Fraunhoffer

I had a great view of the transit this evening. It was a a very sociable 10:30 pm bst too. I found a (skywatcher) UHC filter or a green filter really helped with the atmospheric dispersion at its low angle.

Great. Thanks for sharing.

I made a great white light filter with a collar and solar film about 2 years ago. Never a problem until this week when the hot weather found it and distorted it. It still works, just about, but I'm not happy with the fit of the film now.

So if you make one, suggest keep it cool or make it from something other than standard pla fibre.

I'm old enough to remember staying up to watch it on our little old TV. I watched every Apollo mission after that and persuaded my parents to buy me a small telescope for a birthday present.

I thoroughly enjoyed watching the film when it came out last year.

Great sketches. Thanks for sharing. 

I usually use a yellow filter for these 2. However I used a green filter to help reduce the atmospheric dispersion this time, although that meant the color was not visible, apart from shades of green.

Pleased to see the red spot just before transit.

The RA clutch is usually a very basic device that just jams a bolt with a plastic end onto the side of the large worm pinion and carrier. The clutch lever should have a little  bit of slop when its fully off. My clutch lever engages about half way through its movement. If it's not fully off there will be some drag. The lever can be removed so that the bolt can be rotated to a good place and then the lever put on again. When lever fully off there should only be a small bit of internal bearing drag when the Ra is rotated. 

Ah those cursed 5 screws. A lot of patience, cups of tea, and very very slight adjustments at a time. I see are following the astro baby guide so not much to add. 

My mount is slightly different but same process. I do up the 2 outside screws till they are just taking the slack out but could still be nudged along by the 3 adjusters. Check the worm is not tilted. Then I  do up the outside 2 adjusters and slacken the middle one until it just starts to bind the worm then adjust the middle one just a nudge to release the worm.

They are in a push-pull arrangement with the outside 2 adjusters pulling the worm into the gear and the centre one pushing it out. The outer 2 can also adjust the tilt of the worm.

Then I check the full rotation of the worm and usually find there's a tight spot somewhere, so I readjust there. The downside is that it means the place where I started now has a bit more backlash. But that's just the way it is. 

Then I do up the 2 outer screws that clamp the worm in position. At this point I usually find the worm binds again, so I have to slacken them off and tweak the centre screw in and the 2 other adjust screws out to give the worm a bit more clearance before doing up the 2 outer clamp screws again.

Tedious and very small adjustments. Sometimes it's just a nudge. The threads are small in the alloy so be careful not do things up too tight and strip threads.

You probably knew all that already, but hope it helps.

I've cut plastic washers for various projects from plastic milk cartons in the past. (HDPE).

Caught a glimpse about 3:30 on Monday.  Looked good in 10x50 binos and easy to find. Picture not that great - taken with pocket camera. Sky was too bright by 4. 

Hoping for another look this weekend.

Catching up with these. Many thanks.

I started to get a bit stressy with my EQ mount altitude adjustment bolts when doing my polar alignment in the gloom.
The long bolt would frequently seize up and the pressure have to released before continuing.

I have a Bresser EXOS-2 mount and it looks very similar to the Vixen GP mount / LXD75, EQ5 pro and others of this style.

The altitude is adjusted by 2 long bolts that push against a spur on the mount head altitude axis. The spur is at an angle depending on the latitude setting and this angled surface twists the end of the bolt down when pressure is applied. The bolt then jams in the screw threads making adjustment difficult.

Ive added a sketch.

My solution was to make a shaped block of a hard waxy plastic that would support the end of the bolt to prevent it twisting, and would also slide within the channel where the spur is located.
I had hoped to use some PTFE but used a small block of HDPE plastic instead. This is a hard waxy and durable plastic that is actually used for plastic milk cartons. A hard waxy wood might also be used.
I cut a card template for the shape of the channel and then transferred this to the plastic and cut and filed by hand, removing a little at a time until it fitted nicely in the channel. I checked the height in relation to the altitude bolts so that the top was the same height as the centre of the bolt (bolt removed for this). Be careful not to jam the block in the channel (if this happens a small hand drill or an awl might help dig it out).

The final task was to use a round file and remove material to make a groove in the top at the same height and depth as the adjustment bolt to support the end; removing a little at a time and checking frequently.

The result? A buttery smooth altitude adjustment bolt. I can finely adjust my polar alignment altitude without any bolt sticking or jerking or getting too stiff to turn easily. The first time I tried it I effortlessly managed to achieve 1’30” polar alignment error.

My mount might not be the exactly the same as yours but I hope this may be useful to some. The usual waivers – you modify your own mount at your own risk.

In retrospect this was such a simple fix to an irritation in an otherwise lovely mount.

(PS. I have also made a thin large circular washer from a cut up HDPE milk carton that goes between the tripod and mount head - buttery azimuth bolts too).

Happy Adjustment Bolts everyone 🙂

(PPS. I didn't use a metal block since I thought it would wear the threads at the end of the bolt, whereas a firm plastic would not damage the threads. I expected the bolt to bite into the plastic, but using a hard waxy substance would enable it to slide a sthe bolt was adjusted. It doesn't usually have to move very much anyway)

 

Haha. Await with interest. 

The wire to the motor would be better facing down as well. The number of times I've nearly snagged the loop on a door handle as I carry the base out.

It's now firmly strapped in place with some glued on cable ties.

I was out last night till around 1. Great views of the moon to start with. So clear, found the Areadeus Rille near the interesting rocky formations near crater Julia's Caesar.

Then lots of clusters in Ophiuchus sweeping over to M13 and M57 ring nebula which is quite bright if small. 

Finally comet Panstarrs (again). Its been such a reliable comet. Unlike a couple of others I could mention. 😂

Might spend some time with double stars another evening. So many, for some reason.

Thanks for all the suggestions. Ive got 4 on my shortlist so far. 3 with fluid 2 way heads and one with az gears.
decisions decisions....
 

Orion Tritech II
weight     2.3 Kg
load         6 kg
length packed     69 cm
length extended    153 cm 
+    safety latch on shoe to prevent things falling out
    slotted shoe for sdjusting
    carry bag
- might be a bit short when extended

Celestron Trailseeker
weight        1.81 Kg
load        4 Kg
length packed    48 cm
length extended 178 cm
+    good for tall people
    legs can have different angles
    padded legs for shoulder carry
    compact when folded up
-

Horizon 8115
weight        3.58 Kg
load        unknown (binos upto 100mm dia)
length packed    78cm
length extended    180 cm
+    good for tall people 

-    bit long when packed
     heavy ?

Skywatcher AZ Pronto
weight        3.8 Kg
load        3 Kg
length packed    78.5 cm
length extended 150 cm
+    nice geared controls and locking t bars

-     £ need to add dovetail for camera and scope
      more expensive
      heavy ?

Nice sketch. One of my favourites.

I want to make up a nice hand portable rig using an ST80. (I have the OTA, nice diagonal and spare eps). So looking for a nice not expensive but steady tripod that could fit in a large backpack. 

I might add a tracker later in phase 2. 

Any recommendations for a tripod?

I do some other photography so a photo tripod would be ok. The St80 rings I have include screw fitting anyway. 

Thanks

On 13/12/2016 at 21:23, billyharris72 said:

There is an interesting article by Simon White in Decembers BAA Journal that covers just this issue. He argues that, where the errors in polar alignment are relatively small, the declination of the target is of little practical importance (note that he's assuming PAE of the order of 1 arcminute or so). His little thought experiment is roughly as follows (it's based on the small angle of error meaning we can treat the sky as a flat rotating disk):

Imagine a perfectly polar aligned mount, with the scope focused dead centre on a star (any star will do). Now move the scope out of alignment by a small amount (say 1 arcmin). The star will move exactly this much in the field of view, so it is now offset from the centre by 1 arcminute. If we leave the mount to track for 1 sidereal day (and imagine we could watch the star the whole time) we would see the star describe a circle in the eyepiece, around the centre of the field of view, and return exactly to the point where it started. A distance of 2 x Pi x PAE, or 0.262 arcsecs per minute for a 1 minute error. We know that pixel scale in arcseconds is given by 206 x pixel size / focal length. That means the time to drift 1 pixel (in minutes) is given by:

206 x pixel size  x 24 x 60 / (2Pi x focal length x PAE(arcmin))

He uses this to work out a little table of time (in the article for a Nikon D90) for a one second drift with various lenses and focal length scopes (with an 805mm scope there is 1 pixel of drift every 322 seconds; while a 200mm lens will take 21 minutes for the same drift). The figure from that table can then be divided by the actual alignment error (assuming this is known) to calculate the approximate achievable exposure time. The figure is easy to adjust of you are happy to accommodate more than 1 pixel of drift.

Not mathematically exact, but a straightforward rule of thumb that (according to White) gives results that are very close to the original Hook formulae.

Such a useful post. Thank you. I've been looking for just this information. The numbers are very close to what I get in practice with a DSLR and 400mm Tele bolted on top of my scope when I look up the alignment error I've got. I'm limited by light pollution in the length of my subs. So if I can get 2mins unguided and keep things simple, I'm very happy. 

Finally, I managed to see it last night on day 12 of current lunar. I needed to go to 240x to see it. Thanks for the tip. 

As I sat outside looking at the stars with my jug of ale and binos last night, it appeared to me that Betelgeuse was considerably brighter than it has been recently. Whether it was my alcohol infused observing or the glowing horizon as Orion was dipping into the murk, I'm not sure. I could only judge that it was about the same brightness as nearby Procyon. 

Sorry to resurrect an old thread, with old news, but thought I would just comment that it does seem to be getting back to normal.

I think there is a setting for maximum and minimum altitude somewhere in the settings to try and avoid things directly overhead where the back of the scope can be very close to the tripod legs.

A pier extension (as above) could be used and reduce the leg extension to keep the overall height the same but with less spread, but you will need to check if that is stable enough with your set up and it doesn't tip over.

Bit late sorting my photos and posting this, but it looked very nice. 

Bracketed exposures combined.

Picture from 8th.  45x45s Moonlight and shooting over a streetlight not the best conditions. 

Thoroughly enjoyed it all. When's season 2? 

"Engage..." 😆