focus...

[m37]

Went out with a mini rig tonight. Tripod, DSLR and remote control. Took a few shots over my house at 30 seconds, ISO3200 then took 40 light frames, 10 darks, 10 lights and 10 bias.

Focus was set to infinity. Can you guess what's coming next? Yup, 40 out of focus pictures!

Read up a bit AFTERWARDS and turns out infinity is a bit too far! Never mind, that'll learn me. Oh well, here's one of the mucking about shots from the start of the session. Single frame, 30 seconds, ISO 3200 with heavy photoshop action.

[baggywrinkle]

If you do not have any live view or focusing sw (what camera?) then go out in daytime and set your lens to manual and do manual focusing so you can get a sharp image.

Most lenses go beyond infinity. So doing a manual focus you can either make a little chart or you can make a small tag to go onto the lens barrel. You can then use that chart at nights.

That is what I did with my old Canon 400D and a couple of the telephoto lenses I have.

[nytecam]

Modern electronic focus lenses don't know where infinity is and need to be focus manually. Alternatively get a s/h old Pentax lens with infinity mark - register is usually perfect

[knobby]

Makes me laugh when a lens can focus past infinity do lens manufacturers understand the word 'infinity'?

maybe Buzz lightyear designed lenses before he starred in Toy story!

[m37]

I read up a bit on this. Apparently...

With autofocus, one of the many ways camera companies discovered to save money was to take away the infinity stops. These always had to be calibrated on an optical bench at the factory for each and every lens, but with AF, camera makers take away the stop, and save themselves the cost of calibrating each lens. Since AF works at infinity, few people notice.

There we go. Nearly understood some of that!

I wonder if there's a market for permanently perfectly focused astronomy lenses? You could tether a DSLR and bahtinov mask, focus to perfection using the laptop and glue that baby down!!! Quick 300% markup and off you go.

Does anyone know if 'perfect' widefield focus would ever change? For example, if I were to focus it as close to perfect as possible and mark (or glue) it, would that always be spot on?

cheers

[ollypenrice]

If you lens to chip distance is not perfect you'll be glad to join Buzz beyond infinity!

Olly

[m37]

Ah!!!

[Twisted Lip]

I actually really like that picture! Odd how sometimes the ones you don't plan for turn out great.

I remember I borrowed a friends Canon 17-40mm widefield lens (http://www.canon.co.uk/For_Home/Product_Finder/Cameras/EF_Lenses/Wide_zoom/EF_17-40mm_f4L_USM/)a few months ago for a trip to Finland hoping to get the northern lights. Whilst they didn't appear while I had the camera out, I took a few shots of jupiter and the stars generally and found that the trees were simply out of focus. Very frustrating and while he did try to explain why it wasn't quite right, I have to admit I didn't understand it all fully.

Interestingly he wrote a blog post about his own Aurora exploits here: http://blogs.adobe.com/richardcurtis/?p=297'>http://blogs.adobe.com/richardcurtis/?p=297 which I found useful (his main blog is here - http://blogs.adobe.com/richardcurtis/ - if anyone is interested. We know each other from our time at Adobe and now he is responsible for Photoshop in Europe, hence the very strong PS slant!).

[Matt Scunthorpe]

I also quite like this picture.

What were you going to stack the photos in? Ive dabbled with widefield shots, but Deep Sky Stacker always seems to mess up and only dump out a tiny part of the original photo.

[m37]

I also quite like this picture.

What were you going to stack the photos in? Ive dabbled with widefield shots, but Deep Sky Stacker always seems to mess up and only dump out a tiny part of the original photo.

cheers. I was going to try Registax and DSS.

[Luke]

Lovely colour in the pic