Help! Focusing a DSLR through 8" SN

midnight (Darrin) · #1 15-08-2010, 09:48 PM

Greetings again.

I am getting a little mystified with nailing the focus for the moon.

Basically I am trying to understand the limits of my camera and scope before I target some more difficult objects.

My problem is that when I use the Livefocus and zoom in to 10X (its a Canon 40D) I can fine tune the focus so that the liveview is really sharp despite the resolution of the 40D's LCD.

Then when I take the photo - it just never seems to be as sharp as the liveview - has anyone noticed this?

My setup is :
Canon 40D prime focus via a t-ring into a Meade LXD55 8"SN. The OTA has been laser collimated.
Mirror lockup turned on - I wait at least 6 sec before the 2nd trigger.
Remote release cable so I don't touch the camera.
Mount is steady and tracking well.

3 Photos here : All ISO 100. 1/400th ; 1/350th ; 1/750th taken over the last few months here in the backyard.

Any help would be great. Perhaps it's the limit of the camera maybe?

Cheers,
Darrin...

madwayne (Wayne) · #2 16-08-2010, 07:01 AM

Darrin

These three look pretty sharp to me, particularly the crescent. Not quite sure what you were expecting with your equipment but I think they are great.

You could always Google Bahtinov mask or search the classifieds here, there are members here making them. Great focus aid but as I say in my opinion you have done a super job without one.

Wayne

sheeny (Al) · #3 16-08-2010, 07:12 AM

I agree with Wayne.

I can't pick a problem with the focus you have achieved in these images. Did you reduce their size to post them? Being a single shot there may be some softness due to seeing which could explain maybe why you aren't satisfied with the results on camera.

The best solution for seeing issues is to take many shots and stack and sharpen them using say Registax, K3CCDTools or AviStack.

Generally focusing on a star is easier than focussing on a planet or the moon, so a Bahtinov mask can come into play there and take the guesswork out of focusing.

Al.

midnight (Darrin) · #4 16-08-2010, 10:37 PM

Wayne, I'll try the Bahtinov mask and see whether there is any finer focusing. Many Thanks for the tip!

Al, yes the photos were reduced in size. The Raw from a 40D is about 10MB. I try the star method occassionally but what I notice is that in liveview the image seems really sharp and when you take the shot and review on the LCD again, it seems much softer. I think this may be more of an illusion in that in liveview you are looking effectively at a live video and your eyes may perceive it clearer - either that or I'm getting old!! Anyway many thanks for your guidance.

Thanks for your kind comments and nice to see that you guys see them as focussed well.

I just get blown away with the quality of the shots posted in the deep space section & solar system section and so I'm taking my steps one by one in the hope one day I can get even 1/4 of the way to these masterpieces :-)

Darrin...

midnight (Darrin) · #5 17-08-2010, 12:02 AM

After looking around, I found an excellant thread on focusing by Al which is great if your camera is hooked up to the computer and trying to focus.

Take a look at this simple but very effective program. Thanks to Al for that thread

.

D...

http://www.iceinspace.com.au/forum/s...ad.php?t=62932

AdrianF (Adrian) · #6 17-08-2010, 06:56 AM

I would be happy with those shots.

Adrian

bmitchell82 (Brendan) · #7 19-08-2010, 10:46 AM

hey mate

I use the 40d as well. and i do know what your saying in relation to the Live view is spectacular but when you go for the shot it is.. sometimes less than what you expected.

Why?

Well DSLR's aren't the right thing for taking planetary type photos! there is this little thing called atmosphere

. When you take the image to get it really crisp the atmosphere has to be dead still. if not it wobbles and slightly blurs the image. not to say that you cant "crisp" it up. Deconvolution works a treat. and some high pass filters applied though Photo shop will adjust the wrongs of the atmosphere to a sense!

If you are wanting to really get into planetary, then the only way to go is a dedicated planetary video camera. off my head i think DMK, FLEA are two of the up there ones. they capture up to 60 frames (possibly more) per second. You then dissect the video into its individual frames with something like Registax and it runs a algorithm over it to pick your best frames (where the atmosphere was still for half a second). then stacks them that is how these planetary dudes get their images so sharp.

Hope that gives you a insight into the inner workings.

If you want to look at what your 40d is capable of check my website all of them are 40d goodness spread between the 10" newt and ED80 refractor.

Brendan

Omaroo (Chris Malikoff) · #8 19-08-2010, 11:09 AM

Darrin - just some basic info.

A Bahtinov mask is brilliant if you're working on deep-sky objects when you can use it to focus on an adjacent medium-bright star - a single "point source" of light. Bahtinov masks do not work at all when trained on a disc - i.e. a planet such as Venus, Jupiter or even worse-still, the Moon.

Even if you do focus on a medium brightness star and then slew to the Moon to take photos, the focal points are way different anyway. The moon does not focus at the same point a star does.

DSLR's are great on the Moon - but not necessarily for other planetary bodies. Seeing is a problem as Brendan points out, and while video cameras such as the DBK can give you an easier time of it all (stacking hundreds of frames automagically), they will never give you the all-round resolution a good DSLR will when seeing conditions are good.

I've even used my FS-102 with a 2x barlow followed by a 5x PowerMate giving an effective focal length of 8,200mm and a focal ratio of around f/78 (!!!) to take full-frame photos of Copernicus with great success. To counter what I mentioned before, I've also used the same combination to get this - in a single shot with the Nikon D40. Seeing was utterly wonderful that night... a rarity, but not impossible to encounter.

asimov (John) · #9 19-08-2010, 12:37 PM

Youv'e pretty well nailed focus on all 3 images I think. Bear in mind, the center & the limb have slighty different focal points. It's very slight & hardly noticeable, however it does affect some images depending on the equipment used.

midnight (Darrin) · #10 19-08-2010, 05:52 PM

Fantastic. I really appreciate the help from everyone and it's got me keen to really try a few minor changes.

Brendan, I didn't realise the 40D was genuinely capable at deep sky until I saw some of your images. You must be rapt with them! I am really keen on the idea of stacking and read up about the ability to statistically lower your noise to help in post processing. After reading up about it, (and having done 2yrs of uni maths for my eng degree and hoping I would rarely use it again!) it actually makes quite a lot of sense. So for now I'll try to get my basic skills up and running but you've given me some insight into this. I'm just worried about field rotation at the moment and whether this will affect stacking as I just can't wait to hook up and start clicking. I have learnt to drift align but the temptation gets the better of me for moon photos - I do a rough level and south align though

! Thanks mate!

Adrian thanks mate for the appraisal

Chris, once again you've given more to think about which really opens up some of the finer points to think about which before a few days ago, I had not even contemplated. I see your point about the Jupiter example. I am assuming that at the same temperature and same setup, a stack of say 50 DSLR images would be better than 50 mid range astro CCDs?? Obviously the CCD seems far more suited to the job overall but if you didn't have one yet... Thanks again for your advice

John, thanks too for your comments. It is hard to show the detail on the site. I will need to register at one of the main online photography joints so I can link some higher res pics but this is crux of my issue and after seeing some gems on this site, I just wasn't sure whether I was hitting the limits of my very ordinary gear. I don't think I have yet. I really want to get into the nitty gritty so that when I upgrade, it is not a dissappointment because of some failure to understand the simpler basics of astro photography and basic processing.

Thanks all for you comments and I'll keep pressing on here in the south west (provided the smoke and fog stays away long enough down here in Collie

)

Darrin...

NorthernLight (Max) · #11 26-08-2010, 11:59 AM

Hey Darrin,

do you keep the mirror locked up after focusing with live-view? Not sure if that would solve your issue but it doesn´t hurt to look at all options.
good luck!

midnight (Darrin) · #12 27-08-2010, 12:03 AM

G'Day Max,

Yes, I have tried mirror lock up and after a few days of experimentation, I found it did not matter as much as stacking.

After the great input and guidance from the fellow members here

, I have since changed my expectations on single shots. On closer inspection after taken multiple shots, it had become clear to me the large effect of the atmosphere. In fact, I paid really close attention to the live view and you can see the turbulance with the wavy motion of the video if you study it. My conclusion was that after scanning the single image, about 10% was sharp (sharp as I expected from looking at the live view) and 90% apparently out of focus. On the next image, the in focus/sharp area was in a totally different part

!! So I put myself at ease that statistically it is very difficult to get 1 shot with the whole frame sharp. I then figured well, the affect of the mirror flipping up had much less of an impact than the atmosphere at this focal length.

To cut a long story short, I gave up the idea of mirror lock up and put the camera into rapid shot. The 40D can fire at about 6 shots/sec and it will get to about 20 shots in about 3 seconds and then I stacked about 40 frames from memory and was very suprised to see the sharpness frame by frame as Registax was processing each frame - quite significant actually.

Anyway, thanks for help and this has really tightened my expectations with astro photography and starting to appreciate all the angles even when taking shots of the moon!!

By the way, I tried the aperture mask (as suggested by Chris) and this made a relatively large difference to my quality too. Here is the link .

http://www.iceinspace.com.au/forum/s...ad.php?t=64819

You gotta love this photography and astronomy in one and its challenges!!

All the best,
Darrin...