focusing a dslr lens

[ako]

hi,

i used to image with an atik ccd and autoguided on a heq5 but since moving house i have a very little view of the sky and the light pollution is terrible. i am interested on using a very portable set-up, shooting widefield with a dslr and lens on mayb an astrotrac. i dont want to take my laptop out there so i cant use dslr focus. any ideas, what do u guys use? is there a batinhov mask small enough to fit the standard size of a lens?

the camera would be a canon 350d so no liveview im afraid.

any help useful.

many thanks matt

[Merlin66]

The easiest way is to take a couple of trial shots at the infinity focus. When you find the best, tape the lens to stop it moving.

You may want to consider adding a 48mm (2") LPR filter to the front of the lenses ( you can get step-up/down rings to suit)

[Psychobilly]

I shoot widefield with dslr's either from the EQ3 Pro when I am away from home or the HEQ5 Pro when i am at home....

As Merlins said checking test shots is probably the best way.. although the small screen on the 350D can make this a bit tedious... if you can drag along a laptop or a netbook then using eos utils would allow you to review the images on a larger screen...

I used to use tape to lock the focus - i found micropore surgical tape very good for this.. but now I use blutack as its easier to make small tweaks...

Take you test shots wide open at high ISO then stop the lens down a few stops and drop the ISO before shooting...

You might want to think about adding dewstraps to keep the lenses clear I find the 4" astrozap ones work well and will fit most dslr lenses... they only need to be run from 4-6V DC to keep the lenses clear all night...

I use the cheap programmable timer remotes from ebay to control the exposures...

Here's links to the threads showing the setups...

http://stargazerslounge.com/diy-astronomer/102642-pbwags-psychobillys-widefield.html

http://stargazerslounge.com/diy-astronomer/112274-today-i-have-been-making-guided-dual-dslr-setup.html

and a couple of images taken from home...

http://stargazerslounge.com/imaging-widefield-special-events-comets/103918-first-images-cygnus-nebs-50mm-eq3.html

http://stargazerslounge.com/imaging-widefield-special-events-comets/106224-cassiopeia-nifty-50-a.html

And under darker skies...

http://stargazerslounge.com/imaging-widefield-special-events-comets/106765-southern-milkyway-sagittarius-ophiuchus.html

Peter...

[Beardy Bob]

I used the EQ2 mount with a RA motor drive that came with the skywatcher 130M setup. The 130 reflector was light, but you could get an even lighter one for even greater portability/stability.

The 130 tube rings came with a bolt that was accepted in the bottom of the 350d, so I screw my 350d to the top of the telescope and use the telescope to get rough polar alignment (i.e. getting polaris in the centre of the FOV at high magnification).

I can manage 5-10min subs using a 28mm lens without obvious streaking of stars.

It's absurdly cheaper than an astrotrac and really effective.

I don't know about light pollution filters, but I know that you could scale down a Bahtinov mask template to any size you like on a PC then cut it out from a piece of rigid card yourself. Try this: Bahtinov Mask Templates

[brianb]

I used to use tape to lock the focus - i found micropore surgical tape very good for this.. but now I use blutack as its easier to make small tweaks...

Hmmm. There's an issue here with some lenses - designed for use with autofocus cameras - which have a distinct tendency for the focus position to vary with operating temperature. Expensive wide aperture telephoto lenses of the type popular with bird & sports photographers seem to be the most likely to suffer from this effect.

[Psychobilly]

Hmmm. There's an issue here with some lenses - designed for use with autofocus cameras - which have a distinct tendency for the focus position to vary with operating temperature. Expensive wide aperture telephoto lenses of the type popular with bird & sports photographers seem to be the most likely to suffer from this effect.

Unfortunately - or maybe fortunately I cant afford any of these .. and find that locking off the focus with the lens stopped down a stop or two works fine all night...

The Autofocus lenses on "manual" tend to creep with the slightest vibration otherwise...

Peter...