AstroSystems Laser Collimator with Barlow arrived...problems
Omaroo...Now that I'm back in the country, I'm trying to collimate using this laser collimator. Using it is easy as, but in the end, using my cheshire piece, the collimation looks like the attached image. Any ideas why??? It's as if the secondary isn't centered....?? I'll try a star test tonight and report back as well, but I'm sure this isn't right.
Using the laser, I centre it on the mark on the middle of the primary, then go about collimating the primary...I think what I'm doing is correct.
DJ - is your 2" to 1.25" adapter (that you are mounting the Cheshire in) tight and free of slop? It sounds as though it may be de-centering the Cheshire as you tighten either the 2" focuser clamp or the 1.25" adapter clamp - or both. The new laser collimator is a 2" unit in itself - so it eliminates any misalignment in the second (1.25" adapter) unit as it doesn't use it. Overriding rule of thumb - make sure that you seat the collar around the collimator as FLAT as can on to the edge of the focuser.
If you loosen the clamp ring, how much slop is there if you jiggle the collimator with the laser on?
I'd be interested to see now the star test goes and we'll go from there. I've heard of people discovering that their secondary was way off due to the fact that they never got their Cheshire or other 1.25" devices to sit square in the first place. The secondary holder might actually be offset too - just because the 45° angle is correct (to get the spot hitting the target on the primary) doesn't mean that your spider is laterally centred - and this can be compounded if the clamps put the Cheshire out of centre as well.
My secondary was out by a fair whack because of the cheap and loose adapter.'
Ken - these are nothing like the design of the typical Orion/Bintel/etc laser collimators. They are non-adjustable. Discussion over this got a bit heated last time. See here: http://www.iceinspace.com.au/forum/s...t=astrosystems
Hmmm...I have the 10:1 focuser from Bintel. I removed the base, and attached it to the base of my old focuser cause that's the only way it would fit. I'm at work at the moment, but will have a closer look at this when I get home. If there are no clouds (doubtful), I'll give you the results of a star test as well.
I'll also take close up photos of the focuser and cheshire etc...
Thanks heaps guys.
Oh, and I don't have a spider. It's a Mak Newt or something. It's glass, with the secondary holder in the middle of the glass. All will be revealed in the photos tonight!
Hmmm...I have the 10:1 focuser from Bintel. I removed the base, and attached it to the base of my old focuser cause that's the only way it would fit. I'm at work at the moment, but will have a closer look at this when I get home. If there are no clouds (doubtful), I'll give you the results of a star test as well.
I'll also take close up photos of the focuser and cheshire etc...
Thanks heaps guys.
Oh, and I don't have a spider. It's a Mak Newt or something. It's glass, with the secondary holder in the middle of the glass. All will be revealed in the photos tonight!
A Mac Newtonian! I see that in your sig now - an MN56. Gee... I dunno then. Don't you alter the collimation by screws on the outer meniscus ring or something? I've heard Mac Newts can be a real bear to collimate - so maybe this needs to be addressed by another MakNewt owner - and specifically an Intes one.
The biggest problem I see you having is having to un-clamp and withdraw the entire collimator to put the barlow attachment on and then re-insert - possibly to a different place. The spider on a standard Newtonian lets you reach through it and place the barlow on without having to touch anything else after centring the dot on the primary - giving you a better result I imagine. The fact that you have to remove the whole apparatus between aligning the secondary to the primary's centre dot and then the primary return image to the barlow gives us a new problem to contend with I guess.
Umm.. What I'm wondering, is maybe my secondary needs to move a bit in (towards the primary - direction). When I put the cheshire in, and move the focus as far IN as I can, I can see there's something in the way of the image (at the top). Either focuser, or top of scope...dunno.
I was hoping my secondary wouldn't need to be moved, but maybe that's what it needs. In any case, I'll have a play with it tonight and post many pics so that you can see them.
Location: Tucson, before that Wisconsin, before...
Posts: 231
That straight edge on the full-in focus pic is the focuser drawtube encroaching into the light path. The fact that it's absent in the full-out pic cinches that, I think. That's normal, most newts look the same.
The last two photos are with the Chesire in the focuser tube, or just the appearance thru the focuser with nothing in the drawtube? I can’t see the typical concentric rings I’m used to seeing in a Chesire….just wanted to clarify this, because the last two photos look like simple shots thru an empty drawtube; we see the secondary mirror (no spider, as you say, in a Mak-Newt). Is your primary mirror marked with a donut? Could be the pics are just a bit dark to see all these things….
Can you see the back of the laser’s Barlow attachment thru the meniscus? Or are you just using the primary (without Barlow attachment) laser beam of the collimator to align the secondary, then using the chesire to align the primary? Or using the laser with-then-without Barlow attachment to do both, then checking it with the chesire?
As to that apparent eccentrically located center spot…It seems more like the upper right edge of the image is fuzzy, rather than eccentrically located…this raises the vignetting issue. At least that’s what your last photos suggest. And this fuzzy edge feature is MORE dramatic in the last pic, the full focuser-out version, and covers more than 180 degrees of the edge. Changes in the appearance of things as you rack your focuser in and out are almost always either focuser squaring problems or vignetting of the light cone somewhere along the way.
When you look thru the empty focuser tube in the full-in and full-out positions, centering your eye over the focuser tube as best you can, are you able to see the full circumference of your primary mirror both times? Can you see the full circumference of the secondary mirror itself, also?
S
Quote:
Originally Posted by DJVege
Ok! Here are the pics!!
The first 3 are of the focusser!
The fourth is of the cheshire in the focuser.
The fifth is of the laser collimator in the focuser.
The sixth is what I can see through the cheshire at full IN focus (put the digital camera flush on the 1.25" adaptor).
Seventh is what I can see through the cheshire at full OUT focus.
What do you think? Maybe the secondary needs to move away from the primary a bit?? (In that direction...???)
The last 2 photos are just with the digital camera sitting flush in on the tube (empty tube). I was just making the point that this is also what I see through my cheshire (except with crosshairs).
I use the laser without barlow to align the secondary. All i do is make sure the beam points directly at the circle in the middle of the primary.
I then use the barlow attachment to align the primary. Then I check with the cheshire.
As for your "squaring my eye over the focuser" question, I'm pretty sure that I can. But I'll confirm that tonight when I'm back at home.
One question...what's vignetting? (I'll google this).
Location: Tucson, before that Wisconsin, before...
Posts: 231
vignetting is some form of obstruction of the light cone. For example, if your secondary is not positioned correctly under the focuser, it would miss part of the light cone coming up from the primary. (I don't think that's it in your case). Or, if your tube diameter is just barely larger than your primary mirror and the optical axis is not exactly matched by the tube's axis, the tube itself could vignette the light cone. Or, if you focuser doesn't move straight in and out as it points at the center of the primary mirror; or, consider that the axis of the light coming into the focuser drawtube is at a different angle than the axis of the center of the focuser drawtube...basically means the focuser is not "squared" to the axis of light coming in from the secondary mirror.
The reason I suggested vignetting is that the fuzzy upper-right limb of your picture has that look. Your camera lens could be off-center a bit, but if that's what you see with your eye, it probably isn't just that simple, since most of us will automatically and unconsciously move our eyes to find the best image as we look down the tube...and rule out that as an explanation.
By moving your eye about as you look in the empty drawtube, can you make that fuzzy vignetting-like dark zone disappear...in other words, can your eye find any position in the drawtube that looks like a perfect circle with the center spot and primary center mark in the exact center of the view?
Did you have this same problem with the original focuser or did it start when you added the 10:1?
Try this: point the scope at some bright light in your house, and take the thru-the-focuser picture again. Hopefully we'll see more of the secondary assembly better illuminated, maybe even the bottom of the focuser drawtube. Or have someone shine a torch at an angle through the meniscus aimed at the back of focuser.
I can use the cheshire to collimate the scope and all is good. (According to my amateur opinion, though). I've had everything centered when using just the cheshire...I'll report more when I get back home after work.
I've only just got the laser collimator, so the problem has only started now.
Location: Tucson, before that Wisconsin, before...
Posts: 231
ok
the barlowed laser and a chesire assess the same thing, and should always agree, unless there some anomaly in how the device(s) fits into the drawtube. Even miscollimation of the laser beam shouldn't affect the laser when used in barlow mode....but miscollimation of the primary beam only (without barlow attachment) will affect how it enables you to align the secondary mirror. So, perhaps your primary laser is off collimation itself...Still doesn't handily explain everything....
s
Quote:
Originally Posted by DJVege
I can use the cheshire to collimate the scope and all is good. (According to my amateur opinion, though). I've had everything centered when using just the cheshire...I'll report more when I get back home after work.
I've only just got the laser collimator, so the problem has only started now.
Second image is full OUT focus, with the camera as far left (in the 1.25" adaptor) as possible.
Third image is full OUT focus with the camera as far right as possible.
I think maybe I just have to move the secondary a bit..
But then I'm missing something in my collimation process.
I thought, to fully collimate...you simply shine a laser, adjust the secondary so the laser hits the middle of the primary, then adjust the primary so the beam goes straight back to the source.
I must have to use the cheshire first...actually MOVE the secondary so that it's in the centre of the primary, THEN adjust the rotation of the secondary with the laser, etc...
Ah...I think I need someone to show me how to collimate. LOL!
This is all I got when I collimated with just the cheshire. First is full IN focus. The second is full out focus.
When I put the laser in after collimating with the cheshire, it's a cm off to the left of the mark. (centre of primary).
I think I dunno what I'm doin.
I don't think the images are showing it properly, either. The bottom of the image seems to be chopped off. (Bottom of the tube). The lens may not be exactly centred on the cam. ???
I'm pretty new at collimating Newts but I'll give you my method.
(From reading the instruction book, what I've read on here and a bit of intuition.)
I first look straight down the focus tube and wind the adjustment out until I can no longer see the end of the tube in the mirror reflection. My main mirror has 4 clips holding it in place and if I cant see all of them evenly at the edge of the field of view I adjust the secondary till I can. This secondary adjustment has to be done rarely as once its set it will stay pretty well OK unless the tube or spider gets a hard knock. I then put the laser in and fine adjust the secondary so the dot is on the centre spot of the main mirror. The final stage is adjusting the main mirror so the reflected laser spot on the angled cut out on the side of the laser collimator disappears back down the central hole from whence it came.
I hope this helps, I had a hard time getting it right too, but once you've done it a couple of times its not so bad. I don't use the cheshire, just the laser.
My problem is that I'm a bit worried about moving the secondary. With the focuser flush, I think I need to move the secondary out a bit. But, there is one middle screw for this (the three around are for optical alignment). So I'm not sure if all I have to do is play with that centre screw or not.
The central screw is quite a long one to allow for some adjustment of up/down position. Then you have to adjust the others by the same amount. Its surprising how little adjustment of the screws it needs to get things in line. Probably best to adjust in small increments as slackening it right off will allow the secondary to spin on its axis and upset the perpendicular secondary/focus tube alignment. If you look down the focus tube or cheshire and the secondary is pretty round and in the middle of the field of view its probably OK for position in the tube.
My 6" was due for a check so here's a couple of pics. I checked the position of the 3 clips on the primary using the cheshire as its probably more accurate. Cheshire was removed for pic. Put in the laser, centred the spot and adjusted the primary till the dot disappeared down the hole. Re-check the spot center, as mine is incline to shift a tiny bit when I adjust the primary and tweak the primary again. You'll notice the focus tube is out a bit so the end of it doesn't show in the mirrors.
Took 30 mins all up, but I've had a bit of practice now.
Yeah, with this new focuser, I don't think the secondary is centered properly under it. It's the Bintel 10:1 focuser. However I had to remove the Bintel base, and screw the focuser onto my old focuser's base so that it would fit without having to drill any holes into the scope.
Hopefully I'll get some time this weekend to play with the secondary some more. I'm fairly sure this is all because the secondary is out...
Although...if my secondary is out...shouldn't the cheshire AND laser collimator give the same results???
Anyone in Brissy wanna test this laser collimator for me? And my cheshire while you're at it?