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Old 22-05-2012, 11:30 AM
DJ N
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TS 9mm OAG - suggestions for guide camera?

Hi everyone,

To lessen the load on my EQ6, I have decided to go down the path of an off axis guider in lieu of using the ED80 as a guidescope. As there have been a lot of favourable reports on the TS 9mm OAG, I have now purchased one along with all the necessary adapters to use it with my Hotech flattener and QHY8L camera.

Last night, I had it all assembled and ready to go. Following on from the suggested method from TS in Germany, I have it configured in the following manner (with the correct spacing between flattener and camera)......

Focuser - Flattener - Spacer - OAG - CCD

I am utilising my DMK21 as the guide camera, which I have been using with my ED80 guidescope until now. However, the issue is that I do not have enough inward focus using the OAG. As a trial, I placed the OAG ahead of the spacers to eliminate some of the distance, and in addition, removed the 1.25" nose piece on the DMK to further reduce the distance, but I was only able to focus the OAG by fully retracting the focuser on the scope, hence now unable to focus the CCD imaging camera.

The TS website suggests that they have tested their OAG and recommend the following guide cameras.....

- Lodestar
- Moravian GO-0300

Would sourcing an alternative guide camera give a variable result??? I cannot find the 'official' back focus for a DMK21, whereas for a Lodestar, the quoted figure is 13mm.

Looking for some feedback if anyone could assist me in solving my little problem.

Thanks,

Daniel
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  #2  
Old 22-05-2012, 03:29 PM
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Hi Danny,

focus the main camera first. Then move the guide camera physically via the focusing mechanism on the OAG.

I think the back focus on the DMK is 15mm but it could be 17mm. YOu could perhaps use a focusing disk to obtain focus. Bintel sells them.
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Old 22-05-2012, 03:42 PM
DJ N
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Hi Paul,

Thanks for the reply. That is the process that I followed. I focused the QHY8L first with the Bahtinov in place. Then attempted to focus the DMK21, ensuring I maintain the QHY8L in focus. The focus is way out on the DMK. It seems I need to get the chip on the DMK closer the OAG. I even removed the nose piece on the DMK to have the sensor as close as I could to the OAG (by holding it to the OAG) and still needed considerable in focus. I also tried with the prism fully "out" as well as fully inserted and could not get the DMK even close. This has me really stumped!!!

Better hold on to the guidescope for a while longer


Cheers
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Old 22-05-2012, 03:52 PM
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You have to move your camera further back if the OAG can't get enough in focus. Use a 75 or 50 mm extension tube from Andrewscom.com.au for the lowest price. Then follow Paul's directions.
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Old 22-05-2012, 04:04 PM
DJ N
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Quote:
Originally Posted by allan gould View Post
You have to move your camera further back if the OAG can't get enough in focus. Use a 75 or 50 mm extension tube from Andrewscom.com.au for the lowest price. Then follow Paul's directions.

Hi Allan,

Thanks for that. I am not quite sure what you mean? I need to maintain a specific spacing between the flattener and CCD. The only other option I tried was to bring the OAG directly attached to the flattener, and placing the spacer to maintain the correct distance between flattener and CCD after the OAG, therefore reducing the focus distance to the guide camera. This proved unsuccessful. It would almost seem that I need to put the OAG in front of the flattener, but I am not sure how I could accomplish that as the flattener has a 2" nose piece.


Cheers,

Daniel
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Old 27-05-2012, 01:51 PM
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Daniel

I found that I had to very slowly find the focus for the guide camera - I tried using a very bright object like the moon first for example - that way you can easily see if you're moving the guiding CCD in the right direction; either inwards or outwards - what I finally found is that depending on the rotational position of the OAG port/prism (you can rotate it so that you can "pick" a star) that some of the guide stars are not shaped like what you're expecting - ie I've used stars that look like footy/rugby ball, sorta cigar-shaped and they do guide!

You can easily miss the focus point on either side of focus - in my case I had my FF->OAG->spacer/extension tube to suit->imaging CCD

HTH
Cheers
Bill
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Old 27-05-2012, 02:35 PM
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I have used the QHY 5 with my TSOAG9 and it can be focused if you remove the nose piece and use some T thread extenders. Unfortunately the QHY5 is not sensitive enough with this unit unless you take longish exposures. I am still to try the SBIG ST-i with this OAG but the prism is pretty small so not much light available. In your case you would have to add some spacers between the imaging camera and focuser tube to allow the guide cam to reach focus. If you use a little more then is needed you should be able to hit the sweet spot on both camera's.

Mark
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Old 27-05-2012, 02:53 PM
DJ N
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Hi guys,

Thanks for the replies, but I think I may be on the way to getting it sorted!

I had another play around, this time during the day. I also swapped the elements around such that I have the following....

Flattener - OAG - T thread spacer - CCD

I focused the CCD on a tree. I then played with the OAG, and I was able to achieve focus once I removed the nose piece from the DMK and just held it to the OAG. So now I have ordered a (very) low profile T thread (female) to C mount (male) adapter from Teleskop Express. Hopefully this will do the trick.

I keep kicking myself though! When I ordered the OAG plus all the bits and pieces, I was thinking of ordering this adapter "just in case". I though that for a 15 euro part, I could save more than double that on shipping charges........ oh well......... one to add to the 'lessons learned' database .

Once I receive the part, I will give an update. If this proves to be a success, means I have reduced my payload on the EQ6 from around 14kg to a smidgeon under 10kg, plus should lessen the chance of flexure.

Cheers,

Daniel
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Old 02-06-2012, 05:06 PM
DJ N
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Teleskop Express ROCKS!!

I received an email from them confirming shipment. When I placed the order, the shipping came to 40 euros on a 15 euro part. BUT, get this, they have refunded me AU$40 odd as they indicated that they have selected "normal" postage as it is only a small part.

My daughter looks forward to me receiving more parts from them, as the last two packages had a couple of bags of German lollies!!
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Old 02-06-2012, 05:27 PM
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That's great service and hope it all works out for you.
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Old 03-06-2012, 01:03 AM
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The OAG was basically designed for use on a DSLR with a 55mm back focus.
You'll need a spacer (as you probably already figured!) between the OAG and the CCD....
I use a beamsplitter guider with the Lodestar guide camera (upgrade from the QHY5) No issues, no problems...
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Old 07-06-2012, 08:36 PM
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Woo Hoo.......... Success at last!!!!

I received the adapter from TS today, so I gave it a quick try this evening.

In summary, it works like an absolute charm. Did a couple of trial runs at seeing if I could pick up guide stars on various objects such as Omega Centauri, Centaurus A, M83 and a couple of others, and in every case there were at least a few guide stars to choose from. So all in all, very happy so far!!

Here is a very quick and dirty example, a single frame with the ED120-Hotech Flattener - OAG - QYH8L setup. It is a single 5 minute sub with no darks, flats or bias.

So all in all, have removed around 4kg of gear plus a 5kg counterweight from the EQ6.

At this early stage, I can thoroughly recommend the TS 9mm OAG.

Cheers,

Daniel
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Old 07-06-2012, 08:55 PM
DJ N
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Here are a couple of shots of the set up. Apologies for the poor lighting


Cheers,

Daniel
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