Waiting time between exposures

[emyliano2000]

First of all I would like to wish you all a Happy new year.

Being a complete newb in the art of astro and non photography I don't really know what settings to use.

Usualy when I don't know something I ask google for an answer and most of the times good old google is giving me a link to the nice SGL.

I already found something here but just to make sure I'm gonna ask the question here as well.

As far as I understood, for example, if I wanna take a sequence of more exposures of, let's say, 1 min the waiting time between them should be set to 2 min, 1 min for the camera to process the image and 1 min for the cool down?

Emil

 

[happy-kat]

You should turn off in camera noise removal that means processing takes seconds only. You don't need to leave it that long between exposures 10-15 seconds would probably be fine. What is your camera? Take raw files.

[emyliano2000]

2 minutes ago, happy-kat said:

What is your camera?

Canon 700d. Ok, so I've put the long exposure noise reduction to off. Is 10-15sec gonna be enough for the cool down?

[happy-kat]

Nice

If it new to you get familiar with it during the day so you know how to operate it.

[michaelmorris]

Assuming you are taking simple exposures (i.e. not using in camera processing) there seem to be opposing views on the advantages and disadvantages of leaving a period of time between each sub-exposure in order to reduce the build up of thermal noise in the camera.  Deductive reasoning would suggest this is a good idea and I suspect this may have been backed up by some experimental work by amateurs in the early days of DSLR astroimaging.

However, camera electronics in DSLRs are a lot 'quieter' nowadays and some suggest that with modern DSLR cameras the technique of leaving a pause between exposures just eats into the time when you could be collecting more data.  I would be fascinated to see if anyone has actually done some comparative tests on the two techniques with modern DSLRs.

[emyliano2000]

My autoguider supports dithering so I will have that enabled too. 

[happy-kat]

I leave about 6 seconds though I haven't done longer then 60 second exposures.

[emyliano2000]

What about mirror lockup? Should I activate it?

[happy-kat]

Does your camera support it and if it does yes you should.

[SteveNickolls]

Hi, my experience with DSLR's comes from the ignoble art of Alt-Az imaging where we take upwards of hundreds frames that can last up to a minute each plus x50 dark frames if so minded. Over an imaging session that could add up to quite a lot of time of lost imaging. I use BYEOS to control imaging and one capability of the software is to report internal temperature of the camera from the image exif data (BTW Canon do not say where the sensor is in the camera). I find that over an imaging session the internal temperature of the camera closes into a relatively stable value and I allow just two seconds between frames for the recording and transfer of the frame to the camera memory and my laptop. I don't worry about the problem of temperature variations over an imaging session.

Canon camera algorithms do things to your dark frames before they go into the CR2 file which really makes trying to control noise by controlling temperature a wasted effort.

If you visit the, 'No EQ Challenge thread on SGL this has all been discussed and dissected and experimented on. There are links too to the experiences and experiments of others regarding this.

Best regards,
Steve

[emyliano2000]

yes, it does support it, I already enabled it in the camera menu. the autoguider hand controller want's me to set the mirror lockup: (time, 0 ... 20.0 sec) and I don't know what to set.

[emyliano2000]

[alacant]

45 minutes ago, emyliano2000 said:

 

My autoguider supports dithering so I will have that enabled too. 

 

That's gonna take care of the delay between exposures. The 700d has proper mirror lock so you may as well use it. I set mine to 2s before firing the shutter although with or without I can't see any difference. That and the dither are already giving you around 30s. To get started quickly, you can use APT. It has everything you need to dither and expose with a 700d. HTH.

[emyliano2000]

So to be more precise I should set 30s waiting time and 2s for mirror lock up.

[Adam J]

Take a sequence of exposures and monitor the Exif temperature in each exposure. Not the total temperature rise over the sequence then repeat with a pause between exposures of a variable length for the same number of exposures. I would say that anything less than a 6 degree reduction in average temperature across all the exposures and its probably not worth it.

[ronin]

For the playing around I do I usually try to sort of "round things up". So if taking say a 40 second exposure I would allow 20 seconds for cooling. That make a minute so 30 exposures takes 30 minutes.

Whatever you decide on it takes a long time. Even the previous idea of just 30 exposures is 30 minutes and boy do you get bored while the whole lot is doing it's stuff. Take a pair of binoculars. 60 exposures sound nice but take a copy of War and Peace to read through twice.

My understanding is the Intervalometer basically pushes the exposure button then waits for the duration you have defined as the exposure on the DSLR, then carry's on waiting until that period and then the wait time has gone. Then it seems to push the exposure button again and waits. My interpretation is that it is a start exposure then it just waits for exposure time + wait time, may do a countdown to give you a little feedback. I do not think it actually controls the camera, as in the exposure time set on the intervalometer is "forced" on the camera. Could be wrong but I set both the same and it hasn't yet broken anything.

Set up the intervalometer before you venture out, you do not want to be trying to make significant changes outside in the dark and cold.

Think there is initially a Delay, set that to 10 seconds or more, it allows you to press Go and put the intervalometer somewhere before the first exposure gets under way. So work out where you can/will put it. Then step away and watch.

If this is a first go then make it easy and I find that the 40/20 split is nice and easy. One aspect is the time taken to write to the memory. Which may be a good reason to allow a fair wait time for "cooling". If you cut the wait to say 5 seconds and the write time takes 10 seconds (RAW files are big) then I would expect the camera to lock up. So it might be a good idea to consider the wait as a period for both cooling and writing.

I have the attitude that pushing my luck often results in it going wrong, so if I expect 5 to 8 seconds to write I allow it 15 at least.

 

[emyliano2000]

I'm using a standalone autoguider (lacerta mgen) and I'm controlling the camera with the autoguiders handcontroller. I have to set the number of exposures, the waiting time between the exposures, the mirror lockup time and the exposure time.

What puzzles me is the mirror lockup time.

[happy-kat]

Should be greater than the exposure time as it occurs first then exposure then wait. Not that I've used that software but that makes sense.

[alacant]

12 hours ago, emyliano2000 said:

I should set 30s waiting time and 2s for mirror lock up.

I don't know your guiding setup but with APT and PHD2 it's best to let the software decide when to begin the next frame. I mentioned 30s because that's an average sort of time on my setup: 60mm f4 guiding a 150/750 telescope. The dither hits the guiding hard and you have to wait for it to get back to the guide-star. Then mirror up. Then shutter. Rinse and repeat until you get too cold, bored or -more likely- when something goes wrong! HTH

[emyliano2000]

If I got it right I think this is what happens 

1- Mirror goes up 2- Shutter opens 3- Sensor is exposed 4- Shutter closes 5- Mirror goes down.

From the sequence 4 & 5 the mirror lockup won't have any effect after the shutter closes and ends the exposure

But from sequence 1, 2, and 3 if the mirror goes up action cause vibration in the camera body and the shutter is getting open, the vibration will translate and captured in the exposure.

So, is the mirror lockup time, the time the mirror is lifted up before the shutter opens?

For example if I set it to 2s, does this mean the mirror is being lifted up 2 sec  before the shutter opens to expose the sensor?

This makes a bit of sense to me because if the mirror goes up 2 sec earlier there will be enough time for the vibration to die out until the shutter is being opened and the sensor exposed.

[Knight of Clear Skies]

13 hours ago, michaelmorris said:

However, camera electronics in DSLRs are a lot 'quieter' nowadays and some suggest that with modern DSLR cameras the technique of leaving a pause between exposures just eats into the time when you could be collecting more data.  I would be fascinated to see if anyone has actually done some comparative tests on the two techniques with modern DSLRs.

I haven't carried out a really rigorous test but after a heavy and identical stretch I can't see any difference between the first sub taken in a run (with a 'cool' sensor) and one in the middle of a run. I strongly suspect that excessive cooling time wastes valuable imaging time. It's certainly not essential to let modern DSLRs cool down, I've managed to image dim objects unguided and with a relatively small amount of data, such as the IFN around M82 & M81, using a 5 second pause between 1 minute subs.

This was about 1h40 min at f3.2.

[alacant]

2 minutes ago, emyliano2000 said:

if I set it to 2s, does this mean the mirror is being lifted up 2 sec  before the shutter opens

Yes. But it really doesn't make any difference I've found. Best to go out and take a few snaps and see how it goes. Keep it as simple as possible. HTH.

[wimvb]

Emil, the answer to your question is already in the diagrams/manual you provided. If you want to let the camera cool down between exposures, just make this your wait time. A mirror lockup time of about 2 secs seems enough to dampen vibrations. But read up on the time your autoguider needs for dithering, and how this needs to be added to wait time (section 4.5 of the manual according to the information you provided)

Good luck,

[emyliano2000]

1 hour ago, wimvb said:

read up on the time your autoguider needs for dithering

I did but it doesn't say anything about the time or maybe I'm just too dumb.

[wimvb]

No, it definitely isn't you. (I apologise if I gave that impression, that was absolutely not intended.) The diagram doesn't really explain much, as far as I can tell. It certainly doesn't say anything about wait times. But as I interpret the latest diagram, the "Wait State (W)" on the left hand side, is unrelated to the Wait time from the other section you showed earlier. The Wait State seems to be an internal delay for the dithering and guiding to settle. The exposure sequence from your previous diagram is interrupted during this wait state. That would mean that the wait state when dithering is active, is added to the wait time set in the exposure control. But that is just my interpretation of the diagrams in your posts.

My advice: do some test exposures where you change the Wait time (from your previous timing diagram) from 0 to maybe 10 seconds, and see how this works out. Once determined how the various times work, add wait time if you want the imaging camera to cool down between exposures.

 

Good luck,