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alacant

OAG first light double cluster

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Hi everyone. I tried an OAG with my long reflector having had dropped frames with the separate guidescope. None of the nightmare setup scenarios; it bayonets straight into my Canon. You first focus the main camera (I used Mirfak- it has loadsa stars around it) and then focus the guide camera by simply pushing it slowly into the guide port until you see stars. That's it!

I've still a residual elongation but now it is always along RA. Am hoping that the PHD2 gurus can come up with something; I had to calibrate several times. Hope it's something simple because I can see this as being the way forward into galaxy season. If anyone has any ideas...

700d + t7m on 150mm f8: 45 mins

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Processed at 10000m in GIMP2.9 over the Pyrenees: France is top right.

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Edited by alacant
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Nice! If oag is that simple, I should probably use it as well. I've always thought it to be trickier than a guide scope.

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20 minutes ago, wimvb said:

Nice! If oag is that simple, I should probably use it as well. I've always thought it to be trickier than a guide scope.

It is trickier than a guidescope but anyone can get lucky! It looks as if Alacant's OAG automatically orientates itself to long side of the chip? Or maybe that was just a good decision? This is the first thing. It matters because it allows the prism to go deeper into the light cone than it could at 90 degrees. And then there's the business of getting the prism to the right depth. Maybe Alacant could get rounder stars by sinking the prism further into the light cone, but not far enough in to create a shadow on the image. This is the second step in optimizing an OAG, the first being to sink the prism towards the long side and at 90 degrees to the chip.

It's great that this has worked from the off but that doesn't mean that everyone will be so lucky or that the system is yet optimized.

Olly

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Thanks, Olly. Well, "if it ain't broke ..." I'll just keep using my ST80.

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47 minutes ago, wimvb said:

trickier than a guide scope

I think it's similar to collimation. There's a lot of misleading, confusing and down right incorrect advice out there!  As soon as you have the bits in front of you, you wonder what the fuss was about. The setup is a lot simpler than a guidescope. No drilling, no rings, no mounting plate, no second telescope... And a lot lighter. 

 

19 minutes ago, ollypenrice said:

OAG automatically orientates itself to long side of the chip?

You can place the OAG wherever you like in an arc from the camera hand grip until it hits either the opposite corner or the bit that sticks out where it says 'Canon'. I think it's best to have the prisim along the long edge of the imaging sensor as there's more real estate there. You can see where the chip is and the extent to which you can insert it by eyeballing it. Insert it to coincide with the sensor edge then back off a mm or two; I think I'm already at maximum 'insertioness'. The fun is making it better;)

Thanks for your replies. Cheers and clear skies.

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3 minutes ago, alacant said:

The setup is a lot simpler than a guidescope. No drilling, no rings, no mounting plate, no second telescope... And a lot lighter.

Differential flexure or mirror movement is my main concern. I don't mind tinkering a bit with my gear. What else to do during clouded periods? But the added weight is a concern. Especially since it's further away from the mount than the main scope.

4 minutes ago, alacant said:

I think it's best to have the prisim along the long edge of the imaging sensor as there's more real estate there.

That's probably what Olly meant as well. If the prism is inserted perpendicular to the long edge, it can go further into the light cone without getting in front of the chip.

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17 minutes ago, wimvb said:

keep using my ST80

Unless you're going to 1200mm or more, I don't think you're gonna get much difference. My 8" f3.9 will still be manned by my 60mm f4:) HTH.

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6 minutes ago, wimvb said:

I don't mind tinkering a bit with my gear

I don't own an oag. Maybe borrow one? Club/society/friends?  I find if you've got something they want to have a go with, you can have a go with anything they have!

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10 hours ago, alacant said:

I think it's similar to collimation. There's a lot of misleading, confusing and down right incorrect advice out there!  As soon as you have the bits in front of you, you wonder what the fuss was about. The setup is a lot simpler than a guidescope. No drilling, no rings, no mounting plate, no second telescope... And a lot lighter. 

 

 

Regarding the prism depth, you can set it in the daytime just by taking flats. The shadow will be easy to see. Being a mm or two too far out would make life very difficult on some systems. I used an ODK14 on which it was vital to have the OAG as far in as possible since, with the restricted FOV from a 2.4 metre focal length, finding guide stars could sometimes be marginal. The fact that we were using a full frame sensor also pushed the OAG further out of the light cone.

 

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12 minutes ago, ollypenrice said:

I used an ODK14

Simplest of the simple f8 Newtonians here; only 1200mm. Good idea with the flats if you need it. Thanks.

Edited by alacant

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What a coincidence. Just last night I was tinkering my OAG to get it ready to be used with my TS65 quad. I wanna learn phd2 to see how the mount performs and I wanna use a light setup and exclude the differential flexure. 

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The EOS ring of the OAG was suffering of some movement and I made a 0.2mm ring for a tighter connection.

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I also tried my best to get the prism perfectly centered. The only thing that I managed to do is insert a toothpick and now it's only 0.3mm off center.

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I want to set up the OAG in stellarium to see the stars that I can guide on. Im not sure if I inserted the correct measurements. I measured the prism (that's the little mirror, isn't it?) 6mmx10mm. My question is about the ccd/prism distance. Is it the distance from the center of the prism to the telescope's optical axis? I measured the distsnce from the center of the prism to the center of the OAG, is that rigt?

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Emil

Edited by emyliano2000
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9 hours ago, emyliano2000 said:

set up the OAG in stellarium to see the stars that I can guide on

Looks like we're both in this for the long haul! I can't answer your Stellarium question, but it's a great idea and so I'm hoping someone will be able to confirm your circles. So far, try as I may in barren areas of the sky, there have always been suitable stars. That's with the t7m zwo clone. I know your concentric circle method is going to come in handy when we turn our attention to the spring galaxies with even more barren zones... 

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12 hours ago, emyliano2000 said:

My question is about the ccd/prism distance. Is it the distance from the center of the prism to the telescope's optical axis? I measured the distsnce from the center of the prism to the center of the OAG, is that rigt?

I found it and I measured correctly.

Screenshot_20171208-010827.thumb.png.0f37835e57bd2479eff38234ecd7d8f1.png

 

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With the help of a couple of thin delrin spacer rings at the guide camera side I managed to get close to having the same rotation of the guidecam sensor as the dslr sensor in relation to the optical axis. Now I need to find the focus point of both the dslr and the guidecam. I hope I won't need any extension tubes as I don't have any.

Edited by emyliano2000

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2 hours ago, emyliano2000 said:

find the focus point of both the dslr and the guidecam

Sorry, terrible snap. Here's my setup -looks similar- with both cameras in focus. FWIW, the camera sensor is roughly 5cm from the prisim. Your camera design seems to be different though; I focused by pushing in the guide camera until I could see stars. I think with yours -it looks to be screwed directly to the m42 on the guide table (?)- you'll loosen the table and move it toward or away from the prisim to get focus. Maybe have a go on a distant hill or the horizon in daylight to get close? Good luck and do report back when you get it going.

oag2.jpg.38bc83d180886efa41a1b84be7569fe8.jpg

Edited by alacant

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1 hour ago, alacant said:

Sorry, terrible snap. Here's my setup -looks similar- with both cameras in focus. FWIW, the camera sensor is roughly 5cm from the prisim. Your camera design seems to be different though; I focused by pushing in the guide camera until I could see stars. I think with yours -it looks to be screwed directly to the m42 on the guide table (?)- you'll loosen the table and move it toward or away from the prisim to get focus. Maybe have a go on a distant hill or the horizon in daylight to get close? Good luck and do report back when you get it going.

oag2.jpg.38bc83d180886efa41a1b84be7569fe8.jpg

I used this kind of setup before with my lacerta standalone autoguider and my 8" newtonian. I reached the focus point quite easily but I never fiddled with the rotation and all the other things that I'm doing now and I was getting elongated stars most of the times. I hope focusing is gonna be as easy as with the lacerta. Indeed, on my oag the guidecam screws directly to the m42 thread of the guide table.

Can you rotate you guidecam?

Edited by emyliano2000

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