Jupiter 250810

[Virgoman]

Hi everyone,

Just attaching an image of Jupiter - my first with a C8 SCT acquired in the wee small hours of 26/08/10. Am pleased with the nice sharp globe but there is a distinct lack of detail within the bands. I don`t know why this is.

The scope appears to be well collimated with nice uniform star tests and the planet gave a nice image through the eyepiece. Any comments/suggestions would be most welcome. Imaging was done using a Philips Toucam with IR filter.

regards,

Ralph:)

[brianb]

Any comments/suggestions would be most welcome. Imaging was done using a Philips Toucam with IR filter.

Very bad seeing or/and inaccurate focus, I think. It helps to keep the exposure short even if it means winding the gain up....

[tooth_dr]

Hi Ralph

Very nice image, still plenty of detail visible.

Brian - I always keep my exposures set such that the gain is at its lowest possible setting i.e. my exposures are as short as possible. Is this the wrong approach?

[brianb]

Brian - I always keep my exposures set such that the gain is at its lowest possible setting i.e. my exposures are as short as possible. Is this the wrong approach?

I'm confused ... if I turn up the gain I get shorter exposures ...

Yesterday morning with the DMK21 at f/18 on Jupiter I was using exposure = 1/30 sec, gain was around 650 (a bit less than that for green & a bit more for blue). At min gain (260) the exposure would have been about 1/5 sec. At max gain (1024) the exposure would have been around 1/120 sec or maybe a bit shorter but the noise would have been horrible. There's a compromise somewhere ... the more noisy the individual images, the more you have to stack so it actually takes longer beyond a certain point even though you get a higher percentage of usable frames ... and time is your enemy, especially for Jupiter which is rotating fast!

Different software may of course display gain differently.

[tooth_dr]

You're right to be confused! I meant longer not shorter! There is so much more to this than I initally thought. I was using the longest exposure possible to keep the gain at a minimum.

[riklaunim]

With DMK21 max gain at shortest exposures wins for me. I capture about 1200-1500 frames per channel. It's different for a webcam.

[tooth_dr]

Interesting. Looking forward to getting a DMK soon,.

[Virgoman]

Hi guys,

Thankyou for taking the trouble to reply. I was out last night and took some more images, these are rubbish - I think/hope seeing last night was an issue. I could not get a satisfactory run at all.

Thanks tooth_dr for your kind image comment. Yours are excellent with plenty of fine detail on the disc and moons nicely captured.

Thanks for the suggestion Brian, I also tend to keep the gain as low as possible with short exposures. I don`t think my camera is duff?

Focussing I know is obviously vital and in using the SCT I sometimes find that the focussing mechanism is short on "feel" and only the lightest touch is required. Do you have any experience of the advertised crayford focusers for SCT`s?

Best Regards,

Ralph

[Virgoman]

Hi guys,

Thankyou for taking the trouble to reply. I was out last night and took some more images, these are rubbish - I think/hope seeing last night was an issue. I could not get a satisfactory run at all.

Thanks tooth_dr for your kind image comment. Yours are excellent with plenty of fine detail on the disc and moons nicely captured.

Thanks for the suggestion Brian, I also tend to keep the gain as low as possible with short exposures. I don`t think my camera is duff?

Focussing I know is obviously vital and in using the SCT I sometimes find that the focussing mechanism is short on "feel" and only the lightest touch is required. Do you have any experience of the advertised crayford focusers for SCT`s?

Best Regards,

Ralph

[brianb]

Focussing I know is obviously vital and in using the SCT I sometimes find that the focussing mechanism is short on "feel" and only the lightest touch is required.

And coarse too.

I have replaced the standard focusing knob on my CPC1100 with the Feathertouch unit which has 10:1 reduction gear. The issue with the bolt on Crayfords is that they tend to be spoil the balance of the instrument, and deny access to the zenith when used with fork mounted instruments (the extra length stops the tube swinging through).

The best replacement/add-on focusers in the world are the high end rack & pinion focusers - unlike Crayfords, they don't slip or creep, and are ideal for computer controlled focusing. Very, very pricey, though.

[Virgoman]

Hi Brian,

Thanks for that information, it is much appreciated.

[red dwalf]

if your using a webcam to capture are you using registax for processing, alot can be gained by using the wavelets properly to gain detail, also start with a good frame image and not just the first one on the screen,

i find that focusing is hard with the sct`s i`ve just purchased a crayford for it but as of yet haven`t tried it, the only problem it might have is that it takes the webcam further from the visual back, i hope this does`nt cause any other focusing problems with the webcam

[Virgoman]

Yes, I did use registax, picked a good reference frame and used wavelet sharpening. Worryingly still no detail jumped out. I have used registax many times with images from a different scope and know what an amazing difference it makes from seemingly dull images. That`s why I was disappointed when nothing appeared!

I am wondering if focussing is the problem , red and would be very interested to see how you get on with your crayford. I agree the SCT focuser can be quite difficult to use. If I may ask, what crayford did you purchase?

Best regards,

Ralph:)

[brianb]

i`ve just purchased a crayford for it but as of yet haven`t tried it, the only problem it might have is that it takes the webcam further from the visual back, i hope this does`nt cause any other focusing problems with the webcam

There's plenty of focusing adjustment in SCTs. Adding length to the optical train tends to increase the working focal ratio, you will probably find that the extra extension means you're working at f/11 or f/12 instead of the nominal f/10.

[red dwalf]

thanks for that Brian, thats good news to here,

the crayford focuser i bought was this one

GSO 2" Dual Speed Crayford Focuser for SCTs

nice micro focus knob on it