best camera for all sky use

[tdnicholls]

Looking good there Huw - must have darker skies than me, and not so many close neighbours who leave all the lights on 1/2 the night - i never see that many stars.

[Horwig]

Looking good there Huw - must have darker skies than me, and not so many close neighbours who leave all the lights on 1/2 the night - i never see that many stars.

To my north, my nearest properties are a pair of holiday cottages two fields away. odds on, they leave the outside lights on all night. Even towny friends of ours ask how we can live in such a dark place. Reckon you can guess my answer.

H

[Horwig]

Here's the new housing for the QHY camera, the plan is to connect the focus lever to the dome assembly, which will rotate to focus, well that's the theory at least:

Will have time to do a bit more tomorrow.

Huw

[Gina]

Thought you should know... I found the focus in the Fujinon lens very critical.  I had a dome controlled focus arrangement on my first incarnation and found it quite difficult to focus.

[tdnicholls]

Nice, good to be able to make your own parts.

I used the FWHM feature of EZP to focus, ok if the optical quality of the dome is good enough that does not throw out the focus.

As the weather has warmed I have noticed the focus has shifted slightly as well as the inevitable increase in hot pixels.

[Horwig]

Thought you should know... I found the focus in the Fujinon lens very critical.  I had a dome controlled focus arrangement on my first incarnation and found it quite difficult to focus.

Ohhh, bother, might be a Mk 3 hiding in the wings then.

Thanks Gina, yours is looking good btw.

Huw

[Gina]

You could try it - you probably have a steadier hand than me

Thank you - I think the QHY5 will probably be quite adequate with the nright software

[Horwig]

Interestingly, gone back over the adverts for commercial cameras. None appear to have any kind of clever focus mechanism as far as I can see, but there again, none of them use the same lens as us.

On another tack, what's the best way to stop corrosion on the ali where it's in contact with stainless fittings? It's going to be painted, but would greasing bolts help?

Huw

[Horwig]

Got the metalwork for the housing sorted, and the contraption to focus the lens, not the most elegant solution, but as simple as they come. The dome support ring is sealed to the body with a piece of rubber matting to act as weather seal.

Not sorted the anti dew yet, unsure whether to use Nichrome wire in heatshrink, or a few high power resistors, but the cable for the 12v is run with the usb through the gland into the base. Both cables are run in heatshrink to give some protection from weather and abrasion.

Huw

[Gina]

Shouldn't the front of the lens be at to centre of the dome radius?  (vertically)

[DIYASTRO]

Huw,

That is looking promising! Nice bits of machining and solid just what I like.

I solved a similar problem some time ago with the type of focus mechanism you are using.

It was for an aperture mechanism and I used a threaded rod as a lead screw  with a pivoting  'saddle' driven by the thread to locate on the pin that in your case provides focus. Albeit the pin requires to be extended. I made a post of it on this forum under one of the multi lens cameras that I built. If time I will scan the records and see If I can find a pic for it. It worked really well and although this was driven by a modded servo, no reason why a small stepper could not be employed to give very small linear movement of a fine thread like 6 or 8 ba for example. I even went so far as to attatch a linear potentiometer to the saddle mechanism so to read out the movement via a simple coil analogue meter. 

Boyd

[Gina]

A threaded rod for focussing seems a good idea

[DIYASTRO]

Huw,

Just had a quick look through some of my older posts.

You will see what I am trying to describe under

Multi lens astro GOTO camera  DIYASTRO

Page 1 post 15 dated 13 Aug 2013

I removed this component from the rig as it wasn't required but still have the plate and all the mechanism somewhere! In one of the boxes , crates tea chests whatever! I could think and try to locate it to show better pics if you need.

Boyd

[Gina]

Just run a test on a micro servo modified for continuous rotation and with a supply of 0.5v the output shaft does a revolution in about 8s.  For fine focussing this is pretty fast.

[DIYASTRO]

Gina, Don't want to highjack Huw's thread but I used 'direct' drive from the servo since the resulting linear movement was not quite so critical for the application I was describing.

But nothing to prevent a further gearing from the lead screw to a small micro servo to decrease the linear movement.

A small stepper motor mounted like I described in my thread on modding servos would give literally microns of linear movement per step. If I can find the data, (I think I put some of the records in that thread on servo conversions, will check) the linear movement for an 8 BA lead screw would be .43mm / rev. divide that by direct drive from stepper motor (48 steps / rev) gives .008958mm per step. Couple the drive leadscrew to a stepper gear box and you have focus well into micron levels.

Boyd

[Horwig]

Thanks Boyd and Gina, good to have you both watching over my shoulder.

Having the rig fully working for the first time today has taught me something important about the Fuji lens. It's not that good! (the first draught of this message was not that forgiving, the auto profanity filter would have had a field day)

If you look at the framed photo at 8 o clock you will  see the problem, C.A. and quite a lot of it, in brighter daylight it was screaming, and its not just distance, the stars in my night time shot also displayed it.

There is a reason this lens is a fraction of the price of the Fuji lens that SBIG use in their camera.

Here is where I've deleted the rest of what I typed because it was horribly negative.

Best I give up for now.

Tomorrow is another day

Huw

[DIYASTRO]

Huw,

Tomorrow is always another day! You have got this far and you just need another lens, you have lots of people following your exploits, I hope that in the morning (or sooner) the eureka moment will overcome your doubts and the modification to the practical problems will be clear enough to carry on with the build.

Boyd

[JamesF]

A threaded rod for focussing seems a good idea

Put a bolt on the thread and you have a DIY worm drive

James

[DIYASTRO]

Hue,

Just in case you cannot find the mechanism that I made and described I hunted and found the plate!

taken a few close ups of the contraption which is what I would be thinking of using if ever I was to build an all sky camera that needed focus arrangement like you and others have, i.e. via a lever mechanism.

Of course this is quite large since it was for a 80 mm diaphragm / iris aperture and would need 'miniaturising' but the theory is the same.

For the type and size of lens you require the lead screw would only have to be a couple of cm, with careful placement and alignment

Hope that tomorrow brings good vibes!

Boyd

[Gina]

One point Huw - if you have the lens right up inside the dome you will get distortion and colour fringing due to the acrylic acting as a prism.  I had the lens up high in the dome at first and had distortion.  I recommend putting the top of the lens at the centre of the dome radius ie. just up inside.  HTH

[Horwig]

Thanks for the pics Boyd, yes a miniature version of that would be excellent, but I'm going to try it with the manual adjustment to see how bad it really is.

Gina, I'd been playing with lens position, and came to the conclusion that it was all a compromise, distortion  caused by the perspex is mostly hidden in the chromatic fringing from the lens, and there are much less reflections from the dome with the lens high, also hopefully with the lens high, dew might be less of an issue, if the heat from the dew buster rises to the top of the dome.

Time will tell.

H

[Gina]

Interesting results re. lens position

I find a couple of watts in a ceramic resistor works really well - no dew on the dome even when really heavy dew on everything around   68 ohm resistor running off my standard 13.8v supply.

[Horwig]

thanks Gina, I've had a rummage in by box of bits, I'm out of any suitable resistors, its going to have to be Nichrome wire.

H

[Gina]

You could buy these - either 1 x 68 ohm OR 2 x 33 ohm in series OR 2 x 120 ohm in parallel.  Just a suggestion

[Horwig]

Thanks Gina, brother is on a mercy mission to Maplin tomorrow. 

H