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souls33k3r

Setting up OAG with 1.25" profile guidecam

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Posted (edited)

Hi, 

***Mods please move this thread if you feel this is not the correct category***

I have decided to venture in to the OAG world and bought myself an ASI174MM mini guidecam which will be used with the Orion Thin Off Axis Guider. I've had this off axis guider for a while but have only just started to take this more seriously. 

Now I know the chip size is huge but I'm wondering (and would sincerely appreciate) if someone can assist with what I've got and make it work rather than suggesting I go and spend more on something new. 

While I was setting up the OAG I noticed a few things

1) I couldn't reach focus on the OAG because the prism was slightly far away from the ASI174 chip so I had to loosen the screws to bring up the prism closer to the guidecam chip. When I did that I started to notice that (maybe this is just the way how things are with an OAG) that the object (let's say a window on a brick wall 100m away) i had my main camera focused on the window was now showing focused on my guidecam too but then on the same brick wall there is a second window which  seems to fall slightly to the edge of the prism object that show out of focus. I'm sure this is normal but just wanted to double check

2) The (not sure how to word this properly) bit on the OAG where the guidecam picks the light bounced off the prism is rectangular shaped hole (see image below) which obstructs the view so I'm seeing about good 30% of the viewing screen on either side showing up as total black while only around 30% in the middle is showing me the image. Like I said earlier, I had to lift the prism up a bit so that I can get the guidecam to focus but that's the most I can pick up the prism because otherwise the prism in the imaging train light path will not get there. Also my guidecam can't go any lower than what I have otherwise I feel that the little bump of the rectangular part (again see the image below) might hit the guidecam window and I don't want to risk scratching that.

IMG_20191005_033311.jpg.ee40c72655844652070a6ed493cd7104.jpg

Please advise. 

Thanks in advance. 

Edited by souls33k3r

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You may have to add a spacer between the OAG and the imaging camera to allow you to get the guide camera in focus at the same time.

 

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10 minutes ago, Merlin66 said:

You may have to add a spacer between the OAG and the imaging camera to allow you to get the guide camera in focus at the same time.

 

Don't get me wrong, both cameras are in focus but the two issues that I have are that when both imaging and guidecam are in focus, in the guidecam I'm seeing something which closer to object I've got near perfect focus which shows blurred like out of focus. Tbh I don't think it really is an issue but I just wanted to be sure I wasn't seeing things :)

The second issue is the loss of real estate. 

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I'm having difficulty understanding your problem....

You say the two cameras are focused together - good.

1 hour ago, souls33k3r said:

in the guidecam I'm seeing something which closer to object I've got near perfect focus which shows blurred like out of focus

This is the bit I don't understand. Can you word it differently????

 

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3 hours ago, Merlin66 said:

I'm having difficulty understanding your problem....

You say the two cameras are focused together - good.

This is the bit I don't understand. Can you word it differently????

 

I do apologise for not being able to word it properly in the first instance. I will amend the first thread

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Posted (edited)
4 hours ago, souls33k3r said:

I'm sure this is normal but just wanted to double check

Hi. Normal. You've got the two cameras at the same focus on an object. It doesn't matter where the object is, it doesn't have to be far away but decide on one and get both cameras focused upon it. Forget the foreground whatever it is...

4 hours ago, souls33k3r said:

so I'm seeing about good 30% of the viewing screen

What a nice problem to have!

Assuming you need the T(hin) of the TOAG then something like a binned 120mm -where you could view full screen- would be more suitable. A whopping great 174 isn't necessary. BUT, if you have the back focus, you could move to an OAG with a larger prism that would cover the sensor.

Cheers and HTH 

Edited by alacant
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9 minutes ago, alacant said:

Hi. Normal. You've got the two cameras at the same focus on an object. It doesn't matter where the object is, it doesn't have to be far away but decide on one and get both cameras focused upon it. Forget the foreground whatever it is...

What a nice problem to have!

Assuming you need the T(hin) of the TOAG then something like a binned 120mm would be more suitable. A whopping great 174 isn't necessary. BUT, if you have the back focus, you could move to an OAG with a larger prism that would cover the sensor.

Cheers and HTH 

Cheers mate yes the object was in the foreground as well as to the sides of the Focused object. I hope I'm not imagining things now. 

Unfortunately I do not have the budget to spend on anything anytime soon so have to make do with what I've got. 

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Posted (edited)
8 minutes ago, souls33k3r said:

make do with what I've got.

Yeah, no problem. It just means that you'll be using only a fraction of the camera's capabilities.

Good luck, but with a 174, you shouldn't need much:)

Edited by alacant
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2 minutes ago, alacant said:

Yeah, no problem. It just means that you'll be using only a fraction of the camera's capabilities.

Good luck, but with a 174, you shouldn't need much:)

I agree, that's why I asked if there was a way to make the available area through the TOAG larger somehow? I don't know what or how but I'm sure people are out there using the 174 with smaller prism sizes.

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Posted (edited)
9 hours ago, souls33k3r said:

available area through the TOAG

Hi. Sure. Put an eyepiece 0.5x reducer on the sensor end of the 174. You'll need to stick it well into the camera but try it first on the existing thread. You may just be lucky. Otherwise you'll need your local model steam engine engineer to turn it down for you. After which don't forget to half the focal length on any guide app you may use.

HTH

Edited by alacant

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Couple of things Ahmed, lowering or raising the prism should not affect focus, IMHO all that does is changing the vignetting from the prism, which can usually be removed with good flats and it will change the shape of the star that you are guiding on, it has no affect on focus.

Focus is achieved by having your CCD of the imaging camera at the correct distance and then I adjust the guide camera until that is in focus. Critical focus of your guide camera is not imperative. I made my own adapter up so that I could maintain a 55mm back focus for my Esprits (Haven't used it yet), but I did have to make a thicker adapter as I needed to move the guide camera so that came into focus clearly.

It takes a little messing around, but for me now I won't go back to a guide scope.

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