Improving DSS scores and how many stars needed to stack

[Gem (Grant)]

I am having mixed results so far. For some objects, I can stack no problems. Heaps of stars, scores in the 1000s, etc... but when I turn my attention to a galaxy... I can see the galaxy fine when imaging off a 30 second exposure. I then take dozens of 30 second images. They are a few brightish stars in the FOV. I then go to stack in DSS and get only 3 or 4 stars per image and scores of 100-150. Hence, it won't stack more than one light. Do I simply need to expose for longer? My set up has a long focal length (2350mm) and lots of flex in the guide scope, so I am having trouble with long exposures.
What length of exposure do most people find is ideal to balance being in town, with low-medium budget equipment, no permanent mount and being able to stack ok - when it comes to galaxies?

Pity, since the object (NGC 3166) had potential when you view just a single 30 sec exposure...

[rcheshire (Rowland)]

I don't use DSS, but have tried it here and there. I would try longer exposures to the limit of your equipment and see how that goes. Perhaps there isn't the signal in each sub exposure for DSS to work with. Can you post a sub to get some idea of what you are dealing with?

Exposure time in the burbs is usually around 3 minutes with a DSLR, but I see that you are using an ATIK (OSC?). The limit is the point at which detail is obliterated by the bright sky. Perhaps that's why your galaxy looks good at 30 seconds.

[Peter.M]

In settings under register settings there is a slider bar that is called
"star detection threshold" play with that and it should increase your star scores.

If your images are trailed too much it wont register them though.

[Gem (Grant)]

Here is a compressed version of a single sub (plus darks, etc..) to show that the galaxy IS there from 30 seconds and there are SOME stars...
If only it would stack... I had 60 odd 30 second exposures of similar quality!

[Gem (Grant)]

Originally Posted by Peter.M

In settings under register settings there is a slider bar that is called
"star detection threshold" play with that and it should increase your star scores.

If your images are trailed too much it wont register them though.

The slider is set to the extreme to try to pick up as many stars as possible.

[lepton3 (Ivan)]

Hi Grant,

I have used DSS a few times, and also had problems with it not finding enough stars to stack. It seems the program is just not suited to long f.l. setups.

If you are wanting to stick to free software, one alternative I have used is a package called ImageJ. There are some astronomy plugins which allow you to align and combine stacks. Not as sophisticated as DSS in terms of pixel rejection, but I'm sure it would give you a decent result given the sub you have shown.

-Ivan

[Nico13 (Ken)]

Just getting into imaging myself and using DSS with raw from my unmoded Pentax K5, took this last night and initially had problems with not enough stars recognized but set the slider to max and it worked ok.
Three of five frames lights only stacked about fifteen minutes total from five minute subs.

Getting there slowly.

[rcheshire (Rowland)]

There are not many stars as you say. I agree that the solution is finding an appropriate setting or as the case may be a different algorithm, if DSS has that facility. On the occasions that I have used DSS, recommended settings has been very helpful.

A different program may be the solution.