Adapter confusion and OAG

[Vox45]

Hi all

I will be moving from planetary webcam imaging to DSO imaging using a Canon DSLR that I already own... until I get a decent CCD cam   on a SCT C6... until I get a 80ED

Doing some ressearch I found this OAG that comes with quite a lot of different adapters. I am a bit confused on which is which and what I will need to connect the DSLR to the scope

I know I need a T adapter and a T2 ring (?) as I my setup will be quite basic

scope > focal reducer > stock visual back > OAG > DSLR

So, does this OAG have everything I need or will I need to buy some extras ?

In the box:

Orion Thin Off-Axis Guider for Astrophotography
C-mount to T-threads adapter
Canon DSLR bayonet adapter
Camera T-adapter
Ultra-thin M48 male to T-adapter female adapter
3mm Coma-Corrector spacer
18mm spacer
2" Nosepiece

what about the space between the focal reducer and OAG, would using the stock visual back work or will a Baader click lock be needed ?

If anyone has that kind of setup, pics would be appreciated

[daz]

You need to know the focal length of the reducer - i.e. the distance for the image to be in focus.

From this, subtract the thickness of your visual back, the thickness of the OAG and the distance to the image plane of your camera - and the thickness of any adapters

Example:

FR = 100mm focal length

Visual Back = 25mm thickness

OAG = 11mm thickness

Sensor depth = 17mm

Adapters total thickness = 11mm

100 - 25 - 11 - 17 - 11 = 36 - you would need a 36mm spacer (well, 34-38mm should be ok)

If, however the sum reveals a negative number, the train is too long and you'll need to remove something to reduce the overall length...

So:

FR = 65mm focal length

Visual Back = 35mm thickness

OAG = 11mm thickness

Sensor depth = 17mm

Adapters total thickness = 11mm

= -9mm

You'll also need to know the threads for each component and make sure you have the right adapters.

[Vox45]

You need to know the focal length of the reducer - i.e. the distance for the image to be in focus.

From this, subtract the thickness of your visual back, the thickness of the OAG and the distance to the image plane of your camera - and the thickness of any adapters

Example:

FR = 100mm focal length

Visual Back = 25mm thickness

OAG = 11mm thickness

Sensor depth = 17mm

Adapters total thickness = 11mm

100 - 25 - 11 - 17 - 11 = 36 - you would need a 36mm spacer (well, 34-38mm should be ok)

If, however the sum reveals a negative number, the train is too long and you'll need to remove something to reduce the overall length...

So:

FR = 65mm focal length

Visual Back = 35mm thickness

OAG = 11mm thickness

Sensor depth = 17mm

Adapters total thickness = 11mm

= -9mm

You'll also need to know the threads for each component and make sure you have the right adapters.

Thanks for your clear answer.

Since I don't have the specs (thickness) of all the pieces that are provided, I will have to take a leap of faith and then, after getting the OAG, messure everything and get the correct spacers/adapters if needed...

Time to break the piggy bank once more..

[Xplode]

Go with a finderguider setup instead...it will be much easier to use and will be ok for the C6 since it doesn't have as much mirror flop as larger SCT's.

You might want to get a used focal reducer to save money (for the ED80), there is always some Celestron SCT focal reducers for sale. We probably have one in the astronomy club that haven't been used for at least 5 years that might be for sale too.

[Vox45]

Go with a finderguider setup instead...it will be much easier to use and will be ok for the C6 since it doesn't have as much mirror flop as larger SCT's.

You might want to get a used focal reducer to save money (for the ED80), there is always some Celestron SCT focal reducers for sale. We probably have one in the astronomy club that haven't been used for at least 5 years that might be for sale too.

The idea was to get an OAG for the C6 to futur proof when I switch to the 80ED but I can't really tell what is the trend: do people go for a finderscope setup for guiding a refractor or an OAG ? I see both setups here and really don't know the pros and cons.

I would think that the OAG is harder to use as you have to have a bright star in the FOV which is easier to get using a guidescope but I was also told in another thread that an OAG would be better on SCT's because of mirror flop. Did not know that it was not that bad with a C6

[Xplode]

For a refractor most seem to go for a finderscope setup.  The low FL might seem like a problem for accuracy with longer FL scopes, but i found it can guide at around 0.15 pixels accuracy so a 180mm FL finderguider will be ok to at least 1200mm FL main scope if using the QHY5L-II with small pixels.

[Lonestar70]

You need to know the focal length of the reducer - i.e. the distance for the image to be in focus.

From this, subtract the thickness of your visual back, the thickness of the OAG and the distance to the image plane of your camera - and the thickness of any adapters

Example:

FR = 100mm focal length

Visual Back = 25mm thickness

OAG = 11mm thickness

Sensor depth = 17mm

Adapters total thickness = 11mm

100 - 25 - 11 - 17 - 11 = 36 - you would need a 36mm spacer (well, 34-38mm should be ok)

If, however the sum reveals a negative number, the train is too long and you'll need to remove something to reduce the overall length...

So:

FR = 65mm focal length

Visual Back = 35mm thickness

OAG = 11mm thickness

Sensor depth = 17mm

Adapters total thickness = 11mm

= -9mm

You'll also need to know the threads for each component and make sure you have the right adapters.

Hi Vox45,

Just to add to the confusion,

The backfocus distance (sensor depth) of a Canon camera is 44mm, not 17mm... which makes a big difference to the above calculations.

The SW focal reducer for the ED80 has a backfocus distance of 55mm and the required M48 Canon camera adaptor is sized (thickness) to give this distance. (same applies to Nikon cameras... the adaptor is the required thickness).

You would not be able to use an OFF axis guider with this.

I believe Baader, or Orion make a Focal reducer with around 90 - 100mm backfocus distance so this might be more useable... if it will suite your OTA... but you may still have trouble with the guide camera fouling on the DSLR body.

For DSLR use I would be more inclined to use a finder guider, or a separate guide scope... it puts less strain on the focuser.

Keep happy.

Best regards.

Sandy.

[Vox45]

For a refractor most seem to go for a finderscope setup.  The low FL might seem like a problem for accuracy with longer FL scopes, but i found it can guide at around 0.15 pixels accuracy so a 180mm FL finderguider will be ok to at least 1200mm FL main scope if using the QHY5L-II with small pixels.

Hi Vox45,

Just to add to the confusion,

The backfocus distance (sensor depth) of a Canon camera is 44mm, not 17mm... which makes a big difference to the above calculations.

The SW focal reducer for the ED80 has a backfocus distance of 55mm and the required M48 Canon camera adaptor is sized (thickness) to give this distance. (same applies to Nikon cameras... the adaptor is the required thickness).

You would not be able to use an OFF axis guider with this.

I believe Baader, or Orion make a Focal reducer with around 90 - 100mm backfocus distance so this might be more useable... if it will suite your OTA... but you may still have trouble with the guide camera fouling on the DSLR body.

For DSLR use I would be more inclined to use a finder guider, or a separate guide scope... it puts less strain on the focuser.

Keep happy.

Best regards.

Sandy.

My main reason for choosing an OAG was mirror flop on SCT's. As this is a minor issue on a C6 and the fact that I am going the refractor route, then I'm better off getting a guide scope.

Thanks to you both for your advices on this matter !

Now I just need to choose a good finderscope I see that this one has good reviews and that it is 'designed for use with astrophotography telescopes up to 1500mm focal length' which would suit my need for the C6 and the futur 80ED.

My plan was to use an ASI120MM to do planetary and use the ASI120MM as a guide cam when doing DSO with the DSLR. So, I guess I should skip the starshoot and stick the ASI in this guidescope ... Does that make sens ?

[Lonestar70]

Hi Vox45,

Yes the Orion finder is a good solution, there is also the Altair Astro one which has a micro focuser included: -

http://www.altairastro.com/starwave-50mm-guide-scope-kit-straight-thru-with-non-rotating-helical-focuser-no-eyepiece-or-illuminator.html

 This also has good reviews and the micro focuser is an added bonus... especially as they are both much the same price.

The Orion starshoot camera is a rebadged QHY 5 (early type) so I would not bother with it if you already have the ASI 120MM... it should work just fine as a guide camera.

The other advantage of using a finder/guider is that you will generally get more guide stars to choose from since it has a wider field of view than an OAG.

I think you will find using the separate finder/guider a better solution... especially if you go for the ED80 later on.

Good luck and hope you get it all up and running soon.

Best regards.

Sandy.

[Vox45]

Hi Vox45,

Yes the Orion finder is a good solution, there is also the Altair Astro one which has a micro focuser included: -

http://www.altairastro.com/starwave-50mm-guide-scope-kit-straight-thru-with-non-rotating-helical-focuser-no-eyepiece-or-illuminator.html

 This also has good reviews and the micro focuser is an added bonus... especially as they are both much the same price.

The Orion starshoot camera is a rebadged QHY 5 (early type) so I would not bother with it if you already have the ASI 120MM... it should work just fine as a guide camera.

The other advantage of using a finder/guider is that you will generally get more guide stars to choose from since it has a wider field of view than an OAG.

I think you will find using the separate finder/guider a better solution... especially if you go for the ED80 later on.

Good luck and hope you get it all up and running soon.

Best regards.

Sandy.

Thanks Sandy good point on the micro focuser !

For once I am glad to be on a tight budget...  If I have had the money and gone with my first choices when I started in astronomy, I would have spent more than 2000£ on a setup that would be all wrong.

The fact that I have to wait before buying anything gives me time to dig and ask questions and reads posts like yours and Xplode and all others... This has saved me a lot of cash and headaches

2 things I have learned: don't buy anything on a whim and try to buy second hand as much as possible...

[Vox45]

Just a quick update on this...

I got a SW 80ED from a seller on the forum. It is a beauty ! now if I could just sell my C6 to pay for the swap.

It came without the 9x50 finder but I had already bought the Orion Deluxe Mini 50mm Guide Scope with Helical Focuser that I just had to slide in the mounting bracket built in the OTA. Took me 5 seconds to install and it is quite sturdy !

The only issue for me is that the focuser is 2" so it will cost me more from now on to buy accessories ! but then again I will be setup for the future so not a big issue. Fortunatly I am starting out so I did not have any 1.25 accessories beside my 3x Barlow and webcam nosepiece adapter which will still be useful for the guiding part. Not sure how a webcam will behave for guiding but I'll see and advise when I get there.

Thanks all for your advices now I need to take the plunge