Stardaze

6 minutes ago, Ricochet said:

Yes, you only need the red and black wires to run a 3 pin fan. I also have a basic speed controller in my setup but if the fan is properly isolated this isn't really needed. 

I did start to read up on that and saw a couple of cheap controllers but if I can plug it into one of the dew controller channels and control from that, then even better. I was thinking that it might need its own supply. Already have a 12v 7ah battery powering the dew kit.

So I can lose the molex plug and add some thing like the below to plug into the controller to power?

https://www.switchelectronics.co.uk/male-rca-phono-plug-screw-terminals?gclid=Cj0KCQjwt-6LBhDlARIsAIPRQcJ4aJzLmKOyeV4r65ih2Zw84rIjzU7iSC84boHhMOQ2A3DfHlJ1FCgaAnFIEALw_wcB

16 minutes ago, Piero said:

 

Just checked my data.

The fan I mounted is a Noctua NF-R8 redux-1800, High Performance Cooling Fan, 3-Pin, 1800 RPM (80mm, Grey) and was bought on Amazon. The specifications regarding the 3-pin is available online. I cut the small cable which is redundant for us and connected the two small cables to a plug.

I use a Tracer 12V 7Ah LiFePO4 battery. This connects to a Lynx Astro 4 Port Dew Controller. The channels power: 1) the fan, 2) secondary mirror dew heater, 3) Rigel quick finder dew heater, and 4) a 2" dew heater which I use with the finder, eyepiece, etc whenever needed. While in use, I reduce the speed of the fan to half using the dew controller.

Thank you, that’s great. I have a 4 way controller from Dew Control so I’ll look at that configuration. Can’t seem to find grilles to go on the back now.. 

On 26/10/2021 at 13:17, Piero said:

I use a noctua fan and found it really effective.

I agree with other members that you should install it with some elastic material, or pads at least, to avoid vibrations.

I used an abs plastic panel which is screwed to the back of my mirror cell. Pads were added between the panel and the rungs where the bolts are. My fan is almost always on when I observe and there is no vibration whatever mag is used. 

 

Quick question, what is your fan powered by? Have been looking at 4 pin fans but typically the converter plugs I've found are 2 pin like this one: https://uk.rs-online.com/web/p/dc-power-connectors/8104595/?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_Connectors_Whoop-_-DC+Power+Connectors_Whoop+(2)-_-8104595&matchtype=&pla-362265064714&gclid=EAIaIQobChMIwoulkofw8wIVze3mCh3xBwNpEAQYBSABEgLflfD_BwE&gclsrc=aw.ds

The additional wiring looks to be needed if you add a controller, which I assume isn't really necessary for mounting behind the mirror. Need to get something ordered really. 

The article is a really interesting view, certainly have read a fair bit about the boundary layer and I'd love to be able to implement something for that, but I'll concede that my handcraft skills are average and so cutting a hole to mount the fan on the side, with corresponding holes opposite is probably a little beyond my comfort zone. Though maybe a downlighter hole punch could do the job well enough with some insulating tape on the tube to mitigate slip? Maybe I'll give it some thought..

Thanks @Pixiesfor the link to a white fan. I don't think the look of it all concerns me that much tbh but was thinking it screwed into the bottom would make it look a bit tidier for my OCD but certainly see the benefit above to bungee chord mounting to mitigate vibration, which is probably even easier to implement. Have you considered adding a fan to yours? 

PS. I think my primary mirror may have had some moisture on it the following morning still from a very wet hour I had out Monday evening - everything was sodden/damp around me. Odd though as I kept the OTA horizontal for half hour for cooling beforehand and had it back in an hour later. There's a bit of dust/small particle all over the mirror when shining a light onto it, even a couple of very fine strings of cobweb in the tube itself. I always store it with the top cap and shower cap on the bottom too but it's not as bad as I first thought. I left the cap off the following day for a couple of hours just in case it was moisture. I'm still tempted to clean it all out one evening regardless. 

10 minutes ago, Ricochet said:

My plan was to run a very small length of mini trunking inside the tube with 12V ports out of the tube between the rings (power in from the rocker box) and out at the bottom of the tube. However, five years in and the test cable that was just looped around the ring screws is still sat there. 

The fan I've got on mine is an 80mm Coolink with a fan filter fitted to the incoming side to prevent dirt being blown up into the tube. I did also buy a Noctua for something and that was also a very nice fan that would work well. 

A fan filter isn’t a bad idea either. I’m thinking that 2 core cable up the side isn’t the end of the world.

21 minutes ago, Piero said:

Well.. there are two distinct problems: 

1. cooling down the primary mirror
2. removing the boundary layer above the mirror surface

To tackle the former issue, a fan installed behind the mirror and pushing air to the back of the mirror is the most effective way. Lateral fans pushing air on the mirror surface (not the mirror edge!) can be used for tackling the latter issue.

 

cooling down

Leaving the telescope outside to cool down for 1 or 2h before observing matters but it is not sufficient. The temperature continues to drop over night. The issue is that a mirror takes more time to cool than the surrounding environment. Astigmatism and spherical overcorrection will appear as soon as this temperature discrepancy is 1-2C. A fan will help the mirror cool down faster, approaching the ambient temperature effectively. 

 

 

boundary layer

It does not matter whether the dobson is a truss or solid tube. The boundary layer can be present in both. I believe the S&T articles mentioned by Merlin are these two:

• https://skyandtelescope.org/astronomy-equipment/thermal-boundary-layers-in-newtonian-reflectors/
• https://skyandtelescope.org/wp-content/uploads/Adler-NewtThermal.pdf 

As you can see in the second one (by Adler), a solid tube is used. 

The mirror box of my dobson is quite shallow (11" deep). If the light shroud is lifted up 4-5 inches from the bottom, the flow of incoming air is sufficient for breaking the boundary layer and preventing its reformation. For deeper mirror boxes, the installation of fans would do the same.

In my opinion, the boundary layer 1 inch above the primary mirror surface is one of the unconscious reason why people state over and over that refractors are better than reflectors and that larger apertures suffer from seeing conditions more than smaller apertures. It's also the same reason why people say that they cannot push the magnification much with their reflector (despite the fact that they say they can with their refractors). 

 

 

BTW, my dob is only few months old. 

Great post @Piero

I think drilling holes into the side is probably a step too far for me. Eventually I’d like a nice truss which would make it easier or even a secondhand OO tube. Did think about just butchering mine and adding a better base and mirror in time. Far too many options with dobs 🙂

35 minutes ago, JeremyS said:

The biggest Bressar fan around is our very own John Handleby 

He does like a Bresser with a good ‘andle. It’s all John’s fault that I bought one. Just need to add another sibling now though. 

38 minutes ago, JeremyS said:

Just don’t get tempted to short cut the job

Was thinking of a good old Brillo pad as it comes supplied with the soap too. 😆

Here’s my most exciting Astro purchase to date, my ‘baby’ needs a clean 😂 The mirror that is.. 

42 minutes ago, Merlin said:

Some years ago there was a definitive Sky & Telescope article showing that the most effective way to use a fan is to mount it on the side of the main tube. The fan should be blowing air across the mirror surface and exiting through three or four inch diameter, side-by-side, vent holes on the other side of the tube and on a level with the fan.

This arrangement removes the blob of cold air that settles on the mirror, causing poor definition. We should forget about “tube currents” and go for the blob.

Thanks for this @MerlinI presume that you mean to remove the boundary layer for truss dobs. Mine is a solid tube and so really from underneath just helps cool the mirror itself. 

3 hours ago, Dave scutt said:

Hi stardaze 

I had a tray with 2 fans in it , for cooling down my laptop I attached hair bungees for no vibrations  and use a power pack to keep it running 

Thanks Dave. I had seen @Ricochetdo something similar but thought I'd try to drill it in place but I hadn't thought out the dampening properly. It does make sense to bungee it to stop the vibrations. 🤔

I love seeing these big old dobs - that's a proper job @PieroJust looking at those fans and seem to do a 92mm or 120mm option. The latter is too big but cheaper than the smaller one for some reason?

7 minutes ago, johninderby said:

There are a lot differences in quality of fans. Get one with ball bearings and that is a low vibration one. If you ever run the fan while observing this is important. 

Good place to look is one of the places that deals in computer modding. And yes the price does varryquite a bit, I've found good fans are nearer 10 quid or so but worth checking the cearance sections.

Thanks John. Looking at a dual ball bearing fan for around £16, single bearing seems to be £10. Thanks for the input. 

It looks like I need to clean the mirror of my dob and so whilst I'm at it I was going to add a fan to the bottom. I noticed they do an option with a fan and so it's a 100mm aperture which looks to seat a 4" nicely. There's just a couple of questions I have if anyone can assist please:

Is there any recommendations on a specific brand of fan. They all seem to be Chinese unbranded from £2-£20?

The cable looks to be tucked into the tube still. My dew heater has a 12v out supply so was going to hook up to this. It sits at the front so probably was going to leave the lead trailing from the back of the OTA but sounds a bit untidy, any ideas?

I haven't disassembled yet and so presume the black plate to attach the fan to is part of the mirror cell and is easy enough to drill?

Thanks in advance for any input. 

IMG_0070.HEIC

Thanks for posting this method. I've just discovered that my mirror needs a clean for the first time, not sure how it's got so dirty literally overnight but I'll need to get it done. 

8 hours ago, Dean Hale said:

Me too, a £20 bargain. Never felt quite right stuffing items into my pockets. Wide enough to carry a 10" tablet too.

I didn’t get the funky orange interior version as it was out of stock, so plain old grey for me, but, I love it. Nice and simple and so much easier to use ‘in the field’ or, in the garden like I’ve just been. 😀  Enjoy.

58 minutes ago, johninderby said:

While I’m really pleased with the performance of the CC6” have to admit the CC8” is just in another class and will show a lot more.

The 8” has roughly 77% more light gathering area and resolution increases from about 0.77" arc seconds to 0.57" arc, that's a fairly significant increase. You gain about 0.6 magnitude or about 1.5 times brighter.

The CC6” is a great buy though but would you feel like you settled for the cheaper option rather than the one you really wanted. Of course the solution is to get both like I did. 😁😁😁

Thanks John. I think you’re right, in the end I’ll probably be lusting after the bigger version. Better get saving..

I had got my heart set on a 102ED frac but have really been surprised as to how much I’ve enjoyed the planets again this year. 

2 hours ago, johninderby said:

That’s a Report tripod. Surprisingly solid for it’s size. The 8” is a much heavier OTA and nearly 10kg with all the bits so needs a decent mount. I use my CC8”on a Berlebach Planet with an AZ100 athough a Skytee is a good budget option. 

Yeah the sky tee was what I’ve been thinking. Sorry to butt into this thread but how much extra do you get out of the 8” over the 6” John, is it worth twice the cost plus the extra for a planet?

On 17/10/2021 at 18:42, johninderby said:

And for something different there is the StellaLyra Classical Cassegrain 6” . I use one as a grab’n’go setup. 6” aperture and very fast cooldown and no dewing problems. Is ready to use minutes after putting it out. More suited to lunar / planetary and small DSOs though. Great performer. 👍🏻. 

https://www.firstlightoptics.com/telescopes-in-stock/stellalyra-6-f12-m-crf-classical-cassegrain-telescope-ota.html

Think I fancy one of these next year John. Might push it to the 8” though. Which berleback is that one? 

12 hours ago, SuburbanMak said:

Thank you!
Short answer is it works for me  

I don’t have a lot of experience to give a comparative view but have had what for me are some super nights in my first Mak yesr.  

Optics can be very crisp, the limiting factor more often is seeing. Image is not huge but I’ve been pleased with the level of detail that can be pulled out when conditions allow - 6+ bands on Jupiter, barges, festoons, transits and the GRS with good contrast and what little CA there is seems atmospheric. 
Saturn I’ve seen A&B rings, Cassini division, some banding, crisp shadows of planet on rings & vice versa + 3 moons. 

On the best nights have successfully pushed magnification above 250x - more usually 150-180x is the sweet spot. 
 

It’s also very sturdy and quite small enough to backpack to the park - run mine on an AZGTi and Berlebach Report and it’s very steady. In the garden I can be up running in minutes - my experience has been cooling time is 20 mins or so, (usually put mine out early). 
 

 

 

Thanks for that. I wouldn’t say that the image is large in my dob even at 250x but it does sound like there’s enough detail from the mak. Which model do you have? I nearly bought an SW version last year. 

Great report. How useful do you find the 127 mak for planetary? I keep toying with that idea as a grab and go but then fighting the urge to go all out on a frac next year.

Super Stu. That little setup looks superb!

I’ve often wondered how the AR102 performs for the money. Am thinking I should hold out till I have a bit more to spend though but certainly sounds like it should do a fair job. 

2 hours ago, Stu said:

Nice report @Stardaze, sounds like a good session 👍. I was out last night too, mainly concentrating on Jupiter and Saturn as there was quite a lot of high haze around which kills the deep sky objects. My skies around around 20.5 and I’ve yet to spot M33, must keep trying on nights which are more transparent with no moon. Thanks for the report 👍

Thanks Stu. There was high cloud around on dusk, but it seemed to have disappeared by 9. I’ve been concentrating on the two planets too more recently, there hasn’t been many opportunities of late for DSO observations. 

I've only managed to grab the odd few minutes with the Bino's this last couple of weeks, with work being so busy too but I've been itching to have a hunt around Andromeda with the dob this year. So with that in mind and the possibility of an hour or two without clouds, I set the dob up just after dark.

The first half hour was spent watching Ganymede's transit across Jupiter. The seeing wasn't too bad at all at first but then the cloud rolled in, which was an hour overdue according to CO. I decided to grab a brew and get the dew kit working as it seemed pretty damp already. 

Around 9.30 the cloud had moved on and so I got myself acquainted with Almach to fine tune everything. At this time, Almach was only just above the tree next door and so I must have spent a good while letting my eyes slowly adapt. 

Andromeda needed quite a bit of breathing space and so I changed back down to the 13mm (98x) and settled in. M110 was clear, sat just inside the field stop. I couldn't discern the full shape of M31, very spread out and M32 was completely lost in the haze. I'm still to resolve this fuzzy from the garden which led me on to M33, another galaxy that has evaded me too. The sky didn't seem as dark as I'd like in the RACI, the stars around M33 were not that clear and so after 10 minutes of searching, I drew a blank. I tend to find M33, along with it's namesake M101 tricky, which must be down to my 20 SQM and the spread out brightness?

I headed over to M15. This old girl responded best to 98x of magnification, the 10" didn't quite give me enough light for the 7mm, which I did try at first. There was clear arms branching out with some resolved detail around the edges. 

I dropped down to M2 but the session was about to get cut shorter than I'd have liked. The cloud had started to sweep back in ,which led me quickly back to watch Ganymede exiting from the disc. The autumnal damp air is upon us but I felt happy with a very quick hour+ and back in bed at a normal time to boot.