Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 08-05-2013, 07:54 PM
niko's Avatar
niko
Registered User

niko is offline
 
Join Date: Feb 2007
Location: Melbourne, Victoria
Posts: 1,053
DSLR and a Bahtinov mask - seeking some advice

I'm having trouble figuring out how far from the front of the lens to put the Bahtinov mask. I've tried it right up against the lens and about 2 inches from it.

On both occasions I get the mask pattern on the stars rather than the rays.

Am I missing something simple here?

Thanks everyone

Niko
Reply With Quote
  #2  
Old 08-05-2013, 09:38 PM
White Rabbit's Avatar
White Rabbit
Space Cadet

White Rabbit is offline
 
Join Date: Feb 2007
Location: Sydney
Posts: 1,411
Are you using the dslr on a telescope or a camera lens? If your using a telescope can you focus on anything in the distance? You may need an extender to reach focus.

Tell us a bit more about your set up and we may be better able to help.


Thanks
Sandy
Reply With Quote
  #3  
Old 09-05-2013, 10:56 AM
niko's Avatar
niko
Registered User

niko is offline
 
Join Date: Feb 2007
Location: Melbourne, Victoria
Posts: 1,053
Thanks Sandy

It's just me, the DSLR, a tripod and the mask.

I use a mask on my ED80 with no problems at all. It sits at the end of the dew shield - so, a good few inches from the lens of the scope.

I've made up a little shield to hold the mask an inch or so from the DSLR lens figuring it needs a gap between the lens and the mask in the same way the scope works.

All I get is the baht mask lines on the star instead of the 3 rays to aid focussing.

Then I tried the mask directly on the lens with the same results.

???

cheers

Niko
Reply With Quote
  #4  
Old 09-05-2013, 04:52 PM
rogerco's Avatar
rogerco (Roger)
Roger

rogerco is offline
 
Join Date: Sep 2007
Location: Woodford,NSW,Australia
Posts: 388
Some time ago I picked up a stick on mask to go on a filter so from that I assumed that the mask goes where you would normally put a front of lens filter.

That being said I never had much luck with it, I am not sure it works terribly well on photographic lens and view finders / live view.
Reply With Quote
  #5  
Old 09-05-2013, 06:23 PM
avandonk's Avatar
avandonk
avandonk

avandonk is offline
 
Join Date: Aug 2005
Location: Melbourne
Posts: 4,786
The diffraction pattern is very small with a short focal length lens. Try shorter exposures and zoom in to see it.

Bert
Reply With Quote
  #6  
Old 09-05-2013, 08:02 PM
niko's Avatar
niko
Registered User

niko is offline
 
Join Date: Feb 2007
Location: Melbourne, Victoria
Posts: 1,053
Thanks guys

Bert will try your suggestion

I wonder if a Y mask might work better for DSLRs?

Niko
Reply With Quote
  #7  
Old 10-05-2013, 04:57 AM
SteveInNZ
Registered User

SteveInNZ is offline
 
Join Date: May 2008
Location: Auckland, NZ
Posts: 239
I wasn't aware that the distance in front of the lens makes any difference. If the object is at infinity then the light rays would be parallel, so I can't really think of how the distance in front of the lens would change anything.
Anyhow, I find that my mask works (usefully) on lenses down to around 100mm focal length. Below that, the focus range that you see spikes instead of an out of focus blur with the B mask pattern, is too small to be useful.
For focal lengths less than 50mm, I focus on something terrestrial that is further away than the hyperfocal distance like a street light or red led on a power supply.

Steve.
Reply With Quote
  #8  
Old 13-05-2013, 08:13 PM
Garbz (Chris)
Registered User

Garbz is offline
 
Join Date: May 2012
Location: Brisbane
Posts: 644
The only time the star should take the picture of the mask is when it is HORRENDOUSLY out of focus.

Can you achieve focus without the mask? Then when you put the mask in front of the lens you should end up with diffraction spikes regardless of where you put it. At these focal lengths the distances shouldn't matter.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 04:42 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement