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Am I expecting too much from my setup


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]I have a 75mm obj, f16 refractor telescope with hand held guiding.

With out a barlow I can get a recognizable image of Jupiter.

However, it has been suggested that I should try using a 2x barlow to get a larger and hence more pliable images.

Unfortunately I have had great difficulty getting anything worth while. In general the results are a fuzzy blob.

Finding the focal sweet spot is (for me) impossible. My system will not pickup any bright(?) star with which to use a B-mask.

Hence focus is basied on the image on the screen, or when not using the barlow using a Jovian moon.

For pictorial reference I have attached some images that have been process using Registax 5 (on auto setting)

I have tried using pipp and AS?2, neither yield better results.

The images were captured using SharpCap with the histogram option activated

I have also attached the SharpCap txt file with webcam settings.

Question, am I trying the impossible or is it a focus and/or webcam setting error(s)

(ps I've attached and posted 5 files, but the preview does not show them all???)

regards

Tony

post-9025-0-74593800-1346848157_thumb.jpCapture 03_09_2012 00_10_16pse01.psdpost-9025-0-10727900-1346848219_thumb.jpCapture 04_09_2012 23_54_36..CameraSettings.txtpost-9025-0-20975100-1346848254_thumb.jp

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Because your refractor is quite slow (f16) trying to use a barlow will give you f32 which is asking a lot for small refractor. Your telescope is fairly near to the usual ideal f number (f20) so I would stick to that. I would probably not manually track the planet because this might cause the telescope to shake. I would let the planet drift across the field of view and then run the capture file through Castrator or convert the avi to individual bmps and run them through Ninox http://www.acquerra.com.au/astro/software/ninox/ to crop and centre the planet for stacking in Registax.

Peter

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Because your refractor is quite slow (f16) trying to use a barlow will give you f32 which is asking a lot for small refractor. Your telescope is fairly near to the usual ideal f number (f20) so I would stick to that. I would probably not manually track the planet because this might cause the telescope to shake. I would let the planet drift across the field of view and then run the capture file through Castrator or convert the avi to individual bmps and run them through Ninox http://www.acquerra....software/ninox/ to crop and centre the planet for stacking in Registax.

Peter

There is no need to use Castrator or Ninox if you are using PIPP, that would just be a more complicated was of doing the same thing.

Chris

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For planetary imaging I would never go below F/30 so your F/32 feels about right to me. I am not sure how using such a small aperture affects this, I am not sure but don't think it should since we are talking about focal ratio rather than focal length.

Can you see any detail in the individual frames? I think that if there is no detail in the individual frames than no amount of processing can bring out any detail.

Cheers,

Chris

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You don't mention what webcam you're using, but lets work on the basis that it's like a Philips Toucam.

With a 75mm 1200mm F/L scope, your FoV is about 10 arc minutes. That doesn't make it easy to acquire your planet, but I digress.

At 10', stars will drift through your FoV in about 40 seconds. Now with a webcam that has 640 px horizontally, that's 16 pixels per second, so you'll need to image at 15 FPS or faster to minimise blurring. If you add a Barlow, the FoV halves, drift time also halves and you'll have to image at 30 FPS or your image will blur.

Provided you have a *very* steady hand and a lot of luck :wink: you can cancel out a lot of that movement, just so long as you track smoothly. (Though the Barlow will magnify any jerky movements, either in your adjustments or in the mechanics of the mount).

When I started out I had a little EQ3 with flexi-shafts to hand-track with. I found that I was putting quite a lot of vibration into the flimsy tripod I had it set up on, which made life even more difficult. Adding weights, such as a 2 litre water bottle, suspended from the mount and hanging down the centre of the tripod can help damp out vibrations. If you have an EQ1, 2 or 3 you can pick up a single-speed, one axis motor for about £30, which saves a lot of hassle.

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post-9025-0-37193700-1347029726_thumb.gi Don't mention webcam; F20 v F30; Have to image at 30 FPS or your image will blur; . Adding weights; Single-speed, one axis motor

Dear Peter, Chris and Pete-1.

Thank your for your responses. The above quote is a selection of your thoughts.

Yes, the telescope without a barlow is F16 and with a 2x barlow is f32. At f16 I can get a recognizable image of Jupiter. However, it is small and, as Chris knows, the results do not offer much to work with.. At f32, I get a much bigger rmage but, to date, I have not been able to bring it to focus. I get a fuzzy blob with a texture like a handful of soap bubbles.

The webcam is a unmodified (ex Morgan) spc880nc. The webcam is attached to the telescope by unscrewing the (telescope's) eyepiece assembly and attaching a RAS thread - to- 1.25 adaptor.

I seem to have confused the issue by my phrase hand guided. I do not try to follow the object and keep it in the centre of my laptop screen. What I meant was that I do not have any form of mechanical or computerised guidance on the telescope. Hence I have to find the object by moving the telescope until the object is on the screen. The I let it meander across the screen and hand move (nudge) the telescope to bring the object back to the starting point for crossing the screen.

Regarding motor drive. I cannot see how this could be accomplished. Attached is an image of my telescope and suggestions for its 'automation, would be welcome.

Regarding the cask of water to dampen vibrations. I use a weighted belt over the rear of the telescope barrel that balances the telescope and gives it some stability.

The comments regarding increasing fps surprised me. I thought perceived wisdom with webcams was not to exceed 10fps. Please could I have some clarification on this matter.

Regards and thanks

Tony

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Hi Tony,

We need to be careful not to confuse exposure time and frame rate. Pete-l's maths is based on exposure time not frame rate and it is the frame rate should not be taken above 10fps with webcams. Having said that I am not sure the frame rate and exposure can be controlled independently for webcams, but I think the point still stands.

I am not completely convinced with this argument though as I have seen excellent frames come out with hand guiding in ISS imaging (see http://sites.google.com/site/astropipp/example-uasge/example-4 for example) and that little thing buzzes around the image at ready high speeds.

When you say you can't focus with the barlow in place, it is not something as simple as not having enough focus range on your scope to focus with a barlow in place is it?

Cheers,

Chris

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Hi Tony,

First, can I congratulate you on your telescope - it's certainly a masterpiece!

The bad news is that I had something entirely different in mind when I was talking about motors and flexi-shafts.

The first thing I'd suggest is setting the focus point with your webcam on a stationary object during the day. If you choose something far enough away, that'll be pretty close to the infinity setting you need for planets and stars. That will also inform you of the sort of image you'll get with the Barlow in place (and the difference of focus positions with / without it).

With regard to blur, what I meant was that if the webcam exposure takes longer than the time for the planet to move 1 pixel across the CCD sensor, then you'll get part of the image at the "early" pixel and part at the "later" one. For example the leading or trailing edge of the planet will be spread across 2 pixels. That's the blurring effect I had in mind - just like speed blur on an ordinary camera when the exposure time is too long.

With webcams the 10 FPS "limit" is due to the limitations of the USB data transfer speed. When try to use a fast frame rate, the bandwidth of the USB comes into play and the chip on the webcam will compress the frames to get make each one transmit faster. That compression is lossy, I believe, so you lose data. It's a bit of a quandry: blurry images or lossy ones :huh:. One possibility would be to set the image size to the next size down: 320x240 which gives you ¼-sized images, but you'll get more of them.

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When you say you can't focus with the barlow in place, it is not something as simple as not having enough focus range on your scope to focus with a barlow in place is it?

Hi Garry

Don't think so, The focus rack has 3" (75mm) movement. I arrange the draw tube etc so that it is in the middle of the 3" range.

Moving (2x barlow) through the 3" range I go from completely out of focus - to some kind of blobby focus - to completely out of focus.

Without the barlow I can get an object fairly sharp; both from the target object on the computer screen; OR by focusing a Jovian moon on the computer screen.

The extra complication with the 2x barlow is the speed at which the object crosses the screen. Trying to focus can 'dislodge' the object off the screen or cause such jerking across the screen that it has not time to stabilize.

Another element is that I am trying to capture when the object is low in the sky (ie midnight ish) . Gettitng up at 3am is not my thing.

regards

Tony

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Sorry Chris about the wong name

No worries, you are far from the first person to make that mistake!

Hi Garry

Don't think so, The focus rack has 3" (75mm) movement. I arrange the draw tube etc so that it is in the middle of the 3" range.

Moving (2x barlow) through the 3" range I go from completely out of focus - to some kind of blobby focus - to completely out of focus.

Without the barlow I can get an object fairly sharp; both from the target object on the computer screen; OR by focusing a Jovian moon on the computer screen.

The extra complication with the 2x barlow is the speed at which the object crosses the screen. Trying to focus can 'dislodge' the object off the screen or cause such jerking across the screen that it has not time to stabilize.

Another element is that I am trying to capture when the object is low in the sky (ie midnight ish) . Gettitng up at 3am is not my thing.

regards

Tony

I would suggest using Polaris to get your focus correct since it is not moving anywhere fast, then move onto Jupiter with the focus sorted. This way at least you can prove whether or not your setup is able to focus with a barlow in place.

Chris

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Certainly a masterpiece; Set the focus point with your webcam on a stationary object during the day(and the difference of focus positions with / without it); Set the image size to the next size down; 320x240 which gives you ¼-sized images, but you'll get more of them; Using Polaris to get your focus correct since it is not moving anywhere fast,

Dear Chris and Pete.

Thank you for your comments.

Yes, the telescope is a nice comversation piece of furniture, as well as being a scientific instrument.

Attached, is an image that shows the terrestrial view that I use to try and sort out my focus predicament. The target is some 3km away and with the 2x barlow I can see (dependant upon the sunligh and mist etc) wireless aerials and window frames. Yes, this gives me two repeatable setting dimensions for the webcam. Also out of curiosity I was able to use a motion detector that activated the webcam when two (discernable) people walked along the front of the lightouse building!! My image also shows how the webcam is attached.

I didn't consider using 320x240.

Polaris would be okay, if I could see it! My setup does not appear (no pun intended) to pick up stars! Leastways nothing appears on the screen!!!

regards

Tony

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Polaris would be okay, if I could see it! My setup does not appear (no pun intended) to pick up stars! Leastways nothing appears on the screen!!!

You will need to max out the gain and increase the expose in order to pick up stars, but you should then be able to use Polaris for focusing. This is a technique used by the ISS imaging guys.

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I had a thought as to a possible cause of not getting focus.

The telescope is placed outside (to acclimatise for temperature) and is situated around 5m above mean sea level.

At mean sea level the 'tide' is around 50m away from our house..

When I have been attempting to capture Jupiter I have been 'looking' slightly north of east right across the Irish Sea.

Consequently, I am peering through thermal gradients (sea versus air temperatures); at an inclination of 7 degrees of arc.

At present, on nights with clear skies the temperature difference between air and sea is large (circa 10 degrees) compared with that in a few months time.

Am I grasping at straws?

regards

Tony

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Consequently, I am peering through thermal gradients (sea versus air temperatures); at an inclination of 7 degrees of arc.

At present, on nights with clear skies the temperature difference between air and sea is large (circa 10 degrees) compared with that in a few months time.

Am I grasping at straws?

regards

Tony

Yes, that's a possibility and for another reason, too.

The lower in the sky a target is, the greater the amount of atmosphere you have to peer through to see it.

atmosphere-star-small2.png

Typically astronomers talk in terms of "air masses" for atmospheric distances. So 1 air-mass would be looking straight up, vertically at star A in the diagram. As the angle from the horizon gets smaller, the number increases - the rate is 1/sin(theta). So at 7 degrees, you have 8 air-masses between you and Jupiter. Apart from the thermal effects from the sea, you also have 8 times the "ordinary" atmospheric turbulence (which will exacerbate the thermal "seeing", too). There's an additional factor, that the greater the distance light has to travel through air, the more it's attenuated (atmospheric extinction is the term) at about 0.28 magnitudes per air-mass. So at those low angles, Jupiter is 2 magnitudes dimmer than when it's vertically above.

I'm afraid the only solution to that is to observe it when it's higher in the sky.

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only solution to that is to observe it when it's higher in the sky

Thank you Pete_1

I followed the maths,and (unless I've completely misunderstood you) have arrived at some interesting results.

If (this week) I wait for another hour (ie 0100) Jupiter is at 19 or 20 degrees inclination (Stellarium) and the hypotenuse is around 3x the normal distance.

Thus my target is 2.6 times brighter than if I try to image at midnight (or 7 degrees).

Also if I wait a few weeks then Jupiter will be higher earlier in the evening; and the air:sea temperatures less drastic. Hence all things being equal my experimens with the 2x barlow should (might??) be more acceptable.

Many thanks for the explanation.

regards

Tony

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