Hotech Laser Collimator headaches.

[Anderscn]

Hi,

I am new here, and also new regarding scopes.

For Christmas I got a Hotech collimator - the crosshair version with the 2" to 1.25" adapter piece. I am going to use it with my 10" GSO Dobsonian I bought in May last year. 

The procedure was easy to understand, and I could collimate the scope in less than 5 minutes. But then started the trouble:

When I take out the collimator (using the 1.25" version) after obtaining apparently perfect collimation, and reinsert the collimator again, it is out of collimation?! Not a lot, but still not spot on as before.

I then recollimater till it is spot on again. But if I then rotate the 2"-1.25" adapter ring of the focuser to a different position and tighten it here, it is out of collimation again! And if I use the 2" adapter for the collimator in the 2" hole in the focuser, it is out of alignment again, even though it was spot on using the 1.25" version..!? And vice versa.

There is very little, if any, slop in the focuser. It I slightly "shake" the collimator in the focuser, the laser spot on the primary mirror moves nowhere.

What am I doing wrong? I see only happy users and reviews with this laser collimator, so I must be doing something wrong. I of course make sure, that the collimater is secured absolutely close/tight to the focuser before I tighten the ring on the collimator.

I consider to get a Moonlite focuser in stead - could that help here?

BR,

Anders

[Uplooker]

One of the problems with laser collimators is that sometimes they need collimation themselves. To check it, get a length of wood, 8-10 inches long by 4-5 inches wide. Bang two 6 inch nails in at 45 deg to each other so that they form a cross. Do the same again so that you end up with two crosses to lay the collimator on. Switch on the collimator and aim it at a wall 20 feet away. Rotate the collimator and see if the laser point stays in the same place or if it makes a circle / arc. If it follows an arc, then you need to collimate the collimator. There are usually three off screws at the opposite end from where the laser emits from. Adjustments are made similar to adjusting the secondary on your scope. Keep adjusting and checking until the laser "dot" does not not deviate from a single point. One 5this is achieved the collimator is collimated.

Ian

[zcdawson]

I have a Hotech to and the 2" was off to the 1.25". On mine the 1.25 was good but the 2" was off about 1/16" when slightly tightened in the eyepiece and rotated. I ended up collimating the collimator. I took the 2" extention tube off, put the hotech in the focuser tube with the 2" adapter and rotating it to find the high spot on the mirror. There is a Allen head screw on the main body (mine was marked white) that can be adjusted so that the two are symmetric to eachother. When you use extention tubes with the lock screws they will throw off the collimation because they [removed word] just a little. I marked mine and put them in the same everytime. I want to go to the compression style tubes but I'm spending all my money on AP.

Hope this helps.

[zcdawson]

The [removed word] was not a bad word another way of saying it would be that the screws make it crooked.

[sbooder]

Just don't use a laser, I have tried most of them now and I have never been happy with any laser.  Get yourself a Catseye Blackcat XL Cheshire.  I have had the best collimation in over twenty years since getting mine 2 years ago.

[zcdawson]

I here the catseye's are really good. Thinking about trying one out myself!

[jetstream]

I have the Catseye Cheshire and sight tube-simple and accurate, one of my best investments. Lasers can have issues and are also sensitive to focuser slop etc and are not the best for sec alignment IMHO.

[sbooder]

I am not sure why you are not meant to be able to use the Blackcat XL for collimating the secondary?  I use mine for both mirrors and it works a treat.  It is my only tool now.  Simple, accurate and well made.

[Dave In Vermont]

I use an Orion LaserMate Deluxe II, and it arrived with perfect collimation - as they guarantee. I also use a Cheshire-Sighting-Tube. Both. And they both agree with each other. I actually enjoy collimating my F/4 Newt. Good thing, too. It goes out if I look at it cross-eyed. Finicky thing that it is - but I love it!

Clear & Sharp Skies,

Dave

[jetstream]

I am not sure why you are not meant to be able to use the Blackcat XL for collimating the secondary?  I use mine for both mirrors and it works a treat.  It is my only tool now.  Simple, accurate and well made.

I often wondered if the Blackcat Cheshire can be used as a collimation cap to line up the secondary.... Catseye also makes a combo too.

[Jason D]

I often wondered if the Blackcat Cheshire can be used as a collimation cap to line up the secondary.... Catseye also makes a combo too.

To align the secondary mirror, you need to position your eye in the following manner:

1- Position your eye at the center of the focuser

2- Ensure your eye axis is coincident with the focuser axis

Blackcat can assist with respect to #1 but not #2. A sight tube with a cross hairs will assist with both. 

Jason

[sbooder]

To align the secondary mirror, you need to position your eye in the following manner:

1- Position your eye at the center of the focuser

2- Ensure your eye axis is coincident with the focuser axis

Blackcat can assist with respect to #1 but not #2. A sight tube with a cross hairs will assist with both. 

Jason

It copes with #2 just fine.  Just making sure you are seeing a perfect circle takes care of axis of secondary.

[sbooder]

This is my entire collimation kit (including the piece of white paper). Not even any need for hex key...Ah, the beauty of Bob's Knobs!

[Jason D]

It copes with #2 just fine.  Just making sure you are seeing a perfect circle takes care of axis of secondary.

The secondary mirror can be little off and will still look like a perfect circle. Furthermore, it is natural to re-position the eye to align the secondary mirror with the primary mirror reflection. See first attachment. It is an animation. See if you can judge if the center spot reflection is centered. 

Having said the above, I am not suggesting that without  a sight-tube your secondary mirror will be way off but rather it might not be optimally positioned.

[sbooder]

This is why you block the image of the primary with the cardboard and use the white piece of paper to contrast behind the secondary, this produces the perfect circle with adjustment and you can take an image with a webcam and load to Fireworks or other editing software and measure the distance all round the secondary to the focuser/Cheshire wall if you so desire.

The beauty of the Blackcat for me is the depth of the pinhole.  It is so deep that if you move your eye to try an centre the cheshire tube wall image gets cut by the pinhole wall which forces you centre your eye.

[lensman57]

Hi,

I am new here, and also new regarding scopes.

For Christmas I got a Hotech collimator - the crosshair version with the 2" to 1.25" adapter piece. I am going to use it with my 10" GSO Dobsonian I bought in May last year. 

The procedure was easy to understand, and I could collimate the scope in less than 5 minutes. But then started the trouble:

When I take out the collimator (using the 1.25" version) after obtaining apparently perfect collimation, and reinsert the collimator again, it is out of collimation?! Not a lot, but still not spot on as before.

I then recollimater till it is spot on again. But if I then rotate the 2"-1.25" adapter ring of the focuser to a different position and tighten it here, it is out of collimation again! And if I use the 2" adapter for the collimator in the 2" hole in the focuser, it is out of alignment again, even though it was spot on using the 1.25" version..!? And vice versa.

There is very little, if any, slop in the focuser. It I slightly "shake" the collimator in the focuser, the laser spot on the primary mirror moves nowhere.

What am I doing wrong? I see only happy users and reviews with this laser collimator, so I must be doing something wrong. I of course make sure, that the collimater is secured absolutely close/tight to the focuser before I tighten the ring on the collimator.

I consider to get a Moonlite focuser in stead - could that help here?

BR,

Anders

It is not the laser but the focuser. Almost all of these focusers in my opinion have too large a gap between the EP, adapter , etc and whatever   happens to be inserted into them . Depending on where you stop the rotation  the holding screw will push the body of the adapter to the other side as much as 0.3 of a mm this is more than enough to upset the seating of the laser and in worst cases can actually push the body of the laser to tilt up. My advice is to use the 2"  laser and get rid of the 1.25" adapter as  Hotech has the ability to centre itself to a great degree so at least your collimation will be stable, this will change as you put the adapter back in again.  Hope this helps. Hotech's beam  is centred at the factory so do not attempt to adjust the beam, this procedure is only applied to the cheap lasers which are sold under different brand names BTW.

Regards,

A.G

[Jason D]

This is why you block the image of the primary with the cardboard and use the white piece of paper to contrast behind the secondary, this produces the perfect circle with adjustment and you can take an image with a webcam and load to Fireworks or other editing software and measure the distance all round the secondary to the focuser/Cheshire wall if you so desire.

The beauty of the Blackcat for me is the depth of the pinhole.  It is so deep that if you move your eye to try an centre the cheshire tube wall image gets cut by the pinhole wall which forces you centre your eye.

Getting the secondary mirror centered under the focuser is more important than getting it to look like a perfect circle. If you use a webcam that is centered in the focuser or if you take a photo with a camera that is centered in the focuser to assess the position of the secondary mirror, that will work. But would that be easier than using a sight-tube with cross-hairs!! I guess it comes down to personal preferences. The original point of this discussion is that relying on a collimation cap or on a Blackcat alone might not provide the optimal secondary position. If you use a webcam or a camera then you are using another tool above and beyond the Blackcat.

Bear in mind that centering/rounding  the secondary mirror is one alignment. The other alignment is ensuring it is fine tuned to reflect the focuser axis to the primary center. That is, centering and rounding the secondary mirror is only one part of the secondary mirror alignment.

Jason

[sbooder]

Getting the secondary mirror centered under the focuser is more important than getting it to look like a perfect circle. If you use a webcam that is centered in the focuser or if you take a photo with a camera that is centered in the focuser to assess the position of the secondary mirror, that will work. But would that be easier than using a sight-tube with cross-hairs!! I guess it comes down to personal preferences. The original point of this discussion is that relying on a collimation cap or on a Blackcat alone might not provide the optimal secondary position. If you use a webcam or a camera then you are using another tool above and beyond the Blackcat.

Bear in mind that centering/rounding  the secondary mirror is one alignment. The other alignment is ensuring it is fine tuned to reflect the focuser axis to the primary center. That is, centering and rounding the secondary mirror is only one part of the secondary mirror alignment.

Jason

I know.  And as I said earlier in the thread, after 20 years of doing this I have the best collimation I have ever had using just the Blackcat.  I do not use a webcam myself, this is an idea of Dion's, I just threw it in as an idea if people wanted to check.

[Jason D]

I know.  And as I said earlier in the thread, after 20 years of doing this I have the best collimation I have ever had using just the Blackcat.  I do not use a webcam myself, this is an idea of Dion's, I just threw it in as an idea if people wanted to check.

Please do not misunderstand. I was not trying to convince you to change your collimation method. I was merely trying to explain the limitations of the collimation cap and the Blackcat when used to align the secondary mirror -- at least for the benefit of others.

Just curious, is your primary mirror spotted with the "Hotspot" which is optimal for the Blackcat?

I used a donut, a white triangle, a yellow Hotspot, but ended up with a white Hotspot which I currently have on my mirror. Actually the yellow Hotspot works better with Blackcat (better contrast against the Blackcat white ring) but the white Hotspot works better with the XLKP autocollimator (better contrast against the dark background)

[jetstream]

Great pictures and info Jason.

To the OP-the Hotech laser is a high quality unit, but any unbarlowed laser is open to giving us problems. Sight tubes and Cheshires are low tech that works, can you get a Glatter TuBlug or something for your laser? and a sight tube? Maybe even a simple Cheshire combo tool may work well for you.

If anyone is interested in a perfectly collimated Newtonian, Jason is showing us here. Great to know about the white Hotspot Jason, I'm using a red triangle spot atm, which shows up pretty well in my AC. Open to try the white Hotspot for sure though, I just love when those reflections are stacked !lol!

Thanks Jason.

[Anderscn]

Thank you all,

For the advice and good discussions. I might take a second look at the Catseye.

If it were not that I now consider to sell my scope. Clouds seem to have settled permanently over the skyes in my area. Haven't seen a star since mid december :-( ..

BR

Anders