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Decent image scale on planets, how?

Ant

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Ant

Ant

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I'd like to think that I'm a rung or two up the planetary imaging ladder.

I don't have too many issues with Lunar Imaging, or Venus for that matter.

But I've never really understood why my imaging of Saturn and Jupiter have always been a little pants.

Don't get me wrong, there OKish (I'm not fishing for compliments :) ). But they are small and faint.

I would like to do two things.

1. Increase the Image scale

2. Increase the brightness.

I currently use a Skymax180 and a DMK21 (USB). This setup is a native F15. Even it F15 the scale is small and the get anything at all the exposures are down to 1/5sec.

There are only two methods that I know to increase image scale.

1. Add a barlow.

2. Use the EP projection method.

The barlow will increase image scale but lower brightness. So F/15 becomes F30, and the exposure drops to maybe 1/2sec. Which when you want 1000+ frames - I'm going to be there forever!!!

The Eyepeice projection method is a little less of a known quantity - I've used it before on my F5 newt (using a 10mm EP to project inage onto the chip). It did work quite well and I'll be giving that a go over the next few clear nights. All I can remember is that the Image scale was increased and I recall getting 20Fps from the Toucam.

So the EP projection method on the surface seems to be the holy grail of answers.

You guys that get these great images of Saturn / Jupiter how is your system setup? What am I missing. I do realise that I'm limited by the scope that I use, and buying a C11 or C14 is not an option.

A 7" F15 must be capable of more than I'm getting???

20277d1237680374-saturn-21-03-saturn-21-03-09.jpg

Cheers

Ant

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Ant

Ant

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Cheers Gaz,

The only other settings that I think were important were the Gain / Gamma settings.

Gain was right up - as high as it would go.

The Gamma was low ish (around 60-70 IIRC).

Cheers

Ant

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Ant

Ant

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Ok this is what I'm going to try next.

In the past I've used the EP projection method (But in the past I've used copious amounts of tape to hold the webcam in place - this time with the DMK I'm taking more care).

I have my old projection tube, which holds a nice Orion Orthoscopic 10mm EP, I glued part of an old focuser (the 1.25" adapter part).

In this first image you can see the completed unit...

In this one you can see the 10mm EP inside the projection tube.

To get the eyepeice in and out you have to unscrew and remove the 1.25" adapter part, leaving just

Should be interesting to see if it works at all :)

Ant

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barkis

barkis

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I thought the eyepiece to sensor distance deternined the focal ratio, and therefore Image size. There is a possibility of the projected image being too large to fit in it's entirety on the chip. OK for high res lunar, but if Saturn is the target, you are looking to grab the whole planet. Of course we are in the digital age, so I am unsure of what I'm saying.

Ron.

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GazOC

GazOC

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Cheers Ron.:)

Ant, just a thought on the frame rate issue. Are you still using that IR pass filter? They block a lot of light and might not be needed on nights of good seeing.

I took some lunar shots last time out under good but not great conditions. One set with a red filter (same idea as your IR pass) had to be taken at around 8-10 FPS due to the blocked light and another set without a filter that was able to get up to 30 FPS. I couldn't tell any difference in quality at all, the faster frame rate seemed to do as good a job as the filter in capturing the moments of good seeing and I got the frames captured a damn site quicker!! In future I only intend using the filter on nights of poor seeing or when the Moon is at a low altitude.

Of couse, if you arn't using the IR pass filter, you can just ignore this post...:)

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Ant

Ant

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Morning all,

Ah OK didn't realise that the IR pass filter would block that much light. I've left it on since having it - I'll remove it tonight.

The distance between EP and chip does affect the image scale and the current position of the chip in the imaging train may well be too far.

The bottom section of this adapter should have a T ring screwed on to it for SLR imaging - I've removed that and added the 1.25" Adapter part so that I can securely hold the DMK in place.

I am a little bit concerned that the distance will be too great - but time will tell, hopefully the next few days I'll be able to test it out!

Cheers

Ant

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GazOC

GazOC

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Visible light is roughy from around 400-700 nanometers and that filter knocks out everything under about 670 nm, so thats quite a chunk. For planetary use I think IR frames are supposed to be taken and added to full colour or RGB frames to "sharpen up" the final image rather than used on their own.

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beamish

beamish

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Not sure if this is correct but I seem to recall being told/or read, that image scale could be increased when using a barlow by pulling the w/cam further out/away from the barlow or using a spacer between the barlow and the w/cam. Something to do with the light cone from the barlow being very shallow almost parallel.:)

Karlo

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Ant

Ant

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Quite right Karlo - but only to a point.

I'm trying to avoid a barlow as it lowers brightness...

But I've just looked through the IR pass filter and it block a massive amount of light. I mean MASSIVE.

Just holding it up and looking through it I estimate around 60 - 70%.

Removing the filter will help no end.

Ant

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beamish

beamish

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I would have thought the IR pass (having made one for myself) would only be useful on bright objects when seeing is none too great ( yeah yeah most nights I know), but yup removing that from the equation should certainly help raise the frame rates. I wouldn't be at all surprised if you've underestimated the amount of light the filter cuts out. Mine's opaque to the visible light to all intents and purposes.

Are you suggesting that with higher frame rates and capture you can consider increasing scale through processing and stacking ?? I can see that would work.

Karlo

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GazOC

GazOC

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Karlo,

Removing the filter will allow the image scale to be increased by using x2 or x3 barlows (f30 and f45) at acceptable frame rates without losing too much light. As you you say, the filter cut out nearly all the visible spectrum.

Gaz

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legion48

legion48

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I'm having the same frustrations as you Ant. I want bigger more detailed images of Saturn but I fear I have pretty much hit a wall due to aperture and camera. I think you have a good chance of real improvement with you setup, it's just a case of getting out there at every opportunity and practice, practice, practice. When it all comes together, seeing included, I'm sure you'll be pleased with the results.

P.S. Can you post a single frame from your next Saturn avi please?

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barkis

barkis

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Quite right Karlo - but only to a point.

I'm trying to avoid a barlow as it lowers brightness...

But I've just looked through the IR pass filter and it block a massive amount of light. I mean MASSIVE.

Just holding it up and looking through it I estimate around 60 - 70%.

Removing the filter will help no end.

Ant

The Barlow will lose you about 3% of the light Ant. Not a lot really.

I gleaned that Info. from here.

http://www.astunit.com/tutorials/barlow.htm#%5B2%5D

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Ant

Ant

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Here you go Tony.

We have similar scopes and similar camera's so what we find out should relate to us both.

Here is a pic of the back end of the MAK, with the DMK in place at prime focus.

I've now added in the projection tube, I've marked the rough position of the 10mm EP - it's held in place by the thumb screw that the line goes to.

I am a little worried that the distance between the EP and the chip is way to far - it's about double the distance I used to have it when using the Toucm on the 200mm F5 Newt.

But if needed I'll break the two parts apart and try an method that brings that chip closer to the EP.

Just need clear skies now!

Cheers

Ant

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Ant

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You are right Ron.

The glass within the barlow will lower the brightness by around 3% - I thought that it was a little less than than but 3% is in the right ball park.

But that 3% loss is in addition to the loss through increasing the Focal ratio of the whole set up. A barlow would turn the 7" F15 into a 7" F30, which has the effect of quadrupling the exposure time for the same image brightness - the image scale has been increased by a factor of 2 though.

By doubling the image scale, you quarter the FOV and have to quadruple to maintain the brightness.

The 3% loss just make my life that little bit worse :)

Ant

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