Focussing 450d in dark

[Llamanaut]

Hi gang, having read the sticky primers i tried widefield photography for the first time tonight but couldnt get a crisp focus on my Canon 450d, all the stars came out as blobs of light instead of pristine pinpoints. I tried auto-focussing on an object but as i was in a pretty dark area with no street lights the auto-focus just hunted for a target. I tried in manual too but couldnt see any stars brightly enough in either the viewfinder or on liveview... where am i going wrong?

Im using the 450d on fully manual with 30 secs exposure and wide open at f4 with iso at 800.

[Steve 1962]

Hi Llama

Have a look at this thread from a couple of weeks ago - I'd be interested if any of the ideas work with a DSLR and camera lens

http://stargazerslounge.com/beginners-help-advice/100737-focussing-through-dslr.html

Cheers

Steve

[jgs001]

Use liveview, put the ISO to 1600. Pick a really bright star something like Arcturus works really well, centre it on screen, zoom all the way in to 10x on the liveview, and tweak the focus on the lens till the blob is as small as possible. Reset to your capture settings and away you go. If you're using the kit lens, don't forget to turn off IS, it will activate and cause odd wobbles and what appear to be focus issues. Mars or another planet, also work well for this trick.

[Llamanaut]

Hi Steve, yes i spotted your advice last week, didnt think it would work on just a normal dslr lens but thinking about it i suppose the telescope is just the same. Im in the process of making a mask now, fingers crossed for clear skies tonight to test it out. Ive had a look at the deep sky stacker manual but it doesnt really mention widefield photography... how many pictures should i use in the stack and do i leave the camera in its original position or move it slightly to compensate for movement? I took around 10 light and 10 dark (forgot the offsets) Any other advice?

[Demonperformer]

Lots of good advice here: http://stargazerslounge.com/imaging-tips-tricks-techniques/73737-basic-widefield-camera-tripod.html

[Llamanaut]

Thanks John, i read the basic widefield sticky which is what inspired me to take the camera with me last night. Good advice about live view, i forgot you could zoom in! I'll give all your tips a go on the next clear night

[Llamanaut]

So, had a think about how to go about tackling the Deep Sky Stacker... it requires stacking 4 types of frame.... light frames - the pics of the stars, dark frames - same settings with lens cap on, bias frames - shortest exposure with lens cap on same iso and flat frames - bright and white in AV mode with same iso. Thinking about the settings i used last night ive just taken 20 dark, 20 bias and 20 flat... i've stored them in 3 folders so i know which is which. Hopefully it'll save messing about after ive taken my pics of my chosen starfield. Ive hit snags with the mask device as i cant cut triangles small enough without the cardboard falling apart when applied. Im going to try and focus on mars or venus with liveview x10 then just move around to whatever constellation is brightest... i'll let you know how i get on.

[jgs001]

What you've done is a great idea, but... the Flats need to be taken with no changes at all in the camera.. i.e. the exact same focus point etc. To be honest, given the settings you're using, I wouldn't worry about them. Bias frames I've always had trouble with, and don't now include with my 450d. As for darks, they need to be taken at about the same temperature, so as it seems to be quite warm today, aren't going to work well with your lights.

Don't worry too much about what DSS says, just follow the widefield with a tripod, get lights and darks and see how you get on...

If you do decide to do flats, make sure nothing at all has changed with the camera (including focus), set the camera to Av mode and let it work out the exposure.

[Llamanaut]

ah well it seemed like a good idea at the time! So you just use lights and darks? Thanks for the advice, i'll let you know how it all goes...

[jgs001]

For tripod mounted, that's all I ever use (and sometimes, depending on what I'm shooting, only lights...). I've only ever had problems with bias. I do use flats for my telescope imaging though.

[Llamanaut]

i suppose its trial and error really... did enjoy imaging last night though...

[Demonperformer]

Im using the 450d on fully manual with 30 secs exposure and wide open at f4 with iso at 800.

Just a thought, Rich. When I did my first exposures with the Canon last week, I found 30 seconds gave quite a lot of star-trailing. True I was aiming pretty much at the Celestial Equator, which maximises this, but that could be part of the problem of your 'blobby' stars.

[Llamanaut]

what do you think then 20 seconds? Will i have to move the camera slightly every couple of minutes or will the deep sky stacker sort this out and mosaic the final picture?

[Demonperformer]

As long as the stars on the individual frames are not trailed, DSS should (as I understand it) be able to line everything up. The problem is if the stars trail on the individual frames then there is little you can do to get rid of them.

[jgs001]

well nearly... a small amount of trailling, you have to look real close at the image, and you'll be fine, too much and you won't. DSS will handle the derotation of the individiual frames, but don't take too many, or you start to lose definition in the corners due to the rotation. I never worked out the limit.

[Llamanaut]

fingers crossed i'll have a bash at it tonight, it does look a bit hazy down here on the south coast though - i'll let you know how i get on

[jgs001]

Good luck.

[Llamanaut]

As promised here are the results of tonights foray into the dark art of widefield...

[Llamanaut]

[Llamanaut]

[Llamanaut]

Im guessing i need more practise focussing was a real pain again, even at iso1600 and liveview i couldnt really see anything. I focussed on the thin sliver of moon that was out tonight

[Demonperformer]

Are those full size frames or have you reduced them. If they are full size, I'm quite impressed. There is a small amount of trailing visible on some of the brighter stars, but the fainter ones in the middle look really good.

Here's my first attempt, reduced to 50%, and even the stars in Orion's belt, which is what I was aiming at, show marked trailing.

Stargazers Lounge - Demonperformer's Album: Miscellaneous - Picture

[jgs001]

They look very good. Are they straight out of DSS ?? I'd guess so... did you stretch the histogram at all ? I put the basics in the widefield on a tripod tutorial.

[LukeSkywatcher]

Focusing is a real thorn in my side. I find it near impossible even when imaging the moon. Things look focused on the LCD but on the computer they are slightly off. Sometimes its not a problem but its really hit and miss.

[Llamanaut]

I had problems with focussing so really i had to guesstimate what i was shooting at. I couldnt open the dss tiff file in my editing suite (elements 6) it says it doesnt support hdr images... so i had to copy it to clipboard and paste it into ms paint saving as a jpeg... there is some trailing on the bitmap original. Next session i think i'll hook up my laptop to the camera and see if i can get some better focus. I took one of the moon, venus and pleiades but its over exposed (the moon detail is blown so i need to play with the exposure) Had a brilliant night last night, stayed up quite late and now suffering at work (may even go out again tonight... never learn do we?)