New To Imaging, help with camera settings

[Pete]

Hi, I'm new to this forum and the field of imaging and wondering about some advice on starting out, particularly exposure wise. Thankfully, I see that there's no such thing as a silly question!
I enjoy daytime photography and know how to use the 'exposure triangle' to get good photos at daytime; come to the stars, without my trusted flash, I'm at a loss (well, just haven't quite got there yet)!

I'm interested in starting imaging DSOs (nebulae, galaxies and clusters I guess!) As such, I have an astro-modded DSLR, a couple of filters (visible mainly, like the UHC and visual OIII), telescope and equatorial mount and guiding kit, but using it and nailing down the ideal camera settings still elude me.

I guess it's really the ISO - there's a couple of things I have seen on using the native ISO for the camera sensor which is preferred by some as it maximises the dynamic range of the sensor (this is usually ISO 100-400) but many use higher ISO (800-1600) as this reduces the exposure time required to get the sub, and therefore more subs can be obtained. The latter sounds like a better idea also if using stacking images and dithering in between (every few) frames as noise surely would get cancelled out by signal.

Can you share which you use and why?!
Also, what's an ideal exposure? Is there any 'starting point' for a DSO with magnitude 4 or 8?

eg, starting point is 30sec for Mag4, and 5min for Mag8, 10min for Mag10, with ISO1600 and f/7 scope.

I'd guess the aim is to avoid stars saturating, but that would imply use the max DR of the sensor, so back to first question! Or does one stack multiple exposures in DSS, or is it more deal with saturated stars in photoshop?! That's another topic!

Thank you in advance for any help!

[AstronomyUkraine]

6 hours ago, Pete said:

Hi, I'm new to this forum and the field of imaging and wondering about some advice on starting out, particularly exposure wise. Thankfully, I see that there's no such thing as a silly question!
I enjoy daytime photography and know how to use the 'exposure triangle' to get good photos at daytime; come to the stars, without my trusted flash, I'm at a loss (well, just haven't quite got there yet)!

I'm interested in starting imaging DSOs (nebulae, galaxies and clusters I guess!) As such, I have an astro-modded DSLR, a couple of filters (visible mainly, like the UHC and visual OIII), telescope and equatorial mount and guiding kit, but using it and nailing down the ideal camera settings still elude me.

I guess it's really the ISO - there's a couple of things I have seen on using the native ISO for the camera sensor which is preferred by some as it maximises the dynamic range of the sensor (this is usually ISO 100-400) but many use higher ISO (800-1600) as this reduces the exposure time required to get the sub, and therefore more subs can be obtained. The latter sounds like a better idea also if using stacking images and dithering in between (every few) frames as noise surely would get cancelled out by signal.

Can you share which you use and why?!
Also, what's an ideal exposure? Is there any 'starting point' for a DSO with magnitude 4 or 8?

eg, starting point is 30sec for Mag4, and 5min for Mag8, 10min for Mag10, with ISO1600 and f/7 scope.

I'd guess the aim is to avoid stars saturating, but that would imply use the max DR of the sensor, so back to first question! Or does one stack multiple exposures in DSS, or is it more deal with saturated stars in photoshop?! That's another topic!

Thank you in advance for any help!

Maybe this can help you out with iso settings.

 

https://dslr-astrophotography.com/iso-values-canon-cameras/

 

I don't use a dslr myself, but there are a few settings you need to disable in a dslr. In camera long exposure noise reduction needs disabling, dark frames will remove any noise. Disable in camera sharpening. Enable mirror lockup to stop any vibrations. Only shoot in RAW mode it will give you more signal to work with.

[PeterBolt]

I am fairly new to astrophotography but I find that with my older 12 bit Canon EOS 1000D (modified) I have to use ISO 1600 otherwise the objects are just too faint.  I found the following very helpful.

 

https://www.astropix.com/html/astrophotography/settings.html

 

I am yet to master dark and flat frames so I tend to use dithering and also take BIAS frames.

 

I am not sure if there are any set rules on setting the exposure...I think it's best to experiment on the night by making sure the histogram is approximately 1/3 of the way from the left hand side.

Edited October 13, 2021 by PeterBolt

[paul]

For my aged Canon 550d ISO 800 is recommended as the sweet spot. I sometimes use 1600 if conditions are not good.  Lower ISOs don't really improve the noise performance much because you are warming up the camera and you will need a correspondingly longer exposure to register the same signal.

 

My recent image of M31

(which is a very bright DSO) was done with LP filter, ISO800 and 5 minute exposures with short focal length refractor. Because I wasn't sure, I had also taken 1 minute and 2 minute subs just in case the core was burnt out but it wasn't. So in summary, apart from point sources like stars you are  unlikely to clip signal.

 

In the past I have found that under 2 minutes was a waste of time for galaxies with too little signal compared to the noise. Having said that, if you are imaging a globular and don't want the core burnt out you may need to use 1-2 minute subs. It depends a lot on how fast your scope is of course. (Most of my imaging is done at F4.8).

 

The other limiting factors for exposure is often the light pollution and the quality of guiding. A light pollution filter will allow longer exposure. Use shorter exposures to combat egg shaped stars.

Edited October 14, 2021 by paul

[Pete]

Thank you for your detailed answer @paul - this is exactly what I've been looking for! I've an astro-modded 550D so had spied the same 800 ISO for use.

f/4.8 also is my scope.

I shall try with this now and hope my images improve.

Thanks to others for your input - the astropix website looks to contain lots of useful info so need to just get some reading done during these cloudy nights!

[AstronomyUkraine]

On 10/13/2021 at 4:24 PM, PeterBolt said:

I am fairly new to astrophotography but I find that with my older 12 bit Canon EOS 1000D (modified) I have to use ISO 1600 otherwise the objects are just too faint.  I found the following very helpful.

 

https://www.astropix.com/html/astrophotography/settings.html

 

I am yet to master dark and flat frames so I tend to use dithering and also take BIAS frames.

 

I am not sure if there are any set rules on setting the exposure...I think it's best to experiment on the night by making sure the histogram is approximately 1/3 of the way from the left hand side.

Darks are the easiest of the calibration frames to make. Just cover the scope, and take dark frames with the same settings as your light frames. I would recommend about 50 dark frames.

[Pete]

More research and other posts I've been reading suggest that doing darks with DSLR is fairly pointless - as the camera isn't cooled, the darks that would be taken are fairly meaningless. Only with cooled cameras are darks really important/useful (example)

Dithering seems to be mentioned frequently in the topic of DSLR astrophotography - rather than darks, the consensus is do more lights and dither significantly between frames, with the hope that the signal is captured away from noisy pixels and once stacked, only the signal exists and can be stretched after. Whilst dark libraries can be done offline at predefined sensor temperature, there's no need to do extra frames (time consuming darks) whilst imaging - time to do more lights, which I guess is required for DSLR instead of dedicated astro-camera.

Anyway, in nutshell, ignore darks for DSLR - dither and do more lights if possible.

 

[paul]

10 hours ago, Pete said:

More research and other posts I've been reading suggest that doing darks with DSLR is fairly pointless - as the camera isn't cooled, the darks that would be taken are fairly meaningless. Only with cooled cameras are darks really important/useful (example)

 

 

I don't believe we need to get obsessive about dark frames for DLSRs but they are important. You will notice that the number of hot pixels  varies significantly by exposure length, ISO and temperature. There are a lot of hot pixels in a DLSR. You need to produce the dark frames at the temperature and duration and ISO your lights were produced at. The dark frames are themselves stacked and this noise floor is ultimately removed along with the hot pixels from your images. Similarly Bias frames (lots of short dark shots) provide a figure for the average read out noise. 

 

Personally I haven't been too scientific about my darks. I have one set for each exposure/ISO that I use for the winter months but if I use the camera in the mid year I tend to take darks for that session specifically as the sensor temp can be quite high (25- 30 degrees).

 

If you want to get more scientific and build up  a collection of darks note the temperature of your lights and if they differ by more than 5+ degrees from any other session then produce a new set of darks. Personally I won't worry about the difference between say 25 and 27 degrees.  So a collection of darks at 5, 10, 15,20, 25, 30 and 35 degrees would cover all eventualities and could be reused multiple times. If you find that in subsequent sessions new hot pixels appear then a new set of darks is probably required once it get objectionable.

 

I believe Bias frames are essentially independent of conditions if you take them soon after powering up the camera from cold. 

 

When guiding dithering is essential, the walking noise is significant and cant be removed otherwise. As soon as you begin to stretch your images the walking noise will be apparent. If I forget to dither I consider the session ruined.