https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&pdp_ext_f=%
7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, March 25, 2022 at 2:05:25 AM UTC-7, RichA wrote:

https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&pdp_ext_

f=%7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

I want one!
🙄

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, March 25, 2022 at 5:05:25 AM UTC-4, RichA wrote:

https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&pdp_ext_

f=%7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

_________
Not all lenses are meant to be used as telescope objectives.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, March 25, 2022 at 7:43:39 AM UTC-6, W wrote:

Not all lenses are meant to be used as telescope objectives.

I can attest to that, as I wear eyeglasses, and I also own a camera - in addition to a
smartphone with a camera.

However, a lens that is 74 mm in diameter, but with a focal length of
3,000 mm, I would suspect, _is_ intended to be used as a telescope
objective.

But maybe not. 74 mm diameter is the kind of aperture one would associate
with a department store special telescope. If diffraction limited, a telescope with such an objective could magnify up to 180x. Divide 3000 by 180, and
you get 16 2/3. They do make eyepieces with focal lengths that big, so one _could_ use that lens in a telescope, impractical though it might be.

John Savard

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, 25 March 2022 at 12:42:00 UTC-4, Quadibloc wrote:

On Friday, March 25, 2022 at 7:43:39 AM UTC-6, W wrote:

Not all lenses are meant to be used as telescope objectives.

I can attest to that, as I wear eyeglasses, and I also own a camera - in addition to a
smartphone with a camera.

However, a lens that is 74 mm in diameter, but with a focal length of
3,000 mm, I would suspect, _is_ intended to be used as a telescope
objective.

But maybe not. 74 mm diameter is the kind of aperture one would associate with a department store special telescope. If diffraction limited, a telescope
with such an objective could magnify up to 180x. Divide 3000 by 180, and
you get 16 2/3. They do make eyepieces with focal lengths that big, so one _could_ use that lens in a telescope, impractical though it might be.

John Savard

People always looks at long focal length/ratio scopes differently, but reality is, the same power with the same type of eyepiece
as on another scope yields the same field size. So the concept of "looking through a straw" is only seen if someone is
clueless enough to slap a 10mm eyepiece on such a scope and getting 300x out of it. However, a 55mm Plossl will
provide 55x and a 1 degree (2 moons) field size. If you have some exotic 3 inch eyepiece, you could even get more.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, March 25, 2022 at 2:05:25 AM UTC-7, RichA wrote:

https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&pdp_ext_

f=%7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

I already have a 10-ft telescope and don't need another!

https://www.cloudynights.com/uploads/monthly_06_2006/post-12572-14070975670902_thumb.jpg

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, March 25, 2022 at 12:42:00 PM UTC-4, Quadibloc wrote:

On Friday, March 25, 2022 at 7:43:39 AM UTC-6, W wrote:

Not all lenses are meant to be used as telescope objectives.

I can attest to that, as I wear eyeglasses, and I also own a camera - in addition to a
smartphone with a camera.

However, a lens that is 74 mm in diameter, but with a focal length of
3,000 mm, I would suspect, _is_ intended to be used as a telescope
objective.

But maybe not. 74 mm diameter is the kind of aperture one would associate with a department store special telescope. If diffraction limited, a telescope
with such an objective could magnify up to 180x. Divide 3000 by 180, and
you get 16 2/3. They do make eyepieces with focal lengths that big, so one _could_ use that lens in a telescope, impractical though it might be.

This lens is probably useful in solar spectroscopy, maybe as the objective of a spectrohelioscope or as a collimating lens.

It could make an interesting camera obscura, maybe?

https://bonfoton.com/pages/faq

If one wanted to make it into a "practical" telescope, fold it with a couple of quality first-surface mirrors...

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Friday, 25 March 2022 at 23:47:31 UTC-4, palsing wrote:

On Friday, March 25, 2022 at 2:05:25 AM UTC-7, RichA wrote:

https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&pdp_

ext_f=%7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

I already have a 10-ft telescope and don't need another!

https://www.cloudynights.com/uploads/monthly_06_2006/post-12572-14070975670902_thumb.jpg

Impressive. Most will fold (optically or physically) the lens.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Sunday, March 27, 2022 at 8:41:38 PM UTC-7, RichA wrote:

On Friday, 25 March 2022 at 23:47:31 UTC-4, palsing wrote:

On Friday, March 25, 2022 at 2:05:25 AM UTC-7, RichA wrote:

https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&pdp_

ext_f=%7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

I already have a 10-ft telescope and don't need another!

https://www.cloudynights.com/uploads/monthly_06_2006/post-12572-14070975670902_thumb.jpg

Impressive. Most will fold (optically or physically) the lens.

There is no lens in this telescope, just 2 mirrors... it is just a simple Dobsonian mount Newtonian, one of the simplest designs of all...

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Monday, 28 March 2022 at 00:45:03 UTC-4, palsing wrote:

On Sunday, March 27, 2022 at 8:41:38 PM UTC-7, RichA wrote:

On Friday, 25 March 2022 at 23:47:31 UTC-4, palsing wrote:

On Friday, March 25, 2022 at 2:05:25 AM UTC-7, RichA wrote:

https://www.aliexpress.com/item/4000640306730.html?spm=a2g0o.productlist.0.0.6f302331VGkoXt&algo_pvid=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9&aem_p4p_detail=20220217225309433165067225700107795225&algo_exp_id=c0b2e880-ec51-4bb6-b05a-f14d156bc3c9-9&

pdp_ext_f=%7B%22sku_id%22%3A%2210000004778721146%22%7D&pdp_pi=-1%3B42.26%3B-1%3B-1%40salePrice%3BCAD%3Bsearch-mainSearch

I already have a 10-ft telescope and don't need another!

https://www.cloudynights.com/uploads/monthly_06_2006/post-12572-14070975670902_thumb.jpg

Impressive. Most will fold (optically or physically) the lens.

There is no lens in this telescope, just 2 mirrors... it is just a simple Dobsonian mount Newtonian, one of the simplest designs of all...

I meant the subject of the thread, not the big Dob.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 25/03/2022 16:41, Quadibloc wrote:

On Friday, March 25, 2022 at 7:43:39 AM UTC-6, W wrote:

Not all lenses are meant to be used as telescope objectives.

I can attest to that, as I wear eyeglasses, and I also own a camera - in addition to a
smartphone with a camera.

However, a lens that is 74 mm in diameter, but with a focal length of
3,000 mm, I would suspect, _is_ intended to be used as a telescope
objective.

But maybe not. 74 mm diameter is the kind of aperture one would associate with a department store special telescope. If diffraction limited, a telescope
with such an objective could magnify up to 180x. Divide 3000 by 180, and
you get 16 2/3. They do make eyepieces with focal lengths that big, so one _could_ use that lens in a telescope, impractical though it might be.

A very long time ago some early telescopes had objectives and eyepieces
with insanely long focal lengths for planetary work made form the best
glass that they had available. Striae were a big problem back then.

Professor Allan Chapman had a nice talk about it. A copy might be hidden somewhere on this website but I can't find it in a quick search.

https://societyforthehistoryofastronomy.com

There is brief mention of them at p27 in this edition of their journal.

https://societyforthehistoryofastronomy.com/wp-content/uploads/2016/10/shabulletin20.pdf

But there is or possibly was a full talk with diagrams...

--
Regards,
Martin Brown

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Folks, if you don't like a thread, please just skip it; thanks!

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Wednesday, March 30, 2022 at 4:35:09 PM UTC-4, fred k. engels® wrote:

Folks, if you don't like a thread, please just skip it; thanks!

Yes, that would be appreciated.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)