Celestron c70 Project

[happy-kat]

Test line up and the holes and in dents line up perfect, yey. Now thinking I'll use Velcro to reattach the cover only.

[happy-kat]

For info. The two small screws that hold the original back moulded plastic part on are m3.

I've come up with a mk2 design if in time the fixing positions on the printed part weaken in use. I won't print it until testing of mk1 is thorough with a range of eyepieces, camera and distances.

[happy-kat]

I've ordered for the spares bin 20mm m3 bolts and various washers m3 and m4 of different size so I'm ready if I need to reprint and top mount the m3 with a washer to spread the attachment load on the print.

Velcro attached to ota and rubber casing though the latter is in the airing cupboard to make pliable for when fitting tomorrow.

Just got to find where I've put the erect image diagonal that came with the ST80. I've also got a WO star diagonal.

Oh and heat sink the m3 brass inserts.

I did want to insert a flocked liner to the baffle but the baffle looks way too thin to try this shame as it would be beneficial I think.

I'll add photos when there's something to show.

[happy-kat]

Had an idea yesterday, remove the eyepeice leg off my skywatcher erect image diagonal and then find an adatpor to then be able to fit the Baader T-thread to 1.25 helical focuser to be able to have better fine focus control. So far I have only found the adaptor to do the male 1.25 thread to male T thread in the US (thanks to another poster's link) at the cost of $40.46 before possible import tax.  It's an idea... the OTA cost me about £30 so I don't mind some spend..... an idea for the back bruner if the twiddly focus is well too twiddly, though I plan on fitting a clothes peg as and when needed to help with that last focus adjustment.

Baader helical focuser and adaptor

[happy-kat]

I'm toying with the Baader but use it with a T mount. If I can source some long collimation bolts it will also work with the heritage and it'll work with the ST80 anyway so a three in one focuser upgrade.

[happy-kat]

Earlier in the week I'd attached the exterior use velcro, had to use two different colours was the best use of the stuff I had left.

This morning I used the soldering iron tip to heat sink the brass fittings, worked a treat.

First wrap of covering was a little long had to carefully trim a bit more off though really I went half a mm to far, used a scapel knife as still have mine from poly days. I also trimmed the little thin peice off from near the focuser handle as it was fouling free movement.

Fixed the new backing plate on all fits very well. Hopefully will be able to do some testing later clouds prmitting!

[Stub Mandrel]

You really should have specified black PLA - still it takes paint well.

[happy-kat]

ABS was better choice for this use. And the Printer I used had only white translucent ABS. I think it looks fine.

[Ruud]

Altogether it is an amazing idea and the concept is proven.

Congratulations!

[happy-kat]

Thank you :-)

Preliminary tests using standard issue 25mm and 10mm eyepieces. Close focus is approximately 17 feet and the furthest thing I can focus on from my front door (it's raining) still leaves 21 finger turns to the stop. I then fitted my 2 inch extension and got another 2-3 feet closer on shortest focus distance so I'm going to order that Baader helical micro focuser but use it with a T mount to T thread adaptor which I already have as it currently attaches to my T ring, if it works I'll get another one otherwise I can't use my camera with the C70. Need the Moon out to confirm infinity focus.

[happy-kat]

Moon was out between clouds as went to bed and sat on bed with window open with selection of bits to try hand held. 25mm and 10mm reached focus easy, so did maxvision 16mm, gosh that 10mm has nasty narrow exact placement need! In and out star focus looked to be concentric rings so I didn't knock collimation though I plan to use a webcam and allscollimationaid to test it. Added the 2 inch extension and still had focus with the 25mm. I used the orion erect image diagonal that came with my ST80 I decided that really the optical path wouldn't be that different with the WO diaelectic so didn't test it plus it's much heavier and this was hand held. It had rained really heavy an hour or so earlier so the sky was probably very clear but the Moon was the best I'd seen it using this telescope there was no false colour I'm sure I'd seen a bit on the limb in the past and I was unaware of the secondary which I'd again been aware of it a shadow on the Moon previously. Just got to test the camera next and order that Baader helical micro focuser as I think it will compliment at least 2 of my three scopes. I'm really pleased I started this project even though I did wonder if I was a little mad when I started and had a bag of bits and a none working telescope.

[Stub Mandrel]

22 hours ago, happy-kat said:

ABS was better choice for this use. And the Printer I used had only white translucent ABS. I think it looks fine.

Sorry, I didn't mean my comment to come across as critical

[happy-kat]

It's OK it didn't. I had read up before choosing and ABS gave me the durability and for exterior use so appeared better. Colour who cares it doesn't impact the light path and if it did I'd flock the very small bit not covered by a diagonal.

[happy-kat]

Thought I would share two links I've just found on this mini mak. The first one confirms my observation that I had seen CA before when observing the Moon pre my modifcation. I found the post as have been looking for collimation info should I need it. I will now again consider flocking the interior too though I am not convinced there is room in the tube between the mirror and the tube sides. The post is good read the rest of the thread is well less so.

Link

And a blog post here.

link

[happy-kat]

Hahaha must remember that the webcam won't focus I've you've removed the lens!! That test will now have to wait until I find webcam with a lens on it.

[happy-kat]

Hahaha found webcam but must remember I need a star to be able to see collimation with Alscollimationaid app.

I've decided a job worth doing is worth doing well so I will strip it with the intention to flock the tube. I've become very attached to this little telescope I was very pleased with the image I saw on the Moon but it's main use will be daytime so I think flocking will be good to do.

[happy-kat]

Today's lesson you can flock this mini mak without touching collimation. But I learnt this the hard way but hopefully when I add photos later no one else has to go through recollimation. Once the C70 is bare of it's rubber coat the two halves just unscrew apart.

[happy-kat]

If you have already had the rubber coat off then to get inside the two halves unscrew. I marked up the join twice to know at what point they aligned when done up.

The mirror coating a word of caution is extremely THIN just breathing on it marks it, well not quite that light but I have marked my mirror coating and I hadn't realised I had initially as my first thought was a flocked lining but that back fired and has left me with marks on my mirror coating, nothing ventured but anyway that one bit me back good and proper.

The inside plastic is good and shinny!

The central baffle was too narrow to flock but it was thinly ribbed all the way down so perhaps that wont be a weak point after all in this telescope.

I used cellotape rolling over the flocking to pull the loose fibres off before use.

The top half I flocked with one peice between the lip at the top a bit below the glass lens and the edge of the screw threads, it is a nice area cleanly marked at either end.

The bottom I wound the mirror right back down then flocked in about 8 separate peices as was tricky and fiddly to do in a big peice. Taking my time I worked all the way around and the last bit is just a smidge too small but this meant there is no overlapping on the flock as there is not the clearance between the wall and the mirror carrier for any over lapping. I used a plastic splodger to ensure the flocking was making good contact with the wall where the mirror carrier is, the flat end had clearence to pass down the gap ensuring contact.

This picture shows the bottom flocked and not flocked.

Telescope is back together in one peice.

Still to do, collimate it as the only reason I need to is I had tried to first get the mirror out entirely but I couldn't get that to happen even though everything was undone and screws out! I'll start with doing an inside line up using a webcam face on to the front and using alscollimationaid get the circles I see concentric to take the donkey work out of the alignment so hopefully it will be only final adjustments when star testing.

I will be gaffer taping the supplied eyepeice holder to the back (with a padder) so that I can reach the collimation screws without stripping the back off for every adjustment.

 

 

[Ruud]

27 minutes ago, happy-kat said:

The mirror coating a word of caution is extremely THIN just breathing on it marks it

This is an interesting phase. I wonder: before you reassemble everything you probably want to blow any dust out. Do you suppose using a bulb blower (like the Giotto Rocket Blower) would be safe for the mirror coatings?

Good luck with the rest of the project and thank you for documenting it so well.

[happy-kat]

I had used my rubber blower so maybe you have hit the source of some of the marks though my mirror in the Heritage has been fine with the rubber blower. Just really surprised it is so thin I'd suggest never cleaning it certainly never being able to clean it like you see threads on here of carefully washing etc. This mirror the coating is way too fragile unless it's just mine. Thankfully unless I shine a torch at the mirror I don't see the damage and I think it's unlikely to spoil viewing that I'll notice.

[happy-kat]

It's clear but very hazy but good enough to see how collimation is. A hand held star test showed I will have to fettle the screws I'm thinking a bit of push at the 5 o'clock pair (though it's adjust in pairs of three rather than just one screw).

 

[happy-kat]

My plan now is to design a mk2 backplate that incorporates 6 holes to the collimation screws. So if collimation is needed it's just a swap of backplate.

[happy-kat]

Where does time go! This project has creeped to the top of the project pile...nearly.

[happy-kat]

My desk has had a major sort and file and now the C70 is sitting on it in position so that I can carry on with this project.

[happy-kat]

Realised this morning I can import an image so I imported a scanned image of the end of the C70, yey my model and the scan line up. If I had done this first time around I may have saved some time but I enjoyed the measuring and constructing from scratch. this though will probably help with the positioning of the 6 colimation screws. I will adjust the plane the image is on so that it revels the items needed.