OAG- Lacerta Skyfoto (latest version) opinions please

[appalachik]

Folks, I've been struggling to come up with a cost-effective guiding option to use with my C6-SGT XLT.

I tried the Baader Vario Finder mounted on my OTA with it's dedicated collimateable rings and a borrowed QHY5 but the Baader's floppy drawtube focusing was rubbish, so it was returned.

Side-by side scopes requires a heck of a spend just on bracketry (Looks like £250 or so in bits of aluminium), plus an ST80 and a QHY5 or similar... and I still might have mirror-related problems that can't be easily solved.

I'm hoping that somebody here has experience of the Lacerta Skyfoto, which I can couple to my Rebel T1i and a suitable (yet-to-be-bought) guider such as QHY5.

I realise all the possible imaging routes have pros and cons, and I am wary of OAGs having heard plenty of woes from others here, but I'm looking at this as the "lesser of two evils", keeping my setup pretty lightweight even if it might be a bit fiddly getting onto a guide object.

Please can somebody steer me onto the right course?

Jenna

[appalachik]

Looks like I might be on my own with this question but you never know...

In principal, is there a clear cut way to go with guiding an SCT? Side-by-side mounted scopes or off-axis guider? It seems that Side-by-side only wins if I also buy an SCT fit dual speed Crayford so I can take possible mirror flop out of the equation, further adding to the cost ( and setup weight) of that approach - and times is hard

I guess I'm hoping that somebody can point me towards a tried and true off-axis guider / guidecam solution that will work efficiently with my CG5 GT mount to give good results whilst not loading too much weight onto my mount.

Decisions decisions...

Jenna

[SlipperySquid]

What about a Finder guider? Might not be the answer if you are imaging at really slow scopes though? But would be the cheapest option if you already have a guidecam?

Just a thought.

Matt.

[cgarry]

Looks like I might be on my own with this question but you never know...

In principal, is there a clear cut way to go with guiding an SCT? Side-by-side mounted scopes or off-axis guider? It seems that Side-by-side only wins if I also buy an SCT fit dual speed Crayford so I can take possible mirror flop out of the equation, further adding to the cost ( and setup weight) of that approach - and times is hard

I guess I'm hoping that somebody can point me towards a tried and true off-axis guider / guidecam solution that will work efficiently with my CG5 GT mount to give good results whilst not loading too much weight onto my mount.

Decisions decisions...

Jenna

A Crayford will take mirror shift (mirror movement whilst focusing) out of the equation but will do nothing for mirror flop (mirror movement due to scope movement). I doubt mirror flop would actually be that much of a problem with a C6-SGT XLT, but it is the one that causes problems for guiding if a separate guide scope is used.

I would recommend using an OAG with an SCT, I use the Brightstar Astro Off Axis Guider with my C9.25:

Accessories @ Modern Astronomy

You will of course need a f/6.3 focal reducer to bring the focal ration down for imaging.

Cheers,

Chris

[appalachik]

I tried the finder-guider route with Baader's Vario Finder Matt. Considering the price, I wasn't impressed with it at all. The drawtube focuser was very awkward to use and a sloppy fit in the tube.

Actually Chris, I did mean "mirror shift" as opposed to "mirror flop" - such is the confused state of my mind trying to get my head around all the imaging options

Also, I'm considering which focal reducer to buy as part of this process and even that decision isn't clear-cut... Apart from Celestron and Meade, there are a couple of generic options available but I'm leaning towards the TS 0.8 SC Corrector, into a 2" dual speed SC Crayford and then the OAG... of which the Lacerta Skyfoto is designed specifically to work with Canon DSLRs, so my modded Rebel T1i will go on the back. Guiding via QHY5.

I hadn't considered the Brightstar because I thought it wasn't recommended for use with reflectors... is this wrong?

Jenna

[cgarry]

I agree that there are so many imaging options that it can be more than a little confusing.

I hadn't considered the Brightstar because I thought it wasn't recommended for use with reflectors... is this wrong?

There can be an issue with Newtonian reflectors with limited back focus. This means chip of the camera has to be very close to the telescope and there is not physically enough room to fit a wider OAG in, such as the BS. However, this is not generally a problem with SCTs as they tend to have a large back focus because of the moving primary mirror. Actually, the distance that matters in this set up will be the distance from the focal reducer to the camera chip. For the f/6.3 reducers this distance is 105mm if my memory serves me correct. In this 105mm you will need to fit in your OAG and any filters you want to use.

As for the question of which focal reducer to choose then you need to be careful that you get enough reduction. The TS 0.8 SC you mention will give you a focal ratio of f/8, which is very slow for imaging and will require long subs, especially if you are using a modded DSLR rather than a CCD. As mentioned earlier you need to make sure the distance required by your chosen reducer to the camera chip is large enough.

I spoke to Bern at Modern Astronomy when I was buying my setup and he gave fantastic advice as to which were my best options.

I am not familiar with the Lacerta Skyfoto, but it does look like many of the good quality, thin OAGs available. Generally being too thin will never be a problem as you can always insert spacers in the path to achieve the correct distance from reducer to camera chip. And thinking about it, having a thin OAG does give some future proofing should you change your imaging scope in the future.

Cheers,

Chris

[appalachik]

Thanks for the steer Chris...

I've spoken with Bernard this morning and I'm already feeling far more confident about this subject.

He seems like an easy guy to do business with.

Jenna