Leica M6 TTL?

Discussion in 'Leica and Rangefinders' started by reptkeu, May 10, 2018.

  1. Hi,

    I struggle to understand what's so good about flash and TTL, particularly on my M6.
    From what I understand, TTL tell the flash how much light to burst depending on the amount of light measured by the metering system. Am I correct?

    But then, what about distance?
    If the metering reads the subject is mildly lit, it'll tell the flash to burst a mild amount of light, right? But what happens if the subject is really far? The burst of light will not lit the subject enough, right?
    Does the M6 (and other camera TTL systems) take into account the focusing distance?
     
  2. SCL

    SCL

    Think of TTL as the same as the "automatic" function of flashes for the last half century, except that the measuring occurs thru the lens rather than an arbitrary opening (think medium wide angle) on the flash unit itself. Focusing distance is basically irrelevant, in that the light intensity reflected from the subject is measured by the spot. If you have a subject at a great distance, depending on the power of your flash unit, the duraton or intensity of the flash may adjust accordingly to give proper exposure, depending on what else is in the picture reflecting light back toward the measuring sensor. Think of a situation where the subject is a person 35 ft from the camera...and that is what you are focusing on, but there are lots of other objects at intermediate distance within the frame which also reflect light back to the measuring sensor. The advantage of TTL, IMHO, is that depending on the focal length of your lens and distance from your subject, is that with the right focal length lens, you may be able to exclude measuring extraneous light to secure a better exposure of your main subject. It gets complicated, but that is the gist of it. You might want to secure a copy of Light, Science & Magic to get a robust explanation of lighting systems, techniques, and exposure considerations.
     
  3. Thanks so much for your reply.
    So, if I understand we’ll, the TTL system on my M6 will NOT take distance into account? This means it will send the same light output whether my subject is 20cm or 20m away?
     
  4. SCL

    SCL

    No, that isn't what it means....reread closely the text above. Depending on several factors including the reflectivity of your subject and how much of the field it occupies, as well as other objects in the field, and the focal length of your lens, it will adjust the light output, either its intensity or duration, to secure what it measures as proper exposure.
     
  5. Part of the explanation you first provided is difficult to understand for me (im technically savvy only to a certain point).
    Maybe I can try and clarify my question.

    Flash output should take into account the distance of the subject from the flash.
    Does the M6 take this distance into account when it sends the signal to the hot-shoe?
     
  6. Yes.
    The M6 TTL does not. The specifics of TTL flash metering are different for different camera systems - Nikon, for example, does use distance information provided by the D chip that is in their autofocus lenses, depending on the camera model.

    It is still your responsibility to make sure that the subject is within the range of the flash at the chosen lens aperture (which is not automatically transmitted to the flash). If the subject is too far away then the flash output even at maximum power will not be sufficient to light it properly and an underexposed image will result. If you let the flash know the film ISO and the set aperture, it will display the distance the flash can illuminate.

    The advantage of flash TTL in the M6 TTL is that the flash exposure is directly measured off the film during the exposure - and the flash is cut off when the camera's metering system determines that the subject is properly lit. As I said before, you still have to make sure the main subject is within the range the flash can actually illuminate.

    It does not.
    That's not what it means at all. If the subject is within range of what the flash can illuminate, the output will vary depending on when the camera's flash sensor determines that the subject is properly lit.

    No.
    It does, but not in the way you envision it. The camera does not know the distance, the internal flash sensor measures the light that's reflected off the film during the exposure and cuts off the flash output when it determines that the subject has been properly exposed. The metering characteristics is center-weighted integral, so i your subject is off-center, the flash exposure might be off. Or, as SCL already pointed out, if there are other objects in the sensor's field of view that influence the flash meter.
     
  7. Thanks Dieter for the explanations!
    So, I understand that the distance is indeed taken into account, but by the flash itself, not the camera..
    I wonder how precise the sensor is..
    It would have been good if the flash output could vary depending on the focusing distance set on the lens (focusing distance is already mechanically transmitted from the lens to the rangefinder component, so why not using it to tune the flash output?).
    So, to conclude, I always assumed TTL on the M6 was a really good thing to have, but I now realise that it's pretty useless to me..
    Many thanks for your help on this!
     
  8. Again, there is no distance information (in meter or feet) determined or transmitted at any point in this process.
    That's a misconception on how the rangefinder works - there's not "transmission of a focus distance" but merely a mechanical means to couple the lens helicoid movement with the rangefinder to give an optical means to determine focus; at no point does the camera have information available as to what that focus distance is. You can read the approximate distance off the lens' focus scale but that's it.
     
  9. So even the flash doesn't take distance into account? I thought modern flash units did...

    I feel it's important to vary the flash output depending on the subject distance.
    For example, let's say I take a photo of a wall at night. I take a photo with the flash at 50cm distance. If I want to get the wall to look the same brightness 20m away, my flash will have to output a much higher strobe, no?

    I'm looking for a way to address this issue when I take photos at night..
     
  10. SCL

    SCL

    You keep asking the same question without seeming to understand the nuances in the explanations several of us have provided. To answer your last entry - if the subject wall fills the frame in your camera at 50cm and also fills the frame at 20m, AND your flash unit has sufficient power, yes you can get the same exposure. Remember that with the M6 (and earlier models), there is no electrical distance information transmitted to anything...the rangefinder is mechanically coupled to the lens helicoids, and hence, the distance indicator on the lens barrel. Those lens helicoids, when meeting the the rangefinder cam in the camera body, mechanically superimpose the two images formed in the optical rangefinder mechanism, indicating that the image on the film will be in focus. This requires that all of this has been mechanically adjusted against the actual image at the film plane, a process during camera assembly or a later CLA by a technician. There are NO electrical signals generated in this focusing process. The advantage of the TTL exposure system vs other light measuring systems, is that the only light measured for exposure is that which specifically is transmitted thru the lens rather than being measured independently, which might or might not coincide with that coming thru the lens. Your best bet, IMHO, to achieve what you describe as a desired result, is to: 1) ensure you have a powerful enough flash unit to provide proper exposure at your desired distance and f/stop and, 2) especially for distances beyond 25 ft or so, to have manual control of the flash.
     
  11. I feel they weren't the same questions.

    You were two to reply, not several..

    You don't understand my question. I'm asking if the flash will need a much more powerful output, not if my flash can or cannot get the same exposure.

    Well, no, I don't remember, and never knew. Hence me asking...

    Thanks for the lecture. I knew that actually.

    Thanks for repeating. I wasn't sure if I understood.

    Yes, I came to that conclusion too. About five years ago.

    Thanks for the lecture.
     
  12. I feel like I can answer my initial questions now.

    Yes.

    Kind of yes.

    No, because TTL metering is only about light measurement, not distance measurement.

    No.

    Conclusion: TTL is often regarded as a useful feature. But I find it quite useless because distance is not taken into account in deciding the amount of light to be output by the flash (unless you are in the optimum range of your flash, which, I guess, must be around 2m)
     
    Last edited: May 11, 2018
  13. Nope, you haven't gotten it at all if that's your criticism of TTL flash. It's advantage becomes immediately obvious if you mount the flash on the camera and shoot in TTL and then shoot in the conventional A mode where the flash's onboard sensor controls things and then use the flash in a fully manual manner calculating the aperture from the guidenumber and focus distance. One of the advantages of TTL flash is that you do not need to bother with determining the subject distance - something which we have tried to explain several times above. Another it that the metering takes into account the lens mounted and any possible filter in the light path. As long as you stay within the limits of what the flash can do, you can mount it on the camera, set it to TTL and the camera to the flash sync speed (or slower) and blast away - the result will generally be perfectly exposed images.
     
  14. Ok. Am sorry. Sorry to fail understanding the situation here.
    If you still have the patience to answer, then I have questions that would hopefully help me understand how to improve my flash photography, or at least make it less cumbersome than having to set my flash manually.

    Does the distance from flash to subject have any relevance in flash photography? I veilieve it does, as light decreases as it « travels » towards the subject.

    If yes, then how is it taken into account when I use my Leica SF 24D flash with my M6?

    Hopefully this will make it easier for me to understand..
     
  15. reptkeu, just look up what the range of your flash is and then keep your subject in that range, the ttl flash will use the metering of the focus spot to determine the timing of the flash. It works great if you are not too close or too far. Really, all you need to do is focus and shoot and the ttl flash system, if properly matched to the camera, will give you the right amount of light.
    Have you actually tried using it yet? Just shoot a roll. Go on-line and find the range of your flash unit and I assume you are getting either a Leica flash or a known equivalent that works on your camera, and then just shoot it. The practical strength of using a ttl system is you generally don't have to over worry about exposure if within the flash range. The downside of ttl is when in that mode, it takes away control of how you light a subject, but you will in the great majority of "normal" flash use get a decently exposed photograph. And I assume you know the sync speed of your camera? When shooting in flash, with most flashes whether ttl or not, you cannot have the camera speed greater than the sync speed of the camera. Not sure what the M6 ttl flash speed. But it will be in the manual you can find online if you don't have one. In short, TTL works and makes using flash a lot easier with less over thinking about it.
     
    Last edited: May 11, 2018
  16. The big advantage of the TTL flash is that you can set any aperture on the lens and the flash will compensate automatically - with nothing to change. The TTL system using a compatible flash works very well on the M6TTL. As others say, there is no distance compensation as such, but clearly as an object gets further away the flash will use more power to illuminate the scene as the TTL-measured reflected light will be weaker.
     
  17. You can download the SF-24D manual here - it contains a table with the maximum flash distances for various ISO and aperture settings: Free Leica SF-24D Instruction Book You can, of course, just use the flash itself to give you that information - just input ISO and aperture and the display will show the maximum flash distance.
    1/50s.
     
  18. Ok, thanks for en lighting me.

    - And let’s say I take photos in total darkness with my M6 TTL. Will the scene be too dark for the TTL to be effective?

    - Then in the same total darkness setup, I could be 50cm from my subject, or 10m away from it. Flash output clearly shouldn’t be the same power. What’s happening here? Will the flash overexpose at 50cm away, and underexpose 10m away?

    - and how does the TTL behave when taking photo of a subject in the shadow of a strong light in the background? If the metering read the shadow it is likely to trigger the flash? And if it takes its reading from the strong light, is it likely no to trigger the flash?
     
    Last edited: May 12, 2018
  19. Well 50 cm's seems very close and it may blow out. But essentially the flash will adjust to light the scene as it is metered in the focus spot, in other words it will bring the area in the spot up to med grey. Again, you need to look at the guide number of your flash to determine what its far coverage is. Does your lens focus at 50 cm? If so why don't you just try that and tell us? It should work. Look at some of Bruce Gilden's later work where he uses flash in the street basically right in people's face.
     
  20. Yes, 50cm is close, but you mention Bruce Gilden's latest work. I think he photographs quite close, less than 50cm (even with a 50mm lens).

    Yeah, I know I need to look at the guide number. And I know how to use a manual flash.

    What I'm looking to understand is: if I get a TTL flash compatible with my M6, will it accommodate for all the situations I encounter, which include taking photos at night up-close (50cm) and from afar (10m).
    If a TTL flash does not fully cover these types of situations, then I don't want to get one.
     

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