Is this problem not the reason why scopes such as my Edge HD Celestron have tube vents
They can work remarkably well, with the addition of fans (I added the TEMPest units).
I typically switch them on when I setup the scope and depending on the conditions, often leave them running through the night.
Brisbane is notoriously humid in summer but because of the lack of huge temperature swings, I don’t use a dew heater in summer. In “winter”, which is usually dry, it works out more risky because the temperature drops can be quite rapid, especially just after dark.
You might need to keep your wits about you in the UK, as if there is a lot of moisture in the air the fans can draw it inside the tube...one cool winter evening when I lived in Sydney, I had the corrective dew up on the INSIDE
Anyhow, who wouldn’t love a good Mak?! I wouldn’t say no, but (at risk of being on topic) I think they’re more of a visual pleaser. I don’t remember seeing any great planetary images with a Mak. Sure, plenty of images out there with a SW 127, but with telescopes we’re always caught by The Fever, and a big SCT or new (or <insert design here> ) is always going to capture the imagination more than a 6 or 7” Mak...rightly or wrongly.
This solution follows the conventional thinking around forcing scopes to cool. And while in principle it works, it is not necessarily best practice, but as a selling point it is excellent because this is what people know and expect. It still requires a waiting time and constant monitoring.
Yet the insulation route is totally passive.
Dew formation is a separate matter though. All scopes are susceptible to it, thought needs to go into it, and designed specifically for each scope type, though the principles followed are the same.
As for dealing with dew, one has three options: 1, heating strap around the corrector -not my favourite as you want the scope to cool (slowly or quickly) and then a heat source is re-introduced around an active lens element: 2, rig up a blower system that will evaporate dew, either heated (care needed), or at ambient temp: 3, set up scope at a dew-free location - dew and astro ARE NOT inseparable bed fellows. The dark site location my observing buddies and I use, we are still to experience a night of any dew on our optics in now more than 7 years, a on all types of scopes, Maks included. All about site selection and time into these investigations. Dew-free astro is possible.
One thing I don't want to do is create the impression that I'm saying Maks are the perfect scope. They are not, in the same way no particular scope design is. Maks fill a niche and it is up to the individual to figure out if a Mak satisfies a particular requirement they have. I have some 14 scopes, of these only one Mak, and I still have an SCT as IT fills a niche for me with outreach. And yes Dunk, I do agree with practices being equally important to extract the very best from whatever scope one is using, both photo and visual.
Alex.
Then why do all Sc and MC scopes not have such vents or insulation
Would you say that these scopes are best suited to Summertime (or, at least warmer climate) viewing?
Hard to tell. All locations are different.
When your thick Mac corrector lens departs by more that a couple of degrees from ambient temperature, it will have a flowing proximity layer on the front surface no matter how well the tube is insulated. If the tube is metallic and not insulated, then you will have a similar boundary layer on the back surface of the corrector as well. And one on the primary too.
Would you say that these scopes are best suited to Summertime (or, at least warmer climate) viewing?
Aaron seeing isn’t seasonal - but the prevailing wind direction and the terrain upwind of your observing site will influence it. Some sites simply won’t be much good while others can be good, often.
IMHO there are three factors - transparency, seeing, and what’s up high. At a dark sky site, if the transparency is good but the seeing isn’t, just stick to low power and enjoy the DSOs.
When the seeing is very good, enjoy. But remember there’s no point in high magnificent on objects lower than 60 degreeed above the horizon.
Aaron seeing isn’t seasonal - but the prevailing wind direction and the terrain upwind of your observing site will influence it. Some sites simply won’t be much good while others can be good, often.
IMHO there are three factors - transparency, seeing, and what’s up high. At a dark sky site, if the transparency is good but the seeing isn’t, just stick to low power and enjoy the DSOs.
When the seeing is very good, enjoy. But remember there’s no point in high magnificent on objects lower than 60 degreeed above the horizon.
Last night I was out with my GSO 8 inch classic cassegrain. Dewing was quite heavy. The tube was almost dripping, but at no time was i bothered by it. I gave up on SCTs because of that problem. Was checking a few doubles around Crux. Beautiful intense diffraction patterns. If you have the bank balance, go the Santel, Intes, Tak way if you can, but i am happy with this scope. There is no magic between different types of scope, it's mostly about optical quality.
