ratskrad

I built a dual imaging system over the past 8 months mostly due to extreme boredom caused by the past year. I choose to go with a WO GT81 IV f/5.9 that I can step down to f/4.72 using the WO 6AIII FR/FF going from 478mm to 382mm for the focal length. The other scope is a AT 152EDT at f/8 running 1200mm for a focal length that will with the .72 FR/FF go down to f/5.76 for an 864mm focal length. It took a bit to collect the pieces and on Feb 8th I was able to run both and collect a couple of hours of photons. For me at least I set this up as a test bed to eventually have a remote rig somewhere it is darker than where I live, not to mention weather challenges as it has been snowing the past week with not much of a break being forecast for the next week. Both scopes have ZWO EAF's for automatic focusing and SGP was set to refocus at .5 C temp changes and that happens often during a imaging session during the winter. In the past I always used drizzle but have to figure out how to use it when shooting with two cameras at different sub lengths. The cameras are both based on the Sony IMX571 APS-C chip with one being an Orion G26 OSC and the other a ZWO ASI2600MC-P that has a ZWO EFF attached to it that has some narrowband dual and tri-band filters. While I do not use a FF in the 152 I am using one on the GT81 and it is one I have had for years and is the AT2FF. I did crop the GT81 picture just to bring the objects into view better but the stars did look pretty good all the way to the edge. Guiding is a ASI120MM-S in a WO 50mm Uniguide scope mounted in the Saddle Handle Bar on the GT81. The total weight is 53.4 lbs on a mount rated for 75 lbs of imaging gear. All power and USB is run off of a Pegasus UBP v2 attached to a dovetail plate and the rig is run from a mini PC mounted to the eyepiece tray on the mount. Two wires from the scopes come down in a soft wire loom with one being a USB to PC and the other being 12v DC running to the UPB. I like you don't really care what others think of my hardware choices as they were arrived at based on what was available at the time as I am not one who likes to wait lol and health issues have told me to just do it and yes other equipment choices are possible and time will tell if I make them but this has been fun and a learning experience. For me last week it felt like something was accomplished lol mind you on something 99.99999% of humans will not nor do they care about but I'm in it for myself and with only a few message boards, videos and the stars aligning this was put together and works. When the snow stops and the skies clear I'll be back out in the backyard getting more photons collected to add to these pictures. So native focal lengths on the 2 pictures. Two nights of subs for 2h 29m for the 152 and one night for 1h 29m on the GT81. Took the first night to work out the kinks when it came to running three cameras and two focusers at the same time but between software and ASCOM drivers it all worked.

Here is my latest build. AT152EDT, WO GT81 IV, WO Uniguide 50/200 guide scope. Couple nights back I was able to do a first run with everything working as it's supposed to. Collected photons on M81/M82 running both cameras and scopes at the same time. 53.4 lbs on a mount that is rated for 75 lbs of imaging gear. .23px (.70") or less Total RMS during a three hour run.

So I did some digging and went to the William Optics website and found the instructions for some of the other FR/FF. Now it appears from those pictures and diagrams that you lock the 6AIII at the 5.2mm mark and measure from the edge towards the front of the scope including the gap from the 5.2mm spacing and that is where the 62.5mm line to the image plane of your camera starts. When I measured to the edge of the 6AIII I get 40mm and that means 22.5mm of back focus needs to taken up. That is what you have to work with. I know on my two ccd cameras the set back is 17.5mm. I added a 5mm thick x 46mm wide spacer to get to 45mm and adding the 17.5mm for the setback gets me to 62.5mm back focus for the ASI2600MC-P and for the Orion G26 OSC I have a 5mm thick x 46mm male wide with a 42mm female thread on the other side that fits the G26. Makes a lot more sense than what I thought I was seeing, only human here lol. That's why I like to sometimes interact with others in this hobby/obsession that for now occupies way too much of my time, not complaining. This all helps me and I hope others figure out how some of this stuff works. Brown Dwarf thanks again for getting me to dig into this to better understand as the instructions were lacking as in none and others were confusing lol.

Did you click on the WO 6AII link showing the numbers and technical diagram I was basing what I posted off of. I understand the 55mm as I have been shooting with a DSLR for 8 years but the instructions at WO says otherwise and that different scopes that the flattener uses has different setbacks. The numbers do add up for all of the different scopes that use the 6AIII as far as setback plus 55 equals the totals backfocus. I have not yet had the chance to use the 6AIII as it is snowing here and will be for the next few days or more. I was an engineer in a previous life and am able to read the technical diagrams lol and I will add that the Made in China or in this case Made in Taiwan instruction manuals are either nonexistent or are known to have major issues. I will be reaching out to WO and asking them as I don't know if you have to compensate for the 6AIII offset by adding the the 7.1mm to the 55mm to get to the 62.1, maybe something in the design of the FF/FR and if not the case then like I implied the instruction or lack thereof is a problem in our hobby. Thanks for the reply.

Hi, I just received my WO GT81 IV last week along with the focal reducer. The two numbers to remember are 7.1mm and 60.2 mm. The 7.1mm is the setting for the focal reducer. Spin the pieces until you see the 7mm mark and turn the locking ring. The second number 60.2mm is the distance for the back focus/spacing to the image plane of the camera. There are no instructions for the WO 6AIII but on the webpage for the WO 6AII FR it at least shows the two surfaces that require the 60.2mm spacing. Scroll down and there is a good schematic of the 6AII showing details. Here are the links to the WO pages for both the 6AIII and the 6AII. Hope this helps. https://williamoptics.com/products/accessories/barlows-flatteners/2019-all-new-adjustable-flat6aiii-t-mount-not-included https://williamoptics.com/new-adjustable-flat6a-t-mount-not-included