Just starting in Astrophotography

[DarkKnight (Kev)]

I'm a keen photographer who has recently got bitten by the astro bug.

My interest at this stage is Nightscapes, and finding interesting terrestrial subjects to tie in to the night sky.

At this stage a telescope isn't on my radar and I'm thinking of a mount something like a HEQ5 to start with, as I will be loading up to 5kgs on it with a Nikon D800 and a heavy lens. I like to have a bit of leeway with the stated weight specs plus from previous experience I know that I'll soon be lusting after some sort of modest 'scope.

OK, first dumb question.

For basic astro shots longer than 30 secs I know I'll need to do some tracking. From my internet searching it seems that I'll need at least a RA motor and controller. Will I need to do a polar alignment for basic star tracking if my camera set-up is level ? I do understand that for GoTo set-ups this is mandatory.

Next dumb question.

With a GoTo set-up, if you make sure your tripod/mount is level, and dial in your co-ordinates (from your android app) can it not then give you the settings for finding the SCP ? ie move horizontal axis 9.6° west or whatever ?

Well , I did warn you that they were dumb questions.

Cheers

[Wavytone]

Originally Posted by DarkKnight

For basic astro shots longer than 30 secs I know I'll need to do some tracking. From my internet searching it seems that I'll need at least a RA motor and controller. Will I need to do a polar alignment for basic star tracking if my camera set-up is level ?

Yes.

To keep it tracking for longer shots consider an auto guider as well, this is a small camera and lens that provides corrections so that the image stays put - accurately - on its sensor. Beats the crap out of guiding manually as many of us did 20 years ago.

With a GoTo set-up, if you make sure your tripod/mount is level, and dial in your co-ordinates (from your android app) can it not then give you the settings for finding the SCP ? ie move horizontal axis 9.6° west or whatever ?

Not an unreasonable question but unfortunately the compasses in smartphones are not very accurate and in addition the slightest iron or steel in close proximity will cause it to deviate significantly. In addition, there isn't a bright star near the SCP, and the south polar region is not easily recognised by those unfamiliar with it visually. A better and quick method is this:

1. Assemble tripod and telescope, no need to even level it (don't bother).
2. Choose a known bright star overhead on the meridian (north south), and consult a star atlas to find its declination. Dial up the declination of this star on the dec axis, and point the scope roughly at it - you move it east/west by moving it in RA, and then adjust the mount elevation to move the scope north/south until the star is on the crosshairs of the finder. This sets your mount to the correct elevation. Alternatively you can use a clinometer app in a smartphone to set the elevation of the polar axis to match your latitude, or at least check you have got this right.

4. Choose a known bright star near the east or west horizon, and set the mount to the declination of this star, using the dec circle of the mount, and lock this axis. Leave the mount free to move in RA (up down).
5. Looking through the finderscope, adjust the azimuth of the mount to put the star on the crosshairs (azimuth will permit left-right movement, move the scope in RA to go up/down).

Repeat for a star near the west as a check.

This effectively aligns the azimuth of the mount within the accuracy of the circles. It does assume however that the dec circle has been aligned with the telescope, and the finder and telescope are also aligned.

This will align the mount within the resolution of the dec circle.

[DarkKnight (Kev)]

Originally Posted by Wavytone

Not an unreasonable question but unfortunately the compasses in smartphones are not very accurate and in addition the slightest iron or steel in close proximity will cause it to deviate significantly. In addition, there isn't a bright star near the SCP, and the south polar region is not easily recognised by those unfamiliar with it visually. A better and quick method is this:

I guess I didn't explain myself very well, , possibly due to the fact that I'm an old fart struggling to get a grip on the technology and terminology of all this astro stuff.

What I was alluding to was using GPS co-ordinates, either from a phone app, a plug-in for my camera, or from my Garmin Navigator. The Ephemeris website will give you your altitude, roughly, and my thinking was by using that info, along with the GPS co-ordinates for your location, the GoTo program should know exactly where you are and be able to give you the altitude and longitudinal numbers to point your mount straight at the SCP, or at least somewhere pretty close.

Too simplistic huh ?

[Camelopardalis (Dunk)]

The Skywatcher equatorial mounts with the Synscan goto handsets will tell you the hour angle of Polaris once you've performed a star alignment...completely useless for us down here though

Many computerised goto mounts include a polar alignment routine that helps you hone in on it, but I've had a bit of a love-hate relationship with mine

There is software to assist with polar alignment if you plug the mount into a computer.

But at its simplest, a good old drift alignment is going to give you the best shot and doesn't require goto, just motorised RA drive.

[Wavytone]

Originally Posted by DarkKnight

Too simplistic huh ?

not at all, but you are missing something.

It's one thing to know your GPS coordinates but that won't tell you which direction north/south is, in order to set your mount to the correct azimuth.

I suppose you could note the telescope position then talk a walk for say 50 metres and watching a map app, walk until you are due south or north of the mount according to the map, place a marker and align the azimuth to that. You'd be able to position yourself roughly that way but it won't be very accurate.

Secondly the compasses in smartphones are not all that accurate - take a star map app such as Sky Safari, and you'll see how far off it can be.


The bright stars themselves are easy beacons if you know their declination from an atlas. simplest way to get the mounts azimuth aligned is to use a known star east or west as the azimuth reference, and to use the dec circle on your mount as I described.

Drift aligning has always struck me as a fiddly and slow way to do it, the way I describe will get you well aligned in 5 minutes without trial and error.