Quick maths question...well, not maths

[emadmoussa]

If I flatten down the 11" C11 tube into a sheet, how long will the sheet be?

I'm getting black faux leather sheet to tightly wrap it around the OTA body for protection. I know the width is about 45mm.

[Lorne]

Pi x Diameter should give you the circumference....... if my memory serves me well

[ChrisThePuma]

isn't it Pi x Radius ( r ) squared?

[mallorcasaint]

Measure the circumference with a tape measure.

[Stargazer_00]

You need the sum for circumference of a circle. it probably has pie invovled. I think it's pi x diameter if memory serves.

The primary mirror diamter doesn't allow you to work out a 100% accurate circumference as the OTA will be bigger so that it can house the mirror. If you assume the OTA has a diameter of say 13" then you can do the following sum

3.142 (from memory) x 330mm so 1.03m

Cut it at 1.2m for a bit of overlap

[emadmoussa]

You need the sum for circumference of a circle. it probably has pie invovled. I think it's pi x diameter if memory serves.

The primary mirror diamter doesn't allow you to work out a 100% accurate circumference as the OTA will be bigger so that it can house the mirror. If you assume the OTA has a diameter of say 13" then you can do the following sum

3.142 (from memory) x 330mm so 1.03m

Cut it at 1.2m for a bit of overlap

Cool, thanks! this is what I wanted to know. I'm ordering this now, it should be long enough

[Qualia]

It's already explained but again, simply measure the circumference of the OTA and multiple this number by 3.14. You've also got to take into account the length required to actually tie or sow it down onto the OTA.

[michael.h.f.wilkinson]

isn't it Pi x Radius ( r ) squared?

That is the area of the circle 2πR or πD, with R the radius and D the diameter is correct

[cassiewoofer]

it's a length unit so it can't be r squared!...... that's for are....like everyone said it's Pi (3.142) x diameter.

or 3.142 x 11...

BUT Mallorcasaint's answer is better 'cos your calc will be slightly under,.... the diameter of the material layed over 11" tube will be a bit bigger than 11"

[michael.h.f.wilkinson]

It's already explained but again, simply measure the circumference of the OTA and multiple this number by 3.14. You've also got to take into account the length required to actually tie or sow it down onto the OTA.

Diameter, not circumference (that is what you want to measure).

[emadmoussa]

It's already explained but again, simply measure the circumference of the OTA and multiple this number by 3.14. You've also got to take into account the length required to actually tie or sow it down onto the OTA.

Sure, I'm leaving some extra to attach some velcro. My C11 will wear a tux soon

[DaveS]

Yep, just measure the circumferance with a tape meaasure and add a ha'porth on for luck. No need for mathas at all.

[emadmoussa]

Yep, just measure the circumferance with a tape meaasure and add a ha'porth on for luck. No need for mathas at all.

Yes, I'm aware of that. I'm at work at the moment and needed to order the leather sheet ASAP to have it delivered by Monday. The one I ordered is 130cm min in length and 60cm wide...so it should be enough.

[Qualia]

Diameter, not circumference (that is what you want to measure).

Michael, I was figuring that the diameter might be understood as the aperture of the OTA and feared if that was so the bag wouldn't fit. For example, the diameter on my Tal is something around, say, 100mm but the tube itself is widder. I thought it would be better to take that circumference than simply do 11" x 3.14.

[michael.h.f.wilkinson]

Michael, I was figuring that the diameter might be understood as the aperture of the OTA and feared if that was so the bag wouldn't fit. For example, the diameter on my Tal is something around, say, 100mm but the tube itself is widder. I thought it would be better to take that circumference than simply do 11" x 3.14.

I understand what you are getting at, but I think there is a language issue here. Circumference is not the right word for what you mean: tube diameter is better, and should indeed be distinguished from aperture.

[cassiewoofer]

OH if a C11 is an 11 inch mirror.... then the tube will be around 12.5 inch at least..... meaning 12.5 x 3.142 which is just under 100cm

[AlexB67]

Michael is on the money here w.r.t to wording/definitions.

In fact if you want the length as well while you are at it, to cut an area A it is pi * diameter * length for a cylinder of wrapped material. Personally I'd measure the diameter up to inside of the tube, add on x to allow for a bit of overlap if needed for fixing on.

Not that I ever flocked a tube , theoretically speaking therefore the final formula would be

(( pi * diameter) + bit of overlap distance ) * length for the total area in units of distance squared .

[cassiewoofer]

can't find optical tube diameter in tech specs but tube length is 24 inches.....according to :-

http://www.celestron.com/astronomy/celestron-c11-a-xlt-cge.html

. A decent side on view picture (non distorted) would enable the diameter to be calculated.

But you need something like 24 x 40 inch piece of material. (x2.54 for cms)

[sbooder]

Why not measure around it with a tailors tape (nice and soft)?

[Scott]

Mate....Just measure it...add a bit....order it. really can't see the need for pi on this one.

[Ouroboros]

If I flatten down the 11" C11 tube into a sheet, how long will the sheet be?

if you flatten a tube its length is unchanged. ;-)

[Scott]

If you flatten down the ota then I wouldn't bother flocking it. It ain't gonna be good for anything

[tferrari]

(Outside diameter x 3.14) + small overlap = length of material

(Length of tube) = width of material

You now have the dimensions required.

[emadmoussa]

Like I said I was at work, no telescope around. Just wanted to have a rough estimate while on the site. Needed quick delivery for tomorrow.

[JamesF]

Too late now, but see the yellow box at the bottom of this page:

http://www.telescope-service.com/Celestron/SCT/SCT.html#C11

Which suggests you need a sheet at least 962mm long.

James