Short vs Long Cheshire collimators

[Pixies]

Hi,

I have a shorty Cheshire, which is fine for collimating the primary mirror. However, I am so short-sighted I have problems trying to use the crosshairs when adjusting the secondary. With my glasses off, my close-up vision is fine - but only up to about 20cm for a decent focus - so I can focus on the cross-hairs just great. I need my specs to be able to see the doughnut, but the closest I can focus with my specs is also 20cm, so I can't focus on the cross-hairs!

I realise that a long Cheshire is probably still too short for a good focus on the cross-hairs, but it might be a little bit more easy to use.

However, I'm not clear on the differences between the short and long style. Is there a functional difference? Is one more suited to a particular type of scope than the other?

And a final question. Regarding FLO's "Premium Cheshire Collimating Eyepiece": It has a stepless barrel, so I assume this means you can vary the depth to which you insert it into the focuser? Does this help with anything?

 

Cheers

P

Edited August 14, 2020 by Pixies

[Pixies]

Anyone? (feeling ignored )

[Geoff Barnes]

Chin up @Pixies we're on your side!

I have both long and short cheshires and find I prefer the short one. Mainly because it shows the three primary clips easier.

[andrew s]

As a Cheshire as long as its stable in the focuser length does not matter.

Using it as a sight tube to place the secondary under the focuser you should adjust it so the the end of the tube just encloses the secondary. Length might matter. 

Using the cross hair to adjust the secondary tilt is more accurate with a longer distance between  the peep hole and the cross hairs but I doubt it would be significant. 

Regards Andrew 

[Guest]

I'm going down a similar route and wasn't sure about the Premium version or the Astro Essentials one...   At the moment, the Astro Essentials is the only one Auntie @FLOhas in stock.  It would be to used mainly with my Sky-Watcher Skyliner 200P Dobsonian.

[Daf1983]

I have the astro essentials version with my 200p. I can't see the 3 primary clips at all using it, and I find there is quite a bit of movement when it's in the focuser. Is it's the only cheshire eyepiece I've ever used, so not sure if it's an issue with the eyepiece, the focuser or (most probably) me!

[Dark Vader]

I have the FLO premium one. Have only really used it once and assumed it had to go in up to the hilt, as it were. 😃

The thought behind that was the eye hole would be nearer to the height of the supplied EP when looking through it.

I don't know if I'm using it correctly... I can see the secondary, primary clips and cross hairs through it so shouldn't be far wrong.

Andy 

[AstroNebulee]

Hi @Pixies

I have the astro essentials long one from flo and have found it good for collimating my skywatcher explorer 150p 

[Capstone55]

I have a long Cheshire (Astro Essentials) and to be honest, I mostly use a simple collimation cap. The Cheshire is too long for me to see the whole of the primary when aligning the secondary (admittedly not done very often). The Cheshire is better for aligning the primary but the collimation cap is good enough so I usually use that.

[Pixies]

Here's my review of the FLO Premium Cheshire:

 

[John]

I use a short cheshire to collimate my 12 inch F/5.3 dob. I've been using it for a few years now so it's become 2nd nature to use. I rarely need to do more than adjust one or other of the collimation screws a tiny bit just to completely centre things.

I have tried a number of other collimation aids over the years but having found one that was simple and that worked and was consistently backed up when the scope is star tested, I've stuck with it.

 

 

[LondonSi72]

I bought the Astro Essentials Cheshire and a collimating cap, having had problems using a laser collimator that I got when I first got my scope. I’ve started getting back into using the scope recently, and figured it probably needed collimating.  I followed the instructions in AstroBaby’s guide and she recommended using a collimating cap for the secondary mirror alignment so you can see the primary mirror clips more easily, and the Cheshire for the primary mirror alignment. This seemed to be easier - and more consistent - than using the laser collimator, which seemed to change every time I removed it and reinserted it.
 I have the SW Explorer 130.

[Pixies]

35 minutes ago, LondonSi72 said:

I bought the Astro Essentials Cheshire and a collimating cap, having had problems using a laser collimator that I got when I first got my scope. I’ve started getting back into using the scope recently, and figured it probably needed collimating.  I followed the instructions in AstroBaby’s guide and she recommended using a collimating cap for the secondary mirror alignment so you can see the primary mirror clips more easily, and the Cheshire for the primary mirror alignment. This seemed to be easier - and more consistent - than using the laser collimator, which seemed to change every time I removed it and reinserted it.
 I have the SW Explorer 130.

I'm finding a long Cheshire better as a "sight-tube" to align the secondary under the focuser (step 2 in the AB guide - with the coloured paper). But it is the FLO premium cheshire which doesn't have the 'lip' on the tube, so it can be inserted to any depth.  It all depends on the size of your scope.

For step 3 - Aligning the secondary to the Primary Mirror - all you need to do with a Cheshire is to align the crosshairs with the doughnut centre mark on the primary, you don't have to use the mirror clips (unless you don't have a doughnut). I'm not sure why A-B doesn't mention this. If I have misunderstood, someone please let me know!

Step 4 - Aligning the Primary Mirror - yep, so easy.

I am lucky with my laser collimator that it appears to match my Cheshire and is stable when in the focuser. It's a BST Starguider one, and cost £18. I did check its collimation though and it needed a little tweak when I first got it.

Edited August 31, 2020 by Pixies

[LondonSi72]

On 31/08/2020 at 10:39, Pixies said:

I'm finding a long Cheshire better as a "sight-tube" to align the secondary under the focuser (step 2 in the AB guide - with the coloured paper). But it is the FLO premium cheshire which doesn't have the 'lip' on the tube, so it can be inserted to any depth.  It all depends on the size of your scope.

For step 3 - Aligning the secondary to the Primary Mirror - all you need to do with a Cheshire is to align the crosshairs with the doughnut centre mark on the primary, you don't have to use the mirror clips (unless you don't have a doughnut). I'm not sure why A-B doesn't mention this. If I have misunderstood, someone please let me know!

Step 4 - Aligning the Primary Mirror - yep, so easy.

I am lucky with my laser collimator that it appears to match my Cheshire and is stable when in the focuser. It's a BST Starguider one, and cost £18. I did check its collimation though and it needed a little tweak when I first got it.

A challenge with the SW Explorer 130 is that it doesn’t have a centre mark/donut on the primary. I’ve seen articles describing how you can add one, but on my scope removing the primary mirror looks like a potentially terminal action!. I wouldn’t want to risk removing the mirror and damaging it or not being able to get it back in, just to get that very last tweak of collimation correct. 😁

There are clearly a few variations on the SW Explorer 130, depending on when it was manufactured/purchased.  Mine was bought in 2012 and has captive nuts on the inside of the tube holding the primary mirror apparatus in place.  From the two other members of SGL who seem to have centre spotted similar 130s, it sounds like it's easier to remove the mirror from directly underneath the scope using the locking and/or adjusting screws.  Either way, it seems like a fairly major operation and think I'll only try that if I can see the collimation is off with a star test.  Haven't had a chance to do a proper test since I adjusted it with the cheshire and collimating cap - too much turbulence and the airey ring looked like it had been pebble dashed!  Still got decent views of Jupiter and Saturn, though.

Edited September 2, 2020 by LondonSi72