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Help requested on preventing hot spots
Old 06-08-2005, 04:33 PM   #1 (permalink)
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I continue to have problems with hot spots in my images (see below). My studio is very small (about 15 x15) so I have my lights (Novatrons as they are all I can afford) dialed way down and use either softboxes or umbellas to diffuse. I am metering on what I believe are the highlights and letting the midtones to blacks take care of themselves. As you notice on her chest and arm in particular, I still got hot spots and this is after dodging with PS-CS. I remember metering on her face/chest and shooting with that exposure which I believe was F8 in both locations. In addition, I used a "warm/soft" filter to further soften the image. This is an improvement on other work but still not what I want - any suggestions will be appreciated.

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mark sharfman





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Re: Help requested on preventing hot spots
Old 06-08-2005, 04:55 PM   #2 (permalink)
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First of all, how did you do the metering. Normally you use a incident flash meter for this kind of work. That means you are not really metering a portion of her body but pointing the dome back at the light from her body position. It is difficult to tell much from your image since you've already modified it and the image is small. You might post the orginal full size image to the Post Production forum and let several people play with it. If you are shooting digital then you can use the camera's histogram to deal with most exposure problems using a black/gray/white calibration target. Rareley will you just want to let the shadows and midtones fend for themselves as they often contain key areas of the photo. You want an exposure where idealily the whole range has good information without clipping either shadow or highlight area. This sometimes means you have to carefully control the light to make sure the ratio is not beyond the film or digital camera's range (usually 5 stops). Also with the type of pose you're using where the model's body is not in one plane, you are going to have to do extra work to even out the lighting.
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rfs
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Re: Help requested on preventing hot spots
Old 06-08-2005, 05:19 PM   #3 (permalink)
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Thanks for the comments - I will go ahead and brave the PP forum with the image. I am shooting film/slides with an incident meter as you guessed so I do not have the histogram to help me even things out. Perhaps that is another reason to convert to digital but I can't justify the expense for what I want. I know that I have more than 5 stops in this image as it goes from pure black to almost pure white in the reflection. I was concerned that the reflective material would cause problems, but in other images from the same shoot without the reflective material, I have the same problem. I know I need work on my metering so while PP informaiton would be helpful, I really want to work on getting the image right before hand. I have had a little formal instruction on metering but am mainly learning through trial and error so suggestions are deeply appreciated.

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Re: Help requested on preventing hot spots
Old 06-08-2005, 10:05 PM   #4 (permalink)
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Mark, you said you are shooting film. Is it possible that you are getting the hot spots when you scan? Look very carefully at your film using a magnifier. Is there detail in the spots that are coming out over-exposed after scanning? If there is then check your scanner. You can probably make some adjustments to exposure in your scanner control software. Also, what film are you using. Color neg, slide, b/w? This may provide a clue for the rest of us to offer more advice. Also, out of curiosity, what are you scanning with?
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Re: Help requested on preventing hot spots
Old 06-08-2005, 11:28 PM   #5 (permalink)
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David:

I did not occur to me to look at the negs - thanks for the advice. This image came from a machine scanned CD prepared by the lab that did the processing. However, when I checked the image with my loop and my Nikon Coolscan 4000 scanner, the problem was (as I discussed in the post processing forum with Mike) that I simply over-exposed parts of the image regardless of how many locations on which I metered the model. The film is Ilford FP4.

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Mark Sharfman
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Re: Help requested on preventing hot spots
Old 06-09-2005, 01:05 AM   #6 (permalink)
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Mark, have you used this meter successfully on other shoots? Are you sure that you had the ISO set correctly? Did you drag the shutter any? Did you point the dome of the meter directly back at the light source? There are probably lots more of these but at the risk of being insulting I should stop. There are many variables and it only takes one to screw things up. Another completely different possibility is the lab you are using. They might have over-developed the negs. Just throwing things out. Maybe something will catch.

By the way, where are you shooting the outdoor shots in your port? Just curious since I grew up in Oklahoma.
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Re: Help requested on preventing hot spots
Old 06-09-2005, 07:42 AM   #7 (permalink)
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One thing that I have to consently remind myself when I am shooting is to feather the light away from the subject. I used to always get hotspots ... now I don't!!!

Its all about angles! The angle at which the light is travelilng and hiting the subject and then bouncing to the lens. This is called "angle of incidence"

The angle of incidence is good when your reflecting light, it is bad when the light reflects off the subject to the lens.

Feathering the light toward the lens, this will help!!!! But remember to shade the lens from the light hitting the lens and degrading the image.

E-mail or call me with more info
clark
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Re: Help requested on preventing hot spots
Old 06-09-2005, 09:37 AM   #8 (permalink)
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Mark -

I'm probably a lot less qualified to make suggestions than the others, but I think your real problem is expressed in your second sentence - "My studio is very small (about 15 x15) ... "

If you double the distance between the light source and the subject, the light intensity falls off by a factor of 4 (i.e., you need to open up your lens two stops, or lower your shutter speed two steps). Consider a light source one foot away from a 1' ruler pointing at the light. The light striking the nearest part of the ruler is 1' from the source, but the light at the furtherest part is 2' from the source. The intensity there is 1/(2 x 2) or 1/4th the intensity at the nearest part, a two-stop difference.

If the light were 10' from the ruler, the intensity at the far part is 1/121th, but the intensity at the near part is 1/100th - the fall off is much less.

You need to move your light as far from your subject as possible if you wish to illuminate the subject evenly. Of course, when you do that, your light becomes increasingly small relative to the subject, so you'll need to increase the size if you wish to have "soft" light.

Ultimately, my suggestion is really this - you probably can't move the light much further away, so you need to meter the part of the body closest to the light - not necessarily the face, but whatever skin is closest. Of course, you'll still have fall-off, but you shouldn't have hot spots.

Good luck. Nice work, btw.
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Re: Help requested on preventing hot spots
Old 06-10-2005, 09:33 AM   #9 (permalink)
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[ QUOTE ]
Mark, have you used this meter successfully on other shoots? Are you sure that you had the ISO set correctly? Did you drag the shutter any? Did you point the dome of the meter directly back at the light source? There are probably lots more of these but at the risk of being insulting I should stop. There are many variables and it only takes one to screw things up. Another completely different possibility is the lab you are using. They might have over-developed the negs. Just throwing things out. Maybe something will catch.




By the way, where are you shooting the outdoor shots in your port? Just curious since I grew up in Oklahoma.

[/ QUOTE ]

Thanks for the suggestions - no idea is insulting to me as I still have so much to learn.

Having screwed up little things like ISO and shutter speed before, I am compulsive about checking them and did so this time.

The shutter drag issue is one to check to make sure the lens and camera are working correctly. The camera was recently reconditioned so it is probably OK but it is worth checking the lens.

As far as I know the meter was used correctly. These shots are actually improvements on some previous ones so I have made some progress already,

It probably is not the lab as I have had this problem with negs particularly (more than slides) at two different labs in two different states so it is most likely operator error.

Actually I am looking for a good outdoor site in Central OK with which to work with this wonderful model. The shots in my portfolio all were taken in the mountains of New Mexico - mainly the Santa Fe National Forest.

thanks again

regards

mark
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Re: Help requested on preventing hot spots
Old 06-10-2005, 09:36 AM   #10 (permalink)
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[ QUOTE ]
One thing that I have to consently remind myself when I am shooting is to feather the light away from the subject. I used to always get hotspots ... now I don't!!!

Its all about angles! The angle at which the light is travelilng and hiting the subject and then bouncing to the lens. This is called "angle of incidence"

The angle of incidence is good when your reflecting light, it is bad when the light reflects off the subject to the lens.

Feathering the light toward the lens, this will help!!!! But remember to shade the lens from the light hitting the lens and degrading the image.

E-mail or call me with more info
clark


[/ QUOTE ]

Clark:

Great suggestion!! I generally point the softbox or reflector directly at the model so I will try this on our next shoot.

regards

mark
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