Collimatable collimator!

[BrendanC]

Hi,

I used to have a laser collimator for my 130PDS but discovered it wasn't centred. Then I realised it also wasn't collimatable, ie it didn't have the three screws for adjusting it. So, I chucked it. It was a cheap thing from eBay.

I've decided I'd still quite like a laser collimator however, so I can quickly check things are ok before a session - one that does have the collimation screws so that I can make sure it's ok.

I totally understand the problems with laser collimation regarding focuser slop etc, but I figure that, if I can get close with the laser, it's better than nothing and certainly quicker and easier than checking a Cheshire or cap in the dark.

Problem is, I've looked for quite a while and can't seem to find one! There's the SVBONY one, but apparently the screws are somewhat hidden under the rubber casing which has to be prized off, which I don't much like the sound of (I had exactly the same issue with my astro binoculars). There may be a search term I'm missing here, but try as I might, I can't reliably find a collimatable collimator.

So, any recommendations? I'd rather not go toward the high-end route ie no Howie Glatters and such like. Ideally less than 50 quid if possible.

Thanks, Brendan

Edited November 30, 2020 by BrendanC

[bobro]

I purchased one of these: http://ebay.co.uk/itm/223895728711 though from a different China based seller.

Collimation as delivered was terrible, though the black (silicone?) stuff over the collimation screws was easy to remove, allowing the laser collimator to be collimated by projecting it onto a wall whilst rotating the collimator and adjusting the screws.

A good purchase and did the job for my 2 scopes, which I thought were ok but turned out to be a bit off collimation.

[BrendanC]

Thank you! Maybe it's the same situation then - collimation screws there, but covered.

Seems a reasonable price too.

[Jiggy 67]

The only one I’d use is the HoTech. It comes fully collimated and uses a compression ring in the focuser to perfectly align it. It’s easy to use and very accurate, not cheap but you get what you pay for I suppose 

[Jiggy 67]

Sorry meant to post a link

https://www.firstlightoptics.com/hotech-collimation-tools/hotech-sca-laser-collimator-with-cross-hair.html

[Uplooker]

+1 for the Hotech. Not cheap, but worth it

[Jiggy 67]

Yeh, though when you think about it, if you look after it it will last a lifetime so in that respect it’s a bargain..... I suspect you could buy numerous cheaper ones over the years that won’t do the job, won’t last and cost more in the long run as demonstrated by the OP having to throw his away

[Waldemar]

and another vote for the Hotech

[AlexK]

First of, check the collimation of your laser collimator (LC). It may be just OK as is (~3mm shift at ~7m distance screen is OK), so it doesn't actually need a collimation. As soon as you confirm that the shift in your OTA is smaller than that (if not, you have to do the total re-collimation of your OTA, not the LC), collimate with it as usual, and then move to the Simplified Barlowed LC method (SBLC), which could actually benefit from el-cheapo LC device like the one recommended above (I have that one too, and it is better than the stock LC which originally came with my 15 y/o Zhumell 12" (z12)).

If still in doubt (I know, it's hard to trust a new method, especially when it's "simplified") follow with the star test. I'm using the above flow for over a decade with my z12 and never had the SBLC failing the Star test even with a total garbage LCs used on occasion.

On a side note that short 130P-DS you have have to be collimated only once. So if you don't play football with it it should stay perfect forever if you do the last collimation step with the counter-screws and lock the cell. Thus for that $145 Hotech wants for a $20 LC, I'd rather invest into a dedicated Barlow (with your 650 mm focal you might want a 3x one for a wider light cone to cover the center mark; you don't have a center mark? Just draw it!).

Edited November 30, 2020 by AlexK

[Pixies]

Sky's The Limit (the chap who sells BST Starguiders) also sells the cheap laser collimator with the 3 screws under black silicone.

https://www.ebay.co.uk/itm/Skys-the-Limit-Next-Generation-5mw-Laser-Collimator-1-25-2-adapter-7-levels/164350914583?hash=item264413f017:g:N60AAOSw2glfQ8TJ

I ordered one and it arrived perfectly collimated, but that was probably luck more than anything else. I did build a collimation jig for the laser, though.

I rarely use it since getting a decent Cheshire.

[AlexK]

These cheap LCs might be good enmasses as they have much smaller and lighter laser emitter piece inside (harder to knock it off by typical shipping/handling forces).

I'm collimating my LCs using the 2" to 1.25" eyepieces adapter (comes with that cheap model linked above). Just clamp the adapter in the vises, or by a C-Clamp, (or even drill a hole for a wood screw in the side) to a desk/table what have you steady and rotate the LC in the adapter fixing by the set screw for each mark point angle, making sure it's in contact by the front lip (for the orthogonality). A "V-block" like that classic one above assumes the piece is turned. While in China it might be stamped, so the coaxiality of its body "curves" is not guaranteed actually. I.o.w.: you want your nails on its 1.25" barrel only.

[Waldemar]

3 hours ago, AlexK said:

These cheap LCs might be good enmasses as they have much smaller and lighter laser emitter piece inside (harder to knock it off by typical shipping/handling forces).

I'm collimating my LCs using the 2" to 1.25" eyepieces adapter (comes with that cheap model linked above). Just clamp the adapter in the vises, or by a C-Clamp, (or even drill a hole for a wood screw in the side) to a desk/table what have you steady and rotate the LC in the adapter fixing by the set screw for each mark point angle, making sure it's in contact by the front lip (for the orthogonality). A "V-block" like that classic one above assumes the piece is turned. While in China it might be stamped, so the coaxiality of its body "curves" is not guaranteed actually. I.o.w.: you want your nails on its 1.25" barrel only.

Very good point! One more reason to buy a Hotech SCA laser collimator...

[malc-c]

Been using Hotech for years.  Its self centering fitting and precision makes it well worth the investment.  Most of the cheap collimators from e-bay and the like are not worth the money.

[BrendanC]

Hmmm. Maybe I'll ask the missus for the Hotech for Christmas... 

Thanks everyone! 

[John]

I bought a Hotech a few years back and that was out of alignment as well so even the better ones can have this issue occasionally

Having been through a number of the better ones (a Baader that I had was also not collimated accurately and was a so and so to sort because it's not a symmetrical shape) I bought a low cost collimator and collimated it as accurately as I could using a 10 metre distant target.

99% of the time I use a simple cheshire with my 12 inch dobsonian but when I do use the laser it is with a barlow using the method mentioned here:

http://www.smartavtweaks.com/RVBL.html

My laser collimator is the same as the one used in the above link.

Otherwise I use my laser collimator for checking the alignment of refractor focusers and not a lot else.

 

 

Edited December 1, 2020 by John

[jacobingonzo]

Don't understand the lack of love for a cheshire- Doesn't need collimated, Spot on during daylight and at night shine a small torch in the indent and your scope is collimated as quick as you like 

 

J

[John]

6 minutes ago, jacobingonzo said:

Don't understand the lack of love for a cheshire- Doesn't need collimated, Spot on during daylight and at night shine a small torch in the indent and your scope is collimated as quick as you like 

 

J

+1 for that

[CraigT82]

7 minutes ago, jacobingonzo said:

Don't understand the lack of love for a cheshire- Doesn't need collimated, Spot on during daylight and at night shine a small torch in the indent and your scope is collimated as quick as you like 

 

J

If you can't reach the collimation screws whilst looking through the cheshire then collimating can take a bit longer, with a bit of back and forth between eyepiece and mirror.

Barlowed cheap laser for me, takes seconds. 

[Louis D]

6 minutes ago, jacobingonzo said:

Don't understand the lack of love for a cheshire- Doesn't need collimated, Spot on during daylight and at night shine a small torch in the indent and your scope is collimated as quick as you like 

 

J

They're a little hard to use with a 6 foot tall truss Dob unless you could mount a camera where your eye goes.  I can get the primary quickly on target with the laser by watching the return beam coincide with the outbound beam on the secondary while adjusting the primary knobs from the rear of the scope.  After that, a cheshire is handy for tweaking the alignment in small increments, but with lots of back and forth motions between the focuser and rear of the scope.  I have a 20+ year old AstroSystems laser which doesn't have the handy side cutout invented later.  It is dual fit, 1.25"/2" though, unlike the current version.

[jacobingonzo]

Yeah Craig I understand the laser is easier but as the posters above are discussing the prevalence of the lower end of the market to be off cue I feel that I can live with a little hassle of the back and forth, rather that than spend an arm and a leg and next doors cat on a Hotech etc lol- anyway horses for courses we each love what works for us

 

Thats exactly what I mean Louis, use whatever system works best for you

 

J

Edited December 1, 2020 by jacobingonzo

[John]

My dob is a solid tube 12 inc F/5.3 so the tube is nearly 6 feet long. I find the cheshire really simple and quick to use. Quick check and tweak if needed before I start to use the scope. Takes about 30 seconds.

Having used this method for a few years though I know just what to look for and where to tweak. So that does back up that the way that works best for you and that you are comfortable and confident with (that last word is important I think) is the one to go for. 

For newcomers to collimation it may be necessary to try more than one approach to find out what works for them.

Learning what a decent star test looks like helps too - good for the confidence if what looks to be collimated actually can be demonstrated to be so !

 

 

 

Edited December 1, 2020 by John

[Ricochet]

I agree with the comments about using a Cheshire or barlowed laser. The Hotech I had was complete junk and worse than a £20 eBay laser. 

[Jiggy 67]

You could have put your mortgage on this becoming laser V Cheshire 😂🤣

Edited December 1, 2020 by Jiggy 67

[AlexK]

Also, Cheshire (vs the Barlowed laser) has only about a half of the possible accuracy, due to the Barlowed return beam magnification aiding with significantly more accurate visual centering. But for the OP scope size it looks like a good alternative indeed, as the distance to the image you want to center is just ~650x2 = 1300mm (frankly like checking if your foot nails require grooming ). Try that from 3 meters of the double focal path of a typical 12" F5.

Edited December 1, 2020 by AlexK

[BrendanC]

Thanks for all the suggestions. I guess collimation is equalled only by calibration to set people off!

I already have a Cheshire and a collimation cap. What I'm thinking is that a good, collimatable laser would be more useful in the field (literally) - as in, as a last check in the dark before a session, pop it in, check everything central, off you go. I don't quite see how this could be done with a cap or Cheshire?

Anyway, I'll have a ponder.