Offaxis guiders opinions?

[gregbradley]

My Astrodon MMOAG has been a very workable guiding solution but its quite thick so sometimes it won't fit in the available backfocus. For example when using a reducer.

There are a few thin OAGs out there mostly Teleskop Services. Anyone used one of their OAGs? I am thinking of the larger one.

Anyone used the Hutech ones? Or the ONAG?

I can see the reason for the STXL guider built into the filter wheel or the QSI built in filter wheel and OAG. OAGs are a pain and are fine if you stick to one setup. But change around like I do and it can be a mess of adapters.

Any others?

Greg.

[Terry B]

?On axis guiding?

[strongmanmike]

You need to be more adaptable Greg :P

[Merlin66]

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p5190%26nbsp%3BTS-2--Flip-Mirror-System---Off-Axis-Guider---short-design.html
What about this??
Only needs 35.5mm
I have an ol' Chinese slide mirror version and find it very handy to be able to position the pick off mirror to suit the chip size...

[PRejto]

Hi Greg,

I doubt the ONAG could work for you as it takes up a min of 66mm BF (from memory).

You might consider the SX solutions if using your Trius:

http://www.sxccd.com/the-sx-mini-wheel-oag

http://www.sxccd.com/sx-usb-filter-wheel

Peter

[gregbradley]

The SX filter wheel is an option but a more expensive and less flexible option (I have 2 FLI cameras and at the moment all 3 cameras use the FLI filter wheel). It would also require a new set of filters and extra adapters to fit but yes the mini would work the USB perhaps with a thinner Planewave adapter. The advantage is I could get 36mm 3nm Ha and O111 later for half the price of 50mm square filters.

The 35.5mm TS unit would be too thick as I have about 19mm available for an OAG. The 9mm plus adapters may just make it but its close as to whether it would come to focus.

The ONAG from Foresight Innovations seems interesting especially with their new autofocuser but 66mm and too small an opening for a 16803 chip.

At this stage it seems between a 9mm TS OAG or the SX filter wheels.

Being such a critical piece of gear its surprising how few decent OAGs there are on the market.


Greg.

[gregbradley]

http://www.innovationsforesight.com/products.htm

Its supposed to be less susceptible to seeing as it guides in the NIR rather than the entire spectrum as with OAG. But it has the camera come out the side like a Newt and I wonder if that could cause balance issues. It also requires 66mm. I wonder why its so large?

Greg.

[PRejto]

Greg,

I think it's "large" because the mirror clearly must reflect the entire light cone and the mirror has to be positioned at 45 degrees. I think it is about as small as it can be when you add enough thickness to the box to account for rigid tube fittings.

Did you notice that there is also a large model ONAG now? (ONAGXT)

http://www.innovationsforesight.com/ONAGXTChipIllumination.htm

Peter

[gregbradley]

It looks interesting. I wonder how it would compare to a MMOAG and an AO unit - I suspect not as good.

Greg.

[alistairsam]

Hi

The Atik filter wheel is amongst the thinnest I've seen.
I use the SX wheel with 7x36mm filters and the TS9OAG.
I love the TS9 for the plethora of adaptors that they have for it.
I got the 48mm version on both sides as the load would be spread a bit more on the SX than the T2.
The SX wheel also has almost all the adaptors you can think of.

Cheers
Alistair

[gregbradley]

Thanks for that. I read a few posts about the TS9 that seemed a bit cool towards it. Any flex? The Lacerta one got a good review.

Greg.

[alistairsam]

Hi

I havent noticed any flexure with it. You do need to tighten the guidecam screws well. Other than that no issues.
Holds the wheel and camera as in the pic quite well.

The atik wheel below is a bit pricey but is only 22mm and takes 7 filters. The sx mini has a max of 5.
Sx usb is 27mm. Point to note with these is that the adaptors are 2mm.


http://www.teleskop-express.de/shop/product_info.php/info/p4355_ATIK-2--mot--filter-wheel---USB---for-7x-36mm-unmounted-filters.html

Cheers
Alistair

[gregbradley]

Is that a TS9 with the SBIG camera and Atik filter wheel?

Seems very slim.

Greg.

[alistairsam]

Nope its the sx usb with 7 x36 wheel, stf, ts9 and an mpcc.

Sx is 27mm or 29 with the adaptors on both sides. I'll check.
Ts9 around 10 with the lip on the scope side.

I'll find a better pic

[gregbradley]

Does the SX filter wheel take 50mm filters in that 36mm carousel?
I am not sure how they are mounted and though maybe they might.

Greg.

[alistairsam]

I doubt if thats even possible, but they do have a 5x50mm carousel. so best to use that.
http://www.sxccd.com/sx-usb-filter-wheel

the unmounted filters basically sit in the recess, and there is a plastic screw with a washer that holds it down as you may be able to make out in that page.

TS oag and wheel
https://www.dropbox.com/s/1qtdka4ko5ndwc7/2013-10-09%2023.09.06.jpg

this is the with filters mounted
https://www.dropbox.com/s/k380j8lpml7mi8h/2013-10-10%2001.12.18.jpg

https://www.dropbox.com/s/whasow58nyudxzj/2013-10-10%2001.13.22.jpg
https://www.dropbox.com/s/7hzg1f155ypgni5/2013-10-10%2001.17.49.jpg

What is the max backfocus you're looking for? is this for your CDK?

have you checked if the SX FW and SX OAG suit?

the SX FW and OAG add up to 42mm as per their diagram
http://www.sxccd.com/sx-usb-filter-wheel

the SX FW and TS9OAG add up to 25+4+9+1
39mm

so its not too different mainly due to the 4mm taken up by the scope side T2 or M48 adaptor. they remove this and fix the OAG directly to the FW face which you can't do with other OAG's.

http://www.pbase.com/strongmanmike2002/image/151108788


Cheers
Alistair

[gregbradley]

Thanks very much for the photos and links. Yes this is for the CDK and reducer. Without the reducer there is plenty of backfocus - about 250mm.

The reducer works at various distances with ideal at 45mm and OK up to about 60. I am currently at around 45mm but its guide scope guided. The chip is 17mm in the SX camera, the FLI filter wheel is 19.9mm thick, the adapters on the reducer add about 6.5mm, the adapter on the filter wheel only adds a few mm.

I ordered the mini usb with OAG specifically to get closer to the 45mm. So its 17 to the chip it the camera, around 28mm for the filter wheel +some adapters, maybe 10mm so I would be at 55mm or less if I can get the adapters thin enough. So the FLI CFW and TS9 sounds like about 28mm + adapters. Very similar but does not require a whole new set of filters!

Perhap I should order one and see if I can use it. What adapters did you use for your TS9 to attach it? The FLI filter has about a 76mm opening.

Greg.

[Tandum]

http://www.teleskop-express.de/shop/product_info.php/info/p2751_TS-Giant-Off-Axis-Guider---50mm-clear-aperture---length-10mm---very-stable.html

Greg,
Ring the teleskop shop. This is the OAG I got for a 3" korr reducer but I rang them about connecting a qhy guider to it and they came up with the goods. The oag is 10mm thick. Yes they speak english.
robin.

[gregbradley]

Thansk Robin I will. One concern is the prism able to be lowered enough to catch the light from a 42/48mm adapter as the TS9 is I think more open than that?

My MMOAG prism would not go down but its got a much larger opening - about 85mm or so.

Greg.

[Paul Haese]

Just something I am wondering is why use the reducer? Why not use a larger format camera at native focal length with an OAG, filter wheel and camera? You can always crop and you get rid of the problem you have now.

[gregbradley]

I do use my large format camera with the reducer as well. F4.45 and 17 inches gives faster images. I want the scope to be versatile. An OAG or a self guided camera is a necessity these days at the minimum for best images.

Cropping does not seem to emulate the above.

Greg.

[ericwbenson]

Perhaps Paul meant binning. Cropping would be used to get rid of off-axis aberrations, for the CDK they are low and the reducer would most likely make them worse (but further out in an absolute FOV way). Binning or resizing the image accomplishes the same as the reducer EXCEPT for the smaller FOV. You get the same shorter subs out of the reducer and binning, and of course in both case you don't get more signal per unit time. So again, what is the reducer for...FOV, is this what you are after?
EB

[Paul Haese]

I was thinking that if you crop you could produce a similar field of view. That being with the larger format at native f ratio and the smaller format with reducer. Surely an AO with the larger format camera would produce exceptional results, instead of having to go down this path with the smaller format camera????

What are the sampling rates for both systems?

I had not considered binning either, just cropping.

[gregbradley]

You bring up interesting points. Perhaps it is indeed better to AO the larger camera and crop the result if I want that. I certainly intend to do more imaging with the larger chip. I also intend to take my CDK to my dark site at some point to get access to better skies/seeing for it.

I intend to do both. An AO unit is on my wishlist.

The Trius though works quite well in that its 77% QE and 66% QE in Ha and about 60% in O111 with half the read noise of the Kodak chips.

The reducer gives it a wider FOV otherwise I found in some images it was too close up and that is not always a good look.

Binning the Trius also works well as they are half the size pixels of the 9 micron Kodaks and binning gives a similar look to the Kodaks but at several times the signal to noise ratio. So its a fast road to China.

As far as the CDK goes I don't see any aberrations out wide, its perfectly corrected. So no problem there with the large camera. The smaller camera is less susceptible to gradients, in fact I haven't had any trouble with gradients. Gradients are an issue with the large camera and I have to process them.

The Trius seems to be an excellent narrowband camera with the option of binning available for even a faster boost to data acquisition.
Its not without its faults but I see now FLI and QSI offer models using this chip. Also Wolfgang Promper is now displaying some Namibia images using a FLI MIcroline 694 camera that are quite nice.

I find the camera a bit hit and miss on my large refractor. Perhaps the small one it may be better. I get some bad haloing on bright stars on the TEC180. I don't with other cameras. I am wondering if it needs a bit more UV/IR block on that scope as it may be more sensitive to UV/IR than the other cameras.

Greg.

[SpaceNoob]

If only these sony sensors were just a bit bigger....

[gregbradley]

Yes that is true. They are a bit small.

A full frame one would be amazing.

Greg.