Focussing!

[PaulMakin]

Hi,

I'm just trying to get started with imaging, and had my first serious session last night. Apart from getting the exposure right - way too many overexposures - which I suppose is just down to practice, my big problem is with focussing.

Does anyone have any tips on this? I've tried looking through the viewfinder on the DSLR camera and focussing there, but things still come out blurred. Partly this is because the viewfinder is so small, and deciding if something's in focus is so difficult. Plus, everything's so faint, compared to looking through a normal eyepiece. I've also tried focussing using the LCD screen, but that seems hopeless - most of this time there's nothing there to even try and focus on.

Can anyone give me some advice on this!

Thanks,

Paul

[atmenterprises]

Bahtinov mask may help you. Cheap and relatively easy to get focus with a few test shots on your dSLR.

[PaulMakin]

Bahtinov mask may help you. Cheap and relatively easy to get focus with a few test shots on your dSLR.

Fascinating! I'd never heard of them before. I'll investigate.

[Matt Scunthorpe]

If the moon is about, focus on that then just dont touch it again.

[PaulMakin]

If the moon is about, focus on that then just dont touch it again.

This sounds good, but then I have a problem - how do I find that faint object I want to image again, without taking the camera out and putting an eyepiece in, so ruining the focus?

Aaagh...

[durhamdave]

I am a newbie in regards to astrophotography but for any sort of night shot (of which this is i suppose) I would use the 'live view' setting on your camera if it has one and to locate things, ramp up the ISO and some models this improves the image enough on screen for you to locate what you want, otherwise, take a REALLY high ISO shot to get you in the right ball park location, then reset your ISO to normal

[Daniel-K]

Bahtinov masks only work on bright stars, i hate them!

This sounds good, but then I have a problem - how do I find that faint object I want to image again, without taking the camera out and putting an eyepiece in, so ruining the focus?

Aaagh...

are you using a motorized GEM mount ?

if you using a dslr with live view your finder on your telescope should be aligned with your EP so when you put in your camera (Bigger FOV) you should be able to see the bright star that you just found using you finder, a few more detail on your setup would help too

[PaulMakin]

I am a newbie in regards to astrophotography but for any sort of night shot (of which this is i suppose) I would use the 'live view' setting on your camera if it has one and to locate things, ramp up the ISO and some models this improves the image enough on screen for you to locate what you want, otherwise, take a REALLY high ISO shot to get you in the right ball park location, then reset your ISO to normal

Not a bad idea. I'll try it, next time we have clear skies...some time never

[Black Knight]

Paul, what make of camera do you have? If you have a Canon, you can use APT to output the cameras Live View to a computer or laptop screen. When I image with my Canon, I don't use an eyepiece at all. I perform a 3-star alignment using the camera and APT, and focus at the same time. APT has a built-in routine to assist in focusing.

Edit: You can probably do the same with Backyard EOS as well. APT is here: http://www.ideiki.com/astro/

[PaulMakin]

Bahtinov masks only work on bright stars, i hate them!

are you using a motorized GEM mount ?

if you using a dslr with live view your finder on your telescope should be aligned with your EP so when you put in your camera (Bigger FOV) you should be able to see the bright star that you just found using you finder, a few more detail on your setup would help too

Yes, I'm using a motorised equatorial mount. The telescope's a Skywatcher 200, with motorised EQ5 mount. I'm using - or trying to use - a Nikon D5000 DSLR, with Live View available.

The problem I've had is that when I find an object using the eyepiece (such as M57, which I was looking at), there aren't really any bright stars in the FOV. So when I replace the eyepiece with the camera, there's nothing to see on live view, so nothing to focus on. As durhamdave suggested, I'm going to try cranking up the ISO until I can see SOMETHING, then try focussing, then reduce the ISO again before opening the shutter.

[PaulMakin]

Paul, what make of camera do you have? If you have a Canon, you can use APT to output the cameras Live View to a computer or laptop screen. When I image with my Canon, I don't use an eyepiece at all. I perform a 3-star alignment using the camera and APT, and focus at the same time. APT has a built-in routine to assist in focusing.

Edit: You can probably do the same with Backyard EOS as well. APT is here: http://www.ideiki.com/astro/

I'm using a Nikon, which I've now discovered is not exactly ideal for astrophotography.

I can't use APT, but I do have Sofortbild (http://www.sofortbildapp.com), which I think is similar - but for Nikons.

I use live view, but it's difficult to use when the screen's almost totally dark!

Thanks for the tip about 3 star alignment, that sounds like a good idea.

Paul

[Black Knight]

I'm using a Nikon, which I've now discovered is not exactly ideal for astrophotography.

I can't use APT, but I do have Sofortbild (http://www.sofortbildapp.com), which I think is similar - but for Nikons.

I use live view, but it's difficult to use when the screen's almost totally dark!

Thanks for the tip about 3 star alignment, that sounds like a good idea.

Paul

One of the great things about using APT for star alignment, is that you can place a reticle over the Live View screen on the computer. This allows for a much greater degree of precision when star aligning than you could possibly achieve using an ordinary eyepiece.

[Digz]

A simple alternative to the 'B' mask is a Lord (I think) or 'Y' mask. Basically you take the same dimensions for the 'strands' of a 'B' mask and make a 'Y' shaped mask. Held in place with some tape, easier to make and works just as well. You can make it out of card or wire depending how wide you want to make the limbs. Good thing with a 'Y' mask is they are quick to make so you can try several variations and experiment.

Once you have your mask of choice, pick a bright star and using live view, zoomed in, focus the diffraction spikes into place.

[PaulMakin]

A simple alternative to the 'B' mask is a Lord (I think) or 'Y' mask. Basically you take the same dimensions for the 'strands' of a 'B' mask and make a 'Y' shaped mask. Held in place with some tape, easier to make and works just as well. You can make it out of card or wire depending how wide you want to make the limbs. Good thing with a 'Y' mask is they are quick to make so you can try several variations and experiment.

Once you have your mask of choice, pick a bright star and using live view, zoomed in, focus the diffraction spikes into place.

Thanks for that. Before tonight I hadn't heard of diffraction/focussing masks. A whole new world opens up!

[Digz]

Thanks for that. Before tonight I hadn't heard of diffraction/focussing masks. A whole new world opens up!

And thats just the start of it ;-)

[zakkhogan]

how about the hartmann mask, very is to make and use

http://www.billyard-ink.com/Hartmann.shtml there was apost about this the other month, i see if i can find it

[Digz]

Hartman masks are good but IMO not as accurate as a 'B' or 'Y' mask can be. Still, its another easy mask to make.

[zakkhogan]

here it is

[Mik3]

Slew to a bright star use a Bahtinov mask, use live view and zoom to 10x if you can on a Nikon.

You can make a mask using this generator http://astrojargon.net/MaskGenerator.aspx

[Mik3]

Also dont forget to lock it once you get focus.

[springbok]

Paul, what make of camera do you have? If you have a Canon, you can use APT to output the cameras Live View to a computer or laptop screen. When I image with my Canon, I don't use an eyepiece at all. I perform a 3-star alignment using the camera and APT, and focus at the same time. APT has a built-in routine to assist in focusing.

Edit: You can probably do the same with Backyard EOS as well. APT is here: http://www.ideiki.com/astro/

Yes this is what I do using Backyard EOS, works well.

Not much use for you though as a Nikon chap.

[PaulMakin]

Also dont forget to lock it once you get focus.

Now THAT' S a good tip . I didn't realise you could lock focus until just now, when I checked!

Paul

[VigdisVZ]

I'm using a Nikon, which I've now discovered is not exactly ideal for astrophotography.

The newer Nikons (the ones without star eater) are excellent for AP. The D5100's sensor is really good. So don't count out Nikon just because Canon has better software support.

And as soon as the Backyard Nikon hits we're a fair step along on the software dept.

Speaking about focus, here's how I do it with live view. I just find jupiter and zoom the live view to max, and focus that way. Having a mask here would also help a lot. Strictly speaking, any imaging on done with perfect focus is wasted imaging if you're being hard. Personally I know that on the level I am on now, I just get focus as good as I can with live view.

I realise that I'll probably end up with a focus motor so I can use autofocus in Maxim at some point, but not this season .

Go team Nikon!