Getting into prime focus astrophotography - the basics

Hi all, I hope that you don't mind if all of these questions have been aked already, but I want to get into prime focus/deepsky astrophotography
with my Canon 300D. Now, you know i've done a lot of piggyback stuff - and I want to get in closer to my targets that I want to image, but tracking is a problem once you zoom in above a certain level. For example, I notice that I have some slight trailing of stars when even using an 85mm lens (that's 135mm full frame!), so I was considering buying the Canon ef 70-200mm f4 lens, and doing piggyback with that - but that's not gonna work! This would cost me Euro660!

I have most of that price put away, and have done a lot of reading on prime focus set-ups, so I thought i'd ask you guru guys!

What I have: Canon 300D----Canon T-Mount

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Celestron C8 SCT.

I know you need: Canon 300D---T-Ring----T-adapter

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C8 SCT.

I want to use a radial guider (for manual guiding) and an f6.3 focal reducer - is this practical? Will the radial guiderand f6.3 focal reducer fit together? My guiding would be done manually with a reticule (crosshair) eyepiece through the radial guider, I can't autoguide because of expense (no laptop, guidescope, software) and no motor on the declination axis of this scope.

So - Is this practical: Canon 300D----T-Ring----Radial Guider--focal reducer f6.3---C8???

Any help would be really appreciated
Thanks,
Keith..

Hi Keith and merry christmas

Its an interesting combination, and I can tell you that manual guiding does work but do keep in mind it requires ALOT of effort.
If by radial guider you mean this
www.telescopes.ca/telescopes/RENDER/5/2022/1051/11532.html
then I would be a small bit dubious about it.
This is basically an off-axis guider, the list below are the things to know about these guys.

1, the size of the prism is important, the bigger the better, the more chance of getting a star in the guider port, there is an inherently narrow field of view in the guider port.
2, the mirror cannot be TOO large that it casts an excessive shadow on a 35mm field of view, or whatever camera you are using, you can always crop it out anyway, so the wider the autoguider aperture the better,
some like the GEG cast no shadow.
3, it must be easy to rotate the guider without dismantling the system,
4, using a standard f6.3 FC on many autoguiders can lead to terrible star images in the offaxis port (so I read), but this might not be a serious problem.

The main issue with meade and celestron guiders like these is that the prism is so small that it can be very difficult to get a star in the offaxis fov, you'll see many such off-axis guiders in astromart for practically nothing, its almost impossible to give them away!!!

The following link is the reason I went for a GEG.
www.mapug-astronomy.net/ragreiner/OAG.html#Top

and this is a good one on general autoguiders and guidescopes
www.mapug-astronomy.net/AstroDesigns/MAP...ot2.htm#anchor157770

have fun.

Keith,

First of all you CAN autoguide at least in RA anyway. (assuming you have an autoguide input on your mount or are at least preparedto wire one in to your hand controller).

You can use a radial guider to autoguide too. Basically if you can see a guidestar through an eyepeice you can guide on it. If you polar align well enough dec corrections wont be nearly so important. All you need is a webcam a VERY low und PC/laptop. The laptop I use for autoguiding is an old IBM thinkpad P233Mhz. It works great and would probably cost you next to nothing. The software is free.

Dave is dead right manual guiding is a right pain in the a%^$. I also agree with Dave that the celestron radial guider is a right curse to use. (I have one) like Dave says, finding a guidestar with the small prism is a nightmare and even then even bright stars can appear quite dim (dim enough to be overwhelmed by the glow of an illuminated reticle. The standing peering down the eyepiece for long periods doesnt do your backany good! Also all it takes is you to breath the wrong way and knock off the scope.

A better solution would be to piggy back something like the lidl skylux (this applies to manual and autoguiding). You need to mount it VERY firmly otherwise you get flexure between the guidescope and the main scope. I use the losmandy mounting plate and rings (expensive but well worth it). I've heard of guys making home brew mounting hardware very successfully. With a mounted guidescope you have the double joy of having the full aperture of the scope to select a guidestar from, secondly the guidestar is much brighter and thirdly if you have the right mounting arrangement you can tweak the position of the guidescope to center a guidestar easier.

If I were you heres what I'd use my hard earned dosh on.

Webcam €50
guidescope (skylux) €59 (I think)
Mounting hardware cost about $230USD (losmandy for C8) or make your own.
Cheapo laptop (150-200?)
maybe splashout on a dec motor too (dunno how much that is)

You might say well I dont want to go to all that expense but trust me on this, you will have nothing but frustration if you dont do it right.

In short you can use the setup you describe and knowing your ability you'll probably get great results BUT you will go through hell getting there!

Gents - you know your stuff! I've heard that manual guiding is a right pain to put it mildly, but I was considering putting up with it if it could yield good results.

I did'nt know about the small FOV with the radial guider, maybe autoguiding so is the way to go! My pain threshold is low at the moment - it's too cold out there!
Time to get to lidl for a start!
Thanks for the link & info...

Keith..

Hi Keith,

I bought the 350D just before Xmas.

With it I also bought a 70-200mm (112-380mm full frame :!: ) Sigma zoom.

I'm told that this is a better lens than the Canon equiv., though I'm not sure if that's the one you refer to here.

And it only costs €200.
Though as Canon are currently doing a €150 cashback on the 350D, it really only cost me €50 :lol: .

Perhaps that may be another option...

Happy Shootin' Paul! Please let me know how you get on with that lens, where did you buy it by the way?

Keith..