Printable View
Used a BB several times in the filed and exposure always seems to be blown out even though I have minus exposure as much as four stops. Any feedback and or suggestions will be greatly appreciated. Oh yes, I used aperture priority mode with my 40D and switched from spot to multi etc. with similar results.
Hi Phil - what flash are you using and what flash mode?? Shutter Speed ETC when this is happening??
More info will help diagnose the problem.
which Canon Flash can be set to -4 ?
In what kind of conditions did it happen ?
If your ambient exposure is correct before using the flash... the problem is more than likely you do not have the flash in high-speed sync. The camera will default to normal sync speed and cause the overall exposure increase. If the shutter goes from a higher value to 1/250 when turning on the flash...bingo...the problem is as stated above.
Best,
Chas
This was some time ago as I recall I used aperture priority with Canon 40D and a 550EX flash as a fill flash. I honestly cannot recall the in camera settings beyond that. All of the exposures with the beamer were over exposed even though I minus exposure as much as 2-4 stops. I did not use high sync mode however in Aperture mode the shutter speed will remain @ the ambient light value.
Your problem seems to be exactly what Chas said. If you are not using high speed sync, then 40D is setting the shutter speed to 1/250. Based on ambient light and your aperture setting, if the right exposure needed is1/1000, then at 1/250 that photo will be over-exposed by 2 stops....even if you dial in negative flash exp. comp. In fact, in those conditions, even if u were not using flash and had set SS to 1/250, it will be over-exposed by 2 stops. Its a shutter speed issue and not really a flash or better-beamer issue. Just that the flash not being in high-speed-sync made the camera set the SS to 1/250.
This is probably the biggest issue that people run into when first using a flash, let alone a BB. And it often makes them decide it isn't worth the time to figure out the problem.
It is that often people ignore the camera reading when viewing through the viewfinder. The shutter speed will be flashing, the exposure meter will show an over-exposure.
And in slightly different words from above, the camera set in AV will use flash for fill up to the maximum sync speed usually between 1/200th to 1/300th for most bodies.
So when the shutter button is pressed regardless that you have the light for a shutter speed of 1/1000th the camera will only take the shot at 1/200th or whatever the max sync is on the body.
So when this point is reached and the camera defaults to the max sync speed and that is so it can use the flash and just "ignores" the fact the ambient light will take over-expose the image.
So it is really a very simple problem, and is easily identified before a shot is taken. The solution of course is to change the flash mode to HSS. In fact the 580 I carry in my wildlife gear is always set to HSS, it should be the default mode for this type of photography.
By placing the flash in HSS it basically becomes a constantly on light painting your subject, almost like holding a tightly focused ~75 watt flashlight on top of the camera. In this mode then the camera just "sees" all the light, flash and the sun as ambient and can use any shutter speed up to the maximum possible in the body being used, usally something like 1/4000th to 1/8000th.
Once people new to using flash in wildlife shots get this point down on how the camera and the flash are working at odds or together the rest usually comes pretty easy.
Depending on certain Custom Functions and how they are set, AV will try to balance the flash with ambient light. This can result in lower than expected shutter speeds and over-exposure. Check the EXIF data of the shoots in question and please post what ISO, aperture and shutter speed was used.
Brad
I managed to find the raw files and check the shooting data, as it turns out ISO was set to 800 because of poor lighting conditions. I rarely set ISO above 400, in any event shutter speed was @1/250 at F8 HS flash was not used at the time. I needed to pump the ISO simply to get a shutter speed that somewhat matched lens focal length. This was all based upon available light reading, in hindsight I will tinker with the HS flash setting for future use with the beamer. I have used both Nikon and Canon systems film and Digital over three decades and it seems counter intuitive to me to have to set a system to HS on order to get higher flash sync settings above 250th of a second however I thank you for your patient and thought full response.
Quote:
Originally Posted by Brad Manchas
There is a Custom Function on the 40D Cf.N I-7 that will set the shutter speed in AV Mode so you don't have to raise the ISO.
This function allows one to choose between a floating shutter speed when using a flash up to the maximum sync speed, 1/250th in this case. Or to have the shutter speed fixed at 1/250th when using the flash.Quote:
Originally Posted by Jeff Donald
This doesn't address the issue however unless the shutter speed will always remain below 1/250th.
If the ambient light requires a faster shutter speed at the aperture/ISO choice the camera will still fire at only 1/250th and throw some light from the flash. The result is an over-exposure every single time.
Setting this function to lock the shutter speed at the max sync speed of 1/250th means adjusting: flash output, aperture and ISO to achieve a reasonable exposure. If shooting macro and with the flash as the primary light this is a reasonable situation however for birds it is the long way around in trying to get results.
Here is a link to another more complete decription of using HSS (other than Artie's) but this HSS the solution. http://www.rpphoto.com/howto/view.asp?articleID=1026
When the flash is set to HSS you can use a shutter speed from 1/8000th to how low can go and still be throwing fill light. Actually at and below the max sync speed the flash reverts back to "normal" operation, meaning it is no longer a constant light source but now just a flash.
Once you are in HSS and dependent on the situation, lighting and subject; the flash maybe set at full power or it maybe be dialed down a bit using FEC (FLash Exposure Compensation). This is the easy stuff, adjusting the look by the histogram.
How close were you to your subject?
BB works after 300mm. Any closer and you'll burn.
To further clarify...if you use the beamer with the flash in ETTL at close distance and high ISO the flash will most likely overexpose the subject. The flash algorithm was not designed to handle the higher guide number at close range.Quote:
Originally Posted by Fabs Forns
The better beamer coverage is about equal to 300mm effective focal length, using a a shorter lens will result in vignetting. Note- this can prove an asset and effective way to spot or highlight a subject or avoid over-exposing a closer than the subject foreground element ;).
Best,
Chas
Not close at all maybe 100-150 feet or so , would not try beamer for close up work. At the time I used s 300 F2.8 IS USM with 1.4X
TX
Phil:D
