Astro-imaging for a newbie

[wilkie]

Hi, I’m not going to kid myself by pretending i know what I’m talking about, so let’s say i am very new to this and need as much feed back as you can muster.

I’ve been gazing up to the skies for a good couple of years now and I’ve started to take a keen interest in progressing into Astro-imaging / photography in the not too distant future.

I'm currently using a SkyMax 127 with the SynScan AZ GOTO 127mm Maksutov-Cassegrain along with a Canon EOS 500D SLR.

Before i start getting too carried away and excited can anyone advise if this is a good foundation to start with?

is the scope good enough for a varied number of shots etc?

and more importantly, what would you recommend i look into getting to start things rolling?

I have a 1.25" combined T-mount camera adaptor and eyepiece projection unit to fit onto my Canon........ that i'm affraid is as far as i got before i realised, "i could be here along time without some guidance".

Any Advice would be great thanks

[jgs001]

The scope and mount will work for the moon and planets (although a webcam is a better bet as a camera. You could try using the movie record mode), but isn't ideal for deep sky. The scope is too slow (long focal length, compared to the aperture), and the mount limits your exposure times to somewhere between 40 seconds and 2 minutes (depending where in the sky you're trying to image... E/W is longest, reducing to N/S/Overhead). If you remove the scope from the mount and just fit your 500d. then you should be able to achieve some nice widefield imaging at focal lengths up to 300 to 400mm. You may find it better to put the camera on the skyhawk mount, as I think that's an EQ mount, and use that for widefield, as the tracking is better suited (you'll need to work out how to set it up as accurately as possible though.

I say, give it a go, work up to the limits, you'll need to work those out, and see how you get on.

I started with a Celestron NexStar SLR (near enough the same mount) and an ST80 (400mm scope) and I know what can be achieved with that sort of kit.

Before you go spending money on new kit (excepting a dovetail bar to mount the camera ), I'd recommend getting http://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

[michael.h.f.wilkinson]

Excellent advice, John. For very long tracking, you need an EQ mount. For planets, you could indeed get a webcam (preferably CCD-based rather than CMOS): cheap and a lot of fun. The Skymax 127 is very good in that arena.

[malc-c]

For use with a webcam to do luna and planetary imaging the 127mak on the alt az mount will be fine, provided you limit the captures to around 2000 frames. The high magnification you can get with the long focal length is best suited to this form of imaging

For deepsky objects it will become more of a challenge for several reasons.

• Main reason is field rotation. As you can't follow the arc of the Earths rotation with an Alt/Az mount the subject will appear to rotate in the frame. This then presents issues when you come to stack multiple subs taken over several hours
  
• The 127Mak is around f10 / f11 which is far too slow for faint dso's - typically a scope with f5 or less is better suited for these targets
  

[daniel-lloydw]

The 127Mak is around f10 / f11 which is far too slow for faint dso's

sorry to jum in on a post but What exactly does that mean? F10/F11??????

[malc-c]

The 127Mak is around f10 / f11 which is far too slow for faint dso's

sorry to jum in on a post but What exactly does that mean? F10/F11??????

The focal ratio is the focal length of the optics divided by the aperture of the lens or the diameter of the mirror. So if you have a 1000mm focal length (the focal length is the distance from the mirror / lens that the light is focused to a point) telescope which uses a 200mm diameter mirror the focal ratio (f) is 1000/200 = 5

A lower focal ratio means that when used as a "lens" (ie a camera body attached and the focal point placed on the CCD or film) you don't have to expose as long as you would for a higher focal ratio. It's not quite as clear as saying a 200mm f10 requires twice the exposure than a 200mm f5 telescope, and other things come in to play, but as you ideally want to get as much light in the exposure as quick as possible having long focal length and high f ratio telescopes won't give you that.

Telescopes such as a 10" SCT with a long focal length and high f ratio are ideal for planetary work as they provide a very bright and detailed image which can be magnified higher than with low f ratio scopes

[umadog]

In case you're wondering, cats have a large focal ratio despite the short tube because the secondary mirror is convex. So it works rather like a Barlow.

[daniel-lloydw]

ok so I have a skymax 127 so thats 1500/127 =11 so I have a F11 scope right?

why would a high F make viewing DSO's harder? would that not be better?

[Capricorn]

The longer focal length means a larger image but that means that it will be a dimmer image, you are collecting a fixed amount of light.

Next the long focal length means that the mount has the track better, both smoother and more accurately.

Imagine a stick of say 500mm move it 1 degree and the end moves just a little, try that with a 1500mm stick and the same 1 degree movement means about 3 times as much movement of the end. That is the situation with a long focal length scope.

So you are ending up witj a larger = dimmer image, so longer exposures are required, and also you need a much more accurate mount, first for the long focal length and secondly because of the longer exposures. That means a very expensive mount.

[daniel-lloydw]

ahh thanks guys...... do a dso will be out of my view in just a few seconds.... i see now. more powerful not always best

[JamesM]

If imaging is going to be a long term aim, I would certainly recommend you get hold of a copy of Steve Richards' "Making Every Photon Count" (FLO £19.95) which you can read more about here. It's a comprehensive book providing you with a great instructional overview of what kit you need and why you need it to take good consistent images. Modestly priced, it will certainly help you save money by helping you to avoid buying the wrong kit and will also help you to formulate a more accurate budget from the outset. The other thing to note regarding costs is that although conversations about imaging tend to focus on the data collecting side (i.e scope & mount) there is of course the other half of imaging which is data processing. Thankfully there a re many free programs out there that will are really good to use and will certainly help you get the most out of the data collected, however there are inevitably one or two great programs that will need to be paid for. This book will certainly help you get to grips with the requirements of imaging which will hopefully make it a fun rather than frustrating activity.

Clear skies

James

[wilkie]

Thanks all.

I've officially added this book to the ever growing christmas list........ i if can wait that long.

i think from initial comments my set up will be good for just planetary objects and the moon, which is ok by me for beginners. so i'll give that a go and lets see where it gets us.

i've looked into data processing and to be honest it looks alot more complicated than it actually is i'm sure, but i dont get all this layering stuff just yet, so that may be out of my depth at this stage.

just need these piggin clowds to go away now.

[jgs001]

If you get yourself a medium length dovetail ... http://www.firstlightoptics.com/dovetail-bars/skywatcher-dovetail-mounting-plates.html then mount your camera directly to that, you can use the mount to track and capture some nice widefields. The stacking process will deal with field rotation between frames without issue, as long as you're tracking. You'll be surprised ... I managed to image the bubble nebula (ok, it was very small), an Ha (infrared emissions) target, with an unmodded camera, mounted on the NexStar AltAz mount (150 image frames, over a three nights).

[michael.h.f.wilkinson]

ok so I have a skymax 127 so thats 1500/127 =11 so I have a F11 scope right?

why would a high F make viewing DSO's harder? would that not be better?

For viewing all that counts is the aperture and the magnification. A 150mm F/11 Mak at 150x shows the same image brightness as a 150mm F/5 Newtonian at 150x. The difference impacts imaging only. I use my C8 (8" F/10 SCT) for deep sky observing and have just bagged my 619th DSO (OK some I got with the 70mm bins). I have bagged over 270 galaxies including two of mag 13.2. People often say SCTs and Maks are only for planetary, but that is rubbish.

[VigdisVZ]

ok so I have a skymax 127 so thats 1500/127 =11 so I have a F11 scope right?

why would a high F make viewing DSO's harder? would that not be better?

You might alreadt have got an answer to this but....

Low F = more light passing through it. My newton is F/5. Good camera lenses have F/2.8. Legendary camera lenses can have as low as F/0.95. THATS bright.

Hope this helps.

[malc-c]

Michale's post proves the other point.... that there are exceptions to each "rule". However there will be a few other factors, location being the primary one. I would guess that he has access to some really nice dark skies which will allow his F10 C8 to perform and record those fainer images ? If you are plagued by light pollution and have to use filters then you will find that having an F10 ratio scope will be more taxing when used for imaging than an 8" f4 quattro for example.

To the OP - spend a few hours / days reading through similar threads..... you will see some stunning images taken through very modest equipment (such as faint dso's taken through a 150P on and EQ2-3 mount, or some decent planetary images taken with fast reflectors). This is the thing... there is no "rule". Yes there is a trend that says short f ratio scopes for dso's and long f ratio's for planetary, but you can buck those trends. Heck I've managed a decent large image of Jupiter with no more than a £20 web cam and my Explorer 200P and stacked barlows to extend the magnification (focal length approx f20).

The thing was, I had to work harder to get the above image with the equipment I had, and the conditions had to be exceptionally good, where as for Michale's C8 he's already half way there !

[dph1nm]

One way round the long focal length problem for imaging is to use a detector with large pixels. If you have a CCD with pixels twice the size of your neighbour's. then your F10 scope is equivalent in 'speed' to his F5 (if they are the same aperture). Unfortunately this option is not really available in DSLR-land, as all models tend to have similar sized pixels these days (and all really rather small for imaging over ~1m focal length).

NigelM

[Astrosurf]

I've managed a decent large image of Jupiter with no more than a £20 web cam and my Explorer 200P and stacked barlows to extend the magnification (focal length approx f20).

The thing was, I had to work harder to get the above image with the equipment I had, and the conditions had to be exceptionally good, where as for Michale's C8 he's already half way there !

Cracking shot! I have a 200P and have imaged with a 4x Imagemate and Phillips SPC900NC webcam and only get diddy pics. What barlows did you use?

Alexxx

[malc-c]

Thanks Alex,

I used a 2x barlow that came with the revelation eyepiece kit, and a stock SW 2x barlow. One was placed inside the other and then the camera fitted. I basically started with Jupiter in the centre of the field of view of the camera, then removed it and inserted one barlow and replaced the camera, centred and focused it, then removed the camera and placed the second barlow in the 1st and then replaced the camera and focused again. The problem is that whilst the image gets larger it gets a lot fainter and the depth of field for focus is very tight, hence why the conditions have to be very steady.

[Astrosurf]

I assume my 4X Imagemate would provide the same mag? If that's so, why is your Jupiter so much larger than mine??! Sorry to hijack - this is my final question!