Well... First light for a new toy.. Always exciting... The ST-10 performed exactly as expected and seems to be a very nice match for the 8" RC.. Although a nicer night might be a better time to judge that!
Unfortunately heavy dew seemed to diminish the quality of these images.. the secondary was fogging up in a matter of minutes.. I was having to hit it with a hair drier every 5th sub to try to stave it off... I am in the process of designing a secondary dew heater for the RC and a dew sheild as well.. Hopefully I'll have both countermeasures operational soon,
The affect of the foggy secondary is clearly visible in the image from tonight.. bit of a downer, but I think the shots still show an element of potential from my current rig...
As always, longer subs would be the go.. but i'm currently imaging unguided until I organise a few more toys!!
I'll upload them as I process them...
First up,
M16.
60 x 1min subs Bin 1x1 with 13nm Ha filter... 15x darks & Bias frames.
Alex, I don't know if you can see this on your screen, but your stars have little lighter squares around them. Is this because of some treatment you have applied to them?
the lighter areas around the stars are because of the light being smeared by the dew on the secondary I think, they are noticeable right from the word go.. even before the subs are stacked... Yeah, remember the humidity levels up here are pretty dramatic, coupled with the moderately low temperatures at the moment, dew is crazy... Everything was dripping wet when I packed it in at around 11pm... Shame too.. Wanted to have a crack at the Helix..
Ah yes, nothing like first light with a new system, a mix of excitment, trepidation and nerves
Those squares around stars are not noticable in the Omega and Swan shot, they look like processing or jpeg issues to me..?
Hope you sort out guiding etc soon, as Peter Ward often says (and I agree) it's mount, mount, mount (which basically means tracking tracking tracking) before worrying about any OTA.
Too right, the first light feeling is unlike anything else...
The Omega Centauri image was the first taken for the night, and dew hadn't settled at that point. The swan I was hitting the secondary ever 2 minutes with the hair drier. M16 and M8 were pretty much both dried out before the run, then left for an hour or so to image...
I'm sorting out guiding as soon as possible... As I am quite sure that 6x10 minute exposures will be FAR better than 60x1minute.. I've organised an OAG (just the way I prefer to do things) and a SBIG ST4 guider... That should see me running nice long subs..
I'll re-pro the M16/M8 shots today, taking note of everything I do and doing my best to not cause any squares around the stars... I just can't think of what would be causing it in my processing routine.. But its worth giving it a go I say... Its noticeable in the processed tiff file, so I dont think its jpg artefacts.. but again, will experiment..
Alex, this dew issue has got me stumped. My reasons for this are as follows:
The secondary is not directly exposed to the night sky. Dew only really forms where the surface is in direct line of sight to the night sky. It makes no sense that it gets dewed up pointing down.
Added to this, our average winter humidity is around 80% and night time temps are way lower than Brisbane, so we go past the dew point really rapidly. Now where I have my observatory is on the south coast with on shore breezes we often reach dew point there about 30 minutes after dark. My obs usually is swimming in dew, but my secondary has not once dewed up on the RC.
Installing a dew heater might just negate the sharpness of the optics, it will certainly stop the dew. I reckon if anything using a dew shield is preferrable.
Yeah Paul, It's really strange I think.. Although the Deepsky instruments RC's and the RCOS have built in secondary heaters from the factory... So obviously the secondary dewing is not "uncommon" in this design.
I think its a case of the secondary being closer to the front of the scope, the secondary holder is exposed directly to the cold and it dews rapidly.. I remember the last couple of times I've mentioned it, both you and Trevor had mentioned that you'd had no problems with this, as such, last night I was half inclined to take a photo down the aperture showing the secondary completely covered in dew....
I'm making a 30cm long dew shield as I type this.. its made of thin plastic, I'll be putting a layer of felt around the rear of it so it fits snugly to the OTA, and using matte black paint or flocking material to stop it reflecting light.... and just to keep the overall look of the OTA, I'll be sticking some of that carbon fibre pattern contact around the outside of the shield.. so it will hopefully just look like an extension of the tube..
If your conditions are as damp as you say, I'm amazed that you operate an SCT by choice... My SCT was a dew nightmare here.. I loved the scope, but the dew was impossible to stop.. nothing I did stopped it. heaters, shield, hair drier every 2 or 3 minutes...
I hope a sheild stops ths issue.. a heater is not optimal. As you say, it could negate the sharpness of the optics for one, and a lesser issue, but an issue all the same, is trying to route its power cable in such a way that it does not impede the light path in any way....
The heater will be a last resort, and hopefully it wont come to that...
Mike:
I just opened the original stacked tiff file of M16 and did nothing but a power stretch and those squares around the stars are still evident... Perhaps its a stacking artefact? Maybe I'll try adaptive weighted median combine rather than sigma-clipping to see if that has any affect...
Yeah... the roof on my back veranda was dripping dew droplets into my coffee this morning it was stupendously wet... I was hoping to stick it out another couple of hours and have a shot at the Helix, but by the time that it had cleared the roof line everything was soaked... and I'd already had my neighbours complain about the sound of the hair drier.. (this is, mind you, after they had spot lights flooding my back yard between 6:30pm and 11:00pm.. )
Alex, nice 1st light, but oh that dew is bad. It looks very much like what I get when the CAM dews up. Are you sure its no the cam, would make more sense. There is a desiccant plug that needs to be baked in an oven from time to time, if it has expired, it will always dew up regardless of the weather.
Thanks Fred, I've actually got a refillable dessicant plug from Particle Wave Technologies, It was only filled 1 night of imaging ago, and I did check the optical window of the camera, it was clear, but the secondary mirror was -WET- I'll have to see what I can do regarding this
Believe it or not we I had heavy dew last night but I was using my ED80 and dumped 3 hrs of captured data. Everything I took was shat due to either LP, secondary reflections from the dew and tracking issues the dew did play havoc with all my subs (I don't have a dew heater)
As to the RC couldn't you run something like a Kendrick dew band around the secondary baffle without it obstructing too much then just run the cable along the spider vane
I'm setting the RC put tonight weather staying clear we expecting an overnight min of about 4C
All going well I'll let you know if I have any dewing problems
Looking past the dew problem it looks very promising.
Does your scope have fans? I wonder if they can be fitted
I never had any dew problems with my 12.5 inch RCOS. But that had 3 fans pulling air through the tube and no dew heater.
Trevor - Yeah the dew is a real killer theres no doubt about it! Apart from the Omega Cent image, I think I could have probably trashed the other images without being too upset about it... That was my idea, getting a 3" heater band, putting it around the secondary baffle and running the wire down one of the spider vanes, the problem is that the spider vane you stick it too would be thicker than the rest, causing funny looking diffraction spikes... I'm sure I could figure something out...
Greg, Thanks, I agree, there is promise to those images, I have a ways to go yet before this setup is really reaching its potential, however I think im not too far off having everything I need... Then it just comes down to user input!
The GSO RC doesn't have fans, although Im sure that would help the dew issue also.. drawing air through the OTA might be something to consider trying in the long run... Obviously if I can avoid cutting holes in the rear cell, I will... The primary is fixed, and so mechanical alignment when re-fitting the whole shebang back together would be fairly critical....
There is a desiccant plug that needs to be baked in an oven from time to time, if it has expired, it will always dew up regardless of the weather.
Fred is correct.
Looks to me like you have some serious moisture problems in the ccd chamber. Bake as per instruction manual. (Add salt to taste. )
It also takes a freshly baked dessicant plug a few hours to suck up the moisture from the chamber. This process can be hastened by also purging the chamber with dry nitrogen.
Should I plug the camera in now, cool it to -10c and see if it fogs up?? It didn't appear to last night, however I didnt have a look directly at it, rather, through the aperture of the scope, i looked at its reflection from the secondary in the primary... The refillable desiccant plug im using at the moment was only filled a week ago, and the camera has only been cooled 3 times since then.. Surely they would last longer than that without refilling...
You have to replace it after every imaging session..........
No, im kidding. Dont switch the cooling on, and see what the pic looks like 1st, itll be noisy, but no dew. If you do this before the scope dews up, ittle be obvious. Then switch the cooling on and take another pic (after the cam has reached the new temp), the cam will dew up very quickly if thats the prob, easy test.
Yeah, remember the humidity levels up here are pretty dramatic, coupled with the moderately low temperatures at the moment, dew is crazy... Everything was dripping wet when I packed it in at around 11pm... Shame too.. Wanted to have a crack at the Helix.. 
(I wanna get paid for this kinda post 
)
