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Anupam Basu
08-29-2006, 03:40 PM
Many thanks for starting this forum, Sean. I hope it will become a great source of help and information on macro photography.

To tag a quick question to what is essentially a lame attempt to be the first person to post on the forum :D : is there any way to easily measure the amount of light lost to a diffuser or softbox attached to a flash and come up with a revised GN for doing manual flash photography? I can only think of testing as the alternative but am wondering if there is any other way.

-Anupam

Roger Hicks
08-29-2006, 03:49 PM
...apart from a flash meter, obviously.

They aren't that expensive any more, even new.

Cheers,

R.

Dan Fromm
08-29-2006, 04:29 PM
Not to be a complete idiot, but why do you want to use a softbox/diffuser when shooting closeup. If the flash isn't too far from the subject it is effectively a large, not a point, source of light and will give fairly soft lighting. If I weren't non-digital I'd show you some scans, but since I'm not you'll have to take my word for it.

If your problem is specular reflections, a light tent -- a diffuser around the subject, not around the flash -- is the classical solution.

df cardwell
08-29-2006, 04:35 PM
Well, there are two controls for light:

Size, relative to the subject, and
Distance from the subject.

Distance from the subject affects the gradation across the field,
so if you want an even light across the field, you move the light back,
but if you want a variation across the field, the light belongs close to the subject.

I suppose if one is making a clinical image,
the light should be further away,
but for an expressive image, you can bring it close.

Anupam Basu
08-29-2006, 04:37 PM
If your problem is specular reflections, a light tent -- a diffuser around the subject, not around the flash -- is the classical solution.

Dan, you are right. My problem is indeed specular reflections. But I can't figure out a way to put a light tent around insects in the field, as in this shot (http://www.apug.org/gallery/showphoto.php?photo=17909&cat=501), for example.

The other thing I have been trying is cross polarized flash, but so far my results have been miserable - need to experiment a bit more with it to figure out what the problem might be.

-Anupam

David A. Goldfarb
08-29-2006, 05:10 PM
Flashmeter or testing are the options. It's not that big a deal to test, if you don't have a flashmeter. Before I had a flashmeter, I tested all my studio reflectors and diffusers and came up with guide numbers, and would map out studio setups in advance before shooting, so I would have the right f:stop. As long as I didn't change the light-to-subject distance, I had some flexibility in moving the lights during the session. It was absolutely reliable.

So do a test with slide film at a non-macro distance so you don't have to calculate exposure factor. Figure a softbox is going to cost you between 1.5 and 2.5 stops and shoot a series of frames a half stop apart.

Then when you are shooting macro, don't forget to include the exposure factor for high magnification.

Claire Senft
08-29-2006, 05:14 PM
In a darkened room with a fairly bright light ie 200 watt hold an incident meter in a fixed position reading the central part of the beam. Take a reading at a particular shutter speed without the diffuser in place, note the fstop. Take the same reading with the diffuser in place at the same shutter speed. How much did the fstop change? The change is your correction.

mgb74
08-29-2006, 06:20 PM
(snip) So do a test with slide film at a non-macro distance so you don't have to calculate exposure factor. Figure a softbox is going to cost you between 1.5 and 2.5 stops and shoot a series of frames a half stop apart.


I understand the advantages of using slide film (narrow latitude, no printing compensation), but would using b/w film and viewing the negs themselves be reasonably valid?

David A. Goldfarb
08-29-2006, 06:28 PM
If you are good at reading negs, you could do that, but slide film usually will give you a more precise test. If you're using B&W neg film, you could print a contact sheet at minimum time for maximum black for this sort of test.

naturephoto1
08-29-2006, 07:05 PM
Though small manual flash units are inexpensive, if you are working in the studio you may also want to consider using fiber optic lighting for close-up/macro work particularly as the subject gets smaller and smaller. Metering will be simpler and easier and you can see the actual effect on your subject. Another item that can be useful is to use small mirrors and work with 1 flash or light source.

Rich

Dan Fromm
08-29-2006, 07:16 PM
Dan, you are right. My problem is indeed specular reflections. But I can't figure out a way to put a light tent around insects in the field, as in this shot (http://www.apug.org/gallery/showphoto.php?photo=17909&cat=501), for example.

The other thing I have been trying is cross polarized flash, but so far my results have been miserable - need to experiment a bit more with it to figure out what the problem might be.

-AnupamSorry, Anupam, but as a cheapskate no-good rat of a nonsubscriber I can't view images in the gallery.

I'm not sure that it is relevant, but in my aquarium photography I rely on geometry to control reflections from the tank's front. This might work for you.

Cheers,

Dan

Dan Fromm
08-29-2006, 07:25 PM
Well, there are two controls for light:

Size, relative to the subject, and
Distance from the subject.

Distance from the subject affects the gradation across the field,
so if you want an even light across the field, you move the light back,
but if you want a variation across the field, the light belongs close to the subject.

I suppose if one is making a clinical image,
the light should be further away,
but for an expressive image, you can bring it close.All that you've typed is true, and I don't understand the distinction you make between clinical and expressive images.

But and however, when shooting small mobile subjects in the field when and as they're found there are only two practical flash rigs. A flash bracket that somehow attaches to the camera body. A flash bracket that some how attaches to the lens or the camera's front standard. Flash brackets that stand on the ground aren't compatible with opportunistic shooting.

Both of the setups place the flash(es) near the subject, offer limited depth of illumination (I don't know if the concept is new to you, I've carried it around for decades). The best way I've come up with to get well-lit backgrounds is to have an assistant hold a flash (usually the third one) about the right distance from the background.

Obtaining, training, and keeping an assistant can be a problem. I once solved the problem by building a three-flash bracket for one of my friends. Heard his laments, went into the workshop, and emerged with a wife eliminator. And when his wife saw it, she instantly recognized what it was for. I found the thing too heavy and clumsy, but then it was really more a proof-of-concept prototype than a production version.

Come to think of it, this discussion really belongs in the lighting forum. Moderator, do your duty!

Cheers,

Dan

Claire Senft
08-29-2006, 07:41 PM
Why is this seen as difficult or requiring a flashmeter? The question is: How much light is lost due to a diffuser?

Anupam Basu
08-29-2006, 07:42 PM
A multiple flash setup is exactly what I have in mind Dan, only since I don't have a wife/girlfriend eliminator and since my girlfriend's fidgeting scares away the bugs anyway, I am trying a two flash setup.

The idea is to have two flashes either side of the lens - the smaller flash, an SB-18 without adjustable outputs will light the subject while the other, a SB-28, will be aimed at the background. It's power will be adjusted depending on the distance of the background. I am also hoping that if I put the SB28 on wide angle, it'll spill enough light sideways to act like a kind of fill-flash to balance the SB18's light.

-Anupam
PS: My pic was a standard dewy damsel shot that is in my PN portfolio as well, the kind Arnab takes - so you know what I mean about popping a light tent on it - I'd have a damsel in quite a bit of distress :)

Anupam Basu
08-29-2006, 07:52 PM
Claire, I'll try out your method - I am guessing it might even work with an enlarger, right.

Thanks,
-Anupam

Mark H
08-29-2006, 08:26 PM
What about a ring flash?

http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/EXT-FLASH/RING/RING.html

Claire Senft
08-29-2006, 08:41 PM
I suppose that an enlarger would be workable. Lowere your head yo the bottom, remove your lens and carrier, tape the meter so the cell is in the center of the beam. Take a reading at a constant time. Note the fstop. Put the diffuser in the beam and note the fstop. How much light was lost? I would guess about 1.7 to 1.8 stops. As long as the light is bright enough to be well within the sensitivity ranhe of the meter it should work. As an altenate you could use daylight tomorrow.

Anupam Basu
08-29-2006, 09:06 PM
What about a ring flash?

How would a ring flash help? As far as I can see, it would have the disadvantage of being close to the subject resulting in rapid falloff of light as has been pointed out in the above posts. Along with this it does not address the issue of background lighting, unless you are using an additional flash for that. Thirdly, sidelighting with fill looks nicer and more natural than flat front lighting.

-A

naturephoto1
08-29-2006, 09:25 PM
I have one of the Lepp II brackets made by Saunders. I presume that it or an updated version is available. With the bracket you can mount 2 flash units and a camera. You can position the flash units where you want in relation to each other. The flash distances and angles can be adjusted. If your camera and flash units allow for TTL the flash output can be adjusted through the camera.

Rich

Buster6X6
08-29-2006, 09:59 PM
Hi Anupam
I made a two flash unit out of desposable cameras I got from my photo store for free.I inserted the guts into a small plastic box and attached to commercial flash bracket. Works really good.