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Old 25-04-2014, 08:03 PM
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rcheshire (Rowland)
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Stand alone guiding widefield setup - guide scope FL question

I'm having a look at standalone guiding for my wide field setup. I'll connect the guider outputs to the mount hand controller port (no guide port) - little bit of adaptation required.

What size lens (guide scope) should I use? I see others using ED80s, which is considerably bigger than my imaging setup. I have a 130mm prime lens with an M42 connector, that I can press into service as a guide scope? I understand that the guide scope will influence limiting magnitudes - no experience and seeking advice.

Looking at these for now? Decided not to pursue the SynGuider.

LVI PDF

MGEN

Last edited by rcheshire; 25-04-2014 at 08:15 PM.
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Old 25-04-2014, 09:34 PM
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DavidTrap (David)
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I'm thinking about something similar Rowland.

What mount and imaging lens/scopes are you using?

My understanding is a SSAG/QHY5 attached to a finder-scope (e.g. 9x50) will successfully guide an imaging camera attached to 1000+mm focal length scope. This is when the guider is attached to a computer and doing sub-pixel guiding. Provided the box of tricks attached to the guiders you linked to do the same, I would expect similar results.

DT
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Old 26-04-2014, 03:16 AM
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rcheshire (Rowland)
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David. Mount is a Takahashi EM-200B (1997). It is very accurate unguided, +/-5 arc seconds PtoP, built for manual hand controller guiding. There was a guiding mod for these, which is no longer made. I don't think it's necessary.

No laptop interface, with either of these guiders, which is ideal for my purposes.

Imaging rig is a cooled 1000D and various lenses, principally a Canon 200mm prime and more recently a Nikon f1.8G 85 mm. I bought a 130mm Auto Micronar from an ISS member with the intention of filling the 85mm -200mm gap. It might just make a guide scope - $40.
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Old 26-04-2014, 04:02 AM
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I found this image taken with a C9.25 and guided with the Mgen on a 9x60 finder.

I think the Mgen is an impressive piece on gear! Good idea avoiding the Synguider, it's a piece on rubbish, I figure I have waisted over 50 hours imaging time trying to get it working.

Jo
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Old 26-04-2014, 07:12 AM
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DavidTrap (David)
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Looks like they'll do fine at those focal lengths.

I will ask the question though, with such a great mount, do you need guiding for widefields???

DT
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Old 26-04-2014, 10:47 AM
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I've asked the same, David. Longer exposures, mainly. Under consideration....

agreed Jo - looks good.
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Old 26-04-2014, 01:46 PM
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I'm wondering whether it's worth the effort - I would need to add a modified dual axis drive to my mount, and an Autoguider, so it's not an insignificant cost. I've used a fairly simple technique for polar aligning my EQ3 for widefield work, with pretty good results. I'm hoping to do some stuff around 350mm, so autoguiding might be appropriate.

Basically, using a longish (200mm) lens, you take a 30 second photo pointing at a bright star near the zenith. For the first 15 seconds you slew one way at ~8x siderial rate (this is what the single axis drive on my mount does) and then slew back the other way for the final 15 seconds of the exposure. This produces a V shaped star trail. You then adjust the azimuth of the mount and repeat. If the V gets wider, you went the wrong way. When you have a straight line, you can swing out towards the horizon and adjust the altitude in a similar fashion. Probably best to repeat for both adjustments again before declaring it "polar aligned".

DT

Last edited by DavidTrap; 26-04-2014 at 01:47 PM. Reason: Added a bit
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Old 26-04-2014, 02:04 PM
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Quote:
Originally Posted by rcheshire View Post
I've asked the same, David. Longer exposures, mainly. Under consideration....

agreed Jo - looks good.
I was getting perfectly round stars last night with the 85mm lens doing 10 minute subs, I'm sure with a carefull PA I could go 15-20 minutes easily.
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Old 26-04-2014, 02:26 PM
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MrB (Simon)
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Quote:
Originally Posted by rcheshire View Post
I see others using ED80s, which is considerably bigger than my imaging setup.
I use an ST80 with my LVI SG2.
The LVI's aren't the most sensitive cam around so the aperture and f5 ratio helps a lot.
The ST80 is light, very light, much lighter than an ED80 and much cheaper too.
I use it on my Astrotrac and a side-by-side plate with either my SV70 achro or a manfrotto ball head with DSLR+lens on the other side.
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Old 28-04-2014, 08:09 AM
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ZeroID (Brent)
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Quote:
Originally Posted by DavidTrap View Post
I'm wondering whether it's worth the effort - I would need to add a modified dual axis drive to my mount, and an Autoguider, so it's not an insignificant cost. I've used a fairly simple technique for polar aligning my EQ3 for widefield work, with pretty good results. I'm hoping to do some stuff around 350mm, so autoguiding might be appropriate.

Basically, using a longish (200mm) lens, you take a 30 second photo pointing at a bright star near the zenith. For the first 15 seconds you slew one way at ~8x siderial rate (this is what the single axis drive on my mount does) and then slew back the other way for the final 15 seconds of the exposure. This produces a V shaped star trail. You then adjust the azimuth of the mount and repeat. If the V gets wider, you went the wrong way. When you have a straight line, you can swing out towards the horizon and adjust the altitude in a similar fashion. Probably best to repeat for both adjustments again before declaring it "polar aligned".

DT
That works surprisingly well and is quite quick to implement. I set up my mount initially after the first solar\declinometer adjustments and then refined it using this method.
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Old 28-04-2014, 08:26 PM
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I think it is simple enough with my setup - just pushing the axii around with a simulated handcontoller. It was designed that way.
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Old 28-04-2014, 09:21 PM
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rmuhlack (Richard)
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Hi Rowland - I have recently been using a 200mm focal length f4 Nikkor prime lens as a guide scope with my small newt (130mm aperture f5). Albeit I was using a QHY5LII for a guide cam rather than a stand alone guider (which may not really be relevant anyway), but nevertheless I have found it to be a winning combo. As you are aware I have also used a 500mm f8 mirror lens as a guide scope with my VC200L and that also works well.

I guess the take home here is that if your relative image scales are even closer than the above (because the guide lens is similar to the imaging lens) you should be fine i would think.

cheers, R
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Old 30-04-2014, 05:56 AM
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rcheshire (Rowland)
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Thanks Richard. That makes sense.

I found this interesting.

http://www.wilmslowastro.com/tips/autoguiding.htm
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