Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 I had some dew problems on my primary a couple of nights ago and was wondering if someone could point me in the right direction for some dew prevention please? I have an astrozap dew shield which is working well for my secondary mirror but this is the first time I've had it on my primary. I have a Skywatcher Quattro 8S and the back side of the mirror is exposed to the elements. Is that why it got dew'd up ? I have seen info saying a fan would help so was thinking of going down that route seeing as I have an 80mm pc fan kicking around. I've also thought about making a dew heater strip using either nichrome wire or resistors (leaning towards nichrome wire). I'll be making a dew heater strip for my guidescope anyway but would like some clarification on the best option for the primary mirror please. Thanks in advance Link to comment Share on other sites More sharing options...
Daz Type-R Posted December 16, 2014 Share Posted December 16, 2014 (edited) IMO a dew strip for the primary is no good, you would just be heating the metal tube and not the actual mirror cell. Instead, I have gone down the primary mirror fan option, here is mine prior to installation.... It cools the scope quicker, then you can even leave it running on low while imaging/observing and some say it even improves the view. Lots of people on here with newts have done this, I'm not sure of anybody using a dew heater. Edited December 16, 2014 by Daz Type-R Link to comment Share on other sites More sharing options...
tuckstar Posted December 16, 2014 Share Posted December 16, 2014 I have been using a dew band around my primary on the 250px. Panicked at Kelling, but it kept the dew off. I will be going down the fan route as well. Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 Thanks for your advice guys. Seeing as I've got a fan kicking around I'll do a trial with that and go from there. I think I'll order enough nichrome wire to do both the guidescope and the primary just in case. Fingers crossed the fan will do the job though and I won't have to have to add the heater, keeping down the amount of cables down etc. My only concern with the fan was vibration but I'm guessing that as long as the fan is a well balanced one this would not cause any issues. Thanks again ps. anyone know the theory behind how the fan method works ? (I like to know why I'm doing mods) Link to comment Share on other sites More sharing options...
Daz Type-R Posted December 16, 2014 Share Posted December 16, 2014 (edited) The fan pulls cold air from outside of the telescope and draws it into the OTA, as you want your scope to be at the same temperature as the outside air temp to reduce thermal currants which will distort the image you are trying to observe/image. The next benefit is that the fan somehow while blowing the ambient air up and around the mirror, creates at really thin layer of air that sits just above the primary surface and acts as a shield, preventing moisture from forming on the optics. So a fan is win/win really, faster cool down times and no dewed up primary. With regards to vibration, obviously the better the fan the lower the vibration but set to its lowest speed, nobody has complained on here yet about wobbly pictures. Edited December 16, 2014 by Daz Type-R Link to comment Share on other sites More sharing options...
Doc Posted December 16, 2014 Share Posted December 16, 2014 Have a read of this. http://www.fpi-protostar.com/bgreer/fanselect.htm Packed with info. Link to comment Share on other sites More sharing options...
Daz Type-R Posted December 16, 2014 Share Posted December 16, 2014 (edited) Also you will need to make sure you seal the back of the OTA, otherwise the fan will blow the air onto the back of the mirror cell which will then bounce off back into space. If you look at the picture of mine above, the 3 lugs will stick onto the mirror cell housing and the inner circle (the bit the fan is attached too) completely fills the back of the OTA and seals it, therefor the cool air can only go up the tube. Just read that link Mick, cracking good explanation, bookmarked that! Edited December 16, 2014 by Daz Type-R Link to comment Share on other sites More sharing options...
Doc Posted December 16, 2014 Share Posted December 16, 2014 Some people attach the fan to the actual mirror cell, I prefer Daz's method so the fan is floating so there is no chance of vibrations. Link to comment Share on other sites More sharing options...
tuckstar Posted December 16, 2014 Share Posted December 16, 2014 Rubber grommets or washers will remove any vibration. Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 Nice one. That website along with your explanation really helped. I'd been scratching my head trying to work out how blowing cold air at the mirror would work. I'd been thinking along the lines of heating it above the dew point and hadn't even considered possible degradation of the images produced. The whole thin layer of air above the primary concept makes perfect sense. Time to pick up a few bits n bobs for mounting the fan I've got and figure out a way to control the speed of the fan. My list of mods n jobs for the weekend is starting to build up a bit now. Ah well, keeps me busy while the kids are at their mums house this weekend Thanks again Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 speed controller ordered - £4. Happy days. I'm pretty sure it's the same one you have Daren. I'll be honest, I'm gonna try and replicate your design too. I hope you don't mind and I hope you take that as a compliment. It's meant as one. Right......now I've buttered you up a bit..... .......just wondering what you mounted the fan on ? plastic or metal ? Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 on the other method........Did you attach your dew heater to the OTA Andy or the primary itself ? I've been doing a bit of reading up on the whole dew control issue over the past couple of days and have read that people do both. Link to comment Share on other sites More sharing options...
Daz Type-R Posted December 16, 2014 Share Posted December 16, 2014 Ha, confession time, I didn't make it! While most of my mods are DIY, this one is not, check this out for all the info you need..... >http://youtu.be/tON69sEH-AY Dion from Astronomy Shed is awesome! Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 lol. good old Dion. Astonomyshed was gonna be my next port of call for a method. Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 I just checked the video and he's got it on a 200P which has very similar dimensions to my Quattro. Looks like he's used 2-3mm plastic to mount the fan on. I now have all the info I need to get making Thanks again. Once again EMS and it's user knowledgebase has helped me out. Happy days Link to comment Share on other sites More sharing options...
tuckstar Posted December 16, 2014 Share Posted December 16, 2014 on the other method........Did you attach your dew heater to the OTA Andy or the primary itself ? I've been doing a bit of reading up on the whole dew control issue over the past couple of days and have read that people do both. Just slung it round the ota level with the primary. Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 Cool. Cheers. Handy to know if the fan doesn't sort the problem. I don't like the idea of putting the heater around the mirror itself. Don't know why, just seems wrong to me. I'm sure the stuff I've read and the people who wrote it have their reasons but I tend to trust the advice on here rather than blogs etc. EMS members have never steered me in the wrong direction Link to comment Share on other sites More sharing options...
Daz Type-R Posted December 16, 2014 Share Posted December 16, 2014 (edited) Thanks again. Once again EMS and it's user knowledgebase has helped me out. Happy days No worries, that's why we are here. Keep us informed of how you get on. Edited December 16, 2014 by Daz Type-R Link to comment Share on other sites More sharing options...
Guest sharpie78 Posted December 16, 2014 Share Posted December 16, 2014 Will do. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now