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Christian Bennich:Norman Tajudin: I actually have exactly 44mm of back focus (37.5mm + 6.5mm for the camera). The lens is the Canon version with the Canon ring removed and the FLO M48 adapter in its place. I have a 7.5mm spacer coming from the lens and then a 10mm spacer between that and the filter wheel. I could have purchased a single 17.5mm spacer but was just using pieces out of my drawer of random astro parts... Here's a link to the 3D files for the riser and the EAF courtesy of Dale Hollenbaugh on Thingverse: https://www.thingiverse.com/thing:4761672 I would not recommend printing threaded spacers between the lens and camera. Way to flimsy for my liking... |
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Just to echo Michael's comment, we'd love anyone with a wide-field setup to join the AB community survey. Fields have been designed with a 135 mm/APS-C (or 200 mm/FF) len/camera combination in mind, so the Samyang 135 mm is a perfect choice. The spreadsheet managing field bookings is here Astrobin All Sky Survey field management tool 6x9 - Google Sheets. Just drop a comment in a field to book (or send me a PM on Astrobin). We're already approaching nearly 10% of the sky covered, but almost all in the southern hemisphere so some northern contributors would be really appreciated. Lots of 'historical' background and discussion on the survey here The Astrobin All Sky Survey: A proposal for a community resource - AstroBin. The current forum topic that's a bit more topical is here Astrobin Community Survey - AstroBin. |
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Christian Bennich:John O'Mahony: I use the Canon adapter from ZWO. Here is my set up and an example image from it with my 2600 MC Pro   |
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I'm ALMOST ready to go  The Samyang is mounted with a ZWO EAF and an ASi120MM guider. The only missing piece now is some M48 spacer rings, that are delayed from Astro-Art in Finland - then I can get my back focus trimmed in. Hopefully, I can start shooting with the lens in the coming weeks. My first target will be in the area of the North American Nebula. I will also try and get some panels done for the Skysurvey - but I need to make sure I can deliver a proper quality. |
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Christian Bennich: Awesome! Keep us posted and please share your first light results! |
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Christian Bennich: Looking forward to having you on board with the survey. Please reach out if you have any questions. I’m building out some automated QC tools for the survey images and can easily give some pointers once you have an image to share. Not that we’re terribly strict 😀 |
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James Tickner:Christian Bennich: Thx @James Tickner - I hope to start practicing a bit with the lens sometime during next week. Hopefully I will be able to focus etc. - but time will tell how difficuly it will be 🤣🤣 |
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Norman Tajudin:Christian Bennich: Absolutely @Norman Tajudin ……it’s almost like prepping for exams. Let’s see if I “pass” the course 😉🤪 |
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| @Christian Bennich Fingers crossed for you! Actually, I found the focus not too difficult even with the F/2 ratio. Originally, I also included the EAF with a DIY printed gear and belt. But I found the focus is quite easy to achieve manually and the lens seems to hold focus through the night even with some temperature changes. In the end I ditched the EAF and went back to manual focus - mainly because I got fed up of transferring equipment between my normal rig and the Samyang setup. |
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James Tickner: HAHA, I noticed the same and this is my first time transferring between rigs. I got myself an extra EAF and convinced myself I needed a new guidecam for my longer focal length other rig - so I could permanently move my ASI120MM mini to the Samyang 🤣🤣🤣 |
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Now I only need to self-convince myself to ditch my ZWO ASI 071 Pro for a Risingstar IMX571 compatible camera.....  But so far my reasonable half only has a strict 'no' when the other half brings up the discussion.... Michael |
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FIRST LIGHT on the Samyang......TILT and Backfocus BONANZA  It will require some work - I have triangles for stars in the far corners. Seriously considering a Photon Cage to solve tilt and back-focus. But lot's of fun getting the rig out and I love the sheer magnificence of the star fields and gas clouds  |
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| Christian, be careful to check how the device affects backfocus before you buy something like the photon cage. Even just a few mm of additonal space could put you over the usable backfocus of the lens. |
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Christian, be careful to check how the device affects backfocus before you buy something like the photon cage. Even just a few mm of additonal space could put you over the usable backfocus of the lens. Yes, I am “painfully” aware of that 😀 It will add 3mm of backfocus and then give you the ability to control up to 5mm of backfocus adjustment “inside” the cage. So in my Samyang scenario, it would replace my current 5mm M42 spacer. |
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| @Christian Bennich : To bring you in the right ballpark, here's the backfocus measurement of my Canon Lens. As I have bought the 48mm adapter the back of my lens may look different than yours but the required distance will hopefully be pretty similar when you also measure at the very border of the lens. Actually I would have to make backfocus a little shorter but for this I would first have to shorten the threads of my 3mm spacer, but that's for another day as stars are already pretty round right now. Michael  |
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Thank you @Michael Ring !! So I assume you have 12,5mm + 5mm from your camera and tiltplate putting you at 44,8mm backfocus. I am currently at 44,5mm backfocus. My filters are 2mm so that should put me on a total of 44,66 mm backfocus. I will try to add a tiny washer and see how much better it gets. But that will not solve the tilt for now 😉 |
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| I guess the nature of the Samyang make it extremely sensitive to these very tiny tolerances |
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For Tilt the 48mm adapter works nicely, it is available @firstlightoptics. I also have 2mm filters, so you can take the distance I measured as a 1:1 starting point when your camera also has 17.5mm to the sensor. https://www.firstlightoptics.com/adapters/astro-essentials-samyang-lens-to-m48-adapter.html Just saw that you already ordered the 48mm adapter, to bad that there is still tilt in your system…. |
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Yep, I use the same adapter but have the ZWO EFW 7x36 in my optical train. So I have 12,5 + 20 + 0,2 + 5 + 5 + 1,5 + very small amounts of additional backfocus between the extenders (approx 0,5mm - I might have to shorthen one of the a bit to remove it and make the total backfocus more controllable) So after adding another spacer, (the 0,2) I am on 44,7-44,8. Adding an Octopi could remove the 5mm extender currently connected to mu EFW - replace it with the 3 mm backfocus from the Octopi and then precisely dial in backfocus and tilt with that. The Octopi would also work with my other scope and setup etc. |
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My Octopi has landed 🤪🤪 Waiting for clear skies to remove tilt and backfocus issues. The Octopi is pretty awesome. It adds only 3mm of backfous and can internally add up to 9mm. |
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| Does anyone know the step size in microns on the ZWO EAF with the Samyang 135 or how to measure it with that lens? |
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I recently gave a talk on the Astro Imaging Channel on how I use this lens for widefield mosaics. You can see my rig as part of that talk: https://www.youtube.com/watch?v=bCLihxC_Ytg&t=1484s |
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Alistair Symon: Your images are amazing @Alistair Symon. The amount of work that has and most likely still goes into it is mindblowing. What I was looking for was to understand how far the lens actually moves on 1 full rotation of the ZWO EAF. I am practicing removing tilt from my system, and need to figure out how far I need to move my adjustment screws on my Octopi. It might be that I just need to do some more trial and error. |
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Since the WO Cat clamp ring is on backorder here in Europe, i built my own version with MyFocuser Pro and openscad. Using FLO's Samyang bayonet replacment adapter i can squeeze in my filter wheel.   |
