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Problems with magnification


welshmy
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Hi,

Probably jumping right in without enough reading but ... I recently received a Nextstar 130SLT (focal length 650mm) for my birthday (very happy about that present), over the last few days I have been trying to look at Jupiter - no problems finding it at the moment early in the morning! 

Using a 2x barlow with 6mm or 9mm lens I am just about able to make out Jupiters bands but not much else and the image in the view finder even with the 6mm lens is very small - I was expecting magnification of ~200 with the 6mm lens.

Is this a setup problem? Or a weather related problem? Or simply user error?

Adding my Sony NEX3N to the mix also fails to get a nice image - just about about to see bands but again a very small image.

Thanks,

Mark.

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Hello and welcome to SGL. I think the problem is not knowing what to expect when you look through the eyepiece. The 130 with the 6mm eyepiece plus Barlow gives you a little over 200x. Using this field of view calculator you will get an impression of how small / big Jupiter will be in the eyepiece http://www.12dstring.me.uk/fov.htm

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With the camera are you shooting through the eyepiece or the camera at prime focus by connecting directly to the scope? If your at prime focus you can increase the barlow - camera separation to increase image scale (at the cost of brightness). You will need some spacers to do this.

Your camera is also capable of recording video, this is the normal way of imaging planets. You record a video and then stack the frames in a program like astrostakkert or registax to get the best bits of the best frames. Try to stay below 2min on Jupiter though as it rotates quickly and detail blurs above that.

I always see far more detail on my images than visually, the camera also sees the colour far better.

Focus is very important of course, at high magnification it is harder to focus. A bahnitov mask can help immensely with this and they can be made at home.

Lastly make sure your scope has cooled down before trying to use it, thermals and contraction of the parts will reduce performance until it reaches a stable temperature.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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I had the 130EQ, so same tube, different mount. Jupiter is a small bright disk in this scope and I personally found the barlow to be tricky to use. The 6mm lens will give a magnification of just over 100 without the barlow, x218 with. The theoretical maximum magnification is usually given as aperture (in inches) x 50, which in this case gives 250, so this 6mm and x2 barlow combination is getting close, and you will only get good results at this magnification when the conditions are really good, which means clear dark skies and not much atmospheric turbulence. Even at this magnification, it will remain small. I would not worry too much, you can still see the Jupiter's moons, some extended time at the eyepiece will result in more detail being teased out and just wait till you see Saturn with your own eyes. This will also be small, but it is still glorious.

I personally think this scope excels at clusters and wider field views. Point your scope and 6mm EP (no barlow) at M13 for instance, and this will certainly not show up as a small pea in the field of view.

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Thanks for your replies. I am using prime focus for camera setup so I will have a look at changing the barlow for more magnification - I guess there is also a possible problem with pixel size from the camera.

I could see the banding quite well but the overall colour was poor, mainly white - would this be a combination of weather and focus? Bahtinov mask was already on the Christmas list to help out on focusing.

From your comments and the shared link I think I shall just have to try a few times on different days and see if I can get a good combination on weather and focusing - without getting up too early at the moment ;-)

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Be aware which way you have your OTA rotated too, I think the stock focuser may creep slightly if it has the weight of the camera on it. Of course adjusting it so the focuser is level could cause the focuser to sag but I imagine your racked quite a way in so the later shouldn't be a problem.

Your not going to see colour visually at that aperture I'm afraid. Your camera should be detecting colour though.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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I think the small scale of even the largest planets through the eyepiece does surprise many folks when they 1st observe them. With planetary observing the maxim "the more you look, the more you will see" is very apt. Even with my 12" scope the initial view of Jupiter and it's surface details is limited but time spent carefully studying the planet starts to deliver rewards as your eye "trains" itself to pick out the more subtle detail and you get glimpses, during the moments of really good seeing, of the details that are there.

I don't find Jupiter responds well to ultra high magnifications, unlike say, Saturn or Mars. I've had some excellent sessions where 150x - 180x has been the optimum even with scopes larger in aperture than your 130mm.

So "keep at it" is probably the best advice :smiley:

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I agree with John. The pupil starts to contract a little after a while, when observing bright objects. This allows more detail to be seen as your eye adjusts to the brightness. Whilst the image / disk is small, it is surprising what detail you can eventually pick up. The more you observe, the more you 'train' your eye to see detail that was previously 'invisible'.

I find that given all the houses around me that often 130x or so is all I can get but on occasional nights it's a lot more.

Ensure your scope is cooled (perhaps for 25-30 minutes for high power observing like this - although for lower powers you can start straight away), collimated and that your scope and eyes are shielded from any local light sources. All this will help you improve your chances of detail. Sketching too, will train you to collect more detail over time and you concentrate a lot more on the object at hand.

Keep at it - indeed :smiley:

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Thanks for all the advice, really appreciated. I am really enjoying myself and will definitely keep at it - just waiting for the clear skies at the moment and taking every opportunity.

The scope is definitely cooled well before I try to use it.

Any recommendations on DLSR configurations? My Sony Nex 3N has a relatively large pixel size (22um).

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For Jupiter try a 2 min video then stack the frames.

The video takes advantage of this brief moments when the seeing is perfect and this allows you to capture fine detail.

It's totally fine if it drifts a bit in the field of view in this time, the stacking software will fix that and the natural dithering will help remove any hot or dead pixels.

For planetary short exposure lengths are beneficial to try and catch moments of good seeing.

Be aware that when setting the gain very low settings may cause data loss and very high setting can cause excess noise.

Make sure compression is at a minimum for video and stills should be RAW.

Good luck :)

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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As others have said, the magnification issue is probably more a discrepancy between expectation and reality than any technical problem. For myself, I'm still in the 'amazed that we can see as much as we do' camp.

I don't know if putting it into numbers is as helpful to anyone else as it is to me but FWIW, in purely round-figure back-of-the-envelope terms, right now Jupiter subtends an angle of about 2/3 of an arcminute from our view point, and at 200x that's about 2 degrees. Which is to say that through the eyepiece it should appear about 4x as big as the moon does to the naked eye. It's over 700 million kilometres away, and yet we can see cloudbelts, and the GRS, and smaller weather patterns, and on and on. That's good enough to blow my mind!  :shocked::grin:

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Some very good ponts raised above and fully agree, the first time I picked out the great red spot on Jupiter (the planets crown jewel no doubt) I was at x150, prior to this I had managed to convince myself I wasn't seeing it because I wasn't at enough magnification. Once I saw it and knew what I was looking for, my eye trained to to this and now its second nature.

Regarding you comment expectations, try this thread here http://stargazerslounge.com/topic/196278-what-can-i-expect-to-see/ It is a sticky in the forum simply because it is such a well written and informative thread. 

Steve  :smiley:

Edited by bomberbaz
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