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

[_Augustus_]

Spider is here. Have installed it and the secondary. Testing tonight!

[_Augustus_]

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!

[wumpus]

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 December 30, 2017 by wumpus
we aren't getting pictures :( YAY PICTURES! (finally noticed the edit commment).

[_Augustus_]

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.

[_Augustus_]

I got the coated mirror back yesterday. The guy said it had the finest polish of any mirror he'd ever seen.

I had a quick look at the Moon through some clouds this evening. It was good. Unfortunately it's going to rain tonight......

[_Augustus_]

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 October 27, 2017 by _Augustus_

[Kevin Kyle]

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.

[_Augustus_]

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.....

[YNM]

Wow. This sounds really envying now !!!

[GDJ]

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!

[_Augustus_]

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.

Made by holding a phone up to the eyepiece.

Edited November 1, 2017 by _Augustus_
better version of pic

[softweir]

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?)

[_Augustus_]

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 October 31, 2017 by _Augustus_

[_Augustus_]

I found an awesome deal on a 12" plate glass blank. Should ship this week, but I won't be able to start until I get some grit/pitch for Christmas. Think I'll do an f/6.

[_Augustus_]

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. 

[_Augustus_]

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.

 

[_Augustus_]

Blank ships Monday, but has to go to Florida, be repackaged, and then get sent back up here. I'm estimating delivery will be on December 26th.

[_Augustus_]

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 December 16, 2017 by _Augustus_

[_Augustus_]

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.

 

[_Augustus_]

For some reason the 12" blank didn't ship until today, and it has to go from New York down to Florida back up here to basically New York. So next Friday is probably the earliest it can get here.

[_Augustus_]

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 December 26, 2017 by _Augustus_

[_Augustus_]

Blanks have arrived at the group buy organizer's place in Florida.

Now mine just has to make its voyage up here. Hopefully gets here by the end of the week.

[Dartguy]

I should have jumped at that chance to buy one or 2 of those.  I was close, but I have never tried grinding a mirror and want to try something smaller for the first time.  Good luck with yours!

[_Augustus_]

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 January 3, 2018 by _Augustus_

[_Augustus_]

Apparently the blanks shipped out TODAY.

Ridiculous.