" custom processing. Jeff K. would have to comment about pushing 100F two stops versus using 400.

-- John


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1/12/2002 6:46:42 PM

 
Ken Pang   Whoa, stop there John. :) I picked up something interesting.

Well first, I should say that this isn't _exactly_ portraiture. I'm trying to create for her a couple sexy (but modest) shots. So I am doing a lot more that just the eyes. (Though for some of them, I really do want to draw attention to her high cheek bones, long eyelashes and stunningly clear blue eyes. The fact that she has no experience posing or modelling is also a bit of a frustration, since I can pose her in a particular position, and by the time I am back to my camera, she's moved subtly.

ANyway - What I wanted more info on is "How out of focus the background is". There are places I can pose her where the background is at least 500m away. There is almost no chance of the background being sharp.

Given that fact, is there some way I can change the focal length/distance/aperture combination to get deeper depth of field without going down to ridiculous f/22 apertures?


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1/12/2002 7:51:01 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
 
 
 
Ken,
How I arrived at a magnification of 1 to 14:
You stated you were using a 200mm lens at a distance of 3 meters. Assuming this is to the film plane, it's 2800mm to the rear lens node. 200mm rear lens node to film plane, to 2800mm subject to rear lens node is a magnifcation of 1:14.

How "out of focus" background becomes with focal length:
Circle of confusion size grows faster behind the DoF as focal length increases. This makes very distant background (as compared to subject distance) more blurred looking as focal length is increased (if magnification remains the same; i.e. same subject size in viewfinder).

The problem with trying to change DoF using only focal length:
This only works for very low magnification. The question arose in another forum about DoF and focal length if magnification remains constant. Changing focal length does not appreciably affect DoF until subject distance is approximately the same or less than the DoF.

I've made a chart showing how changing your focal length and then your subject distance to keep her the same size in the viewfinder doesn't change the DoF. It does show how changing aperture affects the DoF. I use a very conservative maximum circle of confusion size: 0.025mm for 35mm film format. The DoF calculator you used was likely 0.030-0.033mm. My DoF numbers are likely about 80% of those from the calculator you used (e.g. 4 cm versus 5 cm).

-- John


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1/12/2002 10:49:21 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Wouldn't upload the image :-(
-- John


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1/12/2002 11:27:59 PM

 
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