| pepper |
| (journeyman) |
| 06/24/09 02:01 PM |
is my LS dew heater correct?
|
Hi, guys. I ordered a dew heater, but with the LS there is a mount in the way with some of the tube, I put it here and not sure if it's in the correct place. and hope it is as the mount is blocking going any lower, you might be able to put it on the very tip but have not tested. any feedback would be great
| brianb11213 |
| (Carpal Tunnel) |
| 06/24/09 02:33 PM |
|
Re: is my LS dew heater correct?
|
Ummm, doesn't it want to go at the top end of the tube?
| Peter9 |
| (scholastic sledgehammer) |
| 06/24/09 02:57 PM |
|
|
Re: is my LS dew heater correct?
|
As Brian indicates, I think it needs to be somewhere up at the front end.
Peter.
| StarWars |
| (Postmaster) |
| 06/24/09 03:05 PM |
|
|
Re: is my LS dew heater correct?
|
The dew heater should be at the corrector plate end apparently the OTA bracket runs the full length of the OTA..
| brianb11213 |
| (Carpal Tunnel) |
| 06/24/09 03:34 PM |
|
Re: is my LS dew heater correct?
|
Quote:
apparently the OTA bracket runs the full length of the OTA.
Not a problem, just wrap the heater strip round the bracket. So long as most of it is in contact with most of the circumference of the tube it will work OK.
| Astroboy86 |
| (sage) |
| 06/24/09 06:20 PM |
|
|
Re: is my LS dew heater correct?
|
Quote:
just wrap the heater strip round the bracket. So long as most of it is in contact with most of the circumference of the tube it will work OK.
If there's enough of a gap to slide the heater strip under the bracket just ahead of the rear cell, shouldn't there be the same amount of gap just behind the front cell where the strip should be positioned?
The thing I wonder about is how well you can fit a dew shield without either leaving a big gap or cutting a giant notch, since it looks like the bracket extends all the way to the very front of the corrector cell. That is, unless the cell has internal threads like the other ETXes for mounting Meade's special rigid plastic dew shield.
-Harry
| Arthur Dent |
| (Galactic Hitch-Hiker) |
| 06/24/09 06:52 PM |
|
|
Re: is my LS dew heater correct?
|
Hi Pepper
It looks like you've got the dew heater around the wrong end as the guys have already said.
When there is lots of dew, the front glass element (the corrector lens) loses heat faster than the rest of the scope, so dew builds up on the corrector and if fogs up.
The dew heater is intended to raise the temperature just enough that the dew evaporates and doesn't condense on the corrector plate.
Dew shields (like that on my NexStar 6SE) have to have a notch cut in them if the mounting bracket (as in the ETX-LS) or the dovetail (in the case of my 6SE) protrudes out of the side of the scope where the corrector lens is.
On my ETX-105, the dew shield screws into the front of the corrector (where the metal lens cap screws in), so it isn't a problem with the ETX-105 (or the ETX-90 or ETX-125 for that matter).
Hope this helps
Art
| pepper |
| (journeyman) |
| 06/24/09 09:08 PM |
|
Re: is my LS dew heater correct?
|
hey guys, I think I got it now, is it like this? or is it at the other end of the tube? If it is correct, I only have about 1 1/2 inches not on the tube, and I guess I could also cut the bracket? thanks
| Astroboy86 |
| (sage) |
| 06/25/09 12:58 AM |
|
|
|
Re: is my LS dew heater correct?
|
Quote:
I guess I could also cut the bracket?
Pepper, don't cut the bracket!!
(It's rather important.)The way you had the heater strip mounted in the first photo was perfect...just on the wrong end of the tube. Is it not possible to mount it that same way on the opposite end?
Although it might seem as if that position is too far back from the corrector plate, the metal part of the optical tube will transmit the dew-strip's heat more efficiently than wrapping it around the black plastic cell that holds the corrector, especially with the additional air gap created by wrapping around the outside of the bracket.
If it's not possible to slip the heater strip between the bracket and the metal optical tube just behind the front cell, you should still try to get as much of the heat-producing part of the strip as possible in direct contact with this part of the tube. Good luck!
-Harry
| Arthur Dent |
| (Galactic Hitch-Hiker) |
| 06/25/09 10:32 AM |
|
|
|
Re: is my LS dew heater correct?
|
Hi Pepper
It's not too clear from your photo, but I still think you have got the wrong end.
This is the end that the corrector lens is and this is where the dew strap should go:
Hope this helps
Art
| pepper |
| (journeyman) |
| 06/25/09 10:47 PM |
|
Re: is my LS dew heater correct?
|
thanks guys, and arthur
It is mounted how arthur's picture is. I guess I should have taken a picture of the whole scope to make it more clear. You can see if you look close, the cap for the front lens...
So now I'm wondering is the first picture or second picture a better placement?
Hope I can finally see some good stuff tonight now that I have an array of lens' ...
| Astroboy86 |
| (sage) |
| 06/25/09 10:57 PM |
|
|
|
Re: is my LS dew heater correct?
|
I was just looking at Pepper's pictures again, along with those posted by Jason. You know what? I think Pepper had his dew strip mounted exactly right in the very first picture!
I believe what many of us thought was the back of the rear cell was actually the convex, ribbed, dust cover mounted on the front of the OTA. In that first pic above, it really looks like a rear cell with the picture cut off at the bottom just above where the SCT threads would be. The fact that this end of the scope is pointed down also adds to the impression that we're looking at the rear of OTA. This is obviously not the case, though, since the bracket is on the left side of the OTA as viewed from the rear of the scope.
I'd hereby like to withdraw everything I previously wrote in this thread and simply say, "Nicely done Pepper."
(but you still shouldn't even think about cutting that mounting bracket!)
-Harry
| brianb11213 |
| (Carpal Tunnel) |
| 06/26/09 04:40 AM |
|
Re: is my LS dew heater correct?
|
Quote:
I believe what many of us thought was the back of the rear cell was actually the convex, ribbed, dust cover mounted on the front of the OTA. In that first pic above, it really looks like a rear cell with the picture cut off at the bottom just above where the SCT threads would be. The fact that this end of the scope is pointed down also adds to the impression that we're looking at the rear of OTA. This is obviously not the case, though, since the bracket is on the left side of the OTA as viewed from the rear of the scope.
Mea culpa
Sorry guys!
| Peter9 |
| (scholastic sledgehammer) |
| 06/26/09 07:32 AM |
|
|
|
Re: is my LS dew heater correct?
|
Sorry Pepper, you had it right first time.
Peter.
| Arthur Dent |
| (Galactic Hitch-Hiker) |
| 06/26/09 06:47 PM |
|
|
|
Re: is my LS dew heater correct?
|
Me too Pepper
I thought that I could see the flanges of the rear cell in your first picture. I didn't realise that it was the lens cap I was looking at.
So, it looks like you got it right first time! Possibly a little bit too far back, but as I haven't got a dew strap, I'll leave others to make more specific advice.
Art
| brianb11213 |
| (Carpal Tunnel) |
| 06/27/09 06:30 AM |
|
Re: is my LS dew heater correct?
|
Quote:
So, it looks like you got it right first time! Possibly a little bit too far back, but as I haven't got a dew strap, I'll leave others to make more specific advice.
Looks OK to me. If you fit a flexi type dew cap that will fit over the "black bit" at the tube end so you have two choices: place the heater strap behind the dew cap as in the top photo, or wrap the dew cap round the heater strap. Experience indicates that the latter method is a bit unstable even though it gets more heat where it's wanted (into the corrector plate). With a larger scope this may be an issue, on my C11 I solved it by using electrical tape to hold the heater strap firmly in place allowing the dew cap to be fitted reasonably firmly. With a 6" scope I don't think there will be an issue, even the central bit of the corrector plate is fairly close to the heater strap even if the heater strap isn't in the optimal position.
If you're using a "screw in" type rigid dew cap, or no dew cap at all, the issue is moot, fit the heater strap centrally over the black metal corrector cell mount.
In use, the heater strap power setting should be adjusted so that it's at a minimum consistent with keeping the corrector plate clear. A good way of judging this is by dew forming on the outside of the tube; the setting is about right when dew is forming except within a couple of inches of the heater strap. Too little heat = misted corrector (very bad), too much = tube currents (bad but, unless imaging planets at high magnification, not insufferably so). On balance, better to err on the side of a bit too much as it's a lot easier to prevent dew from forming than too evaporate it once formed.