The Starwave 70 EDQ-R refractor has a four-lens system to give a flat field image circle of approximately 42mm at 350mm focal length, with a focal ratio of F5.
Premium Japanese Hoya FCD100 ED glass is used for excellent colour correction. Super-high transmission coating (STM Coating) is used on all air-to-glass surfaces to ensure high contrast.
The telescope tube is made from light weight aluminium alloy with CNC machined components. A tough matte pearl powder coated tube and hard-anodised fittings give durability and great looks.
The Starwave 70 EDQ-R Quad APO is intended for astro photography and the focuser terminates in an M48 Male threaded rotator plate with locking thumbscrew. All screws are teflon tipped and grip on a flange for accuracy. The rotator plate includes a "push-pull" tilt adjustment system to enable you to square up the image sensor to the focal plane.
No extra flatteners are required and the camera sensor is automatically at optimum spacing when focused on infinity.
The backfocus from flange to sensor is 66.78mm with the tilt adjuster at zero tilt. The focuser is a good quality rack and pinion unit which has been modified to improve rigidity.
- Altair Hypercam cameras are en excellent match, especially the 16mp 1600 Series cameras. Simply attach the camera with an T2-Thread Female to M48 Female adapter, or even screw the 2" nosepiece directly to the M48 male thread on the back of the focuser (the nosepiece has an M48 female filter thread nn the front).
- You can attach a DSLR by means of the Altair M48 Canon or Nikon DSLR adapters. (Ensure the inner ring grub screws on any M48 DSLR adapter are tight to reduce the chance of tilt).
- For DSLR use, a clip filter is recommended to control light pollution.
The rack and pinion focuser is compatible with Pegasus motor focusers enabling full autofocus control using various programs, including SharpCap.
For dew control, and to reduce the chance of the outer metal tube losing heat faster than the lens elements and constricting the unevenly, or internal condensation forming in the air gaps between lenses, we recommend the high power Dewzapper "DSLR" heater, product code DEWH-34-DSLR is used. In winter time the dew heater is best left on running at the upper temperature range to keep the whole OTA warm.
For autoguiding and super accurate polar aligment (with Sharpcap's polar align feature), you simply can't beat the Altair Astro 60mm Guide-Scope, or the Altair Starwave 50mm Guide-Scope, and any of the Altair GPCAM camera range. The best configuration would be a side-by-side using the Starwave 110mm Guide scope rings and 200mm Vixen-format Dovetail bar (code: SWGSR-110-200) and dual Vixen dovetail bar kits. (Code: SW-DUAL-VBAR-230MM)
Altair staff comments - the flat field quad story so far: We have always been aware of the demand for a flat field APO for wide field imaging, which can outperform camera lenses in colour correction, and be used with fitler wheels and dedicated astro cameras, while being sensibly priced, and with good QC. A while ago, we were offered some fast focal ratio multi-element refractor designs which had potential for flat-field imaging. We tried design variants using both four, five and even six elements and a range of glasses. These designs placed too much criticality on tolerances. The ability of the lenses to absorb tension caused by temperature changes was not considered practical for use in UK conditions. Stopping down the aperture of the prototypes helped somewhat, but we felt that a different approach was really needed on many fronts, not just optically, but mechanically too. Needless to say we passed up on these designs, and are very glad we did. Back to the drawing board then, or in this case, Zemax optical modelling software.
The Starwave EDQ quad lens uses a more "relaxed" optical design, resulting in a wider tolerance envelope for both internal and external aligment of elements, as well as better colour correction across the field (with excellent control of "blue bloat" on bright stars than any design we've worked with so far. This is due to the use of not one, but two ED lens elements. Vignetting is minimal and only starts to show in the corners of a full frame 35mm field. Some slight star-elongation is also visible with very small pixel cameras if the image is undersampled and blown up to a very large scale, but in our opinion this still improves on big-ticket camera lenses costing about 5 times the price as well as larger quads costing more than twice the price. APS-C / 4/3 Sensors (like the Panasonic sensor found in the Hypercam 1600 series), show no vignetting or star elongation at all. Lens cells are designed to absorb the inevitable tensions caused by contraction of the outer tube as best as possible.
We believe the result is a fast, tractable system, which is more tolerant of temperature changes than other designs we've tested. However, the fact is that there is no design capable of perfect performance at any temperature. This is because glasses conduct heat up to 400 times faster than aluminium. For this reason, amongst others, we do recommend warming the optical tube for the best possible performance when using this scope in extremely low temperatures, a general rule which applies to any multi-element APO or camera lens employing ED glass in very cold conditions. Warming the tube is easily done using the right dew heaters (Dewzapper 3-4" high power dew heater, code DEWH-34-DSLR), and to sum it up, it's very advisable for these main reasons:
- Firstly, dew control. It is almost unheard of to operate an imaging scope in the UK without condensation forming on the front lens very quickly as temperatures plummet.
- As with any telescope, the optics perform best when they are all more or less the same temperature relative to each other and their housings / cells (as we explained, various components have different expansion coefficients depending on materials used).
- With the elements being spaced within a tube with air gaps between them, keeping the unit warm overall stops any possible condensation forming on the inner lens surfaces.
- Because aluminium alloys lose heat around 400 times faster than glass), it helps reduce any sharp temperature gradients between the glass elements and their metal housings for better overall performance.
- Finally, maintaining a constant temperature is essential to keep focus during a set of long exposures. Small pixel cameras tend to be used with flat field scopes like this, and changes in focus are immediately obvious.