Should I Dremmel 3cm off my Altair f/4 carbon fibre tube???

[Chris]

You're going to need something more substantial that your dremel discs if you decide to cut it unless you have hundreds,lol.

I use to work with CF,we used drills coated in industrial diamonds,they would probably last for 30 to 40 holes before they needed re-coating,nasty stuff when grinding/drilling it.The dust is horrible,makes the skin really itchy and itching it makes it worst!So you can imagine what it does to your lungs.

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Thanks Olly, I'm definately not going to touch the CF after what you and others have said!

Cheers

[Chris]

Fit longer springs like I did to move the focus outward (and improve collimation stability)

http://stargazerslounge.com/topic/188976-8-f4-newtonian-mirror-cell-mods/?hl=%2Bsix+%2Bspring

Not sure you'd be able to gain 30mm though? I only moved the secondary up the tube by 10mm.

hehe, I see I commented that your thread will come in handy to others with f/4's, I didn't realise it would be me!

Thanks for reminding me of the link, I did mean to find it

[laser_jock99]

I've got to seriously think what to do because today I found out me and my wife are having twins!!!!!!!!!!!!!    We already have a 2 year old boy so by the summer we will have 3 kids under 3! I'm going to need to sell some kit unfortunately both for the cash (my fiat panda aint going to cut it!)

Wait till they're teenagers taller than you are.....I had to upsize to a Volvo V70 estate for the rear leg room.....

[glappkaeft]

Also unless you cut the tube between the primary and secondary and glue them together afterward you won't move the focus. The tube is there to hold the optical surfaces in place, the only thing that will move the focus is to move the position of either the primary (the usual method) or moving both the focuser and the secondary.

[Chris]

Can you not move the mirror up the tube a bit, redrilling the holes maybe 1/4 turn so there not close to the old holes....???

Unfortunately not Tinker because the primary mirror cell bottom plate wraps around the end of the tube.

[Chris]

You could bond distance pieces to the mirror cell 3cms long and still use the original adjusting screws. 

I did wonder if this would work, I was thinking of fixing a pine wood plate say 18mm think behind the primary and fixing longer bolts to the mirror clips to hold it and the mirror in top all in place, is this similar to what you are thinking?

What do you think the chances are that moving the primary up the tube will cause the outer regions of the primary light come to miss the seconday mirror? I think if I can have some re-assurance about this then it might be worth keeping the scope to give it a go and combine this with stronger longer springs like laserjock suggets

[Chris]

Wait till they're teenagers taller than you are.....I had to upsize to a Volvo V70 estate for the rear leg room.....

[Chris]

Also unless you cut the tube between the primary and secondary and glue them together afterward you won't move the focus. The tube is there to hold the optical surfaces in place, the only thing that will move the focus is to move the position of either the primary (the usual method) or moving both the focuser and the secondary.

The original idea of cutting the tube was so that I could move the primary up the tube, This isn't one of those scopes you can move the primary and re-drill because the primary cell wraps around the bottom edge of the tube. this means that the tube length depicts the distance between the primary and the secondary. I'm not going to touch the CF now its too hazerdous! I'm either going to sell the scope cheap or make some mods with stronger springs and hitching up the primary mirror on a wooden plate. I just need to be sure of the consequence of doing this? I'm hoping the outer regions of the primary light cone dont miss the secondary?

[cantab]

What do you think the chances are that moving the primary up the tube will cause the outer regions of the primary light come to miss the seconday mirror? I think if I can have some re-assurance about this then it might be worth keeping the scope to give it a go and combine this with stronger longer springs like laserjock suggets

If this does occur, then it will occur with any method of reducing the primary-secondary distance. Only a low-profile focuser or a larger secondary would resolve that. But from a quick search I came across the 8 inch Altair f/4 being promoted as having an "Oversize secondary mirror to cover a 35mm CCD frame", so I expect even after shortening the primary-secondary distance you'll fill the frame on your 350D OK.

[Joseki]

I'd be tempted to remove the focuser and see if you can reach focus holding the camera freehand (or poking through a sheet of cardboard etc ) should be enough to get an idea of the focal plane position I reckon - something similar worked for me (when I was messing around with a much cheaper scope).

If you're going to lose a lot of money selling it on I think I'd try cutting it though as a last resort (but I don't understand quite how the lipped bottom bit works).  I understand others who have contributed to this thread have actual experience of cutting it, but

a simple 'cutting carbon fibre' google search comes up with this website:

http://www.carbonmods.co.uk/departments/guides/cutting-and-shaping-carbon.aspx

who suggest a fine toothed hacksaw hand tool will be fine - and which isn't going to generate the same sort of heat.  Personally I love my Ryoba Japanese saw and I'd use that (brilliant for large flush cuts) with a wooden depth jig like you originally suggested.

[Daniel-K]

Wow twins my two and five year old girls are a right handful I think I'd be in shock to. Be a shame to sell that.

[Joseki]

(but I don't understand quite how the lipped bottom bit works)

Ah, just re-read and I understand.

congrats on your twins btw!

[Joseki]

hmm. you could use a tube ring as a saw guide also.  Plus if you were going to lose much money you could always sell the mirror set and other bits what ever happened to the tube.   hmm maybe best not to listen to me - things *sometimes* go badly when I try stuff like this. 

[SnakeyJ]

Congratulations and very best wishes to you, your wife and son, quite a game changer I would imagine, certainly in terms of time and money - you might be considering more painful tube cuts after this   Raising my two with a respectable three year gap has proved quite exhausting enough to me, though I did leave my parenting quite late.    Now it's all football, an endless round of clubs and parties - but my 7 year old spent a couple of hours with me in the observatory last night and will be attending his second IOW Star Party next week.

This scope may require a little careful fettling/modification, but this seems to be a given for all these F4 imaging newts - but provided the optics are good, it looks very nicely made and sure it will produce great images if you can invest the time to get it right.

One major plus is you already have the observatory, so even if you do need to slim things down a bit, you'll be able to get out and running in short order when time, weather and circumstances permit!

[Peter Drew]

I think a wood platform to elevate the primary mirror will be a good proposition. If you can't reach a focus without you are effectivel losing all of the light!

[RAC]

I would cut the tube. A 4inch grinder and a 1mm cut off disk is all it takes apart from a mask. Easy as. Just go slow as to not heat up the resin too much. I did a lot of carbon cutting making this

[Skyline]

Chris, have you thought about adapting this focuser onto the scope. Maybe it will work.

http://www.teleskop-express.de/shop/product_info.php/info/p6122_Skywatcher-2--Linear-Power-Newtonian-focuser---short-design---1-10-transmission.html

[Skyline]

Sorry Mods can't edit my post, i forgot to mention these one as well:

http://www.telescopehouse.com/acatalog/Revelation-Superfocus-2-inch-Newtonian-Rack-n-Pinion-Focuser.html

Al.

[Chris]

If this does occur, then it will occur with any method of reducing the primary-secondary distance. Only a low-profile focuser or a larger secondary would resolve that. But from a quick search I came across the 8 inch Altair f/4 being promoted as having an "Oversize secondary mirror to cover a 35mm CCD frame", so I expect even after shortening the primary-secondary distance you'll fill the frame on your 350D OK.

Thanks for the search, maybe the oversize secondary will give me some room for manouvre like you say. Sounds positive thanks

[Chris]

I'd be tempted to remove the focuser and see if you can reach focus holding the camera freehand (or poking through a sheet of cardboard etc ) should be enough to get an idea of the focal plane position I reckon - something similar worked for me (when I was messing around with a much cheaper scope).

If you're going to lose a lot of money selling it on I think I'd try cutting it though as a last resort (but I don't understand quite how the lipped bottom bit works).  I understand others who have contributed to this thread have actual experience of cutting it, but

a simple 'cutting carbon fibre' google search comes up with this website:

http://www.carbonmods.co.uk/departments/guides/cutting-and-shaping-carbon.aspx

who suggest a fine toothed hacksaw hand tool will be fine - and which isn't going to generate the same sort of heat.  Personally I love my Ryoba Japanese saw and I'd use that (brilliant for large flush cuts) with a wooden depth jig like you originally suggested.

Brilliant idea about removing the focuser and using a camera to find the focal point, this will actually give me a real idea if a low profile focuser will sort it on its own. Its given me another idea off how to do this. Am I right in thinking that the sensor in a DSLR is set back roughly 40mm from the t-ring? in which case can I just find focus with an eyepiece then measure from the top of the eyepiece 40mm down the focuser and see how high this sits off the tube??

Many thanks

I've decided not to touch the tube for both my lungs sake and the scopes sake Its in mint condition as it stands and I can solve the issue either by moving the primary up on a base behind the mirror and or longer screws, or by a low profile focuser.

[Chris]

Wow twins my two and five year old girls are a right handful I think I'd be in shock to. Be a shame to sell that.

 I always thought I'd have two kids, then we had Alex and I realised how physically and mentally exhausting they are, they are also amazing and wonderful at the same time but I thought one was enough then. My wife has been pleading with me to have a second and I finally agreed that we would try but was very worried about coping with two. Now we'll have 3! Dan I'm terrified! I', also a bit saddened because I'm going to have to slim down my little empire of astro kit that I've built up! I will need a much bigger car than the Panda, plus double buggy, and I'll have to go even more part time to look after them as my wife earns the big wage working for the RAS, I'm just a part time radiographer doing 3 days a week, I see this having to go down to 2 x 12 hour shifts over the weekend or something, not sure yet?

Chris

[Christopher Davenport]

Just another idea - is it possible to modify the coma corrector to fit inside the draw tube? Sure I can recall a thread where someone did this with a SW Quattro.

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Agree with jake, old 150 skywatchers all had this problem. Many people did mods to place the corrector on the inside of the focuser tube. Do some searches on this forum on mods to 150. If I find the thread I will post.

[Christopher Davenport]

Btw you got a deal picking it up at that price

[Bukko]

Hi, Chris,

just caught up with the thread again.

Congratulations on the twins!! I hope all goes well.

It would be a good idea, as mentioned, to try and find out exactly how far short of prime focus the system is. If you are really close, then expending the bolts sounds like a good plan. If it comes down to cutting the tube, then seeking expert advice would be my first move. We have a small carbon fibre firm locally, maybe there is one near you? 

Anyway, good luck with the twins.

Gordon.

[Chris]

hmm. you could use a tube ring as a saw guide also.  Plus if you were going to lose much money you could always sell the mirror set and other bits what ever happened to the tube.   hmm maybe best not to listen to me - things *sometimes* go badly when I try stuff like this. 

I'm not going to cut the tube, but if I was that would be a very good idea!