Help with Imaging mars and stars

[The_PSY3NTIST]

Hi guys, Im a total newbie to astrophotography and having problems getting any good shots. The best i can do at the moment i get a blurred disk for mars which is the image below. my gear is listed in my signature. anyone know where i am going wrong here? Whats the best configuration of lenses etc? Im using the CCD imager (celestron say to treat this as 5mm) and a x2 barlow. I was under the impression with a 8inch newtonian that you could get good shots. Iv seen some beauties on the net from other people with the same scope.

Thanks

Dave

[Demonperformer]

I'm no expert, but I was having the same problem with Mars using the neximage. I was getting piccies like the first one I've attached. The problem was overexposure. What I finally hit on was adjusting the settings so that Mars is showing as much detail as possible on the screen, then reduce the shutter speed by one setting down (e.g. 1/10s to 1/25s) and then take the avi. When you process it, (I was using registax 5) it looks incredibley dark, but if you increase the upper brightness slider on the bottom right of the 'wavelet' tab so that it is about the same position as the slider immediately below it, it produces a result like the second piccie I've attached. With an 8" you should get better results than my 6".

Hope this helps.

[brianb]

Whats the best configuration of lenses etc? Im using the CCD imager (celestron say to treat this as 5mm) and a x2 barlow.

Forget about the "5mm", to image Mars you need a focal ratio is excess of f/20 - in good seeing people are using f/40 to f/60. Your 2x barlow gives you only f/10, your image is going to be small.

But the really hard part about planetary imaging is getting the focus right. Probably best to focus on a bright star then move to Mars (OK it takes some finding at f/40, a well aligned 50mm finder is good here).

Welcome to the frustrating, but ultimately rewarding, world of planetary imaging.

[The_PSY3NTIST]

Thanks Demonperformer. Unfortunately the clouds rolled in so havn't had chance to try getting another AVI. Will try next time its clear though. Had a play round with Registax and removed some frames and tweaked some settings and this is what i came up with. A little improvement.

Thanks again

Dave

[jgs001]

Dave, it's a good effort, but it looks like the settings, and possibly the focus. I'd suggest practice on the moon, it's a much easier target, get used to operating the camera (it'll need much less gain as well ). Play with the barlow, it's quite amazing the differing in difficulty with the barlow, you effectively double the focal length of the scope, but at the cost of exposure time as it doubles the focal ratio as well. Try it, you'll see what I mean.

[lukebl]

Hi Dave,

Stick with it! I have exactly the same scope as you, and we won't be able to get the same images as a scope with a longer focal length, but you should be able to get good results.

I think that your image is a bit overexposed and might need better focussing. Perhaps get a 3x or 5x Barlow or Powermate. This is my very first effort with Mars last night, in poor seeing using a webcam and 3x Barlow (i.e. at f/15), and on the more featureless hemisphere. I focussed using a Bahtinov mask on a star before going to Mars. It's hardly up to other's standards, but it's mine and I like it. It shows some detail and what looks like cloud formations on the limbs. How many images did you stack? Mine was around 800 from an original avi of 2400 frames. I reckon your kit could do better than this. Trial & error. Persevere!

Regards,

Luke

[kev 102 42]

Great pic Luke,im glad your pleased with it......kev

[michael.h.f.wilkinson]

Hi Dave,

Stick with it! I have exactly the same scope as you, and we won't be able to get the same images as a scope with a longer focal length, but you should be able to get good results.

I think that your image is a bit overexposed and might need better focussing. Perhaps get a 3x or 5x Barlow or Powermate. This is my very first effort with Mars last night, in poor seeing using a webcam and 3x Barlow (i.e. at f/15), and on the more featureless hemisphere. I focussed using a Bahtinov mask on a star before going to Mars. It's hardly up to other's standards, but it's mine and I like it. It shows some detail and what looks like cloud formations on the limbs. How many images did you stack? Mine was around 800 from an original avi of 2400 frames. I reckon your kit could do better than this. Trial & error. Persevere!

Regards,

Luke

Nice pic. I agree with earlier posts that going to slower f-ratios is better. My best pics of Mars were at F/30. I have an 8" SCT, which should perform comparably with you 8" Newton (if anything the Newton should have the edge). My first shot with an SPC900 (at f30) is attached. It is important not to over-expose, and get the gain down!

[Leegsi]

To get the F ratio up could you use 2 barlows stacked and still achieve focus

[The_PSY3NTIST]

Thanks for the advise everyone and great pics! That more like what i expected. I think i need a lesson in optics! Thats tonight's job while the clouds are over. might sound daft but what are you referring to when you say f/30?

Thanks

Dave

[brianb]

might sound daft but what are you referring to when you say f/30?

The image size is proportional to the focal length but the resolution is proportionate to the aperture. The ratio between focal length and aperture (expressed in the same units) is the focal ratio. So, for example, a 6" scope with a focal length of 48" is f/8.

But you can change the working focal ratio of your scope with a barlow lens ... a 4x barlow, or two 2x barlows stacked, will increase the focal length by a factor of four i.e. in the case above to 196" making the focal ratio f/32.

Too big a focal ratio, the image gets dim, making wobbles due to poor seeing smear the images during the long exposures necessary (and incidentally making it very hard to focus). Too small a focal ratio, the image is small and there is less detail recorded than the scope is capable of capturing. What's right depends on the pixel size & sensitivity of the individual camera, and critically on the seeing conditions, but f/20 to f/40 is a good ballpark region for Mars.

[riklaunim]

If you get white ball, and not a nice image of a planet - to high exposure (Jupiter: overexposed, and with correct exposure time). Lower untill some details will show up. NexImage is a webcam with 1,25" nosepiece so it very basic imaging camera. On low focal lengths you can try some experiments with stars or bright objects (Orion nebula) - practicing focus and exposure times.

Smaller focal lengths also allow good images when the seeing is bad (the scale will be small, but still it's and image )

Saturn at:

750mm fl: Small Saturn on Flickr - Photo Sharing!

750*2x barlow: Saturn IR-Cut Barlow 2x 10-01-14 03-08-43 on Flickr - Photo Sharing!

750*5x barlow: Saturn IR-Cut Barlow 5x 10-01-14 03-42-32a on Flickr - Photo Sharing!

The seeing was bad, which makes images look bad on longer fl in this case

[michael.h.f.wilkinson]

Rather than using 2 2x barlows stacked (which may degrade quality) get either a 4x or 5x barlow, or consider eyepiece projection with e.g. a Plossl eyepiece. Quality gets degraded partly because of correction problems, but also because of the increase in glass/air interfaces, which causes loss of light, and glare due to internal reflections.

[brianb]

or consider eyepiece projection with e.g. a Plossl eyepiece.

Consider - and reject, unless there really isn't an option!

Eyepieces are computed to deliver a parallel beam from the "outside" face, when used as an image amplifier the beam will be converging enough to throw the spherical aberration correction right off. Even a simple eyepiece like a Plossl has as many air/glass surfaces as a stack of two Barlows. BTW orthos work better for projection than Plossls because there is less internal reflection; the "ghosting" in Plossls has a serious impact on the image contrast.