Jupiter

[Legin (Nigel)]

Any suggestions on how to improve my images.

I use an Orion 12in Dobsonian, DMK41 for b&W and a D3200 for colour. I am finding it extremely hard to focus. I know I should be able to get heaps more detail from a 12inch scope. The focal length is 1500mm and these images have both employed a 2.5x barlow.

I understand seeing is a BIG factor and I get the maximum magnification. But if I work it all out I should be getting a magnification of approximately 150x from my dSLR and 468x from the dmk41 when using the 2.5x barlow.

As expected if I use the 3x barlow things become quite difficult to focus. I figure this is largely due to the magnification limit of the scope. Incidentally the DMK gives great images at prime focus.

What I normally do is go outside and set up my telescope get everything in frame with either the dmk41 or the dSLR. Then I zoom in 2x with the camera or software and focus as best I can. Depending on the seeing this can be very tricky some nights.

Then I use the camera to record video which I convert to avi later and the DMK records avi files natively. I usually record about 700 frames with the DMK and a minute or so with the dSLR (which has about twice the frame rate).

Then I use Autostakkert or registax to stack the image. Works pretty well but I still think the focus looks a bit off the entire image seems a bit soft. With the colour images I am recording over 1500 frames and keeping only the top 40%. The DMK41 only records about 6-700 frames within a minute but again the top 40% are kept when stacking.

I have tried other percentages when stacking 10, 20, 30, 50, 60 but 40% seems to be about the best. Depends on the night as well if it was very good seeing then I can get away with a higher %.

However the images still seem soft and lacking detail. I am not sure if it just seeing or focus but I have seen far more detailed images from people using smaller scope or the same set up as myself.

I am getting better with practice but honestly I do not know what else to improve.

I have tried tinkering with the gain and gamma within IC Capture but, as expected, it doesn't really change anything. The image gets dimmer or brighter and that is about it. If anything if I set these settings above anything but minimal it can make the image worse. I usually have my gamma at 60 and the gain set to zero (seem to have troubles with it being any higher).

Any ideas or suggestions. Yeah I know "practice".

[raymo]

nobody seems to be in a hurry to offer any opinions, so I thought I'd
jump in. Firstly, I know nothing about CCD cameras, being a film man
from way back, but some things seem obvious in your post. Firstly,
your DSLR colour images are sharper than the monochrome ones, so
maybe something is slightly awry with your CCD optical train, spacing
of components or something. I find A Bahtinov mask the most
convenient, cheap, and quick way of focusing. Secondly, a barlow
will soften the image a little, or quite a lot, depending on it's quality.
Thirdly, the images taken at lower magnification are sharper. To Take sharp pics at 468x with any scope is only possible when the atmosphere
permits it, which is not that often. Many quality planetary images are
taken with longer focal length scopes which removes the need for a
barlow. I don't know if any of this helped.
raymo

[rustigsmed (Russell)]

Hi Nigel they are some very nice images.

I'm by no means any planetary astrophotographer but here are some points i've read / learnt along the way.

Focus on a bright star in live view at a high magnification, then slew over to the planet. it can be difficult to get it right, fine movements are required!

Seeing is pretty much everything; even if it is a clear and windless night, the earth's jetstream could be tearing along overhead. people use the skyskippy site or bom website to check jetstream conditions. anything over 40kts at 200 hPa as i understand it will severly diminish your chances of good seeing - especially at a higher magnification.

Jupiter is very low in the sky this season, with it better suited to the northern hemisphere. this means we have to view it through more atmosphere which degrades the image. However Saturn will be nice and high this season so that is a bonus! http://www.bom.gov.au/australia/char...t=Refresh+View

Jupiter rotates quite fast and i think i read that movement is detectable in videos of over 1 minute? maybe a bit longer. You could try the derotation program WINJUPOS that many have had success with at getting a sharper results. it can allow you to capture more frames too, which can improve the signal to noise ratio of the image. http://www.damianpeach.com/barbados10rw.htm

anyway thats about all i can add, i think you've done a fantastic job!

clear skies

Russ

[Legin (Nigel)]

Yeah now that I think about it my dSLR images are sharper. Hmmm I didn't expect it as each individual frame is far more noisy than the DMK. The dSLR wins at frame rate though being 25fps compared to the 15fps that the DMK41 can record.

I try not to record over a minute but even so you can see that that extra 10fps adds up fast. Not quite double but nearly.

The problem with my dSLR is that it only records .mov format. In the past I would convert the .mov to image sequence then load that into registax and stack it that way. However now I convert it to avi then I often have to fix it in virtual dub. Then I can stack it. Works an absolute treat now.

I think the main difference between my dSLR and DMK shots is the magnification. As one would expect the higher you go the more problems you will run into. I use the same Barlow/s on my dSLR as the DMK. However the DMK has a much smaller chip size and as such magnifies everything much more. It is fine at prime focus however with the barlow/s it gets to be to high a magnification under anything but pristine seeing conditions.

So if anything all this trial and error has helped me get to know my gear and limitations.

I do have another problem now though. It is becoming addictive.