SCT Dew Shield, Heater - or both ?

[Akiainavas]

Hi guys,

Just some quick opinion gathering.

For an SCT scope do you think a dew shield is necessary if the scope is already equipped with a dew heater band ?

Are there any additional advantages to adding the shield, apart from stray light protection ?

Technicalities aside - from your personal experience, do you feel that it's really necessary for a scope with heated corrector plate to have a shield attached to it ?

[faulksy]

6 minutes ago, Akiainavas said:

Hi guys,

Just some quick opinion gathering.

For an SCT scope do you think a dew shield is necessary if the scope is already equipped with a dew heater band ?

Are there any additional advantages to adding the shield, apart from stray light protection ?

Technicalities aside - from your personal experience, do you feel that it's really necessary for a scope with heated corrector plate to have a shield attached to it ?

in my opinion i think both heater and shield together is better. why you ask, if you have both you can keep the heater on a lower heat setting (less thermal currents in the optical path) and you power supply will last longer. you allready point out the advantage of the shield ,less external light

[PeterCPC]

Astrozap make a combined dew shield and heater. https://www.firstlightoptics.com/dew-prevention/astrozap-flexi-heat-dew-shields.html

Peter

[Akiainavas]

3 minutes ago, faulksy said:

if you have both you can keep the heater on a lower heat setting (less thermal currents in the optical path) and you power supply will last longer.

Excellent point, thanks. That's the sort of thing I was looking for.

[baggywrinkle]

I have the combined heater & shield, great product.

I did try separate to begin with but the shield never fitted snuggly enough over the dew heater for my liking, it was always wonky.

[psamathe]

1 hour ago, baggywrinkle said:

...

I did try separate to begin with but the shield never fitted snuggly enough over the dew heater for my liking, it was always wonky.

I used to fit shield over heater (with the fitting issues) but was then told (by somebody with loads of experience) that the normal way is to fit the heater on the outside of the shield.

Ian

[michael.h.f.wilkinson]

I usually use only the dew shield to save battery, and because even in my fairly damp garden (to avoid words like wet), it is sufficient. Only when there is a huge amount of dew do I attach and switch on the heater. I also find the shield improves balance of the scope with heavy EPs in the diagonal

[cjdawson]

2 hours ago, Akiainavas said:

Hi guys,

Just some quick opinion gathering.

For an SCT scope do you think a dew shield is necessary if the scope is already equipped with a dew heater band ?

Are there any additional advantages to adding the shield, apart from stray light protection ?

Technicalities aside - from your personal experience, do you feel that it's really necessary for a scope with heated corrector plate to have a shield attached to it ?

As others have said.  Both is best.

With the shield on, it cuts down stray light and you can run the heater at a much lower setting.

I'd also add that even though a dew sheild is light, hanging it off the front of the scope helps to balance up against the weight of a DSLR hanging off the back.   The shield might seem lighter, but the mechanics makes it contribute more due to the leverage.   You still need balance weights, but you might be able use less weight overall.

[Stu]

As Michael said, if I had to chose one I would go for shield first for the reasons mentioned ie glare reduction, balance and dew prevention. If still struggling, then use the heater.

I have the combined shield and heater, it just makes life that bit simpler. If using separates I would think the heater needs to go next to the scope as the shield is probably quite a good heat insulated?

[baggywrinkle]

1 hour ago, psamathe said:

I used to fit shield over heater (with the fitting issues) but was then told (by somebody with loads of experience) that the normal way is to fit the heater on the outside of the shield.

Ian

I would have thought that unless you had the heater on full then the shield would prevent it working...but you never know

[BGazing]

depends on your local humidity. i always have to use both.

i also found, the hard way, that separate shield and dew strip are better, as otherwise i am unable to position the dew strip where it should be (behind the corrector plate casting, directly on the ota) and the heating band in the combined version both heats less efficiently and leaks heat into the shielded area when the heat is cranked up.

[psamathe]

3 hours ago, BGazing said:

....i also found, the hard way, that separate shield and dew strip are better, as otherwise i am unable to position the dew strip where it should be (behind the corrector plate casting, directly on the ota) and the heating band in the combined version both heats less efficiently and leaks heat into the shielded area when the heat is cranked up.

I have seen others with heater strip directly behind the plastic front end of the SCT (heater strip running under dovetail.  Struck me as a good place as it can be left fitted so less likely to suffer damage from being fitted, removed, wrapped-up, bent a bit more, stored, etc.  Never tried it.

Being a novice, is this the best place to use the heater band on an SCT as I never tried it as I thought the plastic could insulate the corrector plate from getting any heat and the heat is going to warm the tube away from the corrector plate as much (or more) than where you actually want the heat.

Ian

[BGazing]

28 minutes ago, psamathe said:

I have seen others with heater strip directly behind the plastic front end of the SCT (heater strip running under dovetail.  Struck me as a good place as it can be left fitted so less likely to suffer damage from being fitted, removed, wrapped-up, bent a bit more, stored, etc.  Never tried it.

Being a novice, is this the best place to use the heater band on an SCT as I never tried it as I thought the plastic could insulate the corrector plate from getting any heat and the heat is going to warm the tube away from the corrector plate as much (or more) than where you actually want the heat.

Ian

I really cannot claim to be an expert on this topic, but those are my experiences. Pretty much every recommendation I saw for the dew strip placement from the manufacturers was for the strip to be just behind the plastic casting bit. Plastic is, of course, not nearly as good a heat conductor as aluminium. 

When I realized how strange the design is in the flesh, I emailed Astrozap to inquire about it. Automatic message informed me that they are at vacation, but I am not holding my breath for any reply.

Also, having separate strip and shield is handy when it comes to colimation. If they are a single unit, it is pretty difficult to fiddle with the knobs down there without removing the shield, and once you remove it...it does not take long for the dew to form...and colimation has to be done patiently.