In current years, imaging methodology has moved from aftermarket modifications made to standard telescopes and in the direction of devices designed from the bottom as much as serve the wants of astrophotography. The RedCat71 from William Optics is the brand new child on the block aiming to serve this want, and courtesy of First Gentle Optics, I appeared ahead to seeing if it delivered.
Within the field
High quality is obvious straight from the beginning. Eschewing the cruel and heavy aluminium ‘crates’ beloved by many, this telescope is available in a hard-wearing, padded nylon carry-case that usefully falls inside the dimensions for airline hand-luggage. Nestling inside its protecting foamy womb, the RedCat71 is well-shielded from impression in all instructions. I didn’t throw it encased out of the bed room window, however I’m fairly assured it might not discover.
Optical efficiency apart, one factor that runs by means of the William Optics ethos (virtually a mission assertion) is a really excessive normal of engineering end. Decked out in a lustrous satin crimson, the RedCat71 doesn’t disappoint, and its impeccable coachwork merely seems to be tremendous.
So far as tube furnishings goes, consideration to element begins on the prime, the place the dew cap sits. Cleverly, this incorporates its personal matched Bahtinov masks, a necessary accent for attaining tack-sharp focusing, made attainable by a big helical focuser barrel (2GT Gear Ring) that takes up 100mm of the 335mm tube size. Its rubberised floor could be very tactile and non-slip, with rotational pressure intriguingly managed by the dew tube that acts like a friction clamp.
On the enterprise finish, the tube meeting terminates in a 360-degree rotating M54 thread, to which M54 and M48 adaptors are added. These adaptors incorporate a cell for deployment of 48mm filters and (for probably the most demanding imagers) a tilt mechanism affording microscopic adjustment to match the imaging aircraft.
I’m stunned that the telescope doesn’t come full with photographic M42, T-mount or C-mount adaptors, making an allowance for that the RedCat is designed for use with imaging units.
The tube’s clamp rings provide Arca Swiss and Vixentype dovetail fittings on one facet, and to the opposite a saddle is hooked up (which additionally serves as a terrific toting grip).
Given the aforesaid reward, I need to sadly transfer on to the quick-start information – which is disappointing to say the least. Contemplating the a lot appreciated manufacturing value that’s lavished on the telescope itself, the four-page quick-start information contends itself merely with labelling of the components and promoting potential equipment. There isn’t any info on how the instrument needs to be deployed, used, nor even any major directions on imaging in any respect! The idea right here is {that a} new proprietor is already up to the mark with prior expertise and swapping out one telescope for this one. This can be the case, however somebody new to imaging won’t be in house, however all at sea. It won’t have a novice beginning shortly – certainly with out a set of step-by-step directions a newcomer shall be doing nothing however scratching their head. I do settle for that this is probably not a newcomers’ instrument, however a information with just a bit further instruction would improve this equipment enormously. It might be quick work certainly for a technical author.
Can it’s used for visible astronomy?
The RedCat71 is described by all distributors as ‘designed primarily for astrophotography’. This, I might say, is a masterly understatement. The telescope doesn’t include any technique of utilizing it visually. Certainly, the so-called ‘quick-start’ documentation doesn’t even provide any technique of doing so, however that didn’t cease me attempting.
I first went to the difficulty of buying an M54 adaptor to allow use of a star diagonal, however I discovered that on this mode eyepieces have been too far past focus. I used to be puzzled by this, since quick refractors are typically fairly glad to work with eyepieces hooked up on this means. It indicated that visible use could be troublesome due to inadequate back-focus. Aiming at a daytime goal of a distant tv aerial, I measured the back-focus from one excessive of the helical focus journey to the opposite and located that the focus at most was barely 60mm past the M48 adaptor. No marvel the sunshine was not lasting the trail by means of my diagonal to an eyepiece.
To not be thwarted, I realised that the RedCat’s male M48 adaptor may mate with the 48mm filter thread of a two-inch barrel eyepiece. I used to be happy to find that, with out the back-focus consumption of a star diagonal, eyepieces hooked up on this means might now attain the main target. I’m not certain that I (or William Optics) would suggest this mode of fairly unconventional attachment, however though the consolation of right-angle viewing was not accessible, it did afford some spectacular visible astronomy.
On this method, I used a 3.5mm (110-degreewide area) eyepiece to look at the Moon. Though naturally a high-power eyepiece, used on a telescope with solely a 348mm focal size leads to a magnification of simply 99× – although as a wide-angle eyepiece it nonetheless yielded a area of about 40 arcminutes, comfortably encircling the Moon with sky. A gibbous part revealed Gassendi close to the terminator – and even at this comparatively low magnification the telescope was displaying a riot of element inside the crater rim, together with its distinctive rilles and cracks. I might like to have stretched to the next energy (of which the telescope is clearly succesful) however I couldn’t deploy a 2.5mm, 1.25-inch eyepiece that will have delivered 139× as a result of I had no technique of attaching it.
Optics
The fairly tardy back-focus could also be a priority to these whose imaging prepare incorporates greater than only a digital camera, similar to filter-wheels, off-axis guiders and so forth. In actual fact, I used to be not initially capable of deploy my regular push-fit imaging configuration as a result of my DSLR’s sensor got here to relaxation 30mm distant from the main target. I ended up having to accumulate 4 supplementary imaging adaptors earlier than I might proceed with the overview – and that ought to point out to potential purchasers that you could be not be able to go upon first receipt.
The optics of the RedCat71 are of a brand new apochromatic Petzval design (4 parts in three teams), comprising a doublet goal, a central floating element and a rear corrector. The declare is that this configuration gives a large, flat area with a 45mm imaging circle, absent of the necessity for supplementary flatteners or correctors and appropriate for sensors all the best way as much as DSLR full-frame.
I carried out the overview utilizing an Altair GP-CAM3 290c CMOS digital camera plus three full-frame Canon DSLRs, these being a 5DSr and two 6Ds (one in every of which is astro-modified). Utilizing its Vixen footpad, I had the RedCat71 using on my Meade 355mm LX200.
Earlier than I proceeded with testing the telescope’s imaging credentials, I used to be all in favour of what the native optics have been delivering. That is one thing that an extra-focal picture of a star can clearly present, the star chosen for this honour being Antares. I used to be very impressed by the traditional, defocused diffraction sample; the symmetry and evenly distributed mild have been promising a high-quality supply in use.
The focal size of the RedCat is a scant 348mm, which guarantees very extensive imaging fields. I first wished to take a look at how ‘flat’its imaging circle was, and for this check the Moon was glad to oblige.
One clear, blue night in June, a gibbous Moon hung above the southern horizon simply begging to be imaged. In comparison with a star, its giant floor space strewn with element was simply what I wanted to detect definition variations between the centre and fringe of an imaging circle. Utilizing my full-frame (un-modified) Canon 6D, I fastidiously centered on my obliging topic – whose 0.5-degree disc swam fairly lonely within the large area that the RedCat71 was supplying. I shot the Moon first within the centre of the sector, after which afterwards, with out refocusing, I took one other shot with the Moon snuggled up as shut within the nook as I might handle.
I then sandwiched each pictures collectively to afford simultaneous comparability between every lunar disc. The consequence demonstrated that there was no discernible distinction between the 2 Moons in any way. The peripheral Moon was as crisp, sharply outlined and equally brilliant as its doppelgänger on the area centre. In actual fact, there was no distortion of any type within the corner-bound picture of the Moon, which could be very spectacular, notably for many who may need to make use of the RedCat71 for astrometric work.
My experiment with the Moon additionally offered helpful info on the sector width, for it was attainable to work out that I might place about fourteen Moons throughout the lengthy diagonal of the full-frame area, due to this fact approximating it as seven levels in extent. The alternatives of such a big sky web for deep-sky pictures are apparent and that is the place I turned my consideration subsequent.
Deep-sky astrophotography
In early summer season the Veil Nebula in Cygnus is a magnet for imagers and rightly so. Nevertheless, as its two major arcs span a difficult three levels, it’s generally imaged in components, that includes both its jap or western parts. What I had at my disposal was over twice that extent, making seize of the entire object (also called the Cygnus Loop) not an issue in any respect.
My modus operandi for nebula imaging is to accumulate a agency deal with a close-by star earlier than slewing to my goal, and so this appears an appropriate juncture to speak of the RedCat’s focusing skills.
I discussed beforehand that focus is achieved by way of rotation of a big, rubberised ring located on the telescope’s midpoint. I need to confess to some concern that this torsional power on the RedCat’s tube may very well be transferred to its saddle-plate mounting (notably as you might be having to manhandle the tube to take action) and thus impart motion or vibration through the technique of attaining correct focus, in a means that the traditional longitudinal power of a standard focuser wouldn’t.
Happily, the RedCat’s pressure adjustment on the helical focus mechanism involves the rescue right here. The friction may be adjusted in order that even the very lightest contact on the rubberised ring will impart an impact on the picture. I used to be thus capable of alter the stress in order that little or no opposed power was evident within the picture of the star being centered.
For these wishing to keep away from manhandling the tube throughout a focusing train, it’s attainable to retrofit a drive-belt EAF (electronically assisted focusing) unit to a toothed ring on the RedCat’s focuser to manage the method digitally, thus lowering these microscopic ‘tremors’ to a vanishing degree.
The RedCat’s Bahtinov masks is cleverly put in within the dew cap and it’s only essential to unscrew the tip cap to make it accessible. The masks is made out of a clear disc, which (it’s claimed) makes the ensuing diffraction sample brighter. It served completely all through the overview – the ensuing three-axis starburst pinioning the purpose of focus with uncanny accuracy,
As with all Bahtinov masks, the ‘crossed-swords’ diffraction sample essentially spreads the sunshine of a star. The final word restrict of the sunshine grasp of the RedCat’s 71mm aperture signifies that a fairly brilliant star is required for this process, or a way of accelerating a star’s depth by means of elevating the achieve of the sensor. This focusing constancy was very a lot appreciated, since a consequence of such a brief focal size delivering a flat-field focal aircraft is that the depth of true focus could be very shallow certainly.
This time, utilizing my astro-modified Canon 6D and a dual-band filter, I captured the Veil Nebula throughout a complete publicity time of slightly over an hour. I took care to place the entire Veil to at least one facet of the sector to higher illustrate the digital camera’s yawning seize. The consequence confirmed the RedCat’s potential admirably. Virtually misplaced within the profusion of faint stars that the telescope pulled in, the entire Veil’s parts have been captured simply inside only one half of the sector. It demonstrated to me as soon as once more that whereas ‘up-close’ pictures of nebulae are compelling, seeing objects within the context of their environment can also be beneficial. The profusion of field-wide concise stellar specks additionally confirmed that stars remained stars all through the sector, wherever they have been.
Cygnus, after all, presents that different gem of the summer season sky, the North America Nebula. It too is usually imaged piecemeal by way of its main parts, fairly than in its entirety. The RedCat71 dealt with this huge celestial object with ease. The astromodified 6D, in live performance with a hydrogen-alpha filter, drew in not simply the North America Nebula, however its neighbouring Pelican Nebula and the encompassing HII areas.
I turned subsequent to M13 in Hercules. I’m used to imaging this object with my 355mm Meade ACF, for with the amplification of the Meade’s 3.5-metre focal size the globular cluster comfortably fills the body. Its startling seize within the cavernous area of the RedCat confirmed it nearly misplaced in a sea of stars, giving it the fantastic sense of being a forlorn stellar neighborhood adrift within the immensity of house surrounding our Galaxy.
Conclusion
The RedCat71 comfortably demonstrated its skills as an astrograph, and within the fingers of these extra in a position than I it’s clearly able to unbelievable astrophotography, particularly widefield imaging to which its focal size is suited. The massive tactile helical focuser is a nod in the direction of making it helpful as a terrestrial telephoto too, so those that like to seize candid photographs of wildlife get an additional bonus. I totally loved my time utilizing this wonderful instrument.
Steve Ringwood is a daily contributor to Astronomy Now.
At a look
Aperture: 71mm
Focal size: 348mm
Focal ratio: f/4.9
Design: apochromat, four-element Petzval (quadruplet)
Weight: 2.8kg
Size: 335mm
Focus: Helical (2GT Gear Ring)
Adaptor fixings: M54/M48
Worth: £1,599
Particulars: firstlightoptics.com
