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OAG Prism....which side to camera ???


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Hello , 

i am just trying to put together my ccd + filter wheel + OAG.......

My question is : the oag prism has two sides , one is like flat and the other has a small like circle .....??? which side goes where ????

Nikolas.

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19 hours ago, andrew s said:

I think the first was correct. The light undergoes total internal reflection at the 45 deg face. The light path in the coloured diagram is impossible. 

Regards Andrew 

Actually looking a little closer probably both are correct :) it's just the angle of the prism that threw me.  Regardless of the pictures. Thanks google! The idea is light comes down the telescope to both the camera and the guide camera in the same direction one small part gets refectled up by the prism towards the guide camera. That's the principle which is clearer than pictures obviously in this example. Apologies for any confusion. 

Let us know when it's all working otherwise one of us will pop over to fix the mess I've created :) 

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52 minutes ago, Gerry Casa Christiana said:

Actually looking a little closer probably both are correct :) it's just the angle of the prism that threw me.  Regardless of the pictures. Thanks google! The idea is light comes down the telescope to both the camera and the guide camera in the same direction one small part gets refectled up by the prism towards the guide camera. That's the principle which is clearer than pictures obviously in this example. Apologies for any confusion. 

Let us know when it's all working otherwise one of us will pop over to fix the mess I've created :) 

The second coloured diagram is not correct. The blue prism is the wrong way round. No  known material could deviate the light at a right angle in this configuration.

Regards Andrew 

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13 minutes ago, Nikolas74 said:

Does the OAG Prism has to be parallel with the sensor 

Hi. No. Decide where best you want it e.g. if you have a rectangular sensor, the centre of a long side is a good choice. Now take flat frames pushing the prism toward centre field until you see its shadow. Then back off a little.

The idea is that you can rotate the oag to pick different guide stars but unless you're at a very log FL or you have an old guide camera, choose maximum prism insertion and leave be.

HTH

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46 minutes ago, alacant said:

Looking at yours it must have a reflective coating on the 45 deg face. This is mine https://www.teleskop-express.de/shop/product_info.php/info/p641_TS-Optics-Off-Axis-Guider-TSOAG9---Baulaenge-nur-9-mm.html it uses the prism with total internal reflection. 

You can see they are quite different. It is probably that yours uses reflection as yours is for an EOS camera with a large field.

Regards Andrew

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19 hours ago, andrew s said:

The second coloured diagram is not correct. The blue prism is the wrong way round. No  known material could deviate the light at a right angle in this configuration.

Regards Andrew 

So that's where all the confusion is. Types of prism :) looks like one is reflective another transparent. As you say we live and learn. Wonder what works best in practice. Good to know actually because later if like for me I decide to get a cmos then i might need a different oag. 

All the best

Gerry

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2 minutes ago, Gerry Casa Christiana said:

So that's where all the confusion is. Types of prism :) looks like one is reflective another transparent. As you say we live and learn. Wonder what works best in practice. Good to know actually because later if like for me I decide to get a cmos then i might need a different oag. 

All the best

Gerry

The reflective version should be ok with any camera. A prism adds aberrations when off axis.

I use  mine as the input to a spectrograph. 

Regards Andrew 

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2 minutes ago, andrew s said:

The reflective version should be ok with any camera. A prism adds aberrations when off axis.

I use  mine as the input to a spectrograph. 

Regards Andrew 

A spectrograph. It's a area I know nothing about. Could I ask what you use it for?  Related to spectral analysis of stars etc?

Regards

Gerry

Edited by Gerry Casa Christiana
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15 minutes ago, Gerry Casa Christiana said:

A spectrograph. It's a area I know nothing about. Could I ask what you use it for?  Related to spectral analysis of stars etc?

Regards

Gerry

Yes I study star spectra with a home built echelle spectrograph. I have a guide head on a telescope which feeds the starlight into a fibre optic which guides the light to the spectrograph. This allows the spectrograph to be stable as it does not move as the telescope tracks the star.

Regards Andrew 

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2 minutes ago, andrew s said:

Yes I study star spectra with a home built echelle spectrograph. I have a guide head on a telescope which feeds the starlight into a fibre optic which guides the light to the spectrograph. This allows the spectrograph to be stable as it does not move as the telescope tracks the star.

Regards Andrew 

Wow fascinating. Love to see what kind of results you get. Anyway for another thread. 

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