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Any cheap attachment for acquiring just "darks" remotely?

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18 replies to this topic

#1 rnyboy

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Posted 22 October 2020 - 08:24 AM

I was surfing the forum and I saw a guy asking about a filter wheel issue and he mentioned he uses a "dark" filter for acquiring darks.  I thought cool, because during the cold months when doing DSO stuff the only thing I can't do remotely is obtaining "darks" and that it would be neat to have some cheap device that moves a optical block in and out remotely.  For a dark I have to go outside and put a black plastic bag over my dew shield.   For my current setup this would have to be able to be used on a 6SE.

 



#2 Midnight Dan

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Posted 22 October 2020 - 09:00 AM

Well, it depends on your definition of cheap.  Probably the cheapest is exactly what you mention.  A USB controlled filter wheel and a dark filter.  

 

It may seem like someone would make a simple and "cheap" device to do this, but it is no good without having a computer connection, and software to control it.  So the USB circuitry, ASCOM drivers, etc. all add to the cost of building and selling such a device.  A ZWO 1.25" 5-filter wheel is probably the cheapest you'll find at $200.

 

-Dan



#3 rnyboy

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Posted 22 October 2020 - 09:31 AM

Thanks Dan.  I kind of figured that.  I was hoping for something like a "simple", and cheap (lol),back and forth sliding optical block for my 1.25" back.  Right now at least, with my color 385mc, a filter wheel is just extra weight and I haven't looked into if it can fit on 6SE with the Celestron Focus Motor attached.

 

Just thinking out loud, but what about a flip mirror as a block?  I have no idea about the cost or feasibility of that, and talk about extra length/weight.

 

I was even thinking something like an 1.25" or 2" thin LCD black spacer-like ring that you could simply turn on and off electrically but I'm not at all sure how badly that would effect image quality when the black is turned off, or even if it would be "dark" enough.  That would conceptually be very cheap but may be a disaster for image quality.



#4 Frank Otsuka

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Posted 22 October 2020 - 09:45 AM

Hi,

Google "telescope flap"

 

There are home made and commercial versions, ie

 

https://www.skyatnig...l-and-dust-cap/

https://www.geminite...d-tube-ota-cap/

 

Just need to make a complete light seal.



#5 Midnight Dan

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Posted 22 October 2020 - 10:15 AM

Just thinking out loud, but what about a flip mirror as a block?  I have no idea about the cost or feasibility of that, and talk about extra length/weight.

You did say you want to do this remotely?  Do you know of a flip mirror that can be controlled remotely?

 

I was even thinking something like an 1.25" or 2" thin LCD black spacer-like ring that you could simply turn on and off electrically but I'm not at all sure how badly that would effect image quality when the black is turned off, or even if it would be "dark" enough.  That would conceptually be very cheap but may be a disaster for image quality.

 

Yes it would be a problem for image quality.  But in addition, turning something off and on electrically is not the same as being able to control it remotely.  You would need some connection to the computer, and a driver.  

 

I guess one question is, do you want to do this simply be remote control?  Or do you need it automated so that it's part of an unattended sequence?  Also, is your gear permanently set up in an observatory or do you set up your gear each night, and how do you power it?

 

-Dan


Edited by Midnight Dan, 22 October 2020 - 10:16 AM.


#6 rnyboy

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Posted 22 October 2020 - 10:22 AM

No just remote control, no need for automation, I setup each night, AC house voltage.  I set it up in the backyard just outside my patio door and a laptop by the scope is connected via wifi.  I can control everything remotely from inside the house except for obtaining the darks.  Currently for darks I have to go outside, take back control of the laptop, cover the aperture, acquire the dark, then go back inside and reestablish the connection to the outside laptop.  It's not that hard, just soon to be COLD!

 

When the scope is outside it's not really all that far away from the room where my desktop PC is.  For the LCD idea, or sliding optical block for that matter, turning things on or off for a dark could be done with a simple switch, about 75 ft of wire, and a power supply.  Of course I'd prefer it being a neater solution controlled via wifi.


Edited by rnyboy, 22 October 2020 - 10:30 AM.


#7 Midnight Dan

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Posted 22 October 2020 - 10:57 AM

Ok, well remote-control-only is certainly easier than automated.  You don't need an ASCOM driver, just something to turn off and on.  

 

If you're really trying to keep it cheap, I think your only option is something homemade and motorized like the scope flap that Frank linked above.  However, I've usually found that these kinds of projects, while fun, end up adding up to a lot more money than you think they should. :-).  Unless you do a lot of DIY projects and have leftover materials and supplies, buying all the parts can end up nearly as expensive as buying something pre-made like a USB filter wheel.

 

As for on/off control of a device via wifi, there are lots of options.  Amazon has a wide variety of smart plugs, which are AC outlets you can turn on or off from your phone.  I use this one in my observatory, which is designed for outdoor temperatures:

https://www.amazon.c...e?ie=UTF8&psc=1

 

If you want 12V control, you can use a Shelly 1 relay:

https://www.amazon.c...e?ie=UTF8&psc=1

 

Note that these kinds of devices don't have a huge wifi range so they work better if they're close to your house's wifi signal, or if you have a router at your gear.

 

-Dan



#8 rnyboy

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Posted 22 October 2020 - 11:48 AM

No kidding on the cost of DIY vs an OEM device.  I don't need more weight on the front of my 6SE, the DIY (mostly made with leftovers) heated dew shield is already something of a long lever-arm so Franks flap idea is probably a non-starter for now.

 

Perhaps I'll look more at the filter wheel idea.  Right now I'm worried about my focus motor being in the way but I haven't looked at anything yet so I don't know.


Edited by rnyboy, 22 October 2020 - 11:58 AM.


#9 Raginar

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Posted 22 October 2020 - 12:42 PM

Flip flat works pretty good. 



#10 vakulenko_sergiy

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Posted 22 October 2020 - 04:37 PM

As an DIY option you can build your telescope cap based on Arduino and small servo (add almost nothing to weight).

 

https://youtu.be/7gXEcNOkZpY



#11 iwannabswiss

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Posted 23 October 2020 - 05:33 AM

For less than $60, you can build a version of my ASCOM DarkLight Cover/Calibrator with or without an EL Panel.



#12 rnyboy

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Posted 23 October 2020 - 06:54 AM

Hi iwannabswiss.  I need to look at this more.  The immediate issues I see are weight on my SE mount and my dew shield may not allow the use of any cover.  I'm already dealing with adding weight to keep my OTA back heavy.  Thanks for posting.  The price is right for sure.  I'd still prefer something in a short (thin) package that would move an optical block in and out at the back of the scope though.


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#13 Midnight Dan

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Posted 23 October 2020 - 09:35 AM

Hi iwannabswiss.  I need to look at this more.  The immediate issues I see are weight on my SE mount and my dew shield may not allow the use of any cover.  I'm already dealing with adding weight to keep my OTA back heavy.  Thanks for posting.  The price is right for sure.  I'd still prefer something in a short (thin) package that would move an optical block in and out at the back of the scope though.

You could certainly use the Arduino circuit and ASCOM driver from iwannabswiss's post, but use a different type of servo motor and an off-the-shelf filter drawer with some modifications.  But the filter drawer would still cost some money.

 

For example, here's a single-filter holder and drawer:

https://optcorp.com/...-filter-changer

https://optcorp.com/...2-filter-drawer

 

It would be fairly easy to add some rails to the side to allow the drawer to slide in and out, add a servo motor to move it, and the Arduino board to drive it.  But the drawer and slide costs about $125.  By the time you add the servo, arduino, case, cables, and connectors, you're probably getting close to that $200 filter wheel.

 

If you have access to a 3D printer, you could build your own filter slide for a lot cheaper, which is of course why iwannabswiss's solution is so cheap.  If you don't then neither solution is cheap.

 

-Dan



#14 dghent

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Posted 23 October 2020 - 09:40 AM

Do you shoot dark frames with every session?



#15 Alex McConahay

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Posted 23 October 2020 - 09:52 AM

>>>>>>Do you shoot dark frames with every session?

 

Yeah, it is about time we got to this question. 

 

When imaging from one location, most people get a set of exposure times that work, and just use them repeatedly. This means you need a dark library with several times (and temperatures if your camera is not temperature regulated). You can do this once every six months or so and have all you need. 

 

Furthermore, if your rig is in your back yard, it cannot be all that hard to walk back there and cap the tube, or put a bag over it, or whatever is necessary. Unless you have the Rube Goldberg syndrome, you don't need more than that. 

 

FurtherFurthermore, the engineering and execution of your auxiliary device would have to be awfully good to make sure you do not have any light leaks. 

 

And I am assuming you do not have a shutter in that camera. 

 

Alex



#16 rnyboy

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Posted 23 October 2020 - 12:41 PM

Hi Alex, not every session, but good point.  I only have a few from last late winter/spring because I was doing brighter DSO stuff when I first got the scope out last January and it wasn't till later in the winter I even tried darks.  My 385mc isn't cooled and I need to take more.  A lot of it was due to finding out, and still finding out, the best exposures and gain settings so some of the early darks are less useful.  I started out with lower gain and as things progressed I found I could do better at higher gains with the darks.  The outside temps around here vary from near 0F (below actually but I think the mount wouldn't be happy with that) to around 75F at night during the year..  The 10F night I was out last winter was COLD.  It's been quite a learning experience.  This summer all I've done is planets, so no darks were needed so none were taken.

 

This remote dark topic was something of a fishing expedition to see what maybe available.


Edited by rnyboy, 23 October 2020 - 12:44 PM.


#17 andysea

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Posted 23 October 2020 - 01:29 PM

Unless the camera has a shutter I would be very concerned about light leaks, even with a light blocking filter in the filter wheel there will be light hitting the sensor. Are FLi and Moravian the only manufacturers that make CMOS cameras with a shutter?



#18 Alex McConahay

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Posted 23 October 2020 - 01:51 PM

Might I suggest once a season, you put your plastic bag (if that can be trusted) over your scope, and spend a few hours gathering darks. Just make yourself a dark library.

 

Yeah, if you do not have regulated cooling, you may have to take some at early evening, some early morning, after the temperature has fallen appropriately.

 

And, think about scaled darks.

 

Alex



#19 dghent

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Posted 23 October 2020 - 02:00 PM

Eh, can't really scale darks on CMOS due to amp glow, which is non-linear. The IMX385 has some notable amp glow to it that emanates from the corners, too.

 

In all honesty, the OP would be better served by a camera that has regulated cooling when it comes to DSOs. Planetary obviously works because the signal of a planet is so high and the exposures are very short. But DSOs? Get a cooled camera.




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