skybadger

I would try to model it as the balance between power injection and thermal radiation. The target being to keep the lump of glass in positive power budget to maintain its temperature above the dew point. For example, I put 5 watts in and assume it's all heating the OG. The OG is at 5 Celsius and has say an area of pi*100#2/4 ( ie 100mm diameter). We want to keep the OG above a level which represents the local dew point, say 5 Celsius or 280K The glass is radiating as a blackbody with temperature 280K into a void of temperature 245K (typical night sky apparent temp is about -30). The rate of radiation of energy is...... Which I make as 0.123 mW assuming an emissivity of 0.8. (http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/stefan.html#c3) So, the rate of injection of heat required feels quite low. But losses into the tube probably means the amount of heat we can inject into the glass is a small fraction of the heat we provide. I'm not sure it's as low as 1/5000th though. Feel free to poke holes.this is a thought experiment on the train home. Mike

I have a qhy9 CCD camera. it comes with a little dessicant container that screws to a port on the outside. The first time out it froze on the coverslip of the ccd. And the second , and the third. So I bought some dessicant fabric from Browns and cut it to shape inside the CCD chamber, removing the tiny old dessicant strips. I also added the extra front window to the body which was meant to improve things. What I found out was that the without the 'extra' front window sealing the body, the front of the camera was open to the air and the dessicant wasn't actually doing anything useful since it wasn't connected to the ccd chamber. So I also revamped the dessicant - now I had a great big container of self-indicating dessicant attached, and a line to purge with argon and the front window attached to seal the body. I'd have thought that was enough. It looks enough compared to the few grammes of dessicant in the previous tube. Its a car petrol inline filter btw attached to gas line hose using quick lok gas fittings and valves. At this point I find the argon hissing out through the connector holes and through the body screw holes when I purge. So I sealed the screw holes with teflon washers I also sealed the connectors (usb 2 and 8-pin din power) on the inside with styrene resin , rolled about a touch to make sure it covered all the interior of the connectors. Then I re-purge with argon and find the front window isn't really sealed, you can feel the flow past the edge of the window when you get close. But it operates down to -20 reliably. and has done for about 3 months. Until tonight. when Voyager decides to take it down to -36, as it can do if the camera is disconnected and re-connected. Lord knows why. At that point I suspect the reduction in internal pressure due to the water freezing out pulls in more air from the outside. which should be being dried by the dessicant, but its still got a whale of ice on the front coverslip up past -5 and climbing. Its also got a heater on the coverskip . Well, that seems ineffective. the big silver thing is my homemade rotator slip ring. The green thing on the coverslip immediately surrounding the ccd detector areas is the resistor-heated anti-dew heater. Has anyone got a magic bullet for this or are they all this bad at dewing up and freezing ? Lovely clear night of imaging aborted while I warm it up, remove the camera from the scope, remove the dessicant pad, put it in the oven in a tin with other dessicant to reactivate, re-assemble, gas purge and then reconnect and re-align . FFS.!! Seething I am.

That earth is flat!

I have an. Off the shelf powerbank which came with a 19v output and recharges my laptop 2-3 times before flat. It's one of the ones that double as car starters. It's currently used to power my onstep for about 6 hours continuous alt az tracking. I agree with not going down the asiair route if you want flexibility and compatibility. It depends on how flexible you can be.

I read the docs re synchronising two sessions of as, does this mean it can effectively control 2 main cameras and one guide ? I've always wanted the ability to run more than 2 cameras together from one piece of software.

That needs some photos please.

Heating and tightening might help before going for the loosening.

No hope for all our camera optics with their silicone damping grease then. I used to use a silicone compound in industrial holography. No problem with coatings release or glass contamination there.

Or thread a 2" adapter into the body and use a 2" to camera coupling which allows rotation too.

Things like the difference in balance due to asymmetry in mounting and less than perfect 3d balance causing different loadings on the gears dependent on its position in the sky. I agree that perfect mounts would take best calibration from Dec 0 due to the cos factor but , for me at least, I get better calibration nearer the target.

I wouldn't be happy with the advice to calibrate PhD at dec0 myself, the mount imperfections on either side of the pier are greater than the calibration imperfections . I know I get much better guiding if I do a quick recalibrate near the target, as long as the target isn't too high in dec, if it is, pick a target with a lower Dec but on the same side of the pier.

It's not longer subs , it's more frames leading to more of higher quality to stack to get critical detail.

Do a quick search here, there have been similar topics before but in summary, watch out for the IR leds, they can cause grief while imaging. Otherwise any IP camera will do, I haven't found I e yet sensitive enough to use without illumination of some kind.

The cloudy nights ascom controller for DSLR will control this up to 30 seconds per exposure. For longer you need the ir remote which is a few pounds on Amazon. There are a couple of projects to automate this but I suspect the intervalometer you have will do that job already. The unit needs to in front of the camera and visible to the IR sensor which is a bit more difficult when it's close up to the scope.

What was the gain set to at capture time - high?

That chip fat is the right grease for the worm wheel ... But not necessarily the rest of it. I redistributed mine on the worm and left it at that. Works well.

I've done the mod to put a dovetail either side and put steppers on both axis driven by an onstep to track the stars and do goto, principally for solar and mobile observing, with a stellavue80 on one side and a vc110 o. The other. Works very nicely.

Mine stays on permanently in the obbo, as much to keep damp out. Since they are quite low power in suspended mode, it's enough.

I wouldn't say much higher, I'd aim for slightly higher than expected if all other factors are in your favour. Id want to sample at at least 2x the Dawes resolution per pixel. if Dawes is 0.6, aiming for better than 0.3 per pixel to make sure you don't miss anything. You can focus on a moon or a star to get focus right for each wavelength.

Thanks for reminding me. In that case you don't need the spacers at all. It is fair to say that your 2000mm focal length and x4 powermate are overkill for this and can probably get away with nothing at all; hence the mushy focus. Sample images ?

You only need to get the Barlow in place and a detector behind it. You don't need the filter wheel or spacers unless you want to increase the magnification of the Barlow by increasing the distance between lens and detector. You shouldn't care about the detector being at a particular position, just focus. The position will be different than at prime focus due to using the Barlow. The problem of soft focus is nothing to do with the Barlow other than it magnifying what your scope is capable of. You could check collimation at this point or reduce the magnification slightly, get some video for stacking and see what comes out. Was it soft in the eyepiece or the camera ? If viewing on a screen, the image is quite magnified so will be soft for lots of reasons including scope cooling and seeing.

Those are fine work. Can you tell me what you did to produce the maximum stacking combination please. Impressed to see the satellite motions.

I had an extended session on this last night using my vixen na140. First to find it, next to image it without the centre being overexposed. I was taking 0.8 second images at 1x binning so I mostly lost the other fainter field stars. The Goldy straw colour was prominent even in the haze. I may try for a spectrum tonight..

Hi Wim, I replaced the guts of my old davis station with an esp8266-12, the wind speed sensor just provides a digital counter input on pin 14 and the direction sensor comes in via Adc0. Using the bme280 means the expensive mlx part is not used. Added a hygreon rain counter on another digital pin and it drives the ascom observing conditions monitor in node red. It's a neat and tidy solution using the esp.

I have one. In white so probably eq5 rather than vixen . Interested ?