FranTeryda

On 08/09/2020 at 05:47, John said:

Amazing what is possible with simple tech !

I tried to get the ISS crossing the moon with my DSLR mounted on an undriven scope and got it in a couple of frames which I have made into an animated GIF. The whole crossing took just a second or two and the moons was partially behind tree branches so I was pleased to even get it in 2 frames:

 

 

Nice one! That photograph is way more difficult, you have to be extremely precise! 

Hi! I'm Fran

Not so long ago I took a picture of the ISS I never thought I was going to be able to get with the equipment I have. 

After saving for a long time, I was able to buy my first scope, an OTA Skywatcher 200P. I adapted it to be used in a dobsonian base because it was the cheapest way I had to get it to work.

One night, I thought it might be cool to try to aim and record with my phone an ISS pass overhead. During the first attempt, I messed up the focus extremely bad but you can't  imagine how happy I was to get a white blob in a frame that only I knew was the ISS. 

The following afternoon I tried again. This time the flyby was almost exactly overhead and the night was crystal clear. So I manually tracked the station looking through the finder scope and recording it with my phone at 1080p 60fps. Without much expectations I downloaded the files into my computer to review them.  And was shocked with the results.

The video was processed with PIPP, AutoStakkert and RegiStax. 

If someone told me the image was taken with a phone and manually tracked with a shitty dobsonian base I would not believe him! I got really lucky that night, but I can not be happier with the results. I believe I got to the edge of what I can accomplish with the equipment that I was able to buy. I'm not sure if ext step up should be a real camera or a mount. Anyway, any of them are too expensive 😬

If you want to see the frames before processing (and some nice shots of the moon that night), I'll leave a link to the video where I show them:

Thank you so much for reading it all.

Cheers,

Fran

The mount is done! Many things have changed.

I found in a local marketplace someone who sold a dob mount for the sw250p for REALLY cheap (around 40usd). After asking for some measurements it was perfect for me!

As my scope had the tube rings included, I just had to adapt them to he mount. I designed the 2 parts cut them out of plywood, and painted them.

Here comes the interesting part: the altitude side bearings. As I couldnt get ebonystar or formica anywhere, I designed and 3D printed 2 PLA sleeves that cover the bearing surface. I printed a set of flat ones and a set of rough ones using the fuzzy skin setting in cura to mimic the ebony star texture. The first flat ones suffered from stiction, but the rough ones worked amazingly great. I can make any tiny movement I want extremely easily on the altitude axis.

Now, I have to improve the stock azimuth axis, It is a little difficult to turn it.

After all, I am pretty happy with the results. I believe the scope looks much better than the typical white sw dob

Thank you for your help. Of course it will be rainy all week, so I'll have to wait to try it out

Bye!

Fran

On 14/06/2020 at 13:37, pjsmith_6198 said:

Hello FranTeryda,

You've been given a lot of good advice already. When you buy The SW Explorer 200P are you buying the telescope only or the telescope plus the equatorial mount?  Using the rings to attach the scope to altitude bearings is a nice feature.  I made a new dobsonian mount for my Zhumell Z10 based on the "instructions for building a Dob" that   Louis D provided.  That's a very well known site that's helped a lot of people.  I made the adjustable cradle th site describes. Once finished, the new larger bearings where much better than the original.  Your ring system would take the place of cradle.   Give the site a good read it will explain why large bearings are better than small, proper bearing placement, how to balance the scope and basically everything you need to know.    Using your ring system and large altitude bearings your design will look very close to the Bresser design that Louis D also provided.   Which looks like your original design but modified for larger bearings.

AstroSystems have PTFE bearing kits (https://www.astrosystems.biz/pivot.htm) can ship over seas.   Click on the Secure Order link the to see if that will work for you.  Other alternatives are  HDPE (High Density Polyethylene)
and there's fiber glass material used in boat repair.  Experiment with other materials.   Lack of teflon is not  a show stopper.   

The height of the rocker box depends on the balance point of the telescope.  The bottom of the telescope needs to be able to clear the base when it's vertical.  Add a little  more room so you can re-balance the telescope if you
add extra's such as RACI finder, telrad, heavy EP etc.

Getting an adjustable chair when observing is a good idea.  It's more comfortable and you can see more details  than when hovering over the eyepiece

Phil

I bought just the tube without mount (It's being shipped 😀), and thankfully  it comes with the rings. This will make my job much easier and it will look nicer in my opinion. 

I've been reading that guide and it is extremely helpful. After your advice I modified the diameter of the bearings, it's larger now. It even looks better. 

Regarding the bearing surfaces, thankfully I asked a friend of mine if he knew where I could buy some Teflon to build it. It turns out he had a piece of 5 mm sheet of Teflon lying around so I wont have to experiment or order pieces online to get the bearing surfaces right.

I did not take into account the fact that i might have to shift the scope to keep it balanced, so I modified the design and added a little bit more of "legroom".

Anyway, thank you very much for your replies, your time and your help. It means a lot for me.

Cheers,

Fran

On 11/06/2020 at 16:40, Louis D said:

Here's a design plan for a Dob along the lines of what you want to accomplish.

Here are some instructions for building a Dob.  The structure instructions are toward at bottom under "A Dobsonian Mount".

Thank you! For sure those sites are going to be useful

11 hours ago, Demonperformer said:

Hi, FranTeryda, and welcome to SGL. Good luck with your project.

Enjoy the journey.

Thanks! Cheers from Argentina

12 hours ago, Louis D said:

I would try to make the trunnions as large as possible like the Bresser Dob's.  It really improves the altitude motion a great deal.  Also, try to mount the scope dead center to minimize the swing from horizon to zenith and to get the best possible balance.  This may mean adding weights somewhere for balance (likely at the top end).  There's not much reason if any to cantilever the mount backward as shown in your diagram.  Straight up and down is perfect.

Nylon chair slides can also work great for the bearing surface.  Teflon can sometimes be too slippery.  A matte to satin pebbly surface for the bearings is ideal.  Smooth glossy is actually too "sticky" in use.  It doesn't want to let go easily to track an object.  Some smooth satin surfaces will also work, depending on the material.  Think about a chair sliding on a floor with those glides on the bottom of each leg.  You can actually try out different combinations with this method.

The Dobsonian design at 8" f/5 excels when used while sitting.  You want to be bending over the telescope when viewing about 25 degrees above the horizon, typically about as low as you'll want to go.  You want to be sitting straight up when viewing at (or near) the zenith.  This is why minimizing the swing is important.  Mounting it too far back causes a large low to high swing.  That 1000mm focal length will be just about perfect if you can mount the scope's trunnion's center point about 27 to 28 inches about the ground in my experience.  I'm 5' 8", so your comfortable mount height might be higher or lower depending on your height.

Here are some examples of what I'm describing:

Thank you so much! I’ll take into account everything you suggested, specially the height of the thing. It was undersized. Using your suggested measurements and comparing them to the height of my eye while seating, I believe it is spot on. I’ll make sure to post some updates during the build. Thanks!

Hi! I really want to get into watching the night sky. After a looking at the scopes that are available in my country, I chose to buy a SW Explorer 200P (haven't yet) and build a homemade dobsonian base. 

I really like the aesthetics of the Orion Sky-quest dobsonian bases, so I draw a really similar design to fit the SW scope I want to buy. But while drawing it, I had tons of questions and I hope you can help me. 

First of all, I just could get some aproximate measures of the parts of the scope out of the internet. If any of you has one of these SW reflectors, I would really appreciate if you can take some measurements for me to make the design more precise.  Specially I really need the thickness and size of the holes of the rings.

About the bearing surfaces, I can't get anywhere the Teflon pads you usually use. What can I use to replace them? Also, what about the radius of the altitude bearings, Is it important? 

Finally, which should be the height of a dobsonian mount? I don't want to be bent over to be able to see comfortably, nor I want it to be  too tall. Is it supposed to be used on a stool or something?

I will really appreciate any other tip you can give me. I have never had a telescope, neither have I seen a dob mount. So I can be making a big mistake trying to convert this OTA to use with a dobsonian mount. 

Anyway thank you very much. Cheers from Argentina

Almost forgot to add some pics of the 3D design I made!