Readily Available Long Focal Length Refractors
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Readily Available Long Focal Length Refractors
Hi Folks,
Help me out here. I'm trying to find readily available, affordable, long focal length refractors. Most stop at 1200mm focal length.
There are big APMs and TECs etc out there but they fail in the affordable section.
Mark
Help me out here. I'm trying to find readily available, affordable, long focal length refractors. Most stop at 1200mm focal length.
There are big APMs and TECs etc out there but they fail in the affordable section.
Mark
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Re: Readily Available Long Focal Length Refractors
Ishtar makes a 6” f/10 objective optimized for Ha that runs about $1200. They also make a regular 6” f/10 for less. Their lens cells look nice. One down side of some of the cheaper telescopes are lens cells that can not be collimated. I would imagine this would be important for a long focus refractor with a rear mounted etalon.
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Re: Readily Available Long Focal Length Refractors
Thanks guys!
You make a very valid point JAPP, it was a maul just to get the 127/1200 on my 6' high pier yesterday. The bigger the fracs get, the heavier they are and then the bigger (more expensive) the mounts need to be. 1200mm fl is about as big as they go,much above this and is observatory class.
No such thing as a free lunch!
Mark
You make a very valid point JAPP, it was a maul just to get the 127/1200 on my 6' high pier yesterday. The bigger the fracs get, the heavier they are and then the bigger (more expensive) the mounts need to be. 1200mm fl is about as big as they go,much above this and is observatory class.
No such thing as a free lunch!
Mark
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Re: Readily Available Long Focal Length Refractors
Are you looking for a long focal length or just a higher focal ratio?marktownley wrote: ↑Sun Jan 24, 2021 4:39 pm Help me out here. I'm trying to find readily available, affordable, long focal length refractors. Most stop at 1200mm focal length.
I'm guessing that the market produces what sells in quantity and for much beyond 1200mm it is the territory of the Cassegrains e.g. Schmidt Cassegrain or Maksutov Cassegrain.
An SCT is more forgiving to mount than a long refractor, especially with a "portable" mount.
Simon
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Re: Readily Available Long Focal Length Refractors
What about a high quality TeleVue Barlow/Powermate or Baader Telecentric? At 1200 mm you'd get an EFL of 4.8 meters with a 4 x unit... pretty dang long!
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Re: Readily Available Long Focal Length Refractors
Mark...
I think another question that needs to be looked at is what weight can you handle to setup and what weight can your mount handle? The complete OTA option tends to make a heavy OTA...my 150mm, f8 iStar (Perseus) is at least 30lb...could trim a bit if I get rid of the dew shield but won't change it much...really just aggravates the front heavy nature of the OTA.
If you are after an objective the iStar line has many options in 100-150mm + size and options of standard achromats to ones tailed to Ha use. Their cells are also collimatable. Should have several options to suit the end you wish to reach. I originally ordered the objective alone with the intent to mount it on the Celestron OTA but it was a waste of time and had iStar ship me the rest of the OTA components in the end.
I do like the option suggested to build the skeletal frame and add the objective of choice. if you want to use it for multiple wavelengths the open tube will make it much easier to swap in/out any ERF components too. What filter set do you hope to utilize with the proposed scope?
Just a few thoughts,
Brian
I think another question that needs to be looked at is what weight can you handle to setup and what weight can your mount handle? The complete OTA option tends to make a heavy OTA...my 150mm, f8 iStar (Perseus) is at least 30lb...could trim a bit if I get rid of the dew shield but won't change it much...really just aggravates the front heavy nature of the OTA.
If you are after an objective the iStar line has many options in 100-150mm + size and options of standard achromats to ones tailed to Ha use. Their cells are also collimatable. Should have several options to suit the end you wish to reach. I originally ordered the objective alone with the intent to mount it on the Celestron OTA but it was a waste of time and had iStar ship me the rest of the OTA components in the end.
I do like the option suggested to build the skeletal frame and add the objective of choice. if you want to use it for multiple wavelengths the open tube will make it much easier to swap in/out any ERF components too. What filter set do you hope to utilize with the proposed scope?
Just a few thoughts,
Brian
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10'x15 Roll-off Roof Observatory
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2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
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Re: Readily Available Long Focal Length Refractors
Thanks guys for all your input, I probably should explain more where i'm going with this.
This is the CaK nerd in me coming out. I have unfortunately fickle seeing where I live and so over the last solar cycle rapidly learned that shorter wavelengths are more susceptible to poor seeing (1.6x compared to Ha as a function of wavelength), as a result i've found I get better results at a given focal length by stopping down the aperture. So, to give an example I get better full disks with my 100mm f10 Tal refractor stopped down to 60mm than I do if I use it at full aperture.
There are other things at play here, with my full disk cam the 3.6um pixels are at near optimal sampling at f16 compared to f10 where I am most definitely under-sampling with 3um pixels. There is simply more contrast with the filter at longer focal ratios - the fwhm of a filter broadens with lower f-ratio. There's also less thermal load on the filter at a longer f-ratio which is important - means ERFs can be (suitable) sub aperture UV/IR filters improving filter longevity and reducing failure do to thermal cycling. Throw in by stopping down to get longer f-ratios this does away with the need for a barlow / powermate and then less glass equals more light and a shorter exposure. Possibly for me one of the biggest wins is that stopping down a refractor is the reduction in spherical aberration compared to using it at full aperture.
My experience is using this iterative approach above yields better results when imaging CaK than not using it.
If I give some examples; I get better results using my 100mmf10 scope stopped down to 60mm to give f16 than I do with a 80mmf7.5 scope stopped down to 60mm and using a 2.7x barlow. Using my 127/1200 refractor stopped down to 72mm/f16 absolutely blows out of the water using a 72mm/f6 refractor and a 2.7x barlow.
Some 'back of an envelope' maths tells us that optimal f-ratio for sampling is pixel size (um) x 3 for Ha and x5 for CaK, hence you can see where i'm going with my f16 numbers. The f16 works with ~3um pixels for CaK. If I use my IMX174 chip camera with my refractors at f10, I can use the 2.7x Airylab telecentric to get me close to the ideal f30 needed for sampling.
Given my seeing, I know there's not many times a year when I can use my 8" Hat effectively for Ha, so, being able to run at 120mm aperture in CaK means there's a handful of times throughout the year for using that aperture effectively. Imaging at 100mm can be used more often, and then as the aperture decreases the frequency I can effectively use the aperture increases.
Key here is effective imaging for the seeing - how many times have you tried imaging to end up deleting the files as they are durge? The seeing doesn't support the aperture, that's the reason why. Been there and got the t-shirt last solar cycle, won't be doing the same this solar cycle
I think short of getting a 150mm f10 scope i've got nothing more to gain, and even then I think (for me!) imaging at 150mm in CaK might be a once a year treat, if i'm lucky! Like JAPP says, size then starts becoming an issue as weight increases and portability decreases. Using an SCT (with CaK corrector) would need a full aperture DERF (£££) - would be no point me using a c8/c11 - too big, maybe a c6 or a mak125, but at that aperture i'm back in frac territory...
Mark
This is the CaK nerd in me coming out. I have unfortunately fickle seeing where I live and so over the last solar cycle rapidly learned that shorter wavelengths are more susceptible to poor seeing (1.6x compared to Ha as a function of wavelength), as a result i've found I get better results at a given focal length by stopping down the aperture. So, to give an example I get better full disks with my 100mm f10 Tal refractor stopped down to 60mm than I do if I use it at full aperture.
There are other things at play here, with my full disk cam the 3.6um pixels are at near optimal sampling at f16 compared to f10 where I am most definitely under-sampling with 3um pixels. There is simply more contrast with the filter at longer focal ratios - the fwhm of a filter broadens with lower f-ratio. There's also less thermal load on the filter at a longer f-ratio which is important - means ERFs can be (suitable) sub aperture UV/IR filters improving filter longevity and reducing failure do to thermal cycling. Throw in by stopping down to get longer f-ratios this does away with the need for a barlow / powermate and then less glass equals more light and a shorter exposure. Possibly for me one of the biggest wins is that stopping down a refractor is the reduction in spherical aberration compared to using it at full aperture.
My experience is using this iterative approach above yields better results when imaging CaK than not using it.
If I give some examples; I get better results using my 100mmf10 scope stopped down to 60mm to give f16 than I do with a 80mmf7.5 scope stopped down to 60mm and using a 2.7x barlow. Using my 127/1200 refractor stopped down to 72mm/f16 absolutely blows out of the water using a 72mm/f6 refractor and a 2.7x barlow.
Some 'back of an envelope' maths tells us that optimal f-ratio for sampling is pixel size (um) x 3 for Ha and x5 for CaK, hence you can see where i'm going with my f16 numbers. The f16 works with ~3um pixels for CaK. If I use my IMX174 chip camera with my refractors at f10, I can use the 2.7x Airylab telecentric to get me close to the ideal f30 needed for sampling.
Given my seeing, I know there's not many times a year when I can use my 8" Hat effectively for Ha, so, being able to run at 120mm aperture in CaK means there's a handful of times throughout the year for using that aperture effectively. Imaging at 100mm can be used more often, and then as the aperture decreases the frequency I can effectively use the aperture increases.
Key here is effective imaging for the seeing - how many times have you tried imaging to end up deleting the files as they are durge? The seeing doesn't support the aperture, that's the reason why. Been there and got the t-shirt last solar cycle, won't be doing the same this solar cycle
I think short of getting a 150mm f10 scope i've got nothing more to gain, and even then I think (for me!) imaging at 150mm in CaK might be a once a year treat, if i'm lucky! Like JAPP says, size then starts becoming an issue as weight increases and portability decreases. Using an SCT (with CaK corrector) would need a full aperture DERF (£££) - would be no point me using a c8/c11 - too big, maybe a c6 or a mak125, but at that aperture i'm back in frac territory...
Mark
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Re: Readily Available Long Focal Length Refractors
Thanks for the explanation Mark.
Have you considered making a Newt? Here's what I'd consider doing (and may in the future):
150 mm fused quartz f6 to f10 primary mirror - non-aluminized or partially aluminized. Easy to get or make, thermally stable, relatively inexpensive compared to a refractor objective, easy to support. Reasonably carried by a standard GEM, etc.
25 mm fused quartz secondary mirror - aluminized - consider cold mirror coating for greater heat reduction to filter system.
Curved or wire secondary support for minimal diffraction.
Extend EFL via Baader TZ3 x Telecentric, which is "diffraction Limited" for CaK.
Scale up if you want more aperture. viewtopic.php?t=18204
Just a thought...
Have you considered making a Newt? Here's what I'd consider doing (and may in the future):
150 mm fused quartz f6 to f10 primary mirror - non-aluminized or partially aluminized. Easy to get or make, thermally stable, relatively inexpensive compared to a refractor objective, easy to support. Reasonably carried by a standard GEM, etc.
25 mm fused quartz secondary mirror - aluminized - consider cold mirror coating for greater heat reduction to filter system.
Curved or wire secondary support for minimal diffraction.
Extend EFL via Baader TZ3 x Telecentric, which is "diffraction Limited" for CaK.
Scale up if you want more aperture. viewtopic.php?t=18204
Just a thought...
Last edited by Bob Yoesle on Tue Jan 26, 2021 7:07 pm, edited 2 times in total.
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Re: Readily Available Long Focal Length Refractors
Mark
I was reading that circular supports are not that effective. Have you considered apodization? See the attached chapter of a solar book.
Each jump in aperture, requires an improvement in seeing conditions that may not occur too often, so may not be economically worthwhile?
Simon
I was reading that circular supports are not that effective. Have you considered apodization? See the attached chapter of a solar book.
Each jump in aperture, requires an improvement in seeing conditions that may not occur too often, so may not be economically worthwhile?
Simon
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Re: Readily Available Long Focal Length Refractors
It all depends highly on the thickness of the spider vane materials. Wire spiders would be the best due to their high strength, low thermal mass, and relatively small diameter for their strength.
Mark: also recall that rather than stopping down a refractor it might be just as beneficial for better CaK performance to have a dedicated CaK scope by simply re-spacing the inexpensive achromatic/or simple ED objective to optimize CaK.
viewtopic.php?f=10&t=25115&start=25#p232830
Mark: also recall that rather than stopping down a refractor it might be just as beneficial for better CaK performance to have a dedicated CaK scope by simply re-spacing the inexpensive achromatic/or simple ED objective to optimize CaK.
viewtopic.php?f=10&t=25115&start=25#p232830
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Re: Readily Available Long Focal Length Refractors
Thanks guys.
I've tried re-spacing lenses Bob, it offers an improvement on an objective that shows poor SA in CaK, but have found stopping down gives overall better results.
How would you suggest apodising Simon? Put a central 'spot' on the objective Coronado etalon style?
Mark
I've tried re-spacing lenses Bob, it offers an improvement on an objective that shows poor SA in CaK, but have found stopping down gives overall better results.
How would you suggest apodising Simon? Put a central 'spot' on the objective Coronado etalon style?
Mark
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Re: Readily Available Long Focal Length Refractors
I have a range of dedicated CaK scopes of differing apertures (and focal lengths) to match seeing. Seeing is my issue, it is so variable, the range of scopes (apertures and focal lengths) then allows me to sample optimally with a given camera. Its a case of 'seeing' what the seeing is like each session and picking the optics accordingly.Bob Yoesle wrote: ↑Tue Jan 26, 2021 7:18 pm Mark: also recall that rather than stopping down a refractor it might be just as beneficial for better CaK performance to have a dedicated CaK scope by simply re-spacing the inexpensive achromatic/or simple ED objective to optimize CaK.
My challenge over the past solar cycle has been finding the scopes that work well for CaK
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Re: Readily Available Long Focal Length Refractors
Isn't that just the nature of physics? Effects like diffraction (and sampling) depend on the wavelength of light. Blue, UV, and CaK (shorter wavelengths) are diffracted at a greater angle than red, H-Alpha light, and IR (longer wavelengths).marktownley wrote: ↑Tue Jan 26, 2021 7:50 pm [My challenge over the past solar cycle has been finding the scopes that work well for CaK
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Re: Readily Available Long Focal Length Refractors
Indeed! Scopes that work well at white light and Ha are 'ten a penny' - lots of choice. Scopes that work well at CaK are not - wavelength dependency. My iterative approach to the blue, while not bending the laws of physics, certainly puts the odds more in my favour.SimonM wrote: ↑Tue Jan 26, 2021 10:44 pmIsn't that just the nature of physics? Effects like diffraction (and sampling) depend on the wavelength of light. Blue, UV, and CaK (shorter wavelengths) are diffracted at a greater angle than red, H-Alpha light, and IR (longer wavelengths).marktownley wrote: ↑Tue Jan 26, 2021 7:50 pm [My challenge over the past solar cycle has been finding the scopes that work well for CaK
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Re: Readily Available Long Focal Length Refractors
Hi Mark,marktownley wrote: ↑Sun Jan 24, 2021 4:39 pm Hi Folks,
Help me out here. I'm trying to find readily available, affordable, long focal length refractors. Most stop at 1200mm focal length.
There are big APMs and TECs etc out there but they fail in the affordable section.
Mark
It makes plenty sense; I do this too actually. My biggest is a 150mm that I mask down. But I have 3D printed masks for most of my scopes at this point to achieve F10 at minimum, and go as long as F15 with the masks. For the same reason you pointed out with the long focal-ratio light cone and its behavior with filters, versus using amplifiers (I gave up on my 1.25x badder GPC, and other short small amplifiers, not to mention standard 2x and longer amplifiers for this). I'm far happier with masked focal-ratio long refractors. It's just more simple. And it seems to just be better (maybe less glass, dunno).
My long term project at this point is to get an iStar Optical 150mm F10 achromatic doublet objective. I want to build a truss-build that is open that can have filters inserted nearly anywhere in the light cone. And have masks for the objective to generate F10 through F20 basically. It's not too costly. The truss will cost more likely than the lens. Overall weight, should be around 25lb~30lbs. Pretty heavy. But doable.
http://www.istar-optical.com/achromatic.html
(Specifically the 150mm F10 and the 150mm F15 objectives)
Regarding 393nm and seeing conditions; as you pointed out you need significantly better seeing as its heavily effected by seeing to benefit these short wavelength's resolution with optimal sampling. To put it more into perspective, a 60mm aperture in 393nm at critical sampling would need around 1.6 arc-seconds seeing conditions (not averaged, but at least peaks that happen enough during your capture period). That's already asking a lot and that's just 60mm. 80mm in 393nm at critical sampling needs around 1.2 arc-seconds! And 100mm at 393nm needs 0.99 (1) arc-second seeing conditions (again not averaged, but at least peaks common enough during capture period to get lucky). To compare, 656nm on 150mm needs 1.1 arc-second approximately for seeing. And if you compare wavelength angular resolution and the seeing need to get there, it's a consistent 60% difference roughly no matter how you slice it between 393nm and 656nm. So unless you commonly see 1 arc-second seeing, even once a year with good transparency, topping out a 100mm aperture in 393nm is a tall order, a long with 150mm in 656nm. 393nm in a 150mm aperture at critical sampling needs around 0.6 arc-seconds, super tall order for that! That's mountain side special location type stuff for day time.
So really, 60~80mm is likely a "good working" range for 393nm for anyone that is experiencing 1.2~1.6 arc-second seeing, at best, as peaks with a worse average (say averaging 2 arc-seconds per minute with peaks near 1.2 or 1.6 arc-seconds mixed in there for lucky imaging purposes). That said, 80mm F15 can be done with any of your 1200mm focal length achromatic doublets and F20 with a 60mm mask. That should fit the bill. I do this with an old celestron 150mm F8 objective and its well enough corrected with those focal-ratios when critically sampled.
393nm is critically sampled at F18 on 2.90um pixels.
393nm is critically sampled at F21.5 on 3.45um pixels.
393nm is critically sampled at F23.5 on 3.75um pixels.
393nm is critically sampled at F26.3 on 4.20um pixels.
393nm is critically sampled at F36.7 on 5.86um pixels.
So with approximately 1.6 arc-second seeing, a 60mm masked objective with a 1200mm focal length at F20 would be pretty close to ideal with a 3.45~3.80um pixel size (fairly common on most cameras out there). Another option is a 1500mm focal length objective, masked to 65mm to get to F23 for sampling on 3.75um pixels. That way you could get there without any amplifiers in the mix. Just the objective, the narrowband filter, naturally long focal-ratio, and your camera. Alt; use a smaller pixel (not the 2.4um pixels, they're noisy and really just not good for narrowband much yet), such as the 290MM 2.9um pixels. The sensor is very sensitive, fast, not noisy, no grid artifact or any problems, its fantastic for high speed solar imaging, this allows you to target F18 making the scope choice a lot easier to achieve the focal-ratio with something via an aperture mask.
70mm in CaK, critically sampled, is similar to 115~120mm HA which is already pretty incredible; so that 60~80mm range is pretty sweet before needing extraordinary seeing conditions on top of transparency, no wind, etc, etc.
150mm F8's are pretty common, and would be a good inexpensive platform with minimal work to get it up and running (just masks). If you use a 150mm F8 and mask it to 66mm you get a native 66mm F18 that will sample 393nm on 2.9um pixels (the fast ASI290MM).
https://www.teleskop-express.de/shop/pr ... -tube.html
To go longer, you have to really look at the Bresser line on Teleskop-Service, there's some longer ones in there to mask that are reasonable.
https://www.teleskop-express.de/shop/pr ... embly.html
https://www.teleskop-express.de/shop/pr ... embly.html
(These can be inexpensive 80mm F15's or 60mm F20's; or 84mm F16 or 60mm F22.5 for cheap!)
There are >2,000mm refractors; see link above from iStar. There's a 150mm F15 native objective with 2250mm focal length at $800 USD basically, very reasonable. That would let you do 95mm aperture, F23.6 natural, for sampling 393nm on 3.75um pixels.
The reality of the seeing requirements for 393nm, I'm sticking to the 80~100mm range tops I think, and that's with sub-arc-second seeing I get most of the year in the morning. While I can go 200mm on aperture and have the gear for it, I just don't have the seeing for that, and I sure do hate having a session with nothing to show for it. So will back up to 100mm probably for CaK from this point on unless a rare day shows me consistent 0.6 arc-second seeing!
It's that, or as pointed out by another above, a long focal-ratio mirror can get you there fairly inexpensively too. I have a 200mm F6 Quartz mirror for this very reason and it does perform much better in short wavelength and IR than my faster optics. It's just not ever going to have the seeing conditions to support the aperture in CaK in my location on any given day. But, I could mask it down to 80mm and it would be F15. Ultimately though, it's huge and cumbersome to focus on the mount compared to a refractor. I love newts, but man, I dislike focuser placement. So I generally just use instruments with focusers that are on the rear of the instrument so I don't have to do acrobatics to focus. I don't have auto-focusers.
While I know SCT F2~F3 mirrors are just bad for 393nm in general without specific ways to correct for the SA, I'm also curious if you can mask one to 60mm or 80mm to get the really long-focal ratio, to over-come the bad SA while still having a very compact scope. A C8 comes to mind. But I'm not sure enough about the SA, I need to know more as I don't know how to calculate that to know if it's doable without special correctors for addressing the SA. It would be unobstructed (no spider veins) and 60mm aperture should fit off-axis on a C8's corrector. Or even look possibly at a classical cassegrain to avoid the corrector plate entirely, plus its natively longer? I don't know enough about these mirrors and their speed related to SA and masking apertures to know if that would be an option really. My guess is that it's still poor optically for imaging due to the degree of angle of light being off axis so probably not worth it even at F20. But I'm not sure.
Very best,
Last edited by MalVeauX on Sun Jan 31, 2021 2:24 am, edited 1 time in total.
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Re: Readily Available Long Focal Length Refractors
Bob Yoesle wrote: ↑Mon Jan 25, 2021 6:36 pm Thanks for the explanation Mark.
Have you considered making a Newt? Here's what I'd consider doing (and may in the future):
150 mm fused quartz f6 to f10 primary mirror - non-aluminized or partially aluminized. Easy to get or make, thermally stable, relatively inexpensive compared to a refractor objective, easy to support. Reasonably carried by a standard GEM, etc.
25 mm fused quartz secondary mirror - aluminized - consider cold mirror coating for greater heat reduction to filter system.
Curved or wire secondary support for minimal diffraction.
Extend EFL via Baader TZ3 x Telecentric, which is "diffraction Limited" for CaK.
Scale up if you want more aperture. viewtopic.php?t=18204
Just a thought...
I have an old 6"F8 Criterion with excellent optics and a reduced sized secondary mirror that would make a killer white light scope with an appropriate filter given good seeing.
I was wondering the same. I would guess focal ratio?Are you looking for a long focal length or just a higher focal ratio?_SimonM
James
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Re: Readily Available Long Focal Length Refractors
Thanks guys! I found this bad boy on EBay https://www.ebay.co.uk/itm/FrTelescopes ... %7Ciid%3A1
Shame we're in lock down at the moment and can't go and get it. I may have to message the seller if it doesn't get sold. I have it on my watch list...
I'd forgot about Frank Theys in Belgium...
http://www.frtelescopes.com/
Shame we're in lock down at the moment and can't go and get it. I may have to message the seller if it doesn't get sold. I have it on my watch list...
I'd forgot about Frank Theys in Belgium...
http://www.frtelescopes.com/
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Re: Readily Available Long Focal Length Refractors
This is awesome! A 127mm F12!! An old school long focal length achromat. I hope you can get it. I certainly want to hear how it does.
Mark, It has a lanthanum element so they are being conservative on calling it an achromat. While it is probably not a true APO it may be considered an ED instrument. The long focal length plus the lanthanum glass should reduce the CA to a minimum.
http://www.frtelescopes.com/frt127.html
Mark, It has a lanthanum element so they are being conservative on calling it an achromat. While it is probably not a true APO it may be considered an ED instrument. The long focal length plus the lanthanum glass should reduce the CA to a minimum.
http://www.frtelescopes.com/frt127.html
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Re: Readily Available Long Focal Length Refractors
Mark, hope you can get this scope...has most of the traits you are after (and a handle ).
Brian
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Brian Colville
Maple Ridge Observatory
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Photos: https://www.flickr.com/photos/185395281@N08/albums
10'x15 Roll-off Roof Observatory
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C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM
2.2m Diameter Dome
iOptron CEM70G Mount carrying:
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Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
Maple Ridge Observatory
Cambray, ON Canada
Photos: https://www.flickr.com/photos/185395281@N08/albums
10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM
2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
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Re: Readily Available Long Focal Length Refractors
Hey Mark,
Just an example from this morning.
120mm F8.3 refractor (Celestron Omni XLT 120) masked to 60mm with a 3D printed mask producing F16.67.
Lunt Cak B1200 2.4A filter, nothing else in the imaging train at all.
IMX253 sensor (3.45um pixels)
Click for full res:
Very best,
Just an example from this morning.
120mm F8.3 refractor (Celestron Omni XLT 120) masked to 60mm with a 3D printed mask producing F16.67.
Lunt Cak B1200 2.4A filter, nothing else in the imaging train at all.
IMX253 sensor (3.45um pixels)
Click for full res:
Very best,
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Re: Readily Available Long Focal Length Refractors
It works doesn't it
Great disks Marty. Sampling to the seeing is the way.
Great disks Marty. Sampling to the seeing is the way.
http://brierleyhillsolar.blogspot.co.uk/
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Re: Readily Available Long Focal Length Refractors
Hi Mark, just joining the affray here, can tell you that I have the MEADE-127 ApoChromatic-Triplet 127mm Refractor, which I can tell you is heavy and in my case requires a roof-mounted safety-line attached to it's handle - before trying to lift it onto the motorised-mount (Skywatcher EQ-6). Too easy to loose it before firmly attaching to the mount at a height of about 6-feet. (taller than me even)!!!
952mm; f/7.5 and (L x W x H): 33.3" x 6.125 " x 6.125 " is certainly a nice instrument, but not yet often used at present, as the current Solar Tri-Scope Assembly is the prime-use for the observatory and not really suitable to remove the whole assembly - without all the re-aligning necessary. Also the total weight again is difficult to handle.
Hope this helps
Terry
952mm; f/7.5 and (L x W x H): 33.3" x 6.125 " x 6.125 " is certainly a nice instrument, but not yet often used at present, as the current Solar Tri-Scope Assembly is the prime-use for the observatory and not really suitable to remove the whole assembly - without all the re-aligning necessary. Also the total weight again is difficult to handle.
Hope this helps
Terry
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Re: Readily Available Long Focal Length Refractors
In time I may get an Astro-Tech AT130EDT refractor. It's an F7. I am sure I would have to stop it down at times as Marty has done with his 120mm scope. I have the smaller sister scope of the AT130EDT. The AT72EDII. It performs wonderfully with practically no chromatic aberration. It's a doublet with Lanthanum ED glass mated to a Ohara FPL-53 ED element. The AT130EDT is a triplet with an FPL-53 element.
https://www.astronomics.com/astro-tech- ... t-ota.html
https://www.astronomics.com/astro-tech- ... t-ota.html
Last edited by DeepSolar64 on Sun Jan 31, 2021 8:58 pm, edited 1 time in total.
Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces
Visual Observer
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Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
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Re: Readily Available Long Focal Length Refractors
It will work well for WL and Ha.
http://brierleyhillsolar.blogspot.co.uk/
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Re: Readily Available Long Focal Length Refractors
It should work really well, seeing permitting.
Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces
Visual Observer
" Way more fun to see it! "
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
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Re: Readily Available Long Focal Length Refractors
Mark,
based on my experience - and yours, I understand - a long refractor with an aperture stop will always be better than a refractor with the same focal length and just that aperture. Stopping down means that only the best corrected part of the glass is working and one can also change the stop diameter to match the seeing. For me this is the way as already suggested by Marty.
As pointed out by Bob a newtonian would be a fine alternative, I have made one myself and in spite is a f/5 it works very well. Skywatcher produces a 150 mm f/8 with parabolic mirror and a modest obstruction that is sold by TS for less than 250 euro. Take this one, de-aluminize the primary, replace the closed tube with a truss structure and you'll have a fantastic solar scope for WL and CaK. You would only need a 2x amplifier to get f/16.
based on my experience - and yours, I understand - a long refractor with an aperture stop will always be better than a refractor with the same focal length and just that aperture. Stopping down means that only the best corrected part of the glass is working and one can also change the stop diameter to match the seeing. For me this is the way as already suggested by Marty.
As pointed out by Bob a newtonian would be a fine alternative, I have made one myself and in spite is a f/5 it works very well. Skywatcher produces a 150 mm f/8 with parabolic mirror and a modest obstruction that is sold by TS for less than 250 euro. Take this one, de-aluminize the primary, replace the closed tube with a truss structure and you'll have a fantastic solar scope for WL and CaK. You would only need a 2x amplifier to get f/16.
Raf
My solar images and reports with articles on solar equipment
My solar images and reports with articles on solar equipment
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Re: Readily Available Long Focal Length Refractors
My Criterion 6"F8 reflector works wonderfully on the planets and moon. WL solar would also be outstanding, seeing permitting.
Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces
Visual Observer
" Way more fun to see it! "
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
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Re: Readily Available Long Focal Length Refractors
The iStar OTA is big but I'll bet the views are amazing! My 6"f8 version is big enough...I don't think that scope would fit in the dome
Brian
Brian
Brian Colville
Maple Ridge Observatory
Cambray, ON Canada
Photos: https://www.flickr.com/photos/185395281@N08/albums
10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM
2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
Maple Ridge Observatory
Cambray, ON Canada
Photos: https://www.flickr.com/photos/185395281@N08/albums
10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM
2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
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Re: Readily Available Long Focal Length Refractors
My bad, I forgot that it hadn't been out of the box!
Brian
Brian
Brian Colville
Maple Ridge Observatory
Cambray, ON Canada
Photos: https://www.flickr.com/photos/185395281@N08/albums
10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM
2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
Maple Ridge Observatory
Cambray, ON Canada
Photos: https://www.flickr.com/photos/185395281@N08/albums
10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM
2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM