9 replies to this topic

[AEP64]

I tried google but no luck on my question. I wanted to know if the mask lies on top of the little dow pins at the edge of the scope that the dust cover locks onto or do i slide the mask under them so it lies flat on the glass?

[james7ca]

It doesn't have to be very close to the corrector, so anywhere you can place it should be fine. On my refractors I but the mask on the front end of the dew shield (i.e. inches away from the objective).

[emflocater]

Yeah I put the 3 pegs on the outside of the tube or dew shield.

 

Cheers

Don

[AEP64]

Yeah I put the 3 pegs on the outside of the tube or dew shield.

 

Cheers

Don

so, you are slightly bending the mask to slip it under the 3 pegs so it sits flat, correct?  The mask i bought is the Tri bahtinov, but the star pattern doesn't look like what i see most have from google search and was thinking its either the type of mask im using or its cause i had it on the outside of the pegs. I am tempted to get a second mask ...a standard one for focus and save the Tri for collimation.

[james7ca]

You don't need to slip it under anything. Basically, anywhere you can place it should be fine.

 

That said, I've tried the so-called Tri-masks and I don't particularly like them for use when focusing.

[AEP64]

You don't need to slip it under anything. Basically, anywhere you can place it should be fine.

 

That said, I've tried the so-called Tri-masks and I don't particularly like them for use when focusing.

my first time using one, and i am thinking i should have started off with the basic version for focus

[luxo II]

Don't lay the mask on the glass - that's almost certain to lead to fine scratches in the coating.

There is nothing critical about Bhatinov masks, since they rely on diffraction, not refraction:
- it doesn’t need to be flat;
- tilted makes no difference;
- it doesn't need to be accurately centered;
- you can mount it at the end of a dewcap well in front of the scope;
- size is not important - eg putting a 6" mask in front of a 10" scope will still produce a perfectly useable pattern for focusing;
- the spacing of the bars is not critical - more (smaller) bars = stronger diffraction spikes, fewer = less diffraction.

Edited by luxo II, 23 April 2025 - 09:47 PM.

[AEP64]

Thanks for the information...I was concerned it doesn't seem to lay evenly (flat) on top of the pins that the dust cap attached to, but if that's ok, I rather go that route instead of taking a chance of scratching the glass. 

[emflocater]

This video may help clear up any thoughts you may have. Click HERE

 

Cheers

Don

[OregonAstronomer]

my first time using one, and i am thinking i should have started off with the basic version for focus

I have both basic and Tri- for my C8, C9.25 and C14. I like the Tri- for collimation, but once well collimated, I like the regular one much better for focusing.