han59

FYI, the ASCOM Sky simulator version 1.8 has been released. The default star database goes now up to magnitude 14.  Improved artificial stars.  Deepsky labels can be switched off.  The image dimensions are now set at one place in the program.

Han

Doesn't help you but note that the free alternative GIMP can read FITS file.

Han

It is possible to plot in an spreadsheet both the measured V-curve and the hyperbola fit as found:

Here an early report of my setup
13:22:39  median        Focus=35972    a=1,23909     b=143,37264    _____________        lowest error=0,01187     iteration_cycles=4
13:22:39  center        Focus=35925    a=1,87688     b=212,46136    _____________        lowest error=0,00540     iteration_cycles=4
13:22:39  outer ring        Focus=36028    a=0,30912     b= 37,90557    offset=  103        lowest error=0,02590     iteration_cycles=6
13:22:39  bottom left        Focus=36000    a=1,47225     b=169,40969    offset=   75        lowest error=0,01023     iteration_cycles=2
13:22:39  bottom right    Focus=35825    a=1,52325     b=167,86880    offset= -100        lowest error=0,00695     iteration_cycles=2
13:22:40  top left        Focus=36094    a=1,39523     b=159,90826    offset=  169        lowest error=0,00958     iteration_cycles=4
13:22:40  top right        Focus=35934    a=1,74906     b=200,38594    offset=    9        lowest error=0,00777     iteration_cycles=4

My focuser makes about 1500 steps per mm, so the found differences up to 169 steps are very small a little more then 0.1 mm or 0.004 inch.

The measured curve and the hyperbola fit of the INNER area

The measured curve and the hyperbola fit of the OUTER area:

The spreadsheet used is attached

hfd_center.zip

With this post, I want to introduce a new method for measuring tilt and curvature and it is a request  for some test data.

Thanks, Han

The program  CCDinspecter measures the tilt and curvature by the difference in FHWM (~hfd) values between the center and outer areas of an image.  I have tried to indicate it in a sketch below:

I assume CCDinspecter calculates the curvature by ((A/B)-1)*100%. Where B is the average fwhm/hfd of the center and A of the outer areas. This will not work if the image is not in focus. There is even a focuser position where A=B. It would be better if the curvature would be measured as C expressed in focuser steps.

So ideally you should measure the best focus position for each area.  This can be realised by taking several images like for focusing and find the best focus point of each image area by curve fitting the V-curve of the hfd values measured in each area of the images.

This idea is implemented in the free program ASTAP, tab "inspector".  You can feed it with several images at different focus points and it will report the best focus point for each area of the image.  It is also  possible to copy paste the data into a spreadsheet. Then you create graphs like these:

Graph of the focus curves of  100mm APO astrograph, focal length 580 mm. Plotted are hfd values of median=all, the center of the image, outer area and the image split in four parts:

In the program, the data is presented as a table which can be selected and copied to the clipboard:

The usage is as follows:

• Prepare a series of short exposure images with different focuser positions and a lot of stars. Exposure time a few seconds. Move for each image the focuser a small step but only in one way to prevent backlash problems. Images with stars having an hfd above 12-14 will not be analysed correctly since this was historically not implemented.
• Browse with ASTAP to the images.
• Press analyse
• Optional:  Select all rows by ctrl+a, copy with ctrl+c and copy to your favorite spreadsheet.
• Press curve fitting for report on best focus point for each image area.

This is experimental. I'm interested in more test images.  If anybody can assist, make them as indicated below.

Han

Quote

 

For the images to analyse in the "inspector tab", please use a fixed focuser step since for all  curve offsets the same weight factor is used in curve fitting routine. It is possible to make more then one exposure per focuser position but do the same for all focuser positions.

For example if your focuser is focused around position 1007 and the range to reach hfd=12 on both sides is 900-1100 do the following:

move to 800 {to remove backlash}

move to 900 and make image of 5 or 10 seconds exposure

move to 910 and make image

move to 920 and make image

..

..

..

move to 1100 and make image

This makes 20 steps but probably 10 steps or even less will do. The direction is not important. You could also do 1100 to 900. You should also be able to mix the test series. The detection doesn't work above hfd=12 since it was designed for the alignment & solver and not finding the focus point.

 

That's an interesting option we haven't consired. Note that the sharpeness is also depending on the seeing. The autofocus routine is building a curve where sharpness is a function of focuser position. The program will find the best focus position using curve fitting. The curve fitting will cope with the seeing effects. Manually finding the best focus with the sharpness value will be more difficult. You will get litte unstable sharpness values near the best focus position due to the seeing.

Nevertheless this could be an interesting option which is easy to implement. In setting tab FILES there is currently an option "Automatic HFD measurement for every sequence capture"  Something simular could be done if "Planet" autofocus is selected and without sequence. So report the sharpness in the log after each exposure.

I will propose it to Patrick.

later, proposed. See https://www.ap-i.net/mantis/view.php?id=2264

Yes it will work for terrestrial objects. If measures the intensity slope between dark and light areas. This slope will be less when de-focused.  It has been tested successfully on the Moon without seeing the rim, but for testing it terrestrial objects, select a target with some sudden intensity differences.

Focusing on the Sun rim worked also fine, but unfortunately Sun spots are still missing. One focus test on Venus was also successful. Testing on Jupiter or Saturn has to wait till they show up in the night sky.

Han

For info:

The latest version of CCDCiel (freeware) introduces autofocus for the Moon, Sun and planets. The principle is the same as with autofocus for stars. For planets however, it measures the sharpness of the image instead of the half flux diameter of the stars.

Feedback is appreciated.

Han

Very nice image. The image details of NGC4216 are amazing!

There are more galaxies to see. I can't help you with the PI annotation, but here an alternative annotation by ASTAP of your jpeg file. (but I'm a little puzzled by the SDSS entries around NGC4216):

Unfortunately, I have no other filters then H-alpha.  Maybe I will expose a few hour longer for a better SNR value.

Correction, the location is NNW of the star Meissa. The light areas are part of SH2-264 which center is at the star Meissa. Below the image plotted in a map:

This image is de result of  four nights in December/January. The weather was not very good. I wished I could have exposed longer.

The dark nebula are B30, B31, B32 not very often imaged. Nevertheless they are nice objects to image. There is some similarity with the horse-head nebula more south. These dark nebula are at three degrees NNE of the star Meissa in Orion.

Han

Telescope 100 mm APO astrograph APO100Q, F5,8
ASI1600MM-Cool Camera
Filter H-alpha 7 nm
66x200 sec four nights in December 2019 and January 2020
CCDciel and  ASTAP stack program

In the latest beta version v3.85.1 of APT, you can select ASTAP as astrometric (plate) solver.

4 hours ago, NickK said:

Metal is single precision floating point. So.. it's either write for Octave (a free R clone) or Python.

The old code did phase correlation with the PSF from the guide star in the Z axis to rebuild saturated stars. This works well but expands the dynamic range (hence needing larger range).

I'm surprised you need more then single precision. In my program I define the arrays as single precision by purpose since memory requirements quickly increase if you have a few images in memory.

If your looking for a new challenge, develop and document a de-mosaic routine for astro OSC images.  Especially when stars are saturated in the center and the stars are small, HFD/FWHM value 2 to 3 pixels. 

4 hours ago, NickK said:

My thinking is if you can use some maths to better estimate the noise levels.

Here they are using gems and thieves, however the same could be viewed as a pixel and the composition of noise - how much is signal, signal overlapping from elsewhere (PSF) and the various noise.

 

For me it is just simple statistics, average value, standard deviation....

I'm sorry for you loosing your job. 

Python is an interpreter. For speed a compiler solution would be better. But if your comfortable with Python at least it is muli-platform. What are the ideas?

Han

Your using the V-curve option to focus. This is the oldest method. I have used V-curve option in the past till dynamic was introduced.  The Start focus HFD (2)  default setting is 20 but for me 15 or even 10 was required to get good snr values. The Near focus HFD position (3) setting I had set at 6 or 7.   It uses point 2) and 3) to find the focus at 4) So V-curve  focusing only works if 3) still lies in the linear area. I think you can select for 3) a value twice the mininum so the HFD at focus. 

The problem with this method is that you have to calibrate the V-curve in advance and in most case you have to slew to a bright calibration star for a good SNR value. Too much saturation could also be a problem at focus.  So the star should bright but not too bright.

Later the hyperbolic curve fitting (=dynamic) was developed and since this is implemented, I haven't used the V-curve focusing anymore. I would suggest to try this dynamic focusing + stay in place. In the dynamic method there is less need to de-focus and therefore it is better suited to "stay in place" for focusing: I have tried to describe the performances with plus and minus signs  in the table below:

To change focusing, you have to select "dynamic" and "stay in place". (For sequences "stay in place" is also an option you should set). The minimum snr in this screen shot is probably too low. I would set it at 6 :

It tries find the best hyperbola fit on the measured points. Below a quick sketch I made to illustrate the principle. Hyperbola fitting can work in the non-linear area of the curve. Therefore less defocusing is required. The inputs are focuser positions and the corresponding HFD values, the seven stars in the sketch. The curve is the best fit it can find and the routine knows the bottom position so the best focus position.

The minimum HFD is about 2.5. For focusing you don't have to defocus to a HFD value more then two or three times the minimum value. So in this setup to HFD 5 or 6.

This is how it looks in reality:

-- Han

For narrow band you often need longer exposure times to get stars above the noise.  You can speedup focusing by using 1) "stay at position" and 2) dynamic focusing. 3) Limit the number of step to 7  or  8 or 9 steps .  Furthermore you can reduce the exposure time if you 4) limit the focuser steps such that your focus if going not far off.  For my setup the HFD value at focus is around 2.5. I tune the focuser steps such that the maximum HFD is around 5  maximum.  Example for H-alpha 7 nm, I'm using 4 or 5 seconds exposure for focusing.

Going to a dedicated bright star for focusing takes more time then "stay at position"

If this is abracadabra for you, ask me for more information.

Han

Installing libraw is the intention. That message should also popup if you try to open raw files. This shouldn't effect Astroberry in anyway.

The program using the following file:

/usr/lib/libraw/unprocessed_raw

I switched to libraw only a few weeks ago. Older versions call dcraw.

-- Han

@dannybgoodewhat are the indications showing in your setup? You can see in my last screenshot what to expect. That will identify where the problem lies.  So specific the RA,DEC solution in APT, the RA, DEC position of the mount after sync and the RA, DEC position (J2000 or Jnow or both) of the frame in Stellarium.

I run a simulation in APT and got in the same problem. However there is a APT button "Jnow" near "connect /disconnect telescope" which fixed the problem.  Does this work for dannybgoode?

This test can be done in simulation. Just load an image in APT, solve it and sync the (real) mount. Then check the results.

Han

Before:

Activate the button Jnow

With the button Jnow activated:

Stash remind of an other problem, modeling of eqascom (eqmod). If you use eqascom, the eqascom model could be wrong. The number of  APT retries (goto++ attempts default two times) will indicate this. Reset the eqascom  align and sync data for the alignment.  It could have collected wrong alignment points from telescope sync command.  You can switch this add alignment points behaviour off:

Quote

 Start by clearing out any existing model and put EQASCOM into “dialog mode” (rather then “append on sync”) for alignment. A sync will be treated as standard ASCOM sync rather than as a trigger to add an alignment points.

Solvers can fail but it is very very very rare. In all other cases the error is less then one pixel. If your telescope is not perfectly polar aligned, you could need two syncs rather then one. So check your number of tries, the acceptable error as indicated above and equinox setting(s) J2000 or Jnow.  

 A J2000 vs Jnow error is the most likely cause.

Poor connectors could be a problem. 

As Blinky indicated maybe the hub is spoiling the serial communication.  It's only 9600 baud serial but the timing of the bits is very critical. A club member here is also using a 5 meter USB cable without problems. So I assume a 5 meter usb cable is preferably to a hub connection.  Moving the usb->serial dongle closer to the computer is an other option. The serial cable is possibly less sensitive to long lengths then USB. 

Could be a communication error due to cable quality/length. How long are the USB cable and the serial cable?  If the USB cable is a few meters long, maybe it helps if you use a shorter USB cable.

On 23/11/2019 at 20:20, Skipper Billy said:

I would do but it doesn't fail - it just kept going round in circles but never solving and never failing.

If it is a "sync across meridian" problem and you using Eqmod, note that Eqmod version prior to 2.00n doesn't give a error message: "ASCOM Sync reject exception"  Using Eqmod 2.0.0n or higher will give a this error and if SGP is programmed well it should pass on this messsage. See https://groups.io/g/EQMOD/topic/56626302#49214

This will only help with error reporting. To bypass the problem see my previous remarks.

On 12/11/2019 at 20:33, Laurin Dave said:

Hi David

I have encountered something similar with Mesu Sitech SGPro and Platesolve..  It does the flip ok but if, as last night the target is very close to the zenith/meridian then on target commence the mount will go to the correct side, take a plate solve image then slew to the other "incorrect' (ie just about to hit the pier) side and fail to solve..  I suspect its to do with Sitech settings conflicting with SGPro but have no idea which ones..   I get around it by switching off slew and centre and doing a manual plate solve very close to the target and then a manual slew to it..  When it gets to 30mins or so beyond the meridian it all works fine

Dave 

A solve problem would be difficult to explain. The meridian is not a boundary for a solver. But note that a HEQ5/6 mount (and maybe others) can't sync across the meridian. This could occur if you flip exactly at the meridian.  The mount could think your just past the meridian but your solver tells it is just a few minutes before the meridian and sync will fail. You  can avoid this by flipping 20 minutes after the meridian crossing if your software allows this or just wait 10 minutes or slew to  an object further away from the meridian and sync.

Han

I missed your message. Yes now I have looked to the image. The image has two problems. The resolution is too low and the stars are elongated.

- ASTAP likes minimum resolution of around 1.5 mp so something like 1500x1000 pixels. Your image is 965x635, so close to 0.6 MP

- Stars are too much elongated. Something like ratio 3x1. They are recognised as galaxies. ASTAP will ignore any bright object which is more then 30% elongated/oval. You can see the if you activate the CCD inspector or use test button "Show tetrahedrons".

The exposure duration is more then enough. You can easily expose less, 5 or 10 seconds is sufficient.

Lets continue this on the ASTAP forum. Somehow I didn't get your reply in the email box, but will have look more regulary.

Han

Han