Star Adventurer exposure and 'readout' time setting!?

[lrt75914]

Hey guys,

My dad recently acquired a Skywatcher Star Adventurer for some wide angle night time astrophotography. So far the weather hasn't been kind with us and as a result we've only been able to play around with the advanced firmware in our warm and comfy living room. We tried to hook up his Sony Alpha 77 ii to the SA to use it as an intervalometer but ran into a couple of problems that could severely limit the 'snap' functionality of the mount. The SA only waits 0.5 seconds for the camera to process and save the pictures before it sends out another shutter release signal. The time it takes the Alpha 77 to process and save the images, however, usually exceeds the exposure time and thus you'll end up with a wide array of differently exposed images. All of this could be avoided if the new firmware would allow you to individually adjust the 'readout' time for different exposure time settings. Does anyone know of a workaround for this problem or am I stuck with the 'ample' 0.5 seconds that Skywatcher deems sufficiently long enough for the whole readout process?

PS:

I have searched the forum and didn't find a similar thread that could answer my question. 

[ronin]

Just read the manual and there is no mention of an "interval" between exposures, which is what you need and is on the fairly simple intervalometer I have.

Now this may just be me being unable to see it but also the manual appears not to say that you can do multiple exposures. The section titled SNAP to me reads that you get one exposure and then you have to initiate the next by some means. In effect I cannot read anything that says it would start a subsequent exposure automatically after about 0.5 seconds. In the SNAP section it says:

Everytime the buttons are pushed on, or the mode is switched or the Slide Switch is slid, the selected shutter interval period will restart.

I can see nothing that says that you can set the SA to take a series of say 8 exposures, it reads that you take one then you start off the next manually by one of the above actions. Will say that the manual appears poor. From having a Sony 0.5 seconds to write is not going to work, they take longer then that

Just a thought but what have you set the exposure setting on the Sony set to?

I am wondering if things are a bit mixed up?

Set an exposure of say 30 seconds on the Sony then try.

I am wondering if the SA simply sends a "Press" to the camera every 100 seconds and that the camera has to be set up to accomodate all the actions required within that 100 seconds. In effect the SA is just saying Go.

My thought is the camera is set to 30 seconds, then the camera may take a noise reduction exposure (if on) - another 30 seconds, then everything just waits until the SA issues the next Go is sent out after 100 seconds.

With the above you get 30 seconds exposure, 30 second noise reduction (if set) and 40 seconds cool down for the chip.

[lrt75914]

Hey ronin, 

thank you for your reply and the time you put into reading the manual. You're right, I skimmed through the manual and it doesn't mention the 0.5 second pause between subsequent exposures. There is, however, an advanced manual for the advanced firmware (http://ca.skywatcher.com/userfiles/file/Advanced_Version_Operation_Manual_150605v1.pdf) that goes into detail on how the SNAP feature works when doing long exposures of the night sky. Essentially, you are able to set the exposure time and (if needed) the desired number of pictures. Regarding the interval between each exposure the manual states that:

The 0.5 second between each exposure is for the camera to save and process the previous picture. The value is unalterable.

The exposure setting on the camera is set to bulb so as to allow the mount to control the shutter release. As far as I know the mount will send out two signals indicating the begging and the end of the exposure interval. The camera will use these signals to set the exposure time yet ignores them while processing thus making images with reproducible exposure settings virtually impossible (unless you have a separate intervalometer). It seems like a really stupid way to limit the use of the snap feature. 

There is an astro-time-laps feature that allows you to set an interval time that can act as a buffer period between two consecutive exposures but it will not track the night sky and keep the landscape stationary instead. 

Just read the manual and there is no mention of an "interval" between exposures, which is what you need and is on the fairly simple intervalometer I have.

Now this may just be me being unable to see it but also the manual appears not to say that you can do multiple exposures. The section titled SNAP to me reads that you get one exposure and then you have to initiate the next by some means. In effect I cannot read anything that says it would start a subsequent exposure automatically after about 0.5 seconds. In the SNAP section it says:

Everytime the buttons are pushed on, or the mode is switched or the Slide Switch is slid, the selected shutter interval period will restart.

I can see nothing that says that you can set the SA to take a series of say 8 exposures, it reads that you take one then you start off the next manually by one of the above actions. Will say that the manual appears poor. From having a Sony 0.5 seconds to write is not going to work, they take longer then that

Just a thought but what have you set the exposure setting on the Sony set to?

I am wondering if things are a bit mixed up?

Set an exposure of say 30 seconds on the Sony then try.

I am wondering if the SA simply sends a "Press" to the camera every 100 seconds and that the camera has to be set up to accomodate all the actions required within that 100 seconds. In effect the SA is just saying Go.

My thought is the camera is set to 30 seconds, then the camera may take a noise reduction exposure (if on) - another 30 seconds, then everything just waits until the SA issues the next Go is sent out after 100 seconds.

With the above you get 30 seconds exposure, 30 second noise reduction (if set) and 40 seconds cool down for the chip.

[lrt75914]

Now that I think of it, the mount might just send out one signal that keeps the shutter open during the whole exposure time. That would explain why the camera doesn't just skip an interval and starts imaging mid exposure interval instead. 

[freiform]

The time it takes the Alpha 77 to process and save the images, however, usually exceeds the exposure time [..]

Do you mean a 5 s exposure will take an additional 5+ s to process and store? If so, then most likely the internal dark subtraction is enabled ("long time exposure noise reduction" or the like..). The camera will then take a dark frame with the same exposure as your light frame and use it to reduce the noise.

[lrt75914]

I was wandering what the camera was doing while it was 'processing' the image. Disabled the function and now it works flawlessly. Thank you very much .

Do you mean a 5 s exposure will take an additional 5+ s to process and store? If so, then most likely the internal dark subtraction is enabled ("long time exposure noise reduction" or the like..). The camera will then take a dark frame with the same exposure as your light frame and use it to reduce the noise.

[happy-kat]

You will need to take your own dark frames now but at least you are controlling the situation now.

[lrt75914]

I was planning to take my own dark frames any old how. That seems like a small price to pay for the convenience of having an integrated intervalometer.

You will need to take your own dark frames now but at least you are controlling the situation now.