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Jumping into the bold, new world of SCT's- questions


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After much debilitation over a SW 180 mak cass or a larger aperture scope for planetary imaging and general observing, an opportunity presented itself that I couldn't pass up.

I will soon to be a proud new owner of a preowned but newer model Meade 10" ACF F10 OTA that was well taken care of.  Comes with Bob's Knobs, brand new WO DDG SCT focuser and Meade focal reducer 

I live at 53 degrees north, how long am I looking at cooling times here in Alberta, Canada from room temperature to outside before collimating on a bright star?  An hour? Any decent way to mitigate this?  Or do I set the mount and table, and OTA with the back open and pull out the binos for awhile and hope I dont cloud over?

Is a heated dew shield an absolute must?  I will be purchasing the Astrozap pebble finish blue dew shield initially, but am I pretty much in a scenario where once it finally cools down to use, the corrector will start dewing without a heated one?

Also, any recommendations on better EP's for widest FOV without vignetting with a reducer on?

 Price being a concern,  I was thinking explore scientific 82 degrees or if that is too much FOV, TV Panoptics @ 68 degrees. I would like to fully frame the double cluster and Orion nebula, but take out the reducer and throw in  a barlow for planetary viewing.

The 13mm nagler I have is very impressive in this regard with previous scopes for wide field viewing and then bumping the magnification high for planetary, but it is my only good ep.  My 25mm and 32mm, 7.5,mm and 10mm are Orion's  standard or highlight plossls

Thanks in advance

 

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Hi Tyson -

I certainly hope you're far away from that monster wildfire that's burning entire towns up in Alberta!

Congratulations on your 10" ACF SCT. It should take at least an hour to reach ambient temperature if it's stored indoors in a heated area. Less if in an un-heated shed or garage.

SCT's tend to be quite forgiving on the eyepieces you feed them. As for dew-heaters, if you have high humidity, you may need one. Here at 44.29N I just use an AstroZap Dew-Shield. No heater required. But see if you need one by trying without.

As for non-vignetting EP's with a Focal-Reducer, I haven't tried out mine yet. So someone should come along and give us both the low-down on this.

Enjoy!

Dave

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Don't own a SCT scope, but I keep my three  most used scopes in a cooler room in the house. This reduces the time for my 6 inch Newtonian to cool down. My fracs are normally ready to go straight away, with hardly any cool down time required once outside. It may not be suitable for everyone to do, but even in wintertime I keep the heating off in this room too, except when it may get exceptionally cold. 

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I wouldn't use a reducer for visual. You will reach the limits of the baffle tube with a widefeild 2 inch and no reducer.

Dew heater, almost certainly 'yes.' The slightest humidity fogs up an SCT but a camping mat dewshield helps.

You can cool them by leaving the back open, pointing them downwards and letting the hot air rise out, but keep the insects out! You can also try the other approach, insulating them, to slow down the cooling. It is the temperature gradient which is the problem. This is a popular approach in Europe.

Olly

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First piece of advice would be to dump the focal reducer. They reduce the focal length but have a restricted field size. You are much better off using a longer focal length 2" eyepiece for low power. The actual widest field you can obtain will depend on the size of the baffle tube - I don't know what that is for a Meade but with my C9.25 it allows me to use a 42mm 72° eyepiece.

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I have only got a 8" SCT & heated dew shield is a must. I have even had the

primary mirror misting up , with the heated dew shield going full blast. :happy9:

Edited by Grotemobile
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Best use the SCT for what it's good at perhaps ?

For wide field / low power viewing it's often less expensive and more effective to have another scope. SCT's are just not wide field scopes.

 

 

 

 

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Cooling:

Much depending on temperature differences between observing place and storing place, m 8" took 1 hour or so, better still after 2 hours cooling in windter, when moving from inside house. Some store the scope in unheated garage, which shortens the time considerably. Others add cooling fan(s), which is also helpful.

Dew heater tape:

It denpends on humidity. I can get away with on simple dew shield when humidity is under 60% in winter when it's -10°C, otherwise it's a must.

EPs:

Sicne your're getting the reducer with the scope, your 32mm should give you very close to maximum unvignetted FOV. Try to use those EYPs for a while, find out which are your most used ones, then decide the upgrades. As others have already mentioned, I think 2" EPs are better way for lower observing, epspecially when you feel the need a true wide scope, a small Apo/ED refractor.

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I am convinced that the last hose pipe ban here was caused by my 9.25" SCT corrector plate. As for reducers, not an item for visual and even for imaging they create significant vignetting. The widest field of view I can enjoy is with either my 40mm Celestron Omni or my 24mm ES 82'.

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Although your ACF is not a wide field telescope, it's worth working out which eyepieces will give you widest views as the coma free optics are designed to give you clear stars right to the edge.  

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It seems you got good answers to your questions so i got something else to comment on.

The focal reducer/coma corrector you have isn't suited for your scope, it's made for a Schmidt Cassegrain and your scope is Advanced Coma Free (Ritchey Cretien) which doesn't have coma. Therefore it will introduce optical abberations instead of fixing coma.

Meade haven't made a focal reducer for ACF scopes so it's not unusual for people to think the focal reducer you have also will work for ACF scopes.

 

 

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Wow, thank you all for your excellent replies. 

" I certainly hope you're far away from that monster wildfire that's burning entire towns up in Alberta! "

I am 5 hours south it into the main city where all of the fort mac evacuees have made their exodus to. The fire is out of control and cannot be stopped- it is encroaching upon multiple new targets. No rain forecasted, so it is a tense situation for Alberta and will kill economic growth. Our dollar finally just started its accent, but this will like now fall again down. People have pulled together across the country, and for once people have been helping everyone, petty differences and racism set aside. A warm change out of this disaster. They were hit the hardest with the economic downturn and were the main providers of the country, now they are kicked when they are down at their lowest trying to survive. Everyone in Canada is doing their best to help them in any way they can. Donations and volunteers have been unabatedly streaming in from everyone and their companies they work for. Very heartwarming.  

The reducer comments make a lot of sense, I shame I agreed to buy it for reduced price. Oh well. I am not too concerned as I got everything for 50-60% of its base price.

 The ACF is corrected for coma so yes I will be extracting the larger FOV I can without vignetting. I will look at a 2" larger focal length EP then. Thanks for the suggestion.  I will see how the 32mm holds up, but it is irritating to use when I used it with my previously owned 100 SW f9 frac because of the either the eye relief or the exit pupil. I am not sure which is the culprit, but the light cone is very narrow and easy to black out the view at the EP. It was hard to explain, but it was difficult to use. I once used a 35 Pan in an Edge 11" (not mine), it fully framed the double cluster and was one of the most beautiful views I have experienced. I want something like that. 

 

 

 

 

 

 

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  • 2 weeks later...

I use Lymax Cat Coolers for my LS8 and C9.25 SCTs. They cut the cool down times in half or less. Search on the internet for "telescope cat coolers" and you'll find a lot of articles on how to build your own using inexpensive PVC pipe and a computer 12v fan. I made one about 20 years ago and it worked just fine. When I got back into astronomy about 4 years ago I got lazy and bought the ready made Lymax, not cheap but they do the job very well.

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On 8.5.2016 at 20:52, Tyson M said:

" I certainly hope you're far away from that monster wildfire that's burning entire towns up in Alberta! "

I am 5 hours south it into the main city where all of the fort mac evacuees have made their exodus to. The fire is out of control and cannot be stopped- it is encroaching upon multiple new targets. No rain forecasted, so it is a tense situation for Alberta and will kill economic growth. Our dollar finally just started its accent, but this will like now fall again down. People have pulled together across the country, and for once people have been helping everyone, petty differences and racism set aside. A warm change out of this disaster. They were hit the hardest with the economic downturn and were the main providers of the country, now they are kicked when they are down at their lowest trying to survive. Everyone in Canada is doing their best to help them in any way they can. Donations and volunteers have been unabatedly streaming in from everyone and their companies they work for. Very heartwarming.  

What a terrible situation, a fire that can't be stopped. 

Very nice to hear that the others are helping the evacuees. I hope the evacuees will be able to start up life again when this is over.

 

 

 

 

 

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About the cooling for the scope. For my Mak I have made insulation from camping mattress. But I remove it when I put my scope outside to cool down. When I start observing, I put the insulation on again. I intend to make the same system for my new C8.

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Am still experimenting with eyepieces after buying an 8" Edge recently - also corrected for coma - and the views with the TV Panoptic 35mm are just breathtaking. It's rapidly becoming my favourite eyepiece - (though I've never had the chance to look through a 31mm Nagler which no doubt would be wonderful through an 8-10" SCT.) Don't know if this applies to Canada, but Tele Vue prices are 15 percent off in the UK at the moment. 

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"You can cool them by leaving the back open, pointing them downwards and letting the hot air rise out, but keep the insects out!".

Olly, i'm assuming you mean the corrector plate should be pointing downwards and the open end pointing upwards?.

I say this because even a numpty like myself knows that warm air rises upwards and cool air sinks downwards. Not sure about how to keep insects out while the scope is cooling. Maybe stand guard over the scope with a can of bug spray.

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6 hours ago, LukeSkywatcher said:

"You can cool them by leaving the back open, pointing them downwards and letting the hot air rise out, but keep the insects out!".

Olly, i'm assuming you mean the corrector plate should be pointing downwards and the open end pointing upwards?.

I say this because even a numpty like myself knows that warm air rises upwards and cool air sinks downwards. Not sure about how to keep insects out while the scope is cooling. Maybe stand guard over the scope with a can of bug spray.

Use a piece of window/door screen and place it on top of the exit hole. It won't stop the hot air from exiting the scope but will stop the bugs from getting in.

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My husband who is a phycisian thinks a scope can hardly cool down from having the eyepiece whole open. With the argument that the cool air needs to enter through the same whole as the warm air that leaves. He thinks it cools down mostly through the sides and front/back.

Me, I leave the eyepiece whole open when cooling down, just to be sure, with insect netting. As Olly recommended.

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I keep my 9.25" SCT in the garage which is a big bonus to cooling times.  

The ES 82 degree 30mm is a great eyepiece for these scopes (and others).  Very little difference between it and a Nagler T5 31mm and the price is very good. The Televue Panoptic 41mm should be slightly wider and still shouldn't vignette (though i haven't got one yet) - but obviously at the cost of a lot of magnification.  I wouldn't add a focal reducer for visual, you won't gain any more field as the reducer can't actually make the width of the visual back any larger.

Yes you undoubtedly need a dew shield, preferrably heated; these things suck down dew quicker than a $10 hooker.

 

Have fun!

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Thanks all, I bought a heated dew strap, a dew shield and controller. I just didnt want to take any chances of setting up and having to use a hairdryer constantly that draws a lot of power. I bought a cheap one any ways for emergencies. A lymax is on the list, but for now, Ill leave the back open with a piece of cloth over the top with an elastic band for the bugs 

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As for EP's, so far I have the 56mm 2" Meade eyepiece (cheap but surprisingly good) and a Williams Optics 33mm 2"  72 degree eyepiece..the price was right on both of them. 

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I live in the same part of alberta that you do. Just a little east of you. 

I leave my scope outside most of the year. Just bring it in when we are going away. 

So far, no problems.  Next will be a small obsy and then some dew heaters.:icon_biggrin::icon_biggrin::icon_biggrin:

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