Focusing Masks ( two hole Scheiner disc ) ?

[Mr TamiyaCowboy]

i have tried to make a focusing mask.

i printed out the line mask thing, but when it came to cutting out i found the lines to close

to get a decent straight edge, and all the astro shops online do not sell 114mm masks.

So, this had me thinking there must be other things that work. 

i have had a headache trying to focus my canon lenses at night.

and the scope to when in primary mode with my canon camera. 

i stumbled up a thing called a Scheiner disc, its a round disc with two holes spaced equally apart,

you look through finder/eyepiece, and see two images, you now focus and bring both images together.

remove mask your in focus ? 

this seems to good to be true , has anyone else heard of this mask focus method,

or even used it, and if so how did it work for you. 

[IanL]

Not used a two hole mask (three hole versions are also possible), but I have made a DIY 'Y' Mask which functions in the same manner as a Bhatinov but is considerably easier to make yourself, especially at small sizes.  You just mark out a circle and three legs that meet in a Y shape in the middle.  Here is a thread explaining how:

http://stargazerslounge.com/topic/140075-good-by-bahtinov-hello-the-lord-mask-amen/

You don't really need to make a cut-out mask - three joined legs made from black plastic or painted wood hooked over the dew shield or lens front in a Y-shape would work just as well as a cut-out mask.

[Alien 13]

There are quite a few variations of masks another one uses two triangular holes i have even heard of somone at a remote location who forgot his Bat mask using a Y shaped twig.

I have found that smaller scopes suffer with some masks because of the amount of light lost so its worth trying a few to see what works best but my moneys on the Y mask.

Alan

[Mr TamiyaCowboy]

Ah after reading that other thread it seems like it will not work for me.

silly skywatcher catadioptric 114mm ( ie its got a barlow shoved into it to make it short tube long focal length)

so having an obstruction ie the secondary mirror in the way and no dew shield attachment its going to be a struggle.

also the fact the guys were using high brightness stars, i be lucky if anything is bright being 3miles from large city

and the nearest street light is 20 paces away.

i will also struggle widefield wise to, my camera has no live view being a 350D , so i have to focus via viewfinder squinting 

take shot, check image, reset focus, take shot, just trying to see a star in the eyepiece is hard.

jupiter is a mere dot in a 50mm f1.8. on a 18-55mm lens its a pixel sized pin head. trying to mask up and focus would be a nightmare.

this is what i require masking up 

canon nifty fifty f1.8 II ( true focal length is 80mm )

canon 90-300 mm EF f4.5 - f5.6 ( true focal length  144 - 480mm )

114mm @ 1000mm focal @ f7.9

where i say true focal length it would be equiv to a 35mm full frame 

my canon has a 1.6 crop 

[ollypenrice]

Have you thought of running the camera via a PC and using a dedicated capture software like Backyard EOS? These have focus assist routines like Full Width Half Max which measure the star's diameter at a point half way to its brightest. You simply focus till you get the lowest value. This is far better than groping around under a tiny screen and gettng a hit and miss focus at best. Miss is more likely!!

Olly

[IanL]

Or APT which has BhatinovGrabber built in, works a treat with my Y mask - gives you a really clear set of graphical and numerical displays of how close you are to focus even if the pattern is only minimally visible by eye. Much easier to focus with a laptop than on camera if that is an option for you.

[baggywrinkle]

I made a 3 hole (triangular shape) mask and it works very well. You bring 3 images together.

[Mr TamiyaCowboy]

i have canon capture that allows you to adjust camera settings via PC,

but when camera is put into data mode, windows asks to download and install

a canon file, i try to install and am told the enviroment is not correct. 350D capture only works on XP and below

i only have vista and windows7 , and neither of these work to , same error not a valid enviroment.

yes a lot of my data is thrown away before i have even started, but the 90-300 EF is ok.

i can set the moon in sight zoom into 300 and autofocus it lovely. bash of a few frames reset and bash a few more.

the 50mm is just a total pain in the rear, 

so i am stuck using the old squint n guess method 99% of the time.