Focussing with a DSLR

ferozious · #1 03-05-2007, 07:27 AM

G'day people,
Just wondering how you go about getting perfect focus when using a DSLR that does not have the advantage of "live focussing" such as the Canons or Nikons?
Obviously, visually just isn't good enough. A Hartman mask helps. And doing test images, then connecting to the computer each and every time to check them is a little tedious.
So, is there a way to repeatedly achieve sharp focus in a short amount of time with a minimum of fuss for DSLRs that are unable to do a "live focus" via PC ?
Cheers,
Steve Bain

Muddy Diver · #2 03-05-2007, 07:32 AM

I'm really interested in this too. I'm getting some niceish shots with my new toy but am not moving past the out of focus stage. They look OK in my camera eyepiece but when on a larger screen the stories very different. Would be great if I could use the video out lead to a laptop to focus on a larger screen. Anyone done this? Can it be done?

iceman (Mike) · #3 03-05-2007, 07:39 AM

There's computer software called DSLRFocus which will let you check focus through your computer. I believe some of the other DSLR capture programs (MaxDSLR etc) may have similar functionality.

I usually just take a series of small test shots (10-20s) and zoom in on the LCD until the stars are as small/sharp as possible. Not ideal though. I'd like to do something better.

Ingo · #4 03-05-2007, 09:08 AM

How do you focus a DSLR without a lens? Do you mean focusing the scope?

Sorry, i'm new to DSLR imaging besides planets.

JohnG (John) · #5 03-05-2007, 09:09 AM

Hi

Steve, you don't say what sort of camera you are using so it is a little difficult to advise on what software to use, there are a number of free one's around but whether your camera is supported or not is the question.

MD, your signature say's you have a 400D, DSLRFocus quite clearly say on their website that the 400D is NOT supported although I have heard of a workaround. I use a 350D and use ImagesPlus, this program has support for the 400D, there are other programs around with 400D support but I cannot comment on them as I only use ImagesPlus now for focus, image aquisition and processing.

For exposures less than 30 seconds you can use the cable that came with the camera, for longer than 30 seconds, you need something like a Shoestring Astronomy DSUSB and cables DSCBL-01 and 03. See:

http://www.store.shoestringastronomy...roducts_ds.htm

You will also then have to think about guiding and associated problems/hardware etc.

Cheers

JohnG

iceman (Mike) · #6 03-05-2007, 09:15 AM

The other thing Steve doesn't mention is whether he's talking about using it through the scope (no lens) or as piggyback (with lens).

JohnG (John) · #7 03-05-2007, 09:24 AM

Quote:

Originally Posted by Ingo

How do you focus a DSLR without a lens? Do you mean focusing the scope?

Sorry, i'm new to DSLR imaging besides planets.

Hi

Yep, you attach your DSLR to the focusser vide a T-Ring then take a series of, say, 4 second exposures, and tweak the focus knob until the star, etc is in focus.

Cheers

JohnG

leon · #8 03-05-2007, 11:29 AM

Steve you can easily get away with focusing using a good right angle finder, you dont need software, other than maybe for Planets, but i don't do Planets.

It takes a little practice, but through the scope, or just the lens, it works fine.

leon

ferozious · #9 03-05-2007, 05:15 PM

G'days guys,
Thanks for the varied responses. I think perhaps that I should clarify some points of my query.
Firstly, my camera is a Pentax K100D which I am tring to use at prime focus on my 'scope(s). Although the Pentax Ist cameras were able to be operated remotely via computer, unfortunately this seems not to be the case with the K100D. I have tried using the Ist software, but no go

So the only ways I am currently using to focus the camera/'scope combination are as follows:
1. Straight visual - easy but not very accurate.
2. Hartman mask - still very easy, offers quite a bit more accuracy when used with method #3, but still not perfect and no good at all on faint objects.
3. Image display software - still easy enough, just bloody tedious. Get focus as close as possible visually with the Hartman mask, take exposure, connect usb cable, load image to check focus, adjust focus, detach usb cable, take another exposure, connect usb cable, etc, etc, ...... ad infinitum (or so it seems sometimes).
So, what I'd really like to know, is there an easier way or is that what I have to live with, not having a Canon or Nikon?
I mean, like, how did everyone achieve perfect focus before the advent of digital cameras?
I know there's a lot of very clever people out there, so I have not doubt that a few of you will be able to enlighten me.
Cheers,
Steve Bain

JohnG (John) · #10 03-05-2007, 05:42 PM

Hi Steve

Your testing my memory here but in my film days, I found the use of a Hartman Mask to be very accurate when used in conjunction with a matt foccusing screen and a right angle finder (Olympus OM-1n), I dont know whether or not you have a removeable foccusing screen or not, I doubt it though.

The other way that focus could be achieved with great accuracy was by using a knife edge focusser, you may have to Google this as it has been a long time since I went down that track

and I have forgotten most of it.

Cheers

JohnG

Geoff45 (Geoff) · #11 03-05-2007, 07:03 PM

I haven't tried this, but you can connect the camera to a TV screen and inspect the image there instead of on the camera display screen, so if you get a small portable TV you could try that.
Geoff

Astroman (Andrew Wall) · #12 03-05-2007, 07:11 PM

You will need a fairly high resolution screen such as a TFT or LCD display, something like one of those DVD players with AV input. Normal CRT type screens wont show the star perfectly focused.

Ingo · #13 05-05-2007, 02:04 AM

Can't wait to get the Canon 1D Mark III with live view .

xelasnave · #14 05-05-2007, 03:25 PM

I dont have software to do it, and have used a hartman mask.
The only system I use is to take a test shot, blow it up on the LCD and examine the blow up with a magnifying glass.
I have just fitted a better focuser (crayford) to my imaging scope and after tests last night I think this will help greatly as with the new focuser I dont get any slop if I go in the other direction,which was a major problem with the old focuser.
Also after a while I think you develope a "feel" for just where you are... but the more you do it the better you get at it..
I have taken up to 40 test shots examined each one and even then felt as something better could be reached...
alex