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Do you use a barlow with your SCT?

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#26 azure1961p

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Posted 24 August 2014 - 09:34 AM

My 4mm ortho gives me 400x with my C6 which is as high as needed the vast majority if the time.  For super high power on sub arc second doubles Ive used a Barlow to get as high 1000x.

 

pete


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#27 mclewis1

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Posted 24 August 2014 - 10:22 AM

Hi Sorny,

 

The Evolution 9.25 has a maximum 'useful' magnification of 555x which equals a 4.25 eyepiece, therefore I can use the Barlow with the Zoom and get 2.25x the eye relief than I would get without it for anything less than or equal to a 10 eyepiece . I am more interested in the eye relief at higher magnification than the higher magnification that I might get with the Barlow.

 

I am hoping for good seeing as Jersey is an island and I am on the edge of it, a fair distance from any build up of lights. Once I have negated the nearby light pollution from two street  lights with a filter there should not be much to worry about.

Those magnification numbers are purely theoretical, they should generally be ignored. For most locations it will be rare that you'll be able to get close to them. Most nights it will as Sorny has mentioned.

 

You're seeing conditions are not related to how dark your skies get, it's about stability. For DSO viewing you want skies as dark and as transparent as possible but for high power double star and planetary viewing it's all about stability. To be able to use high magnifications you need very stable conditions and the most stable viewing conditions are dependent on a whole bunch of variables. 

 

First your scope must be acclimatized, that means an hour or more of the scope operating at the temperature of the outside air. An SCT "cat cooler" can accelerate this cooling cycle but the most common issue with SCTs not putting up great high magnification views is cooling.

 

Your scope also needs to be very accurately collimated. Not just with the big doughnut Fresnel images and diffraction rings but with a nice tight airy disk at high magnifications. Highly accurate collimation can usually only be done on those nice stable nights. It's not really tough but it takes some experience to be able to quickly perform a good collimation.

 

Location matters ... you'll need to be away from buildings and not viewing over hot surfaces like roofs and large areas of asphalt and concrete. Large grass and tree covered areas or open water are usually best. You also don't want to be on the downwind side of large mountains.

 

The air above you needs to be stable. No jet stream. Moving air is fine but it should be moving in large smooth sheets. Warm or cold weather fronts are not beneficial as the transitions from one to the other are usually accompanied by unstable air. Marine layers (air trapped by different air temperatures) can often offer nice stable viewing. The best time for stable air is usually very early in the morning - 3 to 4 am. Early evening can feel nice and calm but there are usually lots of heat plumes rising off of buildings and roadways.

 

After some experience you'll be better able to read and predict your local seeing conditions but the fastest determination you can make is to just look up ... if the stars are twinkling it's probably going to be a good DSO viewing night ... and not one for serious planetary work.


Edited by mclewis1, 24 August 2014 - 10:24 AM.

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#28 JerseyBoy

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Posted 24 August 2014 - 10:46 AM

Thanks Mark  ;)

 

I shall bear that all in mind when I am viewing. I am lucky that I live on a small island, it's only 9 miles by 5 miles and is 12 miles from mainland France, although that part has no cities just a few small villages. Nearest City of France is a lot further away. Jersey has one town, it's obviously not very big!

 

I can view across the sea from the front balcony or across fields with a few houses from the side balcony. The local astronomy club goes West, near the sea but a lot higher there. No mountains anywhere near here, the highest point on the island is Les Platons on the North coast at 469 feet.


Edited by JerseyBoy, 24 August 2014 - 10:49 AM.


#29 JerseyBoy

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Posted 24 August 2014 - 01:22 PM

Here is the panoramic view from my front balcony, the image covers east to west, the tree looks bigger than it is as it is quite close, you can clearly see the really annoying street light that's in front of the balcony, hence the need for a light pollution filter. Left of the tree is in front, right of the tree is to the side.

 

Attached File  Pano_0024.jpg   29.75KB   3 downloads


Edited by JerseyBoy, 24 August 2014 - 01:26 PM.


#30 Gil V

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Posted 24 August 2014 - 02:23 PM

Nope. Don't even own a Barlow lens.

#31 azure1961p

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Posted 24 August 2014 - 07:27 PM

 

Hi Ben

This is the reason for shorty barlows. If you inserted your barlow any further it would hit the mirror in the diagonal. I use a celestron ultima 3 element 2x barlow which is actually around 2.2x in reality)

-Rob

+2 on the shorty barlow, I use it with my C5 and old TV plossls and Konigs. They are small eyepieces.

 

 

Oh my goodness that center one with the brass showing looks like a dead finger for my 1970s Edmund Barlow.  Sigh.

 

pete


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#32 A6Q6

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Posted 24 August 2014 - 09:19 PM

Hi Ben
This is the reason for shorty barlows. If you inserted your barlow any further it would hit the mirror in the diagonal. I use a celestron ultima 3 element 2x barlow which is actually around 2.2x in reality)
-Rob

+2 on the shorty barlow, I use it with my C5 and old TV plossls and Konigs. They are small eyepieces.

 
Oh my goodness that center one with the brass showing looks like a dead finger for my 1970s Edmund Barlow.  Sigh.
 
pete

Hi Pete, Yes it is an Edmund Barlow from the 70's, It came with my first Astroscan. Here is a link with more on it: http://www.cloudynig...-out-of-hiding/
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#33 tclehman1969

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Posted 26 August 2014 - 05:39 PM

I have a C8 and I used to use a Barlow years ago, but haven't used one nearly as much. It certainly has it's place but over time I have really enjoyed looking at wider fields of view opting for my 36mm or 26mm Plossls. For planetary or lunar, I will switch over to my 10mm Plossls or 7mm Ortho. Once in a long while I'll toss the Barlow in, but typically just for lunar or planetary. 

 

Also, my experience and what I have seen many people do, is place the Barlow up the back of the scope first, then plug the diagonal into that. I think that is the way it was intended given the design of barlows. Here's a link to a YouTube video from the Astronomy and Nature Center TV from England on barlows: http://youtu.be/ENCbtFpdKJ0. You may find it useful.

 

Hope this helps!


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#34 Geo.

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Posted 27 August 2014 - 04:54 PM

The Earth's atmosphere pretty much limits ALL telescopes to 300X, but maybe you have advanced adaptive optics.



#35 Sarkikos

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Posted 27 August 2014 - 05:26 PM

That's painting with a very broad brush. Unless you live permanently under the jet stream, over 300x is not unreasonable, depending on the object and the telescope.  I often go over 300x with my 10" f/4.8 Dob when viewing planets and double stars. High power can also be useful when viewing planetaries.  I routinely go to 300x or more with my C6 when observing Mars, Saturn and double stars.

 

Mike


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#36 Mariner@sg

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Posted 27 August 2014 - 09:18 PM

That's painting with a very broad brush. Unless you live permanently under the jet stream, over 300x is not unreasonable, depending on the object and the telescope.  I often go over 300x with my 10" f/4.8 Dob when viewing planets and double stars. High power can also be useful when viewing planetaries.  I routinely go to 300x or more with my C6 when observing Mars, Saturn and double stars.

 

Mike

 

Agreed. Going over 300x is not impossible especially on lunar and planets. Have had some success going over the theoretical limit of 600x for some fine views of Jupiter and Mars.


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#37 JerseyBoy

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Posted 28 August 2014 - 05:26 AM

I look forward to trying to max out my Evolution 9.25 when it arrives! :-D



#38 Sarkikos

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Posted 28 August 2014 - 06:22 AM

Hi Sorny, 

 

As you can see from this article, the area where I live should have very good seeing, probably not quite as clear as Sark, an island not far from Jersey, but still very good. If I have any issues from home I can always head 10 minutes to the west coast where there are no street lights and get even better seeing, or I could jump on a boat and go to Sark for perfect skies  :cool:

 

http://www.theguardi...ark-sky-island 

 

Where it shows La Ville Roussel, that is Sark

attachicon.gifchannelmap.jpg

 

Sark sounds like a wonderful place. I much prefer the name "Sark" to "La Ville Roussel."

 

:grin:

Sarkikos (Mike)


Edited by Sarkikos, 28 August 2014 - 06:23 AM.

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