Jump to content

Amateur Telescope Making (UPDATED 9/23/18) - 20" f/4 Nearly Complete


Recommended Posts

I spent 30 minutes looking at Saturn and star testing. Saturn is really nice and shows banding, the Cassini division, and the shadow on the rings. Stars appear as points even at high power, and the in- and out- of focus disks are identical. 

I say it's ready for coating!

Link to comment
Share on other sites

On 10/20/2017 at 6:54 PM, _Augustus_ said:

I spent 30 minutes looking at Saturn and star testing. Saturn is really nice and shows banding, the Cassini division, and the shadow on the rings. Stars appear as points even at high power, and the in- and out- of focus disks are identical. 

I say it's ready for coating!

You can't have a 6 month thread and not include pictures!

Is that even possible with your setup?  I'd assume that for "real" astronomy, you need pictures with fairly significant shutter lengths.  Ouch.

I'd assume that adapting the viewfinder isn't that hard, but tracking costs big bucks.  You might go far with a highly optimistic HDR sensor (you will need plenty of bits "in the noise") that simply sits in place and later moves and combines the images.  This technique works well many places, but if there is no "negative sensor levels" to average out to zero in pictures, it might not work well here.  Certainly any such things are for a much later project.

Edited by wumpus
we aren't getting pictures :( YAY PICTURES! (finally noticed the edit commment).
Link to comment
Share on other sites

24 minutes ago, wumpus said:

You can't have a 6 month thread and not include pictures!

Is that even possible with your setup?  I'd assume that for "real" astronomy, you need pictures with fairly significant shutter lengths.

I can't do any photography with it, unfortunately, and definitely not with an uncoated mirror. I'd need thousands of $ to do it.

Link to comment
Share on other sites

First light:

Albireo - Very different view at ~25x compared to with a longer FL scope.

M31 - Brighter than I'm used to, saw a dust lane.

M15 - Resolved with the 9mm Expanse.

C14 - Ridiculously good.

Pleiades - Like binoculars but better. Maybe a hint of nebulosity?

Auriga open clusters (M36, M37, M38, and a couple NGCs) - All very nice; sometimes more than one in the FOV.

C1 - Boring, but what do you expect?

M35 - Not like what I'm used to, but it is low in the sky just above a dim light across the street.

M57 - A tiny fuzzy star at ~25x with the 32mm Plossl. Didn't have time to switch eyepieces before it went below the trees.

C65 - Lost in the light dome to the south.

Even with lightly-sanded bearings, the altitude friction is way too low and I can't get above 65 degrees or so without the scope heading for the zenith - my M31 and C14 observations were done with me lightly holding the OTA in place. Likewise, the scope tends to have trouble near the horizon. I will sand the bearings some more tomorrow.

Edited by _Augustus_
Link to comment
Share on other sites

Awesome stuff. Ive always wanted to,make my own mirror. I did take an old dob and rebuilt it to a real nice scope. The original had a very nice handmade mirror and its nice in the new scope. Enjoyed reading your post, wish I could see it first hand, Good job, it must be VERY rewarding. :)

Link to comment
Share on other sites

Tonight's observing:

Moon - Lots of detail. Better than my 6" f/8. I can see craters a few km in size.

Saturn - 2 or 3 bands and a hint of the hexagon.

Albireo - The two components had smaller Airy disks than last night thanks to the good seeing.

M27 - First time I've ever seen this. Showed some of the apple-core structure.

M57 - Nice shape with the 9mm Expanse, barely recognizable with the 32mm Plossl.

M13 - Definitely resolved with the 9mm Expanse, very nice.

M31 - No dust lane thanks to the bright Moon.

C14 - Magnificent as usual.

Epsilon Lyrae - Barely split with the 5.5mm UWA.

Eta Cass - Nice split with the 5.5mm UWA.

Pleiades - Nice, but with a lot of stars missing compared to last night.

The Moon really ruins a lot of DSOs - I never really noticed before.....

Link to comment
Share on other sites

1 hour ago, _Augustus_ said:

Tonight's observing:

Moon - Lots of detail. Better than my 6" f/8. I can see craters a few km in size.

Saturn - 2 or 3 bands and a hint of the hexagon.

Albireo - The two components had smaller Airy disks than last night thanks to the good seeing.

M27 - First time I've ever seen this. Showed some of the apple-core structure.

M57 - Nice shape with the 9mm Expanse, barely recognizable with the 32mm Plossl.

M13 - Definitely resolved with the 9mm Expanse, very nice.

M31 - No dust lane thanks to the bright Moon.

C14 - Magnificent as usual.

Epsilon Lyrae - Barely split with the 5.5mm UWA.

Eta Cass - Nice split with the 5.5mm UWA.

Pleiades - Nice, but with a lot of stars missing compared to last night.

The Moon really ruins a lot of DSOs - I never really noticed before.....

Looks like you made yourself one hell of a telescope! Great job!

Link to comment
Share on other sites

I made a new tool for the 8" DK today, this time with pennies instead of tiles.

Also, here's a photo of tonight's Moon with the 6" f/4.5.

sKkQUz1.png

Made by holding a phone up to the eyepiece.

Edited by _Augustus_
better version of pic
Link to comment
Share on other sites

10 hours ago, softweir said:

Impressive image!

Now all you need is some way to attach cameras to the eyepiece, and a bracket to hold counterweights so the 'scope doesn't flop when you do so. (Down near the mirror, on the far side from the eyepiece?)

Thanks. It's not a very good photo - my 60mm refractor has a better image visually. This thing shows far more. I will probably throw together an adapter at some point.

The counterweight bracket is a good idea, but I should be able to just sand the bearings and increase the friction enough that I don't need it.

Edited by _Augustus_
Link to comment
Share on other sites

  • 4 weeks later...

I posted it in the Astro-Imaging thread, but here's the Moon from the other night with the 6" f/4.5:

https://www.astrobin.com/323352/?nc=user

I've decided on an f/6-f/6.5 for the 12" (leaning on the long side). Shouldn't require a ladder at least most of the time, but I figure I'll make a very tall adjustable chair to use with it since I hate standing to observe. 

Link to comment
Share on other sites

Lead time from Swift Glass is 10-14 business days, plus one business day for the guy organizing the deal to repack them, plus 3-4 days for shipping puts arrival between December 14th at the earliest and December 22nd (or possibly the 26th) at the latest. So the blank probably won't be sitting here for long before I get the rest of the stuff I need for Christmas.

 

Link to comment
Share on other sites

  • 2 weeks later...

Still, that's only 10 days away! In the meantime, I've been clearing out my junk drawer of some stuff I don't need and selling it on eBay, and I'm on my way to having enough money to complete the project, so that's good.

Edited by _Augustus_
Link to comment
Share on other sites

Finally got to use the scope for a short little bit tonight on M42. The nebula was dimmer than usual (used my 20mm NPL), but there were clouds around and I'd suspect the many extravagant Christmas displays in our town didn't help. The contrast, however, was excellent - the dark Fish's Mouth stands out ridiculously well. Pretty sure I saw E and F in the Trapezium. I added a record to the azimuth bearing so it wasn't wood-on-felt - much smoother now.

 

Link to comment
Share on other sites

I got a complete abrasives/polish/pitch kit today, along with The Dobsonian Telescope, a new saw, a new drill, and a router. Still no blank... there's a good chance it won't be here before the end of the year now.

Edited by _Augustus_
Link to comment
Share on other sites

I have no idea on when or whether the 12" blanks shipped out. Didn't come in the mail today.

Last night I took out the 6" f/4.5 and saw a greenish color in M42 - never seen that before.

Edited by _Augustus_
Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...