nicks90

This thread is getting way serious and professional...but here's my first proper attempt at a using my new Canon 100d 

M42 210 X 10 second subs. F5.6 and iso800 at about 200m I think. Skywatcher goto altaz mount.

I have 2 versions. One with little nebula and a good core and this one with lots of fluffy but a blown core and what looks like vignetting .

Still have absolutely no idea what to do in gimp ...or even what settings I should use in dss to stack. But it's all good fun.

heres my setup with me being all ghostly

8 minutes ago, Filroden said:

I thought I'd try and show what I meant about light pollution gradients with a graphic as I can't explain it well in words. One of the main issues we face as AltAz imagers is field rotation. Our images rotate over time as we track across the sky. The top three "photos" show the same group of 5 stars taken, lets say, 20 minutes apart and show considerable rotation. I've shown an even light pollution rising from the bottom that impacts the bottom part of each photo. So the stars rotate but the light pollution does not.

When you stack these images, the software registers the locations of the five stars and aligns the photos so they stack over each other. However, now the gradient is in a different location. The lower stacked image shows how the program de-rotates the images to align the stars but this now causes the gradient in each image to be rotated the exact opposite angle in each image and this is stacked - pollution being an additive.

It's much easier to remove the simple linear gradient from each image (but very time consuming) than remove the more complex, bow tie, gradient in the stacked image. I wonder how much this impacts on the final quality of our images. 

 

you are right, the gradient will 'spread' across the bottom of the image and up the sides due to field rotation.

But... how many hours of subs in a single sitting are people taking here? Look at the overall angular rotation of something like Leo over 2 hours by watching it move in stellarium in fast forward... few degrees maybe?

As long as it's perfectly balanced and windless night, worth a stab!

I don't have that installed, but I will certainly be putting it on!

Thanks mate

13 hours ago, The Admiral said:

That's a good start nicks90, and you'd be surprised at what might lurk in the image! As you say, the Flame neb is visible, but you really need a lot more frames.

With those 'scopes and an interchangeable lens camera, how about fitting the camera to the 'scope?

Ian

i would do, but finding the adaptors to connect my camera to the scope is like hens teeth... plus the little f5 frac has a woefully cheap and nasty focuser. Might give it a go though, see what happens

On 07/03/2016 at 16:06, Moonshane said:

Vaseline on the bearings? Seriously?

It's really not that difficult to make a scope that works well if you apply a bit of thought. If you are set up to create this sort of thing then it should be even easier to make it with bells and whistles that all work as you (presumably) have the machinery. I have made things in my back garden with hand held routers and saws. It's just takes longer. Compare what you have with this. OK it's a different scale but they really are simple things in essence and it's annoying when companies cut corners. Stainless screws add almost nothing in the scheme of things.

 

I would be furious to spend that much money on a scope and for it to come with such fundamental flaws.

However this is all too common nowadays.

Brand new landrover discovery and rangerover still fit aluminium bodies to steel subframe units and use plain steel fixing bolts and screws. You would think after 60 years of suffering electrolytic corrosion they would have learnt something. But no. Poor quality fixings, no sacrificial electrolytes, no rubber buffers, no galv coatings... 4 year old discos are needing the angle grinder taking to them to remove body parts when fixing accident damage. Sad state of affairs on a £60k + luxury motor.

might as well add my little first effort at using an az mount to the thread - certainly nowhere near as good as some of them on here, but i'm still quite proud!

Orion widefield all taken in my terribly light polluted back garden using a skywatcher az goto mount

samsung nx100 with antique 50mm Pentax SMC prime at F2.8

38 x 30 sec exposure at iso 400 - no dark or bias

Stacked in DSS using all the default settings then a quick mess with levels in Gimp, but i have no idea about how to do anything else with it. I really need to sit down and watch some processing videos, but its just finding the time!

Even with such hamfisted "processing" and poor focus and horrendous light pollution - you can spot the flame neb!

i'd definitely go for the 32mm panaview ep and 2" 90deg diagonal. having had a go of a st102 with the same ep and diagonal I can say the views were lovely!

 As for lunar, dont go overboard with mag!

your mount isnt sturdy enough, moving the scope to track the moon will induce tears of frustration at over x150 and it'll wobble like hell giving jittery views.

personally I would stick with a max of x100 - even in my 12" dob i rarely go over x100 for lunar viewing! You arent going to see the lunar lander, so accept it and view the craters and rilles with a bit of the surrounding scenery and enjoy the view! A rock steady view of copernicus thats fairly small in the eyepiece will still yield much more detail and enjoyment than a jiggly view that fills the field of vision where you cant make out anything!

Do you have any testing piccies to show the sphere in all its glory?

That all sounds properly complicated Ajohn.

I like the way Mr Dobson did it in a youtube video i watched of his 16" mirror. He stuck the mirror in his scope and pointed it at the glint of sunlight on a power line insulator and just looked at the brighter and darker bits of the out of focus image and went back to work on grinding the errors out. 

Damian,

at what point do you mask off the outer 1/2" of the mirror to 'fix' you TDE? Have you set an maximum limit on man hours, or is that not an option?

might be a daft question.......actually two questions.....

does the temperature of the glass influence the polishing of the mirror? Does the mirror get warm when you polish away due to friction, therefore would the big slab cool down the mirror a lot more than a bit of old kitchen worktop and will that make a difference to the grind? 

does/can the mirror flex under the weight of the tool? if so, is there a chance the scabby swollen worktop was allowing flexure and causing your polishing problems?

I do have a couple of small scratches on the mirror which will have to stay at this point but not caused by the brushing. One will probably be under the shadow of the secondary.

Damian

Damian,

wont those scratches - especially the one in the centre - not dissappear when you parabolise it?

and you didnt think to join the bits of foil with some cellotape?

lovely story so far and really enjoying the read.

would you say these are optically on a par with the legendary televue plossls with some added benefites - such as better eye relief?

good review and an ep i am waiting to get delivered to compliment the 38mm panaview i currently have.

One question though, has anyone tried to barlow these eps yet?

As i am seriously considering getting the 26mm as well to make a full set and using a decent 2" barlow to give me a nice range of 38, 32, 26, 19, 16, 13mm - which should cover the majority of my ep requirements in my 12" dob, except for planetary (my 6.4mm ortho covers that one).

if you have a  bigger car the same would apply to the 12 inch flex I guess, economies of scale as it were  

I profess to actually measuring the dimensions of my 12" flextube and base and using those as a pre-requisite in buying my car. Hence why i ended up with an audi a6 estate. even then, its a snug fit. Fully collapsed the ota just fits in the back seat with about an inch of headroom. It then gets strapped in with the seat belt 'woven' through the flextube tubes to stop it moving and prevent it becoming a flying missile if i have an accident.

the boot is big enough for the tracking dob base lying down with some padding, my EP case and some extra clothes in case i get cold. But thats all quite snug too... they are surpisingly bulky when dismantled and being shoehorned into a car!

edited: beaten to the post...

i would second what Avocette says above,

the 300 flextube is fairly heavy if you are of slight build or have a bad back, joints, [insert malady here].

I collapse my OTA down, but leave a 4" gap between the top and bottom parts. To move it, I grab the primary mirror casting with my right hand and my left hand goes in the 4" gap next to one of the truss sections and i hoik it around like that. That way I have a firm grip with my fingers on two parts of the scope, which in my opinion is slightly safer than one hand gripping and the other 'cuddling' the ota. Also has the advantage of being able to twist your body and tube about to get past obstacles and though narrow gates etc.

The base is big, heavy and awkward - although mine is the tracking version with motors - but either way the truss tube 300 dob bases are taller than non truss tubes and therefore heavier and more awkward.

If i had to move mine about more than the 20 feet from my garage to the back garden / boot of my car, I would seriously reconsider the 12" and look at a 10" non auto / non flextube designed dob.

Nick