How difficult is it to focus a DSLR without live view?

[swag72]

I ask this as I am wondering about a modded DSLR. My top choice would be a 1000D, but money will be an issue. So, if I am using just the DSLR and a 300mm lens, how easy is it to focus without live view?

I currently use a 5D2 and I have learnt that live view is excellent to ensure good focus - Not sure if I'd manage without it.

Thoughts?

[Dave]

Hi Sara

You will get focus, but it will take you a while to make sure you are really there.

On many lenses the infinity setting isn't quite right.

The best way is to take a test shot and inspect the image and keep adjusting until the stars are pinpoints.

Dave

[steppenwolf]

Test shot an examination is the best method as Dave has said but you could make it easier by using a Bahtinov Mask for your 300mm lens by aiming at a bright star before you move to the object you wish to image.

[Freff]

On my telescope I use a Bahtinov mask. I'm not to sure if the same can be used on a camera lens.

Tony

[Freff]

just beat me to it Steve.

Tony

[Uplooker]

I use a Bahtinov mask - recommend it!

[swag72]

I have a Bahtinov mask for my SW 120ED scope (currently in UK, I am going back next week) - How can I use it on my camera lens when they're different sizes? Can I just hold it up to the lens and use it like that? Or just tape it on for the focusing?

[steppenwolf]

I'm not to sure if the same can be used on a camera lens.

I have used one very successfully on a 200mm telephoto lens and fairly successfully down 135mm.

Can I just hold it up to the lens and use it like that? Or just tape it on for the focusing?

You would need to produce one specifically for your lens.

[beamish]

You'd really need one that was designed for the lens &/or you can use the DSLR Focus type software ( as you would for DSO's) and take a test shot as suggested by Steve to determine how far off you may be .

EDIT ah ! there you go ... cheers Steve !

[ollypenrice]

I wrote a positive reviw of these masks and here is another happy customer. They need to know lens aperture, aperture of dewshield or outside of lens, and focal length. http://stargazerslounge.com/supplier-reviews/124368-morris-engraving-bahtinov-masks.html

Highly recommended.

Isn't there also a FWHM measuring programme for DSLRs. DSLR Focus or something like that? I use FWHM to focus my camera lenses when attached to my CCD cameras.

Olly

[swag72]

I have just contacted Morris engraving, thanks Olly. So, I have a 300mm and a 70-200mm lens, both of which have a 77mm thread. Can I not use the same mask on them both as one is an f/4 and the other a f/2.8. Can I just use the 2.8 lens at f/4 and that will be fine?

[Watcher]

My DSLR doesn't have live view as I bought it before getting into Astronomy. It's a total pain to get focus without a mask. Even with it it can be hard to get to the viewfinder without knocking the 'scope. The mask from Morris Engraving is great though, highly recommended.

[beamish]

Don't use the VF, except maybe right at the beginning to check alignment with the guider, using the AF points !

set up DSLRFocus ( if you have it) to take focus pics at 30secs and at high ISO for a fast image and "download pics to computer" check your focus there. ( Tho ideally with a mask too ), then when your happy go to long exposure mode and > "download to camera CF" and off you go

[swag72]

Mmm, reading all of this and struggling even with live view tonight, I think I'll be sticking to live view!! Thanks for your input folks.