off axis guider for meade 14"

[h0ughy]

its been a long time but i am now looking to finishing up the setup for the 14" in the observatory. I now have the pyxis 2” rotator plus adaptors and tube extensions to use with the 0,62 reducer, but as per my stupidity the 14 is a very tight squeeze in the 2.3 Sirius dome. I will be using the cooled 40D to start with and if I like it will progress to a more specialised setup later with a mono camera. But here is the kicker – I know I need to use a off axis guider and I remember a few people saying to get the MOAG? Does anyone have a photo of their setup with their MOAG and guide camera? How do you set it up?

[Poita]

I was talking to Brett the other day, and I'm pretty sure he trash talked the MOAG, but then again, I was pretty wrecked and could have it back-asswards.

[Merlin66]

There are other solutions you may want to consider depending on the filter wheel you selection for the RGB work.
ATiK and Starlight can now supply almost "built-in" OAG's for their wheels...
The Ol' Lumicon GEG is also worth considering...

[Lester]

Hi Dave, I use the Orion delux off-axis guider on my 14" LX200. But if you are set on this other brand that is fine.

All the best.

[h0ughy]

not quite up to the new oag camera yet:thumbsup:;) but the thought has crossed my mind

[h0ughy]

do you have a pic of that on the scope

[Lester]

No Dave, and unfortunately the 14" is not mounted at this stage. I have a Feather touch focuser out of the 14", then a 2" Meade flip mirror, next the OAG and last the Astro 40D. The set-up works well. Flip mirror helps for centring faint objects that are not visible through the camera.

I use a 25mm eyepiece to find a guide star in the OAG, and then replace it with the Orion starshoot auto guider that focuses at the same position.

All the best.

[g__day]

Why not consider an On axis guider?

[h0ughy]

please explain?:)

[gaston]

Hi David,

An on axis guider (ONAG) allows to guide with the same field of view than your imager. Like an off axis guider (OAG) this solves differential flexure problems as well as the the guide scope room and extra load for the mount. However OAG are limited to a narrow donut's like shape field of view way off axis of the main ship. Also an OAG uses small prism to pick up the starlight leading to large F-numbers for the guider.
Most of the time it is challenging to find a guide star this way and most likely it will require to rotate the all camera body to reach the goal, which means you have to take new flat frames all over again each time you do so. An ONAG does not have those limitations.

Innovations Foresight (www.innovationsforesight.com) offers an ONAG, which is associated with an integrated X/Y stage, provides an easy access to your scope field of view by the guider camera. It can use on-axis as well as off axis guide stars, for a scope of 2m focal length the ONAG filed of view is in a range of 1.3 arc-degree.

The ONAG works by splitting the light between the visible range (<750nm) and the near infrared (NIR) range (>750nm). This is done with a dichroic beam splitter, known as a "cold mirror". The visible range is reflected for imaging, pretty much like a star diagonal would do, this insures perfect images, without any distortion, while the NIR light goes through toward the guider camera.
Monochrome, unfiltered CCD/CMOS camera are quite sensitive in NIR, this is why we need UV_NIR blocking filters for imaging with those.

Clear skies!

Happy new year 2012 :hi:

[Poita]

I needed to use my guide-scope to read that tiny text :)
That is intriguing, so the visual part of the image goes through to the camera, and the near infra-red goes through to the guide camera?

Do guide scopes work okay with only seeing NIR?

What is such a thing worth?

[bert]

Hey all,

I fing the onag interesting.... but too much backfocus for my setup. But it would probably work for your scope and imaging train.

You are going to struggle to get any aog to work well. You are using a pyxis le? It has a 42mm output, not 2 inch, which is too small to cover your 40d and a pickoff mirror for the guide chip. Unless you mount the oag in front of the rotator which kinda defeats the purpose.

The moag will not work in your situation houghy, the moag is designed to fit between a sbig camera and an sbig aol adaptive optics device. The mmoag however is designed to use adapters to facillitate use with other imaging trains, but you will have the same issues as mentioned above.

Brett

[renormalised]

Looks like a very interesting bit of kit...well worth investigating.

[gaston]

Hello Peter,

See the attachement (ONAGandNIR.pdf) concerning guiding with NIR. There are some plots and figures I could not add the the thread text format.

[gaston]

By the way, jJust a complement, to be clear.
When I wrote that the ONAG efficiency is 50% for class M stars, I mean from the guider point of view. The imager in any case will receive (by reflection) more than 95% of the visible light (from 370nm to 750nm).

[h0ughy]

Brett i upgraded the pyxis LE to the 2" pyxis. I am beginning to wonder what i will do:shrug:. This system seems like i will have to sacrifice the pyxis in the train in order to use a OAG or the on axis version.:sadeyes:

i also have the leupus 0.62 reducer to put in place. i really need to find out more about this on axis version.

might keep the rotator for the 127:question:

[h0ughy]

Gaston, i see you are involved with the company, so in that respect you would know your product. in my case i have a TCF-S focuser with a leupus 0.62 reducer and wanting to use a cooled Canon 40D on a meade 14". how would your product fit in the image train? would i get focus with the camera and how would the guider work ( DMK 21).

More to the point do you have some more examples of use with a DSLR. And what is the cost?

[gaston]

Hi David,

The short answer is yes.

Below more details:

They are two options to use the ONAG with a FR.

First:

Attached the FR in front of the ONAG (SP), this way imager and guider cameras will see the FR.
In this configuration you would place the imager focal plane (IFP) at a distance (q) from the FR flange in the order of FR back focus (DFR) nominal distance.

A FR can work at a different back focus distance (q ) than the nominal one q=DFR. Doing so will change the reduction factor (h) though.
There is simple relationship here:

h=1-q/f, where f is the FR focal length, about 276mm for the OPTEC 0.62x.

However if the FR is also a corrector, you have to keep q close to the DFR nominal value. For instance the Celestron/Meade 0.63x FR-corrector (field flattener) will work fine if you stay in a range of q= DFR +/- 25mm (1”).

The Optec Lepus 0.62x is designed for corrected scopes, such as the SCT (ACF, EdgeHD), it acts as a simple FR, not a corrector. It is very forgiving on spacing, as we should expect.

Canon DSLR cameras have 44m back focus, and most T-thread to DSLR adapters will add an extra 8mm or so to the back focus, leading to 52mm of back focus.
The ONAG has a 66mm back focus. You will also need an custom adapter to connect the OPTEC FR to the ONAG SP (T-thread). We can make one for you, its expected back focus will 11mm.
Therefore the total back focus from the FR flange to the IF) will be 52+66+11=129mm, or 129-105=25mm, about one each more than the FR DFR (105mm).

This would result in a new reduction factor of h=1-129/276=0.53x, or 14% more reduction.

Second:

Place the FR at the ONAG IP, in front of the imager, this way you can use the standard adapter for the Lepus FR with your DSLR and be at q=DFR. You will need our AFR reducer for the guider port, because the guide does not see the Optec focal reducer in this context. You will also need a T-thread to 2” female adapter to attach the Lepus at the ONAG IP, like you do with your TCS-S.
I use this option in some configuration, I also have a TCS-S focuser, very handy. You can see an example on the website www.innovationsforesight.com (http://www.innovationsforesight.com/) main page (C11+TCS-S+AO-8+ONAG+Celestron 0.63x FR).

Since the Lepus is not correcting for the SCT field curvature I would recommend the first option.
For further information you may want to visit the website, I would also suggest you download the ONAG’s user manual (ver. 3.0) from:

http://www.innovationsforesight.com/Site/Tecnical_Information/ONAG_UserManual_V3_0.pdf (http://www.innovationsforesight.com/Site/Tecnical_Information/ONAG_UserManual_V3_0.pdf)

Clear skies!

[h0ughy]

Gaston i am more than interested now, i will PM you

[g__day]

Sorry I've been away and missed this post, but Gaston has supplied you a lot of good answers.

http://www.cloudynights.com/item.php?item_id=2706

There was a solid write up about ONAG in cloudy nights; I think its a product I will buy into once (when) I become cashed up again. The price I gather for base set-up is around $1,000.

The only question I had was how easy is it to precisely focus the guide camera to the primary camera?

http://www.cloudynights.com/ubbthreads/showflat.php/Number/4951873

My challenge precision focusing the guide camera to the primary camera using an Lumicon OAG - required focusing the primary using a Bhatinov mask - primary using Rigel, guider using Jupiter! Only Jupiter was big and bright enough to let me see the diffraction pattern! Precision focusing the guider wasn't fun at all because the OAG didn't had a threaded tube mechanism to allow the guide camera to be adjusted by fractions of a mm at a time.

I think anyone designing ONAG or OAG should correct this by allowing a micro focus arrangement for at least one of the cameras attached to their rig! All it needed was a threaded sliding inner tube!

example http://www.telescope-service.com/accessories/start/accessoriesstart.html#schneckenfok

[h0ughy]

:D

thanks for the ideas for attaining focus , i may have to emply one of those? i have been in conversation with Gaston in the pM's but i thought i might share a few points here. i will be getting a custom made adapter made for my setup. i went to the web site to order the gear, i found it a tad cumbersome and no PAYPAL available or was it international friendly for the address. i have brought this up with the company and they will apparently rectify this issue. As you may deduce i am ordering the On axis guider - it is the only clear way i can see to use the 14" in the 2.3m sirius dome. I am currently awaiting an email with the paypal link to complete the order:D:D;)

[g__day]

Keen to know how it goes for you! I am stunned folk go through all this effort to split and align the optics - then forget how challenging focusing the second camera is! Even if you simply threaded the outside of a tube and put a larger threaded tube over it and a seperate lock nut - the outside tube would simply very slow slide up or down as you rotated it - this would give the guide camera something to rest against and it would make micro focusing adjustment trival.

I reckon that idea would add less than $2 to the cost and add heaps to the functionality! Maybe suggest it to Gascon!

[Merlin66]

Matt et al,
I've been using ONAG for the past five years. I use a modified Vixen flip-mirror body where the mirror is replaced by a 92T/4R beamsplitter plate.
I now use a Lodestar guide camera and it works 100% on my C11 with the spectroscope.
I have a Baader helical focuser available on the guide port but to be honest it never really gets used. Once the target object is brought to a focus (Batihov mask etc) it's so simple to "ease" the guide camera into focus. You only have to do this once, so its a "Set and Forget" arrangement.
Being able to guide on axis and select any star in the guide FOV is great, for my spectroscopy, but if you're imaging faint fuzzies or nebulae you want to be able to possibly use the whole imaging field to find a suitable guide star...you can't do that unless the guide camera CCD chip is the same size as the imaging chip (unreasonable?) or be able to move the guide camera radially in the housing to look around the field.
Does this make sense?
All in all, it's an easy system to set up and use. The total cost of my 2" ONAG was $120.

[g__day]

Very smart,

How challenging was it maching the beam splitter to fit into the Meade cell and be precisely aligned? As a ONAG for $120 sounds a wonderful poor mans option! Do you have a more detailed how to guide to make one?

Thanks, Matthew

[Merlin66]

It's very simple:
1. Use on Vixen Flip mirror body.
2. Remove the mirror from the flip plate
3. Drill a 12mm hole central in the flip plate
4. Place a microscope slide (!) (or if you want to spend $$$ buy a pellicle and use that) using double sided tape on the front of the flip plate.
5. Re-assemble - job done!

I do have some images - they were used in the book "Astronomical Spectroscopy for Amateurs" to illustrate this guider. I'll see it I can upload them.
Works very well; I use them for guiding my spectroscopes with a Lodestar....

[gaston]

Just few comments.

The PAYPAL option is back on the Innovations Foresight website.

The focusing of the ONAG guider port is done with a compression ring and a sliding drawtube. The design is made for easy focusing, so far user experiences and mine have shown it is simple and fast to do (see Ken feedback on the website for instance).
As Merlin66 wrote you do it once for a given set-up. However any feedback and suggestion is very welcome and I will certainly consider those options to improve the ONAG.

As far as the beam splitter is concern it is useful to make some precisions here.

They are different types of beam splitters, the “classical” one splits the incoming light beam (all wavelengths) in two parts which share the total energy. They are specified as xR/yT where x is the amount of energy reflected by the BS and y the amount of energy transmitted by it (again across all the wavelengths).
The sum of both is near 100%, often below because the BS itself may absorb some of the energy.
For instance a 50R/50T means you split the light energy budget in 50% for reflection and 50% for transmission.

In order to get as much as possible light (energy) for imaging you will need to have a small amount of light available for guiding. For instance 95T/5R, where the 5% reflection is use for the guider.
However imaging through a BS (unless it very thin, such has pellicle BS) with a tilt of 45 degrees will result in significant image distortion, mainly coma, even on axis, this is may be not a problem for astro-spectrography, but it is not acceptable for imaging.
One way to deal with that is to reverse the concept and use a 5T/95R BS, this time the reflected light (95% in this example) is used for imaging, and the 5% left for guiding. The reflection, much like a star diagonal, using a good mirror (BS in this case) does not exhibit optical aberration, the guide star could suffer from some but this is not a problem for guiding.

Yet a better approach is to use a dichroic BS (ONAG solution, patent pending), this is quite different because you do not split the light energy for every wavelength. You select the wavelength range instead for the splitting.
Here you reflect (better again for imaging) all the visible light (370nm to 750nm) toward the imager and every thing above 750nm, the NIR (near infrared), is used for guiding (see my previous reply on NIR guiding). The ONAG dichroic BS reflect more than 95% of the visible range while allowing more than 90% of the NIR to go through for guiding. From my previous comment on NIR guiding, this give you about 50% of efficiency for the guide star, while a classical BS such as 95R5T will give you only 5%.

Good dichroic BS are much more complex and expensive to make than classical BS (95R5T like) because, like good interferential filters used for imaging, they require complex multi-coating (up to 10 layers) to achieve such wavelength splitting.

Finally the ONAG as an integrated X/Y stage allowing the guider to be moved everywhere in the scope field of view to locate a guide star, this is very handy when your guider uses a small chip.

Clear skies!

[g__day]

Gaston,

Love the thought and quality that has gone into your product! Have started saving up!

Matthew

[gaston]

Hi Matthew,

Glad to help.

Like you I am an amateur astronomer first!

The ONAG's design took years of experience and learning curve. I made the first prototypes for myself at the time, and I eventually decided to make a product after that many friends have asked me to do so.

There is no short cut to make good quality astrophotography, you need to stick with high quality material, sound concepts, and consider all the aspects of the problem.

Although the concept seems simple enough, the devil is in the details, trust me.
This makes all the difference between average images and great ones.

However this also means more expensive material, optical parts and assembly cost.
Not to mention that the company policy is to make the best and we do not want to outsource in China either.
We could make the product half the price this way, but most likely at the expense of the quality, and the future of small business in our countries…

I also like the idea that this product is made by and for astronomers, and I do value all comments (good and bad), as well as any suggestions to make it better, everything can be improved. I see this as a way to involve the community with the design process.


Clear skies!

[h0ughy]

well some news. I have received the first part of my order - i now have in my hot cloud infested little hands the On axis guider - and its raining - how unusual? yes this was 100 wife dollars ;) (1 wife dollar = 10 real astro dollars)
i will post some pics later when i can get it out safely with no questions asked......

[g__day]

I am really interested in reading your findings on the new gear for your rig h0ughy - please do paste piccys and do a complete review! My guiding is pretty impressive in my OAG - but I hate the coma I see in the right half of the guider's CCD - I lose half my field of view...

So advice - the thing you give to your friends to see if it works!

I think I too will go down this route if you have great experience with this gear. Must start saving now!

PS

Scince buying a modified DSLR hasn't stopped raining or being cloudy for a minute. Why do astronomy purchases always cure droughts?

[h0ughy]

OK here are the incriminating evidence - its wet

[h0ughy]

and the very odd test

what it looks like where the guider goes, the target and where the imaging camera goes. its exciting - cant wait to try and get it working ;)

:help:

[h0ughy]

just orderd a t- to c thread from myastroshop......