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Equipment Discussions >> Reflectors

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Jason D
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Reged: 10/21/06

Loc: California
Re: Mega-mod thread for Zhumell dobs new [Re: Jason D]
      #3591919 - 01/29/10 04:07 PM

By the way great thread, Tim
Jason


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Jason D]
      #3591952 - 01/29/10 04:18 PM

Quote:

Quote:

However, there are some concentric diffraction rings that show up within the center of the donut that make an excellent "target," as shown here:



I prefer this method over the aperture stop method. See attachment. The method with the barlow is less sensitive to tilts because the barlow lens and the laser window will move in opposite directions cancelling each other -- unlike the aperture stop method.
The negative lens of the barlowed laser method magnifies the returned center spot shadow – that is why it appears larger. Of course, such a problem will not exist with Glatter’s TuBlug.
Jason




Hi Jason,

Hey, help clarify this for me (and other newbies who might also need it). When you said "I prefer this method" I assume you're referring to the barlowed method, right? Will use of a barlow without the aperture stop also produce the inner "target rings" for collimation?

Right now I'm using both. The aperture stop gives me a nice dot for tweaking the secondary alignment, then I pop in the barlow for the primary mirror alignment.

Thanks for your input!


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Jason D
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Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3591981 - 01/29/10 04:32 PM

I meant the method of using the combination of a barlow and a laser collimator is more accurate regradless of whether an aperture stop is used or not. If the aperture stop introduces more rings with the barlow, then I can see how the additional rings would be useful as references.
Jason


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Jason D]
      #3593808 - 01/30/10 04:22 PM

I'd like to get some more links or other info in this thread. Anyone have a good link for collimating the laser? A good "how-to" flocking link (with photos) would be a good addition as well.

Thanks!


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3593864 - 01/30/10 04:46 PM

Here's one I found for how to flock your scope. It's got great pictures, shows clearly how to strip the tube and how to apply the flocking material. If you have been thinking about flocking your dob, this is a great place to start.

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devourment77
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Reged: 05/21/08

Loc: Austin, TX
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3594484 - 01/30/10 09:57 PM

I just did the milk jug double washer "mod" tonight. I was thinking of using one of those foam washers that usually come in a spindle of CD-Rs but ended up just cutting them out of the milk jug instead.

Now I can actually see what screws do what (each one sticks to a single axis). Before the washers, I was turning them at random because they never gave consistent results.


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JayinUTModerator
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Reged: 09/19/08

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Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3594768 - 01/31/10 01:25 AM

Tim,

Here are a couple of links of collimating a laser collimator. The Astromart article is from 2004 and the review from here is 2003 so they are older (wow, I can't believe 2003 and 2004 are 6 and 7 years ago!).

Astromart Collimating a Laser Collimator

Cloudy Nights Collimating a Laser Collimator

I made a base today like what Hugh has in his article, we'll see how it goes.


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: devourment77]
      #3595735 - 01/31/10 03:13 PM

Quote:

I just did the milk jug double washer "mod" tonight. I was thinking of using one of those foam washers that usually come in a spindle of CD-Rs but ended up just cutting them out of the milk jug instead.

Now I can actually see what screws do what (each one sticks to a single axis). Before the washers, I was turning them at random because they never gave consistent results.



Hi Brandon,

I agree totally with you. This is a great and very simple mod to make to the secondary holder. Before I put in the washer, my screws kept wanting to return to the dents they had made in the soft metal washer that comes with the scope. Installing the washer made it easier for me to figure out the movement that each screw controls, also.

I still only have one washer in mine. The second is ready to go, just waiting for when I pull my secondary again to do some other housekeeping on it!

Clear skies,


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Tim L
Carpal Tunnel
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3608569 - 02/06/10 01:24 PM

Here's another simple mod I just did...

My primary was a little loose side-to-side in the cell, so I added some shims to fix it in place a little more securely.

I used two small rectangles of cereal-box cardboard, and placed them between the primary and the cork support that is ABOVE the mirror when the scope is tilted.

In other words, gravity wants to pull the mirror to one side of the cell when the scope looks at the horizon; I shimmed the other side.

Hopefully this will help keep the primary from knocking about when I carry the tube out.

And as a reminder: Don't tighten the mirror clips to try to hold the mirror in place! They will affect your views negatively. There should be a tiny gap between the mirror clips and the surface of the mirror.



Anybody else have good suggestions for inexpensive improvement mods?


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3633289 - 02/18/10 07:31 PM Attachment (138 downloads)

If you're just starting out, and haven't yet bought a collimation combination sight-tube/cheshire eyepiece, you might want to add a homemade collimation cap to let you make a quick visual check in addition to your Zhumell laser.

You can make one easily from an old film canister. Cut off the bottom and drill a hole in the center of the lid. When placed in the focuser, the primary is collimated when the hole in the canister lid appears right in the center of the donut sticker. This is not a precise method of collimation, and other tools will help you fine-tune your results.


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3633302 - 02/18/10 07:40 PM Attachment (143 downloads)

Collimating a laser for the first time can be a time-consuming process. I burned through a set of batteries just trying to get it all figured out! In addition to the links provided above, here are some tips for collimating your laser...

Place the laser in a sturdy jig (some great ideas have already been suggested above. I use a small table-top picture frame holder braced with heavy books!). Start with the on/off screw at the top, aim at a post-it on the wall, and mark where the dot hits with a "1." Rotate in 1/4 turn increments, and mark numbers "2," "3," and "4." Finally, rotate back to position "1." Does it still hit your previous mark? If not, something isn't stable enough with your jig. Brace it and try again.

Now, look at your pattern on the paper. If the laser is out of collimation, it will have made a circle similar to the one below. (Your numbers may be in different positions, that's fine).

The trick to collimating is: move dot #1 to the center of the circle.


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3633318 - 02/18/10 07:54 PM Attachment (124 downloads)

So, how do we bring the dots to the center? Near the back of the laser barrel you will find three small allen-head screws recessed in the body. These take a 1.5mm wrench.

Inside the barrel, the laser module is fixed at the aperture end, and is raised and lowered by the screws at the back end. So, think teeter-totter here: If you TIGHTEN a screw, you push it DOWN, which will make the opposite end (the laser dot) move UP. If you need the dot to move DOWN, you LOOSEN the screw opposite. That's all there is to it.

So, for the pattern in the above post, dot #1 (my reference point) needs to come DOWN. I would therefore LOOSEN the screw on the top of the barrel (see photo below), and then slightly tighten both of the screws on the bottom of the barrell.

Make small adjustments, put it back in the jig, retest, and keep trying until the dot rotates in one place.

Remember: Don't over-tighten or you could strip a screw! If you need to tighten a screw, loosen the ones opposite first.

Tip: It's always easiest if you only have to work in one plane for your final adjustment (as in my example above) Once your #1 dot lines up with one of the 3 axes of the adjustment screws, it gets much simpler.

These lasers work well, but they need often need a little tweaking at the start to get optimum performance out of them.

This is a good project to tackle early on, as it will improve the collimation of your scope, and give you a good useable tool!

Best of luck!

Post what you learn or your mods here to help out other newbies!


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3634208 - 02/19/10 09:08 AM

Tim,

Nice list of mods! Some of these I've already done, others I'm going to do.

Where you place the weight is right on. It just makes good sense. I use a sports pack (also called a "fanny pack") to hold lead shot. You can't get anything heavier in as small a volume as lead, unless you want to go radioactive! That would not be prudent. I pour the lead shot into a small fabric pencil case, the kind you can get from dollar stores. Then I put the fabric case into the sports pack and strap the pack onto the correct position on the OTA.

Another idea is to set up your scope with its heaviest eyepiece, and put enough weight in the sports pack (or whatever you use) to counter that eyepiece. Then when you replace your heaviest eyepiece with a lighter one, you can compensate for the lose of weight and prevent imbalance by placing a small magnetic weight on the OTA near the focuser. I use a flat, felt-covered magnet. I also attach a small strip of Velcro (the side with "ribs") just below the focuser to help grip the felt on the magnet, otherwise the magnet might slide down the OTA during dewy conditions. I think this is a good solution to the problem of a scope losing its balance when eyepieces are changed.

Keep in mind, though, that my 8" Zhumell and my 10" Dob do not have the newer type of altitude bearings that have a tension feature. My 8" just has the springs, and my 10" has no tension device at all!

Mike


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TMK
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Reged: 12/30/08

Loc: A Cloudy Place
Re: Mega-mod thread for Zhumell dobs new [Re: Sarkikos]
      #3634288 - 02/19/10 10:04 AM

Hmmmmmmmm.

That's got me wondering if I have enough flocking material left over to make a makeshift light shield. Looks like some tinkering is in order this evening.

I would think if the backing was left on and I used a sharpie to blacken out, why would it not work? Tim, how do you feel about the benifit of a light Shield? on a scope thats already flocked?

Tim, thanks for posting

Edited by nobody special (02/19/10 10:07 AM)


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Sarkikos
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Reged: 12/18/07

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Re: Mega-mod thread for Zhumell dobs new [Re: TMK]
      #3634302 - 02/19/10 10:10 AM

Tom,

Quote:

Tha's got me wondering if I have enough flocking material left over to make a makeshift light shield. Looks like some tinkering is in order this evening.

I would think if the backing was left on and I used a sharpie to blacken out, why would it not work?




Flocking by itself might not be stiff enough to hold its shape, especially under dew. Go to a crafts store and get some black foam sheeting for the outer layer of the shield, line with flocking, and use Velcro strips to close/open it. The only problem may be finding a foam sheet big enough for a dew shield for your scope. It's better to make it from one continuous piece of foam sheeting if you can find it.

Mike


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Tim L
Carpal Tunnel
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: TMK]
      #3634452 - 02/19/10 11:18 AM

Quote:

Tim, how do you feel about the benifit of a light Shield? on a scope thats already flocked?




Tom,

I would do it. Get something stiff to hold its shape, and just glue the flocking material to it. I just used felt for mine, instead of the velvet I used for flocking.

You've posted before about stray light issues in your backyard--a light shield will help. I noticed this one night when I was getting a bit of a light glow in the EP from one of the neighbor's security lights. I added the light-shield, and got the contrast back. I also use it whenever the moon's bright.

I like using the three pieces of foam on mine because I can fold it up without creasing the foam.

Put your creative mind to the problem and I'm sure you'll come up with a good way to make one!


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3634485 - 02/19/10 11:32 AM

Quote:

I think this is a good solution to the problem of a scope losing its balance when eyepieces are changed.




Hi Mike,

On mine, when I change EP's, I just reach down and shove the magnet up or down a little. A small strip of duct tape gives it enough friction to keep it from sliding.

Working without any tension device like you do certainly makes balancing more critical! Glad you found a way that works.

Clear skies!


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3634489 - 02/19/10 11:34 AM

Regarding milk-jug washers...

I ought to add that I did finally put a second one in (they go right between the secondary adjustment screws and the metal washer on top of the secondary mirror). I like the extra smoothness and ease of adjustment.

Thanks again Jason D for this excellent idea!


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Mega-mod thread for Zhumell dobs new [Re: Tim L]
      #3634687 - 02/19/10 01:16 PM

Tim,

Quote:

On mine, when I change EP's, I just reach down and shove the magnet up or down a little. A small strip of duct tape gives it enough friction to keep it from sliding.

Working without any tension device like you do certainly makes balancing more critical! Glad you found a way that works.




I like to keep the main counterweight where it is and not touch it in the field, because it's in an awkward position under the OTA and sometimes inside the Dob mount. Also, I find that the farther I place this weight toward the bottom end of the OTA, the better, because I will be able to minimize the actual weight used. I keep a small bag of magnetic counterweights hanging near me on the Dob mount, so that when I change eyepieces, I can just reach over and place a weight directly below the focuser as I remove the heavy eyepiece, which keeps the scope in balance when I install a lighter EP. But YMMV. Whatever works is good.


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Tim L
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Reged: 12/17/08

Loc: Missouri
Re: Mega-mod thread for Zhumell dobs new [Re: Sarkikos]
      #3803573 - 05/13/10 03:20 PM

Time to add another cheap improvement to these scopes...

The stock 2"-1.25" adapter is threaded on the bottom for 2" filters (yay!). That means you can use one filter there while you swap your 1.25" EPs for the best view.

However, the adapter is not long enough (boo!). This means that the barrel of many EPs (including the 9mm plossl that comes with the scope) will bump into a filter that is placed on the bottom of the adapter, possibly scratching the filter.

Solution: Lengthen the adapter. I purchased a Hyperion 14mm fine-tuning ring ($13 at Agena), screwed it to the bottom of the 2"-1.25" adapter, and left it there.

Now, I have no worries about something hitting any filter placed on the end of the adapter! I can even put my 1.25" barlow in the adapter and it has enough clearance.

Added benefit: With a 2" polarizing filter on the bottom of the adapter, and a 1.25" polarizing filter on the EP, I can dial in just the right amount of filtration by simply rotating the EP in the focuser. Pretty nifty.


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