# Why does Tv stop at 30 seconds



## Hector1970 (May 15, 2017)

Hi All,
It's always been a matter of curiosity and frustration that Tv only goes to 30 sec. For a longer exposure you need to go to bulb for which you really need a trigger or keep your finger pressed. Why don't Canon allow Tv to go up in steps of 10 secs to whatever value you want. In the age of darker neutral density filters wouldn't it make sense to alter the available values.


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## Mikehit (May 15, 2017)

My guess it is a hangover from film days, when film suffered from something called reciprocity failure (at low light levels you had to increase exposure time by more than twice when closing the aperture by one stop) and IIRC 30 seconds is where this became really obvious on a lot of emulsions.


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## Ray-uk (May 15, 2017)

What Mikehit has said does make a lot of sense.
There is also the problem of power consumption, to perform a long exposure the processor has to perform a timing loop where it continually cycles until the chosen time is reached. This consumes additional battery power and generates more heat from both the battery and the processor, the last thing you need for a long exposure is for the sensor to get hot because that increases noise in the photo.
It is much more efficient to let the user do the timing externally, in any case how often does the average user need long exposures.


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## LDS (May 15, 2017)

A few cameras allowed more than 30", anyway:

1) Most cameras run out of space on dials 
2) Very few camera meters can meter at that shutter speed, even with very fast lenses wide open
3) Longer exposure are not an issue to be handled using B (or T, where available) and a wristwatch or other clock.
4) Very few people usually need longer shutter speeds (many cameras in the past had the lower limit at 1", or even less, especially those without electromagnetic shutters), and those needing them are good customers for specific add-ons for some $$$$$


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## mbiedermann (May 15, 2017)

I'm with Hector on this one... I understand the impact that a, say, 10-minute Tv may have on batteries, but it's a cost I am willing to put up with to have the extra creativity. Plus Canon would sell more batteries 

Regarding LDS's point that cameras run out of space on dials, I think that within a camera generation or two, most of the exotic settings (like a Tv greater than 30 sec) will be set using a touchscreen rather than by dials.

Regarding camera meters not being able to meter at that shutter speed, if external, handheld meters can, then so should cameras. 

Extending the Tv would also be a way for Canon to differentiate itself from the competition. Personally, I would use the convenience of an extended Tv (beyond 30 sec) without resorting to Bulb mode far more often than I would a Tv of, say, 1/8000 of a second.

~Cheers


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## Hector1970 (May 15, 2017)

Thanks for the replies.
I could see how it comes from film days.
Neutral Density filters are flying off the shelves. 
I think too people are more likely these days to be doing a 60s exposure as opposed to 1/5000 sec.
I could understand that the metering may not be accurate but it could be. Usually a stopper comes with an exposure calculator. It doesn't have to be very accurate. Usually I'm in manual mode and guessing the time. I would have guessed it was an easy option to add with very little downside. It would appear an out of date restriction for modern photography.


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## Valvebounce (May 15, 2017)

Hi Hector. 
It might be because there are just so many alternative ways to do it! 
Just a few options. 

Corded third party timer remote. £8.26 looks a bit like the genuine Canon TC-80 which I found for £75. 
http://www.ebay.co.uk/itm/RS-80N3-Timer-Remote-Control-Shutter-Release-For-Canon-EOS-1D-1DS-5D-50D-40D-QM-/232316203074?hash=item36171ff042:g:HQUAAOSwONBZArHi

Cordless third party timer remote. £17.90
http://www.ebay.co.uk/itm/Jintu-MC-36R-C3-Wireless-Timer-Remote-For-Canon-7D-6D-5D-Mark-II-III-50D-1D-1Ds-/171737757554?hash=item27fc5e3772:g:mpEAAOSwv0tVGO51

Or this one, a bit dearer £18.88 but does wired or wireless and is better thought out with the receiver module having a flash shoe fitting giving somewhere to keep the receiver unless you are using a flash too. 
http://www.ebay.co.uk/itm/PIXEL-TW-283-N3-LCD-Wireless-Shutter-Release-Timer-Remote-Control-for-Canon-/162089312626?hash=item25bd46a172:g:i9gAAOSw-itXwPBo

Without checking I cannot be sure, but these probably all work as a dumb shutter release even without batteries (or flat batteries) meaning you can still do a manually timed bulb exposure if necessary, plus these all do delay timer, long exposure timer, interval timer and number of shots to take too! 
Alternatively there are Apps for Android phones to connect with a cable and possibly iPhone for the few Canon cameras with wifi or Bluetooth. 
I have a couple of the wired timers (workshop and home), a wireless remote (like the second one) without the timer and a wireless timer that works with the 3rd party grip for my 7DII, it eats batteries like mad, but as it was an included item with the grip and not a deal breaker must have item I'm not that worried about it, I carry lots of spare rechargeable batteries most of the time anyway. 
Can you have too many remotes?  

Cheers, Graham. 



Hector1970 said:


> Hi All,
> It's always been a matter of curiosity and frustration that Tv only goes to 30 sec. For a longer exposure you need to go to bulb for which you really need a trigger or keep your finger pressed. Why don't Canon allow Tv to go up in steps of 10 secs to whatever value you want. In the age of darker neutral density filters wouldn't it make sense to alter the available values.


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## Hector1970 (May 15, 2017)

I agree that a remote is the way to go. I'm sure all future cameras will also be controlled by phone.
However today without a remote you have to go to bulb and keep the button pressed. 
Remotes get lost or forgotten. Just think it would be an easy firmware addition


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## neonlight (May 15, 2017)

the longest exposure I've needed is 2 minutes for astro pix. It is easily done using a remote switch which is settable - you just need to remember when to stop. Other than the throw back to film I suspect this is a practical limit that longer times aren't often needed.


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## BeenThere (May 15, 2017)

Could be as simple as a cheap timer chip that is so much easier and cheaper than a custom design.


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## foo (May 15, 2017)

Just use the in-camera bulb timer. It goes to 99 hours 59 minutes and 59 seconds.

Slightly inconvenient that you can't combine it with the interval timer - external trigger still needed for that. Again though, that probably falls into the not used much / they want to sell you an expensive accessory area.


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## foo (May 15, 2017)

Ray-uk said:


> There is also the problem of power consumption, to perform a long exposure the processor has to perform a timing loop where it continually cycles until the chosen time is reached.



Actually it's highly unlikely that's how it's done. Virtually every processor these days has a way to go into a low power sleep mode to be woken up at some later point by an interrupt.
You see this sort of thing implemented where the camera goes to sleep after a while and gets woken up again when you half press the power button, just change the interrupt to an RTC alarm three minutes in the future and leave any necessary stuff turned on and you save a lot of power.

It's not a new concept - laptops use a variation of this to save battery when you're not doing anything - turn the CPU off but leave the screen on.


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## iohansen (May 15, 2017)

I can say with certainty that the extra power consumption of the processor doing a timing loop pales into total insignificance when compared to the power used to keep the shutter open. The processor is already running (and will do so even if bulb is used) and such a timing loop will not cause any additional power drain.


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## dak723 (May 15, 2017)

You could always ask Canon. They might welcome your input as well.


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## weixing (May 16, 2017)

Hi,
IMHO, they had to stop somewhere for the Tv and since the incremental is either 1/3 or 1/2 stop depend on your settings, 30s look like a good choice.

Anyway, most newer model had a bulb timer which you can set the exposure time longer than 30s, but too bad, they can't work with the in-camera interval mode, so if you need to shoot interval shot of more than 30s exposure each, you still need an external intervalometer. 

Have a nice day.


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## Ray-uk (May 16, 2017)

iohansen wrote:

I can say with certainty that the extra power consumption of the processor doing a timing loop pales into total insignificance when compared to the power used to keep the shutter open. 
---------------------------------------------------------------------------------------------------

Most electronic shutters don't work like that, one electronic pulse will briefly activate a solenoid that cancels the action of a holding magnet, this releases the first shutter curtain exposing the sensor. After the allotted time another pulse releases the second curtain which ends the exposure. Both curtains are then reset to their original positions by the mirror drive mechanism. There is no continuous current drawn holding the shutter open.

Most Canon DSLRs in live view operate slightly differently using what is called an Electronic First Curtain Shutter where the first curtain is locked open and start of the exposure is controlled by electronically switching the sensor then the second curtain closes to end the exposure. Some Nikons (& possibly Canon) use this method when in mirror lock up mode.


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## LDS (May 16, 2017)

mbiedermann said:


> Regarding camera meters not being able to meter at that shutter speed, if external, handheld meters can, then so should cameras.



30" at f/1.4 is EV -4. How many meters can go lower? An external meter like the Sekonic L-858D-U goes down to EV -5, just one stop lower. Canon 1Dx Mk II and 5D Mk IV just goes down to EV 0, so they wouldn't be able to meter that low.

Sure, 30" at f/11 is EV 2, so cameras usually meters, but in low-light conditions (including a strong ND filter), going past 30" even at full aperture very few meters will still be useful. So, it could be useful in manual mode, but expecting it to work in shutter priority mode and low-light won't work.


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