Advice on Dew and Dew heaters ?

[jabba]

Hi , i've purchased a Celestron - Maksutov-Cassegrain telescope and have been reading about problems with dew. I've not been able to get out with it yet , but would like to be prepared for when i do.

Will i need a dew shield with this scope ?

Will a dew heater be a good investment ?

Any other tips for a first night out appreciated , like best time of night to get out and what times of year dew is the biggest problem?

[Wizz]

Dew is always a problem, yes a dew shield will help as will a dew controller and dew strap. You will need a powertank of somekind to run the dew controller.

As for when are the best times to go out, don't forget your in the UK so anytime you get the chance is a bonus!!

[barkis]

Hi Jabba, have a look here. Read through the thread, and PM Blinky If you are interested.

http://stargazerslounge.com/retailers-product-showcase/68508-blinkys-dew-controllers-bands.html

Ron.

[brianb]

Will i need a dew shield with this scope ?

Will a dew heater be a good investment ?

Any other tips for a first night out appreciated , like best time of night to get out and what times of year dew is the biggest problem?

Yes. It ought to be a criminal offence to sell a catadioptric scope without at least a dew cap....

If you want to be able to observe for several hours at a time, and don't live in a desert, an active system (controller, heater strip & high capacity battery to drive it) will be a good investment.

Best time of night is any time it's clear (still leaves plenty of time for sleeping etc. when cloudy) & dew can be awful, moderate or slight at any time of the year. Two consecutive nights last week, both -7C to -8C, one the scope was covered in 1-2mm of hoar frost (frozen dew) everywhere except next to the dew heater strips & I still had to clear the corrector plate (12V hair dryer) a couple of times, the other the scope was bone dry at the end of the night.

[Demonperformer]

I have used my SCT with nothing more than a cardboard tube which extends 20cm beyond the end of the OTA and have never had any dewing problems with it. Have recently strengthened it with rubber exercise mat, but spending a fortune is not necessary.

[alfingido]

I have used my SCT with nothing more than a cardboard tube which extends 20cm beyond the end of the OTA and have never had any dewing problems with it. Have recently strengthened it with rubber exercise mat, but spending a fortune is not necessary.

Were not all as lucky as this, I had a 50cm dewshield on the end of my 9.25 sct and the corrector dewed up within half an hour a couple of weeks ago!

I just bought a Kendrick dew controller and am waiting for my dew heater strips to arrive. I will use them with the dewshield.

Dew is less of a problem on a windy day but I reckon dew formation is worse between September and August.

Allan

[adamsp123]

Hi Jabba, have a look here. Read through the thread, and PM Blinky If you are interested.

http://stargazerslounge.com/retailers-product-showcase/68508-blinkys-dew-controllers-bands.html

Ron.

I got these as well, they are excellent value, simple to use and work fine.

[jabba]

Thanks guys , great help. Any pics anywhere of home made dew sheilds ? I have some old camping mats kicking around somewhere , red in colour i think ? any good to me ?

[brianb]

I have some old camping mats kicking around somewhere , red in colour i think ? any good to me ?

The material is just about ideal, far better than the vinyl sheet used by commercial dew shields.

Measure the diameter of the outside of the OTA, multiply it by 3.14, form a tube using that much of the mat (cut off a bit more to allow for an overlap), stick it up with duck tape. Job done.

The material is slightly stretchy so marginally (a millimetre or so) undersize is good.

For the full monty, spray paint the inside flat black, or line with black felt leaving a couple of inches at one end clear where it pushes on to the OTA.

[Macavity]

OK then, HERE is a picture of the intermediate stage!

Basically, I used a stanley knife to cut the MAT as accurately as possible. I then secured the join, initially with paper masking tape (as in the picture!). When happy, I applied super-sticky Duct tape along the length of the join and trimmed off the excess masking tape. As noted above, if you make things slighty undersize, the camper mat stretches over the OTA to fit! The finished thing can anyway be fastened on with one of those slightly-stretchy, strap-things with plastic buckle and velcro closure. Or, if you know someone who wears stockings...

[jabba]

Ahh ha ! Just the job , thanks , i'll get on that

[Sparrow]

You could always make your own dew heater controller and band. I did last year to great effect and cheaper than anything I've seen for sale. I started from scratch learning about wiring diagrams and how to create a circuit board - not as hard as you think with the wealth of information available on the internet. The wiring diagrams can also be found. It worked brilliantly on my Schmidt and kept the dew at bay even on the dampest of nights.

If you're interested, pm me and I'll hunt out the links for the wiring diagram.

Regards

John

[Talitha]

To hold a dew shield to the end of the OTA a bit more securely, get a strip of wide waistband elastic from a yard goods store. Sew it into a circle and use it like a big rubberband. Works great on my 8" SCT.