Advice on OTA and guidescope

[MarkyD]

Hi

Haven't been about much on the astronomy front as had other projects but....   I have just acquired an NEQ6 and thanks to a refund from the tax man I'm looking at getting an OTA to make the mount complete   My aim is astrophotography and I have been looking at the Skywatcher 200P-DS and the 250P-DS.  Does the 250 warrant the extra ££.  I will also have my Celestron 102SLT which I am hoping to use as a guidescope - is this feasible or shall I sell it with the Nexstar mount as a package and get a different scope to use?  I have a QHYII5L camera which I could use as the guide camera or maybe as the camera for the OTA with just using the tracking on the mount.  I have a Canon 1D MkIII so I could use that if the tube will take the weight and also just use the camera with the 100-400mm lens on a dovetail with a Manrotto RC2 release plate for prime photography and the 16mm for milky way etc.

My future outlook is to have all this outside with me sat in front of the PC to control the guiding, focusing, dew control, capture etc.

So to sum up my main question is do I opt for the 200 or the 250 with the 102SLT as a guidescope?

Thanks

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Mark

[Tinker1947]

I use a 250P-DS plus St-80 guide scope on a NEQ6, it works and guided sub of 20 minutes have round stars...

[brantuk]

Go for the 200PDS - the 250 is too big for the NEQ6 really. I've used that combo in the past and it's just not stable enough for imaging. Observing was frustrating enough - it's a huge sail in even the lightest breeze and it takes way too long to damp down the vibrations (even on a still night). For problem free imaging the smaller 200PDS is way better - unless you're operating from an obsy - that might be a totally different story. Hth

[DaveS]

First thing to buy is this:

http://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

If you don't already have it. Read it at least twice before even thinking of spending money on kit.

I will, though, suggest that you look at a short, fast apo 'frac as an imaging 'scope. Your QHY5 II will work very well as a guide 'scope, but would hesitate before using a Canon 1D for imaging, as you'll be trying to fill a full-frame sensor which will need a serious 'scope. It'll also be very insensitive to the hydrogen alpha wavelength that is pretty much vital for DSO imaging.You could I suppose take the 102 mm 'frac off its mount but that might be a bit of a waste, I'd be inclined to sell it to fund the rest of the rig. The Skywatcher ST 80 is pretty much ubiquitous as a guide 'scope for the very good reason that it just, plain, WORKS, especially when paired with the QHY5, and that's something of a rarity in AP.

I don't know what your budget is, but for a camera I'd go for a mon CCD, or if that's a bit steep, an astro-modded Canon DSLR.

[nightfisher]

For imaging the 130p ds has to be better

[DaveS]

Agreed, though if you don't like diffraction spikes.... (I don't, I merely put up with them). You'll probably need another balance weight for the 130 OTA to get it to balance with a camera, and a coma corrector.

One of these perhaps:

http://www.firstlightoptics.com/counterweights/baader-dovetail-bar-levelling-counterweight.html

And take your pick from one of these:

http://www.firstlightoptics.com/coma-correctors.html

[ollypenrice]

There is no need to chase aperture in amateur DS imaging. The increase in optical resolution of the 10 inch over the 8 inch will not be a determining factor in the final resolution of your images. Of far more importance will be guiding accuracy, seeing and focal length.

I would not, personally, put a 10 inch Newt on an NEQ6 for DS imaging because I think that to get it to work to its capability would be difficult, though perfectly possible. If you are new to this I really believe the word you should be looking for is 'easier.' Being over mounted is easier. Working at coarser pixel scales (by having a shorter focal length for a given camera) is easier. It's hard enough as it is. (Disclaimer: I'm an imaging provider by trade and so I live in a world where the golden rule is, 'It has to work. Not tomorrow night or after an hour's adjustment but right now.'    As anyone on here will tell you, that's asking a lot so I go for systems most likely to deiver reliability. You might be more adventurous!

The 250 would give you 1.24 arcsecs per pixel. This is not unreasonably fine but would require a guide error of up to about 0.6 arcsecs. That's also possible but it's at the sharp end!

The 200 would give you 1.49 which is easier and the mount is not working so hard.

The 130 would give you 2.29 which would be very comfortable for starters.

Then there's focal length. What do you want to image? Although I have it available I do find, like Sara, that a metre or so is a bit 'in between,' being too short for galaxies (other then the three big ones) and too long for many classic nebulae. (Now that I have a full format chip for the 1 metre FL I do get more out of it, however.)

All of these Newts could work for you but which should you go for first? It's that word 'easy...'

Do read Steve's book before anythng else. This game is so counter-intuitive. The fact that you can do great imaging from small apertures is one example.

Enjoy the adventure.

Olly

[MarkyD]

Thanks all for the replies.  The book is definitely on the list.  Pity it isn't available in pdf or e-book so I can read it over the weekend   It will give me a better idea

Thanks

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Mark