Bahtinov masks

[Granada]

Wondering if Bahtinov masks are typically used for astrophotography or if they're utilised for visual as well? I'm asking because I rarely see any Bahtinov masks for large Dobsonians, so I'm curious if I should get one for my 14" Dobby which I only use for visual only?

[Stonius]

I have one for my 16" Dob.

Useful if I'm trying to get the best out of planetary viewing.

M

[RyanJones]

Hi Granada,

I use all of my OTAs for photography so I’m not 100% on this but my assumption is that everyone’s eyes and more specifically their lenses are different so there is no fixed focus, its dependant on the observer. In this case I’m going to say no to a bahtiov mask.

[glend]

Agreed with the last post. In AP there is a fixed focal point for the specific equipment but human eyes vary considerably. You only have to go to a Star Party or dark site trip with others to realise everyone has to focus for their eyes.

[raymo]

Ryan,
When doing AP, focus should be set as close to technical perfection as possible, not to suit the imager's eyes, [unless you don't expect anybody but yourself to look at your pic.] Your camera's auto focus system doesn't attempt to focus to suit your eyes, it gets as close to technically correct as its designers ability allows. The stunning Nat.Geo pics are focused as close as possible to technical perfection, not to the imager's eyes. If all our members posted their pics focused to their eyes, some of the pics would be quite awful.
If one's eyes are not crash hot, one wears appropriate glasses or lenses
in order to see nice sharp pics. If I focus using live view I have to do that with my glasses on; with a mask it doesn't matter whether I wear glasses or not. Of course some people have really bad eyes, and glasses won't them, but that's another story. A Bahtinov mask [or other focal assistance] allows everyone to see your image as you would like it seen.
raymo

[RyanJones]

Thank you Raymo. I think my post said the same thing just much more succinctly.

[kalon]

With the first clear night in ages here in Sydney, I waited until the wee small hours for the moon to set and headed out to try my wide field shots using a couple of Bahtinovs on a couple of lenses.


Despite researching, I couldn't find a definitive answer, so I was unsure of their efficacy on short/small lenses - in my case 35mm and 12mm. Bintel had the 52mm for my stock 35mm f/1.4 lens, but didn't have stock of the 67mm needed for my Samyang 12mm f/2.0 lens, so I made one myself with a craft knife and some rigid black plastic from Eckersleys.


Here are the two most apparent results - after focusing as best I could using Live View at 10x digital zoom, I got pretty close.



A tiny tweak later fixed the slight focus issue and the focus was perfect. (Until I bumped the focus while putting some Blu Tac to fix the focus ring!)


My home made wasn't the best, but still assisted, and by the time I'd shot and marveled at my focus on 35mm, the series using my 12mm could only grab 7 minutes of exposures (28x15") before light cloud rolled in!


Minimal processing (thanks to Sydney's light pollution dome and the general haze...) https://flic.kr/p/2eeNGeR

[multiweb]

Very brave with yesterday's heat. I had a small bahtinov mask with very fine slits I used for lenses but found there wasn't enough light coming in so for lens I rely on the numbers in Nebulosity fine focus feature and spend a bit of time with the mount tracking to get it as best as I can, then I tape the lens barrel so it won't move and stick a sock on it. That keeps focus for a few nights at least.