Re: Slow telescope focal ratios

jimcoble2000

Thank you Stu. That sums it up. No one who has seen my hands can fail to understand I don't deal in microns when focusing but point taken and well stated. My f 5.6 refractor is famous for being either in focus or not. No in between. If you are not sure, you are not

By the theory, my 4 inch Televue is 68 microns. The 5 inch is 107.8           63% smaller.

On Thursday, January 13, 2022, 01:35:33 PM EST, Stu Beaber <wd4sel@...> wrote:

It's because the critical focus zone (CFZ) is greater with slower telescopes. The CFZ is the distance one can move the focal point without any apparent change in focus, According to Ron Woraski's book "The New CCD Astronomy'', the formula to determine that is CFZ=focal ratio squared times 2.2=answer in microns. He goes on to say that the CFZ for a f/5.5 scope would be one quarter that of a f/11 scope. However real world values for the CFZ are approximately 10-30% greater than theoretical values.

Stu

On Thu, Jan 13, 2022 at 11:12 AM Kent Blackwell <kent@...> wrote:

Most of us prefer "fast" telescope ratios. With fast systems, such as f/4 to 4/6 telescope tubes can be shorter, important for transporting our instruments to dark sky locations. There are exceptions, such as folded telescope systems. Back in the late 1960's Celestron offered a Schmidt-Cassegrain 8" f/10 folded system in a very compact tube. I had one years ago and it was compact enough I even took it to a cruise to Africa on an eclipse expedition.

I currently have a rather rare Meade 10" f/15 Maksutov design. What I've noticed with fast system such as f/4 to f/6 is stars tend to "snap" in and out of focus with just a touch of the focuser. With the above mentioned f/15 system I've noticed I can turn the focusing knob a considerable distance and the stars stay in focus. I also noticed the same with my 4" f/15 Unitron refractor. Focus becomes less critical with "slow" systems such as f/10 to f/15.

I don't know why I brought this up, but last night I just thought it was amazing how far I could turn the focusing knob on the Meade 10" f/15 system and maintain a sharp focus.

Re: Slow telescope focal ratios

Stu Beaber

It's because the critical focus zone (CFZ) is greater with slower telescopes. The CFZ is the distance one can move the focal point without any apparent change in focus, According to Ron Woraski's book "The New CCD Astronomy'', the formula to determine that is CFZ=focal ratio squared times 2.2=answer in microns. He goes on to say that the CFZ for a f/5.5 scope would be one quarter that of a f/11 scope. However real world values for the CFZ are approximately 10-30% greater than theoretical values.

Stu

On Thu, Jan 13, 2022 at 11:12 AM Kent Blackwell <kent@...> wrote:

Most of us prefer "fast" telescope ratios. With fast systems, such as f/4 to 4/6 telescope tubes can be shorter, important for transporting our instruments to dark sky locations. There are exceptions, such as folded telescope systems. Back in the late 1960's Celestron offered a Schmidt-Cassegrain 8" f/10 folded system in a very compact tube. I had one years ago and it was compact enough I even took it to a cruise to Africa on an eclipse expedition.

I currently have a rather rare Meade 10" f/15 Maksutov design. What I've noticed with fast system such as f/4 to f/6 is stars tend to "snap" in and out of focus with just a touch of the focuser. With the above mentioned f/15 system I've noticed I can turn the focusing knob a considerable distance and the stars stay in focus. I also noticed the same with my 4" f/15 Unitron refractor. Focus becomes less critical with "slow" systems such as f/10 to f/15.

I don't know why I brought this up, but last night I just thought it was amazing how far I could turn the focusing knob on the Meade 10" f/15 system and maintain a sharp focus.

Webb distance

jimcoble2000

oops last message obsolete now. Stand by for update

Webb is now.....................

jimcoble2000

84.5910 % of the way to parking

A few more interesting telescope observations

jimcoble2000

An article writes

It is said that as one gets older one’s sensitivity to the extremes of the visual spectrum gets less so more elderly observers may not find the resulting false colour a problem.  One reason being that the yellowing of the eye’s lens tends to filter out the blue part of the spectrum.  I suspect that this is true and was somewhat amazed recently when I turned my 80mm, f/5, achromat onto the Moon and could not really see any false colour near the limb.

This may well be true. After cataract surgery I am very sensitive to blue fringe now where before I was not. Even in well corrected scopes if the eyepiece has any blue fringe I'll find it.

Re: Slow telescope focal ratios

jimcoble2000

Speaking of collimation. From Nasa's update on Webb

The primary mirror wings are now fully deployed and latched into place, but the individual mirror segments remain in their launch configuration. This operation is a multi-day, multi-step activity to activate and move each of the 18 primary mirror segments and the secondary mirror from their stowed launch configuration to a deployed position ready for alignment.

The 18 primary mirror segments and secondary mirror are adjustable via six actuators that are attached to the back of each mirror. The primary mirror segments also have an additional actuator at its center that adjusts its curvature. The telescope's tertiary mirror remains stationary. The primary and secondary mirror segments will move a total of 12.5mm, in small increments, over the course of ~10 days to complete each segment's deployment.

After all individual mirror segment deployments are completed, the detailed optical mirror alignment process begins which is about a 3 month process. In parallel, as temperatures cool enough, instrument teams will turn on their instruments and begin each instrument's commissioning process.

On Thursday, January 13, 2022, 11:12:44 AM EST, Kent Blackwell <kent@...> wrote:

Most of us prefer "fast" telescope ratios. With fast systems, such as f/4 to 4/6 telescope tubes can be shorter, important for transporting our instruments to dark sky locations. There are exceptions, such as folded telescope systems. Back in the late 1960's Celestron offered a Schmidt-Cassegrain 8" f/10 folded system in a very compact tube. I had one years ago and it was compact enough I even took it to a cruise to Africa on an eclipse expedition.

I currently have a rather rare Meade 10" f/15 Maksutov design. What I've noticed with fast system such as f/4 to f/6 is stars tend to "snap" in and out of focus with just a touch of the focuser. With the above mentioned f/15 system I've noticed I can turn the focusing knob a considerable distance and the stars stay in focus. I also noticed the same with my 4" f/15 Unitron refractor. Focus becomes less critical with "slow" systems such as f/10 to f/15.

I don't know why I brought this up, but last night I just thought it was amazing how far I could turn the focusing knob on the Meade 10" f/15 system and maintain a sharp focus.

Re: Slow telescope focal ratios

jimcoble2000

You are absolutely right about the focus differences. May also be related to the view that fast mirrors are more critical to collimate accurately than slower focal ratio mirrors. But..... you will need a 60mm eyepiece to achieve anything less than 1000000x

On Thursday, January 13, 2022, 11:12:44 AM EST, Kent Blackwell <kent@...> wrote:

Most of us prefer "fast" telescope ratios. With fast systems, such as f/4 to 4/6 telescope tubes can be shorter, important for transporting our instruments to dark sky locations. There are exceptions, such as folded telescope systems. Back in the late 1960's Celestron offered a Schmidt-Cassegrain 8" f/10 folded system in a very compact tube. I had one years ago and it was compact enough I even took it to a cruise to Africa on an eclipse expedition.

I currently have a rather rare Meade 10" f/15 Maksutov design. What I've noticed with fast system such as f/4 to f/6 is stars tend to "snap" in and out of focus with just a touch of the focuser. With the above mentioned f/15 system I've noticed I can turn the focusing knob a considerable distance and the stars stay in focus. I also noticed the same with my 4" f/15 Unitron refractor. Focus becomes less critical with "slow" systems such as f/10 to f/15.

I don't know why I brought this up, but last night I just thought it was amazing how far I could turn the focusing knob on the Meade 10" f/15 system and maintain a sharp focus.

Slow telescope focal ratios

Kent Blackwell

Most of us prefer "fast" telescope ratios. With fast systems, such as f/4 to 4/6 telescope tubes can be shorter, important for transporting our instruments to dark sky locations. There are exceptions, such as folded telescope systems. Back in the late 1960's Celestron offered a Schmidt-Cassegrain 8" f/10 folded system in a very compact tube. I had one years ago and it was compact enough I even took it to a cruise to Africa on an eclipse expedition.

I currently have a rather rare Meade 10" f/15 Maksutov design. What I've noticed with fast system such as f/4 to f/6 is stars tend to "snap" in and out of focus with just a touch of the focuser. With the above mentioned f/15 system I've noticed I can turn the focusing knob a considerable distance and the stars stay in focus. I also noticed the same with my 4" f/15 Unitron refractor. Focus becomes less critical with "slow" systems such as f/10 to f/15.

I don't know why I brought this up, but last night I just thought it was amazing how far I could turn the focusing knob on the Meade 10" f/15 system and maintain a sharp focus.

Another fine evening with the moon. Domes, domes, domes.

jimcoble2000

Hope you got out tonight Ian. Another banner night for seeing. The weather here was odd in that there was a haze all day long artificially created by a zillion jets making contrails. Those contrails spread out and created a strata of haze over us.

That said observing tonight was very good. The feature of the night was domes, lots of them. The terminator was perfect and I was able to gather about 5 domes in various regions. Near Copernicus the Hortensias Domes were easily seen. There are about 6 domes there. Another is Milichius close by. Further south Keis Pi dome showed up too. The summit pits were visible in many of them at 170X . Good seeing.

These domes are considered to be small shield volcanoes much like very smaller versions of Mauna Kea and the Hawaiian islands overall. They are fairly flat, low elevation volcanic domes created by very fluid lavas, layer by layer. Not like the steep explosive strato volcanoes such as St Helens or the Japanese Island volcanoes.

A good example is Gillespie Peak in Arizona outside of Phoenix. Here is a link to the Google Maps image.

Re: Observing Last Night

jimcoble2000

Hi George. It was nice to see you and your sister at Paneras last week.

Yes indeed the salt flats are just to the  west of West Wendover. That large white area that is sort of semi triangular. The entire region was once the shoreline of the ocean. California (as we know it today) did not exist at the time (at least where it is now). Later as the sea levels fell and the pieces of California, formed elsewhere, tacked itself on to the coast in stages, large, now inland, lakes were formed and then left high and dry to evaporate leaving a deposit of salt. End of beach front property in Utah!

On Wednesday, January 12, 2022, 05:18:25 PM EST, George Reynolds via groups.io <pathfinder027@...> wrote:

Mark,

That vast white area west of the Great Salt Lake -- Is that the Bonneville Salt Flats?  Was it once the floor of an even bigger (greater) Great Salt Lake?

George

George Reynolds

Back Bay Amateur Astronomers (BBAA)
http://www.backbayastro.org

On Wednesday, January 12, 2022, 10:24:57 AM EST, jimcoble2000 via groups.io <jimcoble2000@...> wrote:

Yes it was a good night Ian. I only had about 1/2 an hours with it. Seeing the previous night was pretty poor. Saturday night was excellent. It sure varies in the winter. The good news is that the moon is riding pretty high so I can easily access it from the balcony. The balcony is pretty solid and I use Celestron vibration pads so the scope is quite steady. There is a double occultation of a couple of stars on Friday around 2055 (8:55 pm). The moon should be in a good position for me. You just need a barlow for the flag! Maybe two.

The straight wall is starting to show also. By looking at where the moon is illuminated from and examining the shadow you can see where the high elevation side of the fault is and the low elevation side. The low side is on the west side of the fault, same as the small crater Birt. It looks steep but is only a 20 degrees slope. Faults can be a bit complex sometimes. I believe the thinking is the straight wall exists because the west side of Ancient Thebit (not visible last night) subsided. BTW "fault" is defined as two rock units that have relative motion between the two. Fractures have no relative motion.

This is different from say the Lunar Alpine Valley which is a horst and graben type faulting (two normal faults) caused by extension of the crust. Think  \-/  where the two sides are pulled apart away from each other and the middle sinks down. You can see an example of this in Utah and Nevada. If you look on google maps, satellite view, going west from Salt Lake City toward Nevada on I-80 notice how, around West Wendover (on I -81), how the land has parallel hills and flats in a north south direction. If you zoom way out you can picture the entire section of that country being pulled apart (which it is, one day to become a sea way again). That is how the Alpine Valley on the moon formed. On Earth it is called Basin and Range.

I think I might start using google maps satellite view as a nice illustration for moon analogs.

On Wednesday, January 12, 2022, 09:40:36 AM EST, Ian Stewart <swampcolliecoffee@...> wrote:

Probably the best evening of lunar observing I have ever had. Seeing was near perfect. I don't have much in the way of eyepieces to get me past 250x but at that power the moon was rock solid. Terminator was in a wonderful position to see the basin in Clavius ringed by Porter and Rutherford both with peaks that were easy to pick out last night. Copernicus was awesome with the east wall brightly lit. I also had a good look at the Apollo 15 site - couldn't see any equipment though :-)
Cheers
Ian

Re: Observing Last Night

George Reynolds

Mark,

That vast white area west of the Great Salt Lake -- Is that the Bonneville Salt Flats?  Was it once the floor of an even bigger (greater) Great Salt Lake?

George

George Reynolds

Back Bay Amateur Astronomers (BBAA)
http://www.backbayastro.org

On Wednesday, January 12, 2022, 10:24:57 AM EST, jimcoble2000 via groups.io <jimcoble2000@...> wrote:

Yes it was a good night Ian. I only had about 1/2 an hours with it. Seeing the previous night was pretty poor. Saturday night was excellent. It sure varies in the winter. The good news is that the moon is riding pretty high so I can easily access it from the balcony. The balcony is pretty solid and I use Celestron vibration pads so the scope is quite steady. There is a double occultation of a couple of stars on Friday around 2055 (8:55 pm). The moon should be in a good position for me. You just need a barlow for the flag! Maybe two.

The straight wall is starting to show also. By looking at where the moon is illuminated from and examining the shadow you can see where the high elevation side of the fault is and the low elevation side. The low side is on the west side of the fault, same as the small crater Birt. It looks steep but is only a 20 degrees slope. Faults can be a bit complex sometimes. I believe the thinking is the straight wall exists because the west side of Ancient Thebit (not visible last night) subsided. BTW "fault" is defined as two rock units that have relative motion between the two. Fractures have no relative motion.

This is different from say the Lunar Alpine Valley which is a horst and graben type faulting (two normal faults) caused by extension of the crust. Think  \-/  where the two sides are pulled apart away from each other and the middle sinks down. You can see an example of this in Utah and Nevada. If you look on google maps, satellite view, going west from Salt Lake City toward Nevada on I-80 notice how, around West Wendover (on I -81), how the land has parallel hills and flats in a north south direction. If you zoom way out you can picture the entire section of that country being pulled apart (which it is, one day to become a sea way again). That is how the Alpine Valley on the moon formed. On Earth it is called Basin and Range.

I think I might start using google maps satellite view as a nice illustration for moon analogs.

On Wednesday, January 12, 2022, 09:40:36 AM EST, Ian Stewart <swampcolliecoffee@...> wrote:

Probably the best evening of lunar observing I have ever had. Seeing was near perfect. I don't have much in the way of eyepieces to get me past 250x but at that power the moon was rock solid. Terminator was in a wonderful position to see the basin in Clavius ringed by Porter and Rutherford both with peaks that were easy to pick out last night. Copernicus was awesome with the east wall brightly lit. I also had a good look at the Apollo 15 site - couldn't see any equipment though :-)
Cheers
Ian

Picture attached

jimcoble2000

Here is the picture for the last message (I hope)

Webb telescope materials.

jimcoble2000

The Webb telescope has pretty exotic engineering. The mirrors are constructed out of a metal called Beryllium and coated in a thin layer of gold. Beryllium is very stable in cold temperatures. It is refined out of a mineral Beryl and another more exotic mineral. I have a sample of Beryl here. It is the white mineral pointed out by the orange arrows.

Re: Observing Last Night

jimcoble2000

I was easily able to split Rigel with no effort so I suspect the app was right.

On Wednesday, January 12, 2022, 10:10:50 AM EST, Kent Blackwell <kent@...> wrote:

Seeing was rated high last night according to one of my apps.

Re: Observing Last Night

Ian Stewart

Hey Mark thanks. Always enjoy your observations and explanations ... Cheers Ian

On 1/12/2022 10:24 AM, jimcoble2000 via groups.io wrote:
Yes it was a good night Ian. I only had about 1/2 an hours with it. Seeing the previous night was pretty poor. Saturday night was excellent. It sure varies in the winter. The good news is that the moon is riding pretty high so I can easily access it from the balcony. The balcony is pretty solid and I use Celestron vibration pads so the scope is quite steady. There is a double occultation of a couple of stars on Friday around 2055 (8:55 pm). The moon should be in a good position for me. You just need a barlow for the flag! Maybe two.

The straight wall is starting to show also. By looking at where the moon is illuminated from and examining the shadow you can see where the high elevation side of the fault is and the low elevation side. The low side is on the west side of the fault, same as the small crater Birt. It looks steep but is only a 20 degrees slope. Faults can be a bit complex sometimes. I believe the thinking is the straight wall exists because the west side of Ancient Thebit (not visible last night) subsided. BTW "fault" is defined as two rock units that have relative motion between the two. Fractures have no relative motion.

This is different from say the Lunar Alpine Valley which is a horst and graben type faulting (two normal faults) caused by extension of the crust. Think  \-/  where the two sides are pulled apart away from each other and the middle sinks down. You can see an example of this in Utah and Nevada. If you look on google maps, satellite view, going west from Salt Lake City toward Nevada on I-80 notice how, around West Wendover (on I -81), how the land has parallel hills and flats in a north south direction. If you zoom way out you can picture the entire section of that country being pulled apart (which it is, one day to become a sea way again). That is how the Alpine Valley on the moon formed. On Earth it is called Basin and Range.

I think I might start using google maps satellite view as a nice illustration for moon analogs.

On Wednesday, January 12, 2022, 09:40:36 AM EST, Ian Stewart <swampcolliecoffee@...> wrote:

Probably the best evening of lunar observing I have ever had. Seeing was near perfect. I don't have much in the way of eyepieces to get me past 250x but at that power the moon was rock solid. Terminator was in a wonderful position to see the basin in Clavius ringed by Porter and Rutherford both with peaks that were easy to pick out last night. Copernicus was awesome with the east wall brightly lit. I also had a good look at the Apollo 15 site - couldn't see any equipment though :-)
Cheers
Ian

Re: Observing Last Night

jimcoble2000

Yes it was a good night Ian. I only had about 1/2 an hours with it. Seeing the previous night was pretty poor. Saturday night was excellent. It sure varies in the winter. The good news is that the moon is riding pretty high so I can easily access it from the balcony. The balcony is pretty solid and I use Celestron vibration pads so the scope is quite steady. There is a double occultation of a couple of stars on Friday around 2055 (8:55 pm). The moon should be in a good position for me. You just need a barlow for the flag! Maybe two.

The straight wall is starting to show also. By looking at where the moon is illuminated from and examining the shadow you can see where the high elevation side of the fault is and the low elevation side. The low side is on the west side of the fault, same as the small crater Birt. It looks steep but is only a 20 degrees slope. Faults can be a bit complex sometimes. I believe the thinking is the straight wall exists because the west side of Ancient Thebit (not visible last night) subsided. BTW "fault" is defined as two rock units that have relative motion between the two. Fractures have no relative motion.

This is different from say the Lunar Alpine Valley which is a horst and graben type faulting (two normal faults) caused by extension of the crust. Think  \-/  where the two sides are pulled apart away from each other and the middle sinks down. You can see an example of this in Utah and Nevada. If you look on google maps, satellite view, going west from Salt Lake City toward Nevada on I-80 notice how, around West Wendover (on I -81), how the land has parallel hills and flats in a north south direction. If you zoom way out you can picture the entire section of that country being pulled apart (which it is, one day to become a sea way again). That is how the Alpine Valley on the moon formed. On Earth it is called Basin and Range.

I think I might start using google maps satellite view as a nice illustration for moon analogs.

On Wednesday, January 12, 2022, 09:40:36 AM EST, Ian Stewart <swampcolliecoffee@...> wrote:

Probably the best evening of lunar observing I have ever had. Seeing was near perfect. I don't have much in the way of eyepieces to get me past 250x but at that power the moon was rock solid. Terminator was in a wonderful position to see the basin in Clavius ringed by Porter and Rutherford both with peaks that were easy to pick out last night. Copernicus was awesome with the east wall brightly lit. I also had a good look at the Apollo 15 site - couldn't see any equipment though :-)
Cheers
Ian

Re: Observing Last Night

Kent Blackwell

Seeing was rated high last night according to one of my apps.

Observing Last Night

Ian Stewart

Probably the best evening of lunar observing I have ever had. Seeing was near perfect. I don't have much in the way of eyepieces to get me past 250x but at that power the moon was rock solid. Terminator was in a wonderful position to see the basin in Clavius ringed by Porter and Rutherford both with peaks that were easy to pick out last night. Copernicus was awesome with the east wall brightly lit. I also had a good look at the Apollo 15 site - couldn't see any equipment though :-)
Cheers
Ian

Virginia State Parks' International Dark Sky Parks

Jeffrey Thornton

As Bruce Powers spoke about at last Thursday BBAA general meeting, Virginia State Parks are embracing the International Dark-Sky Association (IDA) standard for meeting the requirements to become Dark Sky Parks! This is the web address to read all about it and each of these four parks are giving outreach programs throughout the year. https://www.dcr.virginia.gov/state-parks/dark-sky-parks

Re: Last Night

Jim Tallman

Yes you did :-) and I do agree that it was the best I've ever seen the moon. Didn't waver a bit

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