The mirror is an 8 inch f6 so does that mean the sensor needs to be exactly 1200mm from the surface of the mirror to focus? And the EP's need to be further out?
1200mm - pretty sure, or close to this.... What's an eyepiece??
If you point the scope at the moon, and move a piece of white paper in and out from the focuser barrel, you'll see the prime focus point, when a focused image of the moon appears on your paper.... this is the plane where the sensor needs to be....
Wow Jo that's really good work, love the finish on the wood. You must be quite handy for the DIY jobs at your place I'm curious to know how the wooden tube will hold up to the moisture (aka dew) issues and if it'll warp over time? Maybe you should try adding some nichrome wire to the scope to keep the water off?
I'm curious to know how the wooden tube will hold up to the moisture (aka dew) issues and if it'll warp over time? Maybe you should try adding some nichrome wire to the scope to keep the water off?
The tube has had two (will have three) FULL coats of fiberglass resin and is fully sealed, so should be OK. Don't think warping will be a problem, on my 6 inch tube I've had it out in the sun quite a bit and it's perfectly fine
Jo from my understanding the focus plain of an eyepiece is where the field stop is which is the ring inside the eyepiece looking from underneath. So cameras usually need a bit more distance to get focused than an eyepiece.
Also if you go for different rigs for imaging and eyepieces then you might be able to look at different secondary mirrors. With my 16 I use a 70 mm for imaging and an 88mm for visual (don't do that often though) as my camera has a smaller field of view.
You just need to figure out where your even illumination field needs to get to.
Jo from my understanding the focus plain of an eyepiece is where the field stop is which is the ring inside the eyepiece looking from underneath. So cameras usually need a bit more distance to get focused than an eyepiece.
Is that because the camera sensor is generally further in from the top of the nose piece than the eyepiece field stop is? That makes sense I guess.
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Also if you go for different rigs for imaging and eyepieces then you might be able to look at different secondary mirrors. With my 16 I use a 70 mm for imaging and an 88mm for visual (don't do that often though) as my camera has a smaller field of view.
You just need to figure out where your even illumination field needs to get to.
I hadn't thought about that, I will be using APS-C size sensors mainly (probably something like a QHY8) The secondary I have at the moment it a 50mm one.
Here is what I did yesterday, primed and painted the secondary holder and spider. And made a saddle for the scope from some leftover Hoop pine, today I hope to get the aluminium straps made that go over the tube.
It's quite exiting now that it's all coming together, sitting on the table it looks pretty big can't wait to try it out.
The next thing to build is the guide scope, I have a nice 80mm F5 acro lens from Surplus shed that I plan to use. Do you reckon I should make a wooden tube for it as well?
I am thinking of splurging again and getting a focuser for it, where do you reckon I could get one? Just a 1.25 inch, preferably not plastic, rack and pinion would be alright if it has a good locking screw.
Oh, and any ideas on what would be best for mounting option for the guide scope? I'm not massively liking the thought of tube rings any other options?
That's truly impressive Jo.
Amazing worksmanship. What mount will you be using it on.
I'd suggest a slim OAG rather than a guidescope. saves so much hassle with having a separate guide scope and differential flexure and is not expensive either. but then you do need a sensitive guidecam.
check out the Long perng focuser from andrews. its low profile and is pretty good.
the lower the profile of the focuser, the better it is for imaging as you then get sufficient back focus, you can keep the secondary small, and less vingetting although with an F6, that shouldn't be as much an issue as with an F4.
Have you thought of re-inforcing the focuser area? I know the wood would be strong enough but its a thought.
That's truly impressive Jo.
Amazing worksmanship. What mount will you be using it on.
Thanks Alistair, it will be on a Ioptron I45.
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I'd suggest a slim OAG rather than a guidescope. saves so much hassle with having a separate guide scope and differential flexure and is not expensive either. but then you do need a sensitive guidecam.
As this scope will probably not be used for any serious AP I'll be going the guide scope (easier for me to make)
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check out the Long perng focuser from andrews. its low profile and is pretty good.
the lower the profile of the focuser, the better it is for imaging as you then get sufficient back focus, you can keep the secondary small, and less vingetting although with an F6, that shouldn't be as much an issue as with an F4.
Yes they look nice, would it be a bit of an overkill for the guide scope though (already got a 2" 10:1 Crayford for the newt)
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Have you thought of re-inforcing the focuser area? I know the wood would be strong enough but its a thought.
No I haven't thought of that, it's a good idea, on the next coat of resin I'll stick some fiberglass on the inside of the tube in that area.
How did you manage to cut the 6.6 degree angle on the wooden strips and wasn't there any possibility of the cylinder being slightly distorted? did you have to use an inner cylinder to ensure its not pinched anywhere?
How did you manage to cut the 6.6 degree angle on the wooden strips and wasn't there any possibility of the cylinder being slightly distorted? did you have to use an inner cylinder to ensure its not pinched anywhere?
Cheers
Alistair
I borrowed the neighbours saw bench to cut the strips on, it allowed the blade to be tilted a little so I ran them through again to cut the edges, it would have been possible to just cut a 13.3 degree angle on one side and leave the other side at 90.
When the tube was rolled up it was tight and rigid, I didn't use any form of support, just measured across the ends as it was setting to make sure it was nice and round.
The tube has had two (will have three) FULL coats of fiberglass resin and is fully sealed, so should be OK. Don't think warping will be a problem, on my 6 inch tube I've had it out in the sun quite a bit and it's perfectly fine
Cheers
Jo
Ah, well that should definitely do the trick Very nice!
So, I've roughly finished the tube and it has had two coats of epoxy resin, once every thing is fitted and all the holes are drilled I will give it the final coat and start on getting a nice finish to it. The secondary mirror holder and spider has been finished and painted a flat black, and the primary mirror cell is finished as well. Both the mirrors have been mounted in. The inside of the tube is yet to be lined with black velvet. Over all, most of the big stuff is done and I just have to do all the little jobs and the finishing touches.
That's just beautiful workmanship Jo. Very inspiring to see what young minds can achieve when they put their minds to it.
You might have to start taking orders and start a production line.
Look forward to the first light report.
Edit: I'd suggest using a nylock nut for the secondary centre bolt. that'll keep your tension constant and allow the secondary to be rotated during collimation.
with the 4 bolts and nuts, won't you have to hold the nut while tightening the bolt? might be easier if you glue the nut or add a thread so you just need to adjust the bolts.
That's just beautiful workmanship Jo. Very inspiring to see what young minds can achieve when they put their minds to it.
You might have to start taking orders and start a production line.
Look forward to the first light report.
Edit: I'd suggest using a nylock nut for the secondary centre bolt. that'll keep your tension constant and allow the secondary to be rotated during collimation.
with the 4 bolts and nuts, won't you have to hold the nut while tightening the bolt? might be easier if you glue the nut or add a thread so you just need to adjust the bolts.
Cheers
Alistair
Thanks Alistair,
good idea about the lock nut yep, the four other nuts are glued on and they seem to work well.
Here are a few pics of the scope almost finished, I got an iOptron IEQ45 mount for it from OPT along with the Explore Scientific 24, 14, 8.8, and 4.7mm 82 degree eyepieces.
To finish of the tube I sanded it all down with 400 grit sand paper with lots of water and then polished it with a buff and some cutting compound.
I flocked the inside of the tube with black velvet, it make it really nice and dark, I’m thinking of making a baffle to go just in front of the primary mirror as there is a 10mm or so gap between the mirror and tube were a bit of light can come in.
The mirror cell works well, collimation is easy to adjust and holds perfectly. You can see that there are two sets of holes for mounting the mirror cell the tube, well one set is for visual and one it for imaging. Moving the mirror and tweaking the collimation again takes about 2 minutes.
The mount works brilliantly, this is the first GoTo GEM I’ve ever used so it took a few nights to get used to but over all it’s very simple to use, with a rough polar align through the illuminated reticule polar scope and a one star align, GoTo’s place every object smack in the centre of the image with the 1100D.
The ES EP’s I’m very happy with also, certainly a lot better than my Hyperions.
I have started working on a coopered wooden 80mm F5 guide scope, it’s coming along pretty well, I hope to have everything finished in around mid February.
That looks great. very nice work.
yes, goto mounts are very handy. does this mount have an autoguider port or support guiding?
I had two suggestions, pretty sure you've already considered these.
Looking at the pics, if you keep the focuser to one side, it'll end up in odd positions when slewing to different parts of the sky and you'll have an issue with balancing the weight.
is it balanced with the eyepiece?
if you had the find on the other side, that could even it out.
I believe this is for visual use?
its common to have the focuser facing down as that way, balancing in RA is not an issue.
second thing, do you have plans to make the two fasteners removable or adjustable? reason being you'll have to rotate the tube at some point if you use a different eyepiece that's lighter or heavier or even a camera.
so you'd need to loosen the fasteners, rotate the tube with the camera and then fasten it. I noticed both sides have bolts?
you would also need to loosen it if the OTA needs to be slid up or down again due to differing weights with cameras and eyepieces.
I like the idea of two holes for the mirror cell.
Nice work
Alistair
Edit: one other thing you could do is add a wing nut and a nyloc nut underneath it to the collimation bolts.
that way, you won't need a tool to adjust the bolts. you never know when a re-collimation is needed in the field.
Any provision for mounting a dew controller? that'll also be required to keep eyepieces and/or the finder objective dew free. else its a nightmare cause things dew up very fast.
I'm curious to know how the wooden tube will hold up to the moisture (aka dew) issues and if it'll warp over time? Maybe you should try adding some nichrome wire to the scope to keep the water off?
any other options?
(already got a 2" 10:1 Crayford for the newt)
