Bahtinov Mask question

[Thalestris24]

Hi

Anyone happen to know if the smallest mask that FLO offers (for 66mm scope) will still work ok with a 50-55mm (58mm filter) camera lens? 

Thanks

Louise

[iapa]

I tried that.

As I had a dew stop, I put that round the lends first and it seems OK.

I aimed as pleiades I think so there were a few stars in frames that I could focus on.

Don't think that it it necessary that the pattern be dead centre.

 

[Ben the Ignorant]

The bahtinov pattern is always the same, a mask will make clearly visible spikes with any optics provided the slits are more or less in that proportion to the diameter: 3mm for a 3-inch scope, 4mm for a 4-incher, 6mm for a 6 inch, 10mm for a 10 inch scope, and so on. That's the rule for f/10 to f/8 instruments, between f/7 and f/5 the slits need to be a bit narrower.

[iapa]

I sit corrected

[Thalestris24]

Hi

Thanks for the replies. So, er, will the 66mm Bahtinov still work with an f4/200mm lens??

Cheers

Louise

[iapa]

Worked OK of me.

[Thalestris24]

8 minutes ago, iapa said:

Worked OK of me.

Oh, ok  With which lens?

[iapa]

Nikon 75-300mm, 67mm fitting

Canon EF III  75-300mm, which is a 56mm frommmeory

 

I then bought threaded filter size masks for the lenses that i screwed in, focused, and removed - carefully!!!

[Ben the Ignorant]

57 minutes ago, Thalestris24 said:

So, er, will the 66mm Bahtinov still work with an f4/200mm lens??

Yes.

[iapa]

before you ask - looked for it, got them from Gerd Neumann

[Thalestris24]

12 minutes ago, iapa said:

before you ask - looked for it, got them from Gerd Neumann

Ok - expensive! Was that one of the ones designed for a lens? I was hoping FLO's 66mm one would do...

[iapa]

I used the 'hang on the front' mask originally - but kept dropping them.

OK, so I forgot they were still hanging on the front, then when slewing to target, they weren't hanging on the front anymore 

At -10C they shattered

Didn't purchase from Flo, so, may be different plastic. Same design. Just remember to take it of after focusing.

Anyway, this what I went of rate threaded metal masks.

[Thalestris24]

It's ok - I'm used to using Bahtinovs! APT always reminds you anyway  FLO don't do lens-specific masks but hopefully the 66mm one will do

Louise

[John78]

I saw this a while back, it's much too expensive for what it is...

http://www.lonelyspeck.com/sharpstar/

I'd imagine you could easily send a drawing to razorlab and they'll laser you a clone for a few quid.

http://www.razorlab.co.uk/materials/info/?id=172#

[hobsey]

You could always try this.

http://astrojargon.net/maskgen.aspx?AspxAutoDetectCookieSupport=1

It's a mask generator. 

[Thalestris24]

Maybe I'll ask FLO...