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Degree Circles

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#1351 WillR

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Posted 20 April 2021 - 02:59 PM

 

It's convenient, but not necessary.  For my tabletop dob, where the circle is between the ground boards and is stationary, I have the cut out below the eyepiece.  For my 12" dob, the circle is on the top board and the pointer is adjustable, I have it set so the pointer is at the back of the scope where I'm less likely to kick it or otherwise knock it out of alignment.  If I do need to move a few degrees, I can just look down and judge by looking at any part of the scale and if I'm moving more than 10 or so degrees, chances are I need to get up and adjust my chair position anyway.  A buddy has his set to the front of the scope, which I would probably do next time as that is still out of the way, but visible from the ep.

 

I will recommend, if you are putting the circle between the ground boards, set up your pointer so that you have some room for adjustment/fine tuning.  I use a strip of metal on the tabletop base and a magnet glued to a clock hand.  The cut out gives me about 30 degrees of play.  For my 12" I either use a clamp on pointer that can go anywhere or a small tent stake.

 

Here you can see the yellow strip of metal (a piece from an old tape measure)
 
 
I made this from a binder clip, ball point spring and the tine from a plastic fork!
 
 
This is an experiment with a laser pointer.  Works well, except in the cold!

 

I am looking at the photo of your one sky. Is that a finderscope toward the back, behind the angle gauge. If so, what are you using with this scope? Did you put it back there for balance?



#1352 Richie2shoes

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Posted 20 April 2021 - 07:05 PM

I am looking at the photo of your one sky. Is that a finderscope toward the back, behind the angle gauge. If so, what are you using with this scope? Did you put it back there for balance?

That is a laser pointer.  I put it back there partly for balance and partly to keep it out of the way.  I also replaced the stock red dot with a Rigel quickfinder.  The beam goes up between the finder and the focuser.

 

OS QF
QF Mount

Edited by Richie2shoes, 20 April 2021 - 07:06 PM.


#1353 Quinnipiac Monster

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Posted 13 May 2021 - 05:15 AM

Great thread, I am going to add an AZ circle to my 10" f/7 and I learned a lot here. I really need to find quickly planets in daylight, especially Venus and Mercury (sometimes Mars). For Venus the alt circle is OK, level the mount and set the right alt, swing until you get it in the viewfinder. Works fine even when Venus is just a handful degrees from the Sun. With Mercury it's almost impossible as I need to place it into the eyepiece, and at the lowest possible magnification (67x) my field of view is just 40' or so. I use an equatorial table so I need to level first, find the object with the tracking off, then turn the motor on. It's doable but it cuts tracking time in half so you want to be able to recenter the object quickly in case you have to reset.

 

Anyway, my Az circle is going to be a linear one around the base, with moving pointer. Still mulling over how to make it adjustable, which looks like the way to go and I found some great ideas here. For the graduated scale I tried the Blocklayer website which is nice, but the scale is going to be LONG and apparently the website will not let me print it on separate A4 sheets.

 

This was a bummer, anyone knows if there are workarounds? 



#1354 Richie2shoes

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Posted 13 May 2021 - 07:59 AM

Great thread, I am going to add an AZ circle to my 10" f/7 and I learned a lot here. I really need to find quickly planets in daylight, especially Venus and Mercury (sometimes Mars). For Venus the alt circle is OK, level the mount and set the right alt, swing until you get it in the viewfinder. Works fine even when Venus is just a handful degrees from the Sun. With Mercury it's almost impossible as I need to place it into the eyepiece, and at the lowest possible magnification (67x) my field of view is just 40' or so. I use an equatorial table so I need to level first, find the object with the tracking off, then turn the motor on. It's doable but it cuts tracking time in half so you want to be able to recenter the object quickly in case you have to reset.

 

Anyway, my Az circle is going to be a linear one around the base, with moving pointer. Still mulling over how to make it adjustable, which looks like the way to go and I found some great ideas here. For the graduated scale I tried the Blocklayer website which is nice, but the scale is going to be LONG and apparently the website will not let me print it on separate A4 sheets.

 

This was a bummer, anyone knows if there are workarounds? 

I believe I exported the file as a pdf and was able to print it in separate sheets that way.  I used the same website to print the template when I carved the numbers on my ad12.



#1355 Quinnipiac Monster

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Posted 13 May 2021 - 09:56 AM

I believe I exported the file as a pdf and was able to print it in separate sheets that way.  I used the same website to print the template when I carved the numbers on my ad12.

Mumble mumble... I was able indeed to export the file as a single pdf by choosing a custom format, because the website just won't produce a multi-pages PDF (in spite of saying the opposite. I am doing something wrong? confused1.gif ). The graduated scale is 57' long, do you know how to split this monster into separate A4 sheets?

Thanks for helping!



#1356 Richie2shoes

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Posted 13 May 2021 - 02:51 PM

Mumble mumble... I was able indeed to export the file as a single pdf by choosing a custom format, because the website just won't produce a multi-pages PDF (in spite of saying the opposite. I am doing something wrong? confused1.gif ). The graduated scale is 57' long, do you know how to split this monster into separate A4 sheets?

Thanks for helping!

After clicking the "Diagrams to PDF" button on the website, it opens a new window for me.  I make sure the scale is 100% and click "All to PDF", then I download the file to my laptop, and when I open it in Adobe, I have a "Poster" print option that slices it to multiple sheets.



#1357 Quinnipiac Monster

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Posted 13 May 2021 - 02:55 PM

OK I figured that out. Will explain in the unlikely case anyone here is as pathetically limited as myself. 

 

1. Export in pdf. The format must be large enough that the whole project is contained in a single sheet (there is a "custom" format)

 

2. Open with a pdf reader, then "Print". In the window, choose A4 or "Letter", then hit the key "Poster". This will split the project into as many A4 or Letter sheets as needed. 

 

3. Print.

 

The procedure is actually explained on the website, but I thought the "Print" dialogue window should be somewhere on the website rather in the pdf reader, then the project would be saved as a number of different pdf files :p


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#1358 Quinnipiac Monster

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Posted 13 May 2021 - 02:57 PM

After clicking the "Diagrams to PDF" button on the website, it opens a new window for me.  I make sure the scale is 100% and click "All to PDF", then I download the file to my laptop, and when I open it in Adobe, I have a "Poster" print option that slices it to multiple sheets.

Was typing my self-answer at the same time when you posted yours! Thank you anyway! Now, down to cutting and gluing. 


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#1359 Borodog

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Posted 13 May 2021 - 09:35 PM

I have a question about adding circles to my Dob that I use with an EQ platform. Presuming that the rocker box is correctly aligned to the platform, and the platform is correctly polar aligned, and that one has a digital inclinometer on the OTA, is there anything in principle that will prevent your alt-az readings from being accurate on the platform?



#1360 aeajr

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Posted 13 May 2021 - 09:46 PM

I have a question about adding circles to my Dob that I use with an EQ platform. Presuming that the rocker box is correctly aligned to the platform, and the platform is correctly polar aligned, and that one has a digital inclinometer on the OTA, is there anything in principle that will prevent your alt-az readings from being accurate on the platform?

I have never used an EQ platform for a Dobsonian mount so this is based on my assumptions, not experience.


the basis of the altaz coordinate system assumes the mount is level to the ground, we measure position relative to the horizon.

EQ mounting assumes a RA DEC coordinate system where the base of the Dob mount is not level to the ground but polar aligned.

Two different coordinate systems.

It might be close enough. Give it a try.

The angle gauge on the tube will still read the angle of the tube accurately for alt coordinates to work.

Edited by aeajr, 14 May 2021 - 05:24 AM.

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#1361 Borodog

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Posted 14 May 2021 - 10:57 AM

In actuality the base of the scope/top of the platform is not itself polar aligned; that would be impossible as, for example at my latitude of 36°, the platform top would have to be inclined at 54°! Instead, ideally the top of the table is parallel to the ground align the line pointing north, and the table top rotates around the RA axis. So yes, in the east-west direction, the table could be out of level by up to 7.5° either way. But I think this would result in a small error in azimuth, and the digital inclinometer would still read true.

 

I probably will just give it a try, but if there is some "gotcha" that I am not seeing I'd like to know before investing the time and money.

 

Also, what digital inclinometers would people recommend?



#1362 Pokemoncrusher1

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Posted 14 May 2021 - 11:08 AM

I have a question about adding circles to my Dob that I use with an EQ platform. Presuming that the rocker box is correctly aligned to the platform, and the platform is correctly polar aligned, and that one has a digital inclinometer on the OTA, is there anything in principle that will prevent your alt-az readings from being accurate on the platform?

no, just align the eq platform to polaris, then wind it back until its level use a bubble level or something, once your level and the eq platform is aligned to polairs, just find the object with the setting circles like you usually would, then once you have it centered turn on the motor to start tracking, if you want to find something else you need to go back to level.


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#1363 Quinnipiac Monster

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Posted 18 May 2021 - 04:00 PM

I have a question about adding circles to my Dob that I use with an EQ platform. Presuming that the rocker box is correctly aligned to the platform, and the platform is correctly polar aligned, and that one has a digital inclinometer on the OTA, is there anything in principle that will prevent your alt-az readings from being accurate on the platform?

Not that I can think of, as long as the platform is level and the tracking is not running. This a a lot of assumptions though. 


Edited by Quinnipiac Monster, 19 May 2021 - 04:41 AM.

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#1364 Retropad

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Posted 30 June 2021 - 12:10 AM

IMG_20210629_220304212~7.jpg

Thanks to all who have posted their ideas here.  I read the whole string while I was waiting for my AD8 to arrive (ordered in February, received in June).  Your insights have been super helpful.   I have been interested in astronomy for decades but never had the money to invest in a scope until now.  I didn't have the guts to cut my new dob, so decided to make my circle  an inch larger than the base. Spray glued some plumbers strapping, nail epoxied to a magnet from the fridge. Inclometer was really bright, so taped a baby bell wrapper to it to make it red.  Found some Lazer finger toys to light up the pointer.  Now I'm ready for some clear skies!.  Again thanks for taking time to share your wealth of knowledge..it has made me so excited to get out under the stars again.  


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