148 replies to this topic

[ChuppsterXLM]

You can't go wrong with classic glass, Original Naglers 13mm & 9mm do great planetary on my 6" f/8 (weather permitted). You can still find them at great prices at the Classifieds section.

 

 

Edited by ChuppsterXLM, 29 November 2022 - 05:11 PM.

[Nightskyman]

Tonight was my third night out.  I actually had Jupiter with brown bands around 20x but no more. I was only able to focus the moon for a few moments. It was a light breeze and some clouds although I could see the moon with light and dark areas with my eyes. Is this due to atmospheric conditions? I guess I thought I should still have been able to se craters on moon but when I did, it only lasted a few moments?

[Anony]

I think the eyepieces you mention -- especially the 6mm and 9mm Orion Expanse -- should be good for planets.  You can Barlow these to get effectively 3mm and 4.5mm, which are also good.

They are... I own the svbony versions, and they make good eyepieces for the planets.

 

Although my skies never allow me to barlow them (or at least not the 6mm).

 

The 6-9mm can be a little finicky with the moon (just so the OP knows it's not just him if he sees it) -- a bit of kidney beaning may occur... it'll require a little eyeball positioning to get just right.

Edited by Anony, 06 December 2022 - 02:52 AM.

[Anony]

Tonight was my third night out.  I actually had Jupiter with brown bands around 20x but no more. I was only able to focus the moon for a few moments. It was a light breeze and some clouds although I could see the moon with light and dark areas with my eyes. Is this due to atmospheric conditions? I guess I thought I should still have been able to se craters on moon but when I did, it only lasted a few moments?

I'm guessing it was extra cloudy?

 

On a decent night you should make out several bands on Jupiter, very clearly.

As for the Moon, yeah... you should get craters. Like super close-up, cratery craters... 

 

So long as the sky cooperates, you can try to go crazy with magnification on the moon... it sometimes works.

Edited by Anony, 06 December 2022 - 02:53 AM.

[Nightskyman]

When using a dob, should the knobs holding the scope to the base be completely tight when focused on an object? After only a few times using my new scope, there are rub marks on the base from the tension of tightening.

[Chad7531]

When using a dob, should the knobs holding the scope to the base be completely tight when focused on an object? After only a few times using my new scope, there are rub marks on the base from the tension of tightening.

No they should be pretty loose. The az screw should be loose and the weight is the scope puts tension on it. The alt bearings should be loose too. You’re scope needs balanced front to back and then top to bottom.

Edited by Chad7531, 11 December 2022 - 12:24 AM.

[Echolight]

I use a Baader 8-24 zoom and a Celestron Luminos 2.5x 2 inch barlow. This combo, zoom alone or with the barlow, will give you 50x to 375x and everything in between. It’ll give you the ability to find out for yourself exactly what range of magnification is best for each individual object and quickly adjust for atmospheric conditions.

 

Basically, I use around 150x for Jupiter, 190x on Saturn, up to 240x on Mars, and up to 375x on the terminator of the Moon. YMMV.

[Nightskyman]

About collimation… I haven’t had many chances to use my new dob for observing as there have been few nights and those not good seeing. When setting collimation with the included cap and the then checking against a Cheshire and laser….. when the cap shows good the other two show it is off but agree with each other. When the Cheshire and laser are set and they do agree with each other, then the cap is off? What is off which ever way, is the back circle/shadow that’s behind the center circle that represents the focuser. The black shadow is not completely a circle but a bit fatter on one side than the other? Otherwise, the center focuser circle and everything else is perfectly centered. Any thoughts?

[JohnBear]

 

Any thoughts?

Yes!  IF you Don't know how to collimate, then WAIT (i.e., Don Try adjusting things) and  find an experienced Newt owner that will show you how to adjust collimation properly. (from your astronomy club, etc) 

 

In-person ntraining with an experienced scope owner is Easy and usually takes about an hour, but "self teaching" may take several weeks (or months) with your scope way out of whack!.  But once you learn to do it properly, it becomes an almost trivial task. 

 

There are at least 7 different interacting adjustments to fiddle with in the optical chain, so the adjustment procedure is very specific and exacting (and unforgiving) - as well as hard to EXPLAIN in words to newbies, but not-so-hard to Show them in-person.

 

Otherwise save "teaching yourself collimation" for when you have a month of cloudy weather forecast.  

 

If collimation looks reasonably close as yours seems to be - Don't worry about it! - Just enjoy using the scope for now. You are unlikely to notice any difference visually anyway. 

Edited by JohnBear, 12 December 2022 - 06:16 PM.

[Nightskyman]

Wow, I thought you got friendly help here not being chewed out. My mistake, don’t mean to waste anyone time!

[Sky Muse]

This is my 6" f/5 Netownian-Dobson...

 

 

Yours is an 8" f/6, and easier to collimate.

 

This is what I see when looking through a collimation-cap...

 

 

Everything inside comprising the optical system is present within that scene.  I call it the secondary-scene.

 

I lay the optical-tube on a table or other, horizontally, and illuminate the tube...

 

 

I then take a camera, zoom in, and snap a shot of the scene, as shown above.  We can tell a lot by looking at the scene.  If you can share an image of your own like that, that'd be great.

 

[kingsbishop]

This is my opinion
I have been doing visual for almost 3 years and here is what works best for me

For planets do not use any more magnification than your appeture say if your telescope appeture is 200mm then don’t use more than 200x magnification people say that the maximum is double the appeture but I think that is way too much and you lose too much resolution so for me not going past 200x magnification for a 200mm telescope I reckon is the best.

Again this is what works for me this is my opinion so other websites may say you can go twice the appeture but I think that it is false.

[Deep13]

Any advice on viewing the planets using a 8” dobsonian and which eye pieces and magnifications I should use?

I started observing planets 22 years ago with an 8" f/6 Dob. My options for observing planets were a 17mm Orion Plössl, a 12.5mm University ortho, and the 10mm came with the scope Plössl. I used them with or without a Celestron 2x Ultima Barlow, depending on seeing conditions. I replaced the unsharp Orion Sirius Plössl with a 15mm Televue Ploessl, which was a lot better. These days, I use a 10, 7, and 5mm Pentax XW. So, my recommendation is a Pentax XW in 7mm.

 

Make sure the scope is cooled and collimated.

[Nightskyman]

Sky Muse, your picture is exactly what I see, right side of secondary mirror reflection slightly more just like yours. My question was when using the cap and then comparing to laser and Cheshire, the laser and Cheshire agree perfectly showing image like yours but when using the cap it is off in comparison. When aligned with cap to look like yours then the laser and Cheshire are both off equally. This puzzles me? As a new user, I am primarily looking at the moon and Jupiter to start with as they are easy targets.

[Nightskyman]

I should also ask, sometimes the black image of the secondary mirror is quit a bit fatter to the right of the focuser circle than the left side. What does this mean and do you adjust the secondary to correct it?

[Nightskyman]

Also, if the circle is round but you barely see all 3 retaining clips, how is that adjusted? Sorry, last add on question I promise!

[Sky Muse]

I should also ask, sometimes the black image of the secondary mirror is quit a bit fatter to the right of the focuser circle than the left side. What does this mean and do you adjust the secondary to correct it?

That is the secondary off-setting...

 

 

That is normal.  The off-setting occurs automatically during a normal collimation.  There's nothing to do there.

[Sky Muse]

Also, if the circle is round but you barely see all 3 retaining clips, how is that adjusted? Sorry, last add on question I promise!

The opening at the bottom of the draw-tube of the focusser, that defines the circular view.  Have you tried zooming in with a camera yet?  We need an image.  

 

For now, use only the collimation-cap to check...

 

https://www.youtube....VGcGEBmCE&t=19s

[Asbytec]

What is off which ever way, is the back circle/shadow that’s behind the center circle that represents the focuser. The black shadow is not completely a circle but a bit fatter on one side than the other? Otherwise, the center focuser circle and everything else is perfectly centered. Any thoughts?

Are you describing the dark reflection of the diagonal mirror? If so, it's common to see errors in the placement and rotation of the diagonal which can cause it not to look right. Especially when aligning the tilt with a laser because you cannot see what's happening through the focuser. But rest assured, the scope can still be collimated. When the axes are aligned, then the diagonal has the appropriate tilt and rotation. It's just an error in diagonal placement under the focuser, but it can still have the proper tilt and rotation to align the axes.

 

Your cap and laser may disagree because the thin return beam my not be accurate. It's best for tilting the secondary but use a grain of salt with a laser to align the primary. Instead, use the Cheshire or cap to align the primary mirror. Your laser and cap might disagree if you aligned the primary with a laser, but your Cheshire and cap should agree with each other on the primary alignment. 

[NeroStar]

Collimation isn't the witchcraft some would make it seem.  Yes, you can muck it up, or even damage the scope if not done correctly, but I've collimated several of my scopes using instructions I found in manuals or online.  As long as the process is appropriate to the model/type of scope, and you don't deviate or 'wing it,' you'll be just fine, IMO.  If you do reach a point where something doesn't look or feel right, just stop and consult with someone with a bit more experience.  

[Nightskyman]

[Nightskyman]

Sky muse, here is the photos, hope they are what you are asking for

[Sky Muse]

Yes, you want the center-spot of the primary-mirror centered over the pinhole of the collimation-cap...

 

 

...and it appears within your scene that it is centered, more or less. 

Edited by Sky Muse, 15 December 2022 - 03:19 AM.

[Nightskyman]

So does my scope look to be properly collimated or does the picture show any areas of concern? Wasn’t sure what the wider area of black (secondary mirror ?) on the right side meant and if it was ok? That area of black only shows when the collimating cap is on. Also, am I understanding  correctly that it is normal that collimation with the cap and collimation with a laser (even when the laser itself is properly collimated) can or will show somewhat differing results? Do the clips and black area around the clips look ok and one last question, how can you tell if the secondary mirror is placed properly as far as the the adjustment controlled by the center screw between the 3 secondary mirror adjustment screws? Sorry for all the questions, just trying to understand and learn. I realize that once set correctly, the secondary won’t likely need to be done again and I most likely am overthinking this whole thing. Thanks for your extreme patience!

[Sky Muse]

So does my scope look to be properly collimated or does the picture show any areas of concern?

 

It seems very, very close to being so.  I would use it as is for the time being, for all observations.

 

 

Keep in mind that the telescope is not before me.  I can't check it out myself.  

 

Wasn’t sure what the wider area of black (secondary mirror ?) on the right side meant and if it was ok? That area of black only shows when the collimating cap is on.

 

That's the secondary-mirror's shadow.  It is part of the secondary-scene.  You can see all of the components of the optical system inside the telescope, and within that scene. 

 

Here, I had thrown the collimation out slightly in order to identify each component...

 

 

Also, am I understanding  correctly that it is normal that collimation with the cap and collimation with a laser (even when the laser itself is properly collimated) can or will show somewhat differing results?

 

I never use a laser to collimate my reflectors; only a collimation-cap, and a sight-tube...

 

 

if you're going to use a laser, make certain that it's collimated, and before you use it to collimate the 8" Newtonian.

 

Do the clips and black area around the clips look ok

 

Does the draw-tube of the focusser wiggle loosely within its run, especially when fully racked outward?  Is there any slop, looseness, at all?  That can cause concerns like that, also taking a snapshot of the scene with whichever camera, at an angle, instead of straight on.

 

and one last question, how can you tell if the secondary mirror is placed properly as far as the the adjustment controlled by the center screw between the 3 secondary mirror adjustment screws?

 

The secondary-mirror should be centered directly underneath the draw-tube, just before a collimation procedure, using the spring-loaded center-screw of the secondary-hub, and with the cross-hairs of the Cheshire or sight-tube...