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I am having trouble with reflections when I use wireless flash. Even though the popup is not supposed to contribute to the exposure, it appears to be doing so. The setup is D70s/18-200VR/SB600/SB800 as shown in Photo #1 (FM2 in place of D70s as I used d70s to take the photo) Both remotes are behind the plane of the subject.



The camera flash is set for Commander mode TTL
Photo #2 Shows the reflection from the popup. This is proved in photo #3. The only difference is that I put a card (The one on the table) between the popup and the bottle. This removed most of the reflection (I should have used a larger card!) as well as the shadow cast on the backdrop. There is also a drop off in exposure due to the lower light level.
Both photos are 1/500 f5.6 ISO200 56mm Yes I know they are underexposed, but I just wanted to show my problem, not take great photos.

This bottle is particularly problematic as the label is reflective metallic
TIA Greg

Greg - firstly, any subject that has a reflective surface is going to be difficult to shoot unless you use a light tent or place diffusers close to the object. The flash output from the inbuilt flash can be negated by placing an infra red filter in front of the flash (i.e. non-exposed but developed slide film). It will still trigger the remotes.

When I shoot wine bottles I invariably use f/16 at speeds from 1/20th sec, when using trilites, to 1/100th sec and up when using strobes.

Two rough examples, prior to treatment:

When I use my SB-600 in wireless mode with the on-board flash acting as commander I just put a small amount of cardboard (cut to size) taped over it. I think if you search the net you'll find a few sites mention that even though the onboard doesn't fire the pre-flashes still go off to determine exposure just prior. I think its these you are having show up as reflections.

Hmm. I'll have to investigate light tents. Any pointers?
I used to live in a house with white walls & ceiling & had no problems there I guess that acted as a defacto light tent. New house as you can see has problem walls - when you can see them that is.

However, Gary claimed <a href="http://www.dslrusers.net/viewtopic.php?t=23269&postdays=0&postorder=asc&start=0" target="_blank">here</a>

It should be less than trivial.

A couple of months back somebody did some tests of exactly this, and proved that any light added by the popup contributed nothing at all to the exposure/image.

If you find that you're seeing the lighting affecting your exposure, then there's a problem in how you're setting the flash.

That the onboard has no effect whatever. I am seeing an effect, and clearly others are too.
I haven't found the original post that he refers to, so I am not sure what is different in my setup to that one.

TIA Greg

Gary is basically right except for reflective surfaces - a light tent on eBay will cost anything from $30 and up

I see light tents are basically white translucent boxes.
These are available from 30cm up. Now all I need to know is what size to get.

At the moment, I am photographing bottles for a friend. I imagine that 30 cm is too small (The largest bottle is 35cm tall), but will 50 cm do, or would 80 be better.

OTOH I also make furniture. Should I get the largest possible so I can use it for that as well, or is there an optimum size to object ratio? Price is a real consideration, but it may be better to get one large; rather than small, then need to replace it with a larger one later anyway.

In the mean time I will try making a mickey mouse version by draping some some tracing paper or maybe silk around.

Greg

yraen69 wrote:I think if you search the net you'll find a few sites mention that even though the onboard doesn't fire the pre-flashes still go off to determine exposure just prior.

This is correct, but it's due to having the inappropriate settings on your gear. If you have iTTL dialed in, then this would be the expected outcome.

So, you simple switch to a mode that does not cause the pre-flashes.

In a studio environment you are using a constant, known light source, and thus, once you have determined the correct EV, any further metering, given the same shooting conditions, becomes superfluous, and probably detrimental to what you're trying to do.

As a more practical example, at the Sydney portrait workshop last year, we had 10 shooters using Nikon and Canon bodies, and no preflashes, as they would have caused fun and games with the light triggered heads (of three different varieties) that we used thoughout the day.

One other point to note: your metering should be based upon the amount of light that falls onto your subject, but in-camera metering systems typically read the light reflected from the scene, or the subject.

If you're shooting a particularly dark, or light, subject, this affects the amount of light being reflected from that subject, and thus this also affects the exposre values that your camera will be reading.

By all means, use this as a starting point, but chimp with the histogram, switch to manual using the derived EV, and then adjust to get the correct exposure, keeping then that EV constant through the rest of your shoot.

Mr Darcy wrote:At the moment, I am photographing bottles for a friend. I imagine that 30 cm is too small (The largest bottle is 35cm tall), but will 50 cm do, or would 80 be better.

For a 35cm bottle, I would think that 50cm is too small - it really doesn't provide you with a whole lot of clearance around the top of the frame, nor does it provide a great deal of distance from the diffusion surface to the subject.

OTOH I also make furniture. Should I get the largest possible so I can use it for that as well,

How big/small is the furniture that you make that it might fit into a 50cm light tent?

I'm only being slightly flippant here - typically, I wouldn't expect household furniture (I'm thinking chair, table, coffee table, lounge chair) to fit into a desktop style of light tent. Yes, there are much larger versions available, but these are not always practical in a domestic situation, nor would they be optimal for small-product shots, like, for instance, wine bottles.

So, the two shooting scenarios should best be considered as having entirely different shooting demands, even though many of the underlying principals are very similar.

For a larger-product shoot, you might need a clouple of flash heads through soft boxes, shooting perhaps onto a background/base of seamless paper supported through the use of background stands.

or is there an optimum size to object ratio? Price is a real consideration, but it may be better to get one large; rather than small, then need to replace it with a larger one later anyway.

I would think that a larger desktop tent (80cm would handle many things) but don't expect to have the one lighting setup/solution to handle every challenge that you envisage covering.

Yes, look to buying flexibility, but don't expect a panacea.

More practice...
Based on the tips given I have modified the setup:


I have added a silk drape around three sides. Front is still open. I am now pointing flash at subject, rather than bouncing. I have switched to remote manual half power. I am working by day instead of night. I was still getting reflections from the popup so I taped an old blank slide over it. That Problem solved Thanks sirhc55 Then I used my laptop (silver case) as a reflector to provide some diffuse front light
The images are now acceptable, but not good.


First is good exposure, but the gold label is not clear.
Second the gold on the label is good, but otherwise overexposed
The third was using the laptop as a reflector. Better than 1 but still not there.
Sigh.
I don't mind the reflections at the side, they help define the roundness of the bottle.

Will continue playing. and maybe fork out for a "real" light tent.

Thanks for the ongoing help
Greg

Mr Darcy wrote:However, Gary claimed <a href="http://www.dslrusers.net/viewtopic.php?t=23269&postdays=0&postorder=asc&start=0" target="_blank">here</a>

It should be less than trivial.

A couple of months back somebody did some tests of exactly this, and proved that any light added by the popup contributed nothing at all to the exposure/image.

If you find that you're seeing the lighting affecting your exposure, then there's a problem in how you're setting the flash.

That the onboard has no effect whatever. I am seeing an effect, and clearly others are too.

Greg,

Could you please clarify what you mean when you say that you're seeing "an effect"? I was saying that the onboard flash, when controlled correctly, has no effect on exposure.

As Chris has pointed out, it may still appear (as a reflection) in highly reflective surfaces, such as a bottle or other glass surface.

This does not mean that the light that you see has affected your exposure though - the two are entirely different things, and I think we need to be clear about this.

So ... I'm saying that the onboard flash, when properly managed, should have little if any affect on your exposure, but unless you also manage any reflective surfaces, you most certainly can expect to still see a reflection of the flash in a highly reflective subject.

Does this make sense?

home made light tent instruction I posted here last year
http://mcgoffs.net/?page_id=12

The first pair of photos show what I am talking about here.
There are three changes in the two exposures.
1. There is a strong flare from the metal foil on the label. (my main concern here) (first shot)
2. There is a shadow to the right of the bottle (first shot)
3. There is a change in the exposure level

All three effects were ameliorated by simply placing a card to block direct light from the popup reaching the subject. This indicates to me that the popup IS contributing to the exposure. This is contrary to what I have read here and elsewhere. note that I still had reflection issues AFTER I switched to manual. (Popup = Commander mode Manual 0.5 power Camera exposure = manual) AFAIK I cannot remotely fire the 600 and eliminate the preflash altogether, though I can do so with the 800.

The way I see it, light from ANY source while the (virtual) shutter is open is contributing to the exposure. If that light is very weak compared to the other sources, then the effect is trivial (hence my original comment in the other thread). In this case, because of the reflectivity of the subject, it is having a pronounced effect & is therefore not trivial.

When you said that the effect is less than trivial I took that to mean none.
This would be the case if the flash is only firing while the shutter is closed, and is what I expected from the term "pre-flash" as this implies that the flash fires prior to the shutter opening. In my case at least this is not what is happening, and from the suggestions from others that the popup needs to be covered in some way, I take it that others have hit the same issue and found their way around it.

Does this clarify?
Greg PS you can see a piece of furniture that WILL fit in a 50cm light tent <a href="http://www.woodreview.com.au/competitions/innerspace/entries/index14.html" target="_blank" >here</a> I took the photo, but did not make the piece.

Greg - gold or silver reflective labels on a bottle are a bummer - what I usually do is deep etch out a correctly exposed label and place on a correctly exposed bottle - the client then believes I’m a genius

deep etch out

Can you explain what this means. Some sort of PP I assume
I come from a slide background, so don't think in terms of "darkroom" techniques. I do my best to get the image right in camera, then leave it alone. I can see this will have to change.

home made light tent instruction

Thanks. It is similar, but much neater than what I put together. Mine was cheaper though I think I will bite the bullet & buy an 80cm one. It is not a lot more money & I am wthout transport for the next week or so.

Greg

Greg - deep etching - try: http://www.awp.com.au/Newsletters/how_to_deep_etch_images.htm

Greg,

Mr Darcy wrote:The first pair of photos show what I am talking about here.
There are three changes in the two exposures.

Yes, but how can you state that they're due to the onboard flash? Are you using manual, or auto, exposure, on the camera?

And what flash mode is in use?

Please go back and reread my earlier comments: reset your exposure so that you have an EV that is relevant to the light falling on (not being reflected from) the subject, and then set that, in manual mode,, to the exposure that you are going to be using.

At the same time, pull your pop-up flash down to its minimum power.

Again, if you are not controlling everything correctly, then yes, you will see variable exposures in your images. Possibly even from the popup, but I believe that this will be due an issue with incorrect settings being invoked.

Your interpretation of my "less than trivial" statement to men, in effect, nothing, is quite correct.

1. There is a strong flare from the metal foil on the label. (my main concern here) (first shot)

But that's a reflection, isn't it? That's nothing to do with the exposure, and, as you've acknowledged, you need to take action to address any reflections.

2. There is a shadow to the right of the bottle (first shot)

The shadows suggest to me that you don't yet have adequate diffusion of the light sources. They seem to be thin and somewhat well defined. As you acknowledge, this is not what you're looking for.

Move the loght sources a little further forward - towards the plane of the camera position - but further away from the subjects.

Pull your diffusion material further around the subject, to almost envelope it. From the front as well, leaving just small access area for the camera.

3. There is a change in the exposure level

Please see my earlier comments about the light being reflected from the subject and how that may affect your exposuse, and then revisit my comments suggesting that you use your histogram to aid you in determining the correct EV, and then manuallt setting your camera nad flash controls to achieve that expoisure as common exposure for each shot you make.

Remember, again, that your lighting conditions are constant for this type of shooting, so ask yourself why you should be permitting the camera to meter every shot. With constant lighting comes constant EV, which means you should revert to manual exposure with fixed, predetermined settings.

All three effects were ameliorated by simply placing a card to block direct light from the popup reaching the subject. This indicates to me that the popup IS contributing to the exposure.

If this is correct and happening, then you have not yet set the flash to minimal power. In that case, yes, it would be an expected outcome.

But it still comes back to what seems to be incorrect settings.

(Popup = Commander mode Manual 0.5 power Camera exposure = manual)

0.5 power is nowhere near minimal power, and yes, that will certainly affect your exposure.

Pull it back to 1/16, where its light output is several orders of magnitude less.

The way I see it, light from ANY source while the (virtual) shutter is open is contributing to the exposure. If that light is very weak compared to the other sources, then the effect is trivial (hence my original comment in the other thread). In this case, because of the reflectivity of the subject, it is having a pronounced effect & is therefore not trivial.

Well, yes, and no.

In theory, yes, any light source while the shutter is open will affect the total exposure. However, you need to manage the total of the light being captured, and ensure that there is no effective impact on the exposure.

The reflectivity of the subject may have a couple of different forms of impact on the image. First of all, and as I've mentioned several times, it will affect a meter reading if this reading is done in reflected mode. That is one reason I prefer to meter in incident mode, which measure the light falling on the subject.

Regardless, these days you can just chimp the image using the histogram, and use that information to determine the correct exposure. ou then set your camera to those settings, in manual, abd Bob's your mother's father's son. As long as your light sources remain constant, so too does your exposure, regardless of your subject.

The second issue that reflectivity brings to bear is the reflection itself. Hotspots can always appear, but they're nothing to do with exposure. They're a very real problem, but you address them with shooting and lighting technique, not exposure compensations.

When you said that the effect is less than trivial I took that to mean none.

And that would be my intended meaning.

Hi Gary,
We seem to be talking at cross purposes here.

I have two issues :

1. The purely practical: I want to take a good photo of that bottle (and others!) I am addressing this by playing with the suggestions made in this forum. I have made significant progress on this, though I still have some way to go.

2. The theoretical: Understanding the CLS as it applies to my setup, so that I will be able to apply this information to future problems. I am getting more confused, not less on this front.

My system consists of d70s, 1x SB600 1x SB800 18-200VR lens. Good or bad, this is what I have, and I cannot afford to change it at the moment I also have sundry other lenses & bodies, but they are all non-CPU, so I am not using them for now.

I do not have an external exposure meter, so I have to use the in-camera system. The large white background makes the histogram less than useful here. (In my inexperienced hands). It consists of a large block in the lights, then a fairly constant low level across to the darks.

The first two photos were taken with the camera on M at
Shutter = 1/500
F = 5.6
Lens= 56mm
ISO = 200

The Camera's Flash subsystem was set to C-> TTL
The SB800 was set to Remote
The SB600 was set to remote.
The photos were taken at night, with just enough artificial (i.e. constant) ambient light to see by.

Under these conditions my understanding is that the TTL system will provide the same light output from the flashes for each photo, and that the inbuilt flash simply provides the command sequence to fire the remote flashes. The results proved otherwise. The reflection indicated that there was an extra light source from the front of the subject. The shadow indicated that it was slightly to one side. In fact from the location of the built in flash. , and sufficient to alter the exposure

The simple test of covering the inbuilt flash proved that some of its light was affecting the finished photo. This was indicated by the fact that the shadow and reflection were significantly reduced, and that the exposure was darker with some of the light available prevented from reaching the subject. As the exposure was already low, I did not at that stage think to reduce the aperture.

By the time of the second series of photos my practical understanding had progressed significantly, and the photos are better as a result

These were taken at
1/500 f27, f16, f24 respectively, ISO200 Still with Camera = M Lens=50mm or thereabouts.

The flash system had changed significantly though
Camera Custom setting was C->M->1/2
The physical flash setup had also changed as per the posting photo.

you have not yet set the flash to minimal power. <Snip> 0.5 power is nowhere near minimal power

The manual (p150) states that this power setting affects the Wireless remotes only. On the D70s, AFAIK, the master flash (popup) cannot be altered separately. Your post indicates that it can, but I can find no other documentation for this, nor can I find a menu setting to do it. I know it is possible on the D200, but I don't have one of them. I tried the power setting at various levels, and this gave the best results. When in Remote mode, the external Flashes’’ output power is controlled by the camera, so there is no relevant setting there. Also, in another photo I did not publish the reflection is still clearly visible. (Above settings but f32 and popup not covered), so the advice

To prevent the timing flashes...from appearing in the photographs taken at short ranges, use a low sensitivity and a small aperture and a Sync other than rear curtain

(Manual p151) Does not help.

I can't get lower than ISO200 f32 with this combination and I did not use rear sync. It might have helped the first series of photos, but I hadn’t noticed it then.

I am afraid I am back to The popup of the d70s DOES affect the final photograph when used in wireless commander mode.

I have seen evidence to this effect & despite claims to the contrary, none against this statement.

Now I need to continue along the practical path of "What can I do to control this?" Various people here have helped me along this path, and I thank all of them. You have given me the next clues, and I thank you too:

Move the loght sources a little further forward - towards the plane of the camera position - but further away from the subjects.

I had moved them behind the subject in order to eliminate reflections from those sources. I now realise that the fabric will do this for me, so I can move them forward again.

Pull your diffusion material further around the subject, to almost envelope it. From the front as well, leaving just small access area for the camera.

Will do, but I will need to change from silk to an old white sheet to get enough material. Hope it’s not too thick. It will be a day or two before I can try. I have other commitments.

I will also buy a commercial light tent when finances allow. Some weeks yet – still suffering from Xmas.

Sorry to be a pain on this. I am just trying to understand what is going on.
Greg