desperate help with astrophotography focusing !

[cal1985]

Hi all, i have been watching this site for some time now, and very happy with the help other people was getting. looking at other peoples questions helped me to gain my first scope.

loving every minute of this i was taken back and blown away with the pictures people could acquire with a dslr and scope.

understanding this would take a lot of practise and lots of patients ! tried and tried. after nearly 2 months of trying i just cannot seem to get 1 picture that is focused. (the moon! lovely that comes out perfect ) but anything over than this just wont come in to focus.

i know that with the equipment i have focusing with the SW 130 is a huge problem, but this was over come with the use of a barlow lens. then i can focus past the object just cant get that sweet spot !

i have spent hours using the drift method to make sure this is perfectly polar aligned. is the scope not capable of astrophotography, as the mirror is not parabolic. or do i just need to keep practicing ! yet again i would like to say this site has helped me without being a member so so much since i got in to the stars ! your help would be so much apreciated with this. thanks again (sorry for the essay!)

[Demonperformer]

The sweet spot with a barlow is very small. So if the air is not stable, the point of focus can drift in and out very easily. Are you using any kind of focussing aid. If not, using a simple Y-mask should help.

HTH

[cal1985]

many thanks for the very quick reply. i have tried a hartmann mask, although this has made a little improvement its not perfect, after the picture is taken of just a very bright star, sirus for example, the picture looks good on the lcd display, once put on the pc the star is out of focus and there is colour abration, is this because the barlow is not of high quality or the mirror is not parabolic?

[Demonperformer]

I have never used a hartmann mask, but i have seen people say that it is difficult to tell when the two images are precisely merged. I would urge you to try a simple Y-mask (three strips of card formed into a 'Y' shape and held in place over the front of the scope) which gives a 'X' diffraction pattern with another line that exactly bisects the X when it is in focus. Very easy to make, use and achieve focus as precisely as your focusser will go.

As to the CA problem, I would suspect it is due to the quality of the barlow. Having put my neck out, the obvious question is what is the barlow you are using:)?

[cal1985]

its the standard x2 barlow that came with the skywatcher 130 it has no name and no numbers ! i did buy another of off ebay but that was worse, and when viewing through it, terrible !

as for the Y mask i will try this tonight and see what happens.

ill up load a image of the best image so far so u can see what i mean by the focus and colour abrasion. maybe that would be easier to see if it is equipment or human error. (need more practise lol!)

[steppenwolf]

The standard issue Barlow lens is pretty dire especially for imaging use so this could explain the Chromatic Aberration you are seeing. A Bahtinov Mask or the simpler 'Y' mask would make focusing soooo much easier - Hartmann's do not really hit the spot for me as just as you get close to the sweet spot, they are almost impossible to determine the position of the circles or triangles whereas with a Bahtinov, it is very clear!

[cal1985]

[cal1985]

[TheThing]

What camera are you using?

[cal1985]

the last 1 was the best 1 i have ever achived, although the iso was so high when trying to put this through deep sky stacker. there was so many hot spots the programe would not even read this !

how do i make a Bahtinov mask? is this easy and are they avalible to buy?

[cal1985]

the camera is a canon 300d dslr

[brantuk]

Hi Cal - I'd recommend use of a Celestron Ultima 2x barlow which is very good for around £85 new - but there's a couple for sale on the forum at the moment for around £40-£50 second hand.

Unfortunately you'll need 50 posts and 1 month membership to access that section - in the meantime try astro buy/sell website.

My other recommendation is to not use a dslr for snapping planets. The favoured tool by far is a webcam. The best one to get is the Phillips SPC880 which can be flashed up to an SPC900. These are only £30(ish) at Morgans - you need to order the nosepiece on the same page. Ask them to flash it for you for a couple of quid extra.

U.K. Astronomy Buy & Sell

Cheap Philips SPC880 webcam - 49269 - discounts & offers

You'll also need Registax to align and stack the images, and photo processing software like Gimp to tart the final image up a bit (both free downloads).

RegiStax- Free image processing software

GIMP - The GNU Image Manipulation Program

Use the dslr for long exposure pics of dso's when you've had a bit of practise at webcam'ing planets and moon first - it's best to not be in a rush and get the right gear for the job.

Hope that helps

[Demonperformer]

There are templates for making a bahtinov mask downloadable, but they require a lot of cutting out. They produce very similar results to the Y-mask, except that, as more light gets through with the Y, the image is brighter and so (in theory) easier to focus. You could alternatively buy one (they are about £15/£20 a time)

[zedds]

Hello Cal.

I bought two Bahtinov masks for my kit off Ebay from Morris Engraving. There are templates available online to make your own but i just bought mine. Here is a link for your scope. These a really top quality.

Just to let everyone know i have no link whatsoever to Morris Engraving.

[cal1985]

thank you so much, i have tried the planets with a dslr and as you say this does not quite work! my main interest is DSO however im really struggling with just a star in focus! before i bought the dslr i had a 12.5 mp camera using as afocal and got some really nice results with just a point and shoot, i really would like to give the phllips spc a go, this was what i was originally going to get, however the mrs decided to get me a dslr for my birthday instead ! i know this is going to be a painful learning curve but long exposure of DSO is really what i would like to do.

[cal1985]

zedds, thank you, thats much apreciated, i think buying 1 will be more benificial than trying to make 1,

just out of curiosity with the SW200P do you have a focusing problem with this without the use of a barlow ?

[cal1985]

paxo, your images are amazing, how long have you been doing astrophotography? i can only hope to achive something even close to them

[zedds]

With the mask fitted it is very simple to achieve focus with a DSLR for DSOs. I haven`t used a barlow with it though.

[ollypenrice]

Hell Cal.

I bought two Bahtinov masks for my kit off Ebay from Morris Engraving. There are templates available online to make your own but i just bought mine. Here is a link for your scope. These a really top quality.

Just to let everyone know i have no link whatsoever to Morris Engraving.

I have theirs, too. As you say, top quality.

On the wider aspect of the post using a Barlow may make it geometrically possible to focus but it slows down the exposure by four times and greatly increases susceptibuility to tracking errors, vibration and seeing. This is going to be a problem with any Barlow I'm afraid.

Olly

[brantuk]

You're wife did the right thing - I'd much rather receive a dslr for my birthday and buy the SPC for myself - saves a lot of money compared to the other way round lol.

The dslr will come in very handy eventually for dso's when you're ready

[Sinbad]

Hi cal1985,

You are not alone in this quest ! Sharp focus is the bane of all DSLR astrophotographers efforts. I eventually ordered a DVD from Jerry Lodrigus in the States. "A guide to Astrophotography with DSLR Cameras" was a huge help and not expensive. The focus method I use is "Live view" on my Canon 50D. Not sure if it is available on your Canon. It may be worth the effort if you do a "google" search on Larry Lodrigus. This guy has taken some GREAT shots.

[steppenwolf]

i really would like to give the phllips spc a go, this was what i was originally going to get, however the mrs decided to get me a dslr for my birthday instead

You won't regret that purchase if you are interested in DSO's so smile!

You really could do with getting the Barlow out of the equation. You would need to tread carefully but a solution would be to move the primary mirror further up the optical tube to bring the focal plane further out to met the camera's sensor. Many people have done this with success on Newtonians but you may need longer bolts.

Do you have any 'feel' for how far from achieving focus you are?

[ollypenrice]

Hi cal1985,

You are not alone in this quest ! Sharp focus is the bane of all DSLR astrophotographers efforts. I eventually ordered a DVD from Jerry Lodrigus in the States. "A guide to Astrophotography with DSLR Cameras" was a huge help and not expensive. The focus method I use is "Live view" on my Canon 50D. Not sure if it is available on your Canon. It may be worth the effort if you do a "google" search on Larry Lodrigus. This guy has taken some GREAT shots.

It's Jerry Lodigruss for Google but the help on his site is indeed great.

Olly

[Viv]

Hi Cal - if you've not tried already - something that helped me a great deal, was to use software for taking the pictures.

Have a look at APT or backyard EOS - both can be downloaded for trial (for a month)

You just get such a better view of the focus / what you're taking.

[nightvision]

Hi Cal, the 300D you have doesn't have 'Live View' so you will need to keep using the viewfinder for focus. APT features are very limited for the 300D, it is optimised for use with the later EOS cameras. APT actually state on their web site that the 300D isn't supported (it does appear in the demo package!).

Just a basic check; make sure you have adjusted -/+ eyepiece focus in daylight and watch you don't knock it out. This makes a big difference to your ability to focus at night. I have the 300D and it has dim viewfinder which doesn't help. The 'Y' mask seems to be the best way to overcome the dim viewfinder while the Bahtinov may stop too much light. Do a search on this forum and others for 'Bahtinov' and you should find plenty of info on making the simplified Y version.

I will try to dig out a url for a great Y design I came across using just a very thin wire.

Tony.