If I could build, buy, inherit a brilliant telescope for moon photography, what would it look like? I want it to get me in as close as possible and as clearly as possible!
I thought maybe a high f ratio with a large aperture reflector, say f10 20", which would of course be very long, but I am interested in possibilities rather than at this stage thinking how I will house it or drive it.
This is where something like a Shiefspiegler design would be perfect. You could even incorporate a sidereostat into the design to make mounting it simpler, since you only need to make it work on the ecliptic. Hmm - what a cool idea for home!
Cheers,
Andrew.
This is where something like a Shiefspiegler design would be perfect. You could even incorporate a sidereostat into the design to make mounting it simpler, since you only need to make it work on the ecliptic. Hmm - what a cool idea for home!
Cheers,
Andrew.
Hi Andrew,
High contrast seems the go here. I also read there were probs with astigmatism because the light is off axis like a Herschellian.
What about an F20 mirror with a prime focus camera out on the end?
Hi Andrew,
High contrast seems the go here. I also read there were probs with astigmatism because the light is off axis like a Herschellian.
What about an F20 mirror with a prime focus camera out on the end?
Richard
That's a pretty good idea - the ZWO cameras are smaller than the secondary on most 20" newt, so you'd have 'better' contrast from secondary obstruction. Since mounting a 20"f20 would be reasonably expensive, maybe a 20" flat sidereostat in front of the 20"f20, with a small hole in the flat and the camera behind the flat, sort of like an inverse newtonian?
Well, for a start you don't need aperture more than 30cm for two reasons:
A) the moon is very bright, and
B) the atmospheric seeing is very rarely better than 0.2 arc sec from any location you're likely to use as an amateur.
As for the scope:
If you were to use it for nothing else a 30cm f/23 Tri schiefspiegler would do very nicely. The late Barry Adcock (ASV) made one many years ago for photographing Mars and his images were phenomenal.
My next choice is a Santel (Russian) f/15 Mak. Santel doesn't exist anymore and these beasties were rare as hens teeth, though the optics were superlative.
Failing that I'd look for a 25-30 cm f/15 Mak from a reputable maker (TEC or AP come to mind) though you'll need deep pockets and an observatory to mount it someplace with really, really good seeing. Speaking of which there was a 10" TEC for sale on Astromart recently.
Well, for a start you don't need aperture more than 30cm for two reasons:
A) the moon is very bright, and
B) the atmospheric seeing is very rarely better than 0.2 arc sec from any location you're likely to use as an amateur.
Oh! Does brightness affect resolution?
And I was hoping Lucky Imaging techniques would give me a better outcome than what the native seeing state offers: am I wrong?
As for the scope:
If you were to use it for nothing else a 30cm f/23 Tri schiefspiegler would do very nicely. The late Barry Adcock (ASV) made one many years ago for photographing Mars and his images were phenomenal.
My next choice is a Santel (Russian) f/15 Mak. Santel doesn't exist anymore and these beasties were rare as hens teeth, though the optics were superlative.
Failing that I'd look for a 25-30 cm f/15 Mak from a reputable maker (TEC or AP come to mind) though you'll need deep pockets and an observatory to mount it someplace with really, really good seeing. Speaking of which there was a 10" TEC for sale on Astromart recently.
The Schiefspiegler option keeps popping up. Where would I get one?
Brightness doesn't effect resolution except for the fact that it allows shorter exposures. Shorter exposures make atmospheric turbulence less of an issue in they you can "freeze" the good pockets
If you were to use it for nothing else a 30cm f/23 Tri schiefspiegler would do very nicely. The late Barry Adcock (ASV) made one many years ago for photographing Mars and his images were phenomenal.
Mark is right, having worked with Barry at Old Melbourne observatory last thurs night I can tell you he is alive & well..a ghost did appear to open a door whilst I was talking though. his shiefy is a real talking piece when he brings it out, refractor like views, long though
as to where you would get one -make one, relatively simple design
Mark is right, having worked with Barry at Old Melbourne observatory last thurs night I can tell you he is alive & well..a ghost did appear to open a door whilst I was talking though. his shiefy is a real talking piece when he brings it out, refractor like views, long though
as to where you would get one -make one, relatively simple design
Cool! I want to dedicate the scope to lunar observing and photography so it sounds like this design is the way to go here.
What do you think about the 28" F3.5 Lunar scope from Webster? I take it that the mirror is not coated returning only about 5% of the light and therefore giving apparently excellent views....
Cool! I want to dedicate the scope to lunar observing and photography so it sounds like this design is the way to go here.
What do you think about the 28" F3.5 Lunar scope from Webster? I take it that the mirror is not coated returning only about 5% of the light and therefore giving apparently excellent views....
Having looked through a Webster 28" f3.5 I would honestly suggest you get an aluminised one and use a Herschel wedge or ND filter. I regularly use my 25" on the moon (as in looking at it!) and although the image is very bright it's not going to hurt your eyes, and if you are imaging it will let you use a very fast frame rate.
You could even replace the upper tube assembly with a second one with the Barlow and camera mounted instead of the secondary mirror.
This is where something like a Shiefspiegler design would be perfect. You could even incorporate a sidereostat into the design to make mounting it simpler, since you only need to make it work on the ecliptic. Hmm - what a cool idea for home!
Cheers,
Andrew.
These days the cool ATMs are making Stevick-Paul scopes.
The Schiefspiegler option keeps popping up. Where would I get one?
Richard - in these days of digital imaging fast newtonians are also the intsrument of choice for some imagers like twice discoverer of Jupiter impacts Anthony Wesley who in recent years uses 14" to 16" F4 Newts with power amplifiers like the Televue Powermate to get suitable image scale . Anthony found that ability of the optics to equiliberate through the night and the tube design and local seeing quality are by far the biggest factors in planetary imaging resolution .
A short tube keeps the thermal mass down and the Newt design gives you good airflow and keeping the aperture lower gives you a realistic balance between thermal mass to manage and the resolution possible at your site .
Preference for long focal length designs is really a hang over from the old days of visual observing where :
a) mirrors of faster f ratio were often poorly figured as there was not as much understanding at the amateur level on how to make a and measure faster optics . Long focus mirrors had a much greater manufacturing tolerance hence got a reputation for being optically superior.
b) Thanks to computer analysis its much better understood that you can use a much smaller central obstruction with a fast scope and only have a very gradual light drop off from the center of the field - so images can be higher contrast and more refractor like .
c) Short focal length eyepieces are much higher quality and you can actually use a 5mm FL to achieve the magnification you want if you are into visual obeservation . In the bad old days your 25mm 1" ORTHO and an F16 scope gave you a clean image - the nasty 5mm eyepieces with poor contrats , fuzzy field stops and internal reflections would be your only choice with a fast scope. Image amplifiers have also come a long way . Amplifiers such as the Televue powermate can give you the image scale with little loss in image quality compared to old barlow lenses.
d) Collimation tools are just that much better and it is well understood ...in the bad old days you enjoy an F8 or F10 scope and never collimate it or a an F16 cassegrain that never ever gave a sharp image .
All that being said SCT's with quite a few spherical surfaces and their short tubes are also a good choice if the optics are clean and well collimated and you can manage thermal cooling issues of the closed tube at your particular site .
There is no magic solution for Imaging that will give you a big heads start , but appreciating keeping your telescope in optimal condition and being able to understand its thermal behaviour will be a necessity .
Hope this all helps to add some perspective .
Having looked through a Webster 28" f3.5 I would honestly suggest you get an aluminised one and use a Herschel wedge or ND filter. I regularly use my 25" on the moon (as in looking at it!) and although the image is very bright it's not going to hurt your eyes, and if you are imaging it will let you use a very fast frame rate.
You could even replace the upper tube assembly with a second one with the Barlow and camera mounted instead of the secondary mirror.
Yes, I was a bit worried that there was no aluminium on the glass! Makes sneak peaks at other objects a bit disappointing!
Richard - in these days of digital imaging fast newtonians are also the intsrument of choice for some imagers like twice discoverer of Jupiter impacts Anthony Wesley who in recent years uses 14" to 16" F4 Newts with power amplifiers like the Televue Powermate to get suitable image scale . Anthony found that ability of the optics to equiliberate through the night and the tube design and local seeing quality are by far the biggest factors in planetary imaging resolution .
A short tube keeps the thermal mass down and the Newt design gives you good airflow and keeping the aperture lower gives you a realistic balance between thermal mass to manage and the resolution possible at your site .
Preference for long focal length designs is really a hang over from the old days of visual observing where :
a) mirrors of faster f ratio were often poorly figured as there was not as much understanding at the amateur level on how to make a and measure faster optics . Long focus mirrors had a much greater manufacturing tolerance hence got a reputation for being optically superior.
b) Thanks to computer analysis its much better understood that you can use a much smaller central obstruction with a fast scope and only have a very gradual light drop off from the center of the field - so images can be higher contrast and more refractor like .
c) Short focal length eyepieces are much higher quality and you can actually use a 5mm FL to achieve the magnification you want if you are into visual obeservation . In the bad old days your 25mm 1" ORTHO and an F16 scope gave you a clean image - the nasty 5mm eyepieces with poor contrats , fuzzy field stops and internal reflections would be your only choice with a fast scope. Image amplifiers have also come a long way . Amplifiers such as the Televue powermate can give you the image scale with little loss in image quality compared to old barlow lenses.
d) Collimation tools are just that much better and it is well understood ...in the bad old days you enjoy an F8 or F10 scope and never collimate it or a an F16 cassegrain that never ever gave a sharp image .
All that being said SCT's with quite a few spherical surfaces and their short tubes are also a good choice if the optics are clean and well collimated and you can manage thermal cooling issues of the closed tube at your particular site .
There is no magic solution for Imaging that will give you a big heads start , but appreciating keeping your telescope in optimal condition and being able to understand its thermal behaviour will be a necessity .
Hope this all helps to add some perspective .
Hi Mark,
This has clarified much for me, thanks. I have an F4.5 22" from Galaxy Optics made in about 1980. Have posted images on IIS from this scope of hi mag lunar regions but they always have that softness about them that I can't seem to shake and seems independent of seeing to some but not a great extent. I've added a couple here.
I am wondering if I need to get the mirror looked at although I am told that it was made as one of the last mirrors by Galaxy that was significantly hand - finished or figured(?).
The exploration of alternatives was a result of thinking that the short reflector was "too big" for planetary work as some have said over the years. But I think not.
