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10" LX200 Optic questions

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#1 tboss70

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Posted 02 December 2005 - 12:57 PM

Hi all! Went viewing the other night with clear skies, seeing was average, and transparency was below average.
I live on the edge of town (population 12,500) with some street light pollution but back yard is somewhat dark. (My light polluted area) http://cleardarksky....p/MrshMOlp.html

I was viewing Venus and Mars through my 10" Meade but still had some difficulty seeing detail.

Venus had some haze to it, as I've seen it before and Mars had some haze also, though not like Venus. I could make out some cloud detail on Mars but seemed like viewing was more pleasant at 180x. (14mm Meade Series 5000)

I did check my collimation on Vega and did not use a diagnal. I had some concentric rings but could also tell there was a wavy haziness to it. Conditions not too good for seeing huh? My rings seemed to be centered evenly around my CO.

One weird thing I noticed when trying to collimate, and this is not the first time I've noticed it, I would see the outside rings at the top have a little dip, or bend going outward. It would come and go...I wouldn't see it for a second or two then it would come back. Any ideas what this could be?

First, the scope was cooled...it was in the garage all day. Second, I think my collimation is okay although Im not sure about that little dip in the rings at the top going outward.

Im using Meade 5000 Series eyepieces and a meade 2x TeleXtender. I only used the 5.5mm to collimate the scope with no diagnal.

Can anyone give any insight to my problems or hope to better viewing? Thanks!

Todd

#2 tjensen

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Posted 02 December 2005 - 03:23 PM

Hey Todd.

Welcome to CN.

A couple of questions first... what time was it when you were viewing Venus?

If the transparency was poor, that will definately affect the view. And high clouds, dew or frost will make things fuzzy (do you have a dew zapper?).

Vega is way too low on the horizon to use for collimation now... not to mention too bright. Some people use Polaris with good results, but it is a double star so you have to be careful about that when interpreting your ring pattern. Personally, I prefer using a star that is closer to the zenith. It makes it a little harder to reach the collimation knobs, but the air is usually steadier. If the defocused image is producing concentric rings, your collimation is ok. And remember, only collimate on nights of really good seeing. The star image dances around too much otherwise and you end up chasing ghosts. SCTs hold collimation fairly well so once you have it, you shouldn't need to tweak it unless the scope receives a major jaring.

The little "dip" you refer to sounds like tube currents to me. You might need some more outside time for final cooling since garage temps can still be a few degrees above outside ambient temps. Also, depending on the weather, the outside temp can change quickly and the thermal mass of SCTs is pretty large. It can take awhile for them to cool if the air temp drops.

Hope that helped a little.
Cheers

#3 tboss70

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Posted 02 December 2005 - 03:38 PM

Thanks for the reply Tim, I really appreciate it. I was viewing Venus about 6:00 pm and no I dont have a dew zapper yet. You have any recommendations? Will they produce heat waves in front of my secondary?

Transparency wasn't poor but it was below average. I could see some waves while collimating on Vega. Vega is somewhat low here in Missouri but I dont think its too low. I can't get too much higher without using a diagnal.

My garage doesn't have real good insualtion so its fairly cold inside but I did take the scope out and view right away. There could be some cooling issues there. I dont have my ToUcam or DSI yet or I would get some pictures. Hopefully its nothing major.

Again, thanks for the help. I will let you know what I find out. Viewing will not be good here for a few days though.

Todd

#4 NeoDinian

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Posted 02 December 2005 - 03:53 PM

First, you'll never see any "Detail" on venus. Just the cresent shape. It's far too bright, and nothing but cloud cover. :)

Mars is racing away from us right now, and detail on that needs pretty steady skies anyway. I don't think you'll see detail like the photos, but you should make out a 2 tone orange'ish disk...

#5 Psa19one

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Posted 02 December 2005 - 06:13 PM

Hi Todd,

Welcome to Cloudynights! A couple of things: First, remember that your garage could still have enough of a temperature difference that your 'scope still needs to sit outside for awhile (an hour or so). SCTs are quite tempermental about cooling, and I use a SCT cooler to aid in achieving equilibrium (made a difference in my case).

Second, I remember being perplexed by an oval or out-of-circle diffraction rings (not just jumpy ones that happen with tube currents or atmospheric turbulence but consistently out-of-shape). It turned out that my mirror lock bolt used to help prevent mirror flop was pressing on the mirror enough to cause the image to warp. It doesn't take much! Back off this bolt and see if that helps.

I agree with Tim, use polaris to collimate -- and I would add: don't fear using a diagonal when you collimate if you use one when you observe. I know to use or not to use a diagonal when collimating is a matter of opinion, but I have found that using mine when collimating does hurt at all (anyway, I observe with a diagonal, so I might as well collimate with one!) ;) Vega really is too low and will dance like John Travolta -- way too much to help you collimate with much accuracy (and it is too bright). Polaris is a nice choice: high enough and dim enough to be a good choice.

Hope this helps! :)

#6 Jeff Young

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Posted 04 December 2005 - 03:01 PM

Todd --

Mars is a very hard target. You have to really be on top of your game to observe much detail on it. You'll have much more fun starting out with Saturn (starting to move higher at a reasonable hour) and Jupiter (which you'll have to wait a few months on).

The idea of a dew heater is to keep the corrector plate *just above* ambient temp so that it doesn't collect dew. At just above ambient, there shouldn't be enough of a temperature gradient to produce any heat currents. (Note that to do that, you need a variable-output dew controller, not one of the constant-on ones.) I'd recommend Dew-Not for the heater strips (good quality but cheaper than most competitors). As for the controller, all the major brands have their followers (Thousand Oaks, Kendrick, Dew-Buster, etc.).

One other thing -- I think you might be confusing transparency and seeing. Transparency measures how much light the atmosphere transmits through it. It's often measured by naked-eye limiting magnitude (ie: what's the dimmest star you can see without any aids), although this also measure light pollution at your location. Poor transparency won't affect your ability to collimate, but it will control how dim an object you can see.

Seeing measures how much turbulence is in the atmosphere. It affects how much stars "twinkle", how much your out-of-focus star patterns "wiggle", and ultimately, how much detial you can see. You should only collimate when seeing is good.

Often you'll have nights of good transparency but bad seeing (usually just after a storm has blown through). These nights are good for DSOs, but not very good for planets. Other times, you'll get very still but hazy nights (good seeing by bad transparency), which are great for the planets, but not so good for DSOs. If neither one is good, go back inside. ;)

One final note: the lower down an object is, the more atmosphere you're looking through. This will degrade both transparency *and* seeing, although I'd guess that the effects are more dramatic on seeing.

-- Jeff.


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