Djorre
11-26-07, 10:56 AM
Hi all,
while I'm waiting to get my glass prisms I was annoyed that I couldn't use my HT to it's fullest, so I decided to make a couple of water-prisms to ease the waiting period.
I've made two 20° prisms using just plain old pictureframe-glass I had by hand. I built two plastic wedges, glued the glass on with silicone and fillled them up.
Not expecting great results of course, just to see what I could acieve and what I was waiting for,... and as a fun way to spend a sunday-afternoon :)
I guess, every other lens should be better than waterprisms, so what I would get would be a 'worst case scenario'.
Now, as I understand, with waterprisms you should have CA (and in result focus issues) to the left and to the right, but with the colours inversed. This means in the centre you should have little or no CA or focus problems.
Now at the sides I have CA and focus issues, as expected. :)
But, I can't seem to get the focus right in the centre as well, in fact, it's quite a long way off.
When I display a wiregrid I get crisp horizontal lines of about 1mm, however the vertical lines in the centre, where they should be the most accurate, are still smeared over about 3mm,.... :eek:
I'm not actually expecting isco results of course :D but I was wondering if this was just because of the waterprisms or because I may be making a mistake with aligning them.
When I look at the grid it seems like I got the same stretch left and right.
I'm just a little bit alarmed now that the glass prisms will have the same focus issue, and it will be some money down the drain, or is this just normal for these kind of 3$ solutions...
Djorre.
while I'm waiting to get my glass prisms I was annoyed that I couldn't use my HT to it's fullest, so I decided to make a couple of water-prisms to ease the waiting period.
I've made two 20° prisms using just plain old pictureframe-glass I had by hand. I built two plastic wedges, glued the glass on with silicone and fillled them up.
Not expecting great results of course, just to see what I could acieve and what I was waiting for,... and as a fun way to spend a sunday-afternoon :)
I guess, every other lens should be better than waterprisms, so what I would get would be a 'worst case scenario'.
Now, as I understand, with waterprisms you should have CA (and in result focus issues) to the left and to the right, but with the colours inversed. This means in the centre you should have little or no CA or focus problems.
Now at the sides I have CA and focus issues, as expected. :)
But, I can't seem to get the focus right in the centre as well, in fact, it's quite a long way off.
When I display a wiregrid I get crisp horizontal lines of about 1mm, however the vertical lines in the centre, where they should be the most accurate, are still smeared over about 3mm,.... :eek:
I'm not actually expecting isco results of course :D but I was wondering if this was just because of the waterprisms or because I may be making a mistake with aligning them.
When I look at the grid it seems like I got the same stretch left and right.
I'm just a little bit alarmed now that the glass prisms will have the same focus issue, and it will be some money down the drain, or is this just normal for these kind of 3$ solutions...
Djorre.