mental4astro
10-04-2020, 02:19 PM
Hi all,
I've been working on this for a very long time - trying to keep my SCT's and Maks dew free over the course of a night. And one thing I HATE is needing to use heat - we fret so much trying to remove or control heat from our scopes, and then we go and stick heat sources to dry it up. Not exactly logical... :question:
The starting point
As many of you may be aware I've been actively espousing the benefit of insulating our SCT's and Maks instead of waiting for them to cool. By insulating the OTA there is no heat differential created between the cold tube and the warm primary and baffle tube, so no heat plume can be generated as the air inside the OTA stays warm. With no heat plume in the OTA, you can rip high magnification from the scope from the very start, and not need to wait for the scope to reach ambient temperature. And with big SCTs and Maks, this can be several hours.
I've been wrapping my SCT's and Maks for several years now, and I have not waited for any cooling period in all this time. Instead, I set up my scope when I find I have the time (limited as it is), and get to work with sketching straight away. No heat plume, and 300X, 400X as I find best suits seeing conditions.
257534 , 257535
More info on insulating SCT's and Maks can be found in this thread:
Maksutov & SCT insulative dewsheild (http://www.iceinspace.com.au/forum/showthread.php?t=172245)
This wrap-come-dewshield however won't stop dew from forming on the corrector. It will extend the dew-free period, but dew will still form if conditions are right. While the ideal solution would be to have the scope set up in a dew-free environment (like my dark sky site), most times an ideal location is not possible, and we need to work with dew and try to mitigate it (like my backyard - blooming Dew Central).
The heat-free solution - a FAN
I've been working with fans with my truss dobs also for several years. I've also worked out a way to keep my dobs dew free using fans too. But I've struggled to work out how to be able to implement fans with my SCT and Mak.
The solution came thanks to the material I use for the wraps I make for my scopes now, Coreflute.
Coreflute allowed me to cut a suitable flap in the dewshield section to accommodate a 40mm 12V fan. The flap is important here as it allows the fan to be placed at an angle so that it generates a vortex inside the dewshield. This whirlwind of air helps keep the corrector dry, or if dew has started to form, then to dry off the corrector.
I also connected the fan to a small PWM unit so to vary the rpm's. If dew is light, then I can drop the revs. If dew is heavy, I can increase the revs.
Proof of concept was done over a few nights - one of the benefits of the persistent cloud cover of late is it gave me the time in the field. I had the scope wrapped in two configurations, one as an all of scope wrap, and the other as a partial, more conventional corrector only dewshield (though thermally not an insulating design as the OTA is left exposed). I left the scope pointing up and waited for dew to form - with this 9" Mak, that took between two and four hours on the nights dew did form. With dew beginning for form, I turned on the fan, and PRESTO! The dew dried up and stayed away!
The position of the fan in front of the corrector is important. You don't want to place it too close to the corrector lest a cold spot is generated across the corrector which will put strain on the glass and distort it enough to stuff the image. I place my fan no less than 100mm in front of the corrector.
The choice of 12V was obviously to do with what is normally used with astro gear. I also added a DC power socket to the fan to make the connection to the PWM unit a cinch.
This wrap-dewshield-fan arrangement is an easy enough DIY project. Care needs to be taken when cutting the Coreflute to make the length-long slits and the flap for the fan - it's easy to accidentally make the flap too large for the fan, or make a dog's breakfast in making it too small and needing to widen it. By making this flap for the fan, the flap helps hold the fan in place, and if you don't need the fan the flap closes up the dewshield again.
No heat, no optical distortions, no dew and less power. Blooming brilliant! :D
Thanks for reading,
Alex.
I've been working on this for a very long time - trying to keep my SCT's and Maks dew free over the course of a night. And one thing I HATE is needing to use heat - we fret so much trying to remove or control heat from our scopes, and then we go and stick heat sources to dry it up. Not exactly logical... :question:
The starting point
As many of you may be aware I've been actively espousing the benefit of insulating our SCT's and Maks instead of waiting for them to cool. By insulating the OTA there is no heat differential created between the cold tube and the warm primary and baffle tube, so no heat plume can be generated as the air inside the OTA stays warm. With no heat plume in the OTA, you can rip high magnification from the scope from the very start, and not need to wait for the scope to reach ambient temperature. And with big SCTs and Maks, this can be several hours.
I've been wrapping my SCT's and Maks for several years now, and I have not waited for any cooling period in all this time. Instead, I set up my scope when I find I have the time (limited as it is), and get to work with sketching straight away. No heat plume, and 300X, 400X as I find best suits seeing conditions.
257534 , 257535
More info on insulating SCT's and Maks can be found in this thread:
Maksutov & SCT insulative dewsheild (http://www.iceinspace.com.au/forum/showthread.php?t=172245)
This wrap-come-dewshield however won't stop dew from forming on the corrector. It will extend the dew-free period, but dew will still form if conditions are right. While the ideal solution would be to have the scope set up in a dew-free environment (like my dark sky site), most times an ideal location is not possible, and we need to work with dew and try to mitigate it (like my backyard - blooming Dew Central).
The heat-free solution - a FAN
I've been working with fans with my truss dobs also for several years. I've also worked out a way to keep my dobs dew free using fans too. But I've struggled to work out how to be able to implement fans with my SCT and Mak.
The solution came thanks to the material I use for the wraps I make for my scopes now, Coreflute.
Coreflute allowed me to cut a suitable flap in the dewshield section to accommodate a 40mm 12V fan. The flap is important here as it allows the fan to be placed at an angle so that it generates a vortex inside the dewshield. This whirlwind of air helps keep the corrector dry, or if dew has started to form, then to dry off the corrector.
I also connected the fan to a small PWM unit so to vary the rpm's. If dew is light, then I can drop the revs. If dew is heavy, I can increase the revs.
Proof of concept was done over a few nights - one of the benefits of the persistent cloud cover of late is it gave me the time in the field. I had the scope wrapped in two configurations, one as an all of scope wrap, and the other as a partial, more conventional corrector only dewshield (though thermally not an insulating design as the OTA is left exposed). I left the scope pointing up and waited for dew to form - with this 9" Mak, that took between two and four hours on the nights dew did form. With dew beginning for form, I turned on the fan, and PRESTO! The dew dried up and stayed away!
The position of the fan in front of the corrector is important. You don't want to place it too close to the corrector lest a cold spot is generated across the corrector which will put strain on the glass and distort it enough to stuff the image. I place my fan no less than 100mm in front of the corrector.
The choice of 12V was obviously to do with what is normally used with astro gear. I also added a DC power socket to the fan to make the connection to the PWM unit a cinch.
This wrap-dewshield-fan arrangement is an easy enough DIY project. Care needs to be taken when cutting the Coreflute to make the length-long slits and the flap for the fan - it's easy to accidentally make the flap too large for the fan, or make a dog's breakfast in making it too small and needing to widen it. By making this flap for the fan, the flap helps hold the fan in place, and if you don't need the fan the flap closes up the dewshield again.
No heat, no optical distortions, no dew and less power. Blooming brilliant! :D
Thanks for reading,
Alex.