Taking darks - a cautionary tale

[Demonperformer]

I've done some dumb things in my time, but this one is a real doozy ...

I am producing my library of master darks for my cameras at the temp, gains & sub-lengths I will be using. To ensure no light reached the chip (as I have heard the covers on the cameras are not necessarily light-proof) I decided to put the camera in a camera-changing bag from my old celluloid days. I set the cooler to -15 and started producing darks for 15s, 30s, 60s, 120s & 300s and wandered off to do something else while it was going. Came back (while it was doing 120s) to find my cooler was running at 100%, but my temp was no longer -15, but +23!! I quickly stopped the captures and opened the changing bag and removed the (hot to the touch) camera. The temperature continued to climb, peaking at +37 before it started to fall again. I'm just very grateful that I went back to check when I did, before things got any worse. In addition to the fire-risk, and the damage-to-camera risk, I lost all that I had done, as I had no idea of when the temperature started to climb, making the darks useless, so I have had to bin them all and start again. This time I have put the camera in a cardboard box, which I hope will be enough to ensure no light incursion. I am also keeping a much closer eye on what is going on so I can pounce if there are any signs of trouble.

The moral of the story:
Don't assume that, just because something is light-proof, it is a suitable container in which to put the camera to take your darks!

[PeterCPC]

The fridge might be a better option.

Peter

[Demonperformer]

But does the light really go out when you close the door???

[PeterCPC]

Yes

Peter

[Unklewhale]

Yes, an interesting cautionary tale. Shows how much you need to think outside the box about what is going on in the box - errrr, or something !  

[Demonperformer]

Even in the cardboard box, the 120s subs have been pushing the cooler up to the 80s, so I opened the box and draped the bag over the top to allow a little more air movement. It has now come down to 50%.

[tooth_dr]

I take them at night in a room with the light off, and always allow plenty of room round the camera 

[carastro]

I left my rig capturing darks in the middle of the night when it was cloudy.  I mostly have a library of darks, but there are a few missing. 

Carole 

[Star101]

If you think light is getting in....Place the covered nose cap on the camera, then place the camera nose in a dark cup/mug in a shaded part of the room.  Hold the camera in place with sellotape if needed. Thus allowing the air to vent the back of the camera. 

Personally, I have found the nose cap cover on the front of the camera in a shaded part of the room is sufficient. 

 

[RayD]

Like Carole I usually do mine of a night time in my observatory with the lights off and roof closed.  Do you have a shed or similar with power where you can leave the camera out in the dark but with the fan unobstructed?  The fan needs to draw the cool air in for the peltier to work, so maybe even cut a small hole in your box directly behind the fan inlet to allow the flow of cooler air?

Good warning to others thinking of the same thing and glad it didn't end in disaster, as could have been the case.

[henry b]

Your camera is designed for normal air circulation movement, the fan is added to aid this circulation therefore it was never designed to be enclosed within a case. If your darks have light leakage it can only be a poor cover or a problem in your camera. I suspect a poor cover is your culprit!     Avoid a fire at all times ( this helps with current consumption)           Henry b.

[carastro]

Quote

Your camera is designed for normal air circulation movement, the fan is added to aid this circulation therefore it was never designed to be enclosed within a case.

Hmmm, food for thought because when I do flats I sometimes do them in the daytime, but to avoid light leakage  I always wrap a fabric black bag around the camera and EFW.  Hopefully this is OK as it is beathable.  Next time I must look at the sensor temperature.

Carole 

 

[henry b]

Wrapping a cover over a filter wheel  for darks is sensible when doing darks in the daytime, but your camera should not need it!   if you have front light leak suspect the cover ( metal / tin is best) some plastics leak light or air , ensure your cover is tight!!!   Henry b.

[Demonperformer]

I have no reason to believe there is any light leakage, but I always work on the suspicion that there may be a problem. I don't have a shed with a power supply.

I like the idea of a low mug that allows air movement around the back. The other option is to fit it to the scope that has a metal cover at the front - this is how I would do them in situ - but that is just more hassle ...

[Demonperformer]

3 hours ago, Demonperformer said:

But does the light really go out when you close the door???

Schrodinger's fridge.

[Stub Mandrel]

The cooler will produce as much heat as a 40W light bulb. You MUST ensure it is properly ventilated at all times or face disaster.

Take darks with a light-tight cap, not by putting the camera in a closed box.

[Demonperformer]

3 hours ago, Star101 said:

Place the covered nose cap on the camera, then place the camera nose in a dark cup/mug in a shaded part of the room.

This certainly appears to have solved the cooler problem. The edge of the camera is sitting on the rim of the cup, so no room for light to get into the cup (I chose one with a dark-coloured inside - OCD or what!) so just need to be careful not to bang the table. It is currently about half way through a set of 300s high gain darks and the cooler is running at a (if you'll pardon the term) cool 23%.

Thanks for all the input guys.

7 minutes ago, Stub Mandrel said:

Take darks with a light-tight cap, not by putting the camera in a closed box.

I think this is the message I would want everyone to take away from reading this thread.

[iapa]

4 hours ago, Demonperformer said:

But does the light really go out when you close the door???

Schrödinger's cat likely will have the answer to that one

[ollypenrice]

Atik, bless 'em, give you a screw-on metal cap which is absolutely dark and totally effective. Why do I like Atik? That's one reason.

Olly

[Jkulin]

With my Moravian it comes with a thick rubberised black cover, although I do it in a dark room as a precaution, it has never let light through and when I do my darks library it can take a couple of days (I do 30 of each from 1s to 30mins)

Mind you with the cloud we have had this winter there's been no chance of any light getting through whatesoever?

[wimvb]

On 17/02/2019 at 16:05, Demonperformer said:

  the cup (I chose one with a dark-coloured inside - OCD or what!

Matte or glossy? ?

I also found out the hard way, that plastic caps don't work and that cardboard boxes with a lid trap heat, even outdoors at night. Since ZWO don't provide metal screw on caps, I cover the sensor side of the camera with a double layer of aluminium foil, in addition to the lens cap. I wouldn't leave the camera on the scope when taking darks. Light will find a way in.

[dunc]

I use an old film changing bag, I put the cover on the scope (black plastic) and put it over the end of the scope and wrap the arm hole bits round the OAG and guide camera (its a 6" newt) to guard against like leaks. I cover the scope body (carbon fibre) with thick black cloth just in case. I am VERY careful to make sure the cameras cooling vents are clear of any obstruction. The back of the a scope has metal cover, I found a pedal bin lid that fitted perfectly as otherwise the mirror back is exposed and it has an unsilvered centre spot doughnut - big light leak!

BTW I have found the ZWO ASCOM driver doesn't produce dark darks with my camera, as an APT user this has caused endless problems. I have switched to SharpCap for the minute as the native drive doesn't exhibit the same issue. (ASICAP, APT, SharpCap, same stretch applied via menu otpion).

 

[tomato]

I tried putting my camera in the fridge to take darks, but it didn't work, cooling went to maximum on the camera and it could not maintain the set pt (-30 C).

Best to do it outside on a chilly, cloudy day, we still get a few of those.

And no, the light didn't go off, the cables stop the door from closing properly.

[eshy76]

Ha - I did exactly the same thing with my ASI1600 early doors - I put it in its case to shoot darks...luckily I was sitting in front of my computer while this was happening and noticed the sensor temp starting to rise quite quickly...and similarly my camera was hot to the touch. So, erm, lesson learnt...I make sure there is enough airflow and just shoot the darks in a, er, dark room...maybe not 100% light leak proof, but at least it won't kill the camera!

[hughgilhespie]

I had a spare position on my 8-position ZWO filter wheel, so I machined a solid black Delrin insert to fit in the filter holder. It won't help if light is leaking into the camera itself but it is 100% effective at stopping any light coming through from the telescope. That said, I still take my darks at night, with the end cap on the telescope. Belt and bracers!

Regards,

Hugh