What camera for 14” scope for live (near live) viewing?

[tooth_dr]

Any suggestions for camera to use for live viewing / public outreach?

14” F8 scope with / without wedge.

1) Best - no budgetary considerations

2) Best value for money ZWO 290?

TIA

Adam  

 

 

 

[tooth_dr]

Any suggestions?  I have a 178MC, would this work?

[Thalestris24]

Hiya

What scope/mount exactly? Do you have a focal reducer? Is a Starizona Hyperstar an option? You want to plug in your scope data and camera ideas into a fov calculator to see what might work.

Louise

[vlaiv]

That one is going to be tricky. Not in choice of camera, but rather in choice of software for viewing.

In principle, you want largest size CMOS sensor with largest size pixels and lowest read noise possible. 14" F/8 is going to have massive focal length, and you want your image to be sampled at no higher than about 1.5-2"/px.

FOV will also play a part - this is why you need large sensor. Let's do some stats on one such camera: ASI294

With 14" F/8 model you will have about 2850mm of focal length. Pixel for pixel it will sample at 0.34"/px, but since this is color camera - you can safely go for double that, so 0.67"/px. This is still far from target resolution, but luckily you can bin x3 and get almost exactly 2"/px.

Now let's see what sort of output we are going to get:

First FOV:

That is really tiny fov - we are looking at the "heart" of orion nebula, or about x3-4 smaller FOV than is needed to capture that nebula.

You will also be hard pressed to fit M81 inside FOV:

And in terms of image size, you will end up with about 690x470px, which is rather small, but could be all right for showing on lower resolution projector type device (something in WVGA 854 x 480 class - a pico projector for example).

Even if you add focal reducer FOV on such a large scope is going to be tiny and you will be able to get larger size image with larger sensor.

Going back to beginning of my reply - not sure if there is any software currently being capable of doing that level of binning for EEVA and that is major obstacle.

How about doing a bit different approach? What would be your budget and room for experimentation?

First of, I would add nice reducer field flattener to this scope to get large corrected field out of it. I'm assuming it is 14" RC type scope? x0.75 Riccardi FF/FR should provide corrected and fully illuminated field up to full frame sensor - meaning diameter of about 43mm. Let's check FOV of such setup:

Ok, a bit nicer FOV this time - I also left above FOV for comparison:

Still cropped Orion nebula, but much more "viewable":

Ok, that is about as large FOV as you will be able to get out of this scope. But how to get image out of it? Well you can go with above approach and do the similar (this time probably binning x2 after debayering with super pixel), or you can try different approach and use smaller sensor, but in order to use small sensor you will need couple of things - eyepiece with sufficient field stop and good lens for ASI camera and a system for connecting all of them.

If for example you want to use ASI290 type camera with above combination, I would think in following terms:

Sensor diagonal is about 6.46mm and that means that you need something like 43/6.46 = x6.66 reduction factor (or x0.15 reducer ) but we are going to do it differently.

You get Baader Hyperion Aspheric 36mm eyepiece - it has 45mm field stop so entire corrected FOV will fit inside. It also has threads for attachment - which is very good as it solves a part of attachment process.

This eyepiece gives about x60 magnification (this is important to remember as we are going to use it later).

Now let's calculate how to fit above FOV onto 290 sensor. Above FOV has width of about 0.94 degrees, so let's see how much arc seconds that is - 3384 arc seconds. ASI290 has horizontal resolution of 1936px so that sort of FOV will be sampled at about 1.75"/px (very good sampling rate for mono sensor in this role - and mono sensor will be more sensitive than color one as you will be capturing luminance only - but live viewing will be in black and white).

So far so good. But what sort of focal length do we need to be able to sample at 1.75"/px with 2.9um pixel size? You need about 685mm of focal length.

But remember that image that we have is already magnified x60 because we used 36mm eyepiece with this scope, so we need x60 smaller focal length. That is about 11.4mm lens.

So in this setup you will need:

x0.75 Riccardi reducer/flattner with M82 thread capable of correcting up to full sensor diagonal (about 43mm)

Baader Hyperion Aspheric 36mm eyepiece

ASI290 mono camera (or camera from some other vendor with same sensor)

and

11.4mm lens capable of illuminating 1/2.8" sensor size and having very good sharpness.

And btw, you connect them in the order I listed with distance between reducer and eyepiece being important, and distance between eyepiece and camera lens being that of eye relief of eyepiece (which is 19mm).

In the end a disclaimer - I've not done above to confirm it is working, but by all accounts it should. If you have the time and resources to test it out, then I would advise you to give it a go, it is probably the best bet to get anything decent for EEVA out of that scope, but it indeed requires quite a bit of money to test out and fiddling about, so probably not so interesting to try out.

Just a final note, with this sort of arrangement - being scope, ep, lens, sensor - you don't need any fancy binning so any EEVA software will work.

 

[tooth_dr]

@vlaiv thanks for that reply. This is the scope 

https://www.rothervalleyoptics.co.uk/meade-lx600-acf-14-f8-goto-telescope.html

[Thalestris24]

Hi again

Thinking a bit left field, an alternative might be to skip the big Meade itself and just attach a small, lightweight, fast F4 scope e.g something like the Altair 60mm, in place of the finder - I'm not sure what's possible here? If you could do that, you could image with a high qe guidecam e.g. gpcam2 or something like a 183 sensor with SharpCap Pro live stacking. Or even a Revolution 2 video imager (see on YouTube, e.g.

Without a wedge, though, you will be limited in terms of exposure times but I think the above should enable you to get some ok images. Dark skies always helpful...

Louise

[tooth_dr]

1 hour ago, Thalestris24 said:

Hi again

Thinking a bit left field, an alternative might be to skip the big Meade itself and just attach a small, lightweight, fast F4 scope e.g something like the Altair 60mm, in place of the finder - I'm not sure what's possible here? If you could do that, you could image with a high qe guidecam e.g. gpcam2 or something like a 183 sensor with SharpCap Pro live stacking. Or even a Revolution 2 video imager (see on YouTube, e.g.

Without a wedge, though, you will be limited in terms of exposure times but I think the above should enable you to get some ok images. Dark skies always helpful...

Louise

Hi Louise.

Thanks for the replies. Yes there is wedge for it too.

This was a thought that occurred to me also, using a smaller faster scope, but this would need to be explored.

What would be an alternate ‘big scope’ instead of the 14” SCT? Something like a big refractor?

 

[Thalestris24]

Hiya

Sorry, I just saw the 'without wedge' in your OP - I must be more attentive! Having a wedge will help a lot. Is there a reason why it has to be a 'big' scope? Obviously anything with a long focal length could have the same problem as the big Meade in terms of fov and speed. I suppose it all depends on what you want to achieve? I do all my live stacking with an 80mm APO + 0.8x reducer + qhy183m. I have terrible skies though - very bad lp, poor transparency, not much fun... The combination of scope plus small pixel imx183m (5544x3694) lets me bin 2x2 to get a reasonable sized image (2772 x 1847) on an otherwise smallish chip. As I said before, maybe the best thing is to try out various scope/camera combinations via a fov calculator to see a ) what suits and b ) what will practically work. For live viewing / live stacking you ideally want a fast-ish combination - sensitive camera and low focal ratio (via a reducer if necessary).

Louise

 

[vlaiv]

If you plan on putting complete rig, and I'm not quite sure if this is one off thing for some public demonstration or will it be used multiple times, but I'll let you decide on budget in any case, here is what you should consider - in that particular order.

1. Decide if you are more interested in FOV or sampling resolution (you can sometimes match both). FOV will be more useful if you have list of objects you want to showcase - in that case look for FOV that will render all intended targets reasonably. Going by sampling resolution is more for "persona" use - chasing maximum detail in your captures if you like to examine structure / whatnot of objects you are observing.

2. Decide on mono vs color. Mono will be "faster" - render targets in less time but will obviously lack color. Color camera will be slower but will render targets in color of course.

3. Select CMOS sensor with best QE and lowest read noise you can find with sufficient number of pixels. ASI290 is quite reasonable for example, but you might like ASI178 if you want more megapixels.

4. Figure out what sort of focal length you need based on selected sensor size and either needed FOV or sampling resolution (target FOV size or target "/px).

5. Get scope with most aperture that has given focal length.

That is about it really

 

[tooth_dr]

Thanks a lot guys. I am working backwards here as already have the 14”. Now looking to showcase images live via some sort of screen.