Orion OAG First Light

[BlueAstra]

I had my first go with an Orion delux OAG last night. I previously used an ST80 piggy backed on my C8 SCT to guide, with a SX Lodestar guidecam and a Canon 1000d as the imaging cam. In general it worked well, but I did have a few issues that other members may be able to help with.

The first problem was getting the correct focal distance. The recommended camera distance for the Focal reducer is 105mm. With a 55mm 2" SCT adapter and camera CCD depth of 55mm I am at 110mm, which is close. However with the OAG I have:

Slim AE478 30mm SCT Adapter

7mm drawtube gap

30mm OAG

3mm Tmount gap

55mm camera CCD depth

This gives 125mm, which does increase the vignetting slightly, and introduces a slight mag change between ST80 guided images and OAG images. The two M33 subs show the difference. It doesn't look much but it is there. Maybe need that super slim OAG that I saw reported somewhere, but I think is much more expensive. I could screw the OAG direct to the SCT adapter, but then I wouldn't have anywhere for the LPF, and I couldn't do a quick change from camera to visual. The 7mm drawtube gap is because the Orion drawtube is a bit too long for the 30mm SCT adapter. The above may not be too significant a problem if I used the OAG exclusively, or a dedicated astronomy CCD camera which tend to have smaller CCDs.

The 1.25" drawtube guide cam mount held the guidecam at a slight angle when the lock grub screw was tightned, and didn't feel totally secure. I didn't like this so I used a C-CS adapter for a much more secure mounting. A screw on guidecam would avoid this problem.

I also had a problem was with bright star images. A sub of M45 shows some glare artefacts that I presume is reflections from the small prism in the OAG. I didn't adjust the prism after moving from the M33 subs, so I don't know if that would affect it.

Overall, I very impressed with the Orion OAG. It is well made and had lots of accessories included. It reduces the weight load on the mount considerably, has no flexure problems and avoids the cost of an extra guidescope and mounting system. I had no problem finding a guide star, and took a series of M33 subs with it. If I can sort out the vignetting and star glare I will be using it exclusively from now on.

[Merlin66]

Good first results!

I've used many OAG including the Orion Deluxe.

The problem with SCT's and reducers is the DSLR body length! If you use a "conventional" CCD camera the back focus is only about 12.5mm not the 55mm with a DSLR. Not much you can do about it!

I use the SCT threaded 2" Van Slyke filter slot which fits IN FRONT of the reducer and allows you to "drop in" any 2" filter - that way there's no impact on the reducer backfocus distance.

I did find on the Orion OAG that the prism could rotated if not firmed secured - obviously only affects the guide camera.

Never seen halos/ glow from a pick off prism ( well not yet anyway!) so I'm not sure what would cause this. Not visible on the M33 image (??) The prism is far enough off centre that I wouldn't think you'd get any impact on the final image.

What spacer set-up did you use when you had the ST80 guiding? The plate scales of the images lokk pretty similar.

(BTW for the benefit of the "non believers" can you post an image from the guide camera as well - just to show the FOV and possible guide stars)

I only use my set-up now for spectroscope work so I'm more interested in the centree of the field not wide field coverage.

[BlueAstra]

Will try and get a guide photo next time I set up. I set the thing up during daytime while viewing a pylon. I think the field of view of the guidecam is about a third of the Canon, and I maybe saw about 1 deg with the Canon and 0.1 deg with the guidecam. BTW, I think its essential to setup in daylight to get the camera and guidecam focus and view close, with a final tweak at night.

A slot in filter would be great, but I think the Van Slyke system is a bit beyond my means. I would like to maintain the drawtube-nosepiece system because it allows me to remove the camera system and insert a diagonal-eyepiece system fairly quickly. You also don't have multiple cables slowly wrapping themself round as you unscrew it. Maybe attach a drawtube to the SCT and a nosepiece to the FR mounted on the OAG?

In the ST80 guide mode the Canon is about 100-110mm from the FR.

I will check the effect of prism adjustment on bright stars when I next setup. I think the halos may be present on the DSO sub, but everything is at a much lower intensity so it difficult to see without processing. Not tried it yet.

[Merlin66]

The orion (us)prime focus adaptor I think SCS stock them, does exactly that! It splits into two sections: male 2" to male SCT thread, and a female SCT thread to male T2 thread.

The van Slyke if mounted before the reducer just stays in place all the time. The sct to 2" female behind the reducer would be your connect/ disconnect point.

I agree 200% with setting up the guide/ Imaging cameras during the day!!!!

[BlueAstra]

I'm not sure I understand your configuration.

Do you mean this part: Orion Prime Focus Camera Adapters | Orion Telescopes

Is it one item that splits in two, or do you have to get both items?

Could you give me a reference to the Van Slyke part?

[Merlin66]

The #05116 is actually two parts the chrome barrel and the black adaptor.

The Van slyke VSA is shown here:

Versa-Port Accessories

[BlueAstra]

Isn't the 5269 the one with the chrome barrel?

I like the Van slyke adapter, but will have to save the pennies! Do they have a UK supplier?

[Merlin66]

Whooops...

You're correct!!

That's the one.

Don't know of a local supplier for Van Slyke product.....

[BlueAstra]

Just to update this thread, I have now obtained an Orion prime focus adapter #5269. When used in place of the OAG 2" nosepiece I can now locate the focal reducer closer to the camera. The Orion FPA splits in two and the centre thread is an SCT thread! The picture shows the new arrangement.

Old Setup: FR + 30mm SCT Adp + OAG 2" NP + OAG

New Setup: 30mm SCT Adp + Orion PFA 2" NP + FR + PFA SCT Tm Adp + OAG

In the old setup the camera CCD plane was about 125mm from the FR. In the new setup it is about 106mm, but the FR is 47mm further away from the SCT exit aperture. This does not seem to have affected things, and the vignetting is reduced.

My particular setup caused a few scratched heads during alignment. I did it during the day on a distant pylon, but couldn't identify the OAG image as part of the camera frame. It eventually became clear that the OAG was sampling from part of the image circle just outside the camera frame, due to the rotation angle of the camera. The attached photo demonstrates.

Finally, I took an image of the OAG frame during a night session. Plenty of stars to choose from at a 2s exposure. This was a particularly rich star field, but usuually there are at least 3-4 stars to select from.

[Merlin66]

Sounds good!

I'm pleased to see the FOV of the off axis shown against the main imager frame. As you now know the OAG FOV is just out side the main frame, and as you see the size of the guide FOV is not as small as some people would think; and look at the available stars to guide on....majic.

Well done. A great illustration of the set-up.

[Tim]

Welcome to the convinced OAG club

The daytime setup is almsot essential, it can be very difficult to get the focus on the guidecam at night.

You should find you can get much longer exposures now with no flex. There is an info sheet on the celestron website that gives the f ratio of the reducer and how it relates to the spacing. With the DSLR, probably best to get as close to 110mm as you can, 106mm is good. Increasing the distance lowers the f ratio somewhat.

Looking forward to the results now

TJ

[Merlin66]

BlueAstra,

Have you had the chance to put the Orion OAG through its paces yet?

Just interested in the feedback.

BTW I don't think you now need the SCT>2" and the 2"> SCT before the reducer.... it could screw staright onto the rear cell?? Make it even more compact and rigid? What do you think??

Ken

[BlueAstra]

I use the 2" nosepiece for convenience. I can easily slide off the camera equipment and slide on the diagonal & EP for initial alignment and visual. I like to do a bit of both in an evening.

Not had a lot of chance to get out with the weather. I did get a stack of 10x4m on M1, M32 and 10x2m M42 and NGC869 on two evenings with the above equipment. Just got a Hutech IDAS LPF to try and improve chronic LP in this area.

[iandh]

Hi Blue Astra,

"A sub of M45 shows some glare artefacts that I presume is reflections from the small prism in the OAG. I didn't adjust the prism after moving from the M33 subs, so I don't know if that would affect it."

Did you resolve the issue that you had with the glare? Was it due to the prism?

I am thinking of purchasing the Orion Deluxe OAG, just having problems locating one in the UK at present!

Therefore would welcome your feedback on those glare artefacts. It was very helpful to see how you incorporated the OAG into your imaging setup as I will have to do exactly the same on the back of my SCT although I will be going into an SX MX7 camera to start with and then a DSLR.

Regards

Ian

[BlueAstra]

Not had a problem with the glare since I first used it. I think it may have been some alignment issue since after I did s daytime alignment and camer/guidecam focus (essential) it has not re-appeared.

It got my Orion OAG from here:

Orion Deluxe Off-Axis Guider

Here is a recent image with the OAG in place. Unfortunately I had a problem with PHD that prevented me using it, but I think that's a software/cabling problem.

http://stargazerslounge.com/imaging-deep-sky/93581-m42-after-guide-failure.html

[iandh]

Hi Blue Astra,

Thanks for the link to SGS I found they were offering the Orion OAG but had no stock until Christmas Eve. I have therefore ordered it from them but will have to wait until after 5th Jan for them to ship it!!!!!!

Looking forward to getting out there and trying it in the snow and ice!

Hopefully get some images as good as yours!

Regards

Ian

[Jammy]

I know this thread is old but I've just found it while looking up the best way to use an OAG with a 0.63FR on an SCT.  I did wonder how I was supposed to achieve 105mm back focus with my dslr.  This is the only place that I've seen it covered, and if I'm honest, I'm still not entirely sure what is the best way forward.

[BlueAstra]

I would definately recommend the OAG method. The setup I had worked fine and put the dslr more or less on the right working distance for the reducer. The use of the nosepiece also meant that the camera assembly could be removed for storage or visual use very easily. I've now moved on to a CCD, filter wheel and OAG, but learnt a lot from the original setup.

[Jammy]

Thanks for the reply BlueAstra.  Your setup looks really good.  I'm aiming for CCD imaging eventually, but would like to start with a dslr - as you have done.

Could you please tell me what the component parts are called in your dslr setup photo?  I would like to buy the same or similar adapters.

I've seen the new Celestron OAG www.firstlightoptics.com/off-axis-guiders-oag/celestron-off-axis-guider-sct.html

This comes with various adapters and fittings, is everything I need included?

I hope you don't mind me asking - I find all the adapters very confusing.

[BlueAstra]

If I remember correctly these are the components:

Astro Engineering AC478 low profile SCT-2" adapter

Orion Prime Focus adapter #5269

Focal Reducer

Orion delux OAG

Canon 1000d T mount adapter

My Lodestar camera required a 7mm extension tube and a C-CS adapter

The Orion prime focus adapter unscrews so that you can mount the FR in the middle of it. The back part screwed into the OAG. This sets the Canon at about the right distance for the FR, and the nosepiece allows the whole assembly to be quickly removed from the SCT. In any OAG setup, its always a good idea to have a daylight setup first to get the guide and prime camera in coincident focus.

[Jammy]

The Orion prime focus adapter unscrews so that you can mount the FR in the middle of it.

I think that's what was confusing me, I did wonder how you managed to put the FR between the 2" adapter and the OAG. It makes sense now. Thanks again for your help :-)

[Jammy]

The #5269 camera adapter is no longer available. Back to square one!