There is a new link on the left that says “AstroBuySell Alert” that should be useful to UK and Canada users looking for 2nd hand equipment. Just set up an alert for something you are looking for, and the alert service (currently in beta test) will send you an email when something appropriate comes up!
The number one enemy of planetary photography is the atmospheric condition, or “seeing”. Despite modern software being able to select and stack the best frames among thousands, the difference between results with good vs bad seeing can be great. Shooting at high FPS (60 or more) and using shorter exposures with sensitive cameras can help. An even better tool, especially for people who shoot with monochrome cameras, is to get a luminance frame through an IR-pass filter. Here is an example from last night using my C9.25 @ f/25 and a QHY5L-IIm camera, the left photo using for luminance a shot through the usual IR-cut filter, while the right one through an IR-pass (a “generous” one at 630nm), both processed with the same Registax 6 settings:
As you probably know, the best way to capture a good quality video of a planet is to shoot a video and combine the hundreds or thousands of frames using the magic of stacking software. That’s why a simple webcam will give you a better result than a single shot with your fancy Canon EOS DSLR. You also can’t use your DSLR’s regular video mode, as it only captures the large area that a DSLR sensor covers at a low resolution, giving you a low quality planetary image just a few pixels across. What you need is a way to capture in video all the pixels of one part of your large DSLR sensor. If you happen to have a 550D/T2i or a 60D, there is a “video crop mode” that does exactly that (at a nice 60fps). However, even if you have any other Canon EOS with live-view there is a way to get a 1:1 pixel video by capturing your 5x live-view with the help of a connected PC. This will allow you to get better planetary videos than with a simple webcam, so while there are dedicated planetary astro-cameras that are cheaper and much better at this than a DSLR, you can get some good results if you already have a Canon EOS and use the appropriate software:
- Update July 6 2015: Canon SDK update with support for EOS 5DS/760D/750D.
There is a nice little free program called EOS Camera Movie Record that allows you to capture 5x live-view video from your camera, which is the best way to do planetary photography for most Canon DSLRs (with the exception of 550D and 60D which have the superior “video crop mode”). There are better programs like BackyardEOS to do this, but they are not free.
In any case, I sometimes want to use it but don’t want to carry a laptop, so I tried it with my wife’s Windows Tablet. It worked, however the buttons were too tiny to hit without a mouse. Fortunately, the software is open-source, so I build a custom binary with larger buttons. Here it is in case anybody needs it.
Download EOS Camera Movie Record 0.3.3 beta – Tablet Tweak b2
(Changes: Larger buttons, links to the latest Canon SDK with 7D mk II/5DS/760D/750D support)
My first telescope returning to astronomy after many, many years was a Celestron NexStar 127SLT Maksutov-Cassegrain with an alt-azimuth goto mount. I have to admit that I was not very happy with the mount. The biggest problem was that it would vibrate very easily and the vibration would take 5-6 seconds to subside. It made even focusing hard.
So I saw the Celestron Vibration Supression Pads (VSP) and thought I’d give them a try. They are not very cheap, especially in Europe they cost around £60, while they are a more manageable $40 in the US. There are other much cheaper versions, like “Seben” in Europe, or “Solomark” and various Chinese unbranded ones, which might or might not be similar. But I went ahead with the Celestron VSP, just to make sure that if they don’t work, I won’t have to wonder whether the more expensive ones would have worked.
Although I am very happy with my iOptron ZEQ25 mount and would recommend it over the more popular (in Europe) skywatcher offerings, there are some areas where it could be improved. The first thing that comes to mind is the dovetail saddle. On paper and on first look it seems like a winner – it seems like a nice spring-loaded saddle that is not cheaply made and will easily secure your dovetail (without marking it). The biggest problem is that it has sort of an extra extrusion which, if you are not careful (e.g. in the dark) can “grab” the dovetail and you might think it is secure when it is not. The second problem is that the screws come dangerously close to the Dec house mounting, even rubbing against it (giving the motor a hard time) at least on my mount for a specific angle of the thumbscrew. Lastly, the two thumbscrews are not much spaced-apart, and that can make it harder to comfortably get a good grip in freezing temperatures.
Enter the replacement saddle from ADM that various ZEQ25 users have been praising. I decided to order one, even though it does not come very cheap at $99 before tax/shipping (for the UK, First Light Optics has them). Opening the box at least was not a disappointment, quality-wise the money seems well spent – it looks as well made and well finished as you can make a saddle. Replacement was a breeze. In 5 minutes you can remove the Allen screws from your iOptron saddle and use them to secure the ADM one. And then you get to use it…
Well, that’s it for Europe until 2026. We had a nice gathering with a lot of people of all ages at Heaton Park, Manchester today, however the weather was not favorable. We did lose the sun completely near the maximum (and I don’t mean the moon covered it – it was due to thick clouds) and people were trying to figure out why the solar shades were not working (the clouds were already filtering the sun, hence they were not needed), but otherwise it was good, everybody seemed to have a good time.
A few shots with the Canon 550D through the Skywatcher 80ED (Baader astrosolar ND 5.0), with the sun behind the clouds:
As I get some questions, comments and even criticisms about a particular aspect of this article, I thought it was time to do an update to try and clarify some things, and also add images from my newest OTAs. So, some people tell me that images are not a good indication of the overall performance of a telescope in planetary viewing, especially when observing visually. I would say that this is not correct, but not entirely incorrect either. You will notice the article is called “shootout”, so it is primarily about shooting images, but my original intend indeed was to evaluate a scope’s overall performance, so I did make remarks about differences in visual observing. It is just that images are the only objective way to demonstrate planetary performance and they are so easy to take nowadays – any webcam will do – that most people will try them. So, what exactly is different in observing? What is it that photos can’t show? First of all, if you can see a specific detail in an image, there is a chance you can see it visually, but there is no way you can visually see more than an image made of hundreds of frames shows, hence think of the detail in an image sort of like the “ceiling” of what you can see when observing. However, how easy the detail is seen will also depend on things like contrast and color and this is where post-processing an image makes a big difference and “hides” difficulties you might have when observing. Specifically, while the amount of detail you can “pull out” of a picture is quite dependent on your aperture, the telescope design makes a big difference in what you can see in the eyepiece, as a smaller aperture with a smaller “ceiling” of detail that can show up in processed pictures, might have a much more contrasty and colorful image that will actually make some details very prominent and give an overall more pleasing picture. Since the biggest difference in visual vs photo comes from post-processing adjustment of contrast/color/sharpening etc I have added the stacked but not processed (just brightness-normalized) versions of the photos previously posted, which can give a better idea of what you will get visually out of each scope.
When choosing a new telescope you must decide what you want it for. If you want to see wide-field deep space objects, then many types of telescopes are considered inappropriate (Maks, SCTs, long tube refractors etc), since they would be too dim or simply not fit the objects in your field of view. If, on the other hand, you would like to see the planets, these same telescopes would be the best fit. However, could you still use a wide-field capable telescope for planetary viewing or photography? And in general how do various types of OTAs perform in the solar system. Since I have a nice little spectrum of OTAs, including refractors, catadioptrics and reflectors, I though I should try to answer these questions by doing a comparison test under similar conditions with Jupiter as the target.
One of the best and least expensive solutions for observing the sun with a telescope is to use the Baader Astrosolar Safety Film. There are many places that will sell you a pre-mounted filter for your telescope, or you can make it yourself and save money. For example, by gluing strips of cardboard around the end of your aperture you can make a thick ring, on one end of which you can glue an Astrosolar Film, sandwiched between two cardboard holding rings (example on the right). It is not hard, but it does take some time to build, so if you don’t like DIY projects but you would like something quick (e.g. for observing the March 20 eclipse), you can take advantage of two facts:
- You don’t necessarily need your scope’s entire aperture for solar observation. Even a 40-50mm aperture would provide enough resolution for decent results when observing/photographing the sun. Yes, a full aperture filter will give you better views, so go for it if you can do the extra work.
- Many telescopes (especially refractors and Newtonian reflectors) come with covers that have an aperture mask (or “aperture stop”). That’s the smaller hole with the smaller cap you might be wondering about.
If you have an OTA with such a cover, you are all set to convert it quickly for Solar viewing. You still need to purchase some Baader Astrosolar Safety Film. It comes at around £18 per A4 sheet, but since you will need less (a square with a side at least as large as the aperture hole diameter), you can find various retailers (e.g. Agena, ebay) that will sell you a square piece for less.
I often read forum posts of people asking whether they can use a telescope for terrestrial viewing instead of a spotting-scope and also about a recommendation for such a telescope.
The usual answer is “yes you can use most telescopes – with the addition of an image erecting diagonal” and also “go with a Maksutov type”. While I agree that most telescopes are usable for terrestrial viewing, I should warn that each type, including Maksutovs, has advantages and disadvantages. First, I will list the various kinds of telescopes and discuss their suitability as well as any advantages/disadvantages. Note that most astronomical telescopes are paired with “equatorial” mounts, which are good for tracking the stars, but for terrestrial viewing you have to go for a simpler and actually cheaper, “alt-azimuth” mount.
Long-Tube Achromatic Refractors
The simplest “achromatic” refractors are relatively inexpensive instruments. Their design suffers from the inability to focus all colors at the same plane, something called “chromatic aberration” and is easy to see at the edges of bright objects. One simple solution to reduce this effect is to increase the focal length of the refractor, so refractors at around f/9-f/10 (focal ratio = focal length / objective lens diameter) don’t show much of an effect. But they are of course long (a refractor’s focal length is pretty much the length of its tube) and a little on the heavy side, plus they don’t offer a wide field of view – they are made for relatively high magnification.
Decent quality views, comfortable high-magnification.
Good contrast and not much chromatic aberration compared to short refractors.
Very long tubes, relatively heavy. Not very portable.
No wide-field views.
Originally made for myself to compensate my ZEQ25’s polar scope reticle centering error, I made it available through the Apple app store in a free ad-supported version and a paid Pro version with a few extra features (such as manually setting the date, time, location if you don’t want to use the current time/gps location of your phone). For iPad, iPhone running iOS 6 and up.
The lowest cost field flattener / corrector that I could find for my SW 80ED refractor was the Starguider 2″ Field Flattener sold by Sky’s the Limit on ebay.co.uk. They have a £124 buy it now price currently. According to the seller (who is well-trusted in the UK) this is the same as the TS 2″ Field Flattener (TSFLAT2), although the latter (if you order directly from TS) comes at about £167 for the corrector only – adapters are extra.
So, I took a chance with the low cost Starguider one, which comes with adapters (so at a savings of well over £50 overall compared to TS) and should be good for f/5-f/8 refractors – with the f/7.5 of my 80ED falling into that range.
It comes with a T-adapter that adds 38mm to the light path and also a 15mm 2″ filter thread extension. If you use a regular T-ring with your DSLR, the sensor should lie at about 55mm from that, hence with the setup as is you get the sensor at 55+38+15 = 108mm from the Field Flattener thread. According to the TS listing the correct sensor to flattener distances are:
— Focal Length < 450mm: 128mm
— Focal Length 450-490mm: 123mm
— Focal Length 500-550mm: 118mm
— Focal Length 560-590mm: 116mm
— Focal Length 600-690mm: 113mm
— Focal Length 700-800mm: 111mm
— Focal Length from 800mm: 108mm
Hence, for a Focal length of around 800mm or more, you are all set. There is some tolerance (5% according to the instructions), so I guess you could try even a 700mm OTA like that.
But I have a 600mm 80ED, so I would need a little extra length. Luckily, the thread is the common 2″ filter thread (48mm), so my Orion Imaging Filter was just right for the job, adding 7mm to take it to 115mm. Pretty close. So here is the setup I used:
We know how even with APS-C sensor you need a 2″ focuser to avoid significant vignetting. However 2″ filters are significantly more expensive (which can translate to quite some money for some nice AP filters that were recommended to me), and not as many options available (even fewer are available as clip-on and usually even more expensive), so for the sake of not overstretching my budget I looked at whether I could do something about it.
So, to delineate the problem, here we have a nice flat frame from my 200p-DS’s 2″ T-mount:
There is a slight vignetting at the edges, which makes me feel a bit better about not shelling out for a full frame. But it is very little. However, if I would like to use a 1.25″ filter, I would have to use a 1.25″ t-mount to thread the filter on, which results to this flat frame:
I’ve had an interest in astronomy since I was a kid. In ’88 my uncle gave me my first “telescope” (a small 40mm refractor called Halleyscope – although it was a decidedly unsuitable instrument to watch a comet) and I finally managed to get a “real” telescope in 1991. Telescopes were expensive back then. In Europe they we even more expensive. Fortunately, the dissolution of the Soviet Union opened the borders and we got access to some pretty good Soviet technology carried over by immigrants. So I managed to get a 4.3″ Soviet Newtonian telescope called “Mizar” in Greece at probably much better price than something comparable in the US. Still, at around $250 or so back then it was not “cheap” (I guess around $400 in 2015-equivalent currency). That telescope, solidly built on a heavy equatorial mount is still being exported as the TAL-1 and has a good reputation for its optics. But, man, was it heavy!
I was lucky enough to have my sister returning from her studies in the US at that time, bringing along an IBM PS/2 computer and a Canon EOS Rebel film camera. The PS/2 is irrelevant to this article – there was not much an amateur could do regarding astrophotography with a computer back then, but the camera was very useful. You could not hope to achieve much using the cheap point and shoot film cameras of the era, but a serious camera with manual settings did stand a chance. Still, it was a very frustrating experience: You had to get a 24 or 36-exposure roll of decent (and fast) film, so any cheap roll would not do. Popular at the time, if I remember correctly, were the Fuji Super G 400/800, the cooler Kodak Ektar 1000 and for special requirements the Konica SRG 3200. Cost of the roll and the development meant you had to fill that film wisely if you were on a budget. Most importantly, you had to fight with the developer to understand your unusual demands. You see, most astro-images tended not to look like pictures to the developers. They would return the film to you “there’s nothing there”, or cut out the astrophotos. So, you had to insist they develop everything despite the fact that they looked blank, and when printing not try to increase the brightness too much to “show something”. Also you could not shoot many astro-images one after the other, because the developer would not be able to see where to “cut” the film in segments (as my local developers would do). Most importantly, you had no idea whether your method/settings etc actually produced anything, until you finished your roll of film and had it developed. Oh, and did I mention how hard focusing was? No live-view or test-shots! (more →)