Last June I started a post, "Light Weight, Portable, Low Cost EAA Setup ( http://www.cloudynig...ghtweight, +low) ", where I talked about using a Celestron 6SE (6"SCT on a SE Alt-Az Mount) along with either the Revolution Imager 2 analog video camera kit or the ZWO ASI224MC digital video camera. I posted images of the setups and of the pictures I was able to capture with both cameras. At 21lbs the 6SE is light enough to move from inside to outside without disassembling it. And, being an Alt-Az mount it is very easy to setup and align and works very well for EAA. It can usually be found new on sale for $699, whereas either camera is available for $300 keeping the total cost at around $1000. There appear to be many others using the 6SE with great results. And if one can afford a bit more, many have suggested the Celestron Evolution mount with either a 6" or and 8" SCT.
However, I wanted to see if I could put together an even lower cost and lighter setup. After all, $1000 is a lot of money to most of us, especially if we are trying out EAA for the first time. Also, I wanted to try this with a refractor instead of another SCT. "aeajr -Ed" started a post " http://www.cloudynig...80#entry7569515" in which the Meade EXT80 was discussed and demonstrated as an EAA setup. Fortunately, I was able to get my hands on one of these and try it out with the same two cameras.
The ETX80 is certainly a lightweight and highly portable Alt-Az setup. It weighs in at a total of less than 12lbs, which is almost half the weight of the 6SE. And, at $349, the scope, mount and camera can be had for $649, not including tax. If one were to substitute one of the "Rising Tech" cameras with the same Sony sensor as the ASI, the camera cost can be reduced by almost half to $164 (https://www.amazon.c...1N3JZH45PB4CREW). That puts the setup at just over $500. Add another $25 for a focal reducer and filter for either version of the USB camera.
The ETX80 comes with an 80mm, f/5, 400mm focal length refractor, a red dot finder, a 45deg erect image prism diagonal, 9.7mm and a 26mm eyepieces and a detachable dew shield. The mount is very easy to set up in just a few minutes and can be left assembled and carried from inside to outside without breaking a sweat. Alignment is simple, level the mount with a bubble level (not included, but $2 at Home Depot), point the scope north either using the included compass or using the north star, level the optical tube and turn on the mount. The mount can be run with internal batteries and works either off of 9v or 12v. I preferred to use my 12v external battery since I was also powering my dew heater and the R2 (when not using the ASI224). Alignment is a simple 2 star alignment procedure which, if it did not always put the object in the FOV of the 1/3" cameras, it was usually close enough that a little searching brought it into the FOV quickly. The ETX80 is a very light mount which, as John Graham has said, takes a "light touch", especially when focusing. I added a 5lb weight to the hook on the bottom of the tripod which helped steady the scope to my satisfaction. Also, focusing is done with an internal screw attached to one side of the objective, so there is a bit of image shift when focusing. Initially, I found this annoying, but ultimately it became a non-issue once I got used to it. This is part of the price of keeping the cost of the scope so low.
The ETX80 has two possible places to put the camera. It can be placed in the EP port on the side of the OTA or at the back of the OTA in the camera port. It is necessary to use the diagonal to connect either a camera or an EP to the camera port, unless one purchases the 64ST adapter ($15 on Amazon) and a Baader Planetarium 1.25"/T2 EP holder/helical focuser ($56 on Amazon) which moves the camera closer to the focus point. But in this configuration I was limited to 53 deg altitude to avoid the camera crashing into the mount. Since this cuts off way too much of the interesting parts of the sky I preferred to work with the EP port.
With the camera in the EP port there is no danger of crashing into the mount and therefore, the skies the limit, i.e. the scope can be pointed straight up. With no focal reducer and just the 1.25" C-Mount adapter attached to the front of either camera, they both easily came to focus in the EP port providing 400mm of focal length at f/5. This gave a FOV of ~42 x 31 degrees for the ASI224 and 38.5 x 32 degrees with the R2. The same within the error of determining the FOV. I tried several different focal reducers and spacers to see how much reduction I could achieve. With both cameras it is not possible to achieve focus with a 0.5X focal reducer attached to the end of a standard C-Mount adapter, typically 25-26mm in length. I tried several different focal reducers (0.85x, 0.5x) and spacer combinations (0mm, 10mm, 20mm, and 26mm). So far, i have on achieved focus with the RI2 using the 0.5x focal reducer and a 10mm spacer. This gave a focal ratio of f/3. With the ASI224 i was able to use a 0.85x reducer with no spacer to achieve a focal ratio of f/4.3.
Using both cameras, as is my habit, I tried a variety of exposure times, gains or AGCs, with and without Sharpcap stacking. I tried the R2 first while I was still learning how to use this setup but without the presence of the moon. Once I had gained some experience with the scope, I turned to the ASI224, but had to deal with a rising full moon. I think I can do much better with both cameras if it ever stops raining here. Hopefully this weekend. Here is an image of the scope with the R2. In the next post I will show a few images.