DSS Revisited. Problem overcome.

[Kev11 (Kevin)]

I started a thread on this forum recently headed “Why won’t DSS stack more than one frame?” which attracted more than 40 posts. Unfortunately, by the time I decided to call a halt I was still at square one with my unstackable subs. However, yesterday with a bit of lateral thinking I finally found the setting in DSS I needed to change. I describe the process and the result at the end of this post.

But first I want to clear up two confusions about DSS that came up in the course of the previous thread.

The operation of the threshold level setting on the Advanced tab on the Registration menu. Think of the threshold being like the bar on the high jump stand. Ground level is 0% say 3m is 100%. 2% is easy to jump, (INCLUDES heaps of stars), as the bar moves up 20, 40, 60% .... it gets harder to clear (more and more stars EXCLUDED). The effect can be seen if you Register a set of pictures (Lights) at say 50%. After Registration is finished scroll to the right of the screen to find a column headed Stars, click on the down arrow in the header to bring the light frame with the highest number to the top. Write the number down. Repeat with a lower threshold, say 20%, then at again 80% and you will see the way it works. The confusion comes, I think, because we usually think a higher percentage means “better”.

DSS does not refuse to stack out-of-focus or poorly tracked stars. I have had sequences of frames with more doughnuts than an American coffee counter and more tails than a flock of geese; DSS still stacked them. The final picture was rubbish of course, but DSS didn’t tell me I could not do it.

What DSS default configuration cannot handle is what I call low contrast which in the old film days was the result of serious over- or under-exposure (not that one could over-expose a piece of deep sky). With film one played with the time and temperature of the development tank (assuming one knew beforehand it was likely to be a problem – no second chances with roll film!)
In the digital world an answer lies in settings available in the bottom left-hand section of the DSS screen headed Options, namely Settings... Raw/FITS DDP Settings. On the RAW files tab there is a box headed Colors Adjustment with three adjustments: Brightness, Red Scale and Blue Scale each with a default value of 1.0000. I found by increasing the Brightness to 7.5000 and bringing the Registration threshold down to 5%, DSS could find 200-300 stars in each frame (rather better than 0-4 I was getting originally!) and happily stacked. The attached final picture of NGC55 is a stack of the best 80% from 20 subs of 30s exposure at 1600 ISO. Not a prize winner I freely admit, but a hell of a lot better than the “one frame only will be stacked” result.
Cheers from an old dog learning a few new tricks (slowly).

[RyanJones]

Would you like us to :

A) Simply accept your explanation

OR

B) HELP YOU to understand the flaws in your explanation so that you can become a better astrophotographer ?

[xelasnave]

Originally Posted by RyanJones

Would you like us to :

A) Simply accept your explanation

OR

B) HELP YOU to understand the flaws in your explanation so that you can become a better astrophotographer ?

I suspect option A.

You can lead a horse to water but you can't make him drink ...well walk him out to waist deep and hang an anvil around his neck and he will drink alright but the problem here wont be solved that easy I guess.

I will wait for all the other members to chime in saying Kevin is right but I have to tell you I think he is very wrong and will do anything and everything to avoid any admission in that regard...I wish him good luck with that.

Anyways Kevin keep the images coming as with each you will get better..I do applaude you for trying and embracing new technology....try a focuser mask it will help you a great deal...how did you focus when you used film?...and do you have any samples of photos you have taken with film...did you "hype" your film?

All the best.

Alex

[glend (Glen)]

Look let's be charitable. It is hard being a beginning imager, there are many things to learn, and some to not learn. It is easy to get cocky. Experience grinds the bumps off all of us. Let it go.

[xelasnave]

Originally Posted by glend

Look let's be charitable. It is hard being a beginning imager, there are many things to learn, and some to not learn. It is easy to get cocky. Experience grinds the bumps off all of us. Let it go.

I was being charitable Glen....although I have been a little Grumpy having bought the new genny and unable to get it out of the car for a couple of hot days and missing one good night cause the batteries were flat..however late yesterday I constructed a ramp and by using books to jack it up in the back of the car to reach the ramp I managed to get things going to have a perfect night last night and processing in air conditioned comfort today...
Kevin is ok I am ok and we are both no doubt too old to be cocky...wow..a stack just materialised and it is amazing, lunch is Indian takeaway and the ginger beer is ice cold I am in bed learning new guitar licks...and best news of all..last night I saw my first Tardigrad ..water bear thru the new microscope...life is wonderful when you drive a TS 115mm...I hope you are doing as well. I admire you concern and kindness to others.
Alex