Looking at what is available on the market, it seems that would be lunar and planetary imagers are a bit neglected.
There is an amazing range of wide field and deep space astrographs to choose from, but when it comes to planetary, there are very few suitable instruments.
Basically one has to choose between a large Newt or a large SCT.
The large SCTs are proven performers when it comes to planetary imaging, but the optical quality seems to vary and that can be a big problem. Also it is hard to keep the corrector plate from dewing up, just when the seeing comes together. Heaters, while ok for deep sky, are out for sub arc second imaging.
Large Newts are a bit cumbersome and need to be optimized for planetary imaging to perform well, by minimising the size of the secondary, having a primary mirror that is not too thick and providing forced ventilation for the OTA. Of course, the optics need to be really good as well.
There is a third possible option for the planetary imager, but it is not well supported by the market, and that is the Dall-Kirham.
Recently I started designing a dedicated planetary 250mm aperture DK to complement my CDK250 and I would be very interested to hear from people that are intending to try lunar and planetary imaging or even just visual planetary observing.
In my years of experience with planetary imaging, I have found it hard go go past a good Newt, and my favorite was my 10" f5 carbon strut Newt which I built, which used a GSO mirror set. It was a perfect match for my CGX observatory mount. For imaging the planet's I found the ASI 294 MC camera to be ideal, and I use the non-cooled version for planetary, because I am realtime stacking and aligning with Sharpcap and long subs for planetary are unnecessary.
Don't make It harder than it needs to be. My time spent with an SCT was a waste, constant frustration, with mirror flop, condensation problems, etc. I fail to see the attraction of SCTs for anything to do with Astronomy, except maybe they are easy to transport..
I have been meaning to, one night, use a 2.5x Powermate to do some moon and planet imaging but it’s not something I’ve had a chance to test yet.
Colin, don't waste your time unless you are going after medium resolution lunar imaging. The large central obstruction (50%, linear) destroys sub arc second contrast. That is why you won't find cutting edge planetary images made with RCs or CDKs.
Quote:
Originally Posted by glend
In my years of experience with planetary imaging, I have found it hard go go past a good Newt, and my favorite was my 10" f5 carbon strut Newt which I built, which used a GSO mirror set. It was a perfect match for my CGX observatory mount. For imaging the planet's I found the ASI 294 MC camera to be ideal, and I use the non-cooled version for planetary, because I am realtime stacking and aligning with Sharpcap and long subs for planetary are unnecessary.
Don't make It harder than it needs to be. My time spent with an SCT was a waste, constant frustration, with mirror flop, condensation problems, etc. I fail to see the attraction of SCTs for anything to do with Astronomy, except maybe they are easy to transport..
Newtonians can perform well as planetary imagers but they are hard to tame. SCTs, as you say, have problems, but some of the best planetary images are taken with C14s.
Stefan, if you analyse the available equipment solutions, from the standpoint of cost to acquire (an often important consideration these days), a Newtonian will, or should, be the logical choice. If money is not a consideration, well of course there are other options.
Newts that are financially accessible for most tick all the boxes of what doesn’t work for high resolution planetary imaging… inability of spider or primary cell to hold the mirrors still, cheap and flimsy tube that bends at the thought of a slew…
SCTs are common for that use case because their sins are fairly manageable, and they don’t require superhuman strength or observatory class mounts to use them.
Fwiw I’d love a dedicated planetary scope… but it’d have to come with a kind of seeing guarantee
Stefan, if you analyse the available equipment solutions, from the standpoint of cost to acquire (an often important consideration these days), a Newtonian will, or should, be the logical choice. If money is not a consideration, well of course there are other options.
My argument is that even if money is not a consideration, there are not many options, but yes, the Newtonian is the most cost effective one.
Quote:
Originally Posted by Camelopardalis
Newts that are financially accessible for most tick all the boxes of what doesn’t work for high resolution planetary imaging… inability of spider or primary cell to hold the mirrors still, cheap and flimsy tube that bends at the thought of a slew…
SCTs are common for that use case because their sins are fairly manageable, and they don’t require superhuman strength or observatory class mounts to use them.
Fwiw I’d love a dedicated planetary scope… but it’d have to come with a kind of seeing guarantee
You are spot on regarding Newts. It is very difficult to make them rigid and stable without turning the rigidity problem into a thermal problem. A good planetary telescope needs to have a small thermal inertia not only regarding the optics, but the whole structure. The Cassegrain configuration is much more suitable in that respect.
Anyway, I can provide the scope but not the seeing, unfortunately, although I may be able to include a sorcery manual
Not a lot of enthusiasm for planetary telescopes, it seems.
Anyway, I decided to go ahead with the DK250 project and started ordering the materials. I may start a new thread in the ATM section to document the process.
Nice Stefan looking forward to following your build!
I myself use an old Intes Mk-65 maksutov for visual.
At f10 it’s good for visual. Dedicated planetary scope I use it for a lot of objects.
How fast do you plan for a dedicated planetary imaging scope?
Nice Stefan looking forward to following your build!
I myself use an old Intes Mk-65 maksutov for visual.
At f10 it’s good for visual. Dedicated planetary scope I use it for a lot of objects.
How fast do you plan for a dedicated planetary imaging scope?
Thanks Wilso,
It will be f/16, with a focal length of 4000mm.
For imaging Jupiter it will require a 1.4x tele extender and for Mars a 2x Barlow, to achieve its full potential.
Hi Stefan, I would almost be interested in a dedicated lunar and planetary telescope that is a manageable size and weight, but it also , surprisingly, comes down to the cost as well . I have an 250mm f6 newt that I have used for the planets but it is awkward to manage mounting on the EQ6. Don't have a permanent set up unfortunately so I need something with decent aperture that is more portable.
Currently am mostly using my 180mm Mak which is fine but extra aperture would be so nice for the rare night of "good" seeing. A rough guide to pricing would be of interest. A reply by PM is fine if not wanting to advertise to the world yet.
The OTA will be very portable. It will weigh around 10kg and have a length of about 950mm, including the focuser.
I also want one for myself for catching planetary events that are clouded out in Melbourne. Need to be able to throw it in the car and drive north of the divide. I can't do that with my 16" DK
The OTA will be very portable. It will weigh around 10kg and have a length of about 950mm, including the focuser.
I also want one for myself for catching planetary events that are clouded out in Melbourne. Need to be able to throw it in the car and drive north of the divide. I can't do that with my 16" DK
If the 16" doesn't fit in the car then obviously you need a bigger car, or van
Would it have enough back focus for a diagonal and eyepiece for visual as well?
As it is now on the drawing board, the back focal length is 82mm, with the focuser fully retracted. Which is not quite enough for a 2" diagonal but it should be ok for a 1.25" one.
Quote:
Originally Posted by Saturnine
If the 16" doesn't fit in the car then obviously you need a bigger car, or van
That would only solve the size problem, however, there is a weight one too.
Looking at what is available on the market, it seems that would be lunar and planetary imagers are a bit neglected.
.............Recently I started designing a dedicated planetary 250mm aperture DK to complement my CDK250 and I would be very interested to hear from people that are intending to try lunar and planetary imaging or even just visual planetary observing.
Apologies. Totally missed this post, but yes! There is a hole in the market for such an instrument.
Problem might be that the venerable Celestron 14 might be a commercial thorn in the side of your plans. Since Don Parker started using one with photographic
film last century (bugger... I must be old) they have produced remarkable results.
In terms of bang for buck, how would your design, on paper at least, improve on them? (e.g theoretical resolution/contrast)
Problem might be that the venerable Celestron 14 might be a commercial thorn in the side of your plans. Since Don Parker started using one with photographic
film last century (bugger... I must be old) they have produced remarkable results.
In terms of bang for buck, how would your design, on paper at least, improve on them? (e.g theoretical resolution/contrast)
A long time ago when Don Parker was using a 16" Newtonian, I made a 10" Dall-Kirkham as a step up from a 180mm Gregory-Maksutov that I was using at the time - and I was so happy with it that I ended up making a 16" version, a few years later.
A 10" DK cannot compete, of course, with a C14 regarding resolution but it is far more portable and can better handle the seeing. When I moved from the 10" to the 16", the good seeing nights became a lot less frequent.
A problem with C14s appears to be that not all of them are equally good, making it a risky investment. Although this opinion of mine is based on very few samples.
Another advantage of the DK is that it doesn't have a corrector plate that can dew up. At least in Melbourne, the nights with the best seeing tend to be very dewy.
Another advantage of the DK is that it doesn't have a corrector plate that can dew up. At least in Melbourne, the nights with the best seeing tend to be very dewy.
I’m sure you have already thought of this Stefan, but what’s the plan for keeping the dew at bay? Just because the corrector plate doesn’t exist, doesn’t mean the dew remains suspended in the atmosphere.
Not being funny btw, I’m genuinely interested, but lack the means to fund an interesting scope such as this. My first Newtonian dewed then frosted up first time out bush
I’m sure you have already thought of this Stefan, but what’s the plan for keeping the dew at bay? Just because the corrector plate doesn’t exist, doesn’t mean the dew remains suspended in the atmosphere.
Not being funny btw, I’m genuinely interested, but lack the means to fund an interesting scope such as this. My first Newtonian dewed then frosted up first time out bush
A very good question.
Dew in fact does remain suspended until it contacts a surface that is cold enough for it to settle on. If a surface is a bit above ambient temperature it tends to repels the dew.
Anodized surfaces are very good black body radiators and, when pointed towards a very cold sky, quickly cool to below ambient temperature, attracting a lot of condensation.
Shiny metallic surfaces, like the mirrors in a telescope, are not good radiators, at least on their metalized sides.
Therefore a DK secondary will lose most of its heat though its back surface.
On my 16" DK, to prevent dew on the secondary, I added a 3mm thick foam disc topped by a layer of plain aluminium foil that also wrapped around the edge of the mirror. So, by slowing down the cooling of the secondary, I never had dewing problems although the mirror was still able to closely track the ambient temperature through convection cooling.
It is important to take into consideration the different use case scenarios too between planetary and deep sky observing sessions.
Planetary sessions, in my experience, never exceed a couple of hours while deep sky ones can go all night and that also helps with dew management.
I use it for a lot of objects.
