Equipment

The main elements of mi current equipment are the following:

OPTICAL TUBES:

 

150mm f4 Newtonian Astrograph

On March 2011 I started the design of a Newtonian Astrograph. My objectives were to build a short focal and fast telescope specifically for astrophotography. A major condition of the design was to have the chance of using the astograph with a 2" 0.73X ASA coma corrector to work at f2.9 and with the Baader MPCC to work at its native focal ratio.
Once the design was finished and I started to search the materials, I wanted premium components to ensure maximum optical and mechanical quality. After some research I decided the main elements of my tube would be the following:

  • Primary mirror: 150mm f4 1/10PV 97% relectivity (Orion Optics UK)
  • Secondary mirror: 66mm 1/18PV  96% reflectivity (Antares Optics)
  • 7.50" ID solid wall carbon fiber tube (Public Missiles)
  • 4-vane spider (Protostar)
  • 6" Versatile Mirror Cell (OpticalSupports)
  • 2" Extra Low Profile focuser (Crawmach machine)
     



Refractor William Optics Megrez 88FD f5.6

It's an air-spaced Doublet Apochromatic refractor with a 2" 1:10 Crayford focuser, field rotator and retractable dew shield. William Optics has never specified clearly what is the type of glass they used in this OTA and have only stated that they used "similar quality lens as Megrez 90", which has FPL53 glass. At the time I bought it, it was the fastest refractor at its price and aperture ranges. I'm pretty satisfied with it, it's an excellent low-medium price choice for imaging with cameras with sensors up to APS size. However, like all doublets, it needs to be coupled with a good flattener to reduce field curvature.

     

I had the opportunity to try 3 different flatteners/reducers and the one that produced better results with this OTA was the Borg DG-L 0.85X flattener/reducer. This combination produces very acceptable stars in the corners with very little chromatic aberration. However, it seems that the reduction ratio is not that stated by the manufactured, I have calculated its reduction factor is 0.92X. Another colleague which owns a TMB OTA and uses the same flattener/reducer confirmed that point.
The mechanic quality of the OTA is just good, not excellent. The field rotator could be more precise, although with a little tweaking on it and on the focuser, flexures are eliminated completely.

Newtonian Skywatcher 200 f5

This is potentially a very good telescope at its price. I say potentially because the stock adjustments were very bad. The secondary mirror was glued with an incorrect tilt in the spider, the stock focuser was very imprecise and unable to afford a camera without flexing, the spot on the primary mirror was not glued in the dead center. I fixed all these issues. The first thing I did was to replace the stock focuser by a GSO low profile focuser. That focuser was very dissappointing too, and it didn't meet the specifications stated by the manufacturer at all. Definetely I don't recommend it. However, I managed to do some modifications on it by adding a plate with 4 new bearings between the draw tube and the body of the focuser and 2 fixing bolts to control the looseness of the draw tube. Now it performs as a top-class focuser and it's able to hold 3kg without flexing. Once I changed the focuser I wasn't able to do a good collimation yet and realised the secondary mirror was glued tilted to the spider. I unglued it from the spider and did the calculations to glue it with the propper tilt and offset. After doint it, I still was unable to perfectly collimate it, and after dismantling the primary mirror cell from the tube I realised the collimation spot was not well centered, it was displaced 2 mm from the dead center.
Once these issues were fixed, I think it performs pretty well and am happy with it.

   

Lens Nikon Nikkor 180ED AiS


Nikon released in 1981 the Nikkor 180mm ED AI-S lens, a design made with ED glass which that used 5 elements in 5 groups, with a maximum aperture of f/2.8.
This lens is very, very sharp even wide open. The field curvature is very moderate at any aperture. At f2.8 the chromatic aberration is evident, but it improves a lot stopping it down to f4.
The spikes that this lens produces are a bit distracting, so I prefer to stop it down with step-down filter adapters threaded on the front of the lens. I have used it at different focal ratios, f3.3 and f3.8.

   


MOUNT:

Skywatcher EQ6 Pro Skyscan

This is also a good mount at its price that with proper adjustments and maintenance can be autoguided with peak errors below 2 arcsecs. Also, some clever people developed a very good ASCOM driver for it: EQASCOM. This driver coupled with a planetary software makes  controlling the mount from a PC a very simple and intuitive job and, at the same time, it's a very powerful tool. To use the EQASCOM, I built a convertor cable that lets me connecting the mount to the PC without the need of the Skyscan hand controller.

I made several modifications to the mount:

  • The stock bearings for new bearings of brand SKF. SKF bearings are well known for its quality and precission. One 6008 bearing of each axis was replaced by its angular contact equivalent, the 7008 and an inner ring between the two 6008 bearing inside the main gear of each axis was installed to ensure that the axial load of the axis is transmitted through the inner rings to the angular contact bearings, this increases the load capacity of the mount.
  • Replaced the stock altitude adjustment bolts which are bendy for newer ones much more precisse and easier to handle.
  • The transmission of the steppers of both axis to the worms has been changed to belts and pulleys.
  • Part of the housing of the RA axis has been replaced by a machined element made with high quality aluminium, this allows fine-tuning of the contact between RA worm and gear and improves the load capacity of the mount.
     


CAMERAS

QHY5

I use this monochrome camera mainly for autoguiding the mount. It has a CMOS sensor Micron 1/2 inch MT9M001, the pixel size is 5.2um x 5.2um and the active pixels are 1280x1024. The peak QE is 56% and has a USB 2.0 port. It also has an autoguiding ST4 port which I use to connect it to the autoguiding port of my mount. I could also guide the mount through the EQASCOM driver, but I prefer to do it this direct way.
With this camera and my guidescopes I have never had problems to find a star proper for guiding regardless of the area of the sky I pointed. Many people uses it for planetary imaging. I need to try it in that field yet.

     

Cooled Canon EOS 550D

This is a color DSLR camera with an 18.0 Megapixel CMOS sensor and a Canon DIGIC IV image processor. Its pixel size is 4.3um x 4.3um. The 550D is a considerable improvent over my old 350D, its QE is higher, produces much less dark current, delivers 14-bit images and has functions like live view or video recording.

I made some modifications to it to make it more efficient for astrophotography, you can see them HERE.