Parfocal rings for cam focus

[Al.Grant]

Hi,

 

I have a Vixen Flip Mirror diagonal on my VC200L that allows me to switch between ep's or between an ep and cam (dslr or webcam).

 

I'm planning on getting a set of parfocal rings to match the focus of an ep to the cam. 

As I understand it I can use an ep that is close to the cam and then use the parfocal rings to get a really good focal match between ep and cam.  Once I have them matched it should allow me to get a good focus on the ep (using a Bahtinov mask) then flip straight over to the cam and be pretty much in focus (Assuming it works the way I think it does! )

 

 

Does anybody know what ep would be best to use for:

Philips spc900nc webcam  =  ?

Canon eos 400D  =  ?

 

 

For some reason I have a feeling that a 6mm or 7mm is fairly close to the philips spc900, but can't remember where I read this (or did I dream it!), but have no idea for the 400D and don't know exactly how to work it out.

 

As the 400D doesn't have 'live view' this could be really useful if it works the way I think is does!

 

 

Thanks

    Al

 

 

 

[+Graham]

Hi Al.

Nice idea but I think you will be causing yourself a whole lot of unnecessary grief.

To focus using a Bat mask with an EP is going to be next to impossible unless it is a very bright star and you have very dark skies.

Might I suggest you use a program called Back Yard Eos. ( BYE )

It is written specifically for Canon's.

You can set it to take very short subs ( 1 or 2 seconds ) these will then be displayed on your laptop just like live view.

You can then focus the camera using the Bat mask and save yourself a lot of time and certain despair

Once you have focused your camera you can then move your EP in and out of the holder to achieve focus if you require it.

[Al.Grant]

Hi,

Many thanks for that.  BYE has to be worth a good look and add it to the increasingly long list of software that I need to

get my head around!

 

I've got so much that I need to try, but not getting a chance due to work and recent cloudy skies :-(

Had very little observing time since getting my VC200L, so at the moment I'm trying to work out the various options

but not really getting a chance to put them into practice.

 

Thanks again