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Atik OAG Off Axis Guider


FLO
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We have started this separate thread for the new Atik OAG Off Axis Guider as we are receiving a number of inquiries about it. In particular we are being asked how it compares with the TS OAG sold in Germany.

atik_oag_off_axis_guider.jpg

EDIT: Now Available, details HERE

I haven't seen the TS unit but as far as I can tell its main attraction is that it is a slim unit with a thickness of only 9mm (correct me if I am wrong). The new Atik is larger with a thickness of 24mm. This is necessary because the Atik is based on the Takahashi M54 x 0.75mm thread (the TS has a smaller aperture T-thread). This allows the Atik to cater for large-format sensors up to and including 35mm format. Larger format cameras are also heavier so the Atik must be proportionally larger to carry the additional weight.

In short, whilst a slim OAG is desirable, the Atik's larger aperture and heavier construction makes it more future-proof. When you come to upgrade to a larger format you won't need to buy a new OAG.

The larger more robust Atik also incorporates a precise helical focus mechanism (the TS unit uses a regular lock-screw and sliding bar) and will connect directly to a new (incoming) Atik motorised filter wheel, without the need for adapters.

The first of the Atik OAG Off Axis Guiders are due to arrive mid-March. Based on the current exchange-rate it will sell for £189.

We will also make one available for an SGL review :)

HTH

Edited by FLO
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Sounds very promising!

The "generic" areas of concern with the OAG are:

The back focus width..

The positive attachment to the focuser ( It has to support filter wheels, cameras etc behind it!)

The ease of focusing the guide camera - helical focusing?

The ability to attach filter wheels and cameras to the rear (without vignetting)

and the size and position of the pick-off prism...

Ken

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Looks very nice, and if the focusser works for the guidecam that will be a proper revolution!

The Atik cant really be fairly compared to the TS unit, as they seem designed to suit different applications. AFAIK the TS is still the only OAG that can be used with any telescope, including fast newtonians with limited backfocus and requiring a coma corrector. It is the spacing between coma corrector and camera chip which is the killer measurement, especially if filter wheels etc are required. Of course, newtonian telescopes not requiring a corrector like the Skywatcher MN190 are at an advantage, but even they are limited as regards back focus, so the ability of the Atik OAG to join directly to the wheel looks very promising, and it would be good to get a measurement of the two units combined.

Of course, those using refractors or SCTs are not limited in the same way, and by the looks of it, the Atik OAG will be very at home on those telescopes.

The TS unit is inherently flimsy it has to be said, I'm not sure I would be happy hanging a £4k large format camera on the back of it. Focussing it is very tricky, and parts of the assembly, like the walls around the prism stalk, are extremely thin, and easily deformed.

I still believe that off axis guiding will be de rigeur for astrophotgraphy in the future, especially for star parties where the simple set up and accurate imaging with only one scope is very appealing. It is good to see that a reliable company like Atik have taken the OAG and further developed its potential. I'll be very keen to see one of these Steve, and might add one to my OAG stable, that price seems very reasonable.

Although it will link directly to the Atik wheel, it would be great if it did the same to the others out there, do we know what the rear thread is? Is that the M54 x 0.75?

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Interested as well, as we have the TS one on the scopes in Spain... but as you say for putting large format cams, not ideal... fine for the 314L etc, but not the larger ones we're thinking of using

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The largest screw fittings ( to minimise vignetting) throughout the optical path is the way to go.

Unfortunately most of the OAG's / filter wheels etc have T thread connections which WILL vignette the larger CCD chips.

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... do we know what the rear thread is? Is that the M54 x 0.75?
... The largest screw fittings ( to minimise vignetting) throughout the optical path is the way to go.

You will be pleased to here it has a large M54 x 0.75 front and back :)

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Which is a good 6mm wider than the TS unit with its max of M48. Steve, I'd love to take a look at one of these, thanks ;)

I had forgotten about the problem with focal reducers Ken, IIRC the optimum distance between say the Meade f6.3 reducer and the chip is 110mm or so. Increasing this distance or reducing it has an effect on the actual f number. I guess on the plus side, hardly anybody uses a wheel with a dslr, and the CCD cameras mostly have a shorter distance from front of camera to chip than the 55mm of a dslr.

As this thread is likely to attract search enquiries from those new to off axis guiding, it may be worth stating a few things to look for.

Filters. When using an off axis guider, you really want any filters BEHIND the guiders prism, to maximise the available stars suitable to guide on.

Focal Reducers. If using a focal reducer, (or a coma corrector/field flattener), the distance from the reducer to the camera chip is critical, and is usually around 55/56mm. Into that 55mm gap the guider, filter wheel and physical distance from front of camera to chip has to fit has to fit. The guide camera also has to be at the same distance from the reducer as the main camera to achieve focus.

For example, behind my WO FFII or Baader MPCC I have these distances;

FFII - OAG(11.5mm)-FilterWheel(22mm)-Spacer(5mm)-CCD Cam(17mm) =55.5mm

Focussing the guide cam. Oh boy, what a pain! Thankfully it isnt critical to get absolutely perfect focus for a guide star, as most guiding software can cope with that, but you still need to get close, and that can be difficult. I usually par-focalise my OAG during daylight, but the highly sensitive guide camera might need a reducer over the front of the scope. You'll want something a good few hundred meters away to focus on. It is also worthwhile familiarising yourself with the position of your guide camera chip in relation to the main camera, so that if needs be, once you have a bright star centralised on your main camera, you can then nudge the slew buttons to move it into view of the guide camera, where you may be able to use a bahtinov to fine focus. When focus is good on the guide cam, more stars are available - This is where the helical focusser on the Atik looks very interesting. Most OAG's are not easy to fine focus, using a grub screw and manually adjusting the camera position in tiny increments is difficult with cold numb fingers, and it is all too easy to nudge the star you are trying to focus on out of view.

You will need a sensitive guide camera. The ones I have found work very well are;

DSI Pro (exview chip), Starlight Express guidehead, starlight Express Lodestar. There may well be others, but if I was buying again, I'd go for the lodestar. My DSI pro is very sensitive, but the body shape is awkward and needed drastic alterations to get the chip closer to the prism.

I also have a PL-130 camera which proved unsuitable for OAG in my skies, as others have found.

Swapability. When you get hooked on OAG, (and you will), you may want to swap your camera arrangement between telescopes. This is one of the pleasures for me ;) In effect you end up with a twin camera plus filters set up that can be hot swapped between your telescopes as and when required, and as simply as refocussing the new telescope. Once you have the spacings and settings mastered, you will save no end of time. Your old guidescope might even make for a nice widefield picture, or if your mount is capable of taking the weight, you can use your old side by side bar etc to hold a visual scope, high class finder scope, widefield camera (I Piggyback a DSLR to hitch a ride on the accurate tracking.)

I guess we should really do an OAG article for SGL :)

Tim

Edited by Tim
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  • 4 weeks later...
Applogies, the orginal post said you were expecting them mid Feb :(

Ah yes, sorry, I should have updated the post :eek:

Will you be bringing one or two to SGL5? :eek:

Yes, definitely :)

I'd quite like one, let me know how much they are when you have a price please Steve?

We are expecting the Atik Off Axis Guider to sell for around £180-200.
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One of the considerations with OAGs is the ability to position the guide prism in a convenient position with respect to the main imaging chip. For rectangular chips this is generally along the long side, for square chips the corner may be a more appropriate placing. Ideally there is the ability to adjust the position of the prism up and down as well, to minimise shadowing.

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  • 3 weeks later...

The first of the Atik OAG Off Axis Guider are due to arrive mid-March. Based on the current exchange-rate it will sell for £189.

Unfortunately the ETA has slipped, we are now expecting the Atik OAG to arrive sometime in April. Reading between the lines we think Atik have been rather overwhelmed with demand for the new Atik 383L+ camera so are concentrating their manufacturing efforts there.

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I see the 190MN scope is mentioned on this thread also.

I had a Celestron Radial guider (approx 27mm thickness) left over from when I had an SCT, and tried it in my Skywatcher 190MN to test the back-focus.

There *was* good enough back-focus for the imaging camera, but the problem was that the guide-cam / guide-eyepiece holder from the traditional (eyepiece-based OAGs) stick out far too much off the side, and the guide cam sensor cannot move close enough to the prism to achieve focus on the guidecam. If I could get the guide sensor closer inwards then I think I can get a fairly off-axis sharp guide star with the 190MN.

Since the ATIK and TS units are (a) even shorter, and (;) don't have the annoyingly long guide holder on the side, they should be great for the 190MN scope.

At present I'm using the ADM dual mounting bars on my EQ6, with an Equinox-80 on one side and the 190MN on the other. But I'm getting some image shift/flexure caused by the annoying mounting shoe in the Equinox-80. I'm definately going to be experimenting with newer OAGs with the 190MN.

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