Question on dew heaters and EAF

[Adam1234]

Hi, so as luck would have it, despite the weather forecasts saying otherwise, I have a clear night tonight so I'm extending my test of my new ZWO EAF and getting some G and B data to go with the R that I got last night on the Crescent Nebula.

A couple thoughts occured to me just now about the EAF and also the use of dew heaters.

ZWO EAF

 So last night and tonight I have focused automatically with the EAF using the automatic focusing routine in APT based on FWHM, and it took probably less than a minute or thereabouts. Could be a silly question, but I just wondered though how accurate the EAF is on it's own and whether you should just run the routine once, or twice to make sure and also check with a bahtinov mask? I mean the stars look great in my opinion for sure, probably much better than I've got focusing by hand and using bahtinov aid, but I did check the focus with the bahtinov and it was slightly off (according to bahtinov), but it did make me wonder. As I said though, at the moment the stars look great, and I will post the image up once done (in fact I posted just the R data last night in the Deep Sky Imaging section)

Dew Heaters 

I recently bought some dew heaters as well, for main and guide scope, and the HiTec Astro 4 port dew controller, I just wondered

- When the best time to power them on is

- And what setting to use on the controller, - low/midway/high etc)

I.e. power on when setting up before focusing even if temperature hasn't yet reached dew point? Or wait until the temperature is beginning to approach the dew point, or when it has reached the dew point? Which also begs the question, how do I know what the dew point is? I was also going to ask how I know when the temperature is getting near the dew point but then realised that may be a silly question as I have the temperature probe with the EAF so can measure the temperature.

 

Thanks

Adam

[Adreneline]

1 hour ago, Adam1234 said:

I just wondered though how accurate the EAF is on it's own

Hi Adam.

I have owned and used an EAF now for over a year in combination with a belt drive to either a Samyang 135mm of Canon 200mm. The unit itself is amazing and I am delighted with the way it performs with an ASIair. In terms of repeatability it works perfectly with my 135mm because I have glued a toothed belt to the outside of the lens so there is no 'creep' or 'procession'; I've not taken that step with my Canon lens so repeatability is not great.

After the best part of three years doing battle with autofocus in various programs I have given up and am a total convert to the BM and manually focussing between filter changes and rarely checking during imaging with a given filter (like tonight when I am hoping to get 40 SII images over three hours and will probably pause image collection and check the focus half way through). I should qualify my conversion to the BM approach by saying that using the ASIair interface on an iPad lets you use the 'zoom' feature on the iPad screen which makes it very easy to interpret the BM interference pattern.

I pre-process in APP which gives an FWHM value for each frame - I typically achieve 1.3 - 1.8 whereas I used to be lucky to get below 2.5 prior to using a BM and adopting a manual approach to focussing.

HTH

Adrian

[Adam1234]

1 hour ago, Adreneline said:

Hi Adam.

I have owned and used an EAF now for over a year in combination with a belt drive to either a Samyang 135mm of Canon 200mm. The unit itself is amazing and I am delighted with the way it performs with an ASIair. In terms of repeatability it works perfectly with my 135mm because I have glued a toothed belt to the outside of the lens so there is no 'creep' or 'procession'; I've not taken that step with my Canon lens so repeatability is not great.

After the best part of three years doing battle with autofocus in various programs I have given up and am a total convert to the BM and manually focussing between filter changes and rarely checking during imaging with a given filter (like tonight when I am hoping to get 40 SII images over three hours and will probably pause image collection and check the focus half way through). I should qualify my conversion to the BM approach by saying that using the ASIair interface on an iPad lets you use the 'zoom' feature on the iPad screen which makes it very easy to interpret the BM interference pattern.

I pre-process in APP which gives an FWHM value for each frame - I typically achieve 1.3 - 1.8 whereas I used to be lucky to get below 2.5 prior to using a BM and adopting a manual approach to focussing.

HTH

Adrian

Thanks Adrian. After just looking through the Ha subs I've just taken, I think I might go the route of manually focusing using the EAF and a bahtinvov mask too rather than use the auto focus aid - whilst my R, G and B looked ok, my Ha is definitely out of focus! 

[Viktiste]

2 hours ago, Adam1234 said:

Dew Heaters 

I recently bought some dew heaters as well, for main and guide scope, and the HiTec Astro 4 port dew controller, I just wondered

- When the best time to power them on is

- And what setting to use on the controller, - low/midway/high etc)

I never really understood the need for a dew heater controller. I just made a very plain nichrome wire wrapped in duct tape supplying a constant 4 watts of heat to the lens (if I remember correctly).  It feels cold to the touch but it is enough to stop any dew (so far).

So I would say the best time to turn it on is from the start. 

[Seelive]

I also use homemade dew bands with a homemade controller (the commercial ones seem vastly overpriced for what they are). Normally the controls are set between 30% and 50% but there have been a few very damp nights when it's been necessary to wind them up to 100%. OK, I suppose I could leave it at 100% all the time, but to me it just doesn't seem right unnecessarily heating up the lens beyond what's actually required.

[Adam1234]

Bit late for me to make a home made dew heater now, will be a waste of money if I don't use the ones I've bought 😂 30 -50% sounds good though, I'll try that out to start and increase if necessary.

Cheers

[ollypenrice]

You're trying to warm, very slightly, the glass of the objective or corrector. This has quite a high thermal mass and you can only heat it from around the edge so it is best, in my view, to heat it from the outset. I've used both 'full power only' and variable dew heaters and never found any difference, really. It's more important for battery powered systems.

Olly

[Adam1234]

Thanks Olly