DrRobin

I have been a little lapse lately, my first solar imaging session since Sept 2018, can you believe it?

So I dusted everything off on Sat morning and I really do mean dust, then my laptop had lost the camera driver, my phone refused to stay connected to the mount when fiddling with the manual adjustment, then the camera would only capture at 15fps until I rebooted and loaded the driver for a third time, then my PC ran out of hard disk space, several times.  My Quark was reluctant to stabilise and to cap it all I couldn't remember what combination of focal reducers, barlows or extension tubes to use to get a decent sized image and focus.  It was gone mid-day by the time I got these and think the seeing had gone downhill, the Ha was in and out of focus all of the time on the screen.

Somewhat amazing I managed to get anything, I just ran out of time to get any more Ha (for a mosaic), still no bad thing as I can't remember the settings I used for processing and it has taken my until Monday to process these three images.  Imagine if I was doing a 12 pane mosaic, like the good old days.

Sun in White Light, Zenithstar 80mm, Lunt wedge, AS174MM

Sun in Calcium K, Zenithstar 80mm, Lunt K-line filter, ASI174MM

Sun in Ha, Zenithstar 80mm, Daystar Quark, ASI174mm

All things considered I am pretty pleased with the results, now to clean my camera as there are dust spots on it, then find the right combination of focal reducers/barlows before the next session, which will hopefully be sooner than another 3.5 years.

Robin

Summer of 2018 while on holiday in Crete was my last solar imaging session, so once every couple of weeks definately beats mine.  Oh, I did photo the eclipse with my iPhone and a pair of solar glasses in June, does that count?

Mind night time hasn't been much better, nothing in 2021 so far and only a couple of sessions in 2020.  I keep saying next weekend, I will blow the dust off the scope, but bad weather seems to occur.

Robin

Nice Steve,

I have been away for so long, may be one sunny day.

Robin

Hi,

Have a look at this thread on page 2, I stripped down my clutch, there are photos of it, so you should be able to figure out which nut to adjust.  The clutch needs to be just right, too slack and you get the nose dropping all of the time (especially at high alt) and too tight and the motor doesn't seem to turn it correctly.

https://stargazerslounge.com/topic/120594-skywatcher-az-goto-alignment-and-accuracy/page/2/

There is also a photo of the counter weight, it was a magnet I used, not a track on this post

https://stargazerslounge.com/topic/116517-skyliner-250px-flex-tube-auto-tracking-dobsonian/page/2/

Robin

Hi,

There is adjustment for the clutch, it was 9 years ago I had one of these and can't remember where the adjustment was, I think you have to take off the black plastic cover and then use a spanner to tighten.  Basically the clutch is there so you can push the tube and not damage the motor or gearbox, but since I never did that, I tightened mine up so it wouldn't slip.

I also added counter weights to the back of the tube to offset the weight of a camera.  I attached a rail to the tube and could then move the weight to get perfect balance.  Unfortunately, I don't have any photos and I took it off before selling it.

Hope that helps.

Robin

Well done Alexandra, just seen your photo on the BBC website.  

Robin

Nice one Steve. 

All of my solar kit is still in hiding, Sept 2018 was the last outing in Crete, perhaps I will go and have a look to see if it is still there?

Robin

Nice disc.

Robin

It seems to take several seconds (30s?) to transit the disc and is not massively out of focus so it must be a reasonably sized object some distance away.  It's random nature, speed and size rule out an aircraft or satellite, if I had to guess I would suggest something at about 500~1000ft away, moving at around 10~30mph.

It appears to change shape, so your guess that it is a sheet of something been blown along by the wind (tumbling) is consistent, but not as high as you suggest.

It might be a drone, someone at 500ft and moving about 10mph, but been manually controlled and changing angle or been blown a bit in a strong wind?

Anyway nice capture.

Robin

We have all been there, moving telescopes round the garden, chasing the narrow window in winter.  Sadly my solar telescopes haven't made it back out of storage since sometime last year (or was it the year before?), I forget when, but looking at some of the other posts there has been a few spots to look at, so good luck.

The other option is to drive out to a car park, you get some funny looks, but that is all.

I saw a bright flash last night at 23:34 and initially thought it was lightning, but a check on lightningmaps.org confirmed it wasn't and anyway the colour was wrong.  I assumed it was a meteor and the report below confirms this.

https://www.bbc.co.uk/news/av/uk-england-derbyshire-51373851/exploding-meteor-caught-on-doorbell-camera-in-derby

I live 10 miles west of Newcastle Upon Tyne and it was due east at 23:34, I guessed somewhere over the north sea.  It must have been pretty big to be seen so well in Derby and due east of Newcastle Upon Tyne.

My night sky camera caught it, in the 9 o'clock position, due east of me at 23:35, but it runs 60 second exposures.

Did anyone else see it and which direction, we might be able to triangulate it?

It's a simultaneous equation, x is the distance of the train from the bridge, y is the length in the bridge (in terms of time)

x = y/3 and x+y = 2*(y/3)

x therefore equals y and therefore the speed of the train is 3x.

We did these in school.

A focal reducer doesn't change the F ratio of the scope, it changes the size of the sensing element. Your 200mm RC is still F/8, but the pixel size has effectively doubled in size (4 x the area) and this makes it more sensitive at the cost of resolution.

Binning doesn't help that much.  If you use a 2x2 bin (4 times the area), but they way the signal is read it is more like 2x the signal.  To get back to 4x signal you have to use 4x4 bin, roughly speaking.

Smaller pixel sizes often have a lower light sensitive area to total area, due to the need for readout registers.  It's so dfficult to compare different ccds.

If you look at my post from 2013 you will see I differentiated between a DSO (the subject of this thread) and a star.  This is important if you are considering point sources or a light spread out of an area.

2 minutes ago, vlaiv said:

Simply put - this is wrong.

Many people forget pixel size - or assume unchanging pixel size. F/ratio does not determine "speed" of setup - meaning it does not determine how long you will expose.

I was making the assumption that it would be the same camera on both.  If you change the pixel size then everything changes, oh and you might as well change location to above the atmosphere where there is less loss.

5 minutes ago, vlaiv said:

Now you have 8" of light gathering vs 6" of light gathering - both mapping 1.15" of sky to size of pixel. 8" will win on speed, even if F/10 is "slower" scope than F/5 because it is larger aperture.

I doubt this is true either, both systems end up with the same amount of sky per pixel, if both cameras have the same sensitivity (difficult to achieve) then both will image in the same time as they both have the same number of photons to play with.

10 minutes ago, dph1nm said:

Sadly you wouldn't see many objects (in the same exposure time as a typical Hubble shot), as how faint you can see depends on the aperture not the focal ratio.

How faint you can see depends on how many arc-seconds per pixel and the signal to noise ratio of the chip.  Hubble is in space so has very low noise.  The F-ratio, aperture and pixel size all then contribute to the number of photons in each pixel from any given light source.

If you increase aperture and as a consequence increase F/ratio (focal length) then the number of photons per pixel might not change and you won't get any more signal.  If you increase pixel size then you will see faint objects provided you don't increase noise as a result, but at the expense of resolution.

Simply put.....

F ratio determines how long you will image for (your exposure time);

Aperture (and focal length) determine how much you will fit in.

E.g. a 12" F/5 telescope will have the same exposure as a 6" F/5 telescope, its just that the 6" will cover a much wider field.

Hi,

My dad got me out of bed to watch Armstrong and Aldrin walk on the moon, I think it was delayed? but can't really remember, I was only 5.  

Fantastic achievement, this is what can be achieved when everyone pulls together.

Robin

The banding on your Ha is really pronounced, far worse than my set up.  I have a Lunt 60DS and the same cameras as you.  I also have a Quark and here is what I find.

My ASI120 produces bands but they are fairly closely spaced with my Lunt and of course get worse with a Barlow.  I tried a tilt adaptor and after endless fiddling I got rid of the bands, but the camera, especially with a Barlow, was so far out of alignment it wasn't in correct focus and I saw a slight vignetting, so for me it was a non-starter.

My ASI174 produces virtually no banding in my Lunt, it does seem to have a slight smear pattern, rather like a cloud under Ha, but flats applied during capture with Firecapture sort that out. I took it apart and cleaned the chip and optical window and the cloud patern has almost gone.

I get similar results with my Quark, but tend to use a focal reducer on my Quark and this reduces the banding and cloud pattern.

To sort out my banding I do two things, firstly use flats in Firecapture by applying enough out focus to smooth out the features and use the flat feature and then let the sun drift a little in the frame during capture. A drifting sun is fairly easy for me, I generally don't align my mount, just point it in the rough direction of north.  Once the video is stacked nearly all of my banding disappears.

The Moonglow filter looks very interesting, I am glad it has fixed your banding problem.

What does look slightly worrying is you appear to get severe banding in your white light shots, I have got that right? I have never had banding in white light and looks really odd. Do you fit an IR filter between your camera and filter?  I don't bother with a filter on Ha, it is already IR blocked and fit an IR filter before my wedge in white light. If you are fitting an IR filter between camera and Ha blocking filter or between camera and wedge, it might well be the IR filter which is causing the banding?

Also do you notice any difference between an ASI120 and an ASI174?  I think you should find the banding on an ASI174 much less, you might want to check on the ASI website to see what it says.

I hope that helps

Robin

Hi,

I bought one of these in kit form on ebay a couple of years ago, for a good deal less than paying each week.  Mine came with all mags, binders, all pieces in their original sealed packets, so all I had to do was assemble it.  It was fun putting it together, but I wouldn't have wanted to wait 2 weeks for each set of parts.  All the parts are brass (except the planets) and the finished item is nice to look at and gives you a good idea of where the planets are, nice for planning what is coming up as the planet imaging season begins.

My Mrs thought it was nice too, but then decided it would be better in the summerhouse where the rest of my astro kit is kept, perhaps she didn't like it after all?

If you look on ebay, I am sure you will see a few for sale.

Robin

Peter, perhaps it isn't as much as 3mm, but it certainly felt like it.  There was quite a bit of movement in the secondary holder when I did move it.  I didn't undo the corrector plate, it has never been off, so thought it best to leave alone.  The secondary holder has a notch in it to align the secondary when it is replaced after using Fastar.  After my secondary holder became slack it was tightened again, but I noticed just recently that the notch was in the 2 o'clock position and by all accounts it should be in the 3 o'clock position.  The secondary also has a black mark in this position.

I turned it round and then re-centred first by eye (reflection of the secondary and the focus tube) and then replaced the secondary with a paper target and put a laser in place of the eye piece, both confirmed it was now centred.

Bill, I too have a Hotech CT, I think after reading your post before.  I find it difficult to get it spot on, but it did tell me my Crayford was out of line and was useful in re-centering.  I last used the CT before the secondary became loose, but might check it using the procedure you outlined.

I too have been thinking of making an optical bench, a couple of pieces of 4x2 timber, some thick board and a couple of kitchen cupboard levelers should be stable enough to hold the C11 on a saddle plate, or even V-notch and give vertical as well as horizontal adjustment.  The CT has it's own micro adjuster.  Then just put the whole lot on a bench and I will be able to adjust and measure in perfect stability.  It might even work for my Newt?

Now that my C11 has had it's tune up, I just need a bit of clear sky to star test it.

Robin

Agreed. Did you just realign the secondary by eye?

I assume you just collimate on a star? When I do mine the final movement of the collimation knob is just about the smallest movement i can make, not sure if this is 1/32nd of a turn, but it must be a very small amount.

Robin

Mirror flop is another potential issue, but I don't think it moves the primary far enough to throw the collimation out, just moves the centre of field of view a little. My scope has dampeners to lock the mirror in place to stop mirror flop, but of course you can't adjust the focus (of the primary) when they are tightened.

Robin

The secondary holder came loose when I took the secondary out and put a Fastar in. Interesting as looking around a lot of people have had loose secondaries. The secondary holder is slightly smaller than the hole in the corrector, possibly as much as 3mm so it is possible to get it out of alignment.

If you remove the secondary you can sight down the scope and check it is concentric with the main and focus tube, but I understand it needs to be very accurately aligned. I did remove the secondary, put a piece of paper with a bullseye target in place and used a laser in the focus tube, it confirmed that my visual sighting was correct.

The main reason I ask is the secondary was offset, yet it appeared to collimate. The views of Jupiter were however rubbish.

Robin

Thanks Ronin,

I agree with what you say for a newt with a flat mirror, but a SCT uses a convex secondary mirror with typically 5x magnification, I am guessing this doesn't work unless it is exactly centred as it won't present the correct profile to the spread of light.

Robin