Guide Numbers and sync speed in flash.
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These are an indicator of power. High numbers = more power. More power = more reach.
With flash exposure is calculated based on flash to subject distance not camera to subject distance. If the guide number is known ( usually stated in Metres at ASA / ISO 100 ) then aperture can be manually calculated by dividing the guide number by the distance in metres. You can therefore, as long as you know the guide number of your flash work out its reach within the limits of your lens. Sync speed is the MAXIMUM speed that the shutter can run when using flash. At this speed or lower the shutter curtain on an SLR will be fully open when the flash fires. The actual duration of the flash is very short - thousanths of a second. Cameras with high sync speeds can cope with a wider range of subject matter when balancing daylight and flash. I have attatched a graphic by way of illustration. |
Remote flash
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You can quite cheaply arm yourself with a powerful second hand flash to add additional light or as a means of lighting within a tighter budget.
This is NOT a flash that will be directly attatched to your camera. The flash is to be remotely triggered by a camera system flash. Exposure will be a touch of trial and error. There are now growing numbers of older flashguns on the secondhand market that are seriously good deals as they do not link into the modern high tech camera metering systems and people are trading in for those that do. Trigger mechanisms are refered to as ' slaves '. When they register the light from a flash they trigger whatever flash they are attatched to. These come in various forms. When buying one the only real consideration is how in use it will register the ' master ' flash. If the camera with the master flash is to be some distance away then a long lead will be required to permit the slave to be situated near the master flash. These leads are low tech and therefore cheap. For the remote flash get the highest Guide Number you can within your budget. When we come to the subject of diffusing the flash we are going to loose a fair bit of its light output. I have attatched 2 pics of remote flashguns I use that also show a slave attatched. Both of these are well out of date by modern standards and are good buys. Cruising the net I have seen the 45CL for around £70. Mine was nearly £200 new. |
Don,
I cant thank you enough for the effort and information in these posts. Lots to consider but certainly not daunted :-) Stephen Fox |
Good write up Don - I have been following it but I have been side tracked with a plumbing problem with my immersion heater - Any plumbing experts here !! Spent 2 days on it and the dam thing still not right !!
A couple of small points to add to this thread. 1) warning about putting old models of flash gun on digital cameras with a Hotshoe. Most of the older guns have a trigger voltage in excess of 200V which would fry the camera electronics. Fortunately for me the Canon 20D has a Flash sync lead connection under the rubber flap rated at 250V. 2) As you have mentioned modern flash systems work on TTL metering basis. A number of these systems work by emitting a pre-flash (Canon E-TTL for example) to get some idea of the scene. Unfortunately the optical trigger units you illustrated attached to the remote flash are fired too soon by the pre-flash. However there are a few new models of low power guns available for use as an optical slave which can be set to ignore the pre-flash. Rob |
Rob I overcome all these problems by using flash only in manual mode, with the preflash switched of. Just as a matter of interest have a look at the photo I've uploaded, called watersplash. this gives some idea of the delay of the slave flash firing.
Not sure if a pasted link will work, but here goes http://www.worldphotographyforum.com...7&limit=recent |
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Rob |
Rob I have two Sigma guns, the Super and the ST, (ST is the basic one) The Super will act as a slave to the ST, but not the other way around.
Harry |
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Don |
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Don here are the photo's of the flashgun.
Christine |
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Thats super. All you need to have a play today is something to take a picture of. Not too shiney. Even a dull coin will do. The biggest problem you have probably found is focusing as you can only really do that by moving the camera closer to the subject, and fine focus is hard to get. ( hence my comment on a fine focus rail ). We can do it another way as an indoor job. Set yourself up to take the picture with the subject on top of something you can easily slide on a table top. Set your remote flash at an angle to the subject about 18 inches away. A second tripod helps but you may be able to tape it to something. Lay a piece of kitchen towel or other white tissue over the flash to diffuse it. Set up and take a picture starting at f8. If a lot too bright try f16. If still too bright move the flash to 2 feet and go again. - Trial and error job here. When you are happy with the exposure hold a piece of normal white printer paper on the other side of the subject to the flash angling it to bounce light back in and take your picture. Two pics attached. ......... HAVE FUN Don |
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As new life is starting to appear in the garden, I decided to carry out an experiment with flash. I mounted my two Sigma EF 500 flashguns either side of my Canon 300D, using the onboard camera as a trigger.
The attached photo is the result. Not quite mastered the technique as yet, but getting close. This is an uncropped 1-1 macro. As a guide the distance from the tip to the base of the the first pair of buds is 12mm The Sigma's are far to heavy for the brackets, making it very difficult to hold, so will look for a couple of cheap flashguns as substitutes and try again. Harry |
This is a fascinating thread - I personally find using any kind of flash very difficult even for family snaps. Many years ago when I did dabble in studio work I preferred heavy duty, high wattage bulbs and brolleys. I could only have them on for a few minutes at a time as the heat was unbearable!
As soon as I can find a suitable piece of kit i.e. second hand flash gun I'm going to have play for myself following all Don and the other poters advice. This is great stuff I hope the WPF continues to host this type of forum thread. |
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Nice one. Just been to Sigma's web site to check out your flash. Not surprised the setup is heavy. Bit of a job controlling output from 2 big guns G/N 50. I would think at the lens to subject distances you are working 2 small G/N 12 units may do the trick. You can guage the power required if you take a pic with only your pop up ( just checked DP Review and that has a G/N of 13. ) Don |
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I have also been down the bulb and brolly route. Would not even consider it now. What at one time I found hard, is now not so, and if I can help I will. Any questions - just post them here. If you mention the camera you are using I can go to DP Review to check it out - should stop me saying something stupid. Don |
Don, Jessops have a selection of cheap flashguns, I'm going to buy a couple, as I think I can make it work ok. I only ever use manual so cheap may be best.
Will post my next attempt over the weekend. Harry |
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Don |
Yes that's the one I'm thinking of buying
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Thanks Don - I'm now using a Canon 350d. I do have a very old Miranda flash gun, don't know what guide number it is sadly!
My local camera shop has a Cobra model for sale secondhand in Canon AF fit - I've no idea whether this is something I should explore further? Jon |
Jon the flash has to be more than just Canon AF fit for the Canon DSLR cameras. This is why your manual states the models of speedlite that work correctly. Basically the flash must support E-TTL. Some of the newer compatible flashes do support this and will work OK. Unfortunalty I think the 350D does not have a PC connector like the 20D does so that you could trigger an old flash gun at full power.
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Thanks Rob - sadly at present the speedlites are way out of my budget range having recently invested in lenses. More research I think.
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I managed to get the older EX380 off e-bay for £60 mark - It's not the best speedlite but it works well. Some of the Canon fits may fire ( like the Jessops ones they are flogging off cheap) but the exposure is all over the place. The EX380 gives reliable results.
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Another thing to watch out for is the trigger voltage, many of the older type have a trigger voltage far higher than required for DSLS. This could result in "Frying" to cameras electronics.
Have a read here. http://www.botzilla.com/photo/strobeVolts.html Harry |
The Canon flash system.
I have been on a trawl of the net to try and understand Canon Flash Systems and came across this. It has got to be the most comprehensive guide to the Canon system on the net. A lot of reading here. It does list EOS system compatible flash units for those looking to attach the flash to the camera as opposed to remote triggering.
http://photonotes.org/articles/eos-flash/ Don |
Don, a most absorbing and instructive set of flash pictures. I have a Vivitar 283 and a Canon 430ez. Do you know whether or not either of these would fry the 20D electronics if used on the hot shoe? I normally use them with slave flash.
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The Vivitar 283 most certainly WILL fry electronics. The trigger voltage is too high. OK if used off camera and triggered by a slave. I will have to check for info on the canon 430ez. Don |
John,
Canon 430ez does appear to be OK. Here are a couple of links to Canon EOS flash units http://www.kjsl.com/~dave/speedlites.html http://www.bobatkins.com/photography...c.html#3flash0 http://photonotes.org/articles/eos-flash/ That lot should give some reading.:D Don |
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John |
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John. |
Although there are good deals on old flash units to be had, the electronic circuits in modern cameras will, as John says, be fried by the high trigger voltage of old but useable by remote triggering flashguns.
I have found this listing to show how high some of the trigger voltages can be http://www.botzilla.com/photo/strobeVolts.html The moral is definately IF IN DOUBT CHECK. Do not poke around inside these things without knowledge, they contain high voltages :eek: Don |
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