glend
18-05-2020, 01:09 PM
Diagonals seem to be the forgotten gear in many equipment forums, perhaps we just take them for granted, and imagers often don't care about them at all. When I was collimating my Cassegrain, or my long refractors, the diagonal has to be left aside, the reason being that seemingly often they are not very precisely aligned, and when your bouncing a laser out and back, you want to eliminate extraneous sources of light diversion. However, once you have your precious collimated, are you going to stick that questionable diagonal back in the focuser? I suggest you learn how to check the collimation of the diagonal.
It is not hard to do, takes just a few minutes, if that, but it assumes your laser is already collimated to run true.
1. Just stick your laser into the eyepiece end of your diagonal.
2. Hold the scope end tube of the diagonal up against any available flat mirror (bathroom mirror, closet door mirror, etc is fine). This is likely to cause your children or partner much amusement.
3.Turn the laser on and observe the reflected light point; it should be hitting the laser light source opening precisely centred, not off to the side, above or below.
4. If your laser is precisely reflected then your done. If it is not then consider these options:
Is your diagonal collimatible, some are, some good aluminium bodied Star Diagonals have tapped screw holes in the bottom plate, which can be used to nudge the alignment, but you may need to find a source for the screws if they are missing. Shims are another option, but incredibly fiddly to insert and get right.
In fairness to suppliers most good Diagonals are pretty precisely aligned, and many visual users can live with a 1-2mm misalignment. If it is a cheap plastic case diagonal, I would just bin it and buy a good one. The obsessives among us, will seek out the best.
What is a good diagonal, well how much money do you have? Baader has a wonderful click lock one for something like 425 Euro.
https://www.baader-planetarium.com/en/baader-2%22-bbhs-r-mirror-diagonal-with-2%22-clicklock-clamp.html
The GSO Star Diagonals (or their Bintel branded kin), are good value, and the ones I have had are very preciserly aligned.
https://www.bintel.com.au/product/bintel-star-diagonal-2-inch-dielectric/?v=322b26af01d5
So those are my thoughts on the subject. Have fun checking your diagonal.
If you wish to do some detailed reading on diagonal materials, construction, and coatings, this article is useful:
http://www.astrosurf.com/luxorion/reports-stardiagonal.htm
It is not hard to do, takes just a few minutes, if that, but it assumes your laser is already collimated to run true.
1. Just stick your laser into the eyepiece end of your diagonal.
2. Hold the scope end tube of the diagonal up against any available flat mirror (bathroom mirror, closet door mirror, etc is fine). This is likely to cause your children or partner much amusement.
3.Turn the laser on and observe the reflected light point; it should be hitting the laser light source opening precisely centred, not off to the side, above or below.
4. If your laser is precisely reflected then your done. If it is not then consider these options:
Is your diagonal collimatible, some are, some good aluminium bodied Star Diagonals have tapped screw holes in the bottom plate, which can be used to nudge the alignment, but you may need to find a source for the screws if they are missing. Shims are another option, but incredibly fiddly to insert and get right.
In fairness to suppliers most good Diagonals are pretty precisely aligned, and many visual users can live with a 1-2mm misalignment. If it is a cheap plastic case diagonal, I would just bin it and buy a good one. The obsessives among us, will seek out the best.
What is a good diagonal, well how much money do you have? Baader has a wonderful click lock one for something like 425 Euro.
https://www.baader-planetarium.com/en/baader-2%22-bbhs-r-mirror-diagonal-with-2%22-clicklock-clamp.html
The GSO Star Diagonals (or their Bintel branded kin), are good value, and the ones I have had are very preciserly aligned.
https://www.bintel.com.au/product/bintel-star-diagonal-2-inch-dielectric/?v=322b26af01d5
So those are my thoughts on the subject. Have fun checking your diagonal.
If you wish to do some detailed reading on diagonal materials, construction, and coatings, this article is useful:
http://www.astrosurf.com/luxorion/reports-stardiagonal.htm