First time imager!

[cnarayan]

Hello all.. I am a complete beginner at this and have just this week figured out how to capture my first deep sky images. While, I am starting to understand the workflow around imaging and gotten some practice with it, I am struggling with calibration frames. Most of my imaging sequences take several hours and at 3:00 AM or later. My hope is to star the imaging session and go to sleep with the ASIAir sending the scope to the home position and shutting it down. But the shooting dark frames get in the way of that. Do I need a robotic arm to cover my newtonian scope at the end of my session to start the dark frame sequence? This is a real bummer. I have however done some aggressive dithering that might have improved matters a bit.

 

My rig consists of :

EQ6R PRO, 8" Skywatcher Quattro Newtonian,

Synscan WiFi adapter, ASIAIR PRO,

ASI120MM Mini Guide Camera with 30F4 Scope,

Canon T6i DSLR Unmodified Primary Camera,

NO filters, Zwo EAF automatic focuser (not installed yet),

iPad/iPhone only for imaging sessions, Skysafari 6 Plus,

Mac Pro server for Image Stacking and Processing using the fantastic and free SiriL tool (https://siril.org) for macOs.

 

I have completely ditched the hand controller that came with the eq6r replaced with Synscan Wifi.

 

I  am a high-school computer science & math teacher and purchased this telescope and accessories for a 3-week long immersive astro photography session for my students with this setup starting on May 17th.

 

Any pointers on the dark frames conundrum and image processing improvements below will be very helpful indeed. I intend to use this information building lesson plans.

In the meanwhile, this is what I have captured so far in the first 3 weeks of imaging.  Clearly there are issues with calibration& processing  in all of these images.

 

The Pinwheel galaxy M101, 70x180s @400 ISO with dithering, no dark, but used flat and bias fames

Whirlpool galaxy M51, 60x120s @800 ISO no dithering, dark, flat, and bias frames used

Sunflower galaxy M63, 45x180s @1600 ISO, no dithering, dark, flat, and bias frames used (terrible pictures with many issues)

A second attempt at Orion Nebula with Running Man Nebula M42, 200x120s 200 ISO with dithering, dark, flat, and bias frames used

Bodes galaxies M81/82, 300x30s @400ISO, no dithering,  dark, flat, and bias frames used in order below

- chandru

 

Edited March 18, 2021 by cnarayan

[EntropyTango]

Very good start, and nicely guided.

All I would say is keep that ISO to 400 or less

[smashing]

Nice images...I have a DSLR and just dither now rather than using darks.

[Laurieast]

You could try using Gradiant Xterminator on those. You can use it for a trial period.

https://www.rc-astro.com/resources/GradientXTerminator/
 

[bottletopburly]

If using a dslr I would take Flats every session , bias frames can be taken in the house place camera in a bag leave in fridge for a while to cool take 30 bias frames and create a folder , dither at least 15pixels , I use APT for aquasition  and guide if possible don’t bother with darks , load bias frames as your dark frames in DSS or whatever stacker you use , how do you plan to process images, I would recommend Startools free to try as long as you like though you can’t save final image (screen shot to save) but is very competitive in pricing £40 ish  .

[alacant]

15 hours ago, cnarayan said:

the fantastic and free SiriL

Hi

Lovely images and good advice about losing the dark frames. In Siril though, use the bias as a bias; it will eliminate the 6i's banding. Dither between light frames and try Siril's linear clip algorithm for stacking.

I wish someone had recommended a fast reflector when I first began. I spent a year with a miserably dim refractor before seeing the light. Sorry for the pun. Couldn't resist!

+1 for StarTools. It will eat that background alive:)

Cheers

 

Edited March 18, 2021 by alacant

[cnarayan]

6 hours ago, alacant said:

Hi

Lovely images and good advice about losing the dark frames. In Siril though, use the bias as a bias; it will eliminate the 6i's banding. Dither between light frames and try Siril's linear clip algorithm for stacking.

I wish someone had recommended a fast reflector when I first began. I spent a year with a miserably dim refractor before seeing the light. Sorry for the pun. Couldn't resist!

+1 for StarTools. It will eat that background alive:)

Cheers

 

Hi alacant! thanks for the comments. Did you mean to say use the bias as a dark in your comments?  I wasn't sure. I will try substituting the bias as my dark and see if it improves my results, especially on the Sunflower galaxy. I will post the results! Can you provide a link for the Siril linear clip algorithm?  Is it on the menu? Sorry to hear about the challenges with the refractor. I did get a good recommendation  about the Newtonian. However, it is quite unwieldy with contortionist viewing positions.  For imaging it isn't probably much of a concern. Transporting a Newtonian to a dark sky site can also be challenging. 

- Chandru

[cnarayan]

13 hours ago, bottletopburly said:

If using a dslr I would take Flats every session , bias frames can be taken in the house place camera in a bag leave in fridge for a while to cool take 30 bias frames and create a folder , dither at least 15pixels , I use APT for aquasition  and guide if possible don’t bother with darks , load bias frames as your dark frames in DSS or whatever stacker you use , how do you plan to process images, I would recommend Startools free to try as long as you like though you can’t save final image (screen shot to save) but is very competitive in pricing £40 ish  .

Creative choices! I will try startools and see how it works! Thank you for the feedback.

[cnarayan]

21 hours ago, EntropyTango said:

Very good start, and nicely guided.

All I would say is keep that ISO to 400 or less

Thanks! yeah ISO 400 images look very clean indeed!

[cnarayan]

13 hours ago, bottletopburly said:

I would recommend Startools free to try as long as you like though you can’t save final image

Thank you for the recommendation, I will definitely give startools a go

[rickwayne]

I assume that M51 is cropped a lot, given the field of view of the others, which is why  it's  so noisy. I'd say M81-82 is your most successful processing, the black point is maybe a little high. If you leave a smidge of light in  the background (with 8 bits per color channel, something  like 30R, 30G, 30B) you'll be able to retain more detail  in  faint nebulosity. If  these  are your  first  efforts, I'm  pretty jealous!

Late-model DSLR sensors often don't exhibit much dark current or amp glow, the two problems mandating dark frames. My Pentax, for example, seems to do fine without. If you  do decide you  need  them, since dark current depends on temperature, and your rig is most likely cooling down during the entire imaging session, you might be able to either get away without darks or do them first thing. Most likely the temperature is changing more slowly at the end, of course.

Folks with observatories and automation often set up a lighted panel of some sort on the wall, then have the scope slew to point to it at the end of the night and take their darks. Conceivably you could do  something similar with a black panel mounted so that the end of  the dew shield  just grazes it, maybe a 3-sided box to minimize ambient light? I dunno, might just bend the  dew shield or dink your mount  if it  weren't exactly right.

Another strategy would be to take sets of  darks at different  temperatures  (cooling the camera is left  as  an exercise for your ingenuity), then  look at  the EXIF data  for your light  frames afterward to determine which set of darks to choose. It would be tedious, but you could put the bagged room-temp camera in a  freezer, let it shoot for awhile,  take it out,  warm  it  back up, repeat for  a  few  cycles,  then collate  the resulting frames  by  EXIF sensor temperature  into sets. You don't need a bazillion darks to yield  a useful master dark  for a given temperature, so a few cycles would probably  give you darks for several temperatures.

Note that I'm specifying EXIF data rather  than, say, putting a thermometer in  the bag, because  what counts is  not  the ambient temp but the sensor temp.  And  that actually varies even if the ambient does not, since the electronics heat  up in use and cool down when they sit.

I suspect you'll find that flats give you a much bigger bang for the buck than  darks, frankly. And  you can do those before  you  start  the sequence.

[alacant]

10 hours ago, cnarayan said:

use the bias as a dark

Hi

Use a bias as a bias.

There's another trick you can try in Siril to which some dslrs respond, that's dark optimisation where the light frames have been taken at diffent temperatures to the dark frames.

Subtract the master bias from the dark frames then stack the dark frames using median stacking. You now have three entries in Siri'ls post processing one each for bias, dark and light. 

Of several dslrs I've tried, only the eos450d gave better results with dark frames so do let us know if you try with your 750.

Cheers

[cnarayan]

rickwayne! very interesting ideas on using the dew shield for darks and fridging the camera for creating a dark library and using the EXIF to tag it! It seems like a lot of work, but may be worth it not to have to stay up late into the night. For now, I am just going to skip the dark to see if some aggressive dithering fixes it. Yes M51 was cropped - maybe I should try to process without the crop to see if it is any better.  I might have just gotten lucky with M81/82. Good pointers on the black point having about 8 pixels in RGB.  I also think that shooting at 1600 ISO is too much noise for the T3i. From everything I hear, I have had some beginners luck for this first 2 weeks of imaging. It may not hold out.

 

[cnarayan]

alacant. I am not sure how to do the things mention in Siril. Did you develop custom scripts for those? When I tries using their step-by-step processing tabs, I have had poor results. The only thing that has worked for me is to use the OSC_processing script. Are there some pointers you can give for processing  in a tailored manner?  I can then try in on the canon T3i (750D).

[alacant]

we've been here many times;)

 

[cnarayan]

On 19/03/2021 at 14:38, alacant said:

we've been here many times;)

 

Thank you alacant, your video helped a lot!