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Saturn 20/21 Sept 2024 - excellent seeing, but a host of dew related issues.....


geoflewis

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Having missed the excellent seeing on 17 Sept due to cloud at my location, I thought that last night would be my turn. The seeing was indeed very good, but my scope didn't want to play ball, or at least the dew heater strap didn't. The poor image quality seen on screen had me thinking that maybe I was imaging through fog with a bright Moon nearby Saturn, but once I checked the corrector plate on my C14 it was clear that it was anything but clear, instead it was dripping with dew. I had to get a hair dryer to it, then once that was clear I could see that the main mirror itself was completely fogged over. I experienced this a couple of times last year and believe that running the fans had pulled moist air inside the OTA, which then condensed on the mirror. Being a closed tube, there was nothing I could do but turn the fans off and wait whilst the mirror cleared, which took about 30 minutes. However, with the dew heater strap not working, I had to repeat the hairdryer method a few times and was unable to run my usual continuous sequence of SERs, instead it was case of grab some data, apply hairdryer, rinse and repeat. I also lost the best of the conditions just hanging around. When I checked the data today the resulting SERs were a mixed bag, so I've had to pick and chose what to include. The net is that the colour image is from 6x2 min SERs captured over nearly 1 hour elapsed time, so lots of gaps in the data. The IR was from a continuous sequence of 9x2 min SERs, but later in the night when Saturn was well past the meridian and losing elevation. Anyway, I'm pleased to have salvaged something from what should have been a far better session.

2024-09-20-2310_3-GDL-WJ-RGB_AS_IA.jpg.da47e2d09bb1a098ee8024d179680d3d.jpg2024-09-21-0045_9-GDL-WJ-IR_AS_IA.jpg.d2a7447bad2380cb5e512a0e6bdee53b.jpg

The colour image has some nice colour banding, but the regions close to the limb suffer from what I suspect are gaps in data after de-rotation in WinJupos. Both images show the Cassini division quite well. The brightening from the Seelinger effect at opposition is no longer seen.

Thanks for looking.

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  • geoflewis changed the title to Saturn 20/21 Sept 2024 - excellent seeing, but a host of dew related issues.....

Excellent images Geof. I really like the banding you have got, especially in the southern hemisphere. It's a shame excellent seeing was ruined by hardware issues. 

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Thanks Kostas, it was certainly a frustrating session, but I'm glad that I hung in there and tried to make the best of it. I think the colour image is the best one I've got this year, just might have been so much better, but no point crying over spilt milk...🙄

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It's amazing to me how the nights when we are faced with difficulties and tribulations almost always fall on nights of excellent seeing. Despite this you have produced some lovely images of Saturn. Perseverance paid off. Well done Geof.

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21 hours ago, bosun21 said:

It's amazing to me how the nights when we are faced with difficulties and tribulations almost always fall on nights of excellent seeing. Despite this you have produced some lovely images of Saturn. Perseverance paid off. Well done Geof.

21 hours ago, siatnite said:

Lovely shots there Geof despite the dew problems.

17 hours ago, Space Cowboy said:

Very good images despite the dew issues! There is always something trying to frustrate us especially when seeing is good.

Thanks all, it's not the 1st time (probably not the last) when I've experienced very heavy dew during good seeing, especially this time of the year. Still, as they say, what doesn't kill you, makes you stronger.....🙄

 

 

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On 21/09/2024 at 17:55, geoflewis said:

Having missed the excellent seeing on 17 Sept due to cloud at my location, I thought that last night would be my turn. The seeing was indeed very good, but my scope didn't want to play ball, or at least the dew heater strap didn't. The poor image quality seen on screen had me thinking that maybe I was imaging through fog with a bright Moon nearby Saturn, but once I checked the corrector plate on my C14 it was clear that it was anything but clear, instead it was dripping with dew. I had to get a hair dryer to it, then once that was clear I could see that the main mirror itself was completely fogged over. I experienced this a couple of times last year and believe that running the fans had pulled moist air inside the OTA, which then condensed on the mirror. Being a closed tube, there was nothing I could do but turn the fans off and wait whilst the mirror cleared, which took about 30 minutes. However, with the dew heater strap not working, I had to repeat the hairdryer method a few times and was unable to run my usual continuous sequence of SERs, instead it was case of grab some data, apply hairdryer, rinse and repeat. I also lost the best of the conditions just hanging around. When I checked the data today the resulting SERs were a mixed bag, so I've had to pick and chose what to include. The net is that the colour image is from 6x2 min SERs captured over nearly 1 hour elapsed time, so lots of gaps in the data. The IR was from a continuous sequence of 9x2 min SERs, but later in the night when Saturn was well past the meridian and losing elevation. Anyway, I'm pleased to have salvaged something from what should have been a far better session.

2024-09-20-2310_3-GDL-WJ-RGB_AS_IA.jpg.da47e2d09bb1a098ee8024d179680d3d.jpg2024-09-21-0045_9-GDL-WJ-IR_AS_IA.jpg.d2a7447bad2380cb5e512a0e6bdee53b.jpg

The colour image has some nice colour banding, but the regions close to the limb suffer from what I suspect are gaps in data after de-rotation in WinJupos. Both images show the Cassini division quite well. The brightening from the Seelinger effect at opposition is no longer seen.

Thanks for looking.

Really nice work as always! I can't but admire!

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  • 2 weeks later...
  • 4 weeks later...

Tremendous images @geoflewis 👍

Have you thought about putting a couple of layers of reflectix around the C14 ?

There would be no need to cool the scope as the air inside the OTA is thermally stable with the reflectix insulation.

Another plus is the air temperature in the OTA is slightly higher than the external air temperature so it takes MUCH longer for the corrector to dew up.

Reflectix is relatively cheap too 🙂

Edited by MartianHill
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1 hour ago, MartianHill said:

Tremendous images @geoflewis 👍

Have you thought about putting a couple of layers of reflectix around the C14 ?

There would be no need to cool the scope as the air inside the OTA is thermally stable with the reflectix insulation.

Another plus is the air temperature in the OTA is slightly higher than the external air temperature so it takes MUCH longer for the corrector to dew up.

Reflectix is relatively cheap too 🙂

A few folks have suggested that I do that, but I’m not sure how to go about it. How does reflectix work in a dark observatory, where the scope isn’t being heated by direct sunlight, so nothing to reflect? The C14 is already a beast for me to handle, in fact I can no longer do it in my own, so I’ve decided that it’s too much trouble for me to do it.

Edited by geoflewis
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Lovely images of Saturn @geoflewis 👍

The theory around insulating a compound scope is that it slows the cooling of the scope when its taken out to observe and that in turn stops heat gradients setting up near the tube walls so you shouldn't get heat plumes and OTA self-induced air-current wobble in the view. I'm not sure that applies if you leave your scope out in an observatory (i assume it is always nice and stable at ambient).

The side effect of insulating to avoid air current related disturbance to the view is that it keeps the scope slightly above ambient temps and in theory therefore above the dew point for longer and/or means you can run dew bands (under the insulation) at lower settings and still protect against dew. This part you may get a benefit from even in an observatory.

Any old camping mat or foil backed camping mat will do to experiment.

I extend my dew shields with camping mats too - i hate dew! 

Cheers

Edited by josefk
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