Question re high speed shooting and long exposures

[Darvidanoar]

I have been working on some startrails/planetrails shots this week and have noticed something very odd about long exposures and high speed shooting mode on my 7D.

The problem is that even though I have high speed continuous shooting turned ON, I can hear a definite gap between exposures. I'm hearing at least 1/2 second gap between exposures where I should be looking at around 1/8 second (high speed continious shooting mode should yeild up to 8 frames per second on the 7D). There is also a noticable gap in the plane trails caused by this lag between exposures.

I have searched through the manual and turned off those features that will affect high speed continuous shooting performance:

Long exposure noise reduction
High ISO noise reduction


and still no improvemement.

I've tried RAW mode and JPEG mode and there is no difference.

Am I missing something?
:confused013

[I @ M]

What shutter speed are you using David?

[Darvidanoar]

What shutter speed are you using David?

30 second exposures for stacking in startrails.exe
(Sorry, I did originally type that in and then it obviously got lost as I revised)

Settings I use for startrails are: 30s f/4 ISO400

[I @ M]

I am a bit confused as well now, I would think that if you have the camera set to continuous high or low it should simply end one exposure and begin the next basically instantaneously.

Is it possible that high ISO noise reduction is being applied automatically even though it may be disabled in the menu? I think Nikon does underhanded things like that without actually telling the operator on some ISO levels so Canon might too. That may explain a slight lag in the write process and the ability to start a new exposure. :confused013

[Darvidanoar]

Yes, isn't it wierd? There should really be no lag in write time as the buffer is well large enough.

I should also add: high speed continuous shooting mode is super fast when used for shorter exposures, the issue only appears during long exposures.

[I @ M]

Might be a case of sending a tech request email to Canon unless someone else on here has an answer.

[etherial]

I guess you are using manual focus for these type of shots? If not could it be something to do with focusing?? Is the camera taking a moment to try and find focus, which would be difficult in low light. Just thought I'd ask to rule that out.

I think it is more likely the camera processing the image. I understand what people mean by the buffer should be able to handle the file and does for fast shots, but collecting information continuously for say 30 seconds is a different story.

[Darvidanoar]

Yes, manual focus.

Without any technical evidence to back this thought up, I wonder if it's a function of the camera designed to let the sensor cool down a little between long exposures?

[kevinj]

I don`t have an answer for you,but I`ll give it a try tonight and see if mines the same.:confused013

[Astroman]

I found out about shutter lag times when I was testing my lightning trigger. I don't think there is much you can do about it when shooting continuous burst mode. When all the lag in the camera is added up it takes quite a while for the camera to take the next image. Even if you shoot manual mode with everything off ie.. ICNR etc... it wont make it take a photo any quicker.

I think my 400D had a shutter lag of 100ms where as a Canon 1Ds Mk 3 has something like a 55ms lag time, almost twice as fast. So my guess is the 7D would have a shutter lag somewhere around 60-70ms. Combine that speed with other thinking processes the camera makes, you have your total lag time.

The only way around would be to keep the shutter open longer, maybe close the aperture a bit, reduce the ISO to 100 or less if available. You wont get as many stars but the the aircraft trails would be longer, without breaks.

EDIT:

Okay just rethought this, and yes the shutter time is alot quicker during faster shooting, I just did a test of 30s, 1s and 1/4000sec and the high speed is much quicker.... now this is interesting..... OKay time to do some more experiments...

[arthurking83]

I just tested the D300 for something similar, but I only used a 5sec exposure.(I'm now rushed to get going too)
No real delay.. a micro second between mirror down to mirror back up again.

Try to test it out with shorter exposure times too.. say 5sec or something.

Also, do you have your rear review screen coming on between each shot?
Could this cause a delay if you did?

I reckon it's most likely a camera setting.

The D300 is configurable for how fast you set Ch mode at, and I guess that the 7D will be too!

Check that the Ch mode(that's what we call Continuous high mode) is set to the fastest rate with a large burst rate ..etc, etc.

apart from that, I have no idea?

is there any delay in normal exposure times, normal exposure time being equal roughly to something like the conditions where you;d expect to use Ch mode.. sports birds in flight.. short fast bursts that require spraying the scene with 144 million pixels every second! :p

[Darvidanoar]

Ok, now this is getting really wierd.

I decided to try a bit of experimenting with various exposure lengths, so I set the camera up on the tripod with the following settings:


Manual Mode
1/25s f/4 ISO 100
High speed continuous shooting on
Manual focus


As these are just test acuations, I did not bother taking the lens cap off. Oddly, there was a notable delay between exposures, when there hadn't been before (from previous experience).

However, when I take the lens cap off (same settings) the actuations are fast (as they should be).


:confused013 :crzy:


Thanks Arthur, No I don't have the screen come on. Dang, if it is a setting, I wish I could figure out which one :)

[Darvidanoar]

BINGO!

Found in the manual at the bottom of page 93:

In low-light areas or indoors, the continuous shooting speed may become slower even if a fast shutter speed is set

No explanation why .. it just is.



Oh well, I guess I just have to go back to cloning in the gaps :)


Thanks for your help folks. Scooby snacks all 'round :th3:

[kevinj]

Mine was the same and I found the same page in the manual about 20 minutes ago.:confused013

[etherial]

I just did the same tests. Set the camera on 1/4000 full manual and with lens cap on it will only do about 4fps, take it off and you get the full 8fps.

I tried it with all settings on and off, like lighting optimister, WB, Auto ISO etc etc.

Very strange but at least it was in the manual!

[Darvidanoar]

Yes, at least we now know it's 'normal' behaviour, but I'd still like to know the reason ... not knowing annoys me :)

[DesmondD]

Yes, at least we now know it's 'normal' behaviour, but I'd still like to know the reason ... not knowing annoys me :)

If it's in low light , even if you are in manual focus perhaps the auto-focus still has to do a check for the 'focus confirmation' indicator which is what might slow it down when things are dark . Perhaps focusing on the bright moon might confirm this if it suddenly speeds up ?

[James T]

Apparently shooting in LiveView gets your fps back up to 8 (though not very useful for startrails as it'll kill your battery). Also holding the DoF preview button down will sort it, you should be able to tape that down if you want to. So the Googlemachine says anyway, not a problem I've encountered myself.

Seems a very strange situation though, I wonder what the reasoning is, I read the new metering system could be to blame.

[Assassin]

This might be a silly question, but should you be using the 'bulb' setting on your camera for this, and even a lower ISO?
Sass

[Darvidanoar]

This might be a silly question, but should you be using the 'bulb' setting on your camera for this, and even a lower ISO?
Sass

As I understand and from my own experience, the higer ISO enables the sensor to pick up more stars. Remember, the stars ar constanty moving, so changing the length of exposure does not increase the brightness of a star. if you want more stars and brighter stars, then you need to increase the ISO.