Planetary Imaging - is natural image scale always better than resampling?
short answer is No.
I did several runs on Jupiter this morning with the 2.5x and 4x powermates. I've featured the best of the 2.5x run in another thread, but wanted to compare and contrast the image taken with the 4x powermate with one through the 2.5x powermate resampled up to match the same image scale.
The difference is striking at least under the conditions present - ranging from 5-7/10 seeing. The image just breaks down with the 4x powermate, I have to crank the gain up too far to use it. The 2.5x seems optimal for this setup and conditions and so the resample looks much better. Seeing may have been marginally worse for the 4x shot, but not to the extent suggested by the difference here.
I've used the 4x on Jupiter under 8/10 conditions and while the image is better it's still not as good as what I can get with the 2.5x. I reckon I'll be waiting for an elusive 9/10 to really make the most of 4x.
It seems, at least sometimes, it pays to resample rather than push up the image scale.
Robert, the left image looks a little out of focus... not sure if that was contributing to the result.
There are a lot of different steps in processing, and some of these (registax) rely on a good signal-to-noise ratio in your raw data. If the image is too dim, or too grainy due to lack of light or too much magnification then it can misbehave. Registax can not align properly if it can't clearly tell the difference between the features and the noise.
For every aperture there will be the "best" image scale, but it's worth remembering that Damian Peach was using the equivaent of a 4x barlow for his stunning Jupiter images last year from Barbados (or so I assume from his labeling them as "F/42") with a C9.25. You can see his images here: http://www.damianpeach.com/best.htm
Your experiment might be more of a test of the limits of the camera than the scope??
thats what i have been thinking too bird, and i am really keen to see the 900nc in action with the c9.25 and 4x powermate. I believe it should "rock" in this setup!!
Certainly agree that there be other factors at work here. I did spend a fair bit of time on the focus, but another problem with high gain is it makes seeing the focus that much harder. Camera and codec may be limiting as well.
Yeh, I love that image of Damian Peach's which is why I bought the 4x powermate. Suspect though it's only gonna shine on a night of 9/10 seeing!
"All images were taken using a Celestron C11 mounted on an AP900GTO mount. A DMK 21BF04 camera was used. RGB is done using a Homeyer Motorized filter wheel."
It also proved to me that I need to use a CRT to view these. On my laptop screen, this is slightly smudged, along with birds and other top class images. On the CRT, they have fantastic detail
I believe that there is room for this 900nc and 4x powermate in 7/10 or 8/10 seeing in a c9.25.
After that, it is off to the filter wheels and hish speed cameras or Arthurs newie or the one that Mike is getting to test.
I was always confident that Chris and Damien both resample - you can tell simply by looking at the image scale versus the focal length of their setup (scope + barlow + chip size of the camera). But as I said in the other thread, they have great seeing and lots of frames so that the resample doesn't look grainy and dim like it does when I do it
Robert, your comparison is a good one in ordinary seeing.. It's best to have a smaller, sharper image than a large blurry one. The type of image scale you see in Damien's and Chris's resampled images is almost impossible to get with a scope of that aperture and focal length. You'd need a big barlow + a lot of extension tubes, and perfect seeing. In the case of perfect seeing, I would expect that native focal length is better than resampling, as long as the seeing can support it.
If you have a very large aperture scope with a long focal length (like a 25" dob or something), then you could probably get that sort of native focal length as long as the seeing supported it.
Had a quick look at the specs and was a little surprised to see max frame rate of only 30fps???
I would have thought you'd be able to get more frames per sec uncompressed for a genuine USB2????
I'm sure 30fps is plenty enough for just about most targets, but will be really interested to see how it goes. Looking forward to reading your thoughts. Definitely hope the conditions are favourable for you
We won't need to go any higher than 30fps. The higher the frame rate, the less light that's coming in on each exposure and so the image will get too dim.
It's likely that I'll only be using 10 or 15fps as a max - the hope is though, that the higher (uncompressed) frame rate will deliver more sharp raw frames in a shorter period of time when the seeing isn't that great - it's got a better chance of capturing more good frames.
Plus, the fact that the raw data will be uncompressed will hopefully deliver better quality raw frames. I just need to figure out how to stick it down my focuser without breaking the thing, if I have to return it after 2 weeks
The camera's sensitivity would also dictate how high you can push the frame rate without dimming too much, thus more frames on a fast rotating object like jupiter
Very true - this V-Gear camera has the same chip as the ToUcam, so I know what to expect in terms of sensitivity.
Obviously that's where the newer high-end cameras like the DMK's, LU's and DX's excel, as they are more sensitive with less noise. They come at a price, though.
Just back on that point about CRTs.
I see a big difference when I compare images on my laptop.
I do all my processing on the main computer with a CRT and the images look much better. I get a shock when viewing them on the laptop.
I know the flat screens are getting better but my lappy is an older one so not too crash hot.
Do you think this also affects the settings when capturing avi's?
Would it be better using a CRT even for capture?
Just back on that point about CRTs.
I see a big difference when I compare images on my laptop.
I do all my processing on the main computer with a CRT and the images look much better. I get a shock when viewing them on the laptop.
I know the flat screens are getting better but my lappy is an older one so not too crash hot.
Do you think this also affects the settings when capturing avi's?
Would it be better using a CRT even for capture?
Just wondering.
not sure ANdrew... I actually have the opposite problem as I do my processing on a laptop and then get surprised at how they don't look right on the CRT. I've got a fairly new lappy with a shiny high res screen, but when I optimise for this it comes out dark and discoloured (more yellowy) on my CRT at work.
Thinking a little more on this I don't think for capture it's all that important so long as you can see sharply enough to focus. Colour etc can be sorted out later.
