Jump to content

Banner.jpg.b83b14cd4142fe10848741bb2a14c66b.jpg

The effects of dew

MartinB

By MartinB
in Imaging - Deep Sky

Recommended Posts

MartinB

MartinB

Posted
Posted

The QHY8 needs careful handling otherwise it ices up. This happened to me recently leaving a load of dew spots which had this effect

moz-screenshot.jpg

9933_normal.jpeg

(click to enlarge)

Fortunately I've now given the chip a good fettle with isopropyl alcohol and it is as good as new :)

Link to comment
Share on other sites
MartinB

MartinB

Posted
  • Author
Posted

I am delighted that the sensor clean has worked, Martin. Do you use a dew strip on the nosepiece of the camera? This resolves the issue with this camera.

I don't Steve but it doesn't resolve the issue on a QHY8. The problem is that chip isn't sealed, unlike an M25. It relies on it's nosepiece which houses an IR cut filter. Everything is fine until you take the nose piece off whilst the camera is on or if the camera is run pointing downwards for any length of time, then the ice forms. That's one reason why an SXV M25 costs more than a QHY8!

Link to comment
Share on other sites
Dave Sexton

Dave Sexton

Posted
Posted

Martin,

When I first got my QHY8, I had a very similar problem. Initially, the optical window was dewing up. To resolve this I removed the window, but then the sensor frosted. Eventually, I installed a dew heater around the the optical window (see photo below). Dewing is a particular problem on the QHY8 when used with Newtonian telescopes where the camera is often pointing towards the ground. When this happens, chilled air form around the cooled sensor falls onto the optical window which is in contact with ambient air on the other side. Dewing is inevitable. Anyway, glad the clean worked.

Dave

9938_normal.jpeg

(click to enlarge)

Link to comment
Share on other sites
MartinB

MartinB

Posted
  • Author
Posted

Steve, the problem wasn't around the I/R cut filter which Dave's dew strap will prevent if the scope has to be used pointing downwards, it was caused by icing of the chip which a dew strap wont prevent. Most of my use of the QHY8 has been with refractors so the nosepiece filter hasn't been a problem but now I am going to be using it with a newt it probably will be.

What sort of dew heater is that Dave. Would certainly like to get sorted with something like that

Link to comment
Share on other sites
Dave Sexton

Dave Sexton

Posted
Posted

Martin,

Having had a fit in the middle of the night over my sensor frosting over, I was disparate to test the camera with a dew strip. So, I purchased an Astro Engineering Small Telescope Dew Removal System (AC369). It did the job, but I wish I had been more patient and purchased something more suitable as I also need to heat my guide scope. This is not a “glamorous” thing to spend cash on, so I am going to opt for something inexpensive like a Dew-Not two channel controller with heater strips.

By the way, my sensor only frosted over when I removed the optical window. The space between the windows and the sensor is critical, adjust it and the sensor frosts.

Dave

Link to comment
Share on other sites
MartinB

MartinB

Posted
  • Author
Posted

I have a Gerd Neuman filter drawer. I have had thoughts of ftting an unhoused IR cut filter on the camera side of this and getting rid of the nose piece. I would have to fit this to make the unit air tight. There is a guy in Finland who is doing this and not having problem. The benefit is potentially to reducing the optical path, however, with your comment in mind I might just leave it as it is.

The thing about your dew heater is that it looks very low profile. I can't fit a dewnot strap between the camera and the filter drawer. Can you post a link to your system Dave? Also, do you have any tips to avoid dew on the secondary?

Link to comment
Share on other sites
centroid

centroid

Posted
Posted

Seems like a very basic engineering design oversight by the QHY8 manufacturer to me, and being a well known problem, one they should have sorted by now, but then perhaps they have???.

If not then they really need to do so.

Dave

Link to comment
Share on other sites
FLO

FLO

Posted
Posted

An extra 1500 quid for a sealed nozzle? Yikes! :)

The belief that a QHY8 is simply a SXVF MX25 in a cheap case is wishful thinking. The choice, quality and positioning of components used in the Starlight are all in a different league.

To be fair, the QHY8 is significantly cheaper so it can be forgiven :)

Link to comment
Share on other sites
Tim

Tim

Posted
Posted

Yep, I was being, whats the word.....

I'm sure the price reflects the limited market they appeal to, but I still think all the big CCD cameras are priced out of the largest portion of the market. The day will come I am sure when they are much more affordable, when the current technology is old hat.

Just hope I'm not too senile by then to remember how to use it :)

TJ

Link to comment
Share on other sites
MartinB

MartinB

Posted
  • Author
Posted

That's one reason why an SXV M25 costs more than a QHY8!

An extra 1500 quid for a sealed nozzle? Yikes! :)

Have you had a chance to try the GSO yet Martin? I'm picking mine up this week.

This thread here

http://stargazerslounge.com/index.php/topic,32365.0.html

Actually had another night on M33 but this was a disaster and led to all my dew mark problems. The jist is, don't try to operate a QHY8 without the nose piece even if you think the resulting assembly is airtight.

What I have seen of the GSO so far has been impressive. The Iris image in the above thread was less than 1 hour through some horrible high cloud. The Baader Steeltrack focusser is very precise (I prefer it to the WO 2 speeds) It collimated very easily and the FWHM were impressive - 1.4 on the night in question. The spacing wasn't right for the iris image but it is now and the subs I got of M33 were flat right out to the edge with the QHY8. So, very fast, flat, decent optics and very very reasonably priced.

Link to comment
Share on other sites
Ford Prefect

Ford Prefect

Posted
Posted

Hi martin

I had a similar issue with my QHY8 chip freezing up (accidentally unscrewed noisepiece when removing from the hyperstar) :):D

I seem to have a dried residue on the chip, can you let me know how exactly you had a "good fettle with isopropyl alcohol".

Touching the chip with anything scare me senseless :)

Cheers Jon

Link to comment
Share on other sites
MartinB

MartinB

Posted
  • Author
Posted

Sorry Steve, yes, using the Baader MPCC.

Jon, just used some 70% isopropyl alcohol from the local chemist. You aren't touching the chip, just the glass cover. Dampen a lens cloth with the alchohol and give a good rub. Works best if the cloth is nearly dry. Well that's what I use but don't hold me responsible if you camera never works again!

Link to comment
Share on other sites
  • 7 years later...
Guest

Guest

Posted
Posted

I haven't had any problems with my QHY8 frosting up - keeping it in an air tight case as suggested by Bern at Modern Astronomy.

I've never used a dew strap with it to image.

Once - a long time ago now I thought I'd remove the nose piece and run with just the LP filter (as it cuts IR anyway) 

The chip frosted up - but then cleared as the night progressed (at Kelling in 13' I think)

Then, the other day, I thought I'd try it without the nose piece in place and got it ready for the next clear night.

Last night was very clear - I had imaged the California Nebula with my AltAir 115 and was now going to capture it widefield with my TS65

Got everything running - first test shot (taken while guiding was calibrating) came down the pipeline and this is what I got for my experimentation (see below)

So everything said here is spot on, leave the nose piece in place, keep the desiccant tube attached and keep it in an air tight box  - no dew (with a refractor at least)

David

QHY8%252520FOD.PNG

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.