Dss stacking problem

[jonnydreads]

First night using dss tonight, I put in 63 subs @ 20s, 20 darks, 20 bias. No flats.

Something came up and said only 1 image out of 63 will be stacked do you want to continue. I stupidly pressed yes and it obviously stacked 1 image....anyone any idea why?  I don't know the interface at all and it seemed like it was going well up until this point 

[vlaiv]

This is usually due to star detection threshold. When you are about to stack - check number of found stars - if it's too low - increase your threshold (or lower it? ).

[jonnydreads]

10 hours ago, vlaiv said:

This is usually due to star detection threshold. When you are about to stack - check number of found stars - if it's too low - increase your threshold (or lower it? ).

Do you mean registered settings? There is a setting for stars preset at 10%

[vlaiv]

1 hour ago, jonnydreads said:

Do you mean registered settings? There is a setting for stars preset at 10%

I remember bringing it down to 2-3% for some of my images - try lowering it and see how much stars are detected by DSS with lower setting. You need at least 10-15 stars for DSS to get good registration.

[jonnydreads]

42 minutes ago, vlaiv said:

I remember bringing it down to 2-3% for some of my images - try lowering it and see how much stars are detected by DSS with lower setting. You need at least 10-15 stars for DSS to get good registration.

thankyou. I did try that... I put it up to 50% because I have no clue what I'm doing ? it detected 1 star.... I had a look at some of the subs and I think I set the iso too high (3200).... I did that thinking I would capture more light because of the short exposures with my alt/az mount.

They looked awful so scrapped all of them... I'm going to try another target tonight and set it at 1600 iso @ 20 secs Instead..... 

12 hours ago, vlaiv said:

This is usually due to star detection threshold. When you are about to stack - check number of found stars - if it's too low - increase your threshold (or lower it? ).

Do you mean registered settings? There is a setting for stars preset at 10%

[vlaiv]

17 minutes ago, jonnydreads said:

thankyou. I did try that... I put it up to 50% because I have no clue what I'm doing ? it detected 1 star.... I had a look at some of the subs and I think I set the iso too high (3200).... I did that thinking I would capture more light because of the short exposures with my alt/az mount.

They looked awful so scrapped all of them... I'm going to try another target tonight and set it at 1600 iso @ 20 secs Instead..... 

Do you mean registered settings? There is a setting for stars preset at 10%

Here is what you should do - bring up above dialog. Lower slider to let's say 5% (sorry about confusion - it's indeed lowering threshold, not raising it), and press Compute the number of detected stars. Look at the number below the button. Does it read 10-15 or above? if not, lower it again. If it goes crazy high - like 500+ you have hit noise floor and DSS is finding noise instead of stars.

You might be having trouble finding your stars if they are too distorted or out of focus, but try above first and if you can't manage to get 10+ detected stars then we'll look into why DSS can't find them.

[jonnydreads]

55 minutes ago, vlaiv said:

Here is what you should do - bring up above dialog. Lower slider to let's say 5% (sorry about confusion - it's indeed lowering threshold, not raising it), and press Compute the number of detected stars. Look at the number below the button. Does it read 10-15 or above? if not, lower it again. If it goes crazy high - like 500+ you have hit noise floor and DSS is finding noise instead of stars.

You might be having trouble finding your stars if they are too distorted or out of focus, but try above first and if you can't manage to get 10+ detected stars then we'll look into why DSS can't find them.

Thanks very much.... I'll will take fresh subs later as it's going to be a great clear night here and I enjoy being out doing them. It's all a learning curve, alignment, focus, everything! 

[dph1nm]

Here's a tip. Do not go straight to "Stack checked pictures", instead use "Compute offsets" first. This will then show you the score, number of stars detected, dx dy and rotation offsets, sky and seeing for each frame. If dx and dy are not given values then that frame will not be used in the stacking process - you can then try and work our why. There must be at least 8 stars (in common) for frames to be registered by the way. - this is usual reason for failures.

NIgelM

[jonnydreads]

1 hour ago, dph1nm said:

Here's a tip. Do not go straight to "Stack checked pictures", instead use "Compute offsets" first. This will then show you the score, number of stars detected, dx dy and rotation offsets, sky and seeing for each frame. If dx and dy are not given values then that frame will not be used in the stacking process - you can then try and work our why. There must be at least 8 stars (in common) for frames to be registered by the way. - this is usual reason for failures.

NIgelM

Thanks.  What does dx and dy stand for?

[vlaiv]

45 minutes ago, jonnydreads said:

Thanks.  What does dx and dy stand for?

number of pixels image must be translated/shifted in X and Y direction in order for star centers to match.

Dx, Dy and Rotation mean  - translate image Dx pixels in X direction, translate image Dy pixels in Y direction and rotate by N degrees and it will align to your reference image "perfectly" (not really perfectly, there is always some residual error, but small to notice by eye).

[jonnydreads]

2 hours ago, vlaiv said:

number of pixels image must be translated/shifted in X and Y direction in order for star centers to match.

Dx, Dy and Rotation mean  - translate image Dx pixels in X direction, translate image Dy pixels in Y direction and rotate by N degrees and it will align to your reference image "perfectly" (not really perfectly, there is always some residual error, but small to notice by eye).

Wow. Head blown off 

[vlaiv]

6 minutes ago, jonnydreads said:

Wow. Head blown off 

Those are just stats for particular sub - you don't have to do anything your self, DSS will handle all of that for stacking.

You can deduce some things for those stats, like having larger rotation angle can mean couple of things - like you took your data on two separate sessions but failed to orient your camera to sky properly so images are rotated in second session in comparison to first one. If angle is small - it can mean poor polar alignment as there is field rotation during imaging session. If you do meridian flip and have slightly different angle pre and post meridian - it could point to cone error.

If you have significant dx and dy values - this means that you will need to crop quite a bit of image to avoid stacking artifacts at the edges. Depending if you are guiding and dithering it can be indicative of slow differential flexure.

[jonnydreads]

Is there sonethig fundamentally wrong with my camera settings because I am getting no stars at all on dss registration now. My images are really dark too 

[happy-kat]

Show us the histogram on your image you took please.

Review mode then you can probably see it by pressing disp.

[jonnydreads]

3 minutes ago, happy-kat said:

Show us the histogram on your image you took please.

Review mode then you can probably see it by pressing disp.

 

[jonnydreads]

That looks quite low doesn't it.... I dont know much about it but it feels low ?

[happy-kat]

Yes that is too low, try ISO 1600, want to move the peak clear of the left edge.

[jonnydreads]

I was trying to image the whirlpool. Only because it was in perfect location for me.... I did try 1600 last night but it wasn't much different. Whatever I'm doing wrong i certainly don't have to worry about over exposure.  I may as well try out all settings next time it's clear 

[jonnydreads]

5 minutes ago, happy-kat said:

Yes that is too low, try ISO 1600, want to move the peak clear of the left edge.

"want to move the peak clear of the left edge".. 

What do you mean by this 

[happy-kat]

Take a sub at 1600 and show the histogram again to share here.

On My canon 1100d I can not go above 1600 as the noise gets awful.

[jonnydreads]

Yes I will tomorrow. Weather app says it's clear. Thanks.... Shall I take one on each iso setting to see the difference? 

[happy-kat]

aperture would too but you cannot change this with your current setup.

[jonnydreads]

I've never actually seen anyone else's subs so I don't really no what to expect... I think that's been half the problem ?

[jonnydreads]

3 minutes ago, happy-kat said:

aperture would too but you cannot change this with your current setup.

Where would these expected to be on a regular sub?

[happy-kat]

On a regular picture use P or A mode then take a look at the histogram