Bahtinov masks - dumb question alert!!

[daz]

I am thinking the answer is YES, but....

I have a mask for my RC and ED80 for their native f/l - but I assume I also need one for when I use a reducer at the corrected f/l ? So, the RC will go from f/8 to f/5.4 (8 * 0.67) and the ED80 from f/7.5 to f/6.4 (7.5 * 0.85) ?

Again, pretty sure the answer should be yes...!

 

[Bizibilder]

Use the same mask - In theory you do need a different mask for each f/l but in practice one mask will work.  Try bunging your aparture/ focal lengths in the generator:  http://astrojargon.net/(X(1)S(2sns4s552wn1qm45rsw4i055))/MaskGen.aspx?AspxAutoDetectCookieSupport=1   and you will see that there is actually very little difference.

[daz]

Thanks Rog!

[RobertI]

I use the same Bhatinov mask for focussing my RC6 at its native F9 and at F4 and it works fine for imaging (video astro) although I do use a fairly low resolution Lodestar camera, so any shortcomings may not be apparent.

[Stub Mandrel]

I  made one for my 130P-DS which is 585mm with coma corrector, but before that I used the one for my 1200mm 150PL and it worked fine.

[daz]

Thanks chaps

[iapa]

On 9 August 2016 at 10:31, daz said:

I am thinking the answer is YES, but....

I have a mask for my RC and ED80 for their native f/l - but I assume I also need one for when I use a reducer at the corrected f/l ? So, the RC will go from f/8 to f/5.4 (8 * 0.67) and the ED80 from f/7.5 to f/6.4 (7.5 * 0.85) ?

Again, pretty sure the answer should be yes...!

 

I use the same mask for the 200PDS and the 130 SLT OTA

I have a smaller mask for the ST80, but also use with the SLT130

For my Nikon and Canon lenses I have one each - they are threaded and the lenses have different diameters, I though I have held the 58mm mask in front on the 52mm dia lens and had nice sharp images.

My reading did't dig up anything that indicated they it was focal length related - that is not to say it isn;t, I just didn't find anything so obviously bow to greater knowledge in the math involved

 

 

 

[geordie85]

I wouldn't have thought focal length mattered as it doesn't know the focal length your using and is only there to help you find the focus sweet spot

[Stub Mandrel]

I have had an interesting idea for small lenses ... watch this space :-)