With so many different designs and brands around, choosing a telescope for imaging smaller deep sky objects such as galaxies and planetary nebulae can be a difficult proposition. In this guide, I will give you some recommendations that aim to make that decision easier.
What type of scope do you go for when looking to get into deep sky imaging of smaller objects such as galaxies and planetary nebulae? Each design has its own merits, however there isn't a right or wrong answer. It purely depends on a range of factors, such as portability, maintenance and performance characteristics.
Refractors tend to have the highest contrast, as they do not have a central obstruction. But in larger apertures (e.g. 130mm, 150mm), they become quite heavy and long. Therefore, they would be more suited to permanent setups, such as in an observatory. Also, to obtain a field-of-view that is suitable for smaller deep sky objects, a camera with a small pixel size is desirable. Fortunately, the advancement in CCD and CMOS sensor technology has made this easier. Larger designs of telescopes, such as Ritchey–Chrétiens are no longer necessary to obtain amazing deep sky images. Refractors are slowly becoming a more popular choice for deep sky imaging. It is true that refractors are limited by aperture (due to cost and weight etc.), meaning that they generally do not gain as much light as other designs like Ritchey–Chrétiens, as these tend to have larger apertures. However, the surge of CMOS cameras and to an extent, CCD cameras, with newer and more sensitive sensors, has meant that the gap between refractors and large reflectors is narrowing.
Given the rise of large refractors in the world of deep sky imaging, Ritchey–Chrétien telescopes still remain the gold standard for deep sky imaging. As mentioned; they have larger apertures in a more compact design than refractors, making the smaller models somewhat more suitable for portable setups, however larger aperture Ritchey–Chrétiens are seen in professional observatories all around the world and have for a long time, been relatively inaccessible to amateurs, due to their high price tag. However, they have recently become more accessible, as certain manufacturers such as GSO, offer smaller aperture versions at affordable prices. Ritchey–Chrétiens have flat fields throughout the imaging circle, making them ideal for deep sky imaging.
There are a range of other designs that are suitable for deep sky imaging, such as Dall-Kirkham and Newtonian astrographs, which are great choices too.
With all the above considered, I have listed a range of different deep sky imaging scopes below that I think fit the bill, for all budgets. This list is not exhaustive and I recommend that you carry out your own research before committing to any purchase.
TEC 140 F7 Apochromatic CaF2 Fluorite Refractor
Specifications:
Price: £9,199 (including VAT).
Optics: aplanatic oiled triplet objective with CaF2 fluorite crystal middle element.
Aperture: 140mm (5.5").
Focal length: 980mm.
Focal ratio: F/7.
Focuser: 3.5" Feather Touch focuser.
Weight: 9.6kg (including mounting rings).
The TEC 140 is a classic and very highly regarded scope within the astronomy community. It'd certainly be on the list of dream telescopes for most amateur astronomers. Although quite expensive and with a long waiting list, not a lot compares to the optical performance that it offers. Its CaF2 fluorite middle element offers unparalleled colour-correction; optimised for both visual and imaging applications, with a focus shift of less than 0.2% from 436nm to 1,000nm and a Strehl of 0.99 at 546nm. Tests have shown that the average, actual Strehl is very close to this with an RMS wavefront error of less than 1/50 wave. The oiled design also offers greater contrast than a lot of air-spaced equivalents, which is great for observing or imaging fainter deep sky objects.
The scope comes supplied with tube rings as standard, along with the excellent Starlight Instruments 3.5" Feathertouch focuser, which can withstand demanding camera loads. TEC also offer an optional 0.9x focal reducer, along with a 9" Losmandy plate and matching carry handle, at an additional cost.
Find out more about the TEC 140 here: https://astrograph.net/TEC-140-APO-Refractor.
Altair Wave Series 130 F7 ED Triplet Apo Refractor
Specifications:
Price: £2,499 (including VAT).
Optics: triplet ED objective.
Aperture: 130mm (5.1").
Focal length: 905mm.
Focal ratio: F/7.
Focuser: heavy duty 3.7" rack and pinion dual-speed focuser.
Weight: 12kg (including mounting rings and dovetail).
The Altair Wave Series 130 ED apochromatic refractor is another excellent choice for deep sky imaging. I use Altair's smaller 115 ED Apo in my permanent setup and can vouch the high quality design of the Wave series. Also, a 130mm Apo is probably the optimum size for a permanent deep sky setup; not too big and not too small. A new version of their 130 ED model was released for 2022 and now comes with an attractive red and white finish.
Specifically, it features a premium quality triplet ED objective with adjustable tilt, which is free of any stresses that affect large refractors of this type. It also has a generous focal length of 905mm, which frames those smaller deep sky objects quite well; especially when paired with the correct camera. The Wave 130 ED is offers great value for money; performing similarly to scopes costing three to four times as much. The OTA is made from rigid aluminium, allowing rapid thermal equalisation and effective dew heater conductivity. Also, the heavy duty 3.7" rack and pinion focuser has a large enough capacity for most serious imaging setups.
Altair Astro take quality control very seriously; hence the Wave 130 ED is put through rigorous QC and testing, to ensure that you are receiving only the best. They specify that every lens cell must meet their strict criteria of 0.95 Strehl. They also supply a full optical test report with every scope, so you can have confidence in knowing that what you're getting is a high quality item.
An optional 1.0x field flattener and 0.8x M92 focal reducer are also available.
You can find out more about the Altair Wave 130 ED here: https://www.altairastro.com/altair-wave-series-130-f7-ed-triplet-apo-455-p.asp.
GSO Ritchey–Chrétien Series
Specifications:
Price: from £570 up to £6,900 (including VAT).
Optics: quartz hyperbolic mirrors.
Aperture: 152mm (6") up to 406mm (16").
Focal length: 1,370mm up to 3,250mm.
Focal ratio: F/9 for 152 (6") version. F/8 for larger sizes.
Focuser: 2" Crayford for smaller apertures. 3" Crayford for larger apertures.
Weight: 5.5kg (for 6") up to 38kg (for 16").
The GSO range of Ritchey–Chrétien telescopes, sold under many different guises, such as Astro-Tech, Orion, Omegon and TS Optics, have essentially revolutionised astrophotography, by making the design more accessible and less expensive to amateurs.
They offer a similar level of optical performance as some of the more expensive brands, but without the huge price tag and are available in a range of different apertures to suit, from 6" up to 16". The smaller apertures (6", 8" and 10") are available in a solid tube design and the larger apertures (including the 10", 12", 14" and 16") come in a lightweight carbon truss type design, for quick cooldown times and to save weight, making them suitable for a large range of mounts. The larger apertures (from 10" upwards) also come with three cooling fans fitted in the rear mirror cell to aid cooldown.
One of the criticisms of the GSO range in the past was the fact that the focuser was fixed to the primary mirror and could not be collimated independently. However, GSO have taken this into account and redesigned the scope to feature collimation screws to independently adjust the focuser.
These scopes have a large imaging circle of up to 60mm and have a range of accessories available, such as a x0.67 focal reducer, making them suitable for large format sensors, such as the KAI-11000M series. A large backfocus also allows for a variety of different imaging accessories to be used.
A few things to watch out for with these scopes is the focuser and the lack of dew heaters. If you were to go ahead and buy one, I would recommend upgrading the focuser to a better and more heavy duty design, such as a rack and pinion type; especially if your imaging camera and accessories are heavy. The lack of dew heaters may also be less than ideal for some, depending on how much moisture your imaging site gets. However, there are a range of secondary dew heaters available from various manufacturers, such as Kendrick, that can be easily fixed to the secondary mirror cell. However, for the primary mirror, a DIY solution might be the only option.
Despite these small snags; I would certainly recommend the GSO range if you want to dive into the world of Ritchey–Chrétiens, without breaking the bank. Personally, I have owned an Omegon 8" Ritchey–Chrétien and can highly recommend their products.
You can find out more about the Omegon Ritchey–Chrétien range here: https://www.omegon.eu/telescopes/10/m,Omegon/a,Teleskope.Allgemein.Serie=Pro+RC/a,Teleskope.Optik.Bauart=Ritchey-Chretien.
Sky-Watcher Esprit 150ED Apo Refractor
Specifications:
Price: £5,029 (including VAT).
Optics: triplet objective lens (one Ohara FPL-53 and 2 x Schott lenses).
Aperture: 150mm (6").
Focal length: 1,050mm.
Focal ratio: F/7.
Focuser: 3" dual-speed linear power focuser
Weight: 14.52kg.
The Esprit range of triplet apochromatic refractors by Sky-Watcher have earned a reputation in the amateur astrophotography community as being some of the best imaging refractors for the money.
The 150ED version of the scope is the ideal size for imaging smaller deep sky objects, but at an amazing price. For only £5,029, at this aperture it is very hard to beat, especially considering that it has a premium triplet objective with Ohara FPL-53 glass. Equivalent scopes from more premium brands would cost upwards of £10K or more for the same aperture and optics. Having received many acclaimed reviews from around the community, many consider the Esprit 150ED to be almost indistinguishable in terms of optical performance and colour correction to more expensive scopes offered by TEC and Takahashi.
There are many benefits that the Esprit 150ED offers as well; such as the fact that it is lighter than other scopes of similar sizes and has a dedicated field flattener, offering a very flat field throughout the image circle of 44mm. This makes it suitable for a large range of cameras. However, for deep sky imaging, I would recommend matching it with a camera with smaller pixels, such as the Atik 460EX or 490EX range.
The high quality CNC machined focuser supplied with the Esprit 150ED is excellent and has a high load capacity of 5kg, allowing you to carry a large range of equipment. It also comes supplied with a 2" dielectric star diagonal, 28mm 2" LET eyepiece, 9 x 50 right-angled image finderscope, tube rings and dovetail mounting bar.
First Light Optics (FLO) offer a pre-dispatch optical bench test, to ensure that the scope is perfectly collimated and up to scratch before sending it out. Find out more here: https://www.firstlightoptics.com/esprit-professional-refractors/skywatcher-esprit-150-ed-pro-triplet.html.
CFF Ritchey–Chrétien Series
Specifications:
Price: from €10,332 up to €53,900 (including VAT at 23%).
Optics: fine annealed Supremax33 as standard. Quartz/Clearceram-HS as an option.
Aperture: 300mm (12") up to 600mm (24").
Focal length: 2,400mm up to 4,800mm.
Focal ratio: F/8.
Focuser: various options available.
Weight: starting at 19kg (for 12").
If your budget is a little higher and you're looking for something quite special, then the CFF Ritchey–Chrétien range should be on your list. These premium scopes are designed and built exclusively in Europe; the mirrors are made in Romania and the mechanical elements are made in Poland. Again, like the other scopes listed above, these range of scopes have received high praise.
The scope comes in a range of different apertures, including 300mm (12"), 400mm (16"), 500mm (20") and 600mm (24"). Materials used in the scope are excellent throughout; the OTA is a Serrurier truss type design and is made from carbon fibre, along with the primary mirror cage. The optics as standard have a fine annealed Supremax33 substrate, however an optional quartz/Clearceram-HS substrate is available. Supplied with the scope are a field corrector (that provides a 52mm corrected field), upper handle or secondary dovetail (D-type or V-type), along with side plates for additional stiffness. Perhaps the most useful feature is that the scope also comes with built-in primary and secondary dew heaters, along with cooling fans on the rear of the primary mirror cell. All of these have RCA type connectors, allowing you to use them with a large range of dew controllers etc.
The OTAs throughout the range are fairly lightweight, due to the usage of carbon fibre. This makes them ideal for a large range of mounts. The 300mm (12") version is especially light at 19kg. This size would probably be my choice of the range, as it is the most versatile and easiest to live with.
These scopes also come supplied as standard with a heavy-duty Starlight Instruments rack-and-pinion focuser, able to handle a wide range of accessories.
You can find out more about the CFF range of Ritchey–Chrétiens here: https://cfftelescopes.eu/products/reflector.
Astro-Physics 130 F6.3 StarFire GTX "Gran Turismo" Refractor
Specifications:
Price: $7,490.
Optics: triplet objective lens.
Aperture: 130mm (5.1").
Focal length: 819mm.
Focal ratio: F/6.3.
Focuser: 3.5" dual-speed focuser.
Weight: 8.2kg.
Introduced in a re-imagined form in 2015 at NEAF, the Astro-Physics 130 "Gran Turismo" is considered by many to be one the most desirable scopes ever made and the holy grail of apochromatic refractors. It is an all-out, no-compromises triplet that offers the highest level of optical performance that money can buy. Such a premium in quality isn't without its downsides though; the waiting list for the StarFire is long and buyers have been known to have waited up to 10 years before receiving it. However, if you can get hold of one of these, then it is the sort of scope that you would keep for the rest of your life and possibly pass on to your children. Occasionally, they come up in the used market, but are often snapped up very quickly.
In terms of technical properties, the StarFire has a 130mm (5.1") triplet objective with multi-layer coatings offering greater than 97% overall transmission in peak visual wavelengths. This is combined with a premium 3.5" focuser with a silky-smooth, greaseless drawtube and dual-speed mechanism from the Feathertouch 9:1 Micro. A digital focusing system is also available for imaging applications. The focuser can also be rotated using a "captain's wheel" collar for assistance with framing for astrophotography.
The optical tube itself is lightweight, making it suitable for a large range of mounts, such as Astro-Physics' equally as impressive Mach1GTO. The optical tube can also be split into two parts, allowing it to easily fit in carry-on baggage when travelling etc. The felt-lined dewshield is also fully retractable and locks into place using a twist-lock feature.
Find out more about the Astro-Physics 130 f6.3 StarFire "Gran Turismo" here: www.astro-physics.com/130gtx.
PlaneWave CDK12.5
Specifications:
Price: $10,000.
Optics: corrected Dall-Kirkham.
Aperture: 318mm (12.5").
Focal length: 2,541mm.
Focal ratio: F/8.
Focuser: 2.75" Hedrick focuser.
Weight: 20.9kg (with manual focuser and dovetail).
The PlaneWave CDK12.5 is a great scope for a permanent setup in an observatory. Its Corrected Dall-Kirkham design features no coma, no off-axis astigmatism and no field curvature, making it an excellent performer for deep sky astrophotography. It also produces a perfectly flat field with pinpoint stars across a 52mm image circle, making it suitable for a large range of large format cameras, such as those with 16803 sensors.
In addition to being a great performer, the CDK12.5 is simple to use; collimation is straight-forward, thanks to a fixed primary mirror. Only the secondary mirror requires collimation.
Other features include a carbon tube design with three cooling fans built into the rear, which produces faster cooldown times, along with minimising thermal expansion and focus shift as the temperature changes. It also makes the scope relatively lightweight for its size, allowing it to be paired with a wide range of mounts.
The heavy-duty 2.75-inch Hedrick focuser featured on the CDK12.5 has a no-slip design with 1.3" of travel, allowing a broad range of imaging gear to be attached to it.
Finally, it's worth mentioning that PlaneWave also offer their PWI3 software, that allows the user to control a variety of functions on the scope, including the focuser and cooling fans etc.
Find out more about the PlaneWave CDK12.5 here: https://planewave.com/product/cdk125-ota/.
Takahashi TOA-130NFB F7.7 Ortho Apochromatic Triplet Refractor
Specifications:
Price: £7,690 - including VAT.
Optics: ortho triplet ED objective.
Aperture: 130mm (5.1").
Focal length: 1,000mm.
Focal ratio: F/7.7.
Focuser: 4" rack-and-pinion focuser with 7:1 fine focus.
Weight: 12.3kg.
Another dream refractor that is up there with the Astro-Physics 130 StarFire in terms of desirability and prestige is the Takahashi TOA-130NFB. Similar to its larger sibling, the mighty TOA-150, this scope features a three lens objective with the front and rear elements constructed from ED glass. The results in an extremely high level of apochromatic performance for both visual and imaging use. Takahashi engineers undertook a complete redesign of the triplet system, completely eliminating spherical aberration whilst minimising axial chromatic aberration in the visible light spectrum. In typical apochromatic designs, the elimination of chromatic aberration is usually at the expense of increasing spherical aberration at various wavelengths. However, with the TOA series, the focal shift across the entire visible spectrum from 436 nm up to 656 nm is less than +/- 0.01 mm. This is less than 1/100 the aberration of a typical apochromatic design.
The scope has a focal length of 1,000mm, making it perfect for imaging smaller objects. A large mount is recommended however, as it is quite a heavy scope. Other features include a retractable dew shield, 4-inch rack-and-pinion focuser with a 7:1 fine control and a 360 degree camera angle adjuster. A complete range accessories including flatteners, reducers and extenders are available, including the 67-series flattener, which provides a 90 mm imaging circle.
Find out more about the Takahashi TOA-130NFB here: www.firstlightoptics.com/takahashi-toa-130-series-refractor-telescopes/tak_tok13210.html.
Summary
These are just a few examples that I would highly recommend if you are looking to advance your imaging beyond wide-field imaging, to the next level and start imaging those smaller deep sky objects. There are many other amazing telescopes out there for deep sky imaging and I would highly recommend doing your own research to find out what works best for you. However, hopefully this list will make the decision somewhat easier for you.