Astro-imaging noob questions for Nexstar 8SE

[jaquesnoir]

Hi,

This is going to sound really noobish but I have a Nexstar 8SE and don't get much opportunity to use it. Mainly because I'm always working and when I'm not its cloudy. Plus, the light pollution is really bad where I live. I've had it for a couple of years but only really get to use it when I take it away on our annual camping trip. Then it really gets used.

Recently a friend who is a professional photographer suggested that we use it to try and take some images with some of his Canon cameras.

Can anyone offer advice on the best arrangement for fitting Canon cameras to a Nexstar 8SE? I realise that I shall require a T-ring adapter (EOS type) and a T-Ring adapter, but I am mainly concerned about the weight on the back of the scope and whether to fix it directly to the back or use a drop-in adapter for the diagonal.

I've never tried astro-photography.

Does anyone have any advice?

Regards

JN

[martin_h]

I use this on mine Adaptors - Celestron SCT T-Adapter

and you might need - Adaptors - T-thread Extension Tube Set

Slide the scope forward in the arm to get it balanced, but watch out when slewing that the cam doesnt hit the mount when pointing near zenith...Ive done it a couple of times....no damage but it knocks the alignment out

[jaquesnoir]

Thanks for the reply martin.

I looked at that exact adapter and its on my list of options.

I also saw those extension pieces when I was looking at the FLO imaging stuff, but I have to admit I don't really know what they do. Are they essentials or options?

One of my concerns was that the camera body would collide with the mount arm if using an adapter directly onto the back of the scope so I was considering the Celestron universal T-adapter. I presume it drops into the diagonal (I'm not sure though) and may give a bit more clearance to the mount when the scope is approaching vertical.

If your system works I may just go with it.

Thanks for the advice.

JN

[BlueAstra]

I have fitted my Canon 1000D to my C8 tube. I used the following items:

Adaptors - 2" T mount camera adapter

Adaptors - T Rings

Light Pollution Reduction - Skywatcher Light Pollution Filter

Astro Engineering AC307 2" Push-fitting to SCT visual back thread adaptor

I fitted a LP filter to the 2" nosepiece. I got the standard (AE307) and low profile(AE478) adapters, and generally use the low profile version. Make sure you get 2" versions or you will suffer from serious image darkening in the corners of the image. With this setup I can quickly change from imaging with the camera to visual by sliding the camera off and sliding the diagonal back on.

[martin_h]

I use the extension rings because if you think of the distance from the back of the telescope - through the diagonal - through the eyepeice to where your eye is focused, you might not have enough distance with just a camera attached to get focus so the rings just add some length to the setup

[jaquesnoir]

Martin,

Thanks for explaining what the extensions are for. I would never have thought about that. I thought they were for adjusting clearance - doh!

JN

[jaquesnoir]

BlueAstra,

Thanks for replying. Seems like a good idea to be able to simply swap the camera and diagonal. I presume its a fiddly operation to remove the adapter and attach the diagonal and vice versa especially as I would need the diagonal for aligning and finding etc..

That is something I hadn't thought about. I have a 1.25" setup - would it just be case of using 1.25" components where you have used 2" stuff?

JN

[ollypenrice]

Once you have all the adapters sorted out (as seems to be the case) there are two other important issues of which to be aware. The C8 is f10, which is very slow for imaging. That means you will need long exposures. It also has a very long focal length - two metres - which will require very accurate tracking. (The accuracy required goes down as the focal length does likewise.) This is an unfortunate situation - long exposures at a long focal length is doubly difficult. If you are not observatory based you will find it very hard to get a good enough polar alignment and good enough tracking for anything other than very short exposures.

What to do? Firstly use a focal reducer. The standard Meade or Celestron one is nominally f6.3, though it is said to be nearer f7 point something in reality. Ian King lists an alternative f5 reducer which might be better. The standard ones come up second hand. Forget the f3.3 reducer which was intended for tiny webcam chips in the early days.

Secondly think about an autoguider. The Periodic Error Correction, as it is described by most manufacturers, would allow you to take long unguided exposures. I'm afraid this is nonsense and personally I would say it sailed close to the limits of the Trade Descriptions Act.

There is a third small problem. (I'm sorry about this!) Most SCTs have an entirely unsatisfactory focus mechanism involving sliding the primary mirror up and down the tube. This causes image shift and is a very poor way of finding focus in any event. Those using SCTs for imaging (which I do only occasionally) tend to add an aftermarket Crayford focus system which works very well.

In a nutshell what I would do is have a go without spending much money on the setup and see if you like the idea of astrophotography. Hand on heart, though, I would say that, if you do, forget the C8. Sell it and buy the classic setup of ED80 refractor on EQ5 mount with cheap autoguider. Imaging at two metres is absolutely not the way to get started.

I hope you don't feel all this is negative but trying to kit out an SCT for imaging is a slippery slope wallet-wise and may never give great results. (I learned the hard way and would feel bad if I didn't pass on what I learned.)

Olly

[jaquesnoir]

Wow,

Thanks for the advice Olly. I've seen your stuff so I know you know what you're talking about. I'll give it a go with the Nexstar - simply because its all I've got at the moment and I'm itching to have a go. Then, as you suggest, start spending if I get the bug. At least I know what to expect. For now I just want to catch some shots of the usual Solar System suspects to get some practice.

Your post has made me think about the actual optics involved and I've only just realised that the camera won't be looking through an eyepiece - have I got a lot to learn or what. Well, the best way to learn is to have a go. Watch this space for some rubbish photos.

Cheers,

JN

[ollypenrice]

For solar system you can use eyepiece projection to get the focal length necessary and the short exposures won't tax the guiding. I was talking about deep sky. However, for solar system the camera of choice is the webcam or its fancy variants like the DMK or Luminera. Celestron do a webcam prepared for imaging, which makes life easy. You also need the free Registax programme to stack lots of webcam frames. Rather than an eyepiece a Barlow is the easy way to get to the image scale you need for webcam imaging.

The moon should look great just using your DSLR at prime focus, though.

Olly

[Psychobilly]

You'lll also need to mount the scope on a wedge to "convert" the Alt/Az mount into EQ mode...

[BlueAstra]

Using the C8 to image is a bit of a challange. Here is my equipment:

http://stargazerslounge.com/equipment-discussion/90916-orion-oag-first-light.html

[jaquesnoir]

This is starting to make my plastic creak! It starting to get expensive and I haven't started yet.

Anyway I've bought a NexImage - then I find that I will probably need a NexImage reducing lens which I presume is a focal reducer along the lines discussed above. Now I see what Olly meant - the costs are going to rack up even for a minimal set-up. I've got a canon EOS T-ring and adapter on order. Well, its on my xmas list anyway, so I'll have to see what turns up.

I do like your latest set-up BlueAstra. I may go for something similar but I thing in the short term I'm going to try the Solarsytem stuff. I haven't got a wedge and got a bit of a shock when I saw how much they cost.

My ebay watch list seems to be growing daily.

Thanks for all your help and advice guys. Hopefully I'll be able to get the NexImage thing working over the break.

Merry Xmas

JN

[curious99999]

Hi All, I bought my nexstar 8se and am so excited , i have used few times and its great, I am interested in astrophotography and lerning it now, for this reason i bought the EOS T-ring and celestron sct 93633-A T- adaptor to mount my DSLR camera to the scope. My question is how can i do that, does the T-ring thread into the scope (visual back) perfectly? or could anyone of you please help me know how to do that. First i have fitted the T-adaptor and T-ring to canon 550 EOS and - >  fitted the eyepiece (celestron's 25mm) to the back of the scope(visual back)  and when I tried connecting my camera to the scope it doesn't thread in perfectly , but it's very loose, is this the way it fits ? or it threads in perfectly. Please help me know this process.Thanks a lot in advance.

[nytecam]

Hi,

This is going to sound really noobish but I have a Nexstar 8SE and don't get much opportunity to use it. Mainly because I'm always working and when I'm not its cloudy. Plus, the light pollution is really bad where I live. I've had it for a couple of years but only really get to use it when I take it away on our annual camping trip. Then it really gets used.

Recently a friend who is a professional photographer suggested that we use it to try and take some images with some of his Canon cameras.

Can anyone offer advice on the best arrangement for fitting Canon cameras to a Nexstar 8SE? I realise that I shall require a T-ring adapter (EOS type) and a T-Ring adapter, but I am mainly concerned about the weight on the back of the scope and whether to fix it directly to the back or use a drop-in adapter for the diagonal.

I've never tried astro-photography.

Does anyone have any advice? Regards JN

Hi JN - didn't see in your post 'deepsky' image but just imaging with a DSLR ! If that means the moon it will give excellent results with the camera replacing the EP (without using the diagonal - assuming you can balance the scope) and the phases of Venus, Jupiter + moons etc eg bright stuff.

DSOs are another 'ballgame' which I satisfy with f/3.3. focal reducer on my 30cm SCT onto SX Lodestar-C in very brief exposures measured in seconds (not minutes or hours!) as the samples via my link below! I'm not a perfectionist clearly but happy with my modest results . AP apparently starts with a min exp of 20min so I can't be doing AP :-)