Trouble seeing Sigma Octans - Tak polar finder

rcheshire (Rowland) · #1 11-07-2010, 02:44 PM

Folks. I think this is the correct forum for this question.

Essentially - The lighting in my area makes polar alignment very difficult.

I'm on top of the Takahashi finder scope procedure for the Southern Hemisphere, except that the final touch, adjusting the mount in altitude and azimuth, is where I'm having difficulties.

I think it is a combination of wearing trifocals, the luminosity of the reticule balanced with being able to see Sig Oct which I understand is a magnitude 5 star.

The thought that comes to mind, is that I'm not sure how big the trapezoid appears on the reticule, consequently, it is very difficult to identify just what I'm looking at - I can see stars but identifying Sig Oct is impossible through the soft foggy glow of the reticule. I followed the notes and balanced the illumination with the stars that I can see.

Is this making sense - any tips on how to improve the situation.

Many thanks,

Rowland.

RickS (Rick) · #2 11-07-2010, 02:56 PM

I have given up trying to use the Tak polar finder from my urban location. I drift align instead...

Cheers,
Rick.

floyd_2 (Dean) · #3 11-07-2010, 05:09 PM

Hi Rowland,
take a look at this website. It's got some good finder charts at the bottom for how sigma will look thru a finder at various times of the year.

Dean

Dennis · #4 11-07-2010, 05:28 PM

Hi Rowland

The FOV of my EM200 Temma II Polar Alignment ‘Scope (PAS) is 4.4 degrees and the attached files show the view with the Octans “Trapezium” centred in the FOV of the PAS.

Note that this is not polar aligned – this simply illustrates what the Octans “Trapezium” asterism looks like in the PAS and also identifies Sigma Octans.

Once I have this asterism in the FOV I then use the Alt-Az adjustment knobs to place Sigma Octans in the reticule at the appropriate year marker.

This is after I have set the Date/Time scales of the PAS reticule to the current Date/Time for the Southern Hemisphere based on the xls spreadsheet I wrote and posted here.

I actually find it “easier” to identify the Octans “Trapezium” asterism and Sigma Octans from my suburban location in Brisbane as they just poke their heads above the background sky pollution, whereas at a dark sky site, they get drowned in other stars nearby.

I need to turn down the red LED in the PAS to avoid swamping Sigma Octans. I have marked three foot locations in the back garden for the tripod so Octans is usually somewhere in the FOV of the PAS each time I set up – this helps enormously.

Cheers

Dennis

rcheshire (Rowland) · #5 11-07-2010, 05:44 PM

Hi Dennis. Thanks for going to so much trouble to explain this - very much appreciated.

I'll print out the diagrams for ready reference - already have your conversion spreadsheet. As we speak the gear is outside cooling down - it's a clear night in Geelong.

Thanks Dean, I'll have a look there too.

The Stellarium screenshot shows the current alignment of the asterism (actually it's opposite - just realised that)

Cheers

Rowland.

rcheshire (Rowland) · #6 12-07-2010, 12:36 PM

Successfully polar aligned and tracking well for 5 minutes unguided.

I will post a Stellarium view later to show 3 stars including Sigma Octans in line and very easy to recognise, even under suburban lighting - provides some extra cues.

Is there a way to put the EM200B in standby so that it doesn't rotate while polar aligning. I did read that the USDIII has a standby switch position, which the 200B does not?

Thanks again.

Cheers.

Rowland.

Dennis · #7 12-07-2010, 01:23 PM

Hi Rowland

Well done – now all you have to do is mark the locations of the 3 tripod legs and you should be able to return to the same spot and find Sigma Octans in the FOV of the PAS.

When I remove the EM200 head from the tripod, I always unscrew the same azimuth adjustment screw (the West-facing knob in my case) about 7 or 8 turns so when I re-fit the mount, re-tightening the same screw will put the mount very close to being polar aligned.

I set up on grass and have removed 3 small sods of grass where the tripod feet sit and it only takes me a few seconds to tweak the Alt/Az adjustment screws to get polar aligned again each time I set up.

If you don’t have the “Computer Stand By” switch, then with the tripod feet marked and the head fitted as described above, it still only takes a couple of minutes to polar align so it shouldn’t be a issue?

Cheers

Dennis

rcheshire (Rowland) · #8 12-07-2010, 06:09 PM

HI Dennis. I've marked the tripod location and slackened the azimuth adjustment screws slightly - I like your idea however.

I've attached another Stellarium screen shot in EQ mode and marked the 3 stars mentioned earlier. Might be of help to others. These I found to be a dead give-away, with their spacing, and easy to see in the reticule.

Cheers,

Rowland.

Dennis · #9 12-07-2010, 07:56 PM

Hi Rowland

Yes – those are the same 3 stars that I use to confirm that I am actually looking at Sigma Octans, the brightest of the trio. By the way, those screen shots from Stellarium are just gorgeous; I must download the application and have a look at it.

Cheers

Dennis

rcheshire (Rowland) · #10 13-07-2010, 08:46 PM

It's a very useable program. Quite good for beginners like me. When I have a moment I'll try adding a reticule image to the screenshot - rotating the screenshot will help with alignment at different times.

I have an idea, similar to the Jeppesen flight computer - a circular slide rule by any other name. Overlay a Stellarium image with couple of clear plastic disks with reticule markings - possibly add a battery powered LED for backlighting. Rotate the disks as required to display the expected alignment, which may assist in finding Sigma Octans.

rcheshire (Rowland) · #11 18-07-2010, 11:35 PM

Just an idea - Polar finder reticule simulator. Set up polar view prior to attempting polar alignment.

Basically a scaled map of the SCP region overlaid with clear plastic disks. The idea is to know the EQM orientation of Sigma Octans before peering into the polar finder, making it easier to see Sig Oct with some prior orientation.

A further improvement would be a scale that automatically converts North to South dates and times. Shouldn't be too hard to work out.

Advantages - as above and carry it in your pocket. No tables to reference. No need for the laptop if you don't want to take it with you. Can be illuminated with a red led and button battery.

Limitations - not as accurate as spreadsheet and need an accurate timepiece.

Wouldn't be surprised if someone has thought of it already - inspiration from Jeppessen circular flight computer.

Under development - ideas - good bad indifferent.

beren · #12 18-07-2010, 11:50 PM

Theres a good application in the Yahoo Tak uncensored group files section {under HVB-docs and tools} which might fit your description

rcheshire (Rowland) · #13 19-07-2010, 07:00 AM

beren. thanks for the heads-up. I guess the idea that I'm proposing is a manual solution to avoid the need for a computer. it needs a conversion scale for southern hemisphere alignment a direct conversion read off against the northern hemisphere scale. I think flipping the inside scale and scaling it down to fit and align with the time scale will do the job.

Cheers.

Dennis · #14 19-07-2010, 09:23 AM

Send your idea to Takahashi in Japan – they owe it to the Southern hemisphere users to implement something like this!

Cheers

Dennis

Quote:

Originally Posted by rcheshire

Just an idea - Polar finder reticule simulator. Set up polar view prior to attempting polar alignment.

Basically a scaled map of the SCP region overlaid with clear plastic disks. The idea is to know the EQM orientation of Sigma Octans before peering into the polar finder, making it easier to see Sig Oct with some prior orientation.

A further improvement would be a scale that automatically converts North to South dates and times. Shouldn't be too hard to work out.

Advantages - as above and carry it in your pocket. No tables to reference. No need for the laptop if you don't want to take it with you. Can be illuminated with a red led and button battery.

Limitations - not as accurate as spreadsheet and need an accurate timepiece.

Wouldn't be surprised if someone has thought of it already - inspiration from Jeppessen circular flight computer.

Under development - ideas - good bad indifferent.

Dennis · #15 19-07-2010, 09:51 AM

Quote:

Originally Posted by beren

Theres a good application in the Yahoo Tak uncensored group files section {under HVB-docs and tools} which might fit your description

Hi Stuart

Good find – now that is a killer app for the EM200!

Cheers

Dennis

rcheshire (Rowland) · #16 24-07-2010, 09:32 AM

The solution is a lot simpler than first imagined. Sigma Octans is fixed over its desired location on the recticule and the outer scale rotated with a direct conversion for date and time - in white.

I'm pretty sure that the conversion is correct - though not exact I suspect - near enough to orientate the observer with the surrounding stars.