Orienting POSS images to match the dob eyepiece field of view

[akarsh]

Till date, I have only done this "in my head", using relative orientations.

Recently, I coded a feature for KStars (http://edu.kde.org/kstars) planetarium to render an "Eyepiece View", as is present in many other software (not that I've used them, but anecdotal / internet reading / heresay).

The most interesting thing (which I don't know if it is common in other software etc.) is automatic adjustment of the orientation of eyepiece view for a (big) dob. I don't know if this is already widely known information or is too obvious (it was not for me), but the formula seems to be simple:

1. Rotate the DSS image for the location date and time such that the altitude points up. This accounts for the orientation of the POSS image in the sky.
2. Then invert the image (i.e. rotate by 180 degrees). This accounts for the inversion by the telescope.
3. Then rotate clockwise by an amount equal to the altitude of the object. This accounts for the fact that the reference frame of alt/az that is natural to the dob is rotated clockwise by an amount equal to altitude of the scope from the ground reference frame (vertical/horizontal).

Putting these three together seems to work very well in generating the exact orientation for the POSS image that matches the eyepiece view from my dob (which is Obsession, has a focuser that is horizontal; not at an angle like in the smaller dobs, and I configure it so the focuser is on the left of the dob when looking up the OTA).

I've noticed that a lot of us have been manually rotating the POSS to match field-of-view. I wonder if this idea is universal / if there is some fundamental problem with automatically predicting the orientation, although this seems to work very well for my scope.

I wonder if there is a way to extend other planetarium software to incorporate this feature.

Any information / discussion on this subject will be appreciated.

Clear Skies

Regards
Akarsh

[Dragan]

Akarsh,

Megastar has the ability and i use it religiously. A great feature!

[akarsh]

Dragan,

I'm wondering if MegaStar can do this automatically, i.e. calculate the required rotation to make the POSS image match the eyepiece view, and rotate by that amount; or if you have to manually rotate. With Jimi's setup, I have seen him manually adjust the POSS orientation in MegaStar (his is the only observatory where I've seen MegaStar in action) -- so my question is, is there something specific about his dob construction that prevents automatic rotation from working, or does MegaStar not have a feature to automatically figure out the required rotation.

I believe I have a solution (as described above) to automatically calculate the required rotation for my dob. It should technically work for any dob that has a focuser tube that's parallel to the ground, and is on the left side looking up the tube. As a novice observer that star-hops a lot, I have found this solution to be extremely useful on the field, because I already know the orientation, so it helps me match the stars much more easily.

If such a thing is generalizable to most dob designs, and if MegaStar somehow has a way to control it from a script or the like, it would be interesting to implement this feature in MegaStar, as I think it is immensely useful.

Clear Skies,

Warm Regards
Akarsh

[Clear Skies]

Hi Akarsh,

As you know I use my observing guides and an iPad for observations. When observing using a Newtonian I use the MHV edition (images mirrored both horizontally and vertically = rotated 180 degrees), lock the iPad's orientation so the screen does not flip, then simply rotate the tablet itself to match the image's orientation to the view in the eyepiece.
This can of course be done for individual (DSS) images, too, and negates the need for extra software.

Cheers,


Victor

[akarsh]

Victor, your method is quite interesting and simple! Thanks for sharing.

[akarsh]

On a tangentially related note, is an evaluation / demo version of MegaStar 5 still available? I'd like to tinker with it to see what it is capable of, but don't want to pay for something I will not use. I notice an old dead link on Willman Bell's website, that returns a 404 not found.

Clear Skies

Regards
Akarsh

[Jim Chandler]

Both MegaStar and SkyTools can rotate the field of view, but neither can calculate the correct orientation and rotate the field automatically in the way that you describe. My solution for many years has been to include a cheap printer in my field kit. The print out is fully rotatable and easy to carry up the ladder to the eyepiece.

[akarsh]

Dear Jim,

Thanks for that input. I'm surprised that these more professional software don't, given that it seems quite algorithmic. Maybe it is hard to generalize to most telescopes... If there is a plugin framework for either software, I'll be happy to give it a shot.

The cheap printer is a great idea. I shuttle between the eyepiece and the laptop, which is not too hard with a small telescope that warrants a 3-step ladder like mine. Jimi had an interesting thought, of putting a tablet right next to his eyepiece. I think this is a great solution. Even better for me would be a tablet that has velcro or something, and can be fixed next to the finder scope for finding (which sits on my rocker box), and then moved near the eyepiece for observing.

Clear Skies,
Akarsh

[Clear Skies]

This works for me: https://www.twelvesouth.com/product/hoverbar-for-ipad
Many similar contraptions are available. The key is "mountability" and weight.

[Jim Chandler]

... Jimi had an interesting thought, of putting a tablet right next to his eyepiece. I think this is a great solution. Even better for me would be a tablet that has velcro or something, and can be fixed next to the finder scope for finding (which sits on my rocker box), and then moved near the eyepiece for observing.

Clear Skies,
Akarsh

Five or six years ago, Jimi and I thrashed this issue pretty thoroughly. I lobbied for a printer in the observatory; he didn't want no stinkin' printer in his observatory. Jimi already had an iPad, and I found a remote control app that allowed it to control a desktop pc. It worked well enough that we were able to control MegaStar (running on the desktop), including screen rotation, from the iPad. Drag your finger on the iPad screen, and the picture changed on both machines. Pretty cool. The iPad never got mounted on the 48", however, and the prima facie reason was the lack of a suitable mount for the iPad. (Lots of mounts out there, but none of them quite right for this particular situation.) In retrospect, I think the underlying cause was that the additional layer of complexity in the control system crossed the murky line that separates astronomy assisted by hardware from perpetual hardware maintenance with a little astronomy tossed in occasionally.

[akarsh]

Jim

Would velcro not work?

I just realized that one of the pieces of this auto-rotation thing that I have is essentially compensating for the altitude of the telescope. If one mounts an iPad at the eyepiece, the iPad rotates as the telescope moves in altitude, so it automatically compensates for that. So if MegaStar 5 or SkyTools has an "Alt/Az" mode like Cartes du Ciel (or the "Horizontal coordinates" mode in KStars) where altitude is "up" in the map, just inverting the image should produce the correct orientation of POSS images on the iPad...

Clear Skies!

Regards
Akarsh

[akarsh]

Hi

This might be a very nice and amazingly affordable solution to this problem, especially for what Victor uses.

http://www.amazon.com/dp/B00P94RDKM

This is just a 7" (diagonal) display which is designed for use with the Raspberry Pi board computer (which is also equally affordable at $35):
http://www.amazon.com/gp/product/B00LPESRUK

I envision one of these displays mounted right above the eyepiece (with a feature to turn it off and maybe some special electronics to dim the lights all the way down) being very helpful on the field. Especially because the display driver allegedly comes pre-built with a feature to rotate / mirror the display as necessary!

The only question remaining for me, is how easy is it to dim it down all the way so it's compatible with astronomy.

Clear Skies

Regards
Akarsh

[akarsh]

Hi

As one more step towards solving this problem, I put the ability to generate an image like this into the KStars software. This image for M81 was generated for a big Dobsonian (focuser parallel to ground) on Jan 18th for Austin. Times are in CST. It has not been field-tested, so I don't know if it works for sure. Each marking tells you that for the given time of that marking, you should turn the map such that the marking points up to match the field in the eyepiece.

1965

If any regular observers are willing to test this, please PM me with your desired object, location, and date of observation.

Regards
Akarsh