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I'm using the T2 thread onto the QHY spacers (between CC and filter wheel) and it measures at 55mm between the end of T2 thread (as in the left-hand picture) and the sensor. I have tried adding spacers and it hasn't made a difference. My next test (when I get chance) will be to reduce the distance a bit and see if that improves things. Or, does something in the aberration indicate that the FR distance is too small rather than too large? I suspect I may have multiple problems at the same time - maybe tilt (the aberration is always worse on one side and that side is fixed to the starfield regardless of camera orientation indicating a tile somewhere in the OTA), mirror pinch and not-perfect backfocus distance?

That's right. The shadow of the secondary should be offset towards the primary (i.e. the right in that photo). That's what I understand, anyway

Hi all I bought a new scope this summer and I'm a very frustrated with it. I'm desperately hoping someone can help me. My problem is with the stars around the edges of the image. I've so far been concentrating on the collimation and I'm confident that I now have it very well collimated but I still have the problem. My equipment is: ONTC 8" f/4 QHY268M QHY CFW3-M-US QHY OAG Baader MPCC MKIII Antlia filters The below image was a 2 min sub of Andromeda. I took this the first night I used the new telescope and the collimation was a little out at this stage. This is a close up of the corners of the above image (from AberationInspector in PixInsight): You can clearly see the problem especially in the bottom-right sector. I have tried removing the OAG to rule that out. I have measured and re-measured and re-measured again the MPCC to sensor distance. I have even varied the coma corrector to sensor distance (despite measuring that it's already at the proscribed distance) and it has not helped. As I said earlier I have improved the collimation since these first shots but the problem remains. Here is an image from my collimation camera showing the view down the scope with a series of concentric circles showing that everything is collimated. The circles are: yellow circle is the bottom of the focusser tube; blue circle is outlining the secondary mirror green circle is outlining the primary and the red circle is surrounding the central ring on the primary (you'll need to zoom in to see that one): Do you have any idea what could be causing this aberration? So far I have wondered about: Reflections Collimation Bad coma corrector to sensor distance Something in the light path The stars really are that shape and no-one else has noticed? (I did say I was desperate!) Thanks for any help. Steve

First light for my new QHY268M. My own attempt at M51 with Ha. SkyWatcher 200PDS on EQ6R-pro, QHY268M, OAG & filter wheel, Antlia filters, Nina for capture PixInsight for integration and Photoshop for final touches. L: 70 x 60s R: 60 x 60s G: 60 x 60s B: 40 x 120s Ha: 30 x 300s L, R & G collected on first night. B & Ha collected on second night

OK, it's official. I'm an idiot. Here is my test from last night Quite an improvement, isn't it? What did I do to get such an improvement, you ask? All I did was chose a test star which was NOT obscured by the overhead powerlines above my garden! Who'd've thunk it!

The scope is in my roll-off-roof obsy and I'd need a crane to get something high enough to be in view from the obsy, Otherwise, a good idea

Thanks, Peter & David. That's my job sorted for the next clear night - I'll try the card test

Thanks, David. You make it sound so easy 😛 I might have a go at that when I'm feeling brave. So, having marked the position of the cell with the tape, I just remove the four crossheaded screws that are just up-tube from the white collar (I assume the white collar is the outer part of the mirror cell?)? Then the cell will drop out of the tube?

I'm trying to improve the shape of my stars and could do with some advice from you good folk. I use a SkyWatcher 200PDS newt with the stock SW Crayford focuser powered by a Primaluce Sesto Senso. My QHY268M is screwed to the end of the focuser draw tube. When it's at focus, I have a couple of cm of drawtube sticking into the scope. So, I'm thinking that is the cause of my problems. But I'm reluctant to replace the focuser unless I'm sure it's causing me a problem. I've considered the Baader Steeltrack but it's not a painless swap over as I'd need to drill new mounting holes in the scope. I'll do it if I need to but I'd rather avoid it if it's not necessary. I'm also happy with the stock focuser otherwise, it handles the weighty camera with filter wheel and OAG without any slippage problems. Is it possible that my problem is more down to a pinched mirror? I've read that it's a common problem on SW scopes for the mirror clips to be too tight to the primary. I did a star test last night to try to diagnose the problem: Extrafocal: Intrafocal: The line on the right of the extrafocal test and on the left of the intrafocal test (a lot fainter but still visible) suggests to me that the drawtube is the problem, but TBH I don't have much of a clue of how to interpret these images. I'm just guessing. Any suggestions?

I've read that contrast and detail is better with a refractor. And, whenever I drool over someone else's nice shot it tends to turn out to be taken through a refractor.

Just bumping this post in case everyone wss too full of Christmas spirit - that Bailey's really does send you to sleep, does it? - to read SGL over the festive period. Anyone want to help me spend my money?

Hi all Since starting the AP game I've used only Newtonians. Started with a SW 130PDS and then moved to a 200PDS. Now I'm wanting to try a refractor but I could do with some advice. I shoot galaxies and nebulae and the telescope would be mounted on an EQ6R-pro on a pier in my roll-off roof obsy. My first thoughts are something like an F/7 5inch triplet. I was looking at the Explore Scientific ED APO 127mm f/7.5 either Carbon Fibre or Aluminium or the Altair Wave Series 130EDT-F F7. Or maybe a slightly faster StellaMira 90mm ED triplet apochromatic refractor. Not sure if I need to consider the carbon fibre option or not. I know the weight of a 5inch scope would be at the top end of what my mount can cope with so was thinking that carbon fibre would be sensible to reduce the weight but what are the drawbacks (apart from the cost, of course)? Any comments on these choices or other suggestions welcome. Steve

I used V wheels and rail. It's gate opening hardware again. I was going to get box section steel and get it galvanised but when I looked into it, I decided the purpose-made galvanised rails woule be easier to fit and they even worked out cheaper. The rails I used were on ebay - asearch for auto020V (it's the product code) should find them. I bought the wheels from a different ebay seller - a search for '2 inch v-track wheel' should find similar. I envy you being able to image last night. I haven't got my dew control set up yet so I've missed out on on the clear frozen nights we've had recently. I'm off to pick up a Pegesus Powerbox later today to use as the controller. Just in time for the clouds to roll in...

Hi Graeme I builit a support to mount the motor unit at roof height. The toothed rail is attached along one side of the roof and the motor is engaged with this. They're not great photos but it's too cold out there to stand around with a camera I bought the motor off ebay and it was a bit of a project in itself! The gate opener I wanted was one that could connect to three buttons: open, close and stop. Then I could replace the buttons with an Arduino board to simulate the button presses. That was my plan, anyway. But, it turns out the manufacturers all seem to have changed to a single button operation. One button press will open the gate (or roof.) The next button press will close the gate. If the gate is moving when the button is pressed the button will stop the movement and the next button press will reverse the last operation. The effect of the single-button logic is that, if you press the button to open the gate/roof and then press the stop button to interupt it, when you next press the button the roof/gate will close. So, you need to then open the roof, you need press once to stop the closing movement and press the button again to open it. Which is all fine for a roof-to-human interface but not so useful for an automated installation. So, to control the motor via ASCOM - so I can close the roof by command regardless of the current state of the roof (open, closed or moving), I needed to put some logic in place to keep a track of what state the roof is in so that the action that would be performed by the next button pressed could be predicted. So, my Arduino controller now will press and release (virtually, of course) the button the right number of times to get the roof to perform whatever action is requested from the ASCOM client. Also it means I can now open and close the roof with a toggle button in the observatory - left to close, right to open - or from dedicated buttons on the remote control. Anyhow, if you're interested in automating your roof, let me know and I'll send you details of how I drive the motor from the Arduino board - I can even send you my Arduino code if you like.

Nice pic, Nigella. I keep thinking of getting into solar imaging - the hours are better Maybe one day

I think it's about time I gave an update to this thread. Thanks for all your help and encouragement. I now have my very own roll-off-roof observatory at the bottom of my garden! And, it even works! I really enjoyed the build (and as a retired programmer, I especially enjoyed developing the software to automate and integrate the roof and the observatory lights - I love showing off to visitors by opening the roof by pressing a button on my watch). After lots of suggestions from people here and a helpful phone call with one member (thanks, @Martin Farmer), I explored the option of getting a local shed builder to build a custom wooden building to my spec. I found a very helpful shed company not a million miles from my home who was willing to make a building. Ade at Staffordshire Sheds in Lichfield was really good - he spent loads of time going over what I wanted with me. They supplied the shed with the necessary mods for me to add the extra rails and supports for the roof movement. They even came back and helped me to get the roof on once I’d put the shed together and added the roof rail supports. I’d thoroughly recommend Staffordshire Sheds if anyone else in the region is thinking of going the same route, I built a Todmorden pier and had some help from @Peter Drew when I was worried about a little wobble in the structure. I really did enjoy the build, even though I did worry that I’d bitten off more than I could chew a few times. Building the pier was a new experience for me as I had never done any concrete work before. Converting a brake disc into a pier adapter was more in my wheelhouse but still an interesting job. And I enjoyed the woodwork. Hadn’t done much of that for years. Roof opening: The scope in the obsy: I motorised the roof with a gate opener and added a bit of extra electronics so that I could integrate it with an Arduino controller. In fact, I used two Arduino controllers, one to control the roof and the rain sensor and another to add a WiFi interface and to control the lights. The lights themselves were the simple stick-on LED strip lights you can get off ebay. I bought two strips, one white and one red. Then cut each strip into two so that I could have a white and red strip on each side of the obsy. The Arduino controls these so that I can dim them, select which colour and which side (or both) to light up. The Arduino controller coupled with the ASCOM drivers I developed plus a windows app means that the roof will refuse any close instruction unless the scope is parked. If it rains (or I press a certain button), the windows app will park the scope and then close the roof. That protects the scope from being hit by the closing roof when it would otherwise be in the way of the roof. I added a remote control to open/close/stop the roof and turn the lights on and off. Plus pressing and holding the close button will do the same park & close function that would happen when the rain sensor triggers. And, as I mentioned earlier, I developed a phone and smartwatch app to control everything remotely. The switches in the observatory (for the lights and the roof) are all inputs to the Arduino controllers so they’re all nice low-voltage, low-current switches. I used my 3D printer for the switch housings. So, it’s been quite a project - digging holes, erecting posts, building a shed, building a pier & pier mount, a touch of electronics (MOSFET circuit to drive the LEDs), Arduino programming, ASCOM driver programming, Windows app programming, Android app programming, Smartwatch app programming, 3D printing. I’ve loved every second of it! And I now have my very own observatory which will close itself if it rains and at the end of an imaging session. I’ve so far got a very acceptable M33 image. Just need some more clear nights now. I know I’ve gone into a lot of detail here and if you’ve read this far, I applaud you. Reading it back it sounds like a list of my accomplishments but I really wanted to express how multi-facetted the project was and how enjoyable each different element was. Next stages (I need another project for next summer) will be to raise the pier by half a block to get more clearance from the walls and I’m already thinking of upgrading the scope but can’t decide whether to go for a refractor or stick with a reflector.

Yeah. They're white-tailed bumblebees to be exact

An update: I've been persuaded... I've just placed an order for a plastic 6x8 Keter shed which I'm hoping I'll be able to convert to a roll off. Before I start I need to move an existing shed off the patch where I'm going to place the observatory. Sounds a simple step. But, when I emptied the shed I found a bee's nest in there. So, I've been spending my time preparing the new site for the old shed while I wait for the bees to finish nesting and move on (any time now, I'm told). I'll hold off thanking you all for persuading me to take the home-build/plastic-shed-conversion route until it works ... or doesn't... So far all digits still in place

Thanks for the pics, Nigella. The cat looks particularly impressed with that solar image. Is your roof motorised? I notice you haven't lined/insulated the walls. Do you have moisture problems? I also noticed the dome in the background. Which manufacturer is that? Does it work well?

Nice build, Mike. I like the idea of using excercise mats to line the walls - the best use of excercise mats yet!

Thanks for the comprehensive advice, David. If I go ahead with a self-build, I'm going to use this as the basis of my checklist.

I envy you the space, Göran. Sadly 6' on the short side is an absolute maximum. And yes, I'd want to insulate. So it's going to be cosy in there. But my first option was a 2m dome so I'll still have more space than in there!

Thanks, Malcolm. Yes, I've looked at OutsideOlogy. Their prices are quite a bit higher than others - they reckon on about £140/sq ft, which would put the building alone at £6720. Hmmmm.... you're tempting me down the build-your-own path... I was hoping to get lots of people saying 'I bought from x and they were great' but it does seem that the majority of roll-offs owned by SGLers have been self builds. I'm happy enough with the drilling and joining but the problem is I need all my fingers to operate my keyboard and once I get let loose with a jigsaw things tend to go badly wrong. Maybe I will take another look at the self-build options, though.

Thanks, Carole. I've sent them a message asking for a quote

Thanks for the help. I have done plenty of searching, M40, but hoping to get some recommendations from people who have used the companies. I need to do some prep work in the garden (move an existing shed) before I can build a pier and want to make sure I've got a supplier lined up before I even start that I'm thinking of a Todmorden pier Other than HomeObservatoryUK (who I think I'll avoid as I've not heard back from and having read about the problems they've had) I've only found OutsideOlogy whose prices seem a little high and ShedsShedsSheds (thanks, David). Anyone got any experiences, good or bad, of dealing with these or any other suppliers? Steve