Orion xt12

[torr (James)]

Hi folks,
My Orion XT12g arrived a few weeks ago thanks to my amazing partner, sorry for the bad weather in the Geraldton region

Being a fifo worker I finally got to have a big play with it yesterday and last night !

Ill start with I did have a terrible time with collimation on this unit originally, it just wouldn't hold with a change on declination.
After removing the primary mirror cell assembly I found the mirror clamps weren't tight enough and there was a fair bit of play between the mirror and the cell.
While I had the cell out I replaced the original collimation springs with C-702 springs from Bunnings (thanks to these forums).
Now it holds collimation great at all dec angles and I'm happy

After owning a Skywatcher 8" Newt on an eq5 I must say I prefer the dobsonian does suit my usage much better.

I own 32mm TV plossl and 24mm, 17mm, 5mm Orion Stratus eyepieces.
I use the orion chesire collimator and laser mate deluxe for for collimation this seems to work well for me.

I prefer the Orion stratus 24mm over the TV 32mm plossyl , views seem brighter bigger with a similar field of view.

So far I am very impressed with the unit and happy I chose the goto over the pushpull a dob.

I spent a bit of time looking at globular clusters around the southern cross and scorpius, M7, M4, M62, NGC6522, NGC4755 and 5139 and others, they are incredible with the 24mm stratus, i do have light pollution where I live but I'll tolerate it.
Had a peak at Mars and Saturn but id give the transparency a 5 and seeing a III last night , the 5mm stratus wasn't too clear at all , a fair bit of shimmering.

The goto function works great, took me about 5 minutes to setup.
I used stellarium on my phone to find something and then enter it into the hand controller. Considering it was my 1st attempt with goto and I only used 2 star alignment, objects always appeared in the 24mm eyepiece, I was impressed.

Its amazing how many more stars the 12" shows over the 8" and how bright brighter stars appear in the eyepiece.

I would love some suggestions on eyepieces that will easily fit the pleiades into the field of viewand that work well in a 12" f4.9 Newt.
I know its going to something like a Nag 31mm or maybe folks have had luck with the orion Q70 series.

I have to thank IIS for an amazing wealth of knowledge, there cant be too many questions not answered in the history of these forums,

Anyway I'm excited and cant wait to get out again, clears skies to you all.

[barx1963 (Malcolm)]

Torr
Well done on the new scope.

One point. The mirror clamps should not be tight. They should be set so the there is a small gap between them and the upper surface of the mirror. I am not familiar with the cell assembly on these scopes, but any well designed cell will hold the mirror inplace without the clamps being tight.
Although your mirror looks like a solid chunk of glass, even slight pressure on it wll cause deformation and turn your stars into little triangles. If you look near the bottom of this document ( http://www.astro-baby.com/collimatio...on%20guide.htm ) there is an example of what this looks like. It is best seen with a defocused star. I tightened my clips on my old 12" by only 1/2 a turn and it dramatically degraded the performance.
Usually upgrading springs is the best solution for a mirror shifting while moving in alt.

Malcolm

[torr (James)]

wow thanks for that information.
It would appear I may have pinched my optics, Ill adjust them tonight and re-test as I am getting triangular shaped stars when defocused as per the link.
The mirror was originally very loose and moving around, but it does now appear I've over tightended the clamps.

That link was very useful , thanks again Malcom

[sopticals (Stephen)]

Originally Posted by torr

Hi folks,

After owning a Skywatcher 8" Newt on an eq5 I must say I prefer the dobsonian does suit my usage.

Its amazing how many more stars the 12" shows over the 8" and how bright brighter stars appear in the eyepiece.

I would love some suggestions on eyepieces that will easily fit the pleiades into the field of viewand that work well in a 12" f4.9 Newt.
I know its going to something like a Nag 31mm or maybe folks have had luck with the orion Q70 series.

I have to thank IIS for an amazing wealth of knowledge, there cant be too many questions not answered in the history of these forums,

Anyway I'm excited and cant wait to get out again, clears skies to you all.

Congratulations on the new scope. Similar experience to mine re: 8" Skywatcher on EQ Mount, then moving onto a 12" collapsible Skywatcher. How much easier the dob to the EQ. Also noticed what an increase in aperture can do, it can become a problem, in that one can catch the dreaded "aperture fever".

To my mind, (my not be every ones "cup of tea"), the spectacular wide fields of view, afforded by the TV Nagler 31 T5, (or ES 30 82 [I have both-this one is more affordable but still an excellent ocular]), takes a lot of beating. Dont know about the Orion Q70s, but doubt they would be in the same league as the TV Naglers or ES82s.

Anyway all the best. Enjoy the spectacular Southern skies.

[Allan]

Tighten up the screws on the mirror clips with your fingers, no need to use a screw driver, this also prevents the chance of dropping a screw driver onto your mirror. So tighten until the clips just barely touch the mirror, and then back them off a fraction. A good guide is make the gap big enough to slip a piece of paper into.

While you have the mirror cell out, you might want to take the mirror out of the cell and have a look at the floating pads that the mirror sits on. Mine were extremely tight and didn't float at all, meaning more pressure on the back of the mirror. Just get in there with a screw driver and a bit of a wriggle on the 3 mounting pads to loosen them up.

Originally mine also changed collimation as I moved it through altitude. I changed to heavy duty springs and screwed the collimation screws down much further to get a good deal of tension on the springs. Then also screw the locking screws in quite firmly, nothing crazy so you strip the threads mind you. Now the laser stays centre perfect no matter what position the telescope is in.

A 31 Nagler will only just frame M45 in the FOV. But there are tons of other objects were the 31 Nagler really rocks. You should try one on the Carina Neb with an OIII filter sometime.

[barx1963 (Malcolm)]

With the eyepieces to see M45, a good point to start is work out how big the target is (in this case about 1.4deg, or roughly 3 times the diameter of a full moon) and then use the calculator on the Televue site to work out a true field. (the address is here http://televue.com/engine/TV3b_page....212&plain=TRUE )
With your scope the TV eps that do it are
35 Pan
41 Pan
31 T6 Nag
21 Ethos
55 Plossl

Of course the size of M45 is the entire cluster, not just the central bright area, so a smaller ep may suffice.

I believe there is a 35 Pan for sale in the classifieds ATM, I have used one and they are really nice. 68deg AFOV, pin sharp nearly to the edge and surprisingly good contrast for such a low power EP.

Cheers

Malcolm

[torr (James)]

My primary mirror was slightly pinched , after re-adjusting the clamp tension and re-collimation the defocused star patterns are almost perfect and hold now, to my eyes anyway.
When I said I tightened the clamps the other night, it was't very much so I was surprised it had such an effect on the primary
Thanks for that.

I managed too see the cassini division last night for the 1st time using the 17mm stratus (88*) although seeing was far from optimal.

I really am liking the goto system, its making this hobby so much more enjoyable , I must admit I am bit impatient, and the goto helps here a lot.

I would love a wider field lower mag eyepiece but Ill have to be content with what I have for now.
My comment on the 32mm TV was not clear sorry.
I was meaning the 24mm stratus gives brighter views and similar if not slightly bigger field of view then my 32mm TV plossl making the TV obsolete.

I see the 35mm Pano in the classifieds. I am a bit reluctant with 35mm and over as the exit pupil concerns me as it will be over 7mm according to the teleview charts , something I'd like to test before shelling out for it.
I read the 31mm Nag is around 6.3mm exit pupil and the true field is around 1.6 deg

Cheers

James

[astro744]

Originally Posted by torr

My primary mirror was slightly pinched , after re-adjusting the clamp tension and re-collimation the defocused star patterns are almost perfect and hold now, to my eyes anyway.
When I said I tightened the clamps the other night, it was't very much so I was surprised it had such an effect on the primary
Thanks for that.

I managed too see the cassini division last night for the 1st time using the 17mm stratus (88*) although seeing was far from optimal.

I really am liking the goto system, its making this hobby so much more enjoyable , I must admit I am bit impatient, and the goto helps here a lot.

I would love a wider field lower mag eyepiece but Ill have to be content with what I have for now.
My comment on the 32mm TV was not clear sorry.
I was meaning the 24mm stratus gives brighter views and similar if not slightly bigger field of view then my 32mm TV plossl making the TV obsolete.

I see the 35mm Pano in the classifieds. I am a bit reluctant with 35mm and over as the exit pupil concerns me as it will be over 7mm according to the teleview charts , something I'd like to test before shelling out for it.
I read the 31mm Nag is around 6.3mm exit pupil and the true field is around 1.6 deg

Cheers

James

f.l. = 1500mm, f4.9

The 35mm Panoptic has a field stop diameter of 38.7mm. This will give you a true field of TFOV= FSD*57.3/f.l. = 38.7*57.3/1500 = 1.5 deg. Exit pupil = 35/4.9 = 7.1mm. With Paracorr TFOV=1.5/1.15 = 1.3 deg. Exit pupil = 7.1/1.15 = 6.2mm.

The 31mm Type 5 Nagler has a field stop diameter of 42mm. This will give you a true field of 1.6 deg. Exit pupil = 6.3mm. With Paracorr TFOV = 1.4 deg. Exit pupil = 5.5mm.

The 26mm Type 5 Nagler has a field stop diameter of 35mm. This will give you a true field of 1.3 deg. Exit pupil = 5.3mm. With Paracorr TFOV = 1.2 deg. Exit pupil = 4.6mm.

The 21mm Ethos has a field stop diameter of 36.2mm. This will give you a true field of 1.4 deg. Exit pupil = 4.3mm. With Paracorr TFOV = 1.2 deg. Exit pupil = 3.7mm.

A Paracorr acts as a 1.15x Barlow and corrects for primary mirror coma. I have rounded the above numbers.

I think the 31mm Nagler is useable under dark skies but also especially when combined with an O-III filter for some spectacular views of the larger nebulae.

The 26mm Nagler may be a better choice than the 31mm Nagler but note it has a little less eye relief. The 21mm Ethos a little less again but adequate I would think without glasses.

Eye relief:

35Pan = 24mm
31NT5 = 19mm
26NT5 = 16mm
21NT5 = 15mm

I would consider the eye relief of the 35 Pan very comfortable, 31mm Nagler comfortable, 26mm Nagler adequate and I have not used the 21 Ethos. I do not wear glasses.

The 21mm Ethos has a slightly wider true field than the 26mm Nagler and smaller exit pupil. It would be ideal for you telescope, but not quite wide enough for the full Pleiades and for that you need the 41mm Panoptic with 46mm field stop diameter for a 1.8 degree true field but at 8.3mm exit pupil. You will effectively be losing some light due to the large exit pupil but if you have dark skies it really doesn't matter since you have plenty of aperture to play with and you are using the eyepiece for it's maximum true field capability.

The use of the Paracorr is a personal choice and some people don't like coma and others are not bothered by it.

If you can go to a star party and get to try some or all of the above eyepieces and/or Paracorr only then you will know which is best for you. I think the darker background will be more pleasing which the 21mm Ethos will give you.

See http://www.televue.com/engine/TV3b_p...4#.U6uMDZSSy5I for Tele Vue eyepiece specifications.

[barx1963 (Malcolm)]

Torr
With the pinching of the optics, mirrors are accurate to within fractions of a wavelength of light, which is measured in nanometres, so tiny deformations can affect the image. No material is 100% rigid.

With the EPs, don't get too worried about exit pupil. Having an exit pupil smaller than your fully diluted pupil is ideal, but not essential. I have used a 35Pan in my f5 scope with no issues.

Malcolm