Focusing when imaging wide field

[ubertank]

Hi everyone,

Went outside with the 1100d and a tripod tonight to have a crack at getting a wide field star shot. Followed this guide for reference:

So, i went outside and took around 10-15 30 second exposures, 5 darks and headed inside. Sadly DSS started giving me the following error:

"Only one frame (out of 10) will be stacked.

You should check/change the star detection threshold to detect more stars" etc..

No settings I adjusted could find me more than two stars sadly.

So after doing a bit of googline it looks like it could be a couple of things. The first of which was that my image wasn't focussed well enough for DSS tor recognise any stars. My first question then is does anyone have any advice on how to get a decent focus on an 1100D when it's pointing vertically upwards into a dark sky?

My next question is, just how dark a sky do you need to DSS to work properly? I'm in fairly light polluted skies to be honest so thought that could be a big contributing factor.

My final question is probably an obvious one, but I presume that if I'm taking ten 30 second exposures I need to be pretty quick and take every one quickly after the previous to avoid too much field rotation. I've read about "Mirror Lock up" and find conflicting reports as to whether or not the 1100D actually has it. Anyone able to give me a quick laymans on what this is and whether or not I actually have it.

Thanks a lot for any help in advance guys. I plan to go out to a darker sky tomorrow night and have another go at it so a bit of guidance before then would be really helpful.

[ubertank]

Bump. Anyone able to offer any advice here?

[leemanley]

What lense are you using ?

Does the camera have live view ?

Many more learned people on here to help, but I'd have thought you should be able to get some decent results LP or not.

As for dss, what version are you using, I had many issues with it , all it took was a 1 min download to put it right !

[JamesF]

Take a relatively quick shot manually, say about ten to fifteen seconds, and use that to check the focus before committing yourself. If you're using APT then it has a tool to help with focus (I think it will even focus for you if stars are visible in live view) and I believe BYE can do the same.

I think DSS likes its stars to be fairly round, too. If you have "eggy" stars because of trailing then it gets unhappy.

James

[ubertank]

I think it may have been a star trail issue as some of them were a little "eggy".

I actually followed the guide you did James -

This guide says to use 30 sec exposures but they seem like they may be a little too long. I've done it three times now and cannot get DSS to recognise more than one star and fail to stack. I'm doing something wrong somewhere along the line here.

Lee, it's an 1100D with the standard 18-55 kit.

Here's a totally unmodified photo converted to a JPEG from RAW for you to see what sort of detail I'm getting.

http://i296.photobucket.com/albums/mm174/ubertank/IMG_0083_zps11819115.jpg

I was really surprised actually as that's a 30 second exposure and you can see only a few stars in there. Is this lack of stars indicative of a setting I may have overlooked somewhere. It can't be light pollution as you would see an orange colour in the photo, am I right?

Very confused as to why I'm getting such bad results.

Thanks in advance for any further advice. Apologies if asking stupid questions. I'm really appreciative of any advice anyone can offer.

[Guest]

Hi There,

What ISO are you using when taking the pics? you want at least 800 if not 1600, also have you got the lens aperture right open on around 3.5 or 4.0 and at the lowest zoom of 18mm this is a single exposure from a Canon 1000d at 28mm with the settings i mentioned of the area around the north star (in middle of pic) to show you what you should be seeing.

And a stack of 50 of them in DSS here with no tracking:

Olly

[JamesF]

In DSS at the top right of the window there's a slider. If you load in the images, select one and then push the slider to the left a fair it it should stretch the histogram so you can see what's there.

If you could convert one of your RAWs to TIFF, crop it to make a manageable file size and post a link that would be handy. JPEGs really aren't good for this sort of thing because of the compression loss and lack of dynamic range.

James

[dph1nm]

If your stars are too bloated, try using the "Create super-pixels from the raw Bayer matrix" option in the RAW and FITS DPP settings tab. This effectively halves the resolution of the image and DSS then has a better chance of picking up the stars.

NigelM

[Stovetop]

I've tried using RAW in DSS with my Canon T3i (600D). I get a very narrow image in DSS and the program laughs at me. I've read in a couple of places that Canon RAW and Windows 7 are not compatible. I've been so frustrated with trying to work with RAW that I've given up. Canon has not updated a utility for their version of RAW that works with Win 7. I wonder how long it will take them to get around to Windows 8.

[JamesF]

You need a different version of DSS. I'll find the link in a moment.

James

[JamesF]

Here it is:

http://tech.groups.yahoo.com/group/DeepSkyStacker/

Try the beta version (3.3.3b47) linked about halfway down that page. That's usually fixed the problem when people have reported the issue you're seeing as far as I'm aware.

James

[Stovetop]

Thanks James. I'll give it a try.

[Stovetop]

Thanks James:

I installed the DSS version you suggested. I stacked four lights only just to see if it would work, and yes, it does.

This is a wide field of M31.

Thanks for the help.

[ubertank]

This was the exact issue that I as having.

Installed the same version and now it can find stars and stack. The resulting image still doesn't show up many stars, but I think I have to put this down to a bright moon and not the darkest area in the world.

[JamesF]

Excellent news

Have you tried stretching the image histogram, ubertank? The Moon does cause problems, but if you've not tried stretching the histogram you may find there's detail hidden away that you can't see at first.

James

[ubertank]

I had a play around with it yeah and managed to get a few more. DSS is still saying it's only going to stack about 12 stars which is still pretty bad obviously.

I need to eliminate all possibilities really, so next time there's no moon and a clear sky I'm going to a better site to hopefully get better results.

[P_Monty]

Just to add my 2p. www.dpreview.com (which I trust to be accurate) says the 1100D does have mirror lock up, but its a customisable function so you might have to rummage through the menus to see how to set it up.

As to a laymans guide... The camera has a mirror which normally reflects light from the lens up to a prism or mirror and through the eyepiece. When you take a picture, this mirror flips out of the way just before the shutter opens to expose the sensor. This flipping can cause a fair amount of vibration in the camera which leads to a blur in the image. With lock up, the mirror flips out of the way immediately and you open the shutter later after the vibrations have died down. Expanding on this, when in live view - as the image is read from the sensor, the mirror must already be out of the way.

Hope that helps