festoon

Hi @almcl apologies for that...hopefully this helps

DSS (72 light frames, 1 master dark, 1 master flat)

Register = 2 mins

Stack = 4 mins 40 secs

ASTAP (72 light frames, 1 master dark, 1 master flat)

Analyze and Organize = 1 min

Stack (Sigma Clip) = 5 mins

So as I suspected in my previous message, there is hardly anything in it

6 minutes ago, han59 said:

The first new ASTAP version 0.9.526 is ready. 

1) Master flat and master dark can be created based on date.  So you can add all flats to the flats tab and per day a master flat will be created. This is activated by option "classify by date for master creation"

2) For the light the master dark and flat with the nearest date will be selected.  This will happen if more then one compatible flat or dark is found.

Download developments version: http://www.hnsky.org/astap_setup.exe  Feedback is appreciated.

Han

 

 

Thats super cool - I'll give that a go @han59

Thank you for including this

On 10/04/2021 at 14:38, han59 said:

What you could do now is to calibrate only. The dark and flat-dark master is applied to the light and the light is stored as calibrated.  For each night series you do that with the appropriate dark and flat. Then just stack the calibrated lights.  The calibrated files and up in the results tab and can be copied to the lights tab again for stacking.

 

Thanks for the suggestions @han59. If I understand correctly, what you are suggesting here is for for each nights work in ASTAP calibrate the subs with the correct dark and flat then save the result. Then for different night repeat the same procedure. The stack all the results together at the end. Is that correct?

8 minutes ago, bottletopburly said:

I’m assuming the stacked fits can be stacked together from multiple nights of the same target maybe @han59 can  help .

Yes, good point, you can stack stacked results in ASTAP. Not sure of the science of this, but if you have subs n1,n2,n3,...,nn with master dark d1, master flat f1 from night one and m1,m2,m3,....mm subs with master dark d2, master flat f2 from night two - is the resulting signal to noise of a stack of ((n1-d1)/f1+(n2-d1)/f1+(n3-d1)/f1+....+(nn-d1)/f1+(m1-d2)/f2+(m2-d2)/f2+(m3-d2)/f2+....+(mm-d2)/f2) subs equal to the signal to noise of a stack of ((n1-d1)/f1+(n2-d1)/f1+(n3-d1)/f1+....+(nn-d1)/f1) with ((m1-d2)/f2+(m2-d2)/f2+(m3-d2)/f2+....+(mm-d2)/f2)

I've found the speed of stacking in ASTAP to be similar to DSS.

I'm still to find a way of applying different flats to datasets from different nights using ASTAP. Using DSS this can be done by grouping data. To me this is an advantage of DSS, unless it can be done in ASTAP.

That's a very good suggestion to have a play with data sets and try it out.

Last night...we a had a night of clear skies from dusk till dawn in Cambridgeshire and I took hours of data on M81 and M82....However, Murphy's Law - Clear night=Moon out! The forecast is also the same for tonight. I'm debating if I should set up or just wait for the next dark night Or just image the moon  

Hoping for some advice on how to stack data from multiple nights imaging sessions. My set up is with an OSC, and I don't have narrowband filters at the moment (waiting for an NBZ).

If I acquire data on a clear moonless night, does adding data from another night where say its a full moon going to lead to the image signal to noise going up or down? I'm particularly thinking about faint nebula or galaxies. What I'm wondering is - am I wasting my time imaging during full moon. If I add that data will it degrade the image from a dark night or sky.

Having planned this for over a month, I was delighted to have captured the ISS as it transited the moon tonight (21/03/2021). 

I used the webpage https://transit-finder.com/ to find where and when the ISS would transit the moon in a location which I could drive to. The afternoon was overcast, so my expectations were low. However as evening approached the moon was occasionally visible between clouds. So, I packed my stuff up during the day, drove to the planned location (Longstanton, Cambridgeshire), and set up. As the moment approached of the ISS transit, there was intermittent clouds, but luckily I could make it out on Sharpcap as it passed through. 

For this capture I used a Celestron C5 with an ASI385MC mounted on an AZ-GTi in eq mode. Data captured using Sharpcap with 5ms exposure and a gain of 142. I used SER Viewer to extract the relevant frames, then deconvolution in imgppg , then GIMP to create the GIF.

Today will be an imaging session I will never forget!

When I'm planning EEVA sessions I often use https://tonightssky.com/MainPage.php

Once you have put in your parameters, you can select e.g. if you want to look at galaxies, nebula, or clusters. After you click whats in sky tonight, at the bottom of the generated list, you can sort by RA rise time and generate an observing plan.

I often find I spend the night doing EEVA galaxy marathon sessions this way going through the list one by one. I'll spend 5 to 10 minutes on each target and record the image at the end and take some notes in my book showing a log of date and time and what was observed.

This may not sit properly in this thread...apologies if not I'm happy to move it.

I've been thinking about the MTF of optical systems and how to model the MTF of a lens from basic principles.

The minimum spatial resolution in lpmm for ideal lens with diffraction for 550nm light can be modelled as 1812.2/F where F is the focal ratio. From this we can calculate the Rayleigh Criteria as this number divided by 1.22 and MTF50 as half of the Rayleigh Criteria.

So fo an ideal lens the MTF50 at 550nm for a varying F number would be as below

Now in reality this is never the case. The actual MTF50 never reaches the theoretical due to the resolution of the sensor and optical abberations.

I've found this reference below showing the effect of the sensor pixel size on the MTF50 value (https://www.dpreview.com/forums/post/63709384)

Is anyone on here able to please help me to understand how to simulate this? i.e. how to go from the diffraction only to diffraction + pixel

Seems there was a bright fireball/meteor tonight visible in the UK. Very disappointed not to have seen it, it happened between me being out observing and putting the kids to bed. Hope some of you managed to catch it

Not sure of your location but SES-4 was pretty close to there at a similar time. Image taken from https://in-the-sky.org/ 29/02/21 at 20:35, location Colchester, UK

Point taken about zoom and how you sample or re-sample an image - dont go beyond 100% And I guess the point is it depends how you process your data i.e. if you re-sample use a method which smooths.

In terms of the specific lens I have (the Samyang 135mm) the measured resolution at the centre of the image plane at f/2.8 is 47 lpmm (as defined by MTF50, reference https://www.lenstip.com/442.4-Lens_review-Samyang_135_mm_f_2.0_ED_UMC_Image_resolution.html). That corresponds to a size of 21 um. To sample 47 lpmm sufficiently you would need a pixel size of 10.5 um or less. If you use a colour sensor (sampling reduced by x2) and you would require a pixel size of 5um or less not to lose detail.

Is this interpretation correct?

You also might argue that a vanishing resolution of an image could be defined at somewhere between MTF10 and MTF20. That would correspond to smaller and smaller sizes in terms of pixel size....at which point you come down to the seeing limit of perhaps 2 arcsec/pixel and a pixel size of 1.3 um.

1 hour ago, vlaiv said:

Do you think that this image is under sampled and why?

At this zoom you dont see that it is undersampled. I understand that perception and presentation make a big difference. If you look at the stars and galaxy at a higher zoom it is apparent it is underampled

11 hours ago, vlaiv said:

What do you think will be noticeable effect of under sampling

The effect I am thinking is that too few pixels are captured for the resolution of the lens

Just a further thought on this...when I was using the 6.5um pixels at 135mm samyang then if sampling rate is x2 due to it being an osc, the the effective sampling is using an equivelent of 13um.

@vlaiv - do you not think that this will be starting to become noticeable in terms of undersampling as you calculated that good pixel size for such lens is about 10-12µm?

super info - thanks @vlaiv

So what I take from this is - when using an OSC if doing bilinear interpolation debayering sampling is x2 what it would be with a mono camera

However at x2 sampling some sharpness in smaller stars is lost, but image still shows good detail as shown in the GIF comparison you posted. I think the former is what I was experiencing with smaller stars

I'll have to see if I saved any images with the 6.5um OSC. I certainly was not impressed hence why I switched to the ASI224MC Cool sensor with smaller pixels.

I guess undersampling may not be the correct word, but with the larger pixel size the stars appeared more square on the monitor.

Also purely from a understanding point of view I would like to understand if OSC does effect the resolution of the image

Thanks @vlaiv. So I guess what you are saying is the lens is diffraction limited so having smaller pixels makes no difference. The thing is I saw a massive difference in perceived resolution moving from 6.5um pixels OSC to 3.75um pixels OSC. Obviously less blocky even on widefield targets.

Yes this is the Samyang 135mm f/2

10 minutes ago, wimvb said:

Unless you only image planets and galaxies, of course. But for those you’d need a smaller pixel scale and much longer focal length anyway.

Deep sky imaging in general - I did take some images with this set up of M81 and M82 and as expected the resolution was poor. But I was thinking maybe some of that was down to the fact its an OSC sensor. Also from an inquistive point of view is there a way to calculate what sized OSC pixel size would give equivelent results to a mono setup?

Currently I'm imaging at 135mm focal length with a an OSC sensor with a pixel size of 3.75 microns. Thus I'm undersampling at 5.73 arcsex/pixel. But I was wondering is my sampling even worse than this because I'm using an OSC with a Bayer Matrix? If so would I see a noticeable improvement in image resolution if I was to use a mono sensor with the same pixel size?

Just now, Alien 13 said:

Might just be me but there is far more detail in the F2 images to my eyes..

Alan

Yes I'd agree with this...I think there is more signal to noise in the f/2 image (especially on M42).

Thanks @carastro.

To the best of my ability yes these images were processed the same (using Startools).

The results at f/2 (and f/2.8) are pretty amazing.  As I was using a colour CMOS I was not using any filters to begin with, and I did notice bloating of the brighter stars but thanks to advice from @vlaiv to use a UV/IR filter the results were massively improved. I was also advised to try f/2.8 hence the comparison here.

I don't think the difference is massive at f/2.8 compared to f/2 but I think it can be detected in the images above.

Also I'd agree with the comment about how pleasing this lens is - this is a wonderful lens that I am also very pleased with. I've had much more imaging time since I've started using it since its on a lightweight set up that is really easy to carry and set up.

Here are a few images taken using the Samyang 135mm at f/2 and f/2.8

The sensor used is a ASI224MC-cool with a UV/IR filter. I've tried to keep as many of the parameters the same as possible, including the image processing. One difference to note is the f/2 images were taken on 10/02/21 on a moonless night and the f/2.8 images were taken on 18/02/21 with 38% moon.

Going forwards I think I will stick with f/2.8 going forwards, but I'd be really interested to hear what you think. Eitherway, I think its a fabulous lens and give amazing results!

The first target is Orion Nebula M42. In each case the subs were 10s long and about 90 mins of data was collected. Based on this image I think the stars are less bloated with the aperture at f/2.8 - especially the brighter stars. There is a little SNR gained by using f/2 over f/2.8

F/2 Image

Now f/2.8 image

Next target Andromeda galaxy M31. In both cases we have about 2 hours of data. Comparing these two images - they look very similar. Very similar SNR and very similar bloating on stars and star shapes.

F/2 image

Now f/2.8. The difference in the core of M31 in this image is that I purposely did not tame the core in this image as much as in the f/2, as it did not look natural.

Here is my submission for the theme satellites

The title is Starlink, and shows the effect that the SpaceX starlink is having on our sky, astrophotography, and astronomy science. This data was only 1 hour long and taken on 10/02/21. I've processed and merged two images one where the satellite trails where removed from the stack and one where they were not.

Imagine how many subs we will have with satellite trails where there are 50,000+ of these in our sky