Equipment – Page 8

6th September 20197th September 2019

Using the PegasusAstro FocusCube 2 on an Esprit APO 120mm

There are good reasons to switch the a motor controlled focusser:

automating sequences in Sequence Generator Pro
Autofocus
Automated focussing after a filter wheel switch
Getting comfy inside while able to fully control your telescope
Go to sleep while your equipment takes care of image acquisition
no more slipping of the focusser with heavier loads

Why the PegasusAstro focuscube? I actually ordered the Lacerta motofocus first, however there were delivery problems. It first took two months to deliver, after which nothing happened. On inquiry I learned that it would take another two months. I decided to change to the PegasusAstro, and a few days later it was on my telescope, mounted and working…

Both these brands could demonstrate that the motors would actually fit on an 120mm Esprit. That was my main reason, other considerations were the strict requirements of connecting to a PC, working with SGP and similar software, and the ability of attaching a handbox. The PegasusAstro FocusCube was standard delivered with a temperature sensor (option with the Lacerta).

Picture: PegasusAstro.com

It was not difficult fitting the FousCube to the Esprit standard focusser. The only challenge was to shift the L-frame so that the two bolts could fit the focusser body, while a the the same time the axis and the connecting cylinder were also aligned. The two screws were part of the assembly of fixation material delivered with the FocusCube. They fit the smaller screws of the Esprit focusser.

The two bolts fit the smaller sets of predrilled holes, which have tiny little hex screws inside. They are easily removed and replaced with two bolts that are part of the material send along the FocusCube.

The FocusCube attached to the Esprit standard focusser.

Getting autofocus working with Sequence Generator Pro, and the FocusCube was also a matter of trial and error. After two nights the autofocus works very well.

This is the full set of settings that work with my equipment:

when you cannot get a nice ‘V’-curve when autofocus runs, try to increase the exposure time. The image statistics should give you at least 50 stars. Below that value, the HFR values become erratic and unreliable. I use 20 seconds for a 7 nm H-Alfa filter.
remember that autofocus is intended for small corrections, so you should already be near focus before you can run it
always run autofocus before a filter switch. In theory the filters are parfocal, however in practice they rarely are
I only run autofocus per degree Celsius. If the temperature doesn’t change, there is little reason for focus. The whole autofocus process takes time, maybe 5 minutes or so, time that you loose imaging.

This is an actual screenshot of my first run with autofocus, based on the above settings.

5th May 20195th May 2019

Putting the QHY Polemaster beyond the pole

I have been working with the QHY Polemaster to do polar alignement on the EQ8. And it works great. But after alignement is done, the 350€ worth of equipment disappears back in its box.

Here is how I made it useful beyond the pole (click on the image to enlarge)

The Esprit 120mm with the ASI183MM at the focal plane, the 400mm telelens with the ASI290MM, and the QHY Polemaster mounted instead of the finder.

When finding an object, I usually use a red dot finder, or a classic 8×50 finder. However, when firing up Cartes du Ciel, and syncing on a first star to align telescope and CdC, these optical devices require you to step away from the laptop screen. And – because I’m not using a gamecontroller (wired or wireless) to move the telescope, I also need to step back to the laptop to press the arrows and make guestimate corrections (since at the laptop, I don’t see the target moving in the finderscope).

So I removed the finderscope and replaced it with the Polemaster. For polar alignement it does not matter where it is positioned on the scope, as long as it is able to see the pole, and as long as it rotates on RA that’s ok. Works great.

But now, since it is looking directly where the main scope is looking at, I can use the Polemaster as a finder. To do so, I don’t use Sharpcap or Firecapture (to many driver issues). I simply use the Polemaster software, but keep it at step 1 after connecting the camera. I set the gain and exposure to maximum. Yes, I do not have crosshairs, and no that doesnt matter. With any reasonably sized sensor at the 663mm F/5 focus of the Esprit, positioning the target more or less in the center is sufficient to make it appear on the main screen in Sequence Generator Pro or Sharpcap or equivalent. Then it’s only a matter of finetuning, and sync Cartes du Ciel.

The QHY5II is a Black-and white USB2 MicronMT9M001 cmos camera, with a resolution of 1.280 x 1.024 pixels (1,28Mp) with square pixels of 5,2µm. The chip measures 6,7 by 5.3 mm. The quantum efficiency is measured as 56%

Example of the view on Coma Berenice (click to enlarge)

The screenshot above gives an idea what the view looks like. This is Coma Berenice (next to Virgo) and it shows stars to about 8th magnitude.

In combination with the F 1.2 ; 25 mm CCTV lens this sensor gives an image of 921 x728 arc minutes or approximitely 15 x 12 degrees. The resolution is 42″ per pixel.

I’m happy with the solutions as there is no need to buy extra equipment, I put to use what I have and it works without hickhups (on a USB 3 hub); No need anymore to lie down on the ground or bend myself as a snake in awkward angles to look through the finder.

Positioning the view of the Polemaster is done with the two set screws of the “Witty” Alt/Az system I used to position the finderscope.