[mental4astro (Alexander)]

Glen, I completely agree that a closed rear cell with the fan pulling air down out of the scope instead of the blowing onto the rear of the primary is an excellent solution. It was an oversight of mine not to have included that solution in the article. Thank you for bringing it up! If you notice, the article deals with open rear cells. I had used a pulling system on one scope many years ago, and had forgotten about it. Ta for jogging my memory.

Fans pulling air will have a distinctly different affect. While there will be an initial temperature differential in the mirror when the fans are first turned on, I do have to agree that this is a much gentler way of cooling and the mirror will respond differently. A closed rear cell allows for air to be pulled around the mirror from the front of the scope. The air flow is distributed over a large area rather than concentrated on one spot as blowing onto the mirror, particularly if the cell is an open one. You will not get any disagreement from me here. The differential does also occur, but over time it is eliminated. If this is how Planewave uses its fans, then that is a completely different way of doing so from what the article deals with. Faster? Maybe. And if it does, I have no problem with it. I am grateful that the article has started some debate on the matter. If from the debate everyone, including me, learn something new from our peers, then the article has played its role. From some of the posts already made I've found ways to improve the article too.

The added bonus of a closed cell pulling system is that you also get the air flow benefit to controlling dew.

The 'cuff' is mentioned I guess you can call a dewshield, same way Glen describes the 'cuff' he mentioned.. Come to think of it, it really is a dewshield. This was not meant to be fancy but a simple confusion on my part thinking a dewshield was put over an objective lens or corrector plate. James, I agree that dew does not fall from the sky like rain. The cuff, or dewshield, that I put around my mirror boxes can end up soaked, outside an in. But the primary mirror is dry. Temperature difference between outside the mirror box to the outside? I doubt it after an 8 hour session. Water is attracted to water due to its molecular shape, so if the dewshield is wet, dew will gather more readily on where there is water already. This shelters the primary from dew forming.

Using a hairdryer is offered as one solution. If you have caused a corrector plate to crack after using one, then it dryer was set too hot, placed too close, or for too long a period, or the ambient temperature is very cold. I also don't experience frost where I use my C8, so the scope is never exceptionally cold. Common sense needs to play a part in this. I will ask for an amendment to be made to the article about this. Thanks for suggestion.