matus Posted March 10, 2006 Share Posted March 10, 2006 Hi, I am rather new owner(and quite happy one) of the 7D. When I looked at posible settings of the (buit-in) flash I realised, that there are only following modes: 1) ADI, 2)pre-flas TTL, 3)Manual. I have no "D" lenses so the ADI mode is for me most probably useless and so is the Manual mode (though I can of course imagine applications). So I am left with pre-flash TTL - and here comes the problem. If you use pre-flash TTL and synchronize to rear curtain - I take the picture at the time when people are just blinking after the pre-flash resulting very unnatural portraits. So - the question is - Is there no "normal" TTL flash mode - without the pre-flash? Or I have to lear to live with this limitation...:-( ? thanks MAtus.. Link to comment Share on other sites More sharing options...
james_frater Posted March 10, 2006 Share Posted March 10, 2006 For now you will be left with only TTL. I have a 7D, does it have red eye reduction ??? It's 1am in the morning for me right now and cannot be bothered to take the camera out and look. But if so maybe that maybe an option when using flash. Also you got a 7D, did you only buy the body. At worst you should have got the standard lense with it, which would be (D) rated, if you did buy body only spend about $100 bucks and get a D lense for it. Link to comment Share on other sites More sharing options...
tmhutchins Posted March 10, 2006 Share Posted March 10, 2006 I got a cheap D lens, 18-70mm from B&H. Although it is a cheap lens with it's plastic feel, especially when attached to a solid camera like the 7D it takes good photos and is worth the $85.00 I paid for it. B&H can only be congratulated for the speed it takes to get stuff from them. I say get a D lens and for the price if it gets damaged then get a better one. Link to comment Share on other sites More sharing options...
michael_hohner Posted March 10, 2006 Share Posted March 10, 2006 There is no way to eliminate the pre-flash except using manual flash mode. Digital cameras can not use regular TTL-OTF metering. There will be a pre-flash with both pre-flash TTL metering and with ADI. Link to comment Share on other sites More sharing options...
demetri_p. Posted March 10, 2006 Share Posted March 10, 2006 The only way to avoid this is to use an old fashioned thyristor based flash with a 20$ adapter. See for example a <a href="http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00FYwb" >current thread</a> regarding the fs1100 adapter. <P> Some subjects are more prone to blinking than others; my 2yr old is especially prone but I am very happy to use the thyristor flash or using natural light with a f1.8 lens. Link to comment Share on other sites More sharing options...
matt hedgecoe Posted March 11, 2006 Share Posted March 11, 2006 Matus,<br><br> Due to the way the flash exposure is calculated by a digital camera, you <b>must</b> have a pre-flash.<br><br> With a film camera, the exposure is controlled as the photo is being taken by sensors monitoring the light levels reflecting <b>O</b>ff <b>T</b>he <b>F</b>ilm (hence OTF metering). When sufficient light has reached the film for a correct exposure the flash is quenched. Unfortunately this method does not work with digital (you can't measure light bouncing off the sensor in the same way) so all the calculations have to be done <b>before</b> the picture is taken, which is why you need a pre-flash.<br><br> When you press the shutter button on the 7D a series of 14 preflashes are fired, one for each of the 7D's 14 metering segments. The 14-segment exposure sensor reads the light level and the exposure computer factors that information in with the Subject Focus distance and position reported in the viewfinder, the ambient light brightness and the Distance if a D lens is attached. The calculation also considers how much of the flash's capacitor is required for the right exposure.<br><br> Then the shutter release sequence starts, raising the mirror, closing down the aperture, opening the shutter and firing the flash at the calculated percent of its power.<br><br> In your question you said that you were using rear-curtain sync. Personally, for 'normal' photography I cannot see why you would do that. Assuming you are in P or A mode then the camera is going to default to a shutter speed of around 1/60th - 1/120th sec. By synching the flash to the rear curtain, you are increasing the time between the pre-flash and the main flash by 1/60th - 1/120th sec. Try first curtain sync. This will keep the gap between the two bursts of flash to a minimum and hopefully you will have your picture before people get a chance to blink.<br><br> Matt Link to comment Share on other sites More sharing options...
michael_hohner Posted March 12, 2006 Share Posted March 12, 2006 There aren't 14 pre-flashes. There's only one. You can measure with all 14 segments at the same time, just like you can with ambient light. Link to comment Share on other sites More sharing options...
matt hedgecoe Posted March 12, 2006 Share Posted March 12, 2006 <i>Fourteen preflashes or one?</i><br><br> According to Phil Braden (Konica Minolta USA) it's fourteen.<br><br> SOURCE: <a href="http://www.imaging-resource.com/ACCS/56H/56H.HTM">http://www.imaging-resource.com/ACCS/56H/56H.HTM</a> (about half-way down the page)<br><br> Matt. Link to comment Share on other sites More sharing options...
michael_hohner Posted March 13, 2006 Share Posted March 13, 2006 Well, Matt, do you see 14 flashes or just one? Link to comment Share on other sites More sharing options...
matus Posted March 13, 2006 Author Share Posted March 13, 2006 To: -All- Thanks, I really did not realise that OTF is not possible with digital SLR. I was doing some more shooting oveer the weekend and realised that flash sync of 1/125s with AS turned on is really poor. Why not 1/500s as D70/70s ? Would be great! Yes, in standard photography one does not need to synchronise on rear curtain. But without pre-flash the advantage is obvious. When the victim starts to blink - the exposure is over. No, I do not care so much about the "D" lenses as we (me+ my girlfriend) already have 28/2, 50/1.4, 70-210/4, 24-105/3.5-4.5, and 100/2.8 macro is about to arrive. None of these are "D" lenses. Thanks again MAtus.. Link to comment Share on other sites More sharing options...
bill_thorlin Posted March 13, 2006 Share Posted March 13, 2006 Matus - I think you will find that the 24-105 is a D lens. Link to comment Share on other sites More sharing options...
matt hedgecoe Posted March 13, 2006 Share Posted March 13, 2006 Michael, In answer to your question, I can only see one pre-flash. Similarly, when I use High Speed Sync I can still only see one flash, although I know that there are in fact multiple pulses of flash occurring, albeit too closely spaced for the human eye to distinguish. Based on that, I see no reason why the apparent single burst of pre-flash isn't actually composed of a series of flash pulses. I have no desire to get into an argument over this as I cannot say with 100 percent certainty, or provide proof of how the system works. I simply repeated the explanation given by Phil Braden (who I understand to by one of Minoltas flash gurus) in which he said there were a series of 14 pre-flashes. Nikon certainly use a system of multiple pre-flashes with their i-TTL and D-TTL systems. Given that the D-TTL system was around before the launch of the 7D, it is entirely possible that Minolta adopted a similar system. Matt Link to comment Share on other sites More sharing options...
michael_hohner Posted March 13, 2006 Share Posted March 13, 2006 It doesn't make sense to me to use a series of pre-flashes or even a long flash pulse for the pre-flash. This would drain the flash capacitor, leaving less load for the main flash. It makes even less sense if you can do the same with just a single pulse. <p> Anyway, if I have the time I'll hook up the camera to an oscilloscope tomorrow and make a few measurements. Could turn out to be an interesting experiment... Link to comment Share on other sites More sharing options...
matt hedgecoe Posted March 13, 2006 Share Posted March 13, 2006 Michael, I fully agree that it makes no sense and that was my first thought when I read the article! I suppose it's always possible that the man from Minolta was misquoted. Assuming that it did use a series of flash pulses, in that case I'd expect to see only HSS flashes listed as being compatible. However, the non-HSS 2500D is listed as compatible so that kinda 'throws a spanner in works' of that theory... If you do get a chance to hook a flash up to a scope, I'd be very interested to know what the results are. Matt Link to comment Share on other sites More sharing options...
michael_hohner Posted March 14, 2006 Share Posted March 14, 2006 Read the results <a href="http://www.mhohner.de/minolta/flashcomp_diagrams.php">here</a>. You may be surprised! Link to comment Share on other sites More sharing options...
matt hedgecoe Posted March 14, 2006 Share Posted March 14, 2006 Surprised? Very! Some very odd shenanigans going on there! Makes you wonder how we managed with a tape measure and a slide rule... Thanks for taking the time to post your findings. Matt. Link to comment Share on other sites More sharing options...
bill_thorlin Posted March 15, 2006 Share Posted March 15, 2006 To my untutored mind it seems that the 7 behaves pretty much as expected except for the strange little after flash on the first chart. This is one of those intriguing ( but perhaps unimportant ) little mysteries. For the 7D things do not seem so straightforward and perhaps as many questions are raised as are answered - I leave that to those more knowledgeable than I. Again to my untutored mind the message I get is to use and do what the manufacturer recommends and be very careful when trying to get third party equipment to do the job - perhaps this is a deliberate ploy by the manufacturer ! Thanks Michael for adding even further to the Minolta data base Link to comment Share on other sites More sharing options...
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