Auto guider questions - ST-i kit

[lazjen]

In this thread (http://www.iceinspace.com.au/forum/showthread.php?p=979261) I was given advice to sort out auto guiding. So, I've been doing some reading/researching into options.

I noticed that some of the guide cameras can be used as planetary cams as well, so I'd like to take advantage of that.

I found this kit: Guiding Kit Complete with ST-i (https://www.sbig.com/products/cameras/specialty/st-i/guiding-kit-complete-with-st-i/) that looks to me to be a solution I could use.

Does anyone use the ST-i this way? As in with the kit's 100mm lens? Is it likely to work effectively for my gear and location (semi light polluted)?

[LAW]

Check out this thread >>> http://www.iceinspace.com.au/forum/showthread.php?p=976559#post976559

It seems the SSAG/QHY5 are 'good', the ST-i is 'better', and the Lodestar is 'best'. During my testing with the SSAG Ihaven't had trouble finding a star but I haven't had time for a fully guided imaging session yet.

[Terry B]

I would disagree with this. I put the lodestar and the STi as equal. Similar price and similar sensitivity. Minor Plusses and munuses with both.
I haven't used the St-i guiding kit but it seems to be popular. I just prefer to use a bigger guide scope. Most of the guiders can be used for planetary imaging as well but are not terribly easy to configure with colour filters etc.The colour guiders are not as sensitive so you lose out as a guider if you chose to purchace a colour camera.
The reality is that guiders are very good as guiders but are a compromise as planetary cameras. Still can be good but probably not as good as dedicated planetary cameras.

[lazjen]

Thanks for the replies.

How much sensitivity loss are we talking about here for colour vs mono? Or to turn the question around, under what conditions would it be more likely to fail for colour than mono? I also now wonder whether the kit I linked includes the colour version or mono...

Also, I have been following that Auto guider thread, but didn't want to derail it with my specific questions.

I'm not overly concerned about the planetary camera aspect at this time, so the compromise is not a problem for me. At least I'll be able to use it for learning purposes anyway.

[lazjen]

More questions.

If I were to get the ST-i (no kit) and teamed it up with an Orion Guide Scope (ST80)...

...would this be a reasonable thing to do?

...and what would I need to mount this on my RC10?

[Jon]

Hi Chris,

My guess would be it would be a very reasonable thing to do.

In terms of mounting it on your RC10, does your dope already have an extra dovetail bar? I.e. identical to the one you use to mount your scope on the G11, but on the other side of the tube?

If so, you just need these: http://www.bintel.com.au/Accessories/Rings/Losmandy-DVR108-Guide-Scope-Rings/618/productview.aspx

You can get rings cheaper, but you'd need an adapter as well and the losmandy rings are excellent. With long focal lengths, the rigidity of the mount is vital.

[lazjen]

Jon, thanks indeed, that's exactly what I need. The scope does have the extra dovetail bar, but I wasn't sure of what the connecting bit(s) would be for it.

[naskies]

If you're already considering a Lodestar/ST-i, how about an off-axis guider too? It will make guiding easier at the RC10's focal length. I have an ST-i and Lodestar, and have no troubles finding a guide star anywhere in the sky using 0.5 sec exposures with an OAG on my RC8.

I'd recommend thinking carefully about throwing an ST80 on top of the RC10... you may run into flex issues.

For what it's worth, I find my Lodestar more sensitive (I use 0.05 - 0.1 sec exposures for adaptive optics) but the ST-i's built-in shutter is an awesome feature. Some guiding software, such as MaximDL, is ridiculously over-sensitive to hot/warm pixels and so automatically re-taking dark frames every time you start guiding is fantastic. (I normally use my Lodestar, which works fine with a dark library - it's just a bit of a pain to reshoot the darks occasionally.)

[lazjen]

One of the reasons I'd like to go ST-i is because of the built-in shutter. Other than that, I have seen no definitive agreement that either one (Lodestar, ST-i) is better than the other - and I certainly do not have the skills currently to be able to say so either!

I will look into off-axis guiding before I proceed further. Thanks for the info.

[Merlin66]

As mentioned I use the Lodestar (with PHD) for beamsplitter guiding the C11 @ f10.
I find taking a guide dark (in PHD) during the initial set-up to be painless and effective.

[lazjen]

Ok, I've done some reading and can see the advantages of OAG. However I have to consider focus distances and vignetting more now if I understand things correctly.

Currently, from the back of the scope, I have a 50mm spacer, the focuser, then the 40mm diameter camera adapter, then finally the T ring to the camera. I was already concerned with the vignetting I was getting, so I had ordered the True-2 adapter (with a clear filter) from telescopeadapters.com to help with that. That's currently on its way to me. However I suspect the OAG replaces (some of) these bits?

I now need to work out a solution for these requirements:

* OAG that limits vignetting
* OAG that works with/without Focal Reducer (do I need a FF when no FR is in use?)
* Working out how to get my 2" 0.5 FR to focus

It's a bit of a puzzle to put together. Any ideas on possible OAGs that I should consider (going with the ST-i)?

[naskies]

Re vignetting: many people use a 35 mm sensor with the RC10, so your scope is fine. The likely culprits would be either your focal reducer doesn't provide a large enough illuminated image circle (a 2" nosepiece barely illuminates a full 35 mm sensor; I think a 0.5x 2" reducer would vignette severely?) or your T-ring/nosepiece adapters are too small (many scopes use M48 attachments for larger sensors, instead of the standard M42 size).

As for OAGs, there are many brands available on the market. However, if you want to use one with a reducer/flattener then you'll probably need to minimise the amount of back focus between the reducer and your camera. Here's one that's very low profile and can be used with full-frame DSLRs:

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p641_Off-Axis-Guider---nur-9mm-Baulaenge---T2-Anschluss---fuer-CCD.html

The corner stars will be horrible on your 6D without a flattener/reducer (there have been many posts by RC10 owners on here about it). Some people choose to crop out the corners - which reduces your field of view - and others use flatteners/reducers such as the Astro-Physics AP27TVPH which are designed for larger chips.

[lazjen]

I currently use no flattener or reducer. I'm certain it's the adapter that's causing the grief (I guess it's M42), so as I mentioned previously, I'm getting the larger True 2 adapter, which I'm guessing will be the M48 you mention. While I've got a 0.5 x 2" reducer, the current adapter I've got doesn't provide suitable back focus distance, so it's impossible to bring it to focus.

And thanks for that link. I did see that one in my searching and wondered if it would be suitable. It might also mean I can get the FR working as well.

I'll probably also get a FF in the future (or if necessary a better FR) to sort out the corner stars, but for now I'd actually like to get some of the stars close to round...

[lazjen]

Ordered that Teleskop Service OAG, so now it's a wait until it's delivered. Plenty of cloud and rain around now anyway...

[lazjen]

Puzzle time...

Ok, I've got one of these: TSOAG9T2 OAG (http://www.teleskop-express.de/shop/product_info.php/language/en/info/p641_Off-Axis-Guider---only-9mm-length---with-T2-adaptation---Special-Offer.html).

I've also got one of these: True 2 Adapter (http://www.telescopeadapters.com/true2_eos.htm) as well as the usual T Ring/Adapter.

Plus the ST-i guide camera and a 2"? to 1.25" adapter that can hold the ST-i.

I'm trying to solve the problem of putting these things together and working out what's the missing components I need to buy.

I think for hooking up the guide camera, I need one of these: Baader Hyperion M48 / T2 converter (http://www.myastroshop.com.au/products/details.asp?id=MAS-026G2) to go from the OAG to the 1.25" adapter I've got. Correct?

Hooking up the camera is more challenging. If I use the T-Ring, I can connect it to the OAG, but the vignetting remains. I think to be able to use the True 2 Adapter, I'll need one of these: Adapter ring for equipment with M48 thread at the TS OAG 9 (http://www.teleskop-express.de/shop/product_info.php/info/p1650_Adapter-to-M48-thred-at-camera-end-of-the-TS-OAG-9.html), but I'm not sure. And even if it's correct, by using the True 2, the OAG is a significant distance in front of the camera. I assume this will make it more challenging to focus the guide camera?

Any thoughts or ideas?

[naskies]

The TSOAG9T2 appears to have a male T2 thread for the guide camera. The SBIG ST-i has a female 28mm (1.25" filter) thread. There are a few ways to get there:

1. T2 to M28 adapter. Something like this (http://www.teleskop-express.de/shop/product_info.php?products_id=4156) or this (http://www.ebay.com/itm/28mm-T-T2-Lens-Mount-Adapter-Stepping-Ring-/120720913281) should work - but you should double check with the sellers as I can't tell from the listings.

2. You could also use a T2 to C-mount adapter (http://www.teleskop-express.de/shop/product_info.php/info/p2838_Adaptor-T2-female-on-C-Mount-male---only-4mm-length.html) combined with a C-mount to 28mm adapter (https://www.sbig.com/products/accessories/c-mount-lens-adapter/) to attach your ST-i.

Note that you may potentially need a spacer for either your main camera (M48 mount) or your guide camera (T2 mount) depending upon how far away the respective focal planes are.

By imaging camera, I assume you mean your Canon 6D? It sounds like you just need an M48 -> Canon EOS adapter (http://www.teleskop-express.de/shop/product_info.php/info/p3631_TS-Optics-T-Ring-from-M48-Filterthread-to-Canon-EOS-Bajonet.html).

[lazjen]

Yes, that's correct.



It's the calculating the spacing/focal distance required that's doing my head in a bit.

Wrt the guide camera, it was the issue of the spacing that made me cosider the M48/T2 adaptor, plus the existing 2"/1.25" adapter I've got - I can move the camera up/down in this adapter to find the sweet spot for focus. I did read that some people need spacers or 1.25" extension tubes to get focus on their guide cameras.



Yes, it's for the 6D. The pics of the OAG on the link I had in my previous post, don't show the removable connector that's on the camera side. This link (http://www.teleskop-express.de/shop/product_info.php/info/p4101_TS-Coma-Corrector---Off-Axis-Guider-for-Newtonian-Telescopes.html) shows a different view of the connector (it's the widget on the right, of course). The upper part is inserted into the OAG and is held by the 3 pins around the outside. The connector I've got fits the smaller T Ring for the 6D, but I'd like to use the True 2.

I did some "desktop" fiddling (no chance to setup with scope recently thanks to weather) with the setup connected as so: camera -> true 2 -> hand held OAG near/against True 2 -> FR and this got very close to focusing - I may need another very small spacer, but it looked achievable. I hope this is a valid test and I haven't messed up my understanding/assumptions.

As I sort this out, I can see I've got another problem looming as well. The connection of this part of the imaging train to the focuser. It's a stock focuser and it has no threading on the camera side, so I can see I'll either have to get a tube to slot in, or do the focuser upgrade I'm fully expecting to have to do sometime...

[naskies]

The OAG lets you adjust the focus distance by a small amount, which you tweak with a focusing mask on a bright star.

As for figuring out the focus distance, get your 6D attached to the OAG first. Once you've done that, use a pair of callipers/ruler and measure the distance from the centre of the pick-off mirror to where the camera sits flush to the EOS bayonet and add 44 mm (EOS mount to chip distance). Next, measure out that same distance from the OAG mirror and up the guider mount - this will show you what distance (possibly spacers) you'll need.

I'd recommend attaching the DSLR, OAG, and focus all as close to each other as possible - if you add in long distances such as with the TRUE 2 adapter, you'll substantially increase the moment arm on the stock focuser. It's better to use the beefy extension rings on the telescope side of the focuser to minimise your focuser-to-camera distance.

Good luck!

[lazjen]

Thanks again Dave for the useful reply.



I've resigned myself to going the path you suggest, because deep-down I realise it makes the most sense. :) I was just trying to avoid it to re-use what I already had.

I'll put the True 2 adapter aside and just use it for non guided shooting, e.g. the moon.

So, I think for the Camera to OAG, I need the bit you suggested: EOS to M48 (http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3631_TS-Optics-T-Ring-from-M48-Filterthread-to-Canon-EOS-Bajonet.html), plus the other bit I mentioned: M48 Adapter (http://www.teleskop-express.de/shop/product_info.php/language/en/info/p1650_Adapter-to-M48-thred-at-camera-end-of-the-TS-OAG-9.html). That should allow the maximum amount of useable light through.

As I'll be doing a Teleskop Express order for the above, I'll probably get the T2 to M48 adapter you linked - I've sent off a question about it to confirm it's the correct bit required. Given the formula you specify, I'm almost 100% certain I'm going to need a spacer on the guide camera side. I've also asked for the width details of the EOS bayonet so I can attempt to calculate the spacer required.

Given the data on the OAG from TS's website:
-- Distance from prism center to sideward T2 terminal: 26mm ... 38mm
-- Distance from prism center to OAG front side: 6.7mm
-- Distance from prism center to camera terminal: 4.5mm

X = EOS bayonet width.
Y = Guide Camera adapter width (T2 to M48).

Then, using your formula, the camera side is 44 + X + 4.5, so X + 48.5.

The spacer is then = X + 48.5 - (26<->38) - Y; X-Y + (22.5<->10.5).

Although it's near impossible to tell from the photos, I suspect X and Y are going to be very similar values, only a few mm apart. Assuming everything so far is right and I've done the calculations correctly, something like this 17mm spacer (http://www.myastroshop.com.au/products/details.asp?id=MAS-005E) or 20 mm spacer (http://www.myastroshop.com.au/products/details.asp?id=MAS-005F) will be needed - but I can hold off until I get the TS items in hand before ordering the spacer.

The next piece is the connection from the OAG to the focuser. Assuming I keep my current stock focuser, I think I need one of these: https://www.teleskop-express.de/shop/product_info.php/info/p368_Verlaengerungshuelse---2--Filtergewinde---30mm-Laenge.html? If that's not quite correct, it's still going to be something that adapts from the threaded system on the camera side to the tube of the focuser. This to me does not seem ideal. :)

So, I've been looking into focusers now such that I can join the OAG to the focuser via a threaded system, no ring/tubes. The MoonLite 68mm system looks interesting (especially with all the extra toys to motorise/control it :) ). I'll do some searching around to see if anyone has hooked up a similar system for the RC10...

[naskies]

I think this is what you want (i.e. get it to the same configuration):

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p1188_Off-Axis-Guider---nur-9mm-Baulaenge---Direktanschluss---Canon-EOS---AKTION.html

You basically just need to get the equivalent adapter that goes from the OAG9 to the EOS bayonet - without using a T2 adapter.



If you're ordering from TS, the additional shipping might be negligible to just add in the spacer. Depending upon how it works out, you might be in one of three situations:

* no spacer needed - the differential focus adjustment of the OAG is enough to get it and the main camera to focus simultaneously,
* spacer needed for the OAG (T2), or
* spacer needed for the main camera (M48).



Doesn't the TSOAG9 come with a 2" nosepiece with M48 thread? I'm referring to the pictures under the "telescope side adaptation" section:

http://www.teleskop-express.de/shop/product_info.php/info/p641_Off-Axis-Guider---only-9mm-length---with-T2-adaptation---Special-Offer.html

But yes - something that can directly screw in, rather than using compression rings, will be better.

I saw you mention field flatteners on another thread... if you're planning on ordering from TS, it'd be worth looking at their flatteners. I've heard they work reasonably well on RC8s:

http://www.teleskop-express.de/shop/product_info.php/info/p1010_TS-Universal-2--Field-Flattener-for-Refractors-f-5-to-f-8---Flat-Field-for-Astroph.html

http://www.teleskop-express.de/shop/product_info.php/info/p2646_TS-Universal-BIG-field-flattener-for-refractors-from-f-5-to-f-9-for-full-size-sens.html

By the way, I'm using a 2" Moonlite SCT focuser with my RC8. If you think you might upgrade to a mono CCD with filter wheel etc in the future (i.e. something long and/or heavy), you may want to just get the 2.5" Large Format version from the outset since it costs about the same.

My 2" Moonlite works brilliantly with just my 5DmkII (1 kg), works acceptably well with CCD+FW+OAG (2 kg), and is woefully inadequate with my CCD+FW+OAG+AO (2.8 kg).

[lazjen]

Yes, indeed what you link is what I SHOULD have got, not the TSOAG9T2, so now I'm trying to correct the mistake by replacing the camera side adapter in the TSOAG9. I can't find a specific item on their site that is just the OAG EOS Bayonet (since I've got the OAG already). I'll have a good hunt around again though in case I missed it.

But it's not the end of the world - using the 2 items I mentioned previously sorts it out - I think. And it allows me to potentially connect other items in the future at M48.



Yes. I might do that depending on exchange rates and shipping.

I think I've found a better source for the M28 to T2 adapter: SR28T (http://www.telescopeadapters.com/index.htm?steprings.htm) <-- at least I've dealt with them before with no problems.



No, it doesn't. If you check near the end of the web page, it indicates what's in "Scope of Delivery". It's basically the OAG and the camera connection piece. All the other stuff is optional extras.



I was considering adding the FF to the order as well since the evidence was mounting that I was likely to need it. So I will.

I am building this system with an eye to possible mono CCD, etc in the future.

I'm looking at this MoonLite focuser: MoonLite CSL 2.5 inch Large Format Crayford SCT/RC Focusers (http://www.focuser.com/cgi-bin/dman.cgi?page=productdetail&plugin=dstore.cgi&product=CSL) with the RC10 flange, of course, 1.5" travel, with the 68mm thread. Then add the TSFlat2,5 that you linked above, plus an adapter to step it down to the OAG's M48 (still tracking this item down - EDIT: maybe this adapter (http://www.teleskop-express.de/shop/product_info.php/info/p5015_TS-Adapter-to-M48-inside-threat-for-the-MoonLite-2-5--NT-focuser.html) but it's not 100% clear). I'd be completely threaded all the way from the back of the scope to the camera then with the "thinnest" width being M48.

And if I get that focuser, I'll add the "High Resolution Stepper Motor with MoonLite Mini V2 Controller" to continue on my path to computer control of everything.

I think I'm getting closer to doing some orders.

[lazjen]

Just got details back from TS. I can get the adapter separate: EOS Adapter (http://www.teleskop-express.de/shop/product_info.php/language/en/info/p6262.html) - sweet. :)

[lazjen]

Lots of ordering just done (focuser, FF, FR and various adapters/spacers) and credit card abused badly. Now another wait for it all to arrive. Should give me time to sort out the software issues on my netbook, and, of course, time for the next lot of clouds to gather...

[lazjen]

As I wait for bits to arrive, I've been using the ST-i to guide while taking pics with the 6D via piggybacking on the scope. Most of the hassle has been with the stock focuser and getting it to keep close enough focus for the ST-i to work. However, once I reach the sweet spot, and assuming my alignment is adequate and the conditions are not pathetic, it works well (via PHD).