Flats for robotic imaging

[Petergoodhew]

What do people do about taking flats when using remotely-operated gear?  Sky flats,? or a $450 flip-flat?!

[ChrisLX200]

Have a panel on the Obs wall, point the scope at that (use the co-ordinates to 'goto' it). You can set the Home position to be pointing at the panel, but you do need a remote relay to switch the panel on.

ChrisH

[steppenwolf]

I have a fully automated observatory that I often just use remotely and I have built my own automated 'flat-flap'. This works very well indeed and cost around £50.00 UK Pounds to make using a servo and a Pulse Width Modulation generator designed for use with electric train set layouts! It also acts as my telescope's dust cap.

[sloz1664]

Hi Steve,

I've followed your fully automated observatory thread with great interest and, in particular, your DIY automated 'flat-flap'. Any pointers on the build

Steve

[steppenwolf]

Hi Steve,

I'd be happy to give you any information you need. Inside the box that you see in the YouTube video, there are the following components:-

1. Single channel servo controller with adjustable start and end stops - this controller is normally used in electric train layouts to control a servo to open a locomotive workshop door, change points or action a mechanical signal

2. A digital servo

3. Power supply for the electroluminescent panel

4. A 12v DPDT relay that trips the servo controller and turns on the 12v DC power supply for the electroluminescent panel

Items 1 and 2 are available from here - see the first three items under 'Servo Motor'

Item 3 is available with the EL panel from here

The plastic box, relay, flyback diode, Veroboard, power plugs and sockets came from Maplin. The 90 degree bellcrank and other servo mechanical connections to operate the flap came from a local model shop.

I use a homebuilt 8 port USB switch using Velleman control/relay cards for several functions within the observatory and I use one of the ports to trip the flap.

 

[Petergoodhew]

Thanks Steve.  I will have a go at making one too based on your suggestions.

[msh1]

steve any chance of a schematic or a pic of inside of the flip flat box please im setting up my obsy to be automated dont want to spend a fortune on a commercial one thanks 

mark

[sloz1664]

Brilliant. Thanks Steve.

[ollypenrice]

The folks using the remote Observatoire Per Frejvall at my place have sky flats handled automatically via ACP. It points the scope at the appropriate part of the sky, dithers and sets the exposure, as I understand it. Nobody has reported any issues to me. I think the only painful part is paying for ACP!

Olly

[steppenwolf]

Quote

It points the scope at the appropriate part of the sky, dithers and sets the exposure, as I understand it. Nobody has reported any issues to me.

This is a method that can be used too but it doesn't solve the dust cap issue which is why I decided against having a larger EL panel to aim at on the observatory wall, whereas my flat-flap serves both functions. It is, however, an added complication but once built and installed it can just be forgotten apart from an occasional wipe down with a wet cloth!

What do you do about dust control at Observatoire Per Frejvall, Olly?

[steppenwolf]

Quote

steve any chance of a schematic or a pic of inside of the flip flat box please im setting up my obsy to be automated dont want to spend a fortune on a commercial one thanks 

I'll sort something out for you.

[graemlourens]

Hi.

I was also facing this challenge when completing my obsy. My solution surprised myself that it worked, but probably only worked by a good amount of luck.

I had mounted a strip of led going a good length inside the dome based obsy. Just for fun i then tested shooting against a wall-part that had a even illumination and no structure to it.
To my surprise i got perfect flats, and as the led's are not terribly bright, exposure times even for LRGB filters are not too short. I have been using these since.

But i also have to say: If you're obsy is not totally remote (like 10'000km away) and you do not have a rotator on your camera, i don't see a problem to travel to the obsy once in a while to re-take a master flat set? Its takes my around 1-2 hours, and flats for 7 filters are automatically taken with SGP.
I only re-take flats every half a year or so. As i do not rotate the camera, and small changes in focus in my refractor do not require retaking flats, i do not take flats after every session.

But as i said, it really depends on your setup. I doubt my approach would work for OSC...

Just my few cents

Kind regards, Graem

[steppenwolf]

That's a fortuitous solution, Graem.

As promised, a circuit diagram and some photographs of my solution. Please note that this servo is close to the limit of its operational envelope so an A5 panel is probably the maximum it can cope with. This would be usable on a telescope with an aperture up to about 130mm:-

Circuit Diagram of Control Relay

Internal Layout

Servo Linkage

Front Control Panel

 

[sloz1664]

Steve that's something of an engineering feat, in it's simplicity. Well designed and if I may say "finely assembled."  I have to ask this question? Did you have a Mechano set when you were younger.

Steve

[msh1]

3 hours ago, steppenwolf said:

That's a fortuitous solution, Graem.

As promised, a circuit diagram and some photographs of my solution. Please note that this servo is close to the limit of its operational envelope so an A5 panel is probably the maximum it can cope with. This would be usable on a telescope with an aperture up to about 130mm:-

Circuit Diagram of Control Relay

Internal Layout

Servo Linkage

Front Control Panel

 

that is brilliant thanks steve 

[steppenwolf]

Quote

Did you have a Mechano set when you were younger.

I did and I loved it - I really wanted a Mamod Steam engine though but apparently the box wasn't very big and my dad assumed I'd be disappointed ......

Quote

that is brilliant thanks steve 

Thanks, I hope the information is useful.

[steppenwolf]

If you look at the circuit diagram, you'll see that closing the actuation switch turns the EL panel off (and opens the flap away from the telescope) - this is intentional although one would normally think of 'turning it on' on command! The reason for this is that at power-on, the servo will throw to the open switch position which it does at full speed which I don't feel is mechanically sympathetic so I arranged for the servo to be at the 'closed' position when fired up to obviate this. Now it is all calm and smooth and the controller has four speeds, manoeuvring (the one I use), slow, cruise and ramming speed ..........

[ollypenrice]

9 hours ago, steppenwolf said:

 

What do you do about dust control at Observatoire Per Frejvall, Olly?

Very little, Steve. The occasional wipe, as the owners request. Dust on the objective has, in my view, no effect on flats. It is way too far out of focus. Flats seem to me to be affected primarily by dust very close to the sensor. Even filters are rarely affected, though sometimes they are. I don't know if you agree?

Olly

[steppenwolf]

I agree that dust isn't a direct issue for Flats, Olly, it was more a question about just having dust on the optics which is something I try really hard to avoid but not for any 'technical' reason! I also have a fear of insects getting onto the lens surface and dying there - I check regularly especially when the pesky ladybirds are in residence .......

[ollypenrice]

Of course I also run a protection racket: Pay an extra hundred euros a month or blackbirds may nest in your tube...

Olly