Video assisted polar alignment - VAPA

[benzomobile]

It is long time I wondered whether the mount polar scope could be used in a less tiring, but more effective way to achieve a convenient, very quick and fairly precise polar alignment (till better as 1 arcminute), than could be achieved usually, and without having to buy rather expensive devices made for this purpose.
The solution I found – easily achievable and doable for the most of Astro DIYers - is to mount a small video camera attached to the polar scope eyepiece. This will allow us to achieve an excellent alignment to the celestial pole.     

I invented the acronym VAPA (Video Assisted Polar Alignment) to define my mount stationing method.                                                                                                                        

                               NCP on January,  2018                                                                                                                                                                               NCP on May,  2021  (Stellarium)

                                                                           

 

 

Theoretical premises

In addition to the Polaris, there are two stars of mag 6.5 just around the North Pole celestial field, in Ursa Minor constellation.

They are λ (lambda) and HIP 7283 (double star)

As you can see the position of two stars is very interesting, in fact their RA position differs by a value very close to 135°.  In addition, it is possible to see in the same field two other fainter stars whose positions are very peculiar too.

If you draw a line from each tiny star to meet the NCP, you will see that these two lines define a right angle having its vertex at the NCP. (see pics below)

 

I made this modification on my standard HEQ5 (old black 'Heavy Duty' one), but the same arrangement can be applied to any other mount that has a polar scope with removable eyepiece and sliding ring with glass reticle.

Considering that the HEQ5 has a very small polar scope (its objective lens has a diameter of about 14 mm), the system will work even better on other mount models, equipped with polar scopes of much larger aperture.

 

Polar camera construction

Materials 

- 1 IMX 225 (or IMX322) module with 6mm lens, equipped with Video out, OSD and power supply cables (from Aliexpress)
- 1 OSD menu pcb (optional)
- 1 small plastic box
- 1 film plastic can (135)
- 1 rca panel connector
- 1 coaxial power connector (3.5 mm)
- coaxial cable (conductor plus shield)
- some 2mm screws, spacers and bolts
- 1 epoxy resin

The small polar camera looks as you can see from the pictures below

                                      


 

Making the Reticle

Materials (see photos below):

an A4 paper sheet on which we have printed a circle graduated in degrees

0.030 mm (30 micron) fishing wire

3 small truncated-cone springs

scotch tape

cyanoacrilate adhesive

 

                                     

 

 

Construction technique

- Unscrew the eyepiece and remove the three adjusting grubs of the reticle ring.

- Remove the reticle ring and unscrew the threaded flange which holds the glass reticle in place

- Remove the glass and reposition the flange.

- Attach the ring to the centre of the graduated circle with a very small amount of vinyl glue (flange down)

- Stretch (gently!) a piece of wire and fix its ends tightly (with small pieces of scotch tape) at 0° and 180°, in order to precisely bisect the circle and the ring.

- Do the same thing with another piece of wire, stretching it between 45° and 225°.

- Make sure that the two wires cross in the centre of the ring accurately (although extreme precision is not required). See photo below

                                                                     

 

 

- Using a very small amount of cyanocrilate, solder the four wire ends on the ring, just where they get each other into contact.

- Allow to dry.

At the end of this procedure we will have created a wire reticle delimiting two couples of angles, 45° and 135° wide respectively.

- From the inside of the eyepiece barrel, do insert the tiny truncated cone springs into the three grub threads, the smaller base pointing outwards from the barrel.

- Replace the ring in its place with the reticle towards the polar scope objective.

- Screw in the grubs until the ring is secured, but do not tighten them (see photos below)

 

                            
 

 

Calibrating the reticle

- Adjust the eyepiece so that the reticle can get focused (use glasses if you wear them to see well at a distance!) then fix it with a drop of silicone just on the visible part of eyepiece thread.

- Unscrew the locking ring of the polar scope tube and adjust the distance between the reticle and the objective so that you can see a distant object (a bright star, or a detail on the roof of a building) well focused together with the reticle.

- Fix the tube ring.

If there are one or more grubs around the locking ring, they must be screwed in tightly.

 

Displaying the area of the celestial pole

Materials

- 1 7" 1024x600 HDMI screen

- 1 RCA -> HDMI video converter

- Connection cables

 

                                                              

 

Insert the camera nose (135 film barrel) on the polar scope eyepiece and aim the polar axis at the sky area just around the Polaris

 

                                                                                                     

 

If all the connections are correct, we will see the Polaris on the screen (if we don't see it right away, we can easily find it by searching near around) together with a good number of other stars.

In a Bortle 6-7 sky (as it happens in many suburban areas) we can easily find out stars up to 10th magnitude (provided the atmosphere is transparent enough).  The field of view will be about 3°x 5° (see photo).

                                                                                                             

 

Camera configuration by OSD menu

 

The camera menu will get elicitaded pressing central button and you can do your choices pushing up, down, left and right buttons

Fill in the follow parameter:

Push central button to enter Main menu. Push down button to enter submenus and right or Left one to select voice:

- Lens → Manual

- Exposure → Shutter → 15-20

→ AGC → 6

→ Brightness 1

→ Return → Main menu

- Day/night → B / W → Return → Main menu

- NR → High → Return → Main menu

- Special → Defect

- live DPC → On → AGC level 50-60

→ Level 0

→ Return

- White DPC → On → -level 0

→ AGC 5-7

→ Sense-Up 30

→ Start → Follow indications

→ Return → Return → Return → Save & end.

Leave all other voices at default position

Notice: DPC is the dead (hot) pixel control

 

Video assisted reticle alignment

This is done by grubs provided just for this task.

Truncated cone springs make the operation very easy and confortable.   As you find Polaris in your screen, put it at the center of crosshair.

Rotating the polar axis, you can see the star will move from its initial position, so, you should screw the three grubs in and out until Polaris will stay ever at the crosshair center in any direction you can rotate the polar axis.

Grubs should be secured, but they should no be tighted.

 

Video assisted Polar alignment procedure

By adjustement of Alt-Az knobs, you should:

 

1) put the reticle center on the right angle vertex (NCP position on current date) made by tracing two virtual lines, starting from the two faintest stars, as indicated in previous image.

If you are very accurate, you can reach the NCP within a maximum error of 1 arcminute.

 

2) rotate the polar axis till the two brighter stars get both hidden by two crossed hairs of reticle (the pair one crossing until each other at 135°). If it doesn’t happen, it mean your mount is too

much far from NCP, so you must repeat the step 1).

Note: performing step 2) doesn’t be mandatory, but it will enhance alignment precision.

 

                                                                                                                  

 

Photos above are recorded by SharpCap (stacking), thus they don’t display the correct image aspect ratio (12:7) as you can see visually, watching your ‘on the mount’ lcd screen.

In fact, SharpCap do not change aspect ratio (720x576 lines for PAL system) of native analog image captured by a video grabber (Easy Cap or similia).

That is why the above image appears a bit higher as it should be. Obviously, you can align your mount with your notebook screen rather as with lcd display on the mount.

To do that, you must use a video grabber device and OBS Studio to record movies or snap shot.

OBS Studio is a big free software allowing make all necessary image adjustement to reach the correct aspect ratio.

 

Below I posted an OBS Studio clip (sorry for the big amount of dinamic noise due the sudden ‘défaillance’ of my chinese video grabber … )

Beppe

 

Edited May 29, 2021 by benzomobile
Necessary corrections!

[malc-c]

Neat idea, but nothing new.   AstronomyShed was placing cameras attached to the polarscope back in 2011 !!

 

 

[carastro]

I tried to attach a webcam to my polarscope as per the Astronomy Shed video, but I could never get a rigid attachment, and it would flop slightly giving me an incomplete Polarscope view, so I gave up.

Carole 

[benzomobile]

On 18/05/2021 at 12:22, carastro said:

I tried to attach a webcam to my polarscope as per the Astronomy Shed video, but I could never get a rigid attachment, and it would flop slightly giving me an incomplete Polarscope view, so I gave up.

Carole 

Unfortunately, webcams (only the old CCD ones are good for that task) don't  have enough  sensitivity, so you can see  Polaris  and, perhaps four other stars  only  in  their  FOV.

No modern CMOS webcams are useful, due to their very high intrisic noise 😞 

Analog CCTV CMOS sensors  as IMX225 or IMX322 (or few others)  have high  sensitivity (0.005 lux) and low noise.  More sensitive (0.001 lux)  CCD sensors  as Effio A  (ICX810/811) also are  utilized in EAA: 

An Introduction to Electronically-Assisted Astronomy (EAA) | AstronomyConnect

The electronics of the module are also too important as they allow you to configure all the necessary parameters to make these cameras an excellent choice for video astronomy.

Beppe

Edited June 7, 2021 by benzomobile

[malc-c]

40 minutes ago, carastro said:

I tried to attach a webcam to my polarscope as per the Astronomy Shed video, but I could never get a rigid attachment, and it would flop slightly giving me an incomplete Polarscope view, so I gave up.

Carole 

I wasn't suggesting it was any good.... just that the concept of attaching a camera to the polar scope is not new

[malc-c]

16 minutes ago, benzomobile said:

Unfortunately, webcams (only the old CCD ones are good for that task) don't  have enough  sensitivity, so you can see  Polaris  and, perhaps four other stars  only  in  their  FOV.

No modern CMOS webcams are useful, due to their very high intrisic noise 😞 

Analog CCTV CMOS sensors  as IMX225 or IMX322 (or few others)  have high  sensitivity (0.0001 lux) and low noise.  More sensitive CCD sensors  as Effio A  (ICX810/811) also are  utilized in EAA: 

An Introduction to Electronically-Assisted Astronomy (EAA) | AstronomyConnect

The electronics of the module are also too important as they allow you to configure all the necessary parameters to make these cameras an excellent choice for video astronomy.

Beppe

 

Back then the Phillips CCD (SPC800 and 900) based webcams were fairly easy to come by.  Not so much these days.  The CMOS web cameras lack the sensitivity and as you say, are quite noisy.  

Rather than have something that attaches to the polarscope, I would love to see a DIY Polemaster that can use the excellent Sharpcap alignment software

[benzomobile]

3 minutes ago, malc-c said:

 

Back then the Phillips CCD (SPC800 and 900) based webcams were fairly easy to come by.  Not so much these days.  The CMOS web cameras lack the sensitivity and as you say, are quite noisy.  

Rather than have something that attaches to the polarscope, I would love to see a DIY Polemaster that can use the excellent Sharpcap alignment software

Another way to deal with 🙂

[benzomobile]

5 minutes ago, benzomobile said:

Another way to deal with 🙂

DIY Polemaster for EQ6 and LXD75 mounts - IceInSpace

[benzomobile]

On 18/05/2021 at 12:09, malc-c said:

Neat idea, but nothing new.   AstronomyShed was placing cameras attached to the polarscope back in 2011 !!

 

 

I'm sorry to contradict you, but this is something completely different.

What's new: practically everything.

 First of all:  newest technology.  New Sony Exmor sensors have 100  fold  more sensitivity as older  Philips ccd webcam:  0.005 lux  vs 0.5 lux! 

In addiction, integratd modules have  sophisticated controllers, such as  ISP chips (NVP2441 with IMX225)  to process  imaging data.  Absolutely nothing to do with the old SPC webcams ! ! !

Those who say it is the same old thing do not know what they are talking about. 🙂 

 

Edited June 7, 2021 by benzomobile
Putting more accurate data!

[benzomobile]

8 hours ago, malc-c said:

I wasn't suggesting it was any good.... just that the concept of attaching a camera to the polar scope is not new

Oh, I know  that  very well ! 

I  made  my first attempt to make a polarcam  with CCD Logitech QuickCam  (same sensor as Philips Toucam Pro) in 2008 ...  I will be  68 yrs  old  very soon!   🙂

The one I have presented here is a different story, estremely different story.  If you look carefully at my polar field snapshot,  you can find stars up to almost the 11th magnitude.

More than twentyfive years have not passed in vain since the days of Toucam ! !

Edited May 18, 2021 by benzomobile

[benzomobile]

8 hours ago, carastro said:

I tried to attach a webcam to my polarscope as per the Astronomy Shed video, but I could never get a rigid attachment, and it would flop slightly giving me an incomplete Polarscope view, so I gave up.

Carole 

Try it, Carole. You won't be disappointed with this solution that allows you to do a quick, precise and intuitive polar alignment!

What was tried several years ago was not really of much use,   then worse than today now  (I agree with malc-c  in this sense only). 

Moreover, I know it very well because I tried it myself at that old time  🙂

Beppe

Edited May 18, 2021 by benzomobile

[carastro]

I have Polemaster now Beppe.  Was forced to get that after I fractured my knee and could not kneel down, I still have the pins and plate in my knee to this day (4 years on) so kneeling still isn't comfortable.  Polemaster makes it so much easier, but I agree it is not cheap.

Carole   

[benzomobile]

1 hour ago, carastro said:

I have Polemaster now Beppe.  Was forced to get that after I fractured my knee and could not kneel down, I still have the pins and plate in my knee to this day (4 years on) so kneeling still isn't comfortable.  Polemaster makes it so much easier, but I agree it is not cheap.

Carole   

I can understand you, because I'm an old  doctor.  I wish you all the best for a full recovery. Polemaster aside ... 🙂

Beppe

Edited May 18, 2021 by benzomobile