My first dissapointing session

[Nova]

As the sky was nice and clear last night I decided to try out my Tal 3x barlow with my SPC for the first time. I struggled for around an hour to try and achieve a nice sharp focus on Jupiter (with the SW autofocusser) but it just was not happening. The best I could manage was an orb with very faintly visible bands. I tried running what I did capture through Registax but it looked dredfull so after around 4 hours I finally gave up and went to bed in a bad mood. Im curious as to what the problem was. Could it be that conditions were not as good as they looked? Observationally everything looked ok.

This was the first big dissapointment ive had, im sure its not the barlow. Ive heard so many good things about it but could it be thats its just too much for my 150p?

[Shibby]

Probably down to poor seeing I would say; sometimes it's that bad the planet looks out of focus. I tend to focus on a bright star with a bahtinov mask first then slew to the planet. Also, had you allowed the scope plenty of time to cool down first?

[Tinker1947]

Maybe try with out the Barlow, sort of start at the bottom and work upwards until you find the limit of your kit.

[steelfixer]

Hi Steve

Are you using an IR filter ?

[michael.h.f.wilkinson]

A 150P with 3x Barlow should be F/15 which should be OK (I use F/20 and even occasionally F/30 on Jupiter). Play around with exposure time (it needs to be higher with a 3x Barlow). This will reduce photon noise and make it easier to get a sharp image. You can also try to focus on a bright star and then swing back to Jupiter.

[Ant]

Hows the collimation of the scope...?

A webcam is generally equivalent to a 6mm EP I believe. So around 125x without the barlow.

Chuck in a 3x and your up to c375x. The maximum limit is generally accepted as being 50x per inch - so around 300.

The stacking process with generally allow a little movement in that for imaging, but still I think you need a pretty good night seeing wise to really make use of the barlow.

Collimation, cool down and not viewing over houses would be fairly important.

Cheers

Ant

[michael.h.f.wilkinson]

Hows the collimation of the scope...?

A webcam is generally equivalent to a 6mm EP I believe. So around 125x without the barlow.

Chuck in a 3x and your up to c375x. The maximum limit is generally accepted as being 50x per inch - so around 300.

The stacking process with generally allow a little movement in that for imaging, but still I think you need a pretty good night seeing wise to really make use of the barlow.

Collimation, cool down and not viewing over houses would be fairly important.

Cheers

Ant

In webcam or CCD imaging of planets, you want to match the resolution of the scope in the focal plane to the pixel size of the chip. The 50x the diameter rule does not hold. For an SPC 900 F/20 to F/30 holds up quite well. F/15 is on the short side (and therefore should be well within range of the abilities of the scope)

[Nova]

some good points, thanks all. I allowed plenty of cool down time. I have had a few succesfull attemps in the past using a 2x barlow and no barlow so this is kind of the next step up for me. Yep the IR filter is in

Michael, how do I adjust the exposure time in Sharpcap? if I move the exposure slider up the image becomes too bright. I played around with the frame rate but for some reason even when set at 60fps it only ran at 30fps max (possibly down to lap top spec?).

On inspection the collimation was slightly off but it was not noticable when looking through an ep. This possibly contributed. I really hope this was just a bad night.

[michael.h.f.wilkinson]

Two factors control brightness: the exposure time and the gain of the amplifier (sometimes denoted as "brightness", I do not use sharpcap so do not know what they call it). High gain and short exposure time might yield the same overall brightness as low gain long exposure time, but the photon noise will be amplified in the former setting. 30 FPS is the limit I can get on mu SPC900 (original). Anyway, I usually shoot at 10-15 frames, which seems to reduce read-out noise a bit, and still gets me plenty of frames. In wxAstrocapture I first set exposure time to the maximum (1/25th of a second), and then adjust the gain, offset, and colour balance manually to fill the histogram of the captured channels to the maximum extent, without clipping (SharpCap also has the option of showing live histograms for R, G, and . This gives the optimal signal to noise ratio in all bands. Later during processing I can adjust the colours to my own taste.

[Nova]

Im sure this must be possible in Sharpcap but perhaps ill give wxastrocapture a go. Ill have to try again soon and try and figure put what went wrong

[Nova]

Just to add some closure to this I think I found the problem. I noticed before I started that my collimation was off so set about adjusting, as it turned out the secondary was out which is the first time in just under a year ive had to do it. I aligned everything but something didnt look right. I could see top of the secondary and a little of the ota behind it but couldn't see the bottom of the mirror. after half an hour of adjusting and tinkering I could not make this "mis-alignment" go away so decided I must be me looking at it wrong. It bugged me all day yesterday so wen back to it last night for more tinkering. Still the secondary although central in my fov looked as though it was too low when the cross hairs, reflection and doh nut were all aligned. I have to admit frustration was starting to set in but by pure chance I glanced at the 2" to 1.25" adapter that sits in my focusing tube and to my shame and embaresment the dam thing was not in the focussing tube squarely, it was very slightly off square. A quick loosen of the thumb screws and it popped back in fully. Obviously this again threw out allignment but after going through the whole process of collimation again im pleased to say things are now spot on. Went outside for a star test and think the views im getting are now better than they have ever been, a quick star test turned into a 3hr observing session spent mostly staring open mouthed at the orion nebula and surrounding area. Havent yet tried the camera again but im betting this could have been the reason or at least I hope this is the case

Moral of this story....trust your instincts and always ensure your accessories are square in your focussing tube:o

[michael.h.f.wilkinson]

Glad you have found the problem!

[Tinker1947]

Yes, those secondary mirrors can be a bit of a pain..