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DSS help, no better than single image!!


Peco4321

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Last night I was really excited for imaging the Blue Snowball Nebula, so processed 32 x 1 sec exposures (no tracking), 10 darks and 10 bias.  The results however are no better than the 1 sec single image, any advise please?  Below are a couple of processed and stacked images, 2nd one tinkered with in GIMP, 3rd one is single image, converted from RAW file.

23rd Sep.jpg

23rd Sep2.jpg

IMG_1159.jpg

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Agree with @wxsatuser you are wasting your precious imaging time with exposures that short, get decent polar alignment, and go for maybe 30 secs and you will see the difference.. :)

In your image the stars are staring to trail  in the 1 second exposure, the PA must be way way off !!....ignore this second comment just saw you said no tracking, well maybe you need tracking then....but you still need much longer subs

 

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Your signature doesn't say if you have motors on your mount, but I assume you don't, since it says EQ3-2, which is the one without motors, and your post says "no tracking". To do AP you need a tracking mount and longer exposures. As @wxsatuser noted, you won't get anything but the brightest stars with 1 sec exposures.

That being said, if you use a faster lens in stead of the scope, you can get slightly longer exposures. Then, stacking maybe 200 of those, you will get the noise down and be able to stretch more. This will make it possible to image bright, larger DSOs, such as the Pleiades and the Orion Nebula.

And of course, plan to invest in a tracking mount ( EQ3-Pro, EQ5 or higher, depending on your budget)

 

Good luck

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I'm just trying to get the best possible from the kit I have. There is another thread regarding short exposures but I was just wondering why DSS doesn't improve things from just a single exposure.  I have decent images of the Ring Nebula stacking say 40 subs, and the stacked images are better. Not sure why it hasn't worked this time. 

Single exposre processed in ps light on phone. 

image.jpeg

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What do you mean by better? If you compare the Blue Snowball neb to the Ring neb, you also have to consider their brightness.

The stacking process, including calibration, will (only) reduce noise (+ remove hot pixels, vignetting, etc), it will not increase the signal. But by reducing noise, you increase the signal to noise ratio (SNR, S/R), which will allow you to stretch the image more, thereby making weak signal visible. This weak signal would otherwise have been "burried in the noise".

To get the most out of the results from stacking a large number of light frames, you then need software that can process (not just import) at least 16 bit images.

 

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Maybe someone can work it out but were you actually pointed at the Blue Snowball?

Even with a DSLR lens set to around 20mm, so quite wide, it is a bit hit and miss to even getting M31 in the field - I know as I tried, I did get it but a bit higher up then I expected.. So a 3" refractor will be difficult to get it pointed at the exact right location.

Say you had it central to start with, after 32 seconds and likely a bit longer - was there a noise reduction exposure did you allow time for the sensor to cool - would the Blue Snowball be in the field. You may have taken short exposures to minimise star trailing but without a tracking mount the sky just keeps moving for the whole duration of the multiple exposures. If the whole lot lasted 60 second the sky will have drifted 0.25 degree. Consider your scope is half the claimed filed as the value given is edge to edge yet of imaging the object generally starts in the centre, so the travel "distance" is centre to edge.

I suspect that you are going to need tracking of some variety, unfortunately that is the nature of heading into AP, there are a few minimum requiements. Also what is the 3" refractor that you seem to be using?

You will I guess need more then 1 second exposures, my last lot of unguided were 12 expoxures each of 25 seconds, so 300 seconds worth. I also think that DSS threw some out, vague memory said it discarded some, if so did your stack actually use all of yours?

Would there be sufficent light from the Blue Snowball to "fill" or "trigger" the pixels into registering anything with just 1 second. Just thinking that if all was aimed right there may have been insufficent photons to get over a sensor/pixel threashold.

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24 minutes ago, ronin said:

Also what is the 3" refractor that you seem to be using?

The 3" refractor in my signature is my old scope. I use a 150p on non motorised eq3-2 (motors for Xmas!). I am really just 'playing' at AP and loving it, pushing my set up to the limits. 

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3 hours ago, Peco4321 said:

 so processed 32 x 1 sec exposures (no tracking), 10 darks and 10 bias.  The results however are no better than the 1 sec single image, any advise please?

Could it be that DSS only processed 1 of the 32 ? You may have offered it 32 but did it actually say "Stacking x of 32" ( where x counts up from 1 to 32) ? The reason I ask is that I have given your first pic a big stretch and I can not see any stacking artifacts round the edge of it. Perhaps you did a crop though ?? (just to fool us :) )

I think we need a xtalball for this one. 8bit jpgs are not the best for diagnosis. In your original stacked TIFFs can you see any diminution of noise between the stacked and the singles ?

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1 hour ago, SilverAstro said:

Could it be that DSS only processed 1 of the 32 ? You may have offered it 32 but did it actually say "Stacking x of 32" ( where x counts up from 1 to 32) ? The reason I ask is that I have given your first pic a big stretch and I can not see any stacking artifacts round the edge of it. Perhaps you did a crop though ?? (just to fool us :) )

I think we need a xtalball for this one. 8bit jpgs are not the best for diagnosis. In your original stacked TIFFs can you see any diminution of noise between the stacked and the singles ?

Very good point. Think I'll run the process again later to check. 

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29 minutes ago, Peco4321 said:

Very good point. Think I'll run the process again later to check. 

is the pic you showed us a crop ?

and even without running again an inspect of the background noise should indicate something about what is going on, even a stack of just two frames should show a difference in the noise  if the brightness of the stars are low and not remarkable.

Good luck.

 

 

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The stack looks fine to me - but it is oversaturated (the snowball is white, but in the single shot it is green) and lacks colour. You need to up the colour saturation in DSS and play with the sliders to reduce the luminosity saturation . Also, if you are processing with the standard (8-bit) GIMP then always save the changes applied in DSS when you save the file, otherwise you will loose most of the detail.

NigelM

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