Large newtonians

[Lady Fraktor]

In Germany it is quite common in some areas to go to star parties and find many very large newtonian.
I came across an article of Dr. Erhard Hänssgen homemade 107 cm (42") newtonian.
If you scroll down the page a bit you will see him doing full aperture white light solar observation using Baader solar film!

https://www.cruxis.com/scope/scope1070.htm

[Ylem]

Wow! That's a big boy!

My club back in NC had a 36" which I thought was massive!

[SkyHiker]

That's amazing, the views must be fantastic!

Let me also point out Mel Bartel's website and a video he made about his 42-incher that he is currently working on. The amazing thing is that he makes very thin meniscus mirrors. These mirrors have the same thickness everywhere; his 42-incher will be only 5/8" thick. His 30-inchers are also 5/8" thick, a 48:1 ratio. Apparently, it works well! He also makes them with a very small F ratio, the 30-incher is F/2.7, nothing short of amazing. He also makes a nice foldable design, and Alt/Az/Alt designs that have no singularity at zenith.

[JayTee]

Wow, that's devotion to this hobby!

[messier 111]

when we say a bucket that collects light.
my 5 inch serves as a finder.
thx for the story .

[Nakedgun]

~

Better than owning a 42-inch Newtonian, is having a friend who owns a 42-inch Newtonian.



.

[Michael131313]

Great article. Thanks Gabrielle.

[helicon]

Fabulous article Gabrielle. Thanks for sharing.

[bobharmony]

Thanks for sharing that, Gabby. That is a beauty of an instrument. I agree with @Nakedgun that a friend with a 42" scope is better than having one. Say it isn't so, Gabby, that you're not coming over to the dark side after all these years as a mirror-basher!

Bob

[StarBru]

Fascinating article and he really made a nice looking telescope! Thanks for posting this!

[Lady Fraktor]

Say it isn't so, Gabby, that you're not coming over to the dark side after all these years as a mirror-basher!

That will never happen Bob!
Though I would never call myself a mirror basher just because I like to come up with better uses for them.

[Richard]

45 min to set up with 1 person ? , perhaps after at least 10 tries before , for me this is like seeing these cheap scopes that say 525x magnification , yes possible but only for a few , and yes as we know most scopes can Magnify 525

I like my relatively small scopes

[yobbo89]

um is that a 30 ltr trash can used for a dust cover

[Lady Fraktor]

um is that a 30 ltr trash can used for a dust cover

I believe it is for protecting the secondary in transport and assembly.
Looks a bit small in there!

[OzEclipse]

HUGE!

Thanks for posting this Gabby,@Lady Fraktor
Despite its impressive size, there were a couple of things that caught my attention.

When he was asked to comment about magnification, he replied about using 1600 power. But to use a telescope of that aperture and at his age(he looks 50-60 years old) minimum magnification is around 200X. Any magnification lower than that and he is observing with a smaller aperture.

He also talks about using it for solar observing. With the contraction of his pupil, he'd need to use at least 1000 x magnification to use full aperture. At 200x, his 42 inch scope is only transmitting light from10 inches of aperture. Using it for solar observing seems ridiculous. BTW: The sun is blinding bright in a 10 inch with Baader V5 too, so the extra variable filter will still be needed.

cheers

Joe

[SkyHiker]

When he was asked to comment about magnification, he replied about using 1600 power. But to use a telescope of that aperture and at his age(he looks 50-60 years old) minimum magnification is around 200X. Any magnification lower than that and he is observing with a smaller aperture.

He also talks about using it for solar observing. With the contraction of his pupil, he'd need to use at least 1000 x magnification to use full aperture. At 200x, his 42 inch scope is only transmitting light from10 inches of aperture. Using it for solar observing seems ridiculous. BTW: The sun is blinding bright in a 10 inch with Baader V5 too, so the extra variable filter will still be needed.

Let's see if I can follow this, his telescope has diameter D=42*25.4=1067 mm, it's F ratio is fr=4.5, so the primary's focal length is D*fr=4801 mm. If f is the eyepiece focal length, m is the magnification m=F/f and x is the exit pupil then x=D/m=D*f/F=f/fr so for an exit pupil of 5 mm (typical for a 50-year old at night) the matching focal length is f=x*fr=5*4.5=22.5 mm and the minimum magnification to not lose light is m=F/f=213x. During the daytime the pupil is more like x=3.5 mm so the matching focal length f=x*fr=15.8 mm and the minimum magnification is m=F/f=305x. That's not crazy, is it, assuming that he uses an extra filter to keep his pupil at a normal size?

[helicon]

I should add that there is no way I would stand 16 feet up on that homemade ladder. You can buy a tree trimming/fruit tree picking ladder for around $1,000 that's many times safer.

[OzEclipse]

I should add that there is no way I would stand 16 feet up on that homemade ladder. You can buy a tree trimming/fruit tree picking ladder for around $1,000 that's many times safer.

Safer yes, but still going to need bottled oxygen at that altitude.

[OzEclipse]

When he was asked to comment about magnification, he replied about using 1600 power. But to use a telescope of that aperture and at his age(he looks 50-60 years old) minimum magnification is around 200X. Any magnification lower than that and he is observing with a smaller aperture.

He also talks about using it for solar observing. With the contraction of his pupil, he'd need to use at least 1000 x magnification to use full aperture. At 200x, his 42 inch scope is only transmitting light from10 inches of aperture. Using it for solar observing seems ridiculous. BTW: The sun is blinding bright in a 10 inch with Baader V5 too, so the extra variable filter will still be needed.

Let's see if I can follow this, his telescope has diameter D=42*25.4=1067 mm, it's F ratio is fr=4.5, so the primary's focal length is D*fr=4801 mm. If f is the eyepiece focal length, m is the magnification m=F/f and x is the exit pupil then x=D/m=D*f/F=f/fr so for an exit pupil of 5 mm (typical for a 50-year old at night) the matching focal length is f=x*fr=5*4.5=22.5 mm and the minimum magnification to not lose light is m=F/f=213x. During the daytime the pupil is more like x=3.5 mm so the matching focal length f=x*fr=15.8 mm and the minimum magnification is m=F/f=305x. That's not crazy, is it, assuming that he uses an extra filter to keep his pupil at a normal size?

HI Henk,
Yes very similar to the calculations I did.

I looked up and found that pupils can constrict to 2mm in bright light. 1067/2 is 534X for full transmission.
At 200X (24mm eyepiece) the aperture is equivalent to about 16 inches.

I was just calculating in my head when I wrote the post and I think I worked on a pupillary contraction of 1mm which is too small. That's where the 10 inch aperture figure came from.

I love the 18 inch scope I have but it is as big at I can manage (for now). I have no plans to ever go bigger and will have to downsize at some point in the future when I can no longer manage the 100+kgs of the 18 inch.

At Queensland Astrofest, I spent a lot of time observing through a friends 28". Chris, the scopes owner, was also Chair of the Astrofest organising committee but he kindly let me remain in control of the scope when he was frequently called away. Amazingly, many paricipants, coming form light polluted Brisbane remained glued to their own scopes and there were rarely more than 3 or 4 people waiting to observe through the scope and sometimes I was left alone and I took full advantage of the opportunity.

Obviously, the extra light lets you see fainter and I certainly recall easily ticking off the Polarissima Australis galaxy (NGC 2573) 2 arc min and Mv14. In my 18", it's a case of using averted imagination! The 28" has double the light gathering capacity of my 18 inch, almost a full magnitude. The mirror is a Mike Lockwood Optics composite mirror. Despite its open structure and multiple cooling fans, the mirror took half the night to settle, exacerbated no doubt by the fact that the telescope was left out in the sun all day albeit under a scope cover. Chris' own words were, "I'm going to stop apologising for the views of the planets." Chris tells me that at home when he pulls the scope out from under his house at sunset, and the seeing is good, the views of planets are magnificent.

That said, owning an excellent 18" scope, the extra magnitude of light gathering and resolution is unlikely to make me plunge many tens of thousands of dollars into such an instrument letting alone a 40"-60" class instrument. Not for me but maybe ok for some. A friend of mine in New York, Joel Moskowitz, owns a 40" scope and loves it.



In the TSS quiz last month, the poll question asked respondents to chose which large dob telescope they would prefer if one of the following was offered to them free of charge.

These were the results:
Scope .......... Votes
20" f4.5.........13
30" f4............3
40" f3.5.........2
50 f3.5..........0
65 f3.5..........3

The number of people who voted for the smaller 20 inch scope was over 60% and more than all the other responses put together. This surprised me. When I created the question, I thought aperture fever would prevail and responses would be weighted to the large size.

Cheers

Joe

[Lady Fraktor]

You missed none of the above as a response Joe