sshenke

I have been fed up with dew build up on my reflector- Skywatcher 130PDS with no comprehensive solution to this problem. Every imaging session I had recently had been utterly ruined by dew build up within a maximum of an hour. hence thinking of buying a refractor scope instead, as I think dew will be much more manageable with the use of dew shields +/- dew bands. Would appreciate suggestions for a refractor scope for a modest budget (around£500) please. Thanks.

hello all, i am not getting any further with solving this problem. I have looked at the option of adding vent holes behind the primary mirror, if i understood it correctly, but there isn't anything behind the mirror stopping contact with the outside air. As you can see from the attached picture, the only thing that was there was just a piece of circular cardboard, which i have now removed. 

i tried to buy a dew heater band that would go around the ota tube just near the primary mirror, but flo had informed me that this would not work at all as the mirrors of a reflecting telescope do not make direct contact with the outside tube and hence no heat can pass through to the mirror. They also said that they have no suitable dew heaters for reflecting telescopes.  Really frustrated and would be grateful if anyone has any suggestions for me. Thanks. attached is another picture if dew buildup last week. This happened after about an hour of taking the scope outside.  Location wise, i really cannot think of my rear garden to be any different to others'.

2 hours ago, emyliano2000 said:

Thank you guys, I'm really glad you like it. 

I used my eq6. 

Emil

Thanks. Excellent work!

Can i ask what mount you used?

Absolutely stunning. blew my mind away. Well done and thanks for sharing it here.

13 hours ago, Alan White said:

No wonder it is dewing if its at Zenith that long.
Best thing is observe and then drop away from Zenith so dew is not falling
into the primary or indeed lens on a refractor. 

Are you observing or imaging?

Imaging. It would take about that long for my target object to come into view because of obstacles. until then i would just trial image some other dso, as i am very new to this. 

2 hours ago, Alan White said:

I have owned a number of Newtonians, always have Secondary dewing on long observing sessions,
but only once on the Primary Mirror.
Are you viewing to Zenith for a long period?

Ventilation via the tube may well be a fix, rather than heating the primary.

I and others have made vents in out Newts to vent the Primary.

This is the base plate that the Mirror cell is set of from.
Clearly the mirror sits in front of the holes.

Another identical scope, with different holes, belongs to another on SGL,
who has commented already.

You could try this first as a little air movement near the mirror may be all it takes to prevent the dew.

No dew since the vents added by me.

That's really helpful advice, thanks Alan. yes i have been doing zenith viewing for a long time, ie 2 to 3 hours at the most though. That was mainly to get good guiding results. I will certainly give it a go. Will need to learn how to do it properly without breaking anything.

1 hour ago, carastro said:

I no longer have my SW130PDS, but when I did I never used anything for the primary as luckily that never got dewed up.  My secondary I always worried about and so I used to wrap a couple of long dew heaters around the tube either side of the focusser.  Whether it did any good I don't know, but luckily I never got any dew.

With my refractors I definitely use dew heaters.

What made you think I didn't use any dew heaters? 

Carole 

Thanks,  will buy some dew heater band, but i just can't find the right way to attach it to the scope, ie for the primary mirror. as you said that you never bought dew heaters,  i just assumed you never had to use them

it has been absolutely horrendous for me here. Can only manage 30 minutes of imaging ( i am in the Midlands) because of dew building up. 

Carole, how do you manage without any dew preventing device?

Hello everyone, sorry to bring this thread back up, which I came across when trying to find a solution for the dew problem. I have a skywatcher 130PDS (Reflector) and have faced lots of problems with dew recently. As you can see from the attached picture, it is the primary mirror that suffers from heavy dewing. I am sure the secondary mirror has dew as well, but I think the primary seems to be the most difficult to fix. I have used hair dryer, but as rightly pointed out above, it is only a short fix. Can someone offer any suggestions to stop dew forming on the primary mirror? Thanks

Thanks so much for yourhelp vlaiv  really appreciate your time.

i will check the bit type and post thatinfo later. in terms of gain, i always keep it at zero. offset- i didn't even know this functionality existed. also i willfind out howto change the capture format to .fit. thanks. will try and post theimage in zip format as per your suggestion.

the images from my asi1600 come out as .png files

Hi vlaiv, those images posted are straight from the camera, not stretched or processed in any way. the kit i use is heq5 pro mount, asi 1600 mm pro cooled, but cooler was turned off, guidescope is asi120 mini.  

while i can still process the andromeda galaxy, i can see a dramatic reduction in light collection compared to what i have seen before. as i said, the biggest and fundamental issue is that once the mount is set to a new target using the goto function, i can't even confirm if it has reached the intended target without taking 100 second long exposure or centre the target in the fielf of view. All dso's i had imaged previously ( during the summer nights!) would be easily viewable within 20 to 30 second exposure, but that is almost impossible now.also, as you can see from my sub of M31, it is off centre and i left it as it is as attempts at centring failed because of the long exposure needed to see where star has moved to with each manual movement of the scope

main scope is skywatcher 130 pds, focal length of 650mm

when i was targetting the Andromeda galaxy, I could see a better image of it in my guidescope feed ( 3 second exposure loop) on phd2, than i could see on the main camera feed which was on about 30 to 40 second exposure loops.

So, I have attached the images here. the top one was taken on 22 Sep, - exp Time- 240 secs _ Luminance filter

the middle one was on 2 Oct= exp time- 306 secs- Luminance filter

Sorry I have deleted the image with a much shorter exposure time, so cant post it here for comparison.

The other issue I had last night was that I could not even centre the image before starting to take the subs, as the image was too faint and reducing the exposure time (even to around 30 seconds!) to see which way the stars (at least the brightest one) were moving meant that they completely faded away.

also attached at the very bottom is a 300 second Luminance sub of Andromeda galaxy, again taken last night.  pretty unimpressive for an exposure this long. This was the first time I imaged it, so no prev images for comparison.

All the above are unstretched images.

Thanks for all your advice.

as far as my subjective assessment goes, on the recent occasions when we had clear sky, there was no haze or dust and i was so positive that i was going to get fantastic images. Focussing which i do on every session was fine as well.

yes to clarify, the scope was inside the house- around 20 degrees, just before i took it to the garden

sure, will do, as soon as i get access to the laptop, will post the images.Thanks

just to add, i started imaging within about 20 minutes of getting the scope outdoors, not sure if this is enough time for dew to build up. have had this scope and mount only since this summer, so don't have any previous winter experiences to compare with. 

thanks vlaiv, the guiding is done through phd2. RMS error about 0.4 seconds on both the occasions. i think the main issue with the images is poor light gathering. unstretched 15 sec sub taken previously looks absolutely fantastic compared to the unstretched 300 sec one. i will try to post the images here later. like you said, it's only the bright stars that standout

also just wanted to add that the image quality was poor right from the start as it was at the end of 3 hours of imaging, which i think might be relevant when considering the possibility of dew/ condensation being the cause

Tthis might be a daft question,but would appreciate your thoughts  please.

on the last few imaging sessions, i am having to use longer exposure times to see DSO's and even with that, image quality is much much poorer. For example, 3 weeks ago, i only had to do a 15 second long exposure to see the elephant trunk nebula and last night, when the sky was much more clearer, it took me a 300 sec long exposure to see it and the quality was very disappointing. the optical train, filter , time of viewing -( at least 2 hours post sunset ) etc were exactly the same on both occasions. only difference was the temperature - about 4 degrees compared to  14 degrees previously. camera was not cooled on either of the session. the other thing i found out as an afterthought when i looked at the telescope about 10 to 15 minutes after bringing it indoors was the presence of dew/ condensation occupying almost the entire face of the primary mirror and the backing of the mirror was soaking wet. No dew bands or other such stuff were used. Would be very helpful if someone could shed light on what i am doing wrong. sorry for the long post, but i thought it would be helpful to give as much information as possible.

heq5 pro mount, asi1600 mono camera, good guiding ( similar to my previous standards, that is)

thanks

perfect, great idea thanks.  i was only thinking about how to use the spirit level in this situation. thanks.

hello, does anyone know how to ensure that the cross hairs in the reticule of the polar scope are level, ie, zero pointing exactly to the north and the 3 to 9 line lying parallel to the ground?  Thanks in advance. 

i am using a HEQ5 pro mount

Hello all, I am quite frustrated by not being able to get autoguiding going, despite trying to read manuals on various websites. I have an ASI1600 camera on skywatcher 130 PDS with HEQ5 mount and I am trying to use ZWO mini guidescope with ASI 120 camera, the trouble is I cant get the software (ASI cap) or PHD2 to recognise both the cameras simultaneously.  Clearly there is something wrong with what I am doing and so would appreciate any help please. Thanks in advance