RayD

No problem Chris. It probably would on the same scope with or without the FR, but Rodd has 2 different scopes with differing focal lengths and is using the spacing calculated for the FSQ on the TOA. I have a feeling this is where the issue lies as in either case he will need to have the spacer between the OAG and the FW, which in itself is a little unusual, but if the other spacer (FR to OAG) is calculated using the FSQ but is being tested on the TOA it may never work. It's always tough trying to help when you aren't there in front of the kit.

It isn't the OAG "package" that's the issue, it's the fixed spacing between the FR and and OAG on scopes with differing focal lengths. For example, if you look here you will see that depending on the focal length of the scope, the spacing can change. This is what I am questioning, and noting that it may be different when using the same FR on different scopes. If your OAG set up works for you in all circumstances with the same FR fitted on different scopes then happy days. The problem here for Rodd, and the thing he needs to check and query with his supplier, is that if they have calculated and supplied all the equipment and fixed spacers based on the FL of the FSQ but, as appears, he is trying it all with the FSQ FR fitted to the TOA, it may not work.

I would think the back focus distance between the focal reducer and the camera sensor will be different as the 2 OTA's have differing focal lengths. This means the the set ups would be unique to each OTA. If your supplier has given you spacers which he has calculated as correct for the FSQ, it's unlikely that they will be identical for the TOA I would have thought.

I'm still not convinced that there isn't an issue with the OAG itself Rodd. If you can focus the main camera at mid point, but not the guide camera by them moving the focuser in further, then it points towards a problem with the prism. However, if this is on your FSQ 106, then the focus travel is only 30mm, so half way leaves only 15mm, which may not be enough without the spacer installed.

Rodd just to confirm, can you focus the main camera with the filter wheel and spacer on i.e. does your OTA have enough inward focus travel?

I think you accidentally stuck this in the wrong thread Rodd: Here is my setup--please keep in mind that I did try a spacer between the OAG and filter wheel--despite my supplier insisting it was not correct. It did not solve my problem. If you are wondering why the Loadstar is off to the side, its because without a spacer, it can't be rotated to be vertical because the shoulder of the lodestar receptacle impinges on the edge of the filter wheel. This is as far as I can rotate it--Maybe it does not matter where the prism enters the light cone--but I am used to imaging sensors and guide sensors to be oriented the same way (self guiding filter wheel. This definitely won't work, and no matter what your supplier has said, you definitely need spacers between the OAG and filter wheel as your camera only has 6.5mm of back focus, which means from the sensor to the prism in your filter wheel is only about 17mm (give or take), which means your guide sensor can never be far enough away. With all this noted, the one thing we can't confirm is whether you have enough inward focus travel on your actual OTA focuser to reach focus with this short a back focus, but that's another issue.

Where did you fit the spacers Rodd? For it to work they would definitely need to go between the OAG and the FW, not in front of the OAG as you would normally expect.

Yes I've seen those, that's what I wondered if they supplied with the OAG? It's definitely going to be a squeeze I think.

Good job, looks neat. I think Rodd would need to have measure up with the Lodestar as they are C mount with no T2 option. It's 12.5mm from the end of the well, so anything added is simply added. I had the same issue using mine on my SX and Atik OAG's. The only possible help is if the turret is very thin, like on the SX, and it then slides up inside the camera chamber right up to the lens window, which can resolve the issue. I'm not sure his supplier has given him the right spacers. I did ask earlier whether there are spacers for between the OAG and FW but he doesn't seem to think so. I can't see how it can work any other way due to the short 6.5mm back focus on the ASI 1600. Your image is a great visual representation now as the CN post I linked to earlier seemed to indicate that the only reason the guy installed the internal spacer was to align the sensors, but that didn't make sense.

Nice work well done. This confirms what I said earlier, which is spacers are needed between the OAG and the FW otherwise it can never work. Does the OAG come with a shallow profile T2 to C mount adaptor as the Lodestar is C mount, not T2 like the ASI?

Just by coincidence, this was just posted on another thread. https://stargazerslounge.com/topic/311042-guidescope-mount/?do=findComment&comment=3404750

Ok I see. For me personally, if you are imaging with your C11, I would use OAG for sure. As noted above, it isn't impossible to image/guide without one, but to coin a phrase, "it ain't 'arf hard".

Oh crikey a guide scope is definitely easier. I don't think anyone would suggest going with OAG unless you need to. The only reason I have them is because it all worked out easy, but they can be a mare to get right if you are mixing and matching. The main benefit of a OAG is to remove flexure, and this is accentuated at longer focal lengths. At your focal lengths, providing you have a good secure fixing, then this should not be an issue.

I would think something like that would be ideal. My 60mm is 225 fl and it works great. Never had an issue with getting stars and the Lodestar focuses with no issues. It is possible that you could need a short extension, but it would only be a standard eyepiece type one. If you image at a longer fl then you can just look at a bigger guide scope. As is the case with @LightBucket, the 80mm seems to be a good choice, but at your noted fl you probably wouldn't need to go that big, particularly with the X2.

As long as you can stick around the 1:5 ratio, and the aperture is big enough to get a star (shouldn't be an issue with the X2 as it is very sensitive) then there are a lot of options out there. What about the new Skywatcher Evoguide (50mm). Veeeery nice.

Oh yes it can definitely be done; that's why I refer to things as a guide. You just need to have a really good mounting and be brave enough to try it. I'm sure most imagers would recommend OAG at this type of fl, me included, but that's not to say it is essential by any means.

Not at 1000mm focal length, no. I would have thought a good bet for you would be something like an ST80, or something else 60mm +? I have 2 of the Altair 60mm guide scopes and they have been great, but I know a lot of people use the ST80 with great success at longer focal lengths. There's some info here which is a bit of a guide, but I think you could do a lot worse than looking at a 60 to 80mm scope.

I think a rough guide is targeting a ratio of 1:5 or lower (I think some say 4 and some 6, so in between these is probably nearer to reality). Obviously with OAG you could technically be 1:1. Many will guide successfully higher, but I think if you can achieve around this then it will be pretty good. I have heard another thing mentioned of the fl of the guide scope being 1/3 of the main scope, but I'm not sure how accurate that would be as the pixel size of the camera would have an effect. I don't think it needs to be exact, and of course the biggest thing to get right is eliminating flexure. I image with my Esprit at about 2.5 "/p and guide at 7.5 "/p and this works great being a ratio of 1:2.5. This is with a 225mm fl (Altair 60mm) guide scope and Lodestar X2. I'm sure there are others with more expert experience of guiding who could advise in more detail, but I can't emphasise eliminating flexure enough.

No it is about making sure your pixel scales match, so your guide scope just needs to match your camera and your main imaging scale. Use this tool to see what will work best for you.

Absolutely. There are many expert imagers, including @ollypenrice who image superbly at longer focal lengths without OAG. I certainly can't see 1000mm being a huge issue. I would think it is only when you get to pretty long focal lengths (1300 - 1500mm+) that you really need to look at the possibility of going down the OAG route. You have one of the best guide cameras out there, so coupled to a decent FL scope this should work great.

Ah, sorry I can't be of any more help Rodd. It just seems the spacing isn't going to let you get the guide camera close enough. I use a guide scope on my Esprit 100 for this exact reason, as the space needed for the SW FF (55mm) means I can't fit a OAG in with my 16200. I use OAG on the FSQ 106 as I don't use a FR so the spacing isn't an issue. OAG's eh, who'd have 'em!!!!

This thread may also help Rodd, it has some critical dimensions to help work out how much spacing will be needed.

Hmmmm. What spacers/adaptors has he given you? I wonder if he has planned for it to be fitted as the CN thread, as I can't see how it can work with this combination otherwise as the 12.5mm needed by the Lodestar just makes things all very challenging.

Ok there's a thread on CN here which may help. The GPCAM 2 has the same 12.5mm back focus and is the same dimensions as the Lodestar, so this my well be applicable to you, in that you will probably need to add spacers between the OAG and the camera, otherwise you won't be able to get the OAG camera sensor in enough. Otherwise I think you are looking at the 120MM as a guide camera.

Give me half hour and I'll try to find out some dimensions from factory drawings and should be able to tell you whether it will be possible to get it to work. Do you know the type of FF you have, or better still what the recommended spacing is for your FR?