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GSO 12" f5 mirror first light

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#1 John Anderson

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Posted 11 July 2020 - 11:57 AM

My dob is finished, the mirror arrived and I tried it out last night ... the results were pretty good. Managed to find m3 (under Bortle 8 Minneapolis skies) and the stars were nice tiny points, although the view was rather dim and required averted vision to get the full globular effect.

 

Have to say the skies here are a bit disappointing so as a result of that I will probably do a lot of moon and planetary viewing.

 

Right now my highest power is a 9mm plossl ... have a meade 4000 6.4 plossl coming from ebay (only 24 bucks) so I will do some star testing and lunar viewing with that when it comes.

 

With the 9mm (x169) the point of best focus was obvious ... I would stop short of saying the mirror has a hard "snap" focus, but it's close. Higher power will tell more and I can do star testing. I tried some star testing with the 9mm and the out of focus image on either side of focus was very similar.

 

Overall I was pleased with the performance and for $535 from Agena Astro (with free shipping) it seems like a pretty good deal. I passed on the GSO secondary bundle and got a 2.6" 1/18 wave unit from Astro Systems.

12 inch dob.jpg


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#2 coopman

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Posted 11 July 2020 - 12:04 PM

Nice looking scope.  Congrats.



#3 Tim J K

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Posted 12 July 2020 - 07:25 AM

Great looking scope!  Please keep us posted about how it performs.

 

Tim



#4 Spikey131

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Posted 12 July 2020 - 07:32 PM

Nice scope.  You need to take it somewhere dark.



#5 John Anderson

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Posted 01 August 2020 - 09:23 AM

Observed the moon, jupiter, and saturn last night. A 9mm GSO plossl and GSO coma corrector gave x183. Jupiter was only at about 20 degrees elevation and there was a lot of turbulence but in spite of this very good detail could be glimpsed ... due to opposition the disk was large. The moon also showed showed a lot of detail through the high-speed waviness. The turbulence itself was rendered very sharply by the scope. Saturn looked nice overall but I had trouble seeing any detail besides the major division in the rings.

 

Tracking is ok at this power, I used teflon on aluminum for the altitude bearings and teflon on generic laminate for the base. Might try some sort of lubricant.

 

Also tried out the GSO 42mm superview. Yes the exit pupil is too big but the view is nice ... three moons wide and sharp in the middle, a very dramatic view of the moon and it makes a good finder eyepiece. My pupil is probably stopping the scope down to about an 8.5" f7.5 equivalent. I didn't notice any blackout due to the diagonal, however perfectionists should note that this is one of those "fuzzy field stop" eyepieces.

 

It was an all-GSO night and I have to say that the mirror is good, possibly very good. The point of best sharpness comes up nice with the fine focus knob. Saving my pennies for a 7mm nagler and 27mm panoptic.

 

20200801_083749.jpg


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#6 John Anderson

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Posted 01 August 2020 - 09:40 AM

The 6.4mm meade super plossl I ordered off ebay is stuck in the US Mail.

 

I live in South Minneapolis and our post office was burned down in the George Floyd riots ... the package is held up at some other distribution point.

 

UPS is getting through fine so I've been able to get some goodies from Agena Astro.

 

The larger reality impacting the little backyard hobby ...



#7 Mazerski

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Posted 01 August 2020 - 09:43 AM

John,

 

If you can swing it, think about investing in a night vision intensifier device... I have a 12.5” New Moon and live under east coast sky. Night Vision allows me to see DSOs like I never thought possible. I’m not into AP but did recently hold an iPhone 7 to eyepiece to snap a few photos.

Here is a CLoudyNight post where I added some photos - see Post #9

 

https://www.cloudyni...ictures-please/



#8 John Anderson

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Posted 01 August 2020 - 09:50 AM

Interesting ... the aesthetic is somewhat mil-tech but a lot is visible.



#9 jeffmac

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Posted 01 August 2020 - 08:22 PM

Make sure to blacken the inside of that mirror box with flat black paint or flocking. That should add to the scope's performance. Nice looking scope.


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#10 John Anderson

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Posted 05 September 2020 - 11:11 AM

Simulation of Mars as seen on 9-5-2020, 4:30 am Central Time, Minneapolis MN

x183

 

Mars was about 50 degrees above the horizon and almost due south. I found a photo on the internet that looked similar and scaled it and added some blur.

 

The image scale is just guessed at, this simulation reflects the impression of concentrating on the center of the field of view and so it is perhaps a bit "zoomed in" with respect to the actual magnification. I also did some observing with a 6.4mm plossl at x258 but the seeing did not support that magnification and no additional detail could be seen.

 

The photo doesn't show the exact surface features I was looking at but it appears similar, the polar ice cap was very obvious although the dark features came and went with the seeing. The photo also doesn't show the current gibbous phase, which can be seen fairly well at this time. But caveats aside, this is a pretty good representation of the appearance through the eyepiece.

 

The mirror had cooled for about an hour and a half and the seeing was fair ... this was with a 9mm plossl and GSO coma corrector. Collimation was very good via star test at x258.

 

mars 9-5.jpg


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#11 Xeroid

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Posted 10 September 2020 - 10:32 AM

Nice job!

 

What did you do for a mirror cell?



#12 John Anderson

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Posted 10 September 2020 - 11:01 AM

It's a 9-point cell, 1 1/2" laminated birch ply with three 3/8" bolts running through, topped with three 1/2" birch ply triangles.

 

The edge support is two small cap screws at 90 degrees.

cell.jpg


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#13 Auburn80

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Posted 11 September 2020 - 09:19 AM

The 6.4mm meade super plossl I ordered off ebay is stuck in the US Mail.

I live in South Minneapolis and our post office was burned down in the George Floyd riots ... the package is held up at some other distribution point.

UPS is getting through fine so I've been able to get some goodies from Agena Astro.

The larger reality impacting the little backyard hobby ...


Hi John. You may find that Meade SP to be very tight on eye relief. Once you try it out for a while, you might consider something like the Paradigm series from Astronomics. Better eye relief, wider field and pretty friendly to your pocket book.
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#14 stargazer193857

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Posted 11 September 2020 - 10:10 AM

Excellent picture of Mars. I viewed Mars two nights ago and saw a blurry mess in my 6" at 135x.

#15 Achernar

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Posted 15 September 2020 - 12:13 PM

Make sure to blacken the inside of that mirror box with flat black paint or flocking. That should add to the scope's performance. Nice looking scope.

To add to Jeffmac's advice, make sure to varnish the outside first. That way when you paint the inside flat black, flock it or both, if you get any paint on the outside, you can remove it completely with ease with a rag and paint thinner.

 

Taras



#16 BGazing

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Posted 16 September 2020 - 12:19 AM

Simulation of Mars as seen on 9-5-2020, 4:30 am Central Time, Minneapolis MN

x183

 

Mars was about 50 degrees above the horizon and almost due south. I found a photo on the internet that looked similar and scaled it and added some blur.

 

The image scale is just guessed at, this simulation reflects the impression of concentrating on the center of the field of view and so it is perhaps a bit "zoomed in" with respect to the actual magnification. I also did some observing with a 6.4mm plossl at x258 but the seeing did not support that magnification and no additional detail could be seen.

 

The photo doesn't show the exact surface features I was looking at but it appears similar, the polar ice cap was very obvious although the dark features came and went with the seeing. The photo also doesn't show the current gibbous phase, which can be seen fairly well at this time. But caveats aside, this is a pretty good representation of the appearance through the eyepiece.

 

The mirror had cooled for about an hour and a half and the seeing was fair ... this was with a 9mm plossl and GSO coma corrector. Collimation was very good via star test at x258.

 

attachicon.gifmars 9-5.jpg

I tried Mars in the same configuration and it was too bright even at 300x and 430x...easy to find it even without the finder as the difraction spikes are enormous. Tried to kill it with Neodymium, didn't help. Seeing was not that bad actually, it is just that I run out of power to dampen brightness on a 12 inch mirror.

Not sure 27mm Panoptic is what you need...perhaps something shorter around 17-20 and 13mm. 7mm will be excellent for globulars.



#17 Javier1978

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Posted 16 September 2020 - 08:29 AM

Nice looking scope, enjoy it!



#18 John Anderson

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Posted 16 September 2020 - 12:02 PM

I tried Mars in the same configuration and it was too bright even at 300x and 430x...easy to find it even without the finder as the difraction spikes are enormous. Tried to kill it with Neodymium, didn't help. Seeing was not that bad actually, it is just that I run out of power to dampen brightness on a 12 inch mirror.

Not sure 27mm Panoptic is what you need...perhaps something shorter around 17-20 and 13mm. 7mm will be excellent for globulars.

Well it's a simulation and it was quite a bit brighter through the eyepiece than in this pic, also the pic is scatter-free which was not the case in reality ...I debated putting up any picture at all but I though this was a good example of the details visible. The seeing just wasn't that good and higher power was too fuzzy.

 

Here in the upper midwest there is the jet stream to contend with most of the time.

 

My sense is that in very brief moments there is a lot more detail there so it would be fun to take a trip to the southwest someplace where the seeing is really excellent.



#19 rjaszcz

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Posted 16 September 2020 - 12:54 PM

My dob is finished, the mirror arrived and I tried it out last night ... the results were pretty good. Managed to find m3 (under Bortle 8 Minneapolis skies) and the stars were nice tiny points, although the view was rather dim and required averted vision to get the full globular effect.

 

Have to say the skies here are a bit disappointing so as a result of that I will probably do a lot of moon and planetary viewing.

 

Right now my highest power is a 9mm plossl ... have a meade 4000 6.4 plossl coming from ebay (only 24 bucks) so I will do some star testing and lunar viewing with that when it comes.

 

With the 9mm (x169) the point of best focus was obvious ... I would stop short of saying the mirror has a hard "snap" focus, but it's close. Higher power will tell more and I can do star testing. I tried some star testing with the 9mm and the out of focus image on either side of focus was very similar.

 

Overall I was pleased with the performance and for $535 from Agena Astro (with free shipping) it seems like a pretty good deal. I passed on the GSO secondary bundle and got a 2.6" 1/18 wave unit from Astro Systems.

attachicon.gif12 inch dob.jpg

Good looking scope John! Could you post a picture or two of the way you connected the top of the tubes to the secondary cage please. I'd like to see it and/or maybe chat with you about it.

 

Thanks,
Ray



#20 John Anderson

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Posted 16 September 2020 - 05:36 PM

The part bolted to the ring is 1/8" x 1" aluminum angle. The tubes use threaded inserts from Obsession. The tubes connect to the aluminum with pre-drilled steel carpentry reinforcement angle brackets from Home Depot. The wing nuts are delrin/stainless steel and were found on ebay.

 

20200916_164246.jpg

20200916_164326.jpg

20200916_164216.jpg


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#21 rjaszcz

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Posted 16 September 2020 - 07:41 PM

The part bolted to the ring is 1/8" x 1" aluminum angle. The tubes use threaded inserts from Obsession. The tubes connect to the aluminum with pre-drilled steel carpentry reinforcement angle brackets from Home Depot. The wing nuts are delrin/stainless steel and were found on ebay.

 

attachicon.gif20200916_164246.jpg

attachicon.gif20200916_164326.jpg

attachicon.gif20200916_164216.jpg

Thanks John!



#22 Woj2007

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Posted 17 September 2020 - 04:04 PM

I tried Mars in the same configuration and it was too bright even at 300x and 430x...easy to find it even without the finder as the difraction spikes are enormous. Tried to kill it with Neodymium, didn't help. Seeing was not that bad actually, it is just that I run out of power to dampen brightness on a 12 inch mirror.

 

Two days ago I've been observing Mars and I put one part of the Celestron 1.25" polarizing filter on the eyepiece. The brightness was reduced, the contrast improved. Recommended. waytogo.gif


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