After imaging from e-EyE with a short focal length refractor for nearly two years, I finally decided it was time to retire the Takahashi FSQ-85ED of 450 mm focal length for the longer focal length Altair Astro 8" RC of 1625 mm focal length. I have had this telescope for several years but only used it once, locally in Gibraltar. In anticipation of eventually installing it at e-EyE, I bought a focuser tilting plate and Howie Glatter Laser Collimator a year and a half ago. All I needed for installation at e-EyE was a motorised telescope cover with flat field panel. Given the lack of options and availability of such an instrument from Optec Alnitak Flip-Flat for this aperture, I went for a Gemini Telescopes SnapCap 250mm.
The new version of the Gemini Telescopes SnapCap is more like the Optec Alnitak Flip-Flat in that it is designed around a USB connection to your computer, which is then controlled via a program. This is a very welcome improvement over the old version. The Optec Alnitak Flip-Flat has the motor and inverter for the flat field panel integrated into the single unit attached to your telescope aperture. A single USB cable from that to your computer both powers everything and gives you control over the cap's opening/closing and of the flat field panel's on/off and light brightness. I went over this product in detail in this article.
The Gemini Telescopes SnapCap in turn, is bulkier. Its motor is attached to your telescope aperture, with the cap attached to the motor via a metallic arm, fixed with two bolts. The SnapCap comes with the PC control box unit, which takes 12 V power and USB connections (for power and control, respectively). Aside from this, the SnapCap also comes with a small inverter for the flat field panel. The flat field panel has a thin cable coming out of its side. This is connected to the small inverter. The PC control box is then connected to the motor and to the 12 V power and computer via USB, as aforementioned. A little more convoluted and bulky than the Alnitak Flip-Flat but having separate 12 V power allows Gemini Telescopes to make these devices for bigger apertures as the motors and flat field panels can be made bigger and more powerful.
The Gemini Telescopes SnapCap in turn, is bulkier. Its motor is attached to your telescope aperture, with the cap attached to the motor via a metallic arm, fixed with two bolts. The SnapCap comes with the PC control box unit, which takes 12 V power and USB connections (for power and control, respectively). Aside from this, the SnapCap also comes with a small inverter for the flat field panel. The flat field panel has a thin cable coming out of its side. This is connected to the small inverter. The PC control box is then connected to the motor and to the 12 V power and computer via USB, as aforementioned. A little more convoluted and bulky than the Alnitak Flip-Flat but having separate 12 V power allows Gemini Telescopes to make these devices for bigger apertures as the motors and flat field panels can be made bigger and more powerful.
The control program in itself is basic but has every function you need and does its job flawlessly. It can basically open and close the cap, turn the flat field panel on and off and also vary its light brightness. Personally, I cannot fault the product as a whole and Andras from Gemini Telescopes provides excellent, personalised service.
My worry with the Altair Astro 8" RC was collimation. I had heard horror stories about how difficult it was to collimate a Ritchey-Chretien telescope, although these videos by Stephen Kirk were tremendously helpful. The videos were the reason I bought the focuser tilting plate and Howie Glatter Laser Collimator (with the concentric circles attachment). The instructions were simple:
1. Using the Howie Glatter Laser Collimator with the spot attachment, tweak the focuser tilting plate screws to centre the laser spot on the centre spot of the secondary mirror (looking into the telescope).
My worry with the Altair Astro 8" RC was collimation. I had heard horror stories about how difficult it was to collimate a Ritchey-Chretien telescope, although these videos by Stephen Kirk were tremendously helpful. The videos were the reason I bought the focuser tilting plate and Howie Glatter Laser Collimator (with the concentric circles attachment). The instructions were simple:
1. Using the Howie Glatter Laser Collimator with the spot attachment, tweak the focuser tilting plate screws to centre the laser spot on the centre spot of the secondary mirror (looking into the telescope).
2. Using the Howie Glatter Laser Collimator with the concentric circles attachment, look into the telescope at the pattern on the primary mirror and centre it, making it concentric, by adjusting the secondary mirror screws.
3. Using the Howie Glatter Laser Collimator with the concentric circles attachment, look at the pattern on the wall in front of the telescope and make it concentric by adjusting the primary mirror screws.
The three-step process usually requires two or three iterations to get perfectly concentric patterns with a perfectly centred laser spot on the secondary mirror. Adjusting the secondary and primary mirrors in the last two steps tends to slightly offset the previous alignment. This requires you repeat the entire process from the beginning. Each repetition requires increasingly smaller adjustments and eventually no adjustment is required.
Given the lack of break in the cloud cover, I was not able to fully test the collimation while at e-EyE. Thankfully, the other night it cleared and I was able to capture a 15-minute test image of M51 Whirlpool Galaxy in Luminance.
Given the lack of break in the cloud cover, I was not able to fully test the collimation while at e-EyE. Thankfully, the other night it cleared and I was able to capture a 15-minute test image of M51 Whirlpool Galaxy in Luminance.
The above image is the single exposure, calibrated with my master bias and master flat, auto-stretched in PixInsight. I was extremely pleased to see that the collimation was dead-on, without needing any further tweaking. It seems that these telescopes can indeed be collimated perfectly well with just a Howie Glatter Laser Collimator, but from the tweaks I needed to make, the focuser tilting plate was essential to getting it this well collimated.
I used the exposure to measure the effective focal length of the telescope by uploading the exposure to Astrometry.net. The plate solver measured the pixel scale to be 0.588 arcseconds/pixel, which leads to a focal length of 1592 mm and focal ratio of f/7.84. I could use the Astro-Physics CCDT67 Telecompressor to reduce this by a maximum factor of 0.67x but I honestly prefer to keep it at its native focal length to get higher imaging resolution. I can certainly spare the imaging time!
The following are two photographs of the completed installation.
I used the exposure to measure the effective focal length of the telescope by uploading the exposure to Astrometry.net. The plate solver measured the pixel scale to be 0.588 arcseconds/pixel, which leads to a focal length of 1592 mm and focal ratio of f/7.84. I could use the Astro-Physics CCDT67 Telecompressor to reduce this by a maximum factor of 0.67x but I honestly prefer to keep it at its native focal length to get higher imaging resolution. I can certainly spare the imaging time!
The following are two photographs of the completed installation.
