Need help using T20 flash for OM system

[trevor_ware]

<p>I have a T20 flash unit for my Olympus OM-1n. The lens I'm using is a 28mm f/2.8 prime.<br /><br />With the flash connected to the hot shoe I matched the slider on the flash with my film speed, ASA 400. The flash recommends f8 - f16 as an aperture setting in auto mode. At this aperture setting (f8) the lens required an exposure of 1 second to correctly expose my ASA 400 film. This is in a well lit room indoors; not full daylight, but not what I'd consider low light either. I call it a well lit room.<br /><br />An exposure time of 1 second indoors with a flash seems ridiculous. I'm new to this system (and SLR photography in general), is the OM really this poor of a performer in low light? Removing my flash unit made no difference to my meter reading, and a roll I shot with the flash came back overexposed with everyone's faces washed out. Shouldn't the camera be aware that a flash has been connected and thus reduce the required exposure time for various aperture settings? If the connection of a flash makes no improvement to my ability to shoot in low light, whats the point at all? My meter is telling me I need 1 second of exposure in the room with or without a flash attached to the camera. As I understand it currently this system will be useless for me indoors without a tripod.</p>

[david_carroll4]

<p>Forget about what the camera meter is telling you - the OM-1 meter is "dumb", in that it gives you the recommended <em>ambient</em> light exposure whether or not a flash is attached. Also, the OM-1 is a fully mechanical camera - there's nothing the flash can do to alter the mechanically governed shutter speed and aperture. The only communication between the camera and the flash is the charge ready/correct exposure indicator light in the viewfinder - that's it. The T20 gives TTL exposure with automatic OMs (OM-2/n/S, OM-4/T, OM10/20/30/40) and, I believe, the OM-3/T manual SLR. With an OM-1, you'll have to use manual flash exposure or regular auto flash, which is completely governed by the flash unit itself (the flash controls the exposure by shutting off the flash output when it determines that sufficient light has been reflected back to it's own sensor. Assuming that the camera aperture has been set to whatever the flash unit recommended, this should also mean that the correct amount of light has hit the film). Set the camera shutter speed to the requisite flash synch speed (1/60 sec), set the flash to auto, dial in the ISO and set the lens aperture to the setting recommended for the flash to subject distance range. And then let the flash make the running. 1/60sec @ f/8 will mean that very little ambient light is getting to the film, and the meter built into the flash will calculate the correct exposure assuming (correctly, in this case) that it is the <em>only</em> light source. The reason you're getting overexposed pics is that the camera is exposing correctly (1 sec @ f/8), not realizing that the flash is also going to dump a heaped helping of extra light onto the scene when the shutter is pressed, and the flash is providing sufficient light to expose the scene without realizing that the camera speed is sufficiently slow to expose without <em>any</em> flash help. Your scene is getting a double helping of light = overexposed.</p>

[trevor_ware]

<p>This makes much more sense, thank you. Let me make sure I got it all - <br>

Match the flash unit to film speed, in this case ASA 400. Select aperture setting, either f/8 or f/16 based on distance of subject. Set camera to anything below 1/60; the flash will determine shutter speed based on it's own meter no matter what the camera is set at, so long as it's 1/60 or lower.<br>

Is this correct? It leaves me wondering A) How is the flashe's manual mode used, and what circumstances would warrant it's use - would the flash unit still select a shutter speed for me in manual mode?<br>

B) based on the flash slider location for this speed film, in auto mode it appears the flash is usable within a distance range of 8 feet (at f/16) and appx. 18 feet (at f/8). Is this flash not usable at a distance range closer than 8 feet?</p>

[machts gut]

<p>The flash doesn't change the shutter speed of your camera. The OM-1n is a fully manual camera. In auto mode the flash just stops its output when its sensor (on front of the flash) calculates that there is enough light. The advantage to manual mode is, that it takes into account the ambiant light and the pics look more natural. In manual mode it fires with full energy, sometimes you can reduce the enrgy according to the aperture you choose, but I don't know if this is the case with the T20 flash.<br>

The distance indicated on the flash usually is the furthest distance. Sometimes you get an information about the range from min. to max., but again, I don't know how it is with the T20. If you want close distance you should always choose the smallest aperture (f 16) to reduce the risk of blown out highlights, because the flash is too strong.</p>

[harold_gough]

<p>As it is a mechanical camera, unlike the other OM models, you can't rely on it to set 1/60 sec by detecting the flash gun in switched on mode. If you set a slower shutter speed you will get a secondary image from the ambient light. Select 1/60 second. This applies to using any T series flash unit.</p>

[baachitraka_.]

<p>I normally generate a Table for the distance covered based on Guide Numbers(@ full power, 1/2, 1/4...) against aperture value.<br>

I have Speedlite 430 EX II from Canon, which I use it with OM-1n and OM-2sp on manual mode.<br>

First I set the shutter to 1/60(max sync speed), after that it is your wish. Either select the constant flash power and vary the aperture according to the required distance by looking into the table.<br>

With single flash when attached to the camera I personally do not really care about the metering at all.<br>

I had some experience with T32 on OM-1n, which is rather simple when using the scale that comes with the flash unit.</p>

[baachitraka_.]

<p><strong>Working range</strong><strong> </strong>for guidance only (ISO 100):<br /> F/1.2: 3.3-16.7m (11.0- 55.7 ft.)<br /> F/1.4: 2.8-14.1m (9.3- 47.0 ft.)<br /> F/2.0: 2.0-10.0m (6.7- 33.3 ft.)<br /> F/2.8: 1.4- 7.1m (4.7- 23.7 ft.)<br /> F/4.0: 1.0 - 5.0rn (3.3-16.7 ft.)<br /> F/5.6: 0.7 - 3.5m (2.3-11.7 ft.)<br /> F/8.0: 0.5 - 2.5m (1.7- 8.3 ft.)<br /> F/16: 0.25- 1.3m (0.8- 4.3 ft.)<br>

Courtesy: http://www.mir.com.my/rb/photography/hardwares/classics/olympusom1n2/shared/flash/t20.htm<br>

Now, you can set the aperture according to the distance required. My personal choice will be f/4.0 with 50mm or 85mm lens.</p>

[trevor_ware]

<p>So regardless of manual or auto, with any t series flash I should default to 1/60th?</p>

<p>The table you posted is useful, is there a simple way I can convert it for other speed films?</p>

[david_carroll4]

<p>The duration of a strobe flash is in the order of 1/10,000's to 1/1,000's of a second - far faster than most camera speeds. The camera flash synch speed (1/60 sec in the case of the OM-1) is the fastest speed at which the focal-plane shutter is completely "open" for an instant, at which point, the flash is triggered (at faster shutter speeds, the trailing curtain starts to travel before the leading curtain has reached the other side of the film gate, so a fast shutter speed is effectively an open slot traveling across the film. If the flash is triggered at such a speed, only a narrow vertical segment of the frame would be exposed). Different cameras have faster synch speeds (up to 1/250 or even 1/500 sec), depending on the mechanics of the shutter itself - the OM-1 has a horizontally traveling, cloth shutter - about as a slow as it gets - thus the slow synch speed. Regardless of what electronic flash you use, the OM-1 should always be set at 1/60, unless you're getting fancy and mixing up ambient and flash exposure or going for a multiple strobe effect.</p>

<p>From the table above - using ISO 100 as the starting point, as you double the film ISO (eg, going from ISO 100 to ISO 200, you would close the aperture by one stop (eg, f/2 down to f/2.8) for a given distance, close it two stops (eg f/2 down to f/4) if going from ISO 100 to ISO 400.</p>

[george_shihanian]

<p>Let's keep it simple.<br />Check that the flash synch switch on the left side (your left, as you hold it to shoot) of the camera right by the lens mount is always set to "X". Attach the flash to the camera and turn it on. Set the camera shutter speed to 1/60. If you are using the T-20 on autoflash, make sure the calculator panel on the back of the flash is pushed all the way to the left and you see the linear numbers facing you. ( Not the blank side) Set the ASA (ISO) film speed on the flash. Then using the sliding lever that is on the bottom of the back of the flash, place the "AUTO" mark to either the "4" or the "8" F stop. With 100 ASA (ISO) film, if you set it to F8, you will get properly exposed flash shots from a half meter to 2.5 meters distance. (roughly 1.5 to 7.5 feet) At F4, your shots will be properly exposed from 1 meter away to 5 meters away. (roughly 3 to 15 feet) For using flash at longer distances you either need a stronger flash or faster film.</p>

[trevor_ware]

<p>Thanks everyone, I'm going to shoot a roll and I expect they'll come back much better.<br>

And David what you said makes total sense, my last roll came back with a few shots that were just narrow vertical exposures. These were shots I took well above 1/60.</p>

[konrad_beck1]

<p>Note that the T20 coverage angle is roughly equal to that of a 35mm wide angle lens, i.e., with a 28mm lens you will have dark corners.</p>

[harold_gough]

<p>While the T20 covers only the field of a 35mm lens, you can effectively widen this by bouncing off a (white) ceiling. The T32 covers a 24mm lens.<br>

The narrow band of exposed film would not happen with the more automatic OM cameras because the flash would not fire if the selected shutter speed was above that for flash synchronisation. Your manual camera does just what you tell it to, one additional thing you need to remember.</p>

 

[harold_gough]

<p>I forgot to say that for manual, bounced flash you need to take into account the full distance from flash gun to subject i.e. up to the ceiling and down to the subject, two sides of the triangle.</p>

[baachitraka_.]

<p>Guide Numbers are normally given @ISO 100. If you increase ISO say 100 -> 200 you have to multiply by factor 1.44 x GN.<br>

If you decrease ISO 100 -> 50, then divide by the same factor.</p>

[george_shihanian]

<p>If the flash is used on "AUTO" all he does is set the ISO on the flash and the flash's scale will tell him what distances he's good to shoot in. Let's not make this too complicated.</p>