The bestest telescope for lunar photography

[bkm2304]

Hi all,

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.

Any crazy ideas most welcome!:D

Richard

[Atmos]

I'm actually thinking about something along the lines of a 16" F/4.5 Go-To Dob with a 4-5x barlow.

[bkm2304]

Hmmmmm..... Easy to obtain, that's for sure!

Thanks, Atmos.

[rally]

Gladius CF315
Its an F25 Dall Kirkham, specifically designed for lunar and planetary

[alocky]

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.

[bkm2304]

Yes, had a look. Serious beast!:eyepop:

[bkm2304]

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

[alocky]

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?

[Wavytone]

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.

[Satchmo]

Barry gave a great talk on `infrared ' ( ? ) planetary imaging at the 2016 NACAA Convention in April and was looking pretty healthy then ?

[bkm2304]

The Schiefspiegler option keeps popping up. Where would I get one?

[Atmos]

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 :)

[bkm2304]

......and then I came across this one!

http://www.webstertelescopes.com/lunar.htm:eyepop:

[dannat]

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

[bkm2304]

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 (http://www.webstertelescopes.com/lunar.htm) from Webster? I take it that the mirror is not coated returning only about 5% of the light and therefore giving apparently excellent views....

[alocky]

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.

[Mokusatsu]

These days the cool ATMs are making Stevick-Paul scopes.

http://www.amsky.com/atm/telescopes/spscopes/spt.html

[Satchmo]

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 .

[bkm2304]

Will have a look. Thanks.



Yes, I was a bit worried that there was no aluminium on the glass! Makes sneak peaks at other objects a bit disappointing!:rofl:

[bkm2304]

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.

[Satchmo]

Your biggest issue with that rig would probably be the 2" thick mirror which would make it unlikely that you are keeping the core down to 1 degree or so delta to ambient during the night unless you has some pretty slick thermal management . You'd be better suited with a smaller aperture and thinner glass . It also depends on the absolute seeing at the site you are using and this gets a bit lost these days amongst the wonders of digital processing .

When i used to work at CSIRO Applied Physics they had an interferometer setup for testing sky conditions by Sydney Uni as a precurser to the SUZI stellar interferometer and they found the average nightly seeing on the hill aligning with a 150mm aperture at the Lindfield site, so you can't assume you have great seeing where your observatory is located . Having a smaller portable telescope will allow you to more easily find a site with good seeing .

I have a pretty sound testing here and you are not too far away - if you ever want some thorough bench testing of your mirror just PM me .

[Wavytone]

Lo and behold here's the scope for you http://www.astromart.com/classifieds/details.asp?classified_id=920864

[PeterAnderson]

Having a lot of experience and grey hairs means two things, continuing to make a lot of mistakes and having grey hairs!
Having said that I will weigh in. The top lunar/planetary imagers often use C14's, the regular model. I won't rave on, but just give one example, Damien Peach.(Check out his website.) This is where they often operate in collaboration with professionals. So you don't need a gazillion dollars and really special equipment. What you do need are very steady conditions that are hard to come by, and video imaging technique where you grab and stack the best frames.

As a Neanderthal, I have attached a camera to the C14 with 2 X televerter and got some 'happy snaps' but as single images, they still have that 'softness' to them. Now Damien Peach has a lovely image of the central crack running down the Alpine Valley....wow! To see it alone is an achievement, but to image it as well.... Okay he does take his scope to Barbados annually for imaging in the wonderfully steady conditions.

And so it is not only the size of your scope, but what you do with it. Damien was using a C9.25 some years ago and got remarkable results also.

[bkm2304]

Hi Peter,

All very true comments! I do indeed use stacking techniques, collecting up to 6,000 frames and selecting a precious few for stacking and processing. My real interest is to attempt to get in as close as possible. This of course relates to resolution which in turn, of course relates to optical diameter, be it reflecting surface or glass lens. Satchmo has pointed out that well - tuned, fast reflectors with excellent thermal control are the instrument of choice for imagers such as Anthony "Bird Strike" Wesley and our own fearless leader, Mike "Iceman" Salway, whose lunar images rival anyone including Mr Peach.

My goal in all this is actually to get in even closer and cleaner than imagers with C14's and the like can do. Theoretically this is possible and so I should, using a 22" Newtonian under the right conditions of technical prep and seeing, be able to get high quality images. However this is a great effort to achieve and my results thus far over the years have been "OKish" only.

The next "Giant Leap" will be to start a project that will squeeze the very best out of my equipment and work under the conditions that I have here in Clarence Town - great dark sky but only rare times of very good seeing - although there have been nights here when the seeing has been superb and steady and limiting mags of close to 6 have been seen.

So, this is the project! Thanks to all who have contributed to help me understand what it is, exactly, that I am trying to do!:hi:

Richard