First imaging attempt - not so successful

[Shibby 747]

Hi,

A friend and I had our first go at taking a few images through my scope, we didn't have very long until that annoying fog rolled in!

Anyway, we didn't manage to get any decent frames - the image isn't brought to proper focus and (more worryingly) it's blurred radially outwards at the edges. We were using a T adapter with an eyepiece inside...

Focusing was very difficult through the viewfinder and I think we had the focuser as far in as possible, leading me to believe this setup might not work?

Setup:

Explorer 130P AZ GOTO

Nikon D70

Antares T thread adapter with 25mm Plossl

Of course, there won't be any clear nights any time soon but I'd very much appreciate any suggestions of what to try next time?

Thanks,

Lewis

Edit: Oh, I forgot to say - this is a 30s exposure at ISO 1600

[jgs001 1,172]

It's not a bad start, it doesn't look like focus is that far out, although focusing through the viewfinder is only really good for a best guess starting point. Using the EP, appears to have magnified any problems too, so I'd actually put the camera at prime focus, don't use the EP, not sure about being able to get focus there though, I've read that there isn't enough in focus for the camera, but I'm sure that someone with that scope can comment. As for the radial blurring, that's called Coma and is inherent in using reflectors (as I understand it), again I think the ep, has exacerbated the effect. Why not setup during the day, you can check out getting focus on a far away object, and get familiar with all the kit whilst being able to see it easily.

[Shibby 747]

Thanks for the advice. I will certainly try focusing during the daytime or at least by taking pictures rather than through the viewfinder this time.

I'll start with prime focus next time too, though it would be nice to be able to use the eyepieces...

I've also ordered some extension cables so with any luck I can control both the camera and the scope from the comfort of my own lounge! It was *very* cold Monday night

[jgs001 1,172]

I have an adapter that allows me to hook my 450d directly to my Hyperion's for ep projection, and it does work, and you can get some decent image scale, it's actually really rather hard to focus, and tracking accuracy becomes far more important... I don't use the adapter very much... in fact, only about 3 times...

[Shibby 747]

It's possible that the barrel of the adapter I'm using moves the EP too far out for it to focus properly. Unfortunately I can't see this issue being any better with a shorter EP, e.g. the 10mm.

I'll have a play around and see what's possible...

A nice Hyperion is already on my shopping list (probably after xmas)

[Shibby 747]

Was about to give up having read this thread, but I've had a bit of a breakthrough!

What I didn't realise is that by removing the eyepiece holder, you can then unscrew the end (eyepiece insert) from the T-Adapter and screw the adapter straight onto the focuser. This allows me to achieve focus using the 25mm eyepiece! (nb this is inside the adapter)

Note that prime focus is impossible on this scope without moving the primary mirror, even with the camera screwed directly onto the focuser. But that's ok as I was more interested in photographing through the EP anyway.

[skye at night 1]

Other tips..

The D70 is a noisy camera...

Use ISO 800 at max...

Use remote release or timer control...

End exposure by cutting power.. (maybe covering tube/lens as you do it to avoid shake if having to do manually)

This is to avoid the Nikon Noise reduction process which will remove stars from the image...

Steve

[Shibby 747]

Thanks for the tips, they're all very useful. However, we've tried again and are still having the same issue. Heeelp!!

This time, I've got the camera focused as well as possible. The stars in the centre of the image are very well focused, but we're still getting that bad blurring/coma effect towards the edges.

Looking through the eyepiece alone, I of course don't see this effect, but after attaching the camera and re-focusing, this is what we get. Is the eyepiece maybe too close to the CCD? Too far away? We did briefly try moving it closer to the camera, by having it protrude slightly from the T adapter, but this only reduced the AFOV in the image.

[Shibby 747]

Having done a bit more research, it appears that this type of coma might be typical with this type of setup. As I understand it, my only options are:

- Use a higher powered EP (more narrow FOV)

- Buy a coma corrector, such as Baader MPCC

- Cropping

[PhoenixRising 13]

Dont use a higher powered eyepiece on that scope, the problem will probably get worse, also, the image will appear darker and your fov will be tiny (I know, Ive just been going through the same problem.

Have you tried unscrewing the 1 1/4 eyepiece holder from the scope so you can screw the camera and tpiece directly onto the scope, "Prime Focus" I think its called, no eyepieces=lots of light and less glass to deal with, you shold then just be able to concentrate on tracking your target. Have a fiddle with the scopes eyepiece holder and you'll see what I mean. Hope this helps.

[PhoenixRising 13]

Oh, got my eye on a Skywatcher 250-300 with 2" eyepieces, 2" Hyperions are the way to go I reckon, light buckets on a 250 by the looks of it, what do you reckon JGS001?

[brendant 19]

Using eyepiece projection with a DSLR is not practical due the the off axis distortions created by the eyepiece and reduced light transmissions necessitating longer exposures on faint objects. If imaging is what you want to do you must head down the route of prime focus - 2" eyepieces do not make any significant difference with eyepiece projection. A DSLR chip is too large to be illumunated properly, it works much better with webcams and smaller CCD chips where you are only using the central portion of the image.

For deep space astrophotography you will require exposures of at least 90 seconds on bright objects, up to 5 -15 Minutes on fainter objects depending upon your local conditions and light pollution. Eyepiece projection increases the effective focal length and therefore also magnifies any errors in tracking and effictively reduces the light reaching the chip which in turn necessitates even longer exposures.

If imaging is the route then start with a short focal length refractor such as an ED80 or similar, the short focal length is easier to work with and really opens up the number of targets available, then once this is mastered then move on to a bigger scope. You will be surprised how many deep sky objects are so large and require a wider field to capture. For astrophotography the mount is the single most important component - a HEQ5 or EQ6 should be considered minimum, an EQ6 is a minimum requirement for a 250-300mm scope.

Brendan

[Shibby 747]

Last time I attempted prime focus, I couldn't quite achieve focus but since then have collimated the primary mirror which might have reduced focal length a bit? I'm hoping to try move the mirror up as far as possible to see if it will focus... Any idea what sort of FOV roughly can I expect at prime focus? (it's 650mm focal length, 130mm mirror).

The scope is a 130P AZ Goto, not sure what sort of mount that means?

[dark knight 73]

Shibby, as already mentioned the mount is most important. To be honest an Alt/AZ mount (like yours) is less than ideal for astro-photography where long exposures are required. You really do need an equatorial mount. Try practising on the moon and see how it goes.

Edited November 30, 2009 by dark knight