Like most Pentax refractors the Pentax 125 SDP was designed both for visual and photographical use. This true apochromatic refractor excels in both fields. On the optical axis the Strehl ratio lies between 96 and 97%. This is far better than diffraction limited (80% Strehl). What sets the Pentax 125 SDP apart from most other refractors is its excellent image quality over the entire field. This allows demanding astro-imaging with high resolution over a large (6x7cm) film format. On axis you can observe and photograph the moon and the planets with extraordinary detail and contrast. The colour correction is excellent - even at very high magnifications nearly no false colour can be seen.
Focuser
The focuser of the Pentax 125 SDP is a very precise helical focuser. The free diameter of this focuser is 90mm. This allows full illumination of the 6x7cm film format. A large and ergonomical grip allows comfortable and precise focusing. Focusing precision is particularly high with this focuser. A scale on the focuser allows setting with a precision of 0.01mm or better. The focuser is ideally suited for serious astro-imaging. The Pentax 125SDP was the outrider of the new SDP series. The series was extended recently by the introduced of the 150SDP. If the SDHF models were optimized for photographic applications, then the SDP series represents the first telescope from Pentax which supply the best performances for both visual
and photographic applications.
The monochromatically measured value lies for the SDP with approximately 96.4% for the definition brightness after Strehl on the axle like enclosed metrology record optics center North-Rhine/Westphalia being taken. To be reached this outstanding color correction could by the choice of a vierlinsigen optical system. Thus the front lens from SD glass and additionally the third lens from ED glass exists. All optical surfaces are SMC recompensed for the achievement of an optimum transmission. The imaging capacities obtained thereby in practice are sufficient for quite professional requirements (see also for this the test report of Mr. liking Franz Klauser in the star Observer 11/12 1997). Thus the Rayleigh criterion is reached visually clearly, the SDP series exhibits a diffraction limited optics and thus is the Seeing the mostly limiting factor. Photographically is possible and owing to optical designs also from beginning on intended the use of medium format camera - there is here no re-tooling. One takes here exactly the same consistent path in the product philosphy as with the SDHF models.But not only in the optical structure new paths were taken, realized also mechanically a quality of workmanship and precision, which were not considered possible during a quantity production until recently within the amateur range. The tube received an additional lacquer finish from a particularly hard clear lacquer, in order to ensure an optimal scratch protection.So that you can keep and carry the tube also adequately and safely, and each 125 SDP and 150SDP is included with an foam fitted deluxe aluminium case .
Note: Never tighten the rope protective cap too firmly! The spacer ring (17) must be still swivelling without force! During offence it can come to spannings and damages of the high-performance lens. A dramatic degradation of the imaging capacities is the result!
Photographic Use
The Pentax 125 SDP is excellently suited for demanding astro-imaging. Whether you need a particularly high resolution for CCD imaging or a fully corrected field over the large 6x7cm format, the Pentax 125 SDP offers excellent results in all these fields.
Optical Design
The excellent optical performance of the Pentax 125 SDP is due to its special four lens design. A doublet objective lens offers an excellent on-axis image quality. The integrated two-lens corrector offers a large, flat field both for visual and in particular for photographical purposes. No expensive separate field flattener is needed. The front lens of the doublet objective is made of SD glass, the third lens in the layout is made of ED glass. The selection of the right glasses is a key factor for achieving excellent optical properties of the telescope. Of course all optical surfaces feature the excellent Pentax SMC multi-layer coating. Each glass-to-air surface of the Pentax 125 SDP features the excellent Pentax SMC multi-layer coating. Sophisticated internal baffling maximizes contrast. The transmission is appropriate with over 96% below 550nm and with over 90% between 400 - 850nm. Thus a projecting transmission is given in all observation ranges important for the astronomy.
Technical Specifications
Aperture: 125mm
Focal length: 800mm
Focal ratio: 6.4
Resolution: 0.93"
Limiting magnitude: 12.2
Diameter of fully illuminated field: 88mm - corrected flat field
Optical Layout: 4-lens SMC-coated apochromatic refractor with integrated field flattening lens for 6x7cm film format
Tube diameter: 140mm
Weight: 10kg
Tube length: 922mm
