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TS OAG setup questions


Uranium235

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Having just taken the plunge and ordered a TS OAG, I have a couple of questions in regard to getting it going and settled in before SGL7.

My questions rise from the fact that im trying to squeeze it in between the FW and the 0.85x reducer. The spacing is going to be a close call becuase of the stupidly long M48 thread on the reducer (and no, im not putting it in a lathe...lol).

1) How close can the OAG be put to the FW? Can it be butted right up to it? Wouldnt the guide camera mounting bump into the FW when you try screw it on?

2) When you rotate the prisim, does the camera also rotate? If it does, this may present problems with a chip as tiny as the 285 (it will wreck my framing).

3) How often does it actually need to be rotated? As in, does it usually pick up enough stars in its default position? (depends on what im imaging i guess)

Apparently, the one im getting is fresh from Astrofest and there have been a couple of design changes, so Im interested to see how it looks and performs.

Hopefully this this will be the cure for the awful flex problems ive been getting which was brought home by the fact that im having to chuck all of my Ha from the Rosette i did last month becuase of flex (though the guiding was perfect).

Thanks in advance for any enlightenment :)

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Hi,

1) I put mine right against the front of it. You dont want the guide camera looking through the filters. If yours is the same as mine, then it will have a separate little ring which will screw onto the FW, then you attach the rest of the body.

2) You should aim to get the guide prism set along the long side of the imaging chip and square to it, makes it easier to set up the system and you should find plenty of guide stars no matter where you look. I NEVER rotate the prism, evne at F10 :)

3) See above :icon_eek:

I'd like to see the design changes, see you at SGL 7. If you need help in the meantime, just pm. I'll be a bit busy the next couple of days.

Cheers

Tim

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Thanks Tim, its a relief to know I can get it frontside of the FW and not worry about having to move it to find a star (esp. if im imaging at only 500mm). I will align the prisim as you said, along the edge of the chip. But I might have to dig out all the T2 extensions I have becuase I dont yet know how far I will have to space the QHY5. But i remember catatonia saying that you need to sort out the main camera focus first before fiddling with the guide cam.

Im just wondering if the very small focus adjustments I make between filters will mean I need to re-focus the OAG? :icon_scratch: shouldnt think so.

I will take a few pics of it when it arrives, Bern (at modern astronomy) said thay had improved the guide camera mounting and done something about the grub screws. Should get it tomorrow or wed, so we will see :)

Im really looking forward to SGL7, the new tent should be arriving tomorrow (Vango beta 350) so I will have to give it a test-pitch sometime this week.

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The important thing is to get the spacing right between the reducer and the imaging camera. Accept no compromises on that.

When you have done that, mount it up, focus the camera, in daylight is good if you can find a distant target, and then get the guidecam parfocal JUST BY ADJUSTING THE GUIDECAM.

I adjust mine if needed at night, but tiny movements make a huge difference. You'll be clumsy with it first but soon get the hang of it. Using a bahtinov mask, find a bright star and check the focus. As long as you get the 3 spikes, thats near enough, no need to be absolutely spot on like with the imaging camera.

If you can mount the guide prism square to the long edge of the image chip, you'll get less shadow, and moving a bright star in your image camera view up into guidecam view will be easy to do.

You may want to black out the little gaps at the side of the guidecam stalk when you get properly set up, light can get in there from a torch or LED etc.

I use electrical tape shims to make sure that the attaching ring is positioned properly with respect to the filter wheel so that the guidecam sits proud of it.

Cheers

Tim

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Thanks for the tip on blacking out the guidcam stalk, it will help block out the occasional blast from a neighbours secutity light or drivers who decide to park with full beam on the car park next to the bottom of my garden.... or when I look at my setup but forgotten to turn off my headtorch...lol.

You've reminded me that I will be using the bmask for the guidecam too (which will be an interesting novelty). IIRC, switching between filters never causes the loss of spikes with the bmask on the ED80 - sure it needs adjustment, but its not a million miles off.

Maybe if I focus the main camera with a green filter, focus the guide cam then leave it there, im hoping there will be enough focus each way when switching filters to R or B on the main camera. So in theory Id never have to touch the QHY focus again.... worth a go!

Cheers,

Rob

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. So in theory Id never have to touch the QHY focus again.... worth a go!

That's the theory Rob :icon_scratch: Works pretty well too! Setting up with an OAG is quicker than with a separate guidescope when you are confident with the kit.

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To confirm what everyone says.

1. Put the OAG in front of the filters

2. Make sure your reducer to ccd distance is right. This WILL be your biggest problem with adapters etc.

3. Align prism so it is flat along top edge of CCD

4. At 500mm, you will not need to remove or rotate the guide cam.

5. T2 adapters on QHY5, remove the front plate to insert the adapters. I needed a 5mm one, but depends on your CCD to QHY5 focal ratios.

6. Once you have it set, mark it up and tighten. You will never need to adjust unless you change the image train or CCD. Just focus your CCD and your QHY5 guide WILL be focused automatically as the ratio / distance is fixed.

7. The adapters are all interchangeable.

HTH

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Cheers Cat, it arrived today and Ive just spent a couple of hours in the basement getting familiar with it.

Putting it together was surprisingly easy, one side is an M48 fitting so it screwed straight on to my reducer. I took care to get the FF/FR > CCD distance right first, its at 55mm now so thats sorted. For now, Ive popped on a 10mm adapter on the QHY5 but ive got a fair selection of different lengths available should I need them.

Its lined up to the edge of the chip too, which meant a choice of the QHY5 being above or below the focuser. For now ive chosen below, but I may have to change it if theres any danger of it colliding with the mount legs.

Here is a pic of it, sorry if its a bit blurry :icon_scratch: not sure if its anything different to what they made previously.

All I need now is some clear sky..... hmmmm.

Cheers

Rob

post-18171-133877732275_thumb.jpg

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2. Make sure your reducer to ccd distance is right. This WILL be your biggest problem with adapters etc.

Almost impossible, even. Many reducers are set up for approximately 56mm, that being the usual distance for a dSLR with T-ring.

Many CCDS are 17mm

Filterwheels are 29mm

That leaves you 10mm to play with.

The 9mm TS OAG is nice, and perhaps you are OK if it fits perfectly together, but if you need an adapter (the Skywatcher reducers have an M48 fitting, for example), you are screwed.

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Nice and glad you have it sorted. The main reason for the TS OAG is the narrowness of the unit and hence more wiggle room.

The new TS OAG looks perdy too :icon_scratch:

As for focusing during the day, it can be difficult depending on your CCD.

The procedure for focusing the setup is

1. Focus the main CCD with a Bahnitov mask.

2. Lock the focuser

3. Adjust the guide cam distance to get focus stars in PHD or similar.

4. Lock the TS OAG

Now the TS OAG is in focal focus ratio with the CCD and you can now move the focuser as much as you want with out affecting the ratio

Typical night time operation would then be

1. Focus the CCD with the focuser and mask and lock.

2. IMAGE... Simple as that.

My QHY9 is so sensitive it is impossible to focus in day light and hence makes this process impossible.

If you don't use a mask for focusing on a star, you will not be precise enough and spend forever and a day every night adjusting and going around in circles.

I would recommend allocating one night to get this right once and for all. Ok a few hours wasted, but worth it and you WILL curse until you crack it. But follow this method and it will work.

One more point, don't rush this process. Ensure your scope is cooled and steady before starting. If after focusing the CCD and you can't see stars in the guide, then move the prism in and out a few mm (10mm at most) at first. If this fails, reset and adjust the guide distance with T2 adapters. Always check the CCD focus with a mask once you get guide stars to ensure all is correct.

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Great idea Cat, I will leave the scope out for a least 45min before firing it up (the ED80 focus can shift quite a bit in the first hour or two). Im not sure if id get away with using a 314 in daylight, ive never tried it. But what I do have is a Bmask, if i can get a bright(ish) star in PHD as a blob, I can work from there. Shame PHD doesnt have a zoom function (are you listening craig stark?...lol), so windows magnifier will do for now.

Saturday night may be the night to test it, it doesnt matter if its partly cloudy as all I need is a couple of bright stars.

Ive taken a snap of it all put together, in case anyone else want a go at using one with the SW FF/FR.

post-18171-133877732362_thumb.jpg

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Ive been watching this thread with keen interest and just want to check something - Are we saying once everything is assembled and good focus is achieved this can be locked down and left? Assuming parfocal filters etc and that the focussing isnt knocked?

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Ive been watching this thread with keen interest and just want to check something - Are we saying once everything is assembled and good focus is achieved this can be locked down and left? Assuming parfocal filters etc and that the focussing isnt knocked?

Basically YES, that is the beauty as well as weight and flex solved. Assuming you do not move the guide cam distance once set to the active CCD.

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Are we saying once everything is assembled and good focus is achieved this can be locked down and left? Assuming parfocal filters etc and that the focussing isnt knocked?

Thats the general idea :icon_scratch:

Assuming you dont mess about with the spacings etc..

(lol... Cat beat me to it)

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A good informative thread.

I have a further simple question - once both the imaging camera and guide camera have been adjusted and are both in focus can the optical train then be altered by say adding or removing a focal reducer then you just simply refocus the imaging camera and do not have to touch the guide camera ?

ATB, Andy

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