M83 gso rc8

[xcoupeb]

First light with new rc8 its actually my second one, the first being sent back to retailer for replacement as it had a bad reflection problem. The new one has a slightly different secondary housing and spider vane design, maybe this was part of the problem with the first.

I managed to get 20 * 300sec of m83 with 5dmark2 with hotech field flattener on eq6 mount and it was a first for the guiding setup as well with my ed80 piggybacked with ssag.
I was a bit uncertain how this setup would go for guiding but it seemed to work very well.

Darks and flats applied and stacked in dss and processing done with photoshop cs5.

Also i have noticed that the stars in the lower right hand corner are a bit egg shaped, would this be collimation or just a bit of tilt in the imaging train??

thanks Gavin

[stevous67]

Hi Gavin,

Seems the guiding is working well, and a nice result for the image. In the past for me, egg shaped stars in one corner was a collimation issue.

There's nice detail in the core, good effort.

Steve

[Paul Haese]

Looks pretty good. Star colour needs addressing and some selective sharpening needed in the galaxy, but overall a pleasing image.

The egg shape stars might also be tilt in one corner. Check your collimation carefully to make certain collimation is good.

[tilbrook@rbe.ne]

Hi Gavin,

That's a nice image, far better than Iv'e managed thus far, I'll have to give it another go.

Cheers,

Justin.

[multiweb]

Some really great details in the galaxy. Very nicely done indeed. :thumbsup:

[gregbradley]

I'd say tilt. I am not a collimation expert but I thought that would affect all stars not just one side of the image. What you are showing there I have seen on scopes with tilt and fixing the tilt stopped it.

As a generality DSLR images often have blown out white stars instead of coloured stars. I find it odd a 5D mk ii would do that. What ISO did you use?

Better to do shorter subs and more of them than longer subs and blowing out your stars.

What is happening with these white stars is your well capacity of the pixels is being maxed out. They are full and overflowing. So they go to max number of brightness which is white.

Same with the core of M83 which is yellowish.

I'd watch that when using DSLRs. I see it a lot and I think that is the only solution - ISO800 and 2.5 or 3 minutes instead of 5 minutes and lots of them.

You do see some DSLR images (usually a minority so this is a common problem) that retain star colours so they can do it.

CCD cameras usually have larger wells.

Greg.

[xcoupeb]

Thanks everyone for your comments, Greg i did think at the time 5minutes might be a bit too long but i think i was blinded a bit by the fact that i could finally guide for longer than 3mins with round stars!

Next time will try around the 3min mark and see how its looking. The iso was 1000 am i right in thinking if i go shorter i should up the iso to 1600 perhaps? Or does this just depend on sky glow and washout?

Will also try to fix the tilt and/or collimation.
Im very pleased with this scope and hopefully a dedicated ccd wont be too far away and then i guess the learning curve goes very steep!

[gregbradley]

Optimum ISO seems to be a point of debate. Often quoted that ISO1600 is a ceiling. I got my best DSLR image at ISO3200 in winter.

ISO is really just the gain of the amplifier circuit at each pixel. But I did read on another forum that the way it works its not just as simple as amping everything up including the noise.

I think the short answer would be it would depend on your camera.

5D mk ii may be best at ISO1600 and other cameras ISO800. 5D mark iii or Nikon D800 which have superior high ISO low noise performance may be better at ISO3200 or 6400. Perhaps even higher for the mark iii in jpeg. Both cameras shoot up to ISO12800 cleanly and 5D mk iii even higher in jpeg only.

Ideal exposure length would be measured by amount of histogram filled. Some say 1/3rd histogram, another said 3/4. I am not sure of this point.

I would say the point where stars still retain their colour and not beyond.
You may need to find that point by trial and error.

At least in dark skies you don't have to worry so much about sky glow.

I am about to shoot some DSLR astroimaging myself once I get a Nikon D800E but that will be a while as they aren't in the streets yet. Mainly Milky Way widefield mosaics and time lapse but also some deep sky objects to see how 36mp looks on a fast APO with perfect optics.

Greg.

[Ross G]

Sharp and detailed Gavin.

Looks good.

I have also just acquired a GSO RC8. It could be another month before I can start using it so it's good to see what it's capable of.

Thanks.

Ross.

[strongmanmike]

This is a rather classical view of this classical galaxy, nice work Gavin.

Mike

[astronobob]

A great result on this galaxy Gavin, dig the colour and lane detail,
Cool Image !