Modern Classic SLR Series :
Canon EOS-1N Series AF SLR camera
Flash Photography - Part III

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A-TTL (Advance-TTL) Automatic Flash Exposure (Flash Symbol)

After the Manual Exposure Control shooting Mode, I revert back to another two Automatic Exposure Control modes again - but BOTH of the AE modes discussed here now are flash photography related. By using an EOS-dedicated Speedlite, flash photography, including fill-in flash and slow-sync flash exposure, can be automatic and easy. Focal length information of zoom lens is transmitted from the lens to the Speedlite. The head then zooms to ensure proper flash coverage. If the subject is too dark or the contrast too low for autofocusing, the Speedlite emits AF auxiliary light automatically. The AE mode activates the A-TTL program flash AE for fully-automatic flash photography. When the camera is set to aperture-priority AE, shutter speed-priority AE, or manual exposure, the Speedlite automatically sets to TTL flash exposure to suit the camera's exposure mode.

Street Children in Phnom Penh, Cambodia
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Cambodia Documentary Series: -Street children outside CD chop, Russian market, Phnom Penh, December 2002

Credit: Image courtesy of Andy Eames ® who has his Portfolio at Pbase. Image copyright © 2005. All rights reserved. Please respect the visual property of the contributing photographer.
As can be seen in the A-TTL and TTL automatic flash control characteristics shown in the chart below, the EOS-1N's automatic flash output reduction program has been changed slightly with regard to the TTL automatic flash exposure level in high brightness conditions. Every professional system usually has a great system flash to supplement the camera. In this case, the high-performance Speedlite 540EZ is the dedicated flash for the EOS-1N, it links with various EOS-1N features for sophisticated flash photography.

A-TTL flash_chart_compare.gif
A-TTL & normal TTL Program line characteristics --->>> 48K Gif

TTLflashChart-SML.gif

In previous EOS-1 models, the compensation amount was fixed at -1.5 stops at all brightness levels greater than EV 13 (at ISO 100). In the EOS-IN, however, the compensation amount drops to -2 stops at EV 14 and continues to drop at a gradual slope as the brightness level increases.

chart-flash.gif
Although we can conclude safely all EOS SLR cameras (Not sure with the Canon EF-M) would support A-TTL flash but NOT all Canon Speedlites. work with A-TTL. Usable flash units are, like Speedlites. 300EZ, 420EZ, 430EZ and 540EZ (The old Canon 300TL Speedlite, as the dedicated flash for the non-AF Canon T90 - in fact, the camera was actually the first Canon SLR that incorporated with an A-TTL Flash Exposure Control function). Basically as a rough guide, all Canon EZ series Speedlite can take advantage of all the advance flash functions the EOS-1N provides. The multi-segment TTL flash metering in the camera can be regarded as third generation system, which is the current trend.


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Wild life at Samburu National Park

Credit: Images courtesy of Jakob K. Rohrbach®, Switzerland <jaro59@yahoo.com> where I found this picture from his online Portfolio at Pbase. For more of his works, please browse :www.jaro.ch. Image copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer.

TTL Automatic Flash Exposure (Flash Symbol) TTL automatic flash exposure is performed the same way as the EOS-1 except for a slight change in the EOS-1N's automatic flash output reduction program with regard to the amount of flash exposure compensation in high-brightness fill-in flash situations. Just in case you are doubtful what are the differences between A-TTL and TTL. A-TTL was a flash function evolved from a very innovative, classic flash metering called Through the Lens (TTL), Off the Film plane (OTF) system which first developed by Olympus OM2(N.back in 1975/6. But strangely, throughout the '70 to mid '80 - Canon was still very much confined their effort around Auto Flash and has not been keen into offering TTL flash meter for their entire range of film-based SLRs - until 1986 with their debut of the T90 which changes the direction in the adoption of flash metering for other Canon models that followed. Well, that was one hell of an entry into TTL flash with the T90, instead of following other's foot steps, Canon improved prevailing TTL flash metering with an additional, quite innovative A-TTL flash function to the basic which makes the TTL not just only provides OTF metering during a flash exposure but metering actually begins pre-exposure. i.e. an A-TTL capable flash mount, the Speedlite will remit a brief burst of light during the metering phase.

TTL-flashsequence.gif
The reflectance surface and distance of the "preflash" sequence is received via an external sensor on the front of the flash; the recorded data from the burst is then be used for determine aperture value to ensure adequate depth of field. If you decide the take the exposure, the A-TTL Speedlite will then, burst with full capacity until light is adequate for proper exposure. The metering is done at off the film plane, which reverts back to conventional theory of TTL OTF flash exposure control.

LCD-flashexpA.gif
Other than the three segment TTL flash meter system, one important development added to the EOS-1N is - you can perform exposure compensation to a flash operation. This is not NEW because TTL Automatic Flash Exposure Compensation With the previous Canon EOS-1 too, but flash exposure compensation is only possible only when using the dedicated Canon 430EZ Speedlite.

The camera-based flash exposure compensation function in the EOS-IN can be used not only with the 540EZ but with any model in the EZ Speedlite line, and can also be used with EZ flash units connected via EOS direct-connect multi-flash accessories, with compensation settings made in 1/3-stop increments up to ±3 stops., whether directly coupled to the camera or connected using EOS multiple flash accessories. (Compensation can also be carried out in 1/2-stop increments within a ±3-stop range using CF-No. 6.) However, when flash exposure compensation is set on the 430EZ or 540EZ flash unit when the flash is connected directly to the EOS-1N, the flash exposure compensation settings on the flash have priority over the settings on the camera side. When using the command back E1 which is not equipped with a quick control dial, flash exposure compensation can be set by turning the main dial while simultaneously pressing both the flash exposure compensation button and the focusing point selector button. In the case when using the 430EZ or 540EZ directly coupled to the camera's hot shoe, the flash exposure compensation settings on the flash unit have priority over the camera's flash exposure compensation settings. Note: -When flash exposure compensation is set, the ± indicator lights in the viewfinder, but the compensation amount is not displayed. The set flash exposure compensation amount can be checked at any time by pressing the flash exposure compensation on and reading the LCD panel. (The t indicator also lights when AE exposure compensation is set.)

Flash exposure compensation setting procedure

Canon EOS-1N, Flash Exposure Compensation Step 1

Canon EOS-1N, Flash Exposure Compensation Step 2

 

 

Flash exposure compensation using the flash exposure compensation button + quick control dial. While pressing the flash exposure compensation button (also used as the metering mode select button), turn the quick control dial until the desired compensation amount appears in the EOS-IN LCD panel.

Using the flash exposure compensation button + focusing point select button + main dial. When using the camera with the Command Back E I, which is not equipped with a quick control dial, simultaneously press the flash exposure compensation button and the focusing point select button, then turn the main dial until the desired compensation amount appears in the LCD panel.

The exposure compensation level displayed in the LCD panel normally displays the AE exposure compensation level. The flash exposure compensation setting is displayed only while the flash exposure compensation button is pressed on. When flash exposure compensation is set, the ":±' symbol in the viewfinder lights, but there is no display of compensation amount. (The viewfinder's "±" symbol also lights when flash exposure compensation is set on the 430EZ or 540EZ flash unit.). To check the set flash exposure compensation level, press the EOS-1N's flash exposure compensation button and look at the display in the LCD panel.

Notes on exposure compensation when using the EOS-IN with an EZ series flash unit
(1) Performing AE exposure compensation only changes the ambient light exposure level.
(2) Performing flash exposure compensation only changes the flash unit's TTL automatic flash exposure level.
(3) Performing exposure compensation by changing the ISO film speed affects both the ambient light exposure level and the TTL automatic flash exposure level.

Viewfinder Exposure Warnings in A-TTL and TTL Automatic Flash Exposure Modes (Using 50mm f/1.4 lense)

Subject
brightness

* Numbers enclosed by
a dotted line
blink at 2Hz.


Low brightness
General flash photography


Medium brightness
Daylight fill-in flash


High brightness
Daylight fill-in flash

           


digioutlinedotgif

Underexposure warning
based on overall average metering

Correct exposure
based on overall average metering

digioutlinedot.gif
Overexposure warning
based on overall average metering

           

Exposure mode

TTL flash exposure - Correct

TTL flash exposure - Correct

TTL flash exposure - Correct

TV AE

TV set
digi125.gif

Av AUTO
digif14dot.gif icon-plus.gif
-2

TV set
digi125.gif

Av AUTO
digi56.gif

TV set
digi125.gif

Av AUTO
digif22dot.gif icon-plus.gif
-6

Av AE

Tv AUTO
digi1sec.gif
Note 1

Av set
digi56.gif

Tv AUTO
digi125.gif

Av set
digi56.gif

Tv AUTO

Av set
digi56.gif icon-plus.gif
-7

Program AE

Tv AUTO
digi60.gif
Note 2

Av AUTO
digif1422.gif

Tv AUTO
digi125.gif

Av AUTO
digi56.gif

Tv AUTO

Av AUTO
digif22dot.gif icon-plus.gif
-5


Note-1: Automatic slow synchro exposure state indication at EV 5. When the brightness drops to a level requiring a shutter speed of 30 sec., 30" blinks for warning. Note-2: General indoor shooting in program AE mode. Underexposure warning is not available in this state. Note: When using flash in DEPTH mode, exposure is carried out the same as in program flash mode.

Note-1: Automatic slow synchro exposure state indication at EV 5. When the brightness drops to a level requiring a shutter speed of 30 sec., 30" blinks for warning. Note-2: General indoor shooting in program AE mode. Underexposure warning is not available in this state. Note: When using flash in DEPTH mode, exposure is carried out the same as in program flash mode.

In the case of Canon EOS-1N RS + 540EZ combination

All system operations are the same as with the EOS-1N + 540EZ combination. However, there is one point of difference between the EOS-1N and EOS-1N RS related to flash use: Whereas the EOS-1N uses a quick return mirror that allows 100% of the light passing through the lens to reach the film, the EOS-1N RS uses-a fixed pellicle mirror (reflection: 35%, transmission: 65%) that is always present in the optical system. Because of this, only 65% of the light passing through the lens actually reaches the film. In other words, the presence of the pellicle mirror reduces the amount of light reaching the film by approximately two-thirds of a stop. Accordingly, there are two points of precaution that the user should be aware of when using flash: The flash coupling distance range is shortened by approximately 20%.

A) When the 540EZ is used with the EOS-1N RS, the TTL automatic flash coupling range displayed in the 540EZ's LCD panel is automatically corrected for the 35% light loss. Thus, the guide number must be corrected when using the flash in manual mode. B) When using the flash unit in manual mode (by calculating the aperture setting according to the guide number and shooting distance), the user should use the following formula to calculate the correct aperture: (Nominal guide number x
0.8) divided by Shooting distance = f/No. for correct exposure

Comparison among some EOS-models in TTL Auto flash control. During the prevailing product cycle of the EOS-1N era, body metering during EOS automatic flash shooting has been weighted toward background metering. However, even though the Canon EOS-1n uses basically the same multi-points focusing and multi-zone metering system as the Canon EOS 5, the EOS-1n, in this case, is designed to carry out overall metering while the EOS 5 carries out rather extreme peripheral metering (peripheral frame metering). This change in body metering characteristics, which weights the main subject the same as the rest of the scene, was made in consideration of most professional photographer's practices. The current replacement model, Canon EOS-1V has elevated Canon flash metering /exposure control to new height, but we will only be confined matter within the EOS-1N and leave that to future discussion when the said model is featured.

Credit: Image courtesy of Andres Harambour® from Argentina, where I found these lovely images (including the bottom two) from PORTFOLIO. Image copyright © 2006. All rights reserved. Please respect the visual property of the contributing photographer.

Anyway, EOS-1n supremacy in wrecking Nikon's stronghold in the professional users market has its basis. Although a few small areas are not exactly technologies pioneered by Canon (such as Evaluative Meter) but the careful adoption of applicable/practical applications has made this top of the line EOS model of the early '90 a one-sided affair as a choice for many pros in this highly competitive market place. In the hands of a thinking photographers, various metering systems discussed here should be more than adequate to handle 95% of photographic needs. At worst scenario, the experienced one should know how to make use of respective accumulated experience to tackle other uncertainties in exposure calculation, which of cause - made them a pro, hehe ..come to think of it, the pros working back in those days of the '70 & '80 only has a manual focus body with, at most, partial and spot in aids of a conventional center-weighted metering for exposure guide; the Canon EOS-1n embodied capabilities is really a gift from "somewhere up there"...., so when compared, don't complaint too much with other tiny hick ups with your camera now, okay ?

| previous | NEXT | 3/4 The high performance Canon 540EZ and system accessories for Canon Flash photography .. ...

Flash Photography:- Part 1 | 2 | 3 | 4 - Canon 540EZ site

Selective Canon TTL Flash Models:- 160E | 200E | 300EZ | 300TL | 420EZ | 430 EZ | 480EG | 540EZ | Macrolite | Other non-TTL Canon flash models
Useful Resources at Julian Loke site: - Instruction Manual(s (PDF) for Canon 420EX | 580EX AF-TTL Speedlites

Suggestive weblink:- Canon Flash Resources at Photonotes.org or Bob Atkin Flash FAQ section

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Background and Various Issues | The Basic Features & various Setup
Manual & Auto Focusing | Metering Systems | Exposure Control | Viewfinder Optical
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Flash Photography (with Speedlite 540EZ extension & Selective info on Canon TTL Flash Models:-160E | 200E | 300EZ | 300TL | 420EZ | 430 EZ | 480EG | MacroLites | Other non-TTL Canon flash model

Reliability Issues:- Body Chassis | Shutter Unit | Electronic Circuitry | Film Transport & film handling Secondary Functions:- Custom Function Part One | Part Two | System Accessories:- Film Back Options - instruction for Command Back E1 | Macro/Close Up Part one | Part two and Part III Flash for Macro-Photography | Power Sources -BP-E1 | PDB-E1 | Focusing Screens | Remote Control with Wireless Remote Set LC-3 | System compatibility

Variants of Canon EOS-1N:- Canon EOS-1N RS | Canon/Kodak Digital DCS-1, 3 -5 & 520/560 Series | Full Technical Specification | Main Reference Map / Nomenclature | Resource Centre:- Comparative Charts between EOS-1 & EOS-1N / or with its active Competition(s) (Nikon); Quick Operational Reference Card (278k Gif File); Listings of 7-segment digital numbers/letters appeared on LCD display panel/viewfinders (HTML page); External Link:-Instruction Manual (3.3MB PDF file applicable for both Canon EOS-1N (RS). | Using EOS system for your photography | Bots & Nuts of EOS System - by Philip Chong |

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