Solar Scintillation Monitor SSM3 and SharpCap

After downloadoing the latest version of SharpCap (adjusted for the SSM3 bug) I connected my Solar Scintillation Monitor SSM3 (See https://www.analog-astronomical-device.ch/solar-scintillation-monitor). . Using the tools menu and selecting Solar Scintillation Monitor, the SSM3 can be connected. The result works very good with a good graphic follow up.

Overal seeing below 2 arcs with moments even lower.

The increase is due to upcoming high clouds

For instructions to connect the SSM3 with SharpCap see https://forums.sharpcap.co.uk/viewtopic.php?p=48907#p48907 (New Feature : Support for Solar Scintillation Monitors).

First Light with Skywather Star Adventurer 2i

I expanded my equipment with a transportable travelmount: a Skywatcher Star Adventurer 2i. I will install this mount on my Manfrotto tripod. The purpose is to image wide field using my DSLR at home and when I travel.

After putting all together I did some testing last week; unfortunately not successful. I did a more accurate  polarallignment, but stars were still not tracked. Last thursday I found out that I forgot to set the direction of the tracking. Once done, the SA2i is following up to 70s (I did not test longer). To test accurancy over time, I shot 190x30s pictures of Orion using my Nikon D7500. So far this works really good. 

 

Stacking was done using APP and final editing in CS4.

Lacerta Herschel Wedge - Brewster Angle

TLAPO80/480 with Lacerta Herschel Wedge and ASI290MM

Some information about my new Lacerta Herschel Wedge. According reviews a Herschel wedge or Herschel Prism would provide more details then the use of Solar film.

My objective is to get more details of the photosphere and the more specific on the granulation itself. Another objective is to use the wedge with my Sol'Ex. 

The Herschel Wedge is equipped with a neutral density filter ND3. On the back of the wedge it's noted that the total light reduction with ND3 filter us ND4.07.

This means that the wedge itself has a light reduction of  4.07 - 3 = ND1.07 . For both visual and photografic observation a value of ND1.07 is too low and even dangerous. To compare with my Solar film ND3.8 I would need to install a filter ND2.7 or  ND2.8. on the wedge. But for now I will keep using the ND3filter.

A value of ND1.07 means a transmission of :  T= 10 exp (-ND) = 10 exp (-1.07) = 0.0851 or 8.51%.

Another interesting one is Brewster Angle.The Brewster angle, named after the Scottish physicist Sir David Brewster, is the angle at which the reflected light rays from a non-metallic surface are fully polarized. In other words, the light waves that strike a surface at the Brewster angle are reflected in only one specific direction (polarized light), while the perpendicular light waves are absorbed.

The Brewster angle can be calculated with the following formula:

tan⁡(θB​)=n2/​n1​​

where θB​ is the Brewster angle,

n1​ is the refractive index of the medium from which the light comes (e.g., air),

n2​ is the refractive index of the medium in which the light is reflected (e.g., glass or water).

At the Brewster angle, the resulting reflection of light for a particular polarization direction is minimal, which can be useful in various optical applications such as my use of the Sol'Ex.

Air typically has a refractive index of approximately 1 (as an approximation), while the refractive index of glass (like in the Lacerta Herschel wedge) is typically between 1.4 and 1.6, depending on the type of glass.

Let's assume a refractive index of 1 for air and a refractive index of 1.5 for glass for simplicity. So, in this example, the Brewster angle for air and glass is approximately 56.31. According the website the Brewster Angle is 56.6°.

Above picture is taken with TLAPO80/480 f/6, ASI290MM and Herschel Wedge. Editing using new beta release of IMPPG and CS4 after stacking with AstroSurface Urania V1.

Scan time for Sol'Ex

The scanning of the solar disk using a Sol'Ex can be calculated using following formula

T = 8.79 * P / (f * v * Cos (delta))

• T = exposure time in s
• P = pixelsize in micron; include binning
• f = focal point of telescope in mm
• v = scanning time of telescoop, typical 4, 8, 16
• delta = declination of the sun

It looks like that the outcome of the exposure time compared with the scanning time is rather exponential.

Effective focal length and best sampling factor

My Helios collegue, Walter, asked me about the effective focal length of my set up when imaging Saturn (august 22, 2023).

So here it is:

I uploaded my picture of  Saturn in WinJupos. Using the measurement - adjustment tab it's possible to obtain the diameter of the planetary disk in pixels (Di). The apparent diameter of the planet in arc seconds  (Dp) is provided by ephemerides tab. 

Sampling S = Dp/Di = 19/128.8 = 0.1475 arc seconds per pixel

The image sampling is equal to :

S = 206 P / F  (P = pixelsize of the camera and F = effective focal length in mm)

So F = 206 P / S = 206 3.75 / 0.1475 = 5237 or F/D = 5237/200 = 26.18 

Conclusion :

My set up with barlow x2, ADC and ASI224MC (3.75 micron) on TAL200K f/8.5 has an effective focal length of f/26.18. This means that my magnification is 26.18/8.5 = 3.05

Based on this f/26.18 and a Dawes resolution power (RP=1.02 wavelenght/diameter telescope) of 0.5838 it possible to measure the sampling factor k (k = RP / S).

k = RP / S = 0.5838 / 0.1475 = 3.95. 

Conclusion :

The Nyquist-Shannon theorem requires a k>2 but in practice a sampling factor of  3 to 3.5 is recommended according to Christian Viladrich - Solar Astronomy page 300 - Planetary Astronomy page 80). Increasing the sampling factor k beyond this would not bring a significant gain. Wirh my set up of 3.95 I will investigate how to reduce this to a value of 3 to 3.5. 

For information: the formule on page 81 of Planetary Astronomy should read F =206 Tp Di/Dp and not using factor 260.

First light with ASIair plus - M81 Bode's Galaxy

A couple of weeks ago I bought a second hand ASIair Plus. The idea is to have two set ups for my telescopes: one telescope equiped with PC (N.I.N.A.), the other with ASIair Plus.
Having two skywatcher mounts and all camera's from ZWO, the purchase of an ASIair Plus is a good alternative in stead of an extra PC.

I installed the ASIair Plus on my TAL200K f/8.5 telescope. The main camera and guiding camera was connected using USB A 3.0 cables. After powering, connection was made with my mini Ipad. In order to make connection, the wifi should be swithed to ASIair signal. Then open the ASIair app. There are numerous youtube video's how to start using the ASIair Plus. Below some learnings using the ASIair Plus with a skywactcher EQ8-R mount.

- polar allignment and 3-star allignment was done without connection of the mount to the ASIair plus.

- allignment was done using the maincamera which was connected to ASIair Plus (experiment with the exposure time)

- once allignment completed, I connect the synscan of the mount via a USB B cable to USB A 2.0 port of the ASIair Plus.

- polar allignment was redone; take first a picture and plate solve before running the PA - polar allignment.

- to find an object, just select the target and through imaging and plate solving, the object is set in FOV.

- same with guiding, connect the camera and calibration starts automatically; guiding is done using multistar guiding. 

- autorun set up was used to make the pictures.

- afterwards bias, darks and flats were made using the autorun. Pictures are saved under the folders on the e-MMC 

- I used a 32Gb micro SD card to copy the images and to transfer them to my PC. 

- I disconnect the USB A2.0 - USB B cable between ASIair Plus and syncscan when I finishing my imaging session and to park the telescope. Keeping the cable on and choosing the park function in ASIair Plus did not gave the proper coordinates

- so far, no experience with meridian flip, live stacking and planning function. Also no experience with autofocus.

- connection inside the house was lost a couple of times but the session kept running. 

Conclusion:

Connection with camera's went well, guiding was done properly, finding the object through plate solving was fantastic (first time experience). I made 24 pictures (24x300s) on day 1 and 20 more on day two. Transfer via micro SD card was easy. 

Result:

M81, Bode's Galaxy

TAL200K f/8.5, ASI2600MC, ASI224MC on 50x240 guiding scope with EQ8-R

Lights: 40x300s, darks, bias and flats

Software: ASIair plus, APP, CS4, DeNoise AI

Balancing a telescope & mount using a clamp meter

Balancing your scope and mount is very important. Typically I do this by hand moving the scope from one side to the other side,  trying to find the tipping point. A couple of weeks ago, Walter, my astronomy collegue, send me a video from Cuiv, The Lazy Geek - see the video 

In this video a clamp meter is used (with Ampere DC features) to measure the current (Ampere) when moving the scope up or down. When the current is the same for both directions, the scope would be balanced.  If not, adjust the weight and measure the current again... and again. 

So... does it work?  To test it, I borrowed from Walter a clamp meter. It's a Chauvin Arnoux F205AC/DC. The test was done with my AZ-EQ6 with TAL200K f/8.5 including all camera's.

Results: the clamp meter is able to measure the current when the mount moves. There is a difference in current when the mount move up or down. The deviation is about 0,1-0,2A when the scope is out of balance. The deviation is reduced to 0,03-0,05A for a balanced mount.

Conclusion: it's possible to balance your mount & scope using a clamp meter. There is an error of about 0,03 - 0,05A even when the scope is balanced. For that reason I stay with my current workprocess balancing my scope by hand, finding the tipping point.

ADC set up

How to set up an ADC or Atmospheric Dispersion Corrector? Currently I'm using my ADC only for planet astrophotography and have experience with Mars, Jupiter and Saturn.

When using my TAL200K, the ADC connected to my camera (ASI224MC) and screwed after the barlow and eyepiece holder of 1.25"- see picture below.

Left to right: ASI224MC, ADC, Barlow, 1.25inch eyepiece holder

During operation I'm adjusting the ADC visualy but recently I was told that adjustment can be done using FireCapture, SharpCap aswell as ASICap (ASIStudio). This will be tested next time when I'm out for a planet astrophotography session. 

Atmospheric Dispersion Corrector ADC

An ADC is used to corrects light dispersion typically for planets and the moon when low above the horizon. At the ATT in Essen I bought an Omegon ADC. Hopefully I can start testing it the coming days as both Jupiter and Saturn are getting into opposition. More to come with my review and results.

Again Wrong Working Distance from Sensor - Messier M8 Lagoon Nebula

Seeing was very good on August 2nd with low Moon impact till UT24h. So ideal to make pictures of deepsky object. Based on my earlier learnings I changed the position of the flattener in order to increase the working distance between camera sensor and flattener. Unfortunately I did not measure the final distance. The result showed still aberration at the edged. Not so big as with the flattener just in front of the sensor; but still, it clearly can be seen.

So, I did some detailed measuring and found out the picture was taken with the flattener at a distance of 151mm. The pictures taken earlier had a working distance of 117.8mm; wich is below 5% of the ideal working distance according the technical data.

Focal plane of my camera is shown below :

The recommended distances from the M48x0.75 thread to the corrector via technical data is shown below. In principle this rule applies: the shorter the refractor´s focal length, the longer the working distance to the sensor has to be.

♦ focal length < 450 mm: 128 mm
♦ focal length 450-490 mm: 123 mm for my TLAPO 80/480 f/6
♦ focal length 500-550 mm: 118 mm
♦ focal length 560-590 mm: 116 mm
♦ focal length 600-690 mm: 113 mm
♦ focal length 700-800 mm: 111 mm
♦ focal length as from 800 mm: 108 mm

An underrun or an overrun of the distance of up to 5% has no visible effect on the sharpness in the field of sensors with formats up to APS-C. With larger sensors, the tolerance is reduced to 1-2%.

Flattener correcting the view field - Importance of working distance.

Flattener at a distance of 10mm from sensor showing clearly aberration at the edges.

I was not aware about the importance of distance from the flattener to the sensor. Below pictures show the difference. The picture with Messier M56 was taken with the flattener fixed at a distance of 10mm. This pictures shows clearly aberration at all edges.  The aberration is almost gone on the picture with M39. For this picture the flattener was located at a distance of 100mm.
According to the technical data the ideal working distance to the sensor is depended of the focal length of the refractor :

♦ focal length < 450 mm: 128 mm
♦ focal length 450-490 mm: 123 mm
♦ focal length 500-550 mm: 118 mm
♦ focal length 560-590 mm: 116 mm
♦ focal length 600-690 mm: 113 mm
♦ focal length 700-800 mm: 111 mm
♦ focal length ab 800 mm: 108 mm

An underrun or an overrun of the distance of up to 5% has no visible effect on the sharpness in the field of sensors with formats up to APS-C. With larger sensors, the tolerance is reduced to 1-2%.

Flattener 100mm - Picture is sharp at the edges

Very Cold Observation testing SE 9mm 100° Ar purched ocular

Clear sky and moderate seeing this evening and very cold with temperatures up to -8°C. 

Observations done using Dobson OrionXT12 and my new Ocular. This is a Scientific Explorer 9mm 100° wide angle, argon purched and waterproof consisting of 9 elements. It was bought directly from Bresser in Germany.

Observations done on M1, M35, M36, M37, M38, M42, M43, M81 and M82. Also the moon was with 41% a perfect object for testing. I'm very happy with my new ocular and the starclusters are showing up very bright and sharp. The 100° wide angle and field of view makes it necessary to have your eyes travel around to see all the details. Very good quality, good contract and bright immense view. The ocular was delivered safely in a nice big box  without any issue.

Moon 41% Afocal using iPhone 6 on SE 9mm 100° -  Dobson 12"

DIY Making solar pictures using your DSLR on PST

How to make pictures using your DSLR on PST.  Using my D60 it's difficult to make prime focus pictures on the PST40. That's why I changed strategy and take pictures afocal using zoomlens 8-24mm with 24mm zooom. In order to bring the sun's surface into focus I need about 53mm to bridge. For that I need to install some spacers and finally the Nikon T-ring.

Chromatic Aberration CaF2 material - FCD100 Hoya & FPL53 Ohara

As lenses (like in refractors) have different refractrive properties depending the wavelenghts and the fact that the focal length of a lens is depending the refractiveness results in colors not focussing into a one single point behind the lens. This means that colors will shift in pictures (color glow around moon, planets) which we call chromatic abberation.

Over time refractors became better with double lenses (achromatic lens; the lenses compensate for two wavelengths) and triple lenses (apochromatic lens, lenses compensate for three wavelenghts). For the latter one the flint lens is made of ED glass. This is glass with a very low dispersion properties or high refraction indeces. Typically CaF2 is favorite but expensive, heavy and difficult to manufacture. Therefor the use of other fluorite glasses are used. Currently the use of FPL53(Ohara, JP) and FCD100 (Hoya, JP) are common in small f/ratio refractors and closing the gap with CaF2 glass.

The table below shows that the bigger the F/ratio the lower the chromatic aberration.

Looking into the data, FCD from Hoya has a slightly better refractive indices then FPL53

How to take lightning pictures

Taking ligthning pictures is a matter of patience. During night it might be possible the use open shutter position of your camera. My recent pictures are taken during day time. Shutter time used was around 1/30s and focal length 18mm  f/3.5. ISO was automatic and between 200 and 1000 depending sky. Using manual settings for focussing and all other aspect automated I was able to take up to 5 pictures continiously everytime the camera was loaded from previous shoots.
About 5 pictures out of 500 did results in a ligthning picture which was usefull.

Startrail : What's the max exposure time still seeing stars and not trails

Still want to see stars when taking a picture of the evening sky? So what is the maximum exposure time of your DSLR without seeing tracks of stars on your picture.
Rule of thumb : 600 divided by the focalpoint (mm) x cropfactor DSLR.

Example 1 : Nikon D60 with f 18mm : 600/(18*1.5) = 22s
Example 2 : Nikon D60 with f 200mm : 600/(200*1.5) = 2s
Example 3 : Nikon D60 with Celestron 400 : 600/(550*1.5) = 0,7s

Cropfactor Nikon D60 = 1.5

Text changed on August 5th.