a couple of images from a couple nights ago

[Russe]

mhm - phd graph looking ok?! ...

[Thalestris24]

Hi Russe

Guiding looks fine to me but any jumps on the graph whilst you were taking the subs? Do you have a log file? I think flexure or vibration are often causes of misshapen stars but I'm not very experienced at analysing problems.

Louise

[Russe]

So what I've done is - started over. Stopped guiding. Went with Astrotortilla to 3 stars around M51. Then re-started PHD and re-calibrated.

Mhm.

[Russe]

Oh, and the settings for my 9x50 finder guider with a QHY5...

[Ags]

Getting back to the ISO thing lensman, are you saying that ISO should be set to 400-1000 in general, and not to say 100 or 200. I've been experimenting with very low ISO settings to try and keep some star color (without success). I didn't know it might hurt other parts of the image.

[Russe]

Sorry - I've hijacked the thread...

[Russe]

Did we post this link on ISO settings yet? http://www.blackwaterskies.co.uk/2014/01/do-high-isos-make-dslrs-more-sensitive.html?m=1

[Ags]

From Russe's link: "For Canon cameras Unity Gain is likely to be somewhere in the region of ISO 200 or 400." So that would mean my experiments with ISO 100 were doomed to failure.

[Russe]

Seems so. Sry

[lensman57]

Thanks - I'm not able to explain that as well as you have - I was just wondering, whether you thought, if I change to 600s exposures (and have to renew my darks library) - should I at the same time go for ISO400 imaging to reduce noise (if there is a big noise difference between ISO400 & 800 in the Canon 450D). the weather is just too bad to TRY things out...

I have done some ISO 400 exposures but to be honest I would stick to either 800 or 1600.

Regards,

A.G

[lensman57]

From Russe's link: "For Canon cameras Unity Gain is likely to be somewhere in the region of ISO 200 or 400." So that would mean my experiments with ISO 100 were doomed to failure.

This is not failure but by going so low you'd be resticting the dynamic range even further, remember that DSLRs are already at a disadvantage because of the 14 bit capture( at best ) against a  full 16 bit of the CCD, this is a huge difference so no need to reduce it any further, for unity gain if in doubt always opt for a higher gain value, that is why iso 800 is usually accepted as the best compromise.

A.G

[lensman57]

Getting back to the ISO thing lensman, are you saying that ISO should be set to 400-1000 in general, and not to say 100 or 200. I've been experimenting with very low ISO settings to try and keep some star color (without success). I didn't know it might hurt other parts of the image.

Your iso setting will only brighten the captured data it will not increase sensitivity, otherwise there would be no need for mega box imaging telescopes coupled to hugely  expensive astro imaging CCDs, we'd all be buying a Canon or a Nikon with ISO 25600 shooting capability and be done with it. But as you have found out the reality is rather different. I still maintain that some experimentation is required to determine what works best between ISO 400~ 1000. Just to make matters even more complicated a Nikon iso 800 may not be the same as  Canon iso 800 as the two sensors are different and the iso setting  is really an arbitrary  measure of gain. The ISO settings are a hark back from the good old times of the film cameras  ( I did film photography for over twenty years ) where an  emulsion with a speed of iso 400 was really and measurably twice as fast as an emulsion of iso 200 for a panchromatic spectral response, digital does not have such straight forward equations.

A.G